Forming the Future

Innovative self-correcting process control techniques which adapt to the initial geometric characteristics of the strip are a promising approach to fix the local varying distortion of coiled strips by optimizing the leveling process. This paper presents an innovative strategy to improve straightening of AHSS materials (1.4310). This implies optimized leveling, adding minimal plastic deformation, and, thus, strain hardening. Therefore, an “intelligent straightening machine”Intelligent straightening machine is being developed which will be presented. To operate an intelligent straightening machineIntelligent straightening machine a reliable online measurement of the surface defects is fundamentally essential. This paper describes an approach towards the measurement of a bent steel strip for an automatic straightening process. Therefore, various ways of measuring the bending curvature are investigated. Optical, tactile, and the electromagnetic induction testing MagnaTest are compared with each other. The bending measurement is linked to open-loop control, providing an optimal straightening result in regards of formability, leveling, and reduced strain hardening.

Here I lay out a vision for hybrid autonomous manufacturing. Imagine you have a robot-automaton machinist who really likes and knows deformation. What would this enable? What’s needed to get there? Use cases and brief research agenda are presented.

Narrow channels or ribs can be commonly found in sheet metal products. These narrow with high length-to-width aspect ratio channels are often integrated into sheet metal panels for functional features such as stiffeners or guide rails of various topographies, i.e. straight line or composite of curves. This work focused on the development of Single Point Incremental FormingSingle point incremental forming (SPIF) as a cost-efficient forming alternative to stamping or embossingEmbossing of these features in short-series production. These channels present unique forming challenges, i.e. effects of channel spline geometry, varying cross section, end geometries on part formability, and geometrical accuracy. SPIFSingle point incremental forming of SS316L 0.5-mm-thick narrow channels of three different geometries with a maximum width of 20 mm and its length-to-width aspect ratio larger than 5, i.e. (1) straight channel, (2) taper channel, and (3) curvature channel, was investigated. Based on the experimental results, 5 mm dia. carbide tool and 0.1 mm step-down size were recommended to optimize SPIF of these narrow channels. The effects of the different part features and their interactions with SPIF forming parameters on part formability and deviations are presented and analyzed for further development of die-less narrow channel formingChannel forming for sheet metal industry.

A die designDie design architecture for axisymmetric forgings which minimizes the residual contact pressure at the die–workpiece interface during the ejection stroke is proposed. The underlying principle of this die designDie design is that during the forging stroke a tapered die can move in the direction of the forging load thus inducing negative radial elastic strain on the die. When the forging load is removed, the elastic strain energy stored in the die is released thus reposition the die to its initial state. With this design architecture the workpiece can be ejected at no load. Finite element (FE) warm forging simulations for constant velocity joint and pinion gear blank were successfully carried out to evaluate the viability of the process. In addition to reducing residual contact pressure which enhances tribological conditions, the FE simulations conducted have shown that a total energy saving of up to 15% can be achieved with the proposed die designs.Die design

The determination of the plastic deformation properties of materials under high-speed loading is a challenge. The system ringing in a conventional servo-hydraulic tensile machine deteriorates the quality of force measurement. A precise determination of the plasticity and damage is thus difficult. In this work, the system ringing effect of the entire test system, including machine, sample, etc., was analyzed. We found that the system ringing is location- and geometry-dependent. Inspired by the principle of the split-Hopkinson bar, a new type of tensile sample has been developed. In a certain restricted area of this new sample, the tensile forces can be measured without any oscillation effect. The plastic deformation and damage behavior can be determined by using this type of specimen for a wide strain rate range of 10−4−103/s. To explain the functionality of the sample and sample design, a one-dimensional stress waveStress wave model has been developed.

Thanks to the high stiffness-to-weight ratio given by the closed-section geometry, tubular components are particularly suitable for automotive applications that require extreme lightness to reduce energy consumption and increase crashworthiness. Tube bendingTube draw bending processes are traditionally performed in cold conditions, but to overcome the dramatic problems of accuracy and formability that the new high-strength steelsHigh-strength steels present, a novel draw bending set at high temperature has been proposed. This paper presents the results of the investigations carried out on the tribological conditions of the hot draw bending of 22MnB5 tubes to obtain tubular parts with tailored mechanical properties. Investigation about the process thermal cycle has been performed with focus on the influence of the contact pressure on the heat transferHeat transfer. The results show the practicability of the new process chain to obtain hot stamped tubular parts.

Due to increasing variant diversity and mass customization, time and cost-efficient process design has gained importance for several years. TribologicalTribology investigations are playing a key role as part of the process design. In particular, the desires for extended process limits, reduction of lubricant amount, and reliable determination of friction coefficientsFriction coefficient for FE simulations place high requirements on tribometersTribometer in sheet metal formingSheet metal forming. For quite some time, the strip drawing testStrip drawing test with several variations has been considered as an efficient and meaningful method for tribological investigations. This paper summarizes the development of the strip drawing testStrip drawing test to date. In particular, design principles for experimental modelling of tribologicalTribology conditions of deep drawingDeep drawing processes and approaches for friction measurement are described. Moreover, the current state and future requirements for the development of the “perfect” tribometerTribometer are discussed in this review paper.

Galvanized steelGalvanized steel sheets are increasingly used in the automotive industry due to excellent corrosion resistance, sufficient weldability, and formability. During sheet formingSheet forming of galvanized metals, material failures such as exfoliation and cracking can be found in the zinc coated layers of the sheet under severe friction. Thus, the evaluation of the influences of surface topography, pressure, and lubrication on friction could provide valuable guidance in forming of galvanized metals. A hot-dip galvannealed sheet and a hot-dip galvanized sheet are chosen in this tribology study. The surface topographies of the materials are measured using profile meter and the fractal parameters are calculated using the fractal theoryFractal theory. The contact model between the sheet and the die is established using the real contact area. The friction model concerning the surface topography of galvanized sheet and the pressure is thus formulated. The friction coefficients of the theoretical values are in reasonable agreement with the experimental.

This paper is focused on the formability limitsFormability limits by fracture of thin-walled tubesThin-walled tubes. It provides, for the first time ever, the fracture forming limit lines associated with crack opening by tension (mode I), by in-plane shear (mode II) and by mixed-mode consisting of crack opening by modes I and II of fracture mechanics. This is accomplished by an experimental methodology that combines digital image correlation (DIC) and determination of gauge length strains in double notched tensile test (DNTT) specimens, staggered DNTT specimens and shear test specimens. Results are plotted in principal strain space and the crack opening modes are confirmed by fractographyFractography analysis performed with a scanning electron microscope (SEM). DNTT specimens are also used to determine fracture toughnessFracture toughness in specimens that failed by tension. Results show that the use of DNTT, staggered DNTT and shear tests allow obtaining the strain loading paths and fracture loci across a wide range of forming conditions, ranging from plane strain to pure shear. The fracture forming limit (FFL) line, the shear fracture forming limit (SFFL) line and the transition region between these two lines are similar to those recently published for sheet and strip materials, and their use is of paramount importance for the design and optimization of tube formingTube forming processes.

The contribution to frictionFriction stemming from dissipation of plastic energy is studied by numerical simulations and experiments. The geometrical setup consists of a single model asperity, which is first flattened against a tool with grooves on a smaller length scale. Relative, tangential sliding between the model asperity and the tool is induced subsequently until a steady state is reached. The flank angle of the grooves on the tool is varied. Comparison between the simulations and the experiments leads to validation of the simulations at low tool flank angles, while the current numerical implementation cannot handle the complicated flow around the tool grooves with a large flank angle. At low flank angles, the simulated tangential tool force is in agreement with experiments when keeping one determined friction factor. This proves that the change in tangential force, corresponding to a change in apparent frictionFriction factor, is only due to the dissipated energy from the plastic wavesPlastic waves. The validated numerical model can be used to determine a wider range of apparent frictionFriction factors for strain hardening materials.

The reduction of energy consumption and CO2 emissions in aluminium profile production can be achieved by solid-state recycling. By direct hot extrusion, aluminiumAluminum chips can be directly processed into semi-finished or near-net-shape products requiring relatively low energy and having a high material yield. Since the mechanical properties of the extruded profiles highly depend on the welding of the individual chips, the main focus is to achieve a sufficient bonding between the chips. For this, the oxide layer covering the aluminiumAluminum surface has to be broken. In order to predict the welding of the individual chips and estimate the process success a weld prediction model is developed. The influence of process parameters such as extrusion ratio, temperature, and speed is analysed. The weld model is applied to further profiles and validated by experimental tryouts.

Every year billions of micro parts are produced. In mass production, cold bulk forming offers considerable technological, economical, and ecological potentials compared to alternative production methods. Due to the occurrence of scale effects, high tool stresses, and handling problems, cold bulk forming is not used for the mass production of multi-stage formed metallic micro partsMetallic micro parts. Within this paper, multi-stage bulk microformingBulk microforming from sheet metalSheet metal is investigated on the laboratory scale with the material Cu-OFE. Throughout this process, the sheet metalSheet metal strip serves both as a semi-finished product and as a handling aid. In the first forming stage, a pin is extruded from sheet metalSheet metal, which is then extruded in a cup during the second stage. For the identification of size effectsSize effects and the evaluation of such effects on the part quality, the tests are carried out on macro- and micro-scale. In the first step, the process-influencing variable of the blank holder pressure is investigated in the first forming stage in order to derive measures for the highest possible material utilization. The two-stage forming of the pin with cup is compared with a single-stage process to assess the part quality and material utilization depending on the process strategy. Using the correct geometric scaling, size effectsSize effects are identified and their effects on the forming process are evaluated. The experimental results reveal that it is possible to fabricate micro parts with a diameter of 470 µm and a minimum wall thickness of 36 µm reproducible by using the presented cold bulk microformingBulk microforming process strategy.

Bent tubes are extensively used in the manufacturing industry to meet demands for lightweight and high performance. As one of the most significant behaviors affecting the dimensional accuracy in tube bendingTube bending, springbackSpringback causes problems in tube assembly and service, making the manufacturing process complex, time-consuming, and difficult to control. This paper attempts to present an accurate, efficient, and flexible strategy to control springbackSpringback based on Machine LearningMachine learning (ML) modeling. An enhanced PSO-BP network-based ML model is established, providing a strong ability to account for the influences of material, geometry, and process parameters on springback. For supervised learning, training sample data can be collected from the historical production process or, alternatively, finite element simulation and laboratory-type experiments. Using the cold bending of aluminum tubes as the application case, the ML model is evaluated with high reliability and efficiency in springbackSpringback prediction and compensationCompensation strategy of springback.

With the increasing demand for the reduction in energy consumption and enhancement of automobile safety, ultra-high-strength steel are widely used in the automobile industry. Due to the high achievable strength, hot stampingHot stamping process can be used to supply promising automobile components. The increasing use of high-strength steels provides particular challenges to fracture modeling due to their microstructures and processing conditions. This paper is concerned with plasticity and ductile fractureDuctile fracture modelling of hot-stamped boron steelBoron steel 22MnB5, where martensite phase with high yield strength, work hardening, and ductility are present. The modified Mohr–Coulomb criteria as well as Hosford–Coulomb criteria are implemented using VUMAT in ABAQUS. Parameters of the selected fracture criteria are determined using calibration tests with various kinds of specimen. Fracture properties and flow curves up to large strains are determined from single-phase tensile experiments using digital image correlation. The final hole expansion test shows that the Mohr–Coulomb ductile fractureDuctile fracture criterion is more suitable to model ductile fracture in metal forming proc

Magnesium alloysMagnesium alloys have been of growing interest for their low density and high specific strength, but their applications are impeded by their poor formability at room temperature. This work employs the state-of-art experimental and modeling techniques to understand the joint effect of thickness and grain size on the plastic behavior and deformation mechanism of wrought Mg alloy. Equal channel angle pressing was applied to AZ31 Mg alloy to fabricate billets with different grain sizes but the similar basal texture. Interrupted micro-tensile tests combined with ex situ EBSDEx situ EBSD characterizations were carried on the fine-polished specimens with different grain sizes and thicknesses. It shows that mechanical twinning is significantly affected by both grain size and thickness. In particular, the volume fraction of extension twins decreases with the number of grains in the thickness. Full-field crystal plasticityCrystal plasticity simulations demonstrate that both the contributions of basal slip and twinning are rather sensitive to grain size.

This presentation reviews the key features of a macroscopic plasticityPlasticity framework applicable to numerical simulations of practical forming processes in industry. The constitutive relationships are developed for anisotropic materials with an anisotropic hardening assumption. The framework relies on mathematical concepts, physical understanding of deformation mechanisms, and experimental results. Lower scale simulation results are essential for the introduction of relevant features in the macroscopic framework. The experimental investigations on plasticityPlasticity conducted by Professor Tozawa in the 1960s and 1970s is of fundamental importance for the development and validation of the theory.

Finite element analysis (FEA)Finite element analysis of hole expansion forming is investigated to clarify the effects of material models on the predictive accuracy of the FEAFinite element analysis. The multiaxial plastic deformation behavior of a hot rolled steel sheetSteel sheet with a tensile strength of 440 MPa was measured using biaxial tensile tests with cruciform specimens (ISO 16842, 2014) and tubular specimens subjected to servo-controlled axial force and internal pressure. Many linear stress paths in the first quadrant of stress space are applied to the specimens to measure the contours of plastic work (CPW) and the directions of plastic strain rate (DPSR) up to a reference plastic strain of 0.22. It is found that the Yld2000-2d yield functionYield function (Barlat et al., 2003) accurately reproduces both the CPW and DPSR. Isotropic (IH) and differential hardening (DH) models are determined using the Yld2000-2d yield functionYield function; in the DH model the values of exponent and eight material parameters of the Yld2000-2d yield functionYield function change as functions of reference plastic strain. Moreover, a hole expansion forming experiment was performed. The thickness strain distribution along the hole edge was measured and compared with the FEAFinite element analysis results obtained using selected yield functionsYield function. The DH model correctly predicts the minimum thickness position that matches the fracture position of the specimen in experiment. It is concluded that the yield functionYield function best capturing both the plastic work contours and the directions of plastic strain rates leads to the most accurate FEAFinite element analysis results.

The effect of torsional oscillation on the surface quality of an extruded sidewall of a workpiece was investigated in backward cup extrusionExtrusion with an extrusion ratio of 2.0 at room temperature. In this extrusion process, a cylindrical aluminum workpiece lubricated with mineral oil was extruded in the axial direction and simultaneously twisted in the circumferential direction between extrusionExtrusion and knockout punches. The two punches were controlled with an axial speed of 0.1 mm/s, an alternating amplitude of 5°, and a maximum angular speed of 0.5 rpm. The torsional oscillation tilted the traction direction at the container–workpiece from the radial direction to the circumferential direction with approximately 25% lower contact pressure on the container. As the result, the surfaceSurface of the extruded sidewall was uniformly smoothed.

Inclined rotary formingRotary forming (IRF) combines bending and axial compression with rotation and is employed for forming flange shaft-structured parts from round rod billets. Although the forming load is smaller than the one in conventional processes, cracks may develop during this process. However, it is difficult to predict the onset of cracks using conventional ductile fractureDuctile fracture prediction equations. In this paper, an equation for predicting ductile fractures is proposed, which considers anisotropic ductile damage. The proposed equation is expressed as a second-rank tensor resulting from the inner product of the stress tensor and the strain increment tensor. Referring to the previously published results on the compression of cylindrical specimens, the difference between diagonal and longitudinal sidewall cracks was clarified by considering the anisotropy of ductile damage. The proposed equation was then applied to the IRF process, wherein diagonal cracks developed at the outer rim of flange. Consequently, it was possible to estimate the requirements for reducing diagonal cracks by controlling lubrication conditions.

For the production of large heat-resistant components, improving the prediction accuracy of microstructural behavior by the finiteFEM element method leads cost and time reduction in process optimization. To perform this task, it is essential to predict the recrystallizationRecrystallization behavior accurately, during hot forging and heat treatment of Ni-base superalloys. So far, many researchers have used the Avrami equation to predict the recrystallization behavior. However, this uses experimental coefficients determined empirically for each process, so it is not suitable for predicting the microstructureMicrostructure of large-scale hot forged parts with different complex deformation and thermal histories at different locations. Because the recrystallizationRecrystallization behavior is considered to depend on the path, and on the temperature, strain, and strain rate at that time. Therefore, an incremental form of a prediction model based on the Avrami equation has been developed as a solution. Optimized parameters for the incremental model were obtained by using a genetic algorithm which is an adaptive heuristic search algorithm. At this time, it is not enough to use only the results of small tests at the laboratory level as training data for genetic algorithm. This is because the thermal histories and distributions have a large difference between the small specimens and the large parts. In this study, 1,500 and 50,000 t class forging tests were performed, and the parameters in the prediction model were determined using these results as learning data. As a result, the average error of prediction was reduced to about half.

In this study, we investigated the influence of microscopic structures of highly cold-rolled pure aluminum A1050 on macroscopic mechanical properties based on the crystal plasticityCrystal plasticity finite element (FE) analysisFinite elements analysis. Uniaxial tensile tests and biaxial tensile tests were performed, and the contours of plastic workContour of plastic work were plotted. The comparison of experimental results and results obtained by the crystal plasticityCrystal plasticity FE simulation with a small number of grains indicates that the yield strength for the rolling direction was higher than that for the transverse direction of the rolled sheet; however, the experimental and numerical yield surfaces did not agree. Extreme value analysisExtreme value analysis was used to estimate the variation of mechanical properties in simulated results due to the combination of crystal orientation in the computational models employed.

The low lattice symmetry and limit deformation modes of wrought magnesiumMagnesium (Mg) alloys restrain it from wide use in aerospace and automobile industries. Addition of rare earthRare earth (RE) elements has been used as the textureTexture modifier to improve the formability of Mg alloys. Mg-1Al and Mg-4Y extruded alloys were investigated to probe the effects of the Y addition on the textureTexture and microstructure of Mg alloys. It is demonstrated that the non-RE alloys exhibit a $$ \left\{ {10\bar{1}0} \right\} $$ 10 1 ¯ 0 or $$ \left\{ {10\bar{1}0} \right\} - \left\{ {11\bar{2}0} \right\} $$ 10 1 ¯ 0 - 11 2 ¯ 0 texture depending on the recrystallized fraction, whereas the yttrium (Y) Mg alloys develop a $$ \left\{ {11\bar{2}1} \right\} $$ 11 2 ¯ 1 “RE texture” component. The mechanism of “RE textureTexture” component’s formation was studied by using the electronic backscattered diffraction (EBSD) technique. The results indicate that the formation of both $$ \left\{ {11\bar{2}0} \right\} $$ 11 2 ¯ 0 and $$ \left\{ {11\bar{2}1} \right\} $$ 11 2 ¯ 1 textureTexture components is closely related to the continuous dynamic recrystallizationDynamic recrystallization (CDRX) of the grains which nucleate in the mantle regions of the original grains.

Double-Sided Incremental Forming (DSIF) is a rapid-prototyping manufacturing process for metal formingMetal forming that, for low-volume production, is competitively energy-efficient. However, controlling the DSIF process in terms of accuracy and formability is an ongoing challenge. These control challenges arise due to a lack of understanding of the underlying deformation mechanisms in DSIF, which finite elementFinite element simulationsSimulation can help to unravel. However, DSIF pushes the limits of modern finite element formulations due to true strains that approach one, finite rotations, nonlinear contact, and triaxial stress states that range across multiple length scales. To confidently develop a finite elementFinite element model of DSIF, an extensive verificationVerification process must be considered, which is the objective of this study. In this work, different finite element types and varying amounts of artificial acceleration are investigated, and recommendations based on efficiency and accuracy are summarized. A simplified, axisymmetric geometry was considered to reduce simulationSimulation time. For this geometry, accelerating the explicit finite element simulation by a mass factor of 105 or greater affected the stress triaxiality in the sheet by as much as 40% in some locations with respect to the quasi-static case. Additionally, the ratio of the kinetic energy to internal energy of the sheet was not a reliable indicator of whether a DSIF simulation is approximately quasi-static.

In typical crystal plasticityCrystal plasticity framework, the constitutive functions for the slip rate is commonly described by the rate-dependent formulation to avoid the non-uniqueness of the active slip systems due to the interdependency of the slip systems. These rate-dependent models are computationally expensive as these models impose numerically stiff, highly nonlinear equations that need to be solved at every integration point. Alternatively, the rate-independent crystal plasticity model uses the crystal yield function to describe the slip deformation and plastic spin by the active slip systems without the non-uniqueness problem. In this study, the effect of nonlinearity between resolved shear stress and slip rate on the shape of the crystal yield function in the formulation of the rate-independent crystal plasticityCrystal plasticity was rigorously investigated. In addition to the effects of the crystal plasticityCrystal plasticity model, the influence of the nonlinearity of the single crystal yield function on the evolution of anisotropyAnisotropy for various polycrystalline materials was evaluated.

The true stress-strain curves of 2024 aluminum alloy plate are investigated under different deformation conditions through the cyclic bendingCyclic bending and uniaxial tensile tests. Under this condition, the equivalent strain limit is improved with the increase of the times of circle bending, which is linear accumulated along the line that is perpendicular to the neutral layer on which the bending strain is zero. Furthermore, the tensile test with the cyclic bended plate samples were carried out. The equivalent strain of layer is calculated and compared with original tensile test. It is found that the ultimate strain limitUltimate strain limit of average equivalent strain of the layers on section is extended with a significant value.

Professor Wang once served as the president of the China Society for Technology of Plasticity (CSTP). He also hosted and chaired the 4th International Conference of Technologies of Plasticity (ICTP) in Beijing, in 1993, to bring the event for the first time to China. During the 60 years’ academic career life on metal forming, he has published 17 books and more than 300 academic papers, and won international and national Awards 5 times, including invention award and science & technology progress award, etc. The main contributions of Professor Wang include: developing the engineering plasticityEngineering plasticity theory and promoting its applications, inventing the dieless hydroforming method for large-scale spherical shells, solving the technological problems of several key national projects of China, leading internationalization of Chinese community of plasticity engineering, and supervising a group of talents on metal forming.

The metal formingMetal forming industry is responding to changing technical and commercial demands of customers and increasingly stringent legislative restrictions. In addition, on demand delivery requires lead times having to contract. Also Original Equipment Manufacturers are demanding deliveries just-in-time on changeable schedules and for many products batch quantities have become smaller than they were a few years ago. Thus, lead times must be shortened. To meet these challenges, in the metal formingMetal forming industry, the rate at which new and existing process technologies and production practices are being developed is increasing. Computer-aided design and manufacturing systems have been allied to computer process simulation, to form powerful Cloud based, knowledge-based tools for producing parts right-first-time through identifying the customers’ needs. The purpose of this paper is to illustrate the contribution made by the authors to enhance the added valueAdded value of metal formed parts, through advancing scientific process knowledge and developing software to support computer-aided manufacture.

Magnesium alloyMagnesium alloys cylindrical parts with inner ribsCylindrical parts with inner ribs (MACPIR) are attractive as lightweight components for improving the performance of high-end equipment in various industrial sectors. Induction-heating-assisted spinningInduction-heating assisted spinning (IHAS), an effective way to manufacture cylindrical parts made of difficult-to-deform materials, was used to form the MACPIR. However, when using this process for MACPIR, nonuniform deformation and other forming defectsForming defects can easily occur between the cylindrical wall and inner ribs. A FEM model of MACPIR during IHAS was developed via ABAQUS, and experimental verification was conducted. Forming defects that occurred during the spinning process of MACPIR were analyzed, and evaluation indexes of forming qualityForming quality were proposed. The results show that the concavity of rib back, and nonuniform distribution of rib height along tangential and axial directions are the main forming defectsForming defects. Additionally, the influence of process parameters on the forming qualityForming quality was discussed. The results indicate that the forming qualityForming quality of MACPIR can be improved under a forming temperature of T = 300 ~ 350 ℃, roller feed rate f = 0.4 ~ 0.6 mm/r, and thinning ratio of wall thickness Ψt = 65 ~ 75%. The simulation results confirm well with experimental ones.

Integrated casting and forging processIntegrated casting and forging process (ICFP) is a feasible manufacturing method which significantly improves the mechanical properties of casting due to forging process eliminating porosity defects. In this study, a new model that predicts the law of porosity closure during forging is proposed, which considered the variation of stress triaxiality ratioStress triaxiality ratio, Lode parameter and effective strain, was implemented into finite element package FORGE2.1. A356 was used as specimen materials subjected to X-ray computed tomography (CT) scanning. The comparison between the simulation results and the experimental results shows that the proposed model can accurately predict the maps of porosity closure volume in the forging process of A356 aluminum alloy. With the model, the ICFP design and optimization will be convenient.

Pulsating hydroformingPulsating hydroforming and impact hydroformingImpact hydroforming are two advanced technologies to increase the formabilityFormability of material compared with other traditional forming technologies. They were systematically investigated from aspects of technical principle, forming mechanism, equipment, and applications. Pulsating hydroformingPulsating hydroforming can improve the forming ability by altering the friction condition of sheet/tubeSheet and tube parts or by utilizing the effect of transformation induced plasticity of stainless steels under the pulsating loading. As for impact hydroformingImpact hydroforming, the strain rate can reach 103–104/s and the instantaneous pressure can be GPa level, which can obviously increase the elongation of hard-to-form material by 20–60%. The effect of flexible liquid and impact impulse was investigated by both experiment and simulation, while the mechanisms were related to the compatible deformation of the second phase, strain decentralization, and defect stabilization. The technologies have been used on the manufacturing of complex, thin-walled components for the fields of aeronautics and aerospace, automobile, nuclear power, etc.

Incremental sheet forming (ISF) is a promising flexible forming process in fabricating low-batch or customized sheet metal parts, and has potentials in reduced process lead time and cost, and increased formability. In the plenary talk, recent investigations on ISF fundamentals and the technologies for ISF industrial application will be presented, which cover tool pathTool path algorithms, forming tool development, surface roughness and forming load predictions, new variants of ISF, deformation mechanismDeformation mechanism of different ISF variants, and several industrial application cases. Finally, an outlook about ISF will be made as well.

Applied mechanical vibration in various manufacturing processes, usually at ultrasonic frequencies of 20 kHz, has been shown to influence the forming and friction forces. The material softening behavior under superimposed ultrasonic vibrations is known as acoustoplasticity. This paper investigates the effect of acoustoplastic softening phenomenon on material movementMaterial movement in incremental forming of AA7075 sheets. A 45° cone is formed using a two-point incremental forming strategy (TPIF). Added ultrasonic vibration shows higher amount of material movementMaterial movement, which is supported through quantitative measurements including greater bulgeBulge height, surface profilometry, and thickness distribution around the tool contact area. Surface roughness measurements, relative to the depth of the geometry, increase with progressive forming. This coincides with the notion of greater material movementMaterial movement, accumulation, and surface deformation.

Thin-walled steel profiles are the key to cost efficient lightweight structures. Structure parts and design elements in cars and trucks are often based on curved and hydroformed profiles. The possible production chains for those parts are often long and complex, and the machines and tools are expensive, and the flexibility is low. For smaller production lots, e.g., for applications in aircraft industry, these processes are not efficient. This paper shows a solution for smaller and middle-sized production lots realized by an integrated process for bending and cross section forming of tubular lightweight parts by a forming operation based on a working media made of metal alloys with high plasticity. The paper shows the process idea, fundamental mechanisms, the process analysis, and the process limits. Furthermore, a strategy is given to find a practical process windows.

Rotary formingRotary Forming is an exciting route for forming flanges of different angles from seamless tubes of high-strength materials. True to its incremental nature, the process offers great flexibility, but the issues encountered are atypical and complex. One such issue observed in experimental trials is the internal buckling of tubes during specific instances of flange formation. The origin of this instability is non-trivial, and ordinarily, finite-element (FE) models fail to capture this instability. To analyse and understand the problem, systematic experimental trials were carried out using different tube thicknesses, tube materials, and tool kinematicsTool kinematics. This paper summarises the results from a critical analysis to establish (1) a criteria for quantifying the instability and identifying the instances of its occurrence, (2) a validation methodology to fine-tune FE models for the process, and (3) use of FE models to understand the influence of tool path in the flange formingFlange forming stage.

Beside the manufacturing of finished parts by Incremental Sheet Metal Forming (ISF), final operations within the process chain can also be realized with this technology. The technological capabilities of performing incremental (hole-)flanging operations for sheet metal parts has been investigated in research context. The current topic focusses on the transfer of the incremental formingIncremental forming technology to manufacture tubular parts. An incremental collar formingCollar forming process was developed where all motions are executed by the forming tool. Due to the fixed position of the workpiece, tubes, as well as pipes can be branched. Stainless steel tubes made of 1.4404 (316L) with an outer diameter of 54 mm and a wall thickness of 1.5 mm were used for experimental evidence of functional capability of the incremental collaring process. The influence of different pre-hole geometries and forming tool shapes on the properties of the collar (e. g. geometrical accuracy, wall thickness) was investigated.

The multi-stage incremental sheet forming is a promising forming strategy to fabricate complex shapes through the rational design of intermediate shapes. To further improve the formability, the ultrasonic-assisted multi-stage incremental sheet forming is proposed. The present work aims to reveal the effect of ultrasonic vibrationUltrasonic vibration (UV) on the thickness distribution, strain–stress state and the forming force variation. First, the finite element (FE) model is established through ABAQUS software, in which the trajectory of the forming tool with the high-frequency vibration is defined via the user subroutine VUAMP. Then, after the verification of the FE model, the thickness evolutionThickness evolution, the stress–strain state and the forming force are comprehensively analyzed. It is found that the thickness distribution can be effective improved by introducing UV. In addition, the stress concentration in the bending area is effectively alleviated and the equivalent plastic strain is obviously increased under the UV. Final, the application of UV can lead to a notable reduction of forming force and smoother forming force curves at the latter two stages. The findings of this work provides evidences that ultrasonic assistance is an effective strategy to improve the incremental forming process.

A new test method for sheet metal deformation, Tension under Cyclic Bending and Compression (TCBC), is developed in this study. The TCBC method is capable of testing material deformation under tension, bending, and compression with cyclic loading. The effect of each deformation mode can be independently controlled by adjusting corresponding parameters. Using the TCBC test rig developed, aluminium alloy AA5251-H22 is tested under four different testing conditions: simple tension, tension under cyclic compression, tension under cyclic bending, and tension under cyclic bending and compression. The maximum elongation of the tested specimen at fracture and the tensile force required for material plastic deformation are evaluated. The results show that the maximum elongation increases significantly under the TCBC condition due to localised plastic deformation under compression that delays the fracture. Finite element modelling of the TCBC test is developed to obtain stress distributions to explain the enhanced formabilityFormability. The new TCBC method may be used for testing material formability that resembles double-side incremental forming.

The mechanisation of traditional craftCraft processes can serve as a starting point for novel process development in the increasingly topical field of flexible metal formingMetal forming. This approach presents several challenges, including understanding the underlying mechanics, mechanisation, and providing suitable control methods for such processes. Here, we focus on the underlying mechanics of the process known as the English wheelEnglish Wheel. In this work, the process is studied through validated numerical modelling techniques. The influence of various geometrical parameters is examined and the possible patterns of plastic deformation are presented.

In this study, a new method of ultrafine copperCopper and brass wires production was proposed. The proposed technology is based on the dieless drawingDieless drawing. The workpiece for the dieless drawing is a thin wireWire (100–200 μ) obtained by a conventional drawing method. The proposed technology is based on the implementation of a multi-pass incremental deformation. Moreover, in each pass, strain and strain rate sensitivity of flow stress should be positive and significant. The deformation parameters in each pass are determined based on the flow stress dependency on the strain, strain rate, and temperature. Therefore, plastometric tests of copperCopper and CuZn37 alloy were performed. To estimate the temperature of deforming wire the FE modeling of dieless drawingDieless drawing was performed. The obtained data were used in the practical implementation of incremental dieless drawingDieless drawing technology. RoughnessRoughness analysis was performed for brass samples. In the performed experiments tests, the dieless drawingDieless drawing will lead to an increase of roughness of the wire surface. However, this increase is relatively small. The value of Ra before the dieless drawing was 1.73 μ, and after deformation, it was 2.23 μ.

Robotic roller formingRobotic roller forming (RRF) is a new dieless and flexible forming process using a roller mounted on an industrial robot to form sheet metal products by multiple passes with predefined tool paths. In this study, DP590 (dual-phase) steel sheets are formed to bent specimens having a right angle by RRF with three passes, and edge wavesEdge waves are observed at the flange of DP590 specimens. Finite element analysis is utilized to reproduce the edge wavesEdge waves. According to finite element simulation, longitudinal plastic strains are generated at the flange edges due to excessive tensile and compressive stresses, which results in severe edge waves.Edge waves Two strategies are introduced to eliminate edge waves.Edge waves One has to optimize forming parameters, and the effects of forming angle increment and moving direction of the roller on longitudinal peak strainsLongitudinal peak strain at the flange edges are evaluated. Another strategy to eliminate edge wavesEdge waves is to apply laser heatingLaser heating in RRF, where the heating spot is 25 mm in front of the roller. Experimental results demonstrate that laser heatingLaser heating reduces forming forces, eliminates edge wavesEdge waves as well as the required number of forming passes.

Flow formingFlow forming is an incremental formingIncremental forming process during which a roller tool deforms a rotating sheet metal by applying a force which is local and evolving during the entire process. The finite element software FORGE® is used in order to model this process. The local tool-workpiece contact conditions and the high rotation speed make the modelling of this process difficult with high computation timeComputation time. It is, therefore, necessary to develop optimizationOptimization strategies aiming to reduce the computation time whilst maintaining a sufficient level of results accuracy. A first configuration optimizationOptimization method consists of reducing the geometry of the initial blank and using symmetry planes. The final reduced geometry obtainable is 36° wide. This method is then associated with a second one which consists of reducing the number of calculation time steps during the entire process. The calculation time steps removed are those occurring when the roller tool is not in contact with the deformable sheet metal anymore. The two combined methods give the ability to drastically reduce the computation timeComputation time compared to the reference case. In addition, the global and local results of the reference case are mostly conserved when applying the configuration optimizationOptimization methods.

The industrial application of incremental sheet formingIncremental Sheet Forming (ISF) (ISF) still stays behind the expectations due to the low geometrical accuracyGeometrical accuracy of the produced parts as well as the insufficient predictability of the forming result. This is due to the fact that some mechanisms which cause the geometrical deviations are not fully understood. Many investigations have already been carried out to determine which types of stresses induced by ISF influence the forming result. This paper tries to systematically categorize selected typical geometric deviations and to review their underlying mechanisms based on current literature as well as their own experience. The intention is to provide a structured basis for future scientific discussion and to stimulate an exchange of experience, with the goal that a better understanding may help to improve the geometrical accuracy of parts manufactured by incremental sheet forming.

The roundness and the angle of the edges on the cross-sectional profile at the exit of the fin pass are crucial for the welding quality of the ERW tube. In this paper, the adjustment of the bending angles of the cage rollsCage roll was proposed to make a 9-inch tube. The proposed roll forming machine layout is capable of making tubes in a specific range of outside diameters without changing rolls. The CAE simulations were carried out to verify the proposed roll flower designs and the bending angle control strategies of the cage roll stations. The CAE simulations had verified the proposed flower design using different roll adjustments, and proper bending angle control strategies are able to make the demonstrated tube.

The open die forging/upsetting of bulk material to a cone shape involves high plastic deformation. The plastic strain causes major changes in the material’s mechanical and metallurgical characteristics. In order to gain a better understanding of these characteristic changes, experimental, analytical, and numerical models were developed and studied. First, sample material properties and friction conditions (with several lubricants) were measured. Next, analytical models (upper boundUpper bound and slab method) simulated the forging forces and the results were compared to results from a finite elementFinite element (FE) model. These were then compared with the experimental findings using C101 copperCopper. The preformed samples were surface etched with a grid pattern and the strain caused by the forming operations was measured from the grid changes. The flow pattern was inspected and compared with the outcomes using a similar material and a numerical model. A good resemblance was found between the experimental results and the theoretical models.

Incremental sheet forming with active mediumActive medium (IFAM) is a flexible manufacturing process that creates concave–convexConcave-convex sheet metal parts in one clamping without needing a counter tool or a die. In the first study of this new process (Ben Khalifa and Thiery in CIRP Ann 68(1):313–316, 2019, [1]), a conventional hemispherical tool has been used in interaction with pressurised air to manufacture concave–convex parts. Since the geometric accuracyGeometric accuracy was not satisfying, within the present study, a conical tool with a dedicated angle is introduced to IFAM. The idea behind this tool concept is to restrict the inclined part wall to a target angle. At first, results from the numerical investigation show an improvement of the accuracy when a conical tool is used to manufacture a truncated convex pyramid. Subsequently, experiments validate the numerical model and reveal increased process reliability. The experimental investigations of truncated convex cones and concave–convexConcave-convex parts close the paper and underline the feasibility of the tool concept.

Nowadays, the efficient manufacturing of functional components in short process chains is important due to the goal of a further reduction of greenhouse gases. Additionally, there are also technical demands like functional integration combined with an improvement of the component’s properties. Previous investigations have shown that the application of tailored blanksTailored blank with a defined thickness profile can lead to an improvement of the geometrical and mechanical properties of functional components. However, common forming processes reach their limits. A promising approach to enlarge these process limits is the application of bulk forming operations to sheet metals, the so-called sheet–bulk metal forming (SBMF). Within this process class, one possibility for manufacturing such blanks is a flexible rollingFlexible rolling process. As a result of movement of two rolling tools in combination with a die cavity in the lower tool, a defined geometry can be manufactured perpendicular to the sheet plane. In order to raise the complexity combined with a shorter process chain and thus to fulfil the requirements defined by the subsequent forming operations, a new design that contains a preform of involute gearings is introduced. In order to acquire process knowledge, the mild deep drawing steel DC04 with an initial sheet thickness of t0 = 2.0 mm is used. Furthermore, the subsequent application of the tailored blanks in a combined deep drawing and upsetting process is shown, with a characterization of the geometrical and mechanical properties.

In order to improve the production efficiency and material utilization rate of metal cup with a curved rotary profile, a new method of roll forming (RF) isRoll forming proposed. That is, a roll forming equipment with a set of pre-formingPre-forming rollers and a set of shapingShaping rollers is mounted on the drawing hydraulic press to form a curved rotary profile of cup. The influence of roller number on the roll forming was studied by numerical simulationNumerical simulation. The results show that the open end of the rolled part is extremely uneven when two rollers are used. In addition, metal flows into the gaps between rollers, forming thin flashes which must be cut off after the pre-formingPre-forming step. The open end of the rolled part is relatively even when three rollers or four rollers are used. No metal flows into the gaps between pre-forming rollers, and no folding is found after shapingShaping. The accuracy of numerical simulationNumerical simulation is verified by experiments, and aluminum cups with a curved rotary profile that meet the requirements were successfully formed.

The great potential of machine learningMachine learning models in different domains has been shown in recent years. Based upon initial research regarding preprocessing methods for time series classification in the hot forming technology of radial–axial Ring RollingRing rolling, this paper takes the next step to further investigate the suitability of different machine learningMachine learning models for a classification task regarding the ovality of a formed ring. This is achieved by implementing several models of the time series classification domain in machine learningMachine learning and training them on actual production data of thyssenkrupp rothe erde Germany. The data set consists of different production days and ring geometries, and thus includes a plurality of challenges of radial–axial ring rolling real-world data. Different experiments will be performed and their results will be analyzed regarding performance, interpretability, and usability in the production environment. Thus, a suitable model for the underlying task will be investigated, which is essential for a future model deployment to improve the radial–axial ring rollingRing rolling process further.

In this study, a neural network model is developed to describe the large deformation response of a multi-phase materialMulti-phase material, i.e., a two-dimensional perforated plate. Using the finite element, virtual experiments are performed to generate stress–strain data for monotonic biaxial loading paths. Subsequently, a combination of fully connected and recurrent neural networkRecurrent neural network models are trained and validated using the results from the virtual experiments. The predictions of a network show a remarkable good agreement with all the experimental data. The suggested neural network-based constitutive model does provide a robust solution to the problem at hand, providing a fully anisotropic, three-dimensional material model capable of covering all physical material properties. The suggested procedure promises to be generally applicable to any material class and can be paired with any numerical method.

Several developments in deep drawingDeep drawing aim at systematically determining modifications during tool tryout. Recent work deals with a simulation-based method to discover the current state parameters based on characteristic measurement quantities and infer a tryout proposal by comparing with the simulated robust optimum. While the simulation provides an accurate model of the drawing process, a low fidelity surrogate model is required to predict the influence of process parameters on the targets in a computationally efficient manner. In this work, training data is generated by a stochastic finite element simulation in AutoForm. The data points are used to fit and evaluate linear models as well as neural networks for regressionRegression. These models use process parameters as predictors to estimate the target parameters draw-in and local blank holder forces. Results show that simple models outperform complex models. No evidence was found that the model accuracy increases by using neural networks.

Material cardMaterial Cards generation has a significant role for characterizing the mechanical behaviour to estimate accurate deformation in finite element analysis. Regarding this, the most commonly used characterization test for sheet metals is the uniaxial tension test due to its simplicity and well-defined testing standards. The mechanical properties such as ultimate tensile strength can be determined by tensile tests. However, the strain level can reach to a specific value which is low as compared to strain levels reached in cold forming operations. In this paper, the experimental data is optimized with finite element analysis and a good consistency between experimental and simulation results is achieved. Parameter optimizationOptimization is used as a guiding tool to extend strain levels according to 3 mechanical equations: Swift, Hockett-Sherby, and Combined material model. The user interface is designed with the detailed graphs and optimized parameters with the help of MATLAB tool.

In-plane torsion testIn-plane torsion test has attracted a lot of attention recently. As a novel shear test, it can avoid unwanted reaction torque compared with the traditional in-plane shear test. The in-plane torsion testIn-plane torsion test with circular groove specimens can avoid early fracture at the free edges, and thus achieve actual fracture strain under pure shear state because it has no free boundaries. In this study, digital image correlation is implemented to measure the torsion angle to obtain the precise torque-torsion angle curves. For specimens with slits, strain hardening is calibrated by inverse engineering approach. The strain path at the center of the shear zone during the torsion test is observed to be very close to a pure simple shear state. Cyclic shear loadingCyclic shear loading tests are carried out for twin bridge shear specimen. The combined isotropic-nonlinear kinematic hardeningKinematic hardening model, Yoshida–Uemori two-surface model, and homogeneous anisotropic hardening model are evaluated to characterize the cyclic loading behaviors.

This paper investigates the deformation behaviorDeformation behavior and fracture characteristicsFracture characterization of WE43 Mg alloy under various stress states, including tension, compression, and shear. The digital image correlation technique is adopted to obtain highly accurate experimental data and stress–strain curve. The result indicates that the plastic deformation behaviorDeformation behavior under different stress states has a great difference and fracture already obviously occurs before necking. After calibrating the material constants of yield function and hardening equation, numerical and experimental result are compared. The result shows that the prediction accuracy of FE is very high. The fracture strain under different loading statesVarious loading states is ensured through a hybrid experimental-numerical methodHybrid experimental-numerical method. The fracture locus is constructed based on DF2016 criterion and the predicted fracture strain is compared with the experimental result. The result reveals that DF2016 ductile fracture criterion can correctly predict the fracture limit strain under various stress states.

Strain hardening properties of AA5182-O metal sheet are experimentally studied and analytically modeled at different temperature in this research using a dogbone specimen. The strain rateStrain rate hardening and thermal softeningThermal softening behaviors are then modeled by popular analytical models to consider the strain rateStrain rate and thermal effects. The high nonlinear strain hardening with the effect of strain rateStrain rate and temperature is also illustrated by artificial neural networkNeural network. The results show that the strain hardening with strain rateStrain rate and thermal effect can be accurately modeled by the neural networkNeural network compared with the conventional models, but its computation efficiency is much lower than the analytical models.

The VDA 238-100 tight radius bend test has received significant attention from industry over the past decade because it provides a proportional plane strain–plane stress state until fracture. It will be demonstrated that the adoption of the vertical punch force as the unique metric for failure detection can lead to false positives. The punch force will reduce at large bend angles due to the mechanics of the test even in the absence of material failure. Two novel detection methods based on the nominal principal stress and the plastic workPlastic work were evaluated on six different steel grades with a nominal ultimate tensile strength of approximately 590 MPa. Three 590R590R advanced high-strength steels provided by three different suppliers and three variants of the Ductibor® 500Ductibor® 500 are studied. The stress-based metric can be seen as an improvement over the VDA 238-100 load methodology since it accounts for thinning of the specimen cross-section and can identify false positives when the material forms a full bend in the absence of fracture but drops at bend angles greater than 160°. For performance ranking of materials with the same strength level, the plastic workPlastic work metric is found to be sufficiently sensitive to distinguish between various 590 MPa steel grades since the material hardening rate is directly embedded.

Plasticity of AA7075-OAA7075 extruded tube under tension–tension (T-T) and tension–compression (T-C) was characterized using multiaxialMultiaxial loading tube expansion test method. Three different yield functions, von-Mises, Hill’s 1948, and Yld2004 were considered to model the anisotropic plasticityAnisotropic plasticity of the AA7075-OAA7075 tubes under T-T and T-C. The anisotropic models were calibrated based on the measured biaxial stresses and the conjugate plastic strain rates as strain-rate potential based on plastic work equivalency. As shown, this calibration method is an accurate and more flexible way of calibrating the advanced yield functions with no necessity for having proportional loading paths. It was also shown that the three yield functions predict the strain paths under T-C conditions almost similarly, however, the strain paths under T-T conditions are predicted better as the number of anisotropy parameters in the yield functions increases.

The localization of strain in conventional shear testsShear test and in-plane torsion testsIn-plane torsion test is analysed for three different materials, namely CP1000, DP1000, and DC04. The influence of material properties, such as strength, strain hardeningHardening, and strain gauge length on the measurement of shear strains is investigated experimentally and by a new analytical approach. The weakly hardening high-strength complex-phase steel CP1000 shows experimental and analytical deviations up to 25% of the determined strain depending on the evaluation strategy. Such deviations will lead to crucial errors for the calibration of fracture curves and damage models. By a new grooved in-plane torsion testIn-plane torsion test specimen shear testsShear test can be performed without the influence of the localization of strain. Strain measurements can thus be performed more exactly nearly regardless of the strain gauge length and hardeningHardening behaviour. In the first experimental results, the deviation is below 4.6% for CP1000 and below 0.5% for DC04.

The carbon nanotube (CNT) reinforced aluminum has been expected as one ideal metal matrix composite characterized by superior strength and high elastic modulus. However, the reduction of its ductility is often a serious drawback. Nonuniformity in the microstructure makes it difficult to maintain the structural integrity during the deformation. In this study, the mechanical property of CNT/Al2024 composite sheet of 1.0 mm will be investigated through uniaxial tensile tests. Meanwhile, the simulations based on micro- and macro-mechanical constitutive are conducted to reveal the relationship between the evolution of microstructure, like grain size, dislocation density and interfacial bonding, and macro deformation responses. This work can be helpful to better understand the key factors that influence the plastic deformation and failure of CNT/Al2024 composite under complex loading conditions.

Due to the common discontinuity of the structure and non-uniform load, local high stress phenomenon tends to appear in the mechanical structure under repeated loading, and even local small plastic deformation may occur. In this case, the cyclic elastic–plastic mechanical properties of the structural steel are the key elements for the reasonable and accurate assessment of structural safety. In order to study the cyclic mechanical properties of GS-20Mn5GS-20Mn5, which is a commonly used steel in load-bearing mechanical equipment, corresponding strain cyclic loadingCyclic loading tests were performed. The cyclic elastoplastic deformation characteristics under strain-controlled cyclic loadingCyclic loading with different strain ratios (R = −1,0.5) are studied, and the cyclic hardening/softeningCyclic hardening/softening and mean stress relaxationMean stress relaxation features are revealed. The results show that the cyclic hardening/softeningCyclic hardening/softening features are affected by the strain amplitude and cycles. This test material tends to show cyclic hardening at higher strain amplitudes. The cyclic stress–strain curveCyclic stress-strain curve, The is obtained by the incremental step test, and the corresponding yield strength is about 4.8% larger than that under uniaxial tension. When R = 0.5, the test material exhibits obvious mean stress relaxationMean stress relaxation. When the strain amplitude is 0.16%, 0.30%, and 0.40%, the mean stress decreases and then stabilizes at about 25 MPa, −3 MPa, and −6 MPa, respectively. For the mechanical equipment made of GS-20Mn5GS-20Mn5 with local small plastic deformation under cyclic loadingCyclic loading, the obtained cyclic mechanical performance of GS-20Mn5GS-20Mn5 can provide a reference for the analysis and evaluation of the structural safety.

Cold drawingCold drawing of tubes is a metal forming process that allows manufacturers to produce high precision tubes. The anisotropy is a natural phenomenon in the tube wall thickness, in this method of manufacture. The EBSD measurements have been made on several Ferritic–pearlitic steels (8.9 wt% pearlite content) with different deformations for the detection of the effect composition has on the textureTexture formation. The development of the crystallographic texture can be clearly explained by the stress–strain state at the material flow. This article was pointed out and connected between the development of the texture and stress state during the cold drawingCold drawing process by turning the body-centered K8 grid (BBC). A significant influence on the texture change is also the heat treatment, where grains have the different ability of recrystallization. The cognition of this process will make it possible to achieve a tube with the optimum texture for the cold drawing process.

To study the dynamic softening behaviors of 5083 aluminum alloysAluminum alloy with different initial microstructures under hot compressionHot compression, hot compression tests of extruded and homogenized specimens were conducted at a strain rate ranging from 0.1 to 10/s and deformation temperatures ranging from 350 to 450 °C. The obtained true stress–strain curves of homogenized specimens were lower than those of extruded specimens especially at the initial deformation stage, suggesting that the effect of different initial microstructures on flow stress is significant especially at the initial deformation stage. Electron backscatter diffraction (EBSD) was used to observe the microstructure evolutionMicrostructure evolution process. The characteristics of continuous dynamic recrystallizationDynamic recrystallization, particle-stimulated recrystallization, and discontinuous dynamic recrystallization were confirmed. The experiments deformed at the same temperature and strain rate but with different strains showed the transition from continuous to discontinuous recrystallization. The recrystallization mechanism of 5083 aluminum alloysAluminum alloy with different initial microstructures is thus finally illustrated.

The plastic anisotropic response of stainless steelStainless steel materials is investigated in this paper by using Barlat’s Yld 2000-2d yield criterionBarlat’s Yld 2000-2d yield criterion. A new set of anisotropy coefficients is proposed and calibrated based on material experimental data. The new set of coefficients for the Lankford anisotropy coefficient, normalized yield stress, and equal biaxial stress were numerically obtained using the Newton–Raphson method. Study cases for AISI 409L and AISI 430 materials are presented and discussed. Correlations between predictions and experimental results indicate that Barlat’s yield stress criterion and plastic stress potential for stainless materials are not coincident. Hence, the Barlat’s non-associate flow rule gives better fitting with the experimental Lankford’s coefficient of anisotropy results.

A basic evaluation of a new press forming techniquePress forming technique using in-plane shear deformationIn-plane shear deformation was carried out to suppress fracture and wrinkle of parts bent in the height direction, supposing auto body parts such as the front side member rear. This two-step technique comprises two processes. The first process is deep draw forming with a rectangular blank to induce in-plane shear strain in the blank. The second process is bending the pre-formed blank into a part shape with a U-shaped cross section. According to experiments, in-plane shear deformationIn-plane shear deformation was induced in the blank in the first process when the press stroke changed along the part longitudinal direction, and increasing the induced in-plane shear deformationIn-plane shear deformation made it possible to form a part with a higher bent angle in the height direction in the second process. The results suggested that complex bent parts which were difficult to form by the conventional press forming techniquePress forming technique can be formed without fracture or wrinkle when appropriate in-plane shear deformationIn-plane shear deformation is induced in the blank in the first process.

Cold forgingCold forging is a manufacturing process where a bar stock is inserted into a die and squeezed with a second closed die. It is one of the most widely used chipless forming processes, often requiring no machining or additional operations to get tight tolerances. Because materials to be formed are increasingly harder and the geometrical complexity is greater, the finite element simulation is becoming an essential tool for process design. This study proposes the use of the Chaboche hardening model for the cold forging simulation of a 42CrMoS4Al material industrial automotive ball pin. The material model has been fitted with experimental data obtained from cyclic torsion tests at different reversal plastic strains as well as monotonic torsion tests at different strain rates. Comparison between the classical isotropic hardening and the new mixed hardeningMixed hardening model are presented for the different forging steps.

The reduction of fuel consumption due to restrictions regarding CO2 emissions is one of the major driving forces for lightweight design in the automotive industry. In this context, hot stampingHot stamping of ultra-high-strength steels has developed to a state of the art process for manufacturing safety-relevant components. With regard to passenger safety and weight reduction, further potential lies in the functional optimization of the parts. Prior local carburizationCarburization followed by hot-stamping is a new process variant for tailored properties, which overcomes the limitations of established processes. Due to the varying carbon content after carburization, the sheets have graded mechanical properties. Within this contribution, the influence of temperature, strain rate and carburization on the flow behavior will be investigated. For this purpose, tensile tests at elevated temperatures are carried out in a physical simulator of type Gleeble. The resulting flow curves of the carburized complex phase steel are modeled with a modified Norton-Hoff hardening law and the influence of the carburizationCarburization process is analyzed by means of the initial yield stress. Furthermore, the results from tensile tests are correlated with the phase transformation behavior obtained by a laser ultrasonic sensor.

Electricity-assisted metal forming, especially using pulsed-current, was demonstrated to promote a drop in flow stress and improving formability. To investigate the effect of pulsed-current on stress relaxationStress relaxation, a uniaxial tensile test was conducted with different pulsed-current parameters by changing its pulse-width and frequency. Short pulse-width was used in the range of microseconds, while the frequency was arranged under 1 kHz. Different level of temperature was used to consider the effect from joule heating. Stress relaxationStress relaxation in the tensile test was repeated at constant strain interval at 3% strain. This research presents an analysis of stress relaxationStress relaxation influenced by the time-dependent parameter of short pulsed-current.

The cyclic softening/hardeningCyclic softening/hardening, ratchetingRatcheting effect, and Bauschinger effectBauschinger effect usually occur in the body structure of large mechanical equipment under cyclic loading. This manuscript focuses on Q235 steel commonly used in the welded frame of large mechanical equipment. The experiments were carried out with mean stress varying from −60 to 60 MPa and stress amplitude varying from 300 to 340 MPa, respectively, and the mechanical responses were analyzed comprehensively. The experimental results show that Q235 steel exhibits cyclic softening characteristics at positive mean stress and cyclic hardening characteristics at negative mean stress. The larger the stress amplitude or the absolute value of the mean stress, the greater the absolute value of ratcheting strain. At the same stress amplitude, when the absolute value of the mean stress is equal, the Bauschinger coefficient is almost equal. Based on the experimental results, the evolution formula of ratchetingRatcheting strain is established by a phenomenological method.

The effect of trace nitrogenNitrogen on microstructure, hardnessHardness, toughnessToughness, and tempering stabilityTempering stability of Cr-Mo-V hot-working die steelDie steel was investigated in this study. Results show that trace nitrogen promotes the precipitation of V(C, N), increasing the amounts of undissolved carbides in tempered steel. The undissolved carbides exert a stronger pinning effect on refining austenitic grains during the quenching process and refine the final tempered microstructure. The solid solubility of alloying elements and lattice distortion of matrix decreased obviously by trace nitrogenNitrogen. Trace nitrogen could increase the hardnessHardness and toughnessToughness of hot-working die steelDie steel by refining the microstructure. However, the tempering stability would be decreased obviously due to the decrease of solid solubility of alloy elements, especially V. The results of this research can be used to provide a scientific basis for applications of nitrogen in hot-working die steel.

This paper is concerned with the evaluation of rate-dependentRate dependency hardening behaviorsHardening behavior of autobody metal sheets with novel tension and compressionTension and compression testing devices. Hardening behaviorsHardening behavior in tension and compressionTension and compression are indispensable for accurate numerical simulation of sheet metal forming and subsequent spring-back as well as crashworthiness. In addition, it is important to consider the strain rate effect for hardening behaviors in tension and compression because sheet metal deformation prevails at intermediate strain rates up to hundreds per second in press shops of the automotive industry as well as in car crash. Novel in-plane tension and compressionTension and compression testing devices are developed with a servo-hydraulic testing machine to obtain tension–compression hardening curves of autobody metal sheets at intermediate strain rates ranging from 0.001 s−1 to 100 s−1. With the testing devices specially developed, hardening behaviorsHardening behavior are evaluated in tension–compression for mild steel sheets, TRIP980, TWIP980 steel sheets, and magnesium alloy at various strain rates ranging from 0.001 to 100 s−1 in terms of the flow stress considering the Bauschinger effect and the permanent softeningPermanent softening. It is observed that the stress offset is dependent on the inherent characteristics of metal sheets as well as the strain rates. It is confirmed from the experiments that the Bauschinger effect decreases as the strain rate increases. The permanent softeningPermanent softening defines the stress offset between flow stress curves in tension–compression and monotonic tension with large deformation after loading reversal.

In this study, creep behavior characteristics ofMagnesium alloy sheet (AZ31B) magnesium alloy sheet (AZ31B) according to pre-strain during warm formingWarm forming were analyzed through experiments. In addition, stress relaxationStress relaxation process was analyzed by applying the creep behavior of magnesium alloy sheet to analytical simulation. In the creep test, the strain due to the creep phenomenon of magnesium alloy at room temperature was 0.001 at 1000 s of constant load holding time, whereas it was broken at 8 s at 250 °C. The stress exponent of magnesium alloy at room temperature is 10.60 and the stress exponent is 4.8 at 250 °C. Similarly, in the case of stress relaxationStress relaxation experiments at room temperature, the amount of load reduction was 74 N at 1000 s while the amount of load reduction was reduced by 522 N at 250 °C. The stress exponent and parameters obtained from the experiments were applied to the analysis simulation, and the creep and stress relaxationStress relaxation processes were compared with the experimental results.

Warming forming, or the combination of cold forming, and multiple heat treatment processes are usually used to obtain AA7075 parts in T6 temper. However, the above-mentioned methods increase the forming cycle and cost, and lead easily to change in the microstructure. In this paper, a new forming process is proposed, namely pure electroplastic-assisted thermal forming (PEPATF) process, which can reduce the forming temperature by using pure electroplastic/non-thermal effect to compensate plasticity loss caused by the decrease of temperature. In order to research the mechanism of electroplastic effect,Electroplastic Effect oven-heating uniaxial tensionOven-heating uniaxial tension at different temperatures and electrically assisted uniaxial tensionElectrically-assisted uniaxial tension test at different temperatures and current densities are performed for AA7075-T6. On the one hand, the results show that at the same temperature, the flow stress obtained by electrically assisted heating is lower than that obtained by oven-heating, indicating that pure electroplasticity exists and is more obvious with the increase of temperature. Moreover, at the same temperature, the flow stress decreases with the increase of current density at the same temperature. On the other hand, the elongation obtained by electrically assisted uniaxial tensionElectrically-assisted uniaxial tension is higher than that obtained by oven-heating uniaxial tensionOven-heating uniaxial tension. For electrically assisted uniaxial tension, the largest elongation is at 150 °C.

The effects of pulse currentPulse current on the microstructureMicrostructure and mechanical propertiesMechanical properties of two kinds of ultrahigh-strength steelsUltrahigh strength steel (UHSS) were studied by electrically assisted tension tests. The elongation of the two UHSS (MS1300 and QP980) moderately increases at relatively low current density, while their microstructuresMicrostructure keep almost unchanged. For MS1300 steel, the elongation can be increased from 8.3% at room temperature to 12.4% at the current density of 6.58 A/mm2. The peak stress of QP980 is reduced to 900 MPa at the current density of 7.46 A/mm2, and the elongation is increased from 22.3% at room temperature to 38.4%. If the current density is further increased, the tensile strengths of UHSS are greatly reduced. Meanwhile, their microstructuresMicrostructure are also obviously varied. Therefore, the appropriate current density should be selected in order to maintain the UHSS grades.

The stress relaxationStress relaxation ageingAgeing behaviour and post-form mechanical propertiesPost-form mechanical property of an Al-Zn-Mg alloyAl-Zn-Mg alloy, AA7B04, have been experimentally investigated and modelled. The stress relaxationStress relaxation ageingAgeing tests were carried out under different initial stress levels and durations at 165 °C and subsequent tensile tests were performed at room temperature. The detailed effects of stress and time on stress relaxation and main post-form mechanical properties (yield strength, ultimate tensile strength, and uniform elongation) have been analysed and discussed. Based on the results and analysis, a set of unified constitutive equations has been developed for the first time to simultaneously predict stress relaxation ageing behaviour of the aluminium alloy during the creep age forming (CAF) process and the main mechanical properties of the products after CAF. The model comprises three sub-models, including microstructure, stress relaxationStress relaxation ageingAgeing and post-form mechanical propertiesPost-form mechanical property, and has successfully predicted corresponding behaviour. The developed model provides an effective tool to not only predict the forming process but also support possible industrial applications for CAF products.

Nickel-based superalloys have been widely used to produce high-performance components in advanced engines. In present research, isothermal compression tests of GH4065A nickel-based superalloy were conducted at deformation temperatures of 1020–1140 °C and strain rates of 0.001–1.0 s−1. The deformation temperature and strain rate have a significant effect on the flow curves, from which the intrinsic connection between the flow stress and deformation behavior can be systematically investigated. The deformation activation energy of the studied alloy was calculated to be 521.65 kJ·mol−1 at the strain of 0.5 when the flow stress was steady. Meanwhile, the constitutive equation was constructed for modeling the hot plastic deformationHot plastic deformation, and the prediction accuracy of flow stress was well verified. Based on the combination of processing mapProcessing map and microstructural observation, two instability domains were delineated as follows: Domain #1: 1020–1065 °C/0.25–1.0 s−1; Domain #2: 1130–1140 °C/0.001–0.002 s−1. In addition, the instability mechanism of these two domains was deeply discussed. The results obtained in this research would provide effective theoretical guidance for manufacturing high-performance components in advanced engines.

Ni-based superalloysNi-based superalloy are widely used to manufacture the key components of a gas turbine engine because of their superior mechanical properties at elevated temperatures. In the present work, the hot deformation behavior of a novel Ni-based superalloyNi-based superalloy was investigated by compression test at temperatures of 1020–1140 °C and strain rates of 0.001–10 s−1. At low temperature and high strain rates, the flow stress rapidly increased to a peak value due to work hardening. However, at high temperatures and low strain rates, the flow curves exhibited a typical dynamic softening stage. The hot deformation activation energy of the studied superalloy is determined to be 735.4961 kJ/mol, and a strain-compensated Arrhenius-type constitutive equation is obtained. On comparing the predicted and experimental values, the developed constitutive equation can accurately describe the deformation mechanism and the flow behaviorFlow behavior. Meanwhile, the influence of hot processing parameters on microstructureMicrostructure has been deeply explored, which can optimize the process parameters for manufacturing key components in gas turbine engine.

This paper evaluates and criticizes the Swift model of expressing strain hardeningStrain hardening behaviours of metals at room temperature using an experimental tensile test and its FE prediction. A concept of reference flow stressFlow stress curve composed of two ranges of strain divided by the true strain at the necking point is proposed, which predicts tensile test exactly from the standpoint of engineering and is thus employed to evaluate the Swift model. It has been shown that it has a weak point in describing the flow stress of typical strain hardening material with emphasis on necking. An improved Swift model is applied to obtain accurate flow stress of a commercial steel AISI1025 and it is employed to simulate a sequence of cold forging processes by precision complete analysis for process and die optimal design in terms of die life, which should be conducted under an accurate analysis model.

Stress-relaxation age formingStress-relaxation age forming (SRAF) of a component (820 × 300 × 3 $${\mathrm{mm}}^{3}$$ mm 3 ) with complex and large curvatures has been simulated and a corresponding SRAF test of an Al–Mg–Si alloyAl-Mg-Si alloy, AA6082-T6, has been carried out in this study. An FE model is established to simulate the stress-relaxation ageing (SRA) behaviour of AA6082-T6 during SRAF at various stress levels, ranging from elastic to plastic regions, and a unified constitutive model for SRA of the material has been implemented in the finite element (FE) software ABAQUS via the user-defined subroutine CREEP. An optimised tool surface was determined from the FE simulationFE simulation through springback predication and compensation and was used for manufacturing test. A good agreement of the formed shape has been achieved between the FE simulationFE simulation and the SRAF test, with a maximum shape error below 4 mm, satisfying the industrial requirement. The hardness results from the formed plate showed an insignificant change of strength during SRAF, and are in good agreement with the simulation. The effects of the initial plastic strain and creep strain generated during loading and stress-relaxation stages on the formed shape have also been analysed.

Manufacturing technologies for parts made from ultra-high-strength 7xxx series aluminum7xxx series aluminum sheet material have been the focus of research in recent years. A promising approach is W-temperW-temper forming, where sheet material is cold formed after heat treatment. Conventional heat treatment routes are very time-consuming and inefficient. In this study, a new more efficient and industry-orientated transfer tool concept has been developed. Heating and cooling of the sheets take place in separate contact temperingContact tempering stages, which allow superior heating and cooling rates in comparison to conventional methods. To analyze the influences of temperature rates and deformation on microstructure and mechanical behavior, thermo-mechanical experiments in a Gleeble simulator were carried out. The results prove the great potential of the transfer tool concept with inline heat treatment for series production. The process-dependent mechanical properties determine a suitable process window for the industrial application of the W-temperW-temper forming of the analyzed alloys.

Stress–strain curveStress-strain curve in the high-strain region is one of the most important models that must be taken into consideration for high-precision sheet metal forming simulation. In this study, using mild steel sheetsMild steel sheet, tensile tests were conducted with a necked shape specimen at the center in order to generate non-uniform elongation. Using image analysis, strain–load relationships were obtained using multiple gauge lengths, and stress–strain relationships were obtained by inverse analysisInverse analysis using FE simulation. With a sufficiently small gauge length it is possible to get stress–strain curveStress-strain curve in the high-strain region. The advantage of this method is that the experiments can be implemented only with a uniaxial tensile testUniaxial tensile test. For validation, the original hole expansion test model that is not affected by friction is proposed. The thickness strain distribution along the hole with large plastic strain is compared with the experimental and numerical results to indicate the validity of this method.

Due to the low density and high tensile strength, the aluminium alloy EN AW-7075 offers a high lightweight potential for structural components. In recent years, 7xxx-aluminium alloys7xxx Aluminum Alloys have been the subject of numerous investigations in the field of warm and hot forming and suitable heat treatments to fully use their potential for applications in automotive bodies. Alternatively, forming blanks of these alloys at room temperature in the W-temper state is favourable since conventional tools can be used. However, this condition is unstable. As the ageing duration after quenching increases, the formability decreases due to natural ageing. Hence, the objective of this investigation was to determine the formabilityFormability of EN AW-7075 as a function of the ageing time. Furthermore, since the quenching rate after solution heat treatment influences the resulting mechanical properties, an adapted process route to manufacture components with tailored properties was explored. For this purpose, samples were partially quenched after solution heat treatment and then artificially aged. To determine the influence of the quenching rate, hardness tests were carried out.

The hot tensile deformation behavior of 5052 aluminum alloy5052 aluminum alloy is investigated by uniaxial tensile tests with the temperature range of 523–723 K and strain rate range of 0.001–0.1 s−1. The constitutive equation is established based on the Arrhenius-type equation and Zener–Hollomon parameters, which are applied to numerical simulationNumerical simulation for solid boss forming by plate forgingPlate forging process. As a result, the flow stresses obtained from the constitutive equation are consistent with the experiments, and the proposed constitutive equation is succeeded to predict the deformation behavior in the plate forgingPlate forging process. The best forming temperature for boss solid forming is 673 K based on the boss forming ability analysis.

In order to study the tensile properties of Al–Li alloy 5A905A90 at high temperature, the Al–Li alloy sheet metal with a thickness of 1.6 mm was obtained by rollingRolling the original plate with the original thickness of 7.3 mm. Universal tensileUniversal tensile tests of the previously rolled sheet metals were carried out in the temperature range of 375–450 ℃ with a strain rate of 0.002 s−1. The experimental results show that the elongation of the material reaches 600% at the temperature of 425 ℃, the true strain reaches 2.0, and the peak stress at this temperature is 8.0 MPa.

A combination of dissimilar AA7075/6060 aluminum alloys benefits the advantages of high strength and good corrosion resistance in one hybrid component. Static compound castingCompound casting using appropriate casting conditions can achieve intermetallic bonding at the interface of the core AA7075 and sleeve AA6060. The inhomogeneous bonding due to non-uniform thermal conditions during static compound castingCompound casting can be eliminated by the following co-extrusionCo-extrusion procedure. Direct hot extrusion of compound-cast AA7075/6060 bilayer billets at a temperature of 420, 450, and 480 °C is conducted to analyze the influence of extrusion temperature on the interfacial bonding. The evolution of the interfacial bonding properties at different extrusion temperatures of as-cast billets is depicted by light optical metallography and mechanical push-out test.

Nearly 20% of the aluminum produced globally is extruded. Up to one-quarter of this aluminum is scrapped in the form of extrusion butts and segments of extruded profiles that contain weak solid-state “transverse” welds that are created between consecutively extruded billets in direct extrusion. In this article, extrusion of differently colored clay billets is used to conduct a parametric study on the effect of extrusion ratio, die angle, friction coefficient, profile shape, and dummy blockDummy block profile on the transverse weld length. Shorter transverse weldTransverse weld lengths require smaller lengths of the extruded profile to be extracted and scrapped. The results show that the transverse weldTransverse weld length can be reduced by decreasing the extrusion ratio, die angle, or friction coefficient. The profile shape also has a strong influence; the transverse weldTransverse weld length was found to scale with the cross-sectional perimeter to area ratio of the extruded profile. Additionally, it is shown that the dummy block profile (a previously unexplored design variable) can be modified to decrease the weld length. A concave dummy blockDummy block was designed using an estimated velocity field for axisymmetric extrusion of solid rods, decreasing the weld length by 44%. The industry implications of this work and the need for further research are discussed.

The new extrusion process combines the conventional methods of direct and indirect aluminum hot extrusionHot extrusion by an innovative container and die setup with a moving or stationary valve. The process enables the continuous extrusion of aluminum profiles without any interruptions. With both variants, moving or stationary valves, the usual dead cycle times can be used for a continuous extrusion process. Furthermore, due to the continuous material flow, a stationary profile exit temperature can be achieved, which leads to constant material properties. As of now, a continuous extrusion pressExtrusion press for aluminum is not available. The new process concept is analyzed on the basis of scaled experimental models using the model material plasticine and numerical simulations. The similarity of the model material was validated by aluminum extrusion experiments. Various model material colors were investigated, and the resulting material flow and process forces of the new process were analyzed.

In recent years, an aluminum double-skin panelDouble skin panel, which has a complicated and wide cross-sectional shape, is manufactured by extrusion and used for railway vehicles. It is difficult to manufacture a double-skin panel exceeding 600 mm width in the current forward extrusion process. However, from the viewpoint of weight saving, there is a demand to make a double-skin panel with larger widths. So we propose to manufacture double-skin panelDouble skin panel with complex extrusionComplex extrusion of multi-billets. Complex extrusionComplex extrusion of multi-billets is suitable for producing complicated and wide extruded shapes. We focused that the joint part of the double-skin panelDouble skin panel is joined in a plate shape. In this study, industrial pure aluminum A1050 and representative extruded alloy A6063 were extruded into a plate shape, and the joining state was evaluated by tensile test, micro Vickers hardness test, microscopic observation, and numerical analysis.

Conventional tube drawing methods have the disadvantage that thickness reductionThickness reduction in one pass is small. This paper proposed a tube drawing method for overcoming this disadvantage, and the method expands the diameter at the same time of drawing. At first, the tube is flared by pushing the plug into the tube end. After that, the plug is drawn by chucking the flared end, and the entire tube is expanded. Tensile circumferential and axial stress reduces the tube thickness effectively during the plug drawing. In this study, the effect of expansion ratioExpansion ratio on formability, such as thickness reductionThickness reduction and dimensional accuracy, was investigated by experiments and finite element analyses (FEA) for verifying the effectiveness of the proposed method. As a result, the thickness reductionThickness reduction increased with an increase in the expansion ratio, and the maximum thickness reduction ratio was 0.3 when an aluminum alloy of AA1070 was used. Furthermore, the deformation mechanism was considered by FEA.

As a kind of extrusion process, the forward–backward–radial extrusionForward-Backward-Radial Extrusion (FBRE) process can be used to produce complex-shaped parts with hoop protrusions or flanges. The control of metal flowMetal flow is the key to affect forming, strain distribution, and forming load during the FBRE process. On the basis of summarizing the research of the FBRE process, this paper presents the numerical and experimental results of aluminum alloyAluminum alloy hub production using this method. Material flow behavior and strain distribution within the final product were investigated by finite element methods. The parameters such as billet size, die corner radius, and friction conditions are optimized and determined to control the material flow in different sections. While the uniformity of extrusion deformation is greatly improved, the extrusion forming load is reduced, and the aluminum alloyAluminum alloy hub was manufactured by the FBRE process. The comparison between the theoretical and the experimental results shows good agreement.

SiC-coatedSiC coated dies SiC die and punch were used for forging titanium wire to have a triangular cross-section higher than 30% reduction in wire diameter. Computer numerical control (CNC) stamper was utilized to describe the elasto-plastic behavior of titaniumTitanium wire in dry forging. Precise analyses on the contact interface between SiC coating punch and titanium work were made to investigate the mass transfer of metallic titanium as well as titanium oxide debris particles onto SiC coating surface. On the basis of these experimental results, how to design the die materials for dry metal forming of titanium was reconsidered for biomedical applications of wrought titanium.

Spur gearsSpur gears are an important transmission part used widely in many industries. Precision forgingPrecision forging of spur gears has a lot of advantages compared with the conventional mechanical cutting method. However, it is very difficult to fill the corner well and the forging load is also very large, especially in the final forming stage during the precision forging of spur gears. So, a three-dimensional (3D) finite element (FE) model for precision forgingPrecision forging of spur gears was built by DEFORM-3D software. The stress and strain states in different forming stages and positions of billet have been studied. Also, the Lode parameterLode parameter μσ was calculated, and the metal flow line method was used to reveal the deformation mechanismDeformation mechanism of the tooth material. Results show that the Lode parameterLode parameter of the tooth shape is negative at the beginning of the tooth filling and is positive at the final stage of the tooth filling. Also, the stress state changes from two-directional compressive stress and one-directional tensile stress to three-directional compressive stress.

EPITHER is an innovative way of shaping composite materials that seek to combine the strength of continuous fibre reinforced thermoplastic (CFRT) composite materials with the high production rates existing in the forging industry. The use of composites in the manufacture of structural parts must make it possible to lighten the driving parts of vehicles and to give part of the solution to the reduction of CO2 emissions. Good material health is crucial for the production of structural parts, and some of the parameters associated with it are a direct consequence of the shaping conditions and have an influence on the strength of the final product. With a view to controlling and optimizing the shaping parameters, this study begins by defining the relevant material characteristics to be measured in order to judge the quality of the latter, then studying the links between the process and the finished product.

In this paper, a cold orbital forgingCold orbital forging process is proposed to manufacture thin parts with high circular ribs. First, a FE model was established for the numerical process analysis. Then a verification experiment was performed to verify the validity of the FE model developed above. By using the FE simulation method, the influences of several forging parameters on the cold orbital forging of thin parts with high circular ribs were investigated. The results show that effective strain can be obviously improved by increasing feed velocity of cavity die, but has less change with different friction factors. Synchronism of metal flowing between the inner rib and the outer rib can be improved by decreasing feed velocity of cavity die and friction factor. Moreover, the circumferential metal flowing degree can be slightly reduced by increasing feed velocity of cavity die and friction factor.

Multi-stage forgingForging process chains are often used for the efficient production of complex geometries. Typically, these consist of homogeneous heating, one or more preform stages, and the final forgingForging step. By inhomogeneously heated billets, the process chains can be simplified or shortened. This shall be achieved by setting various temperature fields within a billet, resulting in different yield stresses. These can influence the material flow, leading to easier production of complex parts. In this study, the influence of inhomogeneously heated billets on the forming process is investigated by means of FEAFEA. For this purpose, two process chains including inhomogeneous heatingInhomogeneous Heating and three homogeneously heated reference process chains are developed and compared. Each process chain is optimized until form filling and no defects occur. Target figures for the assessment are necessary forming force, the amount of material necessary to achieve form filling and die abrasion wear. For process chains with inhomogeneously heated billets, the results showed a small time window of about 5 s for a successful forming in terms of form filling. Forming forces and die abrasion wear increase for inhomogeneously heated billets due to higher initial flow stresses. However, the flash ratio decreases when billets are heated inhomogeneously. Depending on their size, inhomogeneously heated billets show up to 11.8% less flash than homogeneously heated billets. This shows a potential for the use of inhomogeneous heatingInhomogeneous Heating to make forgingForging processes more efficient. Subsequently, experimental tests will be carried out to verify the results of the simulations.

When designing a closed die forging process, it is necessary to determine the process conditions with respect to various evaluation points such as forging load and shape accuracy. Two examples of process conditions are the number of stages and the die surface shape of each stage. It is particularly difficult to determine the combination of these two process conditions, which is called “process layout” in this paper, because there are numerous potential patterns that lead to a long development period for the design. Our objective is to generate a draft of the process layout for closed die forging. In this study, the authors focus on the forging process for disk-shaped products. To design a die surface shape with high flexibility, the authors propose a new method for die surface shape called the functional surface connection method and have developed an automatic design method for process layout by combining the proposed method with FEMFEM and an optimization algorithmOptimization algorithm. The evaluation results showed that a process layout in which forging load restriction and forged shape accuracy were satisfied could be generated automatically.

In forging processes, the determination of blow efficiency is very important, as it quantifies the part of the stroke energy actually transmitted to the billet. Thus, forging processes should be deeply analyzed in order to better understand the stroke energy conversion, accurately estimate blow efficiency, and thus better predict process parameters. In this paper, a spring-mass-damper vibration model is proposed to describe forming operations of a screw press. Parameters specially adapted to the machine-tools system are identified, thanks to a stroke without billet. Thereafter, the experimental upsetting of a copper cylinder is realized, and two independent numerical simulationsNumerical simulation are performed. First, the billet upsetting is simulated by FE simulationFE simulation with no consideration of the elastic and damping effect due to the machine-tools behavior in order to determine a relation between the load and the billet height. Then, forging load from the FE simulationFE simulation is used to perform another simulation of the forging process with the spring-mass-damping model. Results show that the model is relevant to simulate load and ram displacement. Moreover, simulation can predict the distribution of the energy during the simulation and the blow efficiency can be calculated. This new way to obtain blow efficiency might improve productivity in process development and provide a better understanding of energy-driven machines.

Besides achieving the intended final shape, one main aim of open-die forgingOpen-die forging is the adjustment of the mechanical properties by transforming the cast structure into a fine-grained microstructure. To achieve this, the process needs to be designed in a way that ensures achieving all the required part properties, such as grain size, which up to now often requires a lot of operator experience. This paper presents the concept of a forging assistance systemAssistance system, since during forging small deviations from the previously designed pass schedule might add up to unacceptable errors. Such an assistance systemAssistance system requires the evolution of part geometry and surface temperature as input, which are captured with a thermographic camera. The assistance system then uses fast models for equivalent strain, temperature, and microstructure which allow calculation of these properties for the core fibre within seconds on the basis of semi-empirical and physical formulae. However, in the context of an assistance systemAssistance system, which gives real-time advice in case of process deviations, these calculation times are still fairly long, if the hundreds of iteration necessary for process optimization are taken into account. Therefore, three scenarios of deviations, which have to be solved within different time frames, are examined to explore the limits of the chosen classical optimization algorithm.

A forgingForging process planningProcess planning method, including blankingBlanking and punchingPunching, termed General Step Reduction and Enlargement (GeneSteR+E), is discussed for cold- and warm-forged products. It is applicable to non-axisymmetric forged products that consist totally of non-axisymmetric shapeNon-axisymmetric shape elements and can generate multiple process plans without relying on design cases. The shape of a forged product is split into outer and inner shapes, which are then split into axisymmetric and non-axisymmetric shapeNon-axisymmetric shape representation units termed basic elements (BEs) according to shape separation rules. Process plans are generated in reverse order from a final forged product by applying shape transformation rules that reduce the number of steps between BEs until a billet (or a blank) is obtained. The shape transformation rules are defined not only for forgingForging, but also blankingBlanking and punchingPunching. An experimental knowledge baseKnowledge base was implemented and applied to several non-axisymmetric forged products, such as an electrical connector. The results show that the GeneSteR+E method is applicable to the design of forgingForging processes including blankingBlanking and punchingPunching of totally non-axisymmetric products and can generate satisfactory process plans comparable to those developed by an experienced engineer.Umeda, Masanobu Mure, Yuji Katamine, Keiichi Matsunaga, Kazuya

Due to the processing of high-strength materials in fine blankingFine blanking, the lifetime of conventional high-speed steel punches decreases rapidly. Materials with higher wear resistance and compressive strength, such as cemented carbideCemented carbide, are investigated for use in fine blanking processes. However, cemented carbideCemented carbide punches often fracture during the stripping offStripping off phase due to the combined tensile and flexural stress collective. The understanding of fracture mechanisms and subsequent fracture prevention supports the application of cemented carbides. The fracture mechanisms during stripping offStripping off are mostly unknown. The objective is to identify fracture mechanisms of cemented carbide punches. The fracture mechanism of cemented carbideCemented carbide punches was metrologically monitored by means of acoustic emissionAcoustic emission (AE) and process forces. The fracture pattern was analyzed related to the measured signals. In order to interpret the AE signal, basic process analyses were performed. Subsequently, a punch fracture of cemented carbide was provoked with the high-strength steel 1.8974. Cemented carbideCemented carbide punches tend to fracture during stripping offStripping off as a cause of asymmetrical interactions with the scrap web.

The quasi-beta forgingQuasi-beta forging behavior of Ti-55511 alloyTi-55511 alloy is systematically studied by hot compressive deformation experiments and electron back-scattered diffraction (EBSD) tests. The results show that the strain rates have obvious effects on the hot deformation behaviors of the studied alloy. With the increase of strain rate, the flow stress increases. At low strain rates, the work hardening rates hardly change until a critical strain, and then the work hardening rates slightly increase. At a medium strain rate (0.1 s−1), the work hardening rate gradually decreases until a critical strain, and then the work hardening rate shows little variation with strain. However, at high strain rates (1 s−1), the positive work hardening rate indicates the obvious work hardening at the initial deformation stage, and the work hardening rates change to negative and then to positive with strain when the strain rate is further increased to 10 s−1. The main soften mechanism of β grain is DRV. With the increase of strain rate, the fraction of DRX grains and the sub-grains decrease. Too high strain rate leads to the formation of flow localization.

HammerHammer forgingForging is a widely employed manufacturing process to produce parts with excellent mechanical properties. Although the rheological behavior and the microstructural transformation phenomena of metals under hammer forging conditions are of great industrial interest, few materials have been tested in such intermediate strain rates (10–103 s−1) due to the lack of laboratory machines for intermediate speed testing. With the objective of addressing that gap, this paper presents a novel automatic forging simulator comprising an instrumented forging hammer capable of performing intermediate speed deformations, up to 5 m/s. Three data acquisition approaches were evaluated to select the most appropriate approach and obtain valid rheological data from intermediate strain rate tests performed on the developed hammer. First, the data obtained by both a high-speed camera and a load cell was combined to calculate reference flow curves. Then, two additional data monitoringMonitoring approaches were then analyzed, employing independently first the high-speed camera and then the load cell data. It was concluded that flow curves obtained utilizing only the load cell data offered accurate results without the need for an expensive and complex high-speed camera.

In this work, the latest developments on the electromagnetic (EM) module of FORGE® and the derived improvements for simulating the magnetic pulse formingMagnetic pulse forming process are presented. The following aspects are covered: advanced material description for high-intensity magnetic fields where coupling with the material database software JMatPro® is extended to account for the EM phenomena; integration of the forming limit diagrams (FLD) for analysis of thin sheets forming; improved meshing/remeshing for large displacements in the fully immersed multi-objects approach, where a particular focus is given to the fields transfer stage, showing how the overall CPU time can be reduced by half or more; and introduction of an advanced second-order time-stepping integration method based on an asynchronous interpolation that was previously developed for thermal-shock problems and is now extended to the computation of EM fields showing excellent convergency and stability properties.

Since high-strength lightweight Al-Li alloysAl-Li Alloys gained much attention recently, investigating the dynamic behavior of high-strength lightweight AA2060-T8AA2060-T8 sheets is crucial because of their outstanding mechanical properties. Thus, uniaxial tensile tests were performed under high strain rate conditions using universal testing machines and split Hopkinson tensile bars. The ductility of AA2060-T8 sheets was improved under HSR deformation because of the adiabatic softening with increasing strain rate and the inertia effect, which may diffuse necking, slow down the necking development, and delay the onset of fracture. The present study results can efficiently develop a new manufacturing route based on impact hydroformingImpact hydroforming technology (IHF) to manufacture sound thin-walled-complex shape components from high-strength lightweight Al-Li alloy sheets at room temperature.

HighHigh-velocity shearing-speed shearing was studied to potentially improve the sheared edge quality of advanced high-strength steels. The AIRAM pneumatic pressPneumatic press can provide significantly higher speed than a conventional press, up to 1.5 m/s depending on equipment setup at a low energy cost. The study evaluated the pneumatic pressPneumatic press that could increase the slide speed up to 1.5 m/s. Various grades of AHSSAdvanced High Strength Steel (AHSS) steel, DP780 and GEN3-980, were sheared using the pneumatic pressPneumatic press with two different operating pressure levels as well as using a conventional press with 0.2 m/s with the same tooling. The edge quality of the sheared blanks was evaluated using half-specimen dome test (HSDT) and microhardness tests. The effects of high-speed shearing are discussed in this paper.

Magnetic pulse technology is used for high-speed forming as well as for joining. Joining by magnetic pulse welding (MPW) is the combination of high-speed forming, impact, and a resulting weld in the collision zone of the accelerated flyer and the impacted target. This MPW process allows the welding of dissimilar metals, like aluminum and steel for lightweight constructionLightweight construction or aluminum and copper for E-mobility applications. Investigations showed up scattering in binding strength and failure for comparable welds. The effects leading to the bond formation and the reasons for the quality variation are not fully understood until now. For further understanding, a combined experimental investigation of integral and local mechanical weld properties supported by simulations and microstructure analysis was performed considering dissimilar metal joints of aluminum EN AW1050 H14/24 and copper Cu DHP R240 for different configurations and impact energies. Lap shear tests served for quantifying integral mechanical properties, while local mechanical properties were determined by microtensile tests on samples prepared in the thickness direction of the welded metal sheets and microstructural analysis. These local microscopic testing and analysis results provide information about the weld strength distribution. These investigations give new hints on the bond-forming mechanisms and local processProcess effects depending on material effects.

The use of lightweight materials such as high-strength steel, aluminum alloys, and composites is increasing. The joints of dissimilar alloys as the aluminum alloy 6082-T6 and the HC420LA steel are studied in this work. The selected joining process is the magnetic pulse weldingMagnetic pulse welding (MPW) (MPW) which enables welding of these two alloys, being non-joinable by other traditional welding technologies. The technology involves a strong electromagnetic–mechanical–thermal interaction. The investigation will be developed mostly on computational modeling by means of using LS-DYNA software, taking into account the key process parameters and their influence. The work includes experimental results for validating the numerical analysis. All the analyzed cases showed welding of the blanks, which was confirmed by metallographic characterization. The simulations show the same deformation behavior as experiments.

Since Blaha discovered the beneficial effect of superimposing high-frequency oscillations to the metal formingForming process, the occurring force and stress reduction are well-known phenomena. Leading to an immediate flow stress reduction, the so-called ultrasonicUltrasonic assistance is a promising approach to enable forming with reduced process forces. While the achievable force reduction has been investigated intensively, only a few analyses have been conducted in the context of the impact of ultrasonic superposition on the forming limits. The latest investigations state earlier material failureFailure due to localized forming with recurrent high strain rates. Within this paper, the influence of superimposed vibrations on the forming limits of C35E is investigated with regard to distinct oscillation amplitudes and press velocities. It was found that superimposed 20 kHz oscillations of 10 and 20 µm cause considerable earlier material failureFailure. In comparison to conventional testing, the crack initiation, as well as the shear zone formation, is alternated due to the ultrasonicUltrasonic assistance.

Magnetic pulse weldingMagnetic pulse welding (MPW) is a high-speed joining process that uses pulse electromagnetic force to achieve welding. It is a clean welding process and it can be applied to dissimilar metals weldingDissimilar metals welding, which has a wide range of application prospects. However, this technology is currently mainly used for welding small-diameter thin-walled tubes. This is because the energy and electromagnetic force required for welding increase significantly as the tube size increases, which consequently places strict requirements on welding tools, including pulsed power and coil. To solve this issue, this work developed a two-dimensional (2D) axial-symmetry finite element model to optimize the tube weldingTube welding process and designed a high-performance magnetic actuator with a high-strength coil to generate a strong enough electromagnetic force. On this basis, both numerical and experimental studies were performed to investigate the welding behavior of a 6061 aluminum alloy tube and a 304 stainless steel tube with 110 mm diameter and 3 mm thickness. Finally, a mechanical test and scanning electron microscope (SEM) were used to verify the joining quality, and the results show that the metallurgical bonding occurred between the two tubes. The presented optimization method and tool design could be of significance to the practical applications of MPW technology.

Magnetic pressure seam welding has attracted attention as a new joining method for aluminum sheetsAluminum sheet. Magnetic pressure seam welding is a collision welding process for producing metallic bonds of similar and dissimilar materials, utilizing electromagnetic force as the acceleration mechanism. Pressure seam welding is a method of abruptly adding a high-density magnetic flux around a metal material and utilizing the generated electromagnetic force to deform the sheet at high speed and pressure welding. This paper deals with the deformation behaviorDeformation behavior of aluminum sheetAluminum sheet with single and parallel coils. The sample used for this analysis is assumed to be a sheet made of aluminum and composed of quadrilateral elements of plane strain. Numerical analysisNumerical analysis of the dynamic deformation process of the metal plate is performed by the finite element method. As a result, it was shown that the collision point velocity is very fast at the initial collision point, but decreases continuously during welding. In addition, the thinner the sheet, the wider the gap length for obtaining higher equivalent stress and frictional stress. The initial collision point velocity, equivalent stress, and friction stress at the time of collision in the parallel coils showed the same tendency as in the single coil.

Modern car body design includes parts with sharp-edged elements, which are challenging for conventional sheet metal forming technologies. This is especially critical when implementing aluminum parts in order to consider lightweight design requirements. Applying high strain rates allows increasing formability for numerous materials, including typical aluminum alloys used in the automotive industry. Therefore, integrating high-speed forming into a conventional process can help to extend forming limits. The feasibility of locally sharpening a deep-drawn radius by integrated electromagnetic formingElectromagnetic forming was proved in the literature, but up to now, the investigated target radii were much larger compared to the sheet thickness. The presented paper shows that target radii in and below the size of the sheet thickness are possible by this process combination. Based on a simplified 2D component geometry, complementary experimental and numerical investigations served for developing different variants of a modular test tool and analyzing the influence of important process and tool parameters on the forming result.

The use of a chemical explosive mixture to augment the vaporizing foil actuator (VFA)Vaporizing foil method and laser impact welding (LIW) processes is introduced in this study. A liquid explosive known as Picatinny liquid explosive (PLX) was used to augment the capabilities of both the VFA and LIW processes. The 304 stainless steel flyers 3 mm thick driven by PLX augmented VFA and unaugmented VFA are compared. Similarly, 0.442 mm thick Al3003 flyers driven by laser impact and PLX augmented laser impact are compared. In all cases, a photon Doppler velocimetry (PDV) system was used to collect the velocity–time profiles of the flyers. All PLX augmented experiments showed increases in both flyer acceleration and peak velocity over the same time scales as the unaugmented experiments. This indicates that the PLX-provided impulse occurs at the same time as the VFA/laser impulseLaser impulse. The augmented VFA experiments showed a 28% velocity increase over the unaugmented experiments at 10 kJ input energy. The augmented laser impact process exhibited peak flyer velocities 236% higher than laser impact using only the laser. Here we demonstrate that chemical augmentation is capable of significantly increasing flyer velocities for both VFA and LIW at the same input energies and under similar conditions. This development should expand the repertoire of flyer materials and thicknesses that can be impact welded by VFA and LIW.

Vaporizing foil actuator (VFA)Vaporizing Foil Actuator (VFA) is an impulse or high-speed manufacturing technology using electrically driven rapid vaporization of thin conductors to produce short-duration pressure pulses of high magnitude. This impulse technique has been implemented for various applications such as high strain rate forming, shearing, collision welding, and springback calibration. VFA technology for manufacturing processes potentially offers improved accuracy, reliability, and environmental safety and creates opportunities to design new products by joining similar and dissimilar material combinations. The paper includes the results of industrially relevant “work-in-progress” research with the VFA tool. The applications of the process, mainly regarding advanced manufacturing such as metal-matrix composite (MMC) weldingMetal-matrix Composite Joining, axisymmetric weldingAxisymmetric welding, and impact-mediated additive manufacturing processes, are presented and discussed. The applications of the method characterize adequate responses to support the manufacturing process.

It has been revealed that the grain size effectSize effect has a great effect on the formabilityFormability of metal foils during quasi-static forming processes. However, there is little research on how size effects influence the formability of metal foils during the high-speed forming process, e.g., electromagnetically-assisted forming. To characterize the grain size effect in electromagnetically assisted micro-bulging, a miniaturized Nakazima test was conducted using a specially designed device. Pure titaniumPure titanium foils of thickness 103 μm and different grain sizes were utilized in the experiment. In addition, SEM and TEM methods were used to clarify how grain size influences the fracture surface and microstructure in electromagnetic forming.

Laser shock peeningLaser shock peening (LSP) can induce residual compressive stress on the component surface, thus improving the fatigue life of the component. Therefore, LSP has been extensively employed in aerospace, vehicle engineering, and other industrial fields. To research the influence factors of residual stress holeResidual stress hole (RSH) which often occurred in LSP, a “volcano shape” mathematical model was conducted. Indexes for quantitatively describing RSH were proposed, such as relative crater depth, relative crater width, and stress loss ratioStress loss ratio. Preliminary analysis based on the experimental study was carried out. The results showed that the relative crater depth is the main impact factor to RSH. Overlapping LSP is suggested to be adopted when the relative crater depth is more than 10%. In addition, the spacing of the adjacent spot centers should be equal to the “crater” radius of RSH so as to get the uniform residual stress under the premise of higher LSP efficiency.

The magnetic pulse spot weldingMagnetic pulse spot welding studied in this paper can achieve the connection of sheet metal with the aid of a field shaperField shaper. The magnetic field shaper which is placed between the metal components and an electromagnetic coil has the function of concentrating the magnetic field, enhancing the electromagnetic forceElectromagnetic force around the weld zone; meanwhile, it can protect the electromagnetic coil. This paper carried out a numerical simulation of the principle of the field shaper for magnetic pulse welding of sheet metal by means of the FEA software COMSOLCOMSOL. The electromagnetic and structural parameters of the high-strength coil and field shaperField shaper have been designed, and an electromagnetic welding platformWelding platform is built, the welding experiments of 304 stainless steel sheet and 1060 aluminum sheet both with a thickness of 1 mm are carried out, respectively. The experimental results show that the method can achieve the connection of sheet metal very well.

In this work, an indirect extrusionIndirect extrusion process was designed to manufacture a stainless steelStainless steel reinforced aluminium composite. The design utilized a feeding mandrel to prevent the deformation of the stainless steel wire and to facilitate the embedding of the wire within the aluminium alloyAluminium alloy during extrusion. By using this method, a 12 mm diameter 6061 aluminium alloy embedded with a 2 mm diameter 304 stainless steel wire was successfully fabricated. Energy-dispersive X-ray spectroscopy revealed that aluminium and iron elements had diffused into the interfacial layer between the aluminium/stainless steel to induce some degree of metallurgical bonding. The yield strength, tensile strength, and elongation to failure of the extruded composite after solution and ageing heat treatment were 343.8 ± 5.5 MPa, 405.3 ± 5.1 MPa, and 18.0 ± 1.3%, respectively. As compared to extruded aluminium, yield strength, ultimate tensile strength, and elongation to failure were improved by 41.8%, 31.6%, and 6.3%, respectively. This result suggests that the composite material has better strength and toughness as compared to aluminium alone.

Pre-stressing is often used in civil engineering to increase the load-bearing capacity of bridges and buildings. In order to exploit this potential in sheet metal structures as well, efficient processes for joiningJoining and pre-stressing of tendons are required. Therefore, an approach to join and pre-stressPre-stress fiber-reinforced plastic (FRP) straps and sheet metals during a formingForming process is proposed. The FRP strap is placed around two collars drawn into the sheet. A punch plastically expands the collar, while the FRP strap is elastically elongated, resulting in beneficial pre-stresses after unloading due to the different spring-back. In this paper, the predominant mechanism is verified and parameters influencing the pre-stress are identified by experimental and numerical investigations. The hypothesis is investigated that a customized pre-stressPre-stress and thus a higher strength during the structure’s usage can be controlled by varying the collar’s expansion. Possible applications include bumpers and side-impact beams.

As a non-detachable and point-acting joint, thermoplastic stakingStaking is primarily used for the production of electronic and sensor elements as well as for the joining of components in the automotive interior and exterior. Commonly, the advantages of staking processes are its cost-efficient and seemingly simple process control. Regarding the industrial application, stakingStaking is principally a well-established forming process. However, despite the high number of applications, the joint design and the process settings are mainly based on extensive empirical tests. At present, the FE simulationFE-simulation of these thermoplastic staking processes is not state-of-the-art. Due to these facts, within the frame of the paper, these gaps are to be closed by the computer-aided modeling of the hot forming staking to map the heating and forming behaviorForming behavior of this process close to reality. This procedure demands the associated experimental validation of the simulation. In summary, the numerical model shows high conformity to the experimental data and allows a simulative mapping of the morphological characteristics of the riveted joint as well as indicative statements to the process parameters, which means in particular the minimal heating time for forming and the optimized post-heating time for a morphological homogenization.

Duplex steel, aluminum alloy, carbon fiber-reinforced composites, and other materials have become the preferred lightweight materials for automobiles. The self-piercing riveted joints of dual-phase steel DP590DP590 and aluminum alloy AA6061AA6061 were selected for fatigue tests, and the fatigueFatigue characteristics properties of the joints were analyzed. The typical fatigue failure fractures were observed by scanning electron microscopy (SEMSEM), and the microfailure mechanismFailure mechanism of the joints was analyzed. The results show that the fatigue properties of self-piercing riveted joints are different with different upper substrates. The failure modes of the AA35 joints are all fractures of the lower substrates. When the upper substrate is DP590DP590 plate under high fatigue load, the cracks are easy to initiate in the rivet area. The cracks of the other self-piercing riveted joints originate on the side of the lower plate and extend along the riveted area to the width of the substrate.

The fatigue tests of self-piercing riveted joints of AA5052 aluminium alloy were carried out by axial tension-tension loading mode. The microfracture characteristics of the specimen were analyzed by a scanning electron microscope. The fatigue property as well as the fretting damageFretting damage failure mechanism of SPR joints with different parameters (distance, stress ratioStress ratio, load level and riveting directionRiveting direction) were studied. The results show that the fatigue cracks occur in the fretting damageFretting damage area where stress concentration exists. The form and the distribution of the fretting debris are important factors that affect the fatigue property of the joint. Within the value range, fatigue life increases with the increase of stress ratioStress ratio, however, decreases with the increase of loading level adopted. The fatigue property of joints differs between different riveting directionsRiveting direction. Better strength property could be obtained when the riveting directionRiveting direction reverses.

Fabricating lightweight assembly of auto parts is of great importance and joining technology using plastic deformation is very attractive because of high strength and structural reliability. In developing such assembling processes, prediction technology with high accuracy is essential to optimize the structural system and minimize the manufacturing cost. However, the related technologies are still insufficiently developed for the sake of application because of complexity of the problem. In this paper, an improved methodology of conducting elastoplastic finite-element analysis of multi-body metal formingMulti-body metal forming processes is given with emphasis on the contact condition treatment. The presented approach is applied to simulate a rotary forgingRotary forging process of assembling a third-generation hub bearing unit. The inner races of the duplex pair taper roller bearings are considered elastic materials. Prestresses imposed on them are predicted.

To pursue better quality, there is a strong need for efficient and robust non-destructive testing methods for joining processes. A new approach has been proposed to detect loose bolted joints using acoustic waves. This method measures the dissipation of energy by recording the propagated waves on the surfaces of the joining partners next to the joint. The authors show a link between the torque moments applied to the bolt and the ability of the joint to transfer acoustic energy using both simulations and experiments. In this article, the method’s ability to detect variations of certain process parameters of the clinching process was investigated numerically. To this extent, results of FEM calculations of the joining process are used to simulate the non-destructive testing method. By varying parameters of the clinching model, their influence on the transmission of energy within the joint is studied.Lafarge, Rémi Wolf, Alexander Guilleaume, Christina Brosius, Alexander

Physical bond rolling experiments of aluminum sheets have been investigated in this study. In addition to native oxides on surface of aluminum, a thick oxide layer was deliberately added to AA3xxx aluminum sheets by anodization. For better monitoring of evolution of the oxide layer during roll bondingRoll bonding, the anodized layer was colored with Indigo Carmine in the anodization process. A progressive reduction per pass ranging from 2 to 70% has been performed in consecutive experiments at a constant rolling speed to develop different degrees of oxide surface expansion leading to its fracture and leaving disparate oxide fragments. The evolution of the oxide fragmentation and bonding of aluminum sheets were systematically characterized as a function of deformation by electron microscopy. It was revealed that the crack width between fragmented oxides increases exponentially while the oxide fragment size decreases exponentially as a function of the reduction ratio.

The development of electrical equipment has resulted in an increase in the demand for electrical switches whose key element is contact. The orbital rivetingOrbital riveting technology has been successfully applied in assembling silver contacts. With the increase in production, attention has been paid to the possibility of obtaining significant savings by replacing part of the rivet with copper. As a result, bimetallic contactsBimetallic contacts have been created. It has also been proved that the direct transfer of orbital rivetingOrbital riveting technology from monometallic to bimetallic contactsBimetallic contacts narrows the technological window that the cost-effectiveness of the whole process is debatable. One of the factors behind the use of orbital forming is the decisive reduction in friction. A similar effect is given by ultrasonic assistance in microforming processes. Within this work, based on the laboratory experiment results, it was suggested to replace the orbital rivetingOrbital riveting with ultrasonic rivetingUltrasonic riveting in relation to the miniature bimetallic contactsBimetallic contacts.

Self-piercing rivetingSelf-Piercing Riveting (SPR) is an established technique for joining multi-material structures in car body manufacturing. Rivets for self-piercing riveting differ in their geometry, the material used, the condition of the material and their surface condition. To shorten the manufacturing process by omitting the heat treatment and the coating process, the authors have elaborated a concept for the use of stainless steelStainless steel with high strain hardening as a rivet material. The focus of the present investigation is on the evaluation of the influences of the rivet’s geometry and material on its deformation behaviourDeformation behaviour. Conventional rivets of types P and HD2, a rivet with an improved geometry made of treatable steel 38B2, and rivets made of the stainless steels 1.3815 and 1.4541 are examined. The analysis is conducted by means of multi-step joining tests for two material combinations comprising high-strength steel HCT780X and aluminium EN AW-5083. The joints are cut to provide a cross section and the deformation behaviour of the different rivets is analysed on the basis of the measured changes in geometry and hardness. In parallel, an examination of the force–stroke curves provides further insights. It can be demonstrated that, besides the geometry, the material strength, in particular, has a significant influence on the deformation behaviourDeformation behaviour of the rivet. The strength of steel 1.4541 is seen to be too low for the joining task, while the strength of steel 1.3815 is sufficient, and hence the investigation confirms the capability of rivets made of 1.3815 for joining even challenging material combinations.

Applying the rotary forging process (RFP)Rotary forging to the shaft-end riveting assemblyRiveting assembly of hub bearing units (HBU)Hub bearing unit is an important technological innovation with promising application prospect. Due to its advantages of stable pre-tightening, low cost and high integration, shaft-end riveting assemblyRiveting assembly have become a vital process in assembling the third generation HBU. However, due to the lack of systematic application research on RFP, there are still gaps between the domestic hub bearings and the imported products especially in terms of accuracy and consistency of performance. In the study, a numerical simulationNumerical simulation platform (NSP) was adopted to simulate the assembling processes of HBU, in which the interference assembly, loading, and unloading of RFP were simulated with ABAQUS/Standard, ABAQUS/Explicit, and ABAQUS/Standard, respectively. The influence of processing parameters on product quality has been carried out by investigating several levels of feed displacement and feed rate, and relevant experimental research has also been conducted. It is found that the experimental results are in consistence with the numerical simulationNumerical simulation results, demonstrating that the NSP adopted could be an alternative in determining and optimizing the processing parameters of RFP.

A thick sheet ironing process is normally used to manufacture a uniform wall thickness of products. To evaluate the performances of lubricants by conventional tests, such as Ring Compression Test (RCT) is not suitable due to the limitation in low levels of contact pressure, surface expansion ratio, and relative velocity. In this research, Ball Ironing TestBall ironing test (BIT) was proposed as a new simulative tribo-testTribo-test to evaluate the lubricants of the thick sheet ironing process. Finite Element Modeling (FEM) together with statistical analysis was employed to determine a frictional indicator (i.e., maximum load and final height of specimen). According to the results, the maximum load is very sensitive to the friction and used as an indicator to evaluate and approximate the friction coefficient via Frictional Calibration Curve (FCC). Different types of lubricants were tested experimentally and demonstrated different performances by the BIT. In conclusion, the BIT is suitable for evaluating the lubricants of the thick ironing process.

In the cold forgingCold forge process, lubricantsLubricants are essential because they prolong die life and improve product surface quality. In contrast, it is well known that lubricants are exposed to very severe conditions such as high contact pressure and processing-induced high temperatures. Oil-based cold forging lubricants induce processing defects when the oil film is insufficient. In the search for better alternatives, we explored the possibility of phase transitionPhase transition materials that changeover from liquid to solid under high-pressure conditionsHigh-pressure conditions. In this study, we developed new oil-type cold forging lubricants with phase transition material additives. Moreover, we found that these hybrid materials show superior lubricating performance in the cold forging process to conventional lubricants. These results indicated that phase transition behavior under high-pressure conditions supports more efficient cold forging process lubrication.

In deep drawingDeep drawing processes, drawbeadsDrawbead are frequently used to control the material flow while forming. It is well known that material parameters are changed significantly after a drawbead passage. Also, there are many references that the tribological system after a drawbead is changed and that this has influences on the ongoing forming process. In this study, the connection between work hardeningWork hardening and the tribological system after a drawbead is analyzed with respect to the initial state. Therefore, sheets are drawn through a gap controlled drawbead passage while parameters like the gap between blank holder and die or the materials are varied. Afterwards, hardness measurements will be carried out as well as 3D surface measurements to correlate them. For these investigations, three different sheet metals are used: a conventional deep drawingDeep drawing steel, an advanced high strength steel AHSS, and an aluminum alloy, as they represent the variety of industrial used sheet metal.

The existence of clearance in the joints of multibody systems can significantly influence the system behaviors. The introduction of joint clearance in the dynamic analysis of the mechanical pressMechanical press can generally lead to a higher analysis precision. In this paper, a lubricant revolute joint and a translational clearance jointClearance joint are conducted in the dynamic model of a mechanical pressMechanical press, to identify their combined influence on the system dynamics. The Pinkus and Sternlicht approach is employed to obtain the hydrodynamic forces, while the IMPACT function is used to evaluate the contact forces. Simulations are carried out in the cases where the translational joint is assumed to be ideal or with clearance. The results show that the lubricated revolute joint presents practically similar to an ideal one in the global responses while the existence of the translational joint will lead the slider trajectory into chaos. Moreover, the translational clearance jointClearance joint seems to have little influence on the local dynamics of the lubricated joint, due to the limited amount of contacts resulted from a low input crank speed. This observation indicates that in the dynamic analysis of heavy-load mechanical pressesMechanical press with a low operation speed, the effects of these two joints can be analyzed separately.

Magnesium alloysMagnesium alloys have been used in the automotive and aerospace industry for several years, thanks to their high strength-to-density ratio. Their mechanical characteristics at room and even at elevated temperature have been well studied, whereas, when it comes to temperatures lower than room one, only a few studies are available in the literature. To this aim, the present paper investigates the mechanical behavior of AZ31 magnesium alloyMagnesium alloys sheets deformed at different temperature regimes. Tensile tests till fracture were carried out at room temperature, −100, −50, 100, and 300 °C using different specimen geometries in order to vary the stress triaxiality. The fracture strain values were identified making use of a combined numerical–experimental approach, whereas the fracture surfacesFracture surface were qualitatively characterized by means of stereoscopy and scanning electron microscopy. Finally, the AZ31 fracture locusFracture locus as a function of the stress state and temperature was constructed.

The process used to fabricate tensile specimens inevitably introduces imperfections at their edges, which can affect the resulting experimental mechanical properties. It has been reported that, for ambient temperature testing, tensile specimens prepared by less aggressive machining methods yield more accurate data due to the absence of plastic deformation at the edges. However, for superplastic forming (SPF)Superplastic forming (SPF) where forming is performed at elevated temperatures, the results are different. In this study, AA5083 sheet specimens were prepared using different machining methods: wire-electro-discharge machining, waterjet cutting, and conventional milling. Mechanical properties were determined from tensile tests carried out at 450 °C and at a quasi-static strain rate. The edges of tensile specimens were observed under optical and scanning electron microscopes (SEM) both before and after testing. It was found that milled specimens resulted in greater values of total elongation. The microscopic investigation revealed that specimens whose edges have a lower arithmetic mean roughness (Ra) have greater values of elongation. The SEM investigation also revealed that micro-cracks are more prevalent at the edges of specimens that have a greater surface roughnessSurface roughness. Therefore, tensile specimens used to characterize sheet mechanical properties in view of SPFSuperplastic forming (SPF) applications should be fabricated by a process that yields a lower surface roughness, such as conventional milling.

Evaluating the shear edge quality and edge crackingEdge cracking is important in forming the advanced high-strength steel (AHSSAdvanced High Strength Steel (AHSS)) for automotive structural parts. This paper introduces the eddy currentEddy current-based NDE method to evaluate the sheared edge quality. Different shear clearances from 5 to 25% of the sheet thickness were used to create different work-hardening levels on the sheared edges, which change the local formability. The NDE sensor scanned the sheared DP780 blanks to obtain the NDE data. The micro-hardness at the sheared edge was measured to compare the NDE data to the work-hardening level of the sheared edge. The edge formability was evaluated using the half specimen dome test (HSDT) with digital image correlation (DIC). The measured HSDT failure strain was correlated with the NDE data. The NDE result showed a good correlation with the DIC measured failure strain and micro-hardness. With further development effort, the eddy currentEddy current-based NDE method can be implemented to inspect the sheared edge quality in a production environment.

An uncoupled ductile fractureDuctile fracture model, based on Mu–Zang model, is extended by incorporating a hydrostatic stressHydrostatic stress term. An aluminum alloy material (Al 6016-T6) is selected with a series of static ductile fracture tests performed on four different specimens, which can cover a wide range of stress states. A robust simulation-experiment approach is adopted to characterize the correlation between the material’s ductility and distinct stress states. The extended model is then calibrated using least-squares optimization. The resulting 3D fracture surface demonstrates acceptable deviations from the tested data, manifesting a promising capability of the extended model to describe the ductility of the considered material within a wide stress state range. In addition, the comparison against other representative ductile fractureDuctile fracture models further confirms a good prediction performance of the model proposed.

Shear cuttingShear cutting is a prominent process in the chip-less separation of metallic sheet materials. The cut surface characteristics have been the basis for quality assessment but the shear-affected zoneShear affected zone becomes increasingly important with regard to the functionality of the produced components, such as further processing or its final application. Multi-stageMulti-stage shear cutting processes may be used to specifically adjust the mechanical and geometrical properties of shear cut edges. Originally, multi-stageMulti-stage shear cutting was aimed at producing smooth and clean-cut surfaces with high-dimensional accuracy and improved load capacity. However, nowadays, it is also used to reduce the sensitivity to edge cracking, for example. In this paper, we present a novel approach for the experimental analysis of multi-stage shear cutting as a basis for advanced process analysis and validation. Moreover, the achieved results may serve for future database process design, modeling, and control. We developed an in-situ test design and measurement setup that preserves the real process boundary conditions of shear cutting. An enhanced high-speed optical full-field evaluation method based on optical flow methods allows local and time-resolved measurement of strainStrain fields and strain rateStrain rate fields for each shear cuttingShear cutting stage. A mapping of these state variables between the individual cuts enables us to analyze consistently the shear-affected zoneShear affected zone throughout the whole multi-stageMulti-stage process and thus to characterize the final state of the shear-affected zoneShear affected zone experimentally.

Hot forming has been proposed to improve the formability of high-strength aluminum alloys. The main objective of this paper is to formulate a continuum damage modelContinuum damage model and to describe the damage evolution features of AA7075AA7075 aluminum alloy alloy at elevated temperatures. Hot uniaxial tensile tests and hot Nakajima tests were conducted. Subsequently, a novel continuum damage modelContinuum damage model was proposed and incorporated into a set of multi-axial visco-plasticVisco-plastic constitutive model constitutive equations to describe the thermal flow behaviors and predict the thermal forming limit diagramForming limit diagram (TFLD) of AA7075AA7075 aluminum alloy. Material constants were determined based on the experimental data with a genetic algorithm. Moreover, the TFLD of AA7075AA7075 aluminum alloy was numerically simulated by implementing the multi-axial continuum damage constitutive equations (CDCEs) via the user material subroutine VUMATVUMAT in commercial software ABAQUS. Simulation results agree well with experimental results and theoretically predicted results, which indicates the set of multi-axial CDCEs is capable of predicting the formability of AA7075AA7075 aluminum alloy at elevated temperatures.

TNW700 titaniumTNW700 titanium alloy”, as a new near-α high-temperature titanium alloy, is designed to work at 700 °C for a short-term service. Superplastic deformation behavior of TNW700 alloy at 900–975 °C and strain rate of 0.0005–0.01 s−1 was investigated to identify the optimum deformation temperature and strain rate. The microstructure evolutionMicrostructure evolution after high temperature tensile was investigated using scanning electron microscope. The research found that TNW700 alloy has an excellent superplasticitySuperplasticity. The elongation exceeds 200% at various deformation conditions except 975 °C with higher strain rate of 0.005 and 0.01 s−1, and the maximum elongation of 613% was obtained at a temperature of 925 °C and strain rate of 0.001 s−1. The flow stress is sensitive to temperature and strain rate, and it increases with decreasing temperature and increasing strain rate. In addition, the flow stress exhibits strong work hardeningWork hardening with increase in true strain, and the instantaneous work hardeningWork hardening exponent n as well as critical hardening strain is accelerated as the strain rate decreases. The strain rate sensitivity exponent (m) is higher than 0.4 when the temperature is lower than 975 °C, which corresponds to dynamic recrystallization and grain boundary sliding mechanisms. The m is 0.229 at temperature of 975 °C, corresponding to dynamic grains growth mechanism. The deformed microstructure of TNW700 alloyTNW700 titanium alloy consists of β grains and equiaxed α grains. Increasing the temperature is beneficial to the transformation of α phase into the β phase, which resulted in an increase in the volume fraction of the β phase. The β grains grow rapidly at higher temperatures and lower strain rates due to the higher diffusion coefficient.

A ductile fractureDuctile fracture criterion (uncoupled type, originally presented at ICTP2017), which is endowed with both stress triaxiality (T) and Lode parameter (L) dependence, is selected to define the ductile damage accumulation from hole-blanking simulation to the subsequent hole-expansion simulation for a DP780 sheet. The calibrated ductile fractureDuctile fracture criterion yields an asymmetric 3D fracture surface, which can well describe the material’s ductility within a wide range of stress states from simple shear to balanced biaxial tension. With the help of a fully integrated simulation framework, the ductile damage induced by the hole-blanking is completely mapped into the hole-expansion simulation to incorporate the pre-damage field for the sheared edge. We find that after considering the pre-damage field, the accuracy of edge fractureEdge fracture simulation is significantly improved in terms of both hole-expansion ratio and fracture propagation path.

In this work, dynamic creasing characteristics of liquid-container-purpose paperboardPaperboard of basis weight 313 g/m2 (a thickness of t = 0.47 mm) were investigated, when varying the holding time of two creasingCreasing knives (a round edge and/or a flat edge) at an indentation depth of d = 0.8 mm. In a scoring process, the relationship between the time-dependent behavior of reaction force f and the permanent scored depth das was approximately linearized with a logarithmic function of the elapsed holding time tep = 0-60 s. When using the paperboardPaperboard scored with the specified indentation depth and varying the tracking holding time Tep, the relationship of the bending momentBending moment M and the rotation angle θ was investigated. The effects of the tracking holding time at the scoring process on the bending moment resistance (as the maximum strength) M90(0) at θ  =  90° and the initial gradient C1 =  $$\partial M/\partial \theta $$ ∂ M / ∂ θ (θ  =  0–5°) were characterized with a logarithmic function of Tep, and also an explicit expression of C1 with M90(0) was revealed. Namely, a time-dependent relaxationRelaxation of scoring reactional force f and the time-dependent relaxation of C1 (and/or M90(0)) in a foldingFolding process has occurred with a logarithmic term of the holding time.

Parts made of press-hardened steelPress-hardened steels are cut in general by laser cutting. Shear cutting at room temperature of materials with a tensile strength above 1,500 MPa is not an alternative due to insufficient tool life quantity. The presented investigation relates to the hot cuttingHot cutting of press-hardenable materials such as 22MnB5 and 34MnB5 and includes the determination of the cutting parameters (measuring rate of 100,000 Hz), the temperature, the formation of the microstructure, and the dimensional accuracy of the cut parts during different heat treatments. The results of this investigation show that, when comparing two process routes, the maximum cutting force was reduced to approximately 70 % when cutting in the austenitic range, the acceleration during the cutting impact was close to zero and the deviations from the target geometry were very small. With regard to the measurement results, hot cuttingHot cutting can be an alternative to laser cutting.

Conventionally, a defected tool steel is repaired by welding; however, that repairing does not guarantee homogeneous quality. Hence, this study focused on developing an alternative repairing technique using direct energy depositionDirect energy deposition (DED) to minimize thermal effects. To investigate a repairRepair using powder-fed DED, AISI H13AISI H13 powder was deposited onto heat-treated JIS SKD61. The deposited material was observed through scanning electron microscopy and its hardness and tensile propertiesTensile properties were determined at 25, 200, 400, 600, and 800 °C. The deposited material showed different hardness distributions in its cross-section, revealing four representative features. The deposited region and dilution showed a hardness of 620 HV with a dendrite structure. The hardness decreased to 490 HV in the heat-affected zone, revealing a tempered martensite structure; however, it increased to 550 HV in the substrate and revealed a typical martensite structure. At all temperatures, the deposited material showed higher hardness than heat-treated SKD61. Moreover, it showed higher ultimate tensile strength and lower elongation in the deposited region. Therefore, this result indicates that without pre- or post-heat treatment, a part repaired using powder-fed DED can have better mechanical properties than heat-treated SKD61.

In this paper, new tailored structure design has come forward based on ultra-high-strength steel (UHSS) material properties. The analytical modelAnalytical model and finite element modelFinite element model are established in this study for the investigation of the energy absorption properties of the plane strain sheet. Via analytical calculation, the mechanical characters of the tailored sheet are deeply investigated before fracture initiation under extreme conditions. An optimized structure geometry configuration is obtained according to the quantity of structural energy absorptionEnergy absorption. The promotion of energy absorption of the tailored structure before fracture initiation is not obvious comparing with the pure material ones. In the FE model, the properties of the energy absorption of the tailored sheetTailored sheet after fracture initiation are investigated. Under a designed geometry setting, the energy absorption of the tailored sheet can provide 135% and 77% promotion, respectively, compared with the pure material ones. Besides, the designed configuration can also provide a good effect of crack inhibition, which shows great potential for further engineer applications.

Recently, a series of duplex stainless steelsDuplex stainless steel (DSSs) have been developed by replacing Ni–Mo with Mn–N, which makes DSS more economical and produces TRIP effectTRIP effect with higher strength and plasticity. In this work, the mechanical properties of a TRIP-assisted DSS under monotonic and cyclic loadingCyclic loading conditions were studied and the micro-structure under cyclic loading was analyzed by transmission electron microscopy (TEM). The test steel exhibits enhanced mechanical properties and a typical “three-stages” hardening characteristic due to TRIP effectTRIP effect under monotonic loading conditions. Cyclic hardening/softeningCyclic hardening/softening characteristics of the test steel are affected by strain amplitude and the number of cycles. With smaller strain amplitude, cyclic hardening occurs first, and then shifts to cyclic softening and gradually trends to stabilization. With larger strain amplitude, after initial rapidly cyclic hardening, the test steel still changes to cyclic softening, however, no stabilization occurs until failure. The dislocation walls in ferrite during cyclic deformation are responsible for the overall cyclic softening of the test steel; While austenite produces ε martensite transformationMartensite transformation at larger strain amplitude, which suppresses the cyclic softening, so that with an increase in strain amplitude the cyclic softening rate increases rapidly, followed by a slow increase and a final decrease.

Structured materials can be progressive alternatives to commonly used flat sheets because of their higher bending stiffness and stability compared to flat sheet metals, made of the same alloy. The application of sheet metals requires accurate information regarding their strength and deformation behavior. Such data are not commonly available and have to be measured by specific test setups and implementation of tests. The aim of this work is to obtain new knowledge about deformation mechanisms of structured sheet metalsStructured Sheet Metals (SSM). Structured sheet metals (SSM) made of conventional deep-drawing steel DC04 were investigated by means of tensile testsTensile test. The influence of the structure type arrangement on the deformation behavior was analyzed. The evolution of local strains was analyzed by means of strain gaugeStrain gauge measurements as well as 3D-displacement measurements with an ARAMISARAMIS high-resolution camera system. Local orientation changes in different structural elements were measured using the electron backscatter diffraction technique.

The paper focuses on the development of a static recrystallizationStatic recrystallization model of 6XXX aluminum alloyAluminum alloy based on industrial profiles extrusion analysis. 6XXX aluminum alloys are widely used for complex shapes with smooth surfaces suitable for visible architectural applications. Mechanical properties and surface defects, for example, streaking lines, are dependent on the microstructureMicrostructure. Static recrystallization occurs in alloys such as 6XXX due to high stacking fault energy. At the moment, there is no reliable static recrystallizationStatic recrystallization model of 6XXX aluminum alloysAluminum alloy found in the literature. In the presented paper, a new approach has been proposed to determine the parameters of Johnson–Mehl–Avrami–Kolmogorov equation. It is based on using strain and temperature history during extrusion of industrial profiles and examining the microstructureMicrostructure in their cross-sections and implementing the inverse analysis approach. The developed model has been verified and used for simulationSimulation of the microstructure evolution in industrial extrusion cases and has shown sufficient accuracy.

The effect of T8 heat treatment on 6063 aluminium alloy wearWear behaviour of AA6063 was studied and precipitation kinetics was evaluated by SEM and XRD studies. AA6063 square rods of 9.5 mm X 9.5 mm X 100 mm were solution treated at 520 °C for 2 h and quenched in water. One set of samples was processed by ECAP at room temperature and the other set was processed by Cryogenic ECAP after soaking in liquid nitrogen for 20 min. A die of 108° channel intersection angle and 36° outer curvature angle was used and each sample was given four passes in route A and aged at 180 °C for different timings and results compared. HardnessHardness measurements were obtained at regular intervals and peak hardness was observed after 90 min of ageingAgeing for both Cryo-ECAPed and RT-ECAPed alloys. The solution treated alloy ECAPed at cryogenic temperature has shown maximum wear rate during the initial stages of ageingAgeing and reached the minimum after 90 min and nearly same wear rate was maintained until the overaged condition. The solution treated alloy ECAPed at room temperature has shown minimum wear rate during the initial stages of ageingAgeing and reached the maximum at about 50 min and it was not consistent during the later stages. SEM studies were performed on worn-out samples at different time intervals during ageingAgeing and the wearWear behaviour of the alloy was correlated with the microstructures. The wear results obtained were in good agreement with the microscopic analysis.

As the formingForming of metallic bipolar platesBipolar plates is mostly still in the state of research, the underlying forming mechanisms are not fully understood. This study deals with the topic of different grain sizes in the initial metal sheets and their influence on the forming results. Therefore, a work-hardened 316L316L-foil (0.1 mm) was processed with different heat treatment strategies resulting in three different grain sizes with average grain diameters of 47.4, 19.3, and 7.9 µm. Afterward, all heat-treated blanks were cut and deep-drawn between two rigid dies to form a bipolar plate flow field. Besides force and geometrical factors like thinning and springback, the microstructureMicrostructure was analyzed by XRD and EBSD. Using these characterization methods, the mechanisms of twinning and preferred deformation of specific grain orientations during the forming process can be identified. Therefore, the impact of size effects on the formingForming behavior of metallic bipolar platesBipolar plates is shown. It can be concluded that a fine-grained initial state is preferable.

Mixed grains are often encountered in heavy forgings. Taking 316LN austenitic stainless steel316LN austenitic stainless steel as an investigated material, two kinds of grain structures were tested for observation of microscopic deformation heterogeneity: uniform fine grains and mixed structures with millimeter-grade coarse grainsMillimeter-grade coarse grains (MCGs) (MCGs). Tensile tests, optical microscope (OM) observations, EBSD tests as well as crystal plasticityCrystal plasticity (CP) simulations were performed. Results showed that obvious slip bands were observed in the MCGs. During the deformation, the MCGs exhibited single slip bands if they were with soft orientation, and cross slip bands if they were with hard orientation. The fine grains were seen easily rotated in the deformation, forming distinguished bumpy grain boundaries, while the MCGsMillimeter-grade coarse grains (MCGs) displayed smooth and collapsed grain morphology. The interior MCGs undertook severer deformation than the fine grains, which showed the strain partitioning ability of MCGs was limited. This deformation behaviorDeformation behavior is possible to lead the crackCrack initiation in the interface among MCGs and surrounding fine grains.

This study aims to clarify the transition of mesoscale structure of a drawn wire versus drawing strain. High-carbon steel wiresHigh carbon steel wire 0.276, 0.444, and 0.936 mm in diameter were drawn until wires could be drawn without rupture. Two results were obtained from a crystal orientationCrystal orientation analysis of the electron backscatter diffraction pattern. First, the mesoscale structure in the wire consisted only of a subprimary fiber textureFiber texture {100}<110>-{111}<110> at the drawing limit, that is the largest drawing strain when the wire could be drawn without rupture. Second, it is predicted that the transition of the mesoscale structure versus the drawing strain will occur as follows regardless of the initial wire diameter: In the beginning of wire drawingWire drawing, the wire will have only a primary fiber textureFiber texture {100}<110>-{111}<110>. After a slight increase in the drawing strain, the wire will have the primary fiber textureFiber texture at its outer side and a secondary fiber textureFiber texture {111}<110>-{110}<110> at the inner side. After a further increase in the drawing strain, the wire will have a subprimary fiber textureFiber texture at the outer side and a secondary fiber texture at the inner side. Moreover, increase in the drawing strain, the wire will have only a subprimary fiber texture.

Equal-channel angular pressing (ECAP)Equal-Channel Angular Pressing (ECAP) is an established method for the improvement of mechanical properties by grain refinement through shear strains. While there is a profound knowledge about ECAPEqual-Channel Angular Pressing (ECAP) of bulk materials, there is only a little information on the effect of ECAP on sheet metals. Therefore, a tool was developed that is able to perform ECAPEqual-Channel Angular Pressing (ECAP) tests for metals with a thickness of 1.8 mm. In this contribution, a thermomechanicalThermomechanical analysis simulation model is used to examine the novel process. The simulation is performed to investigate the dissipated forming heat and the heat due to friction. To validate the numerical results, experiments with the ECAPEqual-Channel Angular Pressing (ECAP) tool for sheet metal are performed. By drilling holes in the sheet material, the forming temperature can be measured with thermocouples and friction parameters used in the simulation can be calibrated inversely. Since a detailed material model is essential for the inverse determination of individual parameters, a special focus of this article is on the determination of the thermomechanical parameters. For example, the plastic flow behavior or thermomechanical conversion, expressed as the Taylor–Quinney coefficientTaylor-Quinney coefficient, is examined under a stress state similar to ECAPEqual-Channel Angular Pressing (ECAP) by means of a Miyauchi testMiyauchi test. In this way, fundamental correlations between the heat development in the ECAP process for aluminum sheet metal and the shear strain introduced into the material can be obtained.

Isothermal compressive testsIsothermal compressive tests were performed on a Ti–6Al–2Zr–1Mo–1V alloyTi-6Al-2Zr-1Mo-1V alloy below the beta-transus. The results showed that straining caused a decrease in the primary α phase, indicating that a strain-induced phase transformation of α→β occurred, whereby an additional dynamic softening was shown. This transformation was sensitive to temperature and strain rate. The higher the temperature was, the more the primary α phase transformed. The extent of α→β increased as the strain rate decreased. The α phase even transformed to β phase completely so long as the deformation duration was enough. Besides deformation, the overall heat duration which included the reheating before deformation and the absolute duration during deformation caused the additional dissolution of primary α phase. In this work, a quantitative model for dissolution kinetics of the primary α phase was established considering the strain-induced phase transformation and the overall heat duration.

Aluminum (Al) alloys play a critical role for the transportation applications where weight reduction is a key aspect; however, the poor formabilityFormability at room temperature limits their application for complex components. An innovative methodology to overcome this limitation is based on subjecting the material to a local, short-term heat treatmentHeat treatment before stamping, to obtain a tailored distribution of properties. In addition, Continuous-Bending-under-TensionContinuous-bending-under-tension uses the action of three rollers to remarkably increase the total elongation to failure. In the present work, the combination of the two approaches is investigated to improve the formabilityFormability at room temperature of a strain-hardenable 5xxx Al alloyAl alloys, AA5754-H32. Specimens were subjected to both CBT and pre-forming heat treatmentsHeat treatment, and force-displacement curves were compared to evaluate the formabilityFormability improvements.

A 7A85 aluminum aviation componentAviation component with high ribs and thin webs was successfully formed by the isothermal forgingIsothermal forging process, and its microstructure was investigated by optical microscope (OM), transmission electron microscope (TEM), and cellular automaton simulation. Metallographic images show the recrystallization phenomenon takes place all over the aviation forging, and a uniform grain size is obtained. The cellular automaton model of 7A85 aluminum alloy, including dislocation densityDislocation density model, nucleation rate equation as well as grain growth model was established, and the parameters of the cellular automaton models were determined by the hot compression experiment on the thermal-mechanical simulator Gleeble-1500. The cellular automaton simulationCellular automaton simulation results agree well with the optical micrographs of the aviation forging, showing good homogeneity in both the size and the distribution of grain structure. The TEM images show that a homogeneous distributed dislocations and precipitates of the forging formed by the isothermal forgingIsothermal forging process can be attained, which can inhibit the migration of the grain boundaries, resulting in the small and uniform grains of the aviation forging.

The deformation and microstructure of medium carbon steel during die forgingDie forging process was analyzed by using thermo-simulation test in this paper. The effect of microalloying elementsMicroalloying elements V, Ti, and Nb on the microstructures after deformation was also analyzed. The results showed that there are a critical deformation amount of 6% which increases the grain sizeGrain size of steel in die forging process. The deformation amount during die forgingDie forging process should reach 20% in order to refine the microstructures. The addition of Ti can largely reduce the grain size of the final product while the further addition of Nb doesn’t have significant effect on the grain sizeGrain size. The addition of Ti can significantly increase the ferrite and intra-granular ferriteIntra-granular ferrite in the steel by refining the microstructure and offering the precipitates (V, Ti)(C, N) as the nuclei of intra-granular ferrite. The further addition of Nb in the V-Ti-N steel can further increase the size of the precipitates (V, Ti, Nb)(C, N) but suppress the formation of ferrite by improving the hardenability of steel. Thus, there are few ferrite and intra-granular ferriteIntra-granular ferrite in the V-Ti-Nb-N steel than that in the V-Ti-N steel.

The higher strength of hot rolled steel sheet by compact strip production (CSP)Compact strip production (CSP) process has been restricting its application in higher formability and thinner steel sheet because of higher cold rolling load. Ferrite rollingFerrite rolling process has been widely researched since it has successfully reduced the strength of cold rolling feeds. In this paper, the microstructures and properties of a hot rolled ultra-low carbon steel SPHESPHE by CSPCompact strip production (CSP) process with different rolling temperatures were investigated. Strengthening mechanism was discussed by EBSD and TEM analysis. Results showed the mechanisms why the strength of the steel deformed with the finishing rolling temperature at single ferrite zone was increased while the elongation was decreased. The deformation resistance and microstructure versus temperature and the transformation behavior were analyzed. It was found that deformation at dual phase zone near to Ac1 can further increase the grain size and thus decrease the strength and meantime keep the elongation.

Controlling the microstructure of components is of interest to achieve optimal final part properties, i.e., materials by design. The manufacturing process itself can affect a material’s characteristics by changing the microstructure. For example, past research has shown that austenite to martensite phase transformation in stainless steelStainless steel occurs during deformation. Temperature is known to have a significant influence on this phenomenon. In this paper, the effect of temperature on the austenitic to martensite phase transformation in SS 316L under uniaxial tensionUniaxial tension is investigated. Both a cooling system and a heat exchanger were employed in a uniaxial tensionUniaxial tension experimental setup to control the temperature. Tensile specimens were strained to fracture at four temperatures of −15, 0, 10, and 20 °C. Digital imaging correlation (DIC) and a thermal imaging camera were used for tests at 0 °C and above to capture strain and temperature data, respectively. Strain and temperature data could not be obtained at −15 °C due to the DIC paint flaking during testing. X-ray diffraction was used to measure the volume fraction of martensite in both the as-received and the tensile-tested materials.

Machine hammer peeningMachine hammer peening (MHP) is a high-frequency, incremental surface treatment with a spherical plunger which enables reproducible local plastic forming of metallic surface layers. The elasto-plastic deformation leads to a targeted smoothing or structuring of the surface as well as to the induction of compressive residual stresses and strain hardening. However, since MHP is still a relatively new process, there are still considerably knowledge deficits with regard to the cause–effect relationships of the energy inputs set by the MHP process parameters and the resulting surface integritySurface integrity of technically relevant alloys. Therefore, the objective of this work is to investigate the influence of the peening strategies and the resulting contact energies on the surface roughness, the surface hardness, the residual stresses, and the microstructure of AISI 304. The results show that MHP leads to smoother and harder surfaces resulting from deformation-induced martensite formation accompanied by high compressive residual stresses and subgrain refinement resulting from higher dislocation densities.

A thermo-microstructural modeling setup was developed to model the progress of static recrystallizationStatic recrystallization (SRX) during annealing of hydroformed steel tube under non-isothermal annealing condition. In this model, a coupled Cellular AutomataCellular Automata and Finite Element thermal model was implemented to predict the kinetics of SRX, which accounts for the impact of multiaxial deformation and annealing temperature regime. First, an analytical solution was developed to calculate the flow behavior of the steel tube during hydroforming experiment based on the data extracted from digital image correlation (DIC) measurements. Second, the actual microstructure and texture of the as-deformed material was obtained with EBSD test. Third, the calculated deformation characteristics as well as the obtained crystallographic and microstructural data were imported to the developed Finite Element-Cellular Automata model to predict the progress of SRX and temperature changes during annealing. The results show a reasonable agreement between the experimental data and predictions, confirming the accuracy of the developed modeling setup in the prediction of the kinetics of SRX within hydroformed steel tubes.

The industrial development of new materials in metal forming is a time consuming, iterative process. Although it is already being attempted to predict the properties of new materials using computational methods, experimental production and characterization must always be carried out. This typically involves casting of larger blocks of material, which are then processed to specimens. Particularly in the case of high-alloyed materials (e.g., nickel-base superalloys) pronounced macrosegregations occur, which must be removed by time-consuming homogenization. In this paper, additive manufacturingAdditive manufacturing of small specimens is investigated as an alternative to traditional ways for developing new alloys for metal forming. The microstructureMicrostructure and thermomechanical transformation behavior of as-built material are analyzed and it is shown that thermomechanical treatment of the as-built state allows for transforming the microstructureMicrostructure in such a way that processing parameters for forming and final product properties can be identified.

Post-extrusion cold deformation followed by brazingBrazing has a significant effect on mechanical properties of micro-channel tubes used in heat exchangers. To understand this relationship, cold rollingCold rolling with different thickness reductions (0–15%) and a following brazing are conducted on extruded tubes, and the microstructure and strength are examined. The results show that with increasing rolling reduction, tensile strength and burst strength of the as-rolled tubes increase monotonously. While after brazing, both strengths decline obviously, and them decrease first and then increase with increasing rolling reduction. The change is attributed to recrystallization and grain growthGrain growth observed in the post-braze tubes. Driven by different levels of strain from the rolling, recrystallized grain size increases first and then decreases. At 5% thickness reduction, abnormal large grains form in the web and result in the minimum post-braze strength. Finally, the ductile fraction mode is observed in the web, which shear strength determines the burst strength.

To generate the highly efficient use of material resources for formed parts, local adaptation of the required strength and integrated functions is advised. When using austenitic steel, the volume fraction of deformation-induced α′-martensite, which has an influence on the strength and the magnetic permeability of the material, is highly dependent on the degree of deformation and the workpiece temperature in the deformation zone. Through selective adjustment of the process parameters of wall thickness reduction ∆s and deformation temperature Td it proved possible to produce locally restricted areas with an α′-martensite volume from almost negligible to 80% at an identical stage of deformation, using a spinning or flow-forming process. In this way, axially graded and locally varying mechanical and sensory properties can be produced, such as for a magnetic displacement sensor. The aim of this ongoing work is the closed-loop control of properties through the use of micro-magnetic sensors during spinning processesSpinning process.

To investigate the hot deformation behavior of Ti–5Al–5Mo–5V–3Cr–1Zr (Ti55531) alloyTi–5Al–5Mo–5V–3Cr–1Zr alloy, a series of compression testsCompression tests were performed within the temperature range of 1033–1153 K at constant strain rates 0.001–1 s−1 on a Gleeble-3500 isothermal simulator. The results show that the flow stress decreases with an increase in temperature and a decrease in strain rate. At high strain rate, the flow curves are characterized by obvious discontinuous yielding, followed by slight strain hardening before flow softening and/or steady-state flow. The magnitude of the discontinuous yield drop increases with an increase in temperature. The flow behaviors were described by the Arrhenius equationArrhenius equation in α + β phase region and in β phase region respectively. The processing mapsProcessing map considering strains of 0.05, 0.4, 0.6, and 0.9 were drawn. In combination with microstructural observationsMicrostructural observation, it is found that this alloy represents typical instability of flow localization and flow rotation in an unstable flow region. The optimum conditions for hot deformation were found at 0.001–0.1 s−1 and 1003–1153 K.

In the field of thin-plate plastic forming, the efficient and accurate prediction and control of wrinkles are the basis for product and mold design and process flow formulation. In this paper, a diagonal tensile test of a square plateSquare plate diagonal stretching is taken as an example, and a numerical simulationNumerical simulation model for plastic wrinkle analysis of a thin plate is established by using ABAQUS. On this basis, the morphology and characteristics of the critical wrinkle main strain diagram (WLD) under the condition of nonuniform tension are investigated. The distribution position relationship between the strain value at different positions in the deformation region of the specimen and the critical wrinkle main strain curve (WLD) is discussed. The research content of this paper provides ideas for determining the wrinkle instabilityWrinkle instability and establishing the wrinkle critical line under other various bearing conditions.

As one of the means of lightweight, more and more ultra-high-strength steel (UHSS) has been applied to the car body. Plasticity and fractureFracture behavior of UHSS under a complex stress state is the key to accurate simulation of forming process and crash. In order to describe the various hardeningHardening exponent that lies with the advanced high strength steelsAHSS, a new hardeningHardening law of Modified Power Law (MPL) was proposed and validated for the newly developed high elongation quench & partition steel (QP1180-EL) by Baosteel. Different loading conditions, including shear, uniaxial tension, plane strain tension, and biaxial tension were conducted with the help of digital image correlationDigital Image Correlation (DIC) technology to test the fractureFracture limit of QP1180-EL under various stress states. Based on testing results and numerical simulation, Modified Mohr–Coulomb (MMC) fractureFracture model and Generalized Incremental Stress State Dependent Model (GISSMO) were calibrated and validated. The research results will provide guidance for parts design and structural performance evaluation in the application of ultra-high-strength steel.

This paper is concerned with the design of a new cruciform-like specimen to measure plastic flow under combined tensionCombined tension–shear and shear loading conditions. An AA6013-T4 aluminum sheet is used as example material. The specimen designSpecimen design borrows from the “smiley” shear specimen, which is commonly used for the simple shear experiment, but has four arms, as a cruciform specimenCruciform specimen: two arms are used to induce shearing, while the other two induce tension. The details of the geometry are determined by FEA to promote stress uniformity in the gage-section under combined loading conditions with the force ratio of 1 to 1. Parametric studies are conducted to determine the final design in terms of notch shape, gage-length, gage-width and offset of the notch. The dimensions of the final design are suggested with good uniformity in stress distribution along the gage-length.

In this paper a new anisotropic yield functionAnisotropic yield function that describes the elastoplastic behavior of sheet metals depends not only on the second stress invariant J2Invariant J2 for the yield, but also on the third stress invariant J3Invariant J3, both may affect the shape of the yield surface. The new anisotropic yield functionAnisotropic yield function is general and applicable to three-dimensional stress states. The proposed model is identified by calibration parameters from experimental data of material including uniaxial and biaxial tests. In this study, the predictive capabilities of the new anisotropic yield functionAnisotropic yield function are demonstrated by comparison between the predictions and experimental data for yield locus, normalized yield stress, and r-value. The result indicates that the new anisotropic model is reasonable to predict not only the symmetric shape but also the asymmetric shape of yield surface of the sheet metals.

By following varying deformation pathsDeformation path, e.g., a linear path to equibiaxial loading versus a bilinear path of uniaxial loading followed by biaxial loadingBiaxial loading, the same final strain state can be achieved. However, the stress state that the material is subjected to is considerably different due to the varying deformation. This is of interest in a growing field of stress superposition to improve formability and manipulate final part properties in metal formingForming applications. One potential application is forming patient-specific, trauma fixation hardware with differing strength and weight reduction requirements in various regions. In this paper, experiments were performed on a custom fabricated cruciformCruciform machine with the goal of subjecting stainless steelStainless steel 316L to various deformation pathsDeformation path. A novel cruciformCruciform specimen geometry was designed in collaboration with the US National Institute of Standards and Technology to achieve large strain values in the gauge region. Digital Image Correlation was utilized to measure surface strain fields in real time.

In this work, the plastic anisotropyAnisotropy of AA6022-T4 in hole-expansionHole-expansion is investigated focusing on prestraining effect, and its numerical solution is predicted by Homogeneous Anisotropic Hardening (HAH) model combined with an anisotropic yield function. For the prestraining, the material is subjected to a prestrain of 8% in uniaxial tension in the RD. Then, hole-expansion is conducted in a fully instrumented hydraulic press with a flat-headed punch. In both experiments, Digital Image Correlation (DIC) is used, to confirm the prevalence of uniaxial loading in the prestraining step and to measure thickness strain in the hole-expansionHole-expansion. The results show that the plastic anisotropyAnisotropy is manifested as a non-axisymmetric strain distribution around the hole. The prestraining, leading to non-proportional loadingNon-proportional loading, changes the location of failure from ~45° to RD. The simulation shows the current version of HAH model is limited in capturing the thickness contours and the failure location.

This study identified the work-hardening parameters and fracture strain of a hardened die-steel (SKD11). Herein, a shear punching testShear punching test was used as the low stress-triaxiality suppresses material fracture due to the brittle behavior of SKD11 in tensile tests. Furthermore, a minute punch-die clearance was used to increase the compression stress due to the material deformation. SKD11 steel sheets of 1.0 mm thickness were successfully deformed, and the punching force as well as stroke were recorded for inverse analysisInverse analysis using the finite element analysis (FEA). Subsequently, FEA of the shear punching testShear punching test was repeated to optimize the parameters of Swift’s work-hardening law. Consequently, the Swift parameters were derived to ensure that the measured values of the punching force and stroke correspond with the numerically simulated curve. The fracture strain was identified as the maximum equivalent plastic strain at the punch stroke of specimen rupture.

The purpose of the issue is to present the approaches of complex loadingComplex loading for the possible reduction of energy consumption at metal processing. When forces are applied to isotropic material, there is always an active process of complex loading at which the work of external forces is less than the one under simple loading upon reaching the same strained state. Experiments on complex loading and approaches of the mathematical theory of plasticityPlasticity are used in this article. Empirical results on complex loading were mathematically explained based on the Il’yushin’s theory of elastic–plastic processes.

An innovative tube bendingPipe bending process supported by hydraulic pressureHydraulic pressure was patented in 1995. This process was designed for producing butt-welding fittingsButt-welding fitting which particularly fulfil the dimensional specifications of the ASME B16.9, MSS SP-75, and MSS SP-43 standards. Since the patent has meanwhile expired, the bending process is now available for common use. This work presents a novel finite elementFinite element simulation (FE) model build using the software package LS-DYNA, which enables determining the process window for bending defect-free butt-welding fittingsButt-welding fitting. This model was exemplarily applied for investigating the bending process of a 90° stainless steelStainless steel pipe elbow based on a straight tube of nominal pipe size (NPS) 6. Comparing the calculated geometry of the elbow with the actual geometry of an industrially produced elbow revealed very good dimensional agreement. This confirms that the presented model can be utilized for determining suitable process conditions, which allow for producing defect-free components.

This paper describes injection moldingInjection molding of a new woodWood compositeComposite with a natural binderNatural binder composed of sucroseSucrose and citric acidCitric acid. The wood composite was plasticized to be deformable when heated, making molding possible. In this study, the effects of the natural binder content and mixture ratio of the sucrose and the citric acid on the fluidity of the wood composite on injection molding were investigated. At first, the appropriate molding temperature for plasticizing the wood composite was determined to be 180 °C by thermal analysis. In the injection molding test, products were obtained successfully when the fluidity of the wood composite was high. The fluidity was improved by increasing the binder content, and the optimum mixture ratio of the sucrose and the citric acid was 75:25.

Synchronous measurement of temperatureTemperature distribution with infrared cameras has been increasingly used in the thermomechanical analysis of sheet material behavior. Measured temperatures are used, however, only qualitatively due to the absence of well-developed coordinate mapping methods applicable to thermographic measurements. The study introduces a primitive, easy to use, yet effective approach for accurate coordinate mapping from real to image coordinates, and inverse, applicable to even highly oblique thermographic and photographic measurements of planar deformations. The method is not limited to any camera model and precisely counteracts inhomogeneous image distortion. It can be used as a stand-alone opticalOptical measurement approach, but at the same time, it allows flawless correlation with available digital image correlation systems by enabling accurate mapping between thermographic and photographic measurements of planar deformation in real and image coordinates.

This paper presents the optimum processing condition of spinnerSpinner straightenerStraightener. Spinner straightener straightens wire rod using several straightening tools by subjecting the rod to repetitive bending and unbending with rotational movement. This research investigated the effect of bending intensity on the straightnessStraightness of wire by changing the die positions, which determine the bending intensity. Both the experiment and analysis were carried out for the investigation. One of the unique points of this study is the usage of the actual operation line for the experiment instead of laboratory equipment. Another unique point is the combination of the finite element analysis (FEA) and a purpose-built fundamental analysis. The analysis and experiment were in good agreement and showed the existence of the optimum condition. The straightnessStraightness was improved with the increase in the bending intensity up to the optimum bending intensity. However, the excessive bending intensity deteriorated the straightness.

The incremental formingIncremental forming process Radial Rotation Profile-FormingRadial Rotation Profile-Forming (RRPF) has been developed at the Professorship Virtual Production Engineering of the Technical University of Chemnitz. The aim is to enable the production of profiled hollow parts with low sheet thinning and high geometrical accuracy. Because of low thinning due to the process, a smaller initial sheet thickness can be used, whereby material and weight can be saved. RRPF is a two-step forming process. The two principal steps are the production of the preform by Rotational Swing-FoldingRotational Swing-Folding and the subsequent radial profile-forming of the hollow part in one clamping position. During the preform production, wrinkles occur and these wrinkles can be directly formed in the indentation of the mandrel. In the second process step, the wrinkles are used to form the finished profile of the component. However, due to the geometrical stiffness and the material behavior, there is no wrinkle formed in every indentation of the mandrel. An indentation without wrinkle lead to a high sheet thinning, wich occurs due to forming of the final profile. The best component with less sheet thinning and uniform properties is created for a preform with uniform wrinkles in each indentation of the mandrel. Therefore, the approach of a local laserLaser heat treatment is carried out to control the wrinklingWrinkling for the first time. This extends the original two-step forming process by a further process step. Before forming, local heat treatment creates a tailored blank with locally varying strength. Therefore, wrinklingWrinkling occurs in the area with the lower strength of the basic material. The approach and experimental basic investigations of the laserLaser heat treatment are shown in this paper.

Tube spinningTube spinning is a bulk deformation process used to produce seamless, cylindrical, conical, and contoured tubes. Over the last six decades, tube spinning process has been applied in a wide range of engineering applications; especially in automotive, aerospace, and nuclear industry. However, the process has seen little change, and despite a large volume of literature investigating the process, understanding of the process mechanics is limited and the key references have been published about 50 years ago. This paper investigates the process mechanics, looking into the mechanism of deformation. The process is investigated using a numerical model using an implicit time integration and Arbitrary Lagrangian–Eulerian scheme (ALE). The numerical model has been developed and validated against physical trials. The maximum difference between tube geometry predicted by the model and measured in the trials is 4%. Model results further show that both equivalent plastic strain and plastic strain rate are concentrated in the region immediately under and ahead of the roller and that the process reaches a steady state early in the process. The stress state is dominated by compressive normal stresses in all three directions.

In this study, the surface smoothing effect of friction stir formingFriction stir forming on a JIS A5083 aluminum alloy plate with a mirror-finished die was investigated. A material plate was placed on a mirror-finished die, and friction stirring was conducted on its back surface. The material deformed because of the high pressure and heat caused by the friction stir process, and the surface profile of the die was transferred to the material. The average arithmetical mean height (Ra) and maximum profile height (Rz) of the material plate surface were improved from 2 to 1 µm and 17 to 9 µm, respectively, by using a die with surface roughness and an Ra of 1 µm and Rz of 8 µm. Details of the finished surface, including its surface profile and microstructure, and the transcription mechanism were investigated using spectrum analysisSpectrum analysis with the maximum entropy method.

Applying additively manufactured (AM) metallic sheets with internal cellular structures are formed in a bendingBending operation. This enables a higher degree of lightweightingLightweight potential due to design freedom and strain hardening. Computed tomographyComputed tomography (CT) of those structures with wall thicknesses of 0.3 mm reveal manufacturing inaccuracies of the AM process between the nominal CAD and actual geometry. The CT-data shows that the geometric deviation of the unit cells is periodic. A surface model based on CT-data is used to evaluate volume-meshing strategies in a finite element model, benefiting from the periodicity of the core structure. Model simplifications due to a large number of elements within the simulation are presented and used to convert the CT-data into a volume mesh that can be used in a forming simulation. With the CT-based numerical model, the accuracy in predicting force–displacement response can be increased when compared to the ideal CAD-based model. The influence of the geometric deviation and its impact on the deformation behavior in a bendingBending dominated forming operation is evaluated. It is demonstrated that accurate representation of the actual geometry in the numerical model is critical for a correct prediction of the bendingBending behavior and the investigation of localization phenomena during deformation.

Cutting bladesCutting blades for various food processing applications are primarily manufactured by standardized grinding processes. This results, on the one hand, in time-consuming and hence expensive production and, on the other hand, in the surface roughness not being optimized in a microbiological manner. This leads to high healthcare costs for foodborne infections. Further, the strength of the cutting bladesCutting blades is additionally less-than-ideal, which causes a high expenditure on wear. Current research work at the Department for Metal Forming Technologies (LUF) is focused on innovative flow-formingFlow-forming processes which have a high potential for manufacturing parts with an excellent surface roughness in short process times. Along with the process-integrated thermal treatment, this is fundamental for the research and development of improved manufacturing technologies for high-performance cutting bladesCutting blades. This paper looks into innovative process strategies for manufacturing parts with locally graded characteristics, improved surface roughness characteristics, and greater strength of the cutting edge.

This research investigates the influence of axial feed rateAxial feed-rate on shape and thickness changes in multi-passMulti-pass, mandrel-free tube spinningTube spinning for producing a hemispherical shapeHemispherical shape at room temperature. The target shape is formed experimentally by 7 spinning passes from annealed, pure aluminium AA1070 tube. The experiments are conducted with two different axial feed rates, i.e. 2 and 7.5 mm/rev. It was found that increasing the axial feed rate generates lower elongation and higher thickness change. In every experiment, the tube wrinkled at some point during the process, due to the high radial feed. A 3D elastic–plastic finite element (FE) model of the multi-pass tube spinning process is described. The influence of the axial feed rate on axial wrinkling, tube elongation, and thickness change is discussed through the comparison between experimental and FE prediction results.

This paper presents a brief review of various research done on bar straightening. Bar straightening can be considered as a significant process in the value stream of bar production. The paper dealt briefly on various types of arrangements available in bar straightening process. The theoretical perspectives have been looked into in simplified manner. Residual stresses, curvature, and bending moment thereof due to reverse kinematicKinematic loading bending have been discussed. A system approach has been taken as how development on bar straightening process emerged over the years. The recent developments in bar straightening using modelling / numerical modelling give an insight of reduction in curvature after reverse bending. Simulation/Numerical simulation approaches in bar straightening process have been looked into. Key aspects like positioning of rolls and minimization of straightnessStraightness errors have been considered. How control system is applied with Multi-Step Straightening Control System (MSSC) in reducing curvature has been discussed. The paper has been intended to present an overall view of bar straightening from inception till modern times.

Anti-loosening bolted jointsBolted joint were developed with an innovative double-thread mechanismDouble thread mechanism composed of coaxial single and multiple coarse threads. The number of coarse threads of the multiple-thread was set to 3 (denoted as 3thread DTB-II), and its thread structure was fundamentally modified as follows: (i) one of the three multiple-thread grooves was removed for 3thread DTB-II specimens and one of the two remaining grooves shifted downwards by a half pitch (denoted 3-1thread DTB-IIB) and (ii) the depth of the multiple-thread grooves was reduced by up to 50% of the thread height (denoted 3-1thread DTB-IIC). FEMFEM thread rollingThread rolling simulations were performed using a dedicated die. The two kinds of modified DTB-II specimens were rolled precisely and the thread heights reached the target value at all cross sections. The forming states in the thread rollingThread rolling experiments well matched the FEMFEM simulation states. The performance evaluation tests demonstrated that the 3-1thread DTB-IIC specimens had sufficient tensile strengthTensile strength, and its anti-loosening performance exceeds the reference level given in DIN25201.Takemasu, Teruie Shinbutsu, Toshinaka Amano, Shuichi Shimura, Jyo

Due to the difficulty of knock-out and complex metal flow law caused by the non-parallel internal grooves, the manufacturing of the cross groove CVJCross groove CVJ (constant velocity universal joints) outer races mainly relied on machining. Taking the VL-type outer race as a case study, this paper made an exploratory study on the precisionPrecision metal forming forging of these difficult-to-knockout components. A retractable forming mandrel was developed based on which the metal flow behavior through different metal forming methods, including the multi-ram forgingMulti-ram forging and closed backward extrusionClosed backward extrusion, had been researched. The effect of billet shape on forgings and metal flow were analyzed for the multi-ram forming process, and the deformation load and press on the mandrel were focus of the closed backward extrusionClosed backward extrusion method. Influenced by the V-shaped cross grooves, the filling conditions and the pressureForming pressure distribution between adjacent grooves exhibited regional differences.

To control the undesired deformations like section-distortion and springbackSpringback during incremental tube wall grooving, we examined the effect of discrete fillersDiscrete filler on the deformation of thin-walled tubesThin-walled tube during forming. Al6061 tubes with outer diameter of 38 mm and thickness of 1 mm were used in the studies, with silica sands as the fillers. Generalized plastic mechanics was employed to analyze the coupled deformation of the composite structures of discrete media filled tubes; the aggregation of sands was assumed to be compressible continuous body, of which yield behavior was described by the Drucker–Prager criterion. The results proved that compared with hollow tubes, the forming accuracy of incremental tube grooving can be improved under the support of fillers. Specifically, the maximum springbackSpringback was reduced by more than 3.9%, and the section-distortion also decreased. Moreover, a special deformation mode, the prism-shape distortion, was found to occur when the tool feeding step was large.

In this paper, the effect of a pure iron interlayerPure iron interlayer on the propertiesProperties of the multi-pass hot-roll bondingHot-roll bonding titaniumTitanium/carbon steelSteel plate was studied. The mechanical and microstructural properties of the composite plate were investigated by optical microscopy and scanning electron microscopy, as well as tensile-shear, bending, and tensile tests. The results show that when the reduction ratio is below 18%, the shear strength of the interface is higher with the pure iron interlayerPure iron interlayer than without it. At 35% reduction, the shear strength is similar in both cases. At a reduction ratio of 68%, with the pure iron interlayer, fracture of the bonding interface occurs on the titaniumTitanium matrix, whereas without the pure iron interlayer, fracture occurs on both the titanium matrix and the compound layer on the interface; the pure iron interlayerPure iron interlayer improves the bending and tensile propertiesProperties of the titaniumTitanium/carbon steelSteel plate appreciably.

The main concerns of forming a super-large rectangular ring are forming accuracy, rolling stability, uniformity of deformation, and accordingly the distributed microstructure and related mechanical property of the rolled ring. In this paper, a flat ring with a diameter of 9 m is taken as an example, which is the bearing ring of a carrier rocket. To meet the requirements of formation and performance, the whole forming process, including multidirectional forging, punching, reamingReaming and ring rollingRing rolling is investigated step by step. Due to the poor internal quality of large ingot, three multidirectional forgingMultidirectional forging schemes are compared in order to improve the internal quality of the ring billet. For the reaming process, four different reduction amounts per pass are designed to control the end surface quality of the reamingReaming operation part. To refine grain and minimize the anisotropy of the rolled ring, the ring rollingRing rolling process is divided into high-temperature rolling and low-temperature rolling, the feeding strategy of which are studied respectively. Based on the FORGE software platform, the simulation results show that the seven upsetting and six stretching process, 30% reduction per pass, and the optimized feed strategy are the optimal multidirectional forging process, reaming process, and ring rolling process.

A new printing method for metal using soft materialSoft material tools has been developed. This method uses paper or plastic film with a fine pattern produced by the laser printer as a printing tool. The aluminum disc is compressed with a soft material tool between the upper and lower flat dies. In order to print with high accuracy with a uniformed pattern onto a metal surface, the effects of the process conditions on printing have been investigated. Experimental results using the soft materialSoft material tools showed that the good condition for high accuracy was changed by the combination of the average pressure and the workpiece shape. The new printing method can print patterns easily onto the metal workpiece. The pattern can be observed from each workpiece surface. When using paper, the surface profiles of the workpiece are not clear because the printed pattern is hidden by the surface roughness of the paper. When using the PET film, the surface pattern can be clearly observed. The average pressure is needed to print the pattern clearly and uniformly. When decreasing the diameter and thickness ratio D/t of the workpiece, the required average pressure is decreased.

It is hard to maintain high plasticity for metal matrix composite while increasing their mechanical properties. A new process for preparing carbon nanotubesCarbon nanotubes (CNTs) reinforced magnesium nanocomposites (CNTs/Mg) was developed, which combined friction stir processing (FSP)Friction stir processing (FSP) and ultrasonic-assisted extrusion. It is interesting that the mechanical property of CNTs/Mg nanocomposite materials is improved greatly compared with the supplied Mg alloy at the same time while the plasticity is preserved. The plasticity improvementPlasticity improve mechanism is explained from the effect of interface bonding and the liquid–solid extrusionLiquid-solid extrusion process by different microstructure analyses. HRTEM analysis shows that the Al2MgC2 phase at some interfaces between Mg matrix and CNTsCarbon nanotubes is formed, which contributes to good composite interface bonding. Liquid–solid extrusion process can densify the composite and generate severe plastic deformation which is very useful for plasticity improvementPlasticity improve.

The process investigated in this paper consists of cold rotary swaging of steel bars. In recent work, surface residual stresses were found to be sensitive to process parameters and their fluctuations, leading to variations of residual stresses at different length scales. To properly evaluate the residual stress states in rotary swaged bars, several complementary measurement techniques were applied. Complementary to surface X-ray diffractionX-ray diffraction measurements, the applicability of micromagnetic methodsMicromagnetic method was evaluated for fast mapping of local residual stress distribution at the surface with a spatial resolution down to 20 µm. Additionally, an evaluation of the full residual stress profile over the cross-section was achieved by neutron diffractionNeutron diffraction. The combination of the different methods thus allowed a complete characterization of the generated residual stresses at different length scales. Furthermore, a 3D FE-model was developed and process simulation using the Chaboche material model was carried out to investigate the residual stress generation and compare the results with the experimental data. The results show an overall good agreement of the experimental data with the simulation results.

Highly accurate in-situ measurement of geometric and mechanical quantities is now a requirement for the production of complex and, in particular, incrementally manufactured components. A current research project at the Chair of Forming and Machining Technology (LUF) is thus investigating the application of a 3D digital image correlation3D digital-image-correlation measuring system for in-situ residual stress measurementsResidual stress measurement based on the hole-drilling methodHole-drilling method. The corresponding investigations have initially proven the basic feasibility of the system. It is also shown that the measurement result is affected by thermal influences, unintentionally introduced vibrations, and air flow. These influences can be compensated to a high degree through the appropriate countermeasures. A compensation method is thus presented, taking the example of thermal loads.

The austenitic stainless steelsAustenitic stainless steel 1.43071.4307 and 1.44041.4404 significantly benefit from cold forming, due to their high work hardening capability. Great potential to improve the component's fatigue properties is expected by optimizing the forming process chain such that specific residual stressesResidual stresses are induced in critical component areas. In this work, an analysis of the formation of residual stresses during rotary swagingRotary swaging is carried out. Through this incremental forming process, high strain hardening and a complex material flow history are induced in the workpieces. Therefore, measuring strategies for the residual stress measurement of cold deformed austenitic steels by X-ray diffractionX-ray diffraction, using the sin2Ψ-methodSin²2 Ψ, were developed. Here, especially the 1.4307 is a challenging material due to cold forming-induced martensite formation. Despite phase changes, both cold-formed materials exhibit anisotropic microstructures as well as coarse-grained areas. Moreover, particular notched geometries are produced on the workpieces by rotary swaging. The measuring techniques are further developed for these complex geometries and the residual stresses are investigated.

During the manufacturing of semi-finished products, the material is subjected to various forming steps to achieve the final geometry. In order to reduce the work hardeningWork Hardening introduced and to ensure a good formability, it is annealed before component manufacturing. Forming technologies like forward rod extrusionForward Extrusion are well-established methods for the efficient production of resilient components. In this process, however, an inhomogeneous pre-strengthening of the material influences the stress distribution during forming and therefore the mechanical properties and the residual stressesResidual Stress in the component. Since they affect the parts’ operating behaviour, knowledge of the influence of the delivery condition of the material is necessary. The aim of this paper is to derive dependencies between material properties and the resulting residual stresses and work hardening in the component. Due to the increasing application, ferritic stainless steelStainless Steel X6Cr17 in the skin passed (+LC) and soft annealed (+A) states are used. Residual stresses, microstructure, and microhardness distribution of both material states are compared regarding the rods and extruded parts. The effects of the delivery condition are evaluated by comparing process and component properties.

Residual stresses are an important issue as they affect both the manufacturing process as well as the performance of the final parts. Taking the whole process chain of hot forming into account, the integrated heat treatment provided by a defined temperature profile during cooling of the parts offers a great potential for the targeted adjustment of the desired residual stress state. The aim of this work is the investigation of technological reproducibility and stability of residual stressesResidual stress stability arising from the thermomechanical forming processForming process. For this purpose, a long-term study of residual stresses on hot-formed components is conducted. In order to develop finite elementFinite element analysis models for hot forming, a comprehensive thermomechanical material characterisation with special focus on phase transformation effects is performed. The numerical model is validated by means of a comparison between residual stress states determined with X-ray diffractionX-ray diffraction on experimentally processed components and predicted residual stresses from the simulations.

In reluctance and permanent magnet synchronous machines, flux barriers are crucial for magnetic flux guidance. Designed as cutouts, flux barriers reduce the mechanical strength of the rotor construction. To operate these electric drivesElectric drive at higher rotational speed, an alternative flux barrier design is required. Since residual stressResidual stress influences the magnetic properties of soft magnetic materials, this paper deals with embossingEmbossing induced residual stress as flux barriers in non-oriented electrical steelElectrical steel with 2.4 wt% silicon and a sheet thickness of 0.35 mm. The investigated flux barriers were fabricated with a cylindrical or spherical punch at two different penetration depths and were compared to a flux barrier fabricated as cutout. A residual stress analysis using finite element analysis helps understanding the mechanism of embossed flux barriers. Additionally, the influence of induced residual stress on the magnetic material behavior is measured using standardized single sheet tests and neutron grating interferometry measurements. This investigation aimed at a better understanding of the flux barrier design by local induction of residual stressResidual stress.

Bistable fully closed shells can serve as long supporting structures that can be folded into a compact transport geometry and unfolded at the construction place. BistabilityBistability is achieved by introducing a specific distribution of residual stressesResidual stress through the thickness of the shell, e.g., by incremental die-bending. In order to find a suitable bending radii combination a semi-analytical model was developed and experimentally validated for the steel 1.1274 in previous research. Nevertheless, minor deviations have occurred in the prediction of final curvatures of the different stable geometries and it is still unclear to what extent other influencing variables such as shell thickness or material properties influence the achievability of fully closed bistable shells. Therefore, in this paper, an enhancement and generalization of the existing semi-analytical model for different steels is described and the extended model is used for a comprehensive analysis of the influence of different variables on bistabilityBistability and final shell geometries.

Shear cuttingShear cutting is used for manufacturing various parts ranging from, e.g. simple washers to complex gearsGears. The latter are typically subjected to cyclic loading and fail foremost due to fatigueFatigue damages. Hereby, the part’s lifetime is mainly determined by the geometry, the applied load, the material, the hardness, the roughness, and the residual stressResidual stresses state. While numerous research works deal with the influence of the process parameters on the hardness and the part’s geometry, the influence of the process parameters on the residual stressResidual stresses state and on the resulting fatigueFatigue strength has not been investigated in detail, yet. In an earlier publication, suitable shear cuttingShear cutting techniques, which allow achieving a high amount of clean cut and a favorable residual stressResidual stresses state were compared. In this paper, the influence of the process parameters on the residual stressResidual stresses state and the resulting bending fatigueFatigue strength are addressed. To simulate the bending stress occurring in the tooth root, C-shaped specimens were manufactured by different blanking techniques. The die clearance and punch and die edge radii were varied with these blanking techniques. After measuring the cut-surface geometry, the hardness distribution, and the surface roughness, the fatigueFatigue strength was determined in a pulsating test rig. By carrying out residual stressResidual stresses measurements using X-ray diffraction and simulating the material flow behavior using the Finite-Element Method, basic mechanisms, which are influencing the residual stressResidual stresses state and the resulting bending fatigueFatigue strength, were identified and will be presented and discussed in the paper.Müller, Daniel Stahl, Jens Pätzold, Isabella Golle, Roland Tobie, Thomas Volk, Wolfram Stahl, Karsten

In production engineering, current research focuses on the induction of targeted residual stressResidual stresses states in components in order to improve their properties rather than follow the usual path of minimizing residual stresses to prevent failure. In this contribution, a focus is laid on the investigation of the subsequent cooling process of hot bulk formed parts. Such cooling of a component leads to a microscopic phase transformation, which has to be considered in order to compute residual stressesResidual stresses inside the material. A numerical approach based on a phenomenological macroscopic material model is presented to depict the related stress evolution.Uebing, S. Brands, D. Scheunemann, L. Kock, C. Wester, H. Behrens, B.-A. Schröder, J.

In sheet metalSheet metal forming, embossingEmbossing provides a process for targeted improvement of the mechanical properties of sheet metalSheet metal materials. The local property modification is thereby achieved by uniform residual stressesResidual stresses induced as a result of the one-side embossingEmbossing process. For example, such a targeted induction of the residual stressesResidual stresses can significantly increase the fatigue strength of sheet metalSheet metal components. In order to ensure this kind of component optimization in continuous operation, the induced stresses have to be uniform. In the study presented in this paper, duplex stainless steel (X2CrNiN23—4) specimens having a thickness of 1.5 mm were unilaterally embossed in order to investigate the effects of the embossingEmbossing process on the component properties. The primary objective of this investigation was to find a suitable embossingEmbossing strategy for generating preferably uniform stress distributions into sheet metalSheet metal blanks.

A short route manufacturing process of retaining rings was put forward, which was composed of hollow ingots manufacturing by Electro-Slag Re-melting (ESR), hot ring rollingHot ring-rolling, and cold expanding strengtheningCold expanding strengthening. And microstructure mechanisms, deformation characteristics, and process parameters during both of hot ring rollingHot ring-rolling and cold hydraulic expanding strengthening were investigated. The results show that the multi-pass flow stresses decreased with increase of interval time. During multi-pass compression, grain refined at lower temperature of 1050 °C by static recrystallization, then grain refined at higher temperature of 1150 °C by both of dynamic and static recrystallization. Based on the influence of the contact arc length ratio on strain penetrationStrain penetration in the wall deformation zone, the driving roller radius of 500 mm and the pressure roller radius of 130 mm were determined for the ring rolling process ofφ712 mm/308 mm × 902 mm thick-wall hollow ingot. The optimum rotate velocity of the driving roller should be 0.8 rad/s. And the feeding velocity of the pressure roller should to be 1 mm/s for matching. During cold deformation, planar slip and twinning predominated at small and large deformation, respectively, to increase strength. For the hydraulic expanding process of ϕ937/672 × 1034 mm hollow forging, the optimum matching of 60° punch angle and 5 mm contact seal height can be adopted for obtaining well-shaped strengthening forgings.

Composite ring rollingRing rolling could bring substantial material, cost, and energy savings and allow for lighter weight components, by joiningJoining concentric rings with different material properties. For there to be any possibility of achieving a material bond, an interference fit between the rings must be maintained. In this paper, a force equilibrium-based model is introduced to predict when such a fit is possible. This model, for radial composite rolling, predicts a limit to the flow stress of the inner ring relative to the outer ring, suggesting a maximum ratio of about 160%. It also shows that the inner tool’s diameter must often be significantly smaller than the outer tool’s. The model is tested in four composite ring rolling experiments with two grades of Aluminium alloy, 1050 and 6063, and different tool sizes. An interference fit was achieved in two cases: (1) when the inner ring is Al 1050 (flow stress 52% of the outer ring); and (2) when the two rings are both Al 6063 and the inner tool diameter was 39% of the outer tool. It was not achieved when (1) the materials were reversed nor when (2) the inner tool increased to 59% of the outer tool diameter. These outcomes were all predicted by the model, a potentially valuable new guide to designing composite ring rollingRing rolling processes.

Steel producers are competing to roll non-grain oriented silicon (NGOS) strip with 1.25 m in width, 0.5–0.35 mm in thickness, and a profile deviation that is less than 5 micron-meters. Mathematical ModelsMathematical model are indispensable tools to study the mechanism of work roll contoursWork roll contour during rolling, but they require industrial tryouts to validate their effects on strip profile. Thus, this paper presents the effects of various work roll contours designed for (1) the 6th and 7th stand of a 4-high hot tandem rolling mill; (2) single stand 6-high reversing cold mill; (3) 1st to 3rd stands of a 6-high tandem cold mill. Results show that the NGOS strip profile hit rate of 5 micron-meters is increased by the implementations of advanced work roll contours.

SurfaceSurface roughness textured rolling is designed to transfer roughness onto the sheet from the surface of textured rolls. The authors investigated the influence of rolling conditions on transferability using an ordered texture roll experimentally. To understand such influence, we compared the rolled surface profiles during the experimentsRolling experiment with those during Finite Element Analysis (FEA). However, at reductions greater than 5%, there is a discrepancy, which is believed to be caused by unknown restraint force. As it is difficult to estimate the restraint force with a 3D profile roll, we carried out experimental transformability tests with 3 simpler kinds of ordered texture rolls, namely, (1) RD, (2) TD, and (3) 45-degree groove rolls. In this paper, the apparent friction coefficientsFriction coefficient were evaluated experimentally with these rolls. The friction coefficientsFriction coefficient were found to be affected by several metal flows in the roll bite. In conclusion, it is still difficult to estimate the apparent friction coefficient because these metal flows affect each other.

An auger flightingAuger flighting is a helical-shaped circular product used to transfer bulk materials in broad applications. Continuous auger flightings are formed from straight steel strips by a specialty rolling mill. Because of the geometry and configuration of auger flightings, the rollingRolling process is more complex than the ordinary longitudinal rolling. However, there is little published literature on the theoretical features of auger flighting rolling. In this article, the fundamental kinematicsKinematics and mechanicsMechanics of auger flighting rolling are mathematically developed. From these mathematical models, the contact area, rolling force, and torque are calculated and the affecting factors are evaluated. The slip characteristics between the strip and forming rolls and the effects of roll offset are studied. The article also provides design considerations, primarily for the main roll shafts and required rolling mill power. Finally, the application results are compared to the actual rolling readings and satisfactory agreement is obtained.

The forming process of radial–axial ring rollingRing rolling involves certain instabilities, causing from the underlying principle of the synchronous and continuous deformation in two opposite rolling gaps. To reduce the occurring consequential errors like climbing of the ring in the radial rolling gap, we installed an image processingImage processing system for error detection. Combined with the integration of the camera setting into the control software of the rolling machine, it is possible to test automated rolling strategies to stabilise the forming process in the case of upcoming ring climbingRing climbing. The paper will illustrate how an intervention limit, in form of limit value, for the control system could be evaluated via statistical process control and evaluates if there is a systematic climbing behaviour of the ring. The combination of an expert interview with an effect analysis of the forming parameters on the stabilising impact leads to the development of an ideal forming strategy. The defined strategy is validated in a final design of experiments.

The shape defect called “longitudinal bucklingBuckling” tends to occur inTemper rolling temper rollingRolling of double reduced thin strips. Although previous research investigated the effects of several rolling conditions on longitudinal bucklingBuckling, the effect of large delivery angles of over 4° has not been studied experimentally. In this paper, the effect of large delivery angles was investigated in a laboratory rollingRolling experiment. The results showed that the longitudinal bucklingBuckling pattern becomes more distinct and the number of waves decreases as the delivery angle increases, and buckling disappears when the delivery angle exceeds 24°. At the same delivery angle, the buckling form does not change depending on the distance between the work roll and the auxiliary roll. Following this experimental study, an elementary analysis of the bucklingBuckling characteristics of a sheet winding around a work roll was carried out, and it was found that the change in the number of waves depending on the delivery angle in the analysis was in good agreement with the experimental results when the delivery angle was larger than 10°. It is estimated that longitudinal buckling is initiated around the roll gap and changes under the influence of the shape of the sheet winding around the work roll.

A fast model is presented for the three-dimensional stress distribution in the roll gap. This local data is used to calculate the 3D deformation of the work roll barrel by flattening and deflection using a combined analytical and finite element procedure. Detailed information about the work roll deformation can therefore be obtained because the model does not rely on a constant roll force. The local strip and work roll temperatures are calculated by a numerical solution of the heat equation and the evolution of thermal roll crown is calculated for a given rolling campaign. The strip shape is found by the intersection of the deformed roll with the initial strip shape. An upper-bound technique is applied for the resulting strip flatnessFlatness. Typical methods of profile and flatnessFlatness adjustment are discussed with effects on strip profile and flatness. These are static roll crowns as well as work roll bending, zonal roll cooling, and axially shiftable S-shaped grinded rolls (CVC—continuous variable crown).

Double metal composite ringComposite ring has the advantages of two materials, and is used in specific fields. The traditional manufacture method is welding. And some scholars try to use ring rollingRing rolling process to produce a composite ring. However, the interface connection quality is not good. In this paper, a novel constructiveConstructive hot ring rolling process to manufacture a seamless double metal composite ring is proposed. First, two separate rings with different metals are assembled together. And then the surface interface area on the upper and lower of the assembled ring are welded in an oxygen-free environment, which can suppress the interfacial oxidation during heating process. After that, the surface welded ring is cleaned and heated. Finally, the target double metal composite ringComposite ring is formed by hot ring rolling. An experiment of constructiveConstructive hot ring rollingRing rolling process for double metal composite ringComposite ring was done. The interface healingInterface healing effect of the composite ringComposite ring was studied. The result indicated that the interface healingInterface healing degree was significantly improved by this method.

The compact casting-rolling technique is an advanced method to produce seamless ring parts. The technique has been paid much attention in recent years. To find out the textual evolution rule of materials in this compact process, hot ring rollingHot ring rolling of 42CrMo casting blank was conducted at different mandrel feed rates. The macro-textures of the as-obtained products were studied by X-ray diffraction, and micro-textural associated grain orientationsGrain orientation were examined by electron backscattered diffraction techniques. The dominant textures in hot-rolled rings were similar, with γ-fibre consisted of {111}<110> and {111}<112> orientations as the most intense components. The α-fibre and ε-fibre textures in the entire thickness of hot-rolled rings did not show significant change as feed rate increased. Moreover, shear textures, including Copper-type {112}<111> and Goss {110}<001> components were presented in different regions of hot-rolled rings. The grain refinement was found closely related to grain orientation and micro-texture evolution in the entire thickness. The inhomogeneous distribution of grain size in the hot-rolled ring at a higher feed rate resulted in poor plasticity and toughness, which was caused by inhomogeneous γ-fibre orientations, especially in the center layer of the ring. Overall, these findings look promising for future studies dealing with compact hot ring rollingHot ring rolling processes.

When the larger-size step shafts with small scale are manufactured, both the forging and rolling method bring about high cost for its need for heavy loading or special dies. This paper develops a novel flexible skew rollingFlexible skew rolling (FSR) process to produce step shafts. The process includes four stages: radial rolling, rollers inclining, skew rolling, and rollers leveling. Each roller has three freedoms (circle rotation, radial rotation, and radial-feeding motion), which can manufacture different axles by programming different rollers’ movements that can achieve flexible rolling with the same tools. In order to conduct the experiment and verify the process feasibility, a flexible skew rolling mill with dual-rotatable-shafts (DRM-80) was invented and manufactured, and both rollers have three freedoms that can be dynamically adjusted during the whole rolling process. Feasibility experimentsFeasibility experiment were performed at the DRM-80 millDRM-80 mill, a ∅80 × 390 mm C45 steel billet was used to manufacture a single-step shaft. A large and long shaft (total length 605 mm, minimum diameter 50 mm) was formed and has well dimensional accuracy and no serious defects. The main forming defects include knurled pockmarks, helical grooves, side cavity, and diameter tolerance. The experimental FSR part is free from internal cracks by observing the transverse and longitudinal sections. The study results verified that the novel flexible skew rollingFlexible skew rolling process is positive and the new type DRM-80 millDRM-80 mill is reliable.

The cold rolling process of a thin strip is difficult to continue when the strip has been thinned to a certain thickness. The Stone formulaStone formula is the most common approach for predicting this limit, but it was found that the results obtained from this formula are rather inaccurate when applied in experiments or the production of ultra-thin strip rollingUltra-thin strip rolling. In this paper, a theoretical computational model of producible rolling thicknessProducible rolling thickness for an ultra-thin strip based on the Fleck theory was established and the single-pass reduction can be obtained in accordance with the given unit width rolling force, the technical parameters of the rolling mill, the yield strength of the material, and the initial thickness of the strip. The relationship between single-pass reduction and the ratio of the initial thickness of the strip to the theoretical limiting producible thickness under the condition of the maximum allowable rolling force of the rolling mill was discussed. This study provides theoretical guidance for practical production by defining the product specification ranges and rolling regulations for existing rolling mills and determining the roller diameters and force and energy parameters for the design of rolling mills.

Electrically assistedElectrically-assisted (EA) forming is a promising process due to its advantages, such as reducing forming load, increasing formability, and decreasing springback. In order to reduce material waste and environmental pollution in the manufacturing process of surface textureSurface texture, the EA micro-rolling process was used to form surface texture on T2 copper sheets. The EA micro-rolling system consisted of a micro-rolling device and a power supply. Effects of the voltage, frequency, and pulse duration on feature height were investigated. Compared with conventional micro-rolling, the EA micro-rolling process increased the feature height significantly, improved the flatness of the sheet with surface texture, and decreased the surface roughness remarkably. The influences of electric current for different grain sizes were not identical. The rise of feature height was more significant for rolled sheets than that for annealed sheets. Moreover, the feature height has little variations under voltage magnitude of this study when the grain size was greater. This study proves that forming qualityForming quality of surface textured sheets can be improved under appropriate electric parameters and the EA micro-rolling process would be a promising surface texturing method.

Inter-roll thrust forceThrust force due to roll misalignment in a 4-high strip rolling mill affects the difference in roll forces measured by load cell on the work side and that on the drive side. Since the roll force difference is utilized for strip steering controlSteering control, in which roll gap tilting control is done assuming the roll force difference reflects strip off-centeringOff-centering behavior, the inter-roll thrust force gives a serious disturbance to the steering control and may cause troubles like tail crash. In this paper, an inter-roll thrust force decoupling methodDecoupling method for the steering control is proposed. The method utilizes measured thrust counter forces acting against work roll chocks to obtain effective roll force difference for the steering control. Validity of the decoupling method is confirmed using a laboratory 4-high mill which can control cross angles between rolls and measure the work roll thrust counter forces.

Today, the automotive OEMs and part suppliers are increasing their material suppliers globally. Therefore, the same grade steels are supplied by different steel mills and batch conditions to meet this requirement. However, the variation of the incoming mechanical propertiesMechanical properties can significantly influence the stamping quality associated with necking, wrinkling, and cracking. This increases the overall manufacturing costs and lowers productivity. Nondestructive evaluation (NDE) toolsNondestructive evaluation tool have become useful to reduce this uncertainty by measuring incoming mechanical propertiesMechanical properties. The measured data can be used during production in a feed-forward control to select the optimal process parameters or as forming process parameter optimization using simulations. A detailed evaluation of a 3MA3MA (micromagnetic, multiparametric microstructure, and stress analysis) Fraunhofer IZFP’s device and its viability of implementations in a production environment is introduced. The 3MA3MA equipment was incorporated into an industrial flexible robot and a practical calibration procedure was developed and validated for Bake-Hardening (BH) 340 steel.

Selective embossingEmbossing of sheet metal blanks, prior to processing, offers the possibility of locally modifying material properties. Small indentations applied on the sheet metal surface by a punch lead to increased material strength due to the induced strain hardening. Moreover, such locally embossed sheet metals show an enhanced process window with regard to forming processes and an improved performance under different loading conditions. The experimental study presented in this paper investigates the bendingBending properties of high-strength steelHigh strength steel sheets embossed on the tension or the compression surface of the bent blank. The effect of embossingEmbossing on the bendingBending resistance of two different materials (DP500 and TRIP780) was analyzed by varying the embossingEmbossing patterns by density and depth. As a result, bendingBending forces required in the tests rise when increasing the proportion of the embossed surface. Therefore, the paper reveals potentials of local embossingEmbossing with regard to a specific modification of bendingBending properties of sheet metal components, thus enabling their use in lightweight constructions.

This research evaluates experimental methodologies for determining forming limits by necking and fracture in polycarbonate (PC) sheets by proposing developments of recent methodologies usually used in sheet metal forming. With this purpose, Nakazima tests with different blank geometries are performed on a 1 mm thick polycarbonate (PC) sheet. The experimentation included the use of Digital Image Correlation (DIC) for the evaluation of strains and thickness measurements for the determination of failure strains. The results provided accurate formability limits by necking and fracture, establishing a general framework for analysing specific forming processes (such as incremental forming) on polymeric sheets. Differences in the shaping of the Forming Limit Curve (FLC) and Fracture Forming Limit (FFL) curves for PC compared to those obtained in metal sheet are also discussed.

An indicator for the quality of products that are formed in an embossing process is the contour of the product. Highest contour quality is achieved, if the shape of the forming tool is perfectly imprinted into the material. However, elastic forces and tribological effects, which occur during the forming process, impair the shape-setting progress. In order to improve the embossing process, an electromagnetic actuation unit is presented in this paper, which applies horizontal vibrations into the press ram during the forming process. The actuation unit consists of two strong linear solenoids, which generate oscillating force with variable levels and frequencies. The vibrations improve the shape setting during the embossing process. The concept, design, and the function of the actuators are presented in this paper. Experimental studies on an embossing process in a production environment were performed, to demonstrate the features of the novel system.

This paper presents an engineering procedure for stampingStamping irregular sheet metal parts with an elastic blankholderBlankholder, providing a localized contact pressure to ensure stamped parts without failures of cracks and wrinkles. This is done by arranging the height of the blankholder supporting elements in a die set, which is made using standard manufacturing quality and is implemented in a press line equipped with standard die cushionsDie cushion. However, the contact pressure is very sensitive to the height of supporting elements. To eliminate the inherent noise from the geometric dimension and tolerance of the die set, a finite element model for optimization of the contact pressure must be created according to the actual die set geometry. In this study, the blankholder geometry for stampingStamping a fender-like part was scanned by GOMATOS and the height of cylindrical supporting elements was measured by inserting feeler gauges between the blankholderBlankholder and the supporting elements according to the outcomes of finite element analysis.

Forming limit curves (FLCForming Limit Curves (FLC)) are widely accepted by industry for predicting necking failure during sheet metal forming. FLCs can be developed directly through material testing or by numerical extrapolation from tensile data. This work evaluates the accuracy of FLCs developed from Nakajima testing using the linear-best-fit method to Keeler, Arcelor V9, and Tata Steel FLCForming Limit Curves (FLC) models that are available in the commercial FEM software. Two different stamping shapes and three variations of 980GEN-3 steel were used for physical testing to evaluate the FLC models.

The formability of the corrugated clad cup was investigated to enhance the functionality of the cup. Deep drawingDeep drawing, which is one of press forming, is a plastic processing technology for forming a thin plate into a three-dimensional container. Depending on the application, the functionality of the container itself was required. In the present study, the drawn cup with a corrugated structure on the side wall was formed by deep drawingDeep drawing. In the experiment, the materials were pure titaniumPure titanium TP270, low carbon steel SPCC, and stainless steel SUS304. In the deep drawingDeep drawing process, the composite die combining the roller die was prepared for forming a clad cup. In the side wall of the corrugated cupCorrugated cup, the distance between the waves was approximately 8.6 mm. The thickness strain at the bottom of the drawn cup TP270 was no more than 0.06. It was found that the corrugated clad cups were successfully formed by using the composite die combining the roller die.

Reducing fuel consumption and climate-damaging CO2 emissions are important challenges for the automotive industry. These goals can be achieved by reducing the weight of the car. Extremely lightweight car bodies can be achieved by using exclusively composite materials, which have the major disadvantage of high costs and unsuitability for a large-scale production. A large-scale production of lightweight car body parts with a high stiffness to weight ratio requires more economic materials and new innovative manufacturing technologies. A very promising approach to meet these requirements investigated at the Paderborn University is the combination of high strength steel alloys and unidirectional CFRPCarbon fiber reinforced plastic (CFRP) prepregs in a special hybrid material—fiber metal laminate (FML)Fiber metal laminate (FML)—which can be processed by specially adapted forming technologies such as deep drawingDeep drawing. The paper presents recent results of the combined curing and forming processCombined curing and forming process. The influence of the process parameters, the process limits, the necessary tool systems, and the process strategies are similarly covered by the paper.

Production of high strength, high stiffness, and safety-relevant profile parts is feasible through the sequence of media-based forming and in-die quenching. As forming media, solid granular mediaGranular media have been recently introduced. In this work, the granular mediaGranular media tube press hardeningPress hardening process with additional axial feeding is investigated in order to enhance the tube thickness distribution and to enlarge the process window. The experiments show that, compared to the process with frictional feed, the limits for insufficient forming and wrinkling are unaffected by the change of the feeding system, while the area for intolerable thinning is reduced. Additionally, through the new feeding system, a higher degree of design freedom could be achieved, e.g., shoulder angles of 90° are possible. Furthermore, for the design of the process, an advanced FEM simulation has been developed, which is based on the Drucker–Prager cap model and covers also the thermal interactions.

This study is focused on punch shape designPunch shape design in tube hydro-piercingHydro-piercing processes of aluminum alloy A6005 tubes. The flow stresses of the aluminum alloy tubes obtained by tensile tests are used in the finite element simulations of tube hydro-piercing process with software “DEFORM 3D.” The ductile fracture criterion of normalized Cockcroft and Latham is used during the FE simulations. The critical damage values for the criterion are obtained by comparing simulation results and tensile test data. The effects of various parameters such as the stroke, internal pressure, etc., on hydro-piercingHydro-piercing processes and deformation mechanism are discussed. Experiments are conducted and the experimental shearing surface heights are compared with the simulation results to verify the validity of the analytical models. The effects of various parameters on shearing surface heights are also discussed by hydro-piercingHydro-piercing experiments.

Aluminum-silicon-coated (AlSi-) boron-steels are regarded as standard material in direct hot stampingHot stamping processes. Nevertheless, the material brings along some disadvantages such as the requirement of a long dwell time in the furnace for the generation of a resistant diffusion layer. In this paper, a multilayerMultilayer steel sheet with a boron-steel core-layer and stainless steel outer-layers is introduced and the manufacturing process by hot roll-bonding is described. Due to the stainless steel surfaces, a coating for hot stampingHot stamping is no longer necessary. The multilayerMultilayer is characterized by hot tensile tests and compared with the monolithic multilayer-partners. Hot stampingHot stamping experiments are conducted on a laboratory scale. Corresponding hardness measurements show that the core-layer is hardened while the outer-layers remain ductile. The new multilayer sheets offer the potential to deliver components with higher formability due to tailored properties along the sheet thickness and the use of rapid heating methods.

The challenges in forming titanium alloysTitanium alloys at room temperature are well researched and are linked both to the limitations imposed by the basic crystal structure and their ability to form texture during plastic deformation. One major issue of concern for the sheet forming of titanium alloys is their high sensitivity to surface inhomogeneity. Various machining processes are utilised in preparing sheet hole edges for edge flanging applications. However, the response of edge forming tendencies of titanium to different edge surface finishes is not well investigated. The hole expansion testHole expansion test is used in this project to elucidate the impact of Abrasive Water Jet (AWJ) and Electro-discharge machining (EDM) cutting techniques on the edge formabilityEdge formability of CP-Ti (Grade 2) and Ti-3Al-2.5 V alloys at room temperature. The results show that the quality of the edge surface finish has major effect on the edge formability of the materials. The work also found that the variations in the edge forming performance are mainly the result of the influence of machining induced edge surface defects.

Multi-intersecting high stiffened structures have potential application in aerospace components, which are the main load-bearing structure of manned space station. However, its springback behavior is very complicated due to the interaction of multi-intersected ribbons and intersecting patterns during die forming. In this study, for typical spherical shaped multi-intersecting stiffened structures, a new approach is proposed to quantize the influence on flexural neutral layerNeutral layer of multi-intersected ribs. The strain distribution along the thickness at different radial positions of ribs is derived theoretically. Reverse loading method is used to calculate springback radius of each position assisted by Matlab software and the radial profile of the panel after springback is obtained by numerical integration algorithm. To verify the accuracy and effectiveness of the new approach, finite element simulations based on ABAQUS software and experiments were both implemented. Comparison shows that the results are of good agreement, proving the approach is capable of predicting springback of multi-intersecting stiffened structures.

Springback is a challenging issue in the processing of ultrathin superalloy components whose thickness are usually in the range of 0.1 ~ 0.3 mm, and its prediction is affected by the size effectSize effect. In this research, the cyclic shearing tests of superalloy sheetsSuperalloy sheet with different grain sizes were performed to clarify the relation between size effect and cyclic deformation behaviorCyclic deformation behavior. The experimental results indicated that it is affected by the geometrical and grain size effects. To explore how the size effectSize effect affects the springback of ultrathin superalloy sheetSuperalloy sheet, U-bending tests were performed on specimens with different grain sizes and thicknesses. In addition, different hardening models were compared by multiscale U-bending tests. The results showed that the Yoshida–Uemori (YU) model can well describe the cyclic deformation of superalloy sheetSuperalloy sheet at various scales.

Improvement of formability of aluminum alloy sheetsAluminum alloy sheets is desired because of their lower drawability than mild steel. Therefore, the special sheet forming methods such as a hydro-mechanical forming and a tailor heat treated blankTailor heat treated blank have been developed for aluminum alloy sheets. In this study, we combined both the methods and investigated the limit of drawing ratio of tailor heat treated blanks in a hydro-mechanical forming process. Tailor heat treated blanksTailor heat treated blank of A6061-T6 sheets were produced by the local solution treatment which was conducted by heat transfer from metal plates heated to a high temperature. Hydro-mechanicalDeep drawing deep drawingHydro-mechanical deep drawing tests were performed using a cylindrical punch. The limit of drawing ratio of tailor heat treated blanksTailor heat treated blank in a hydro-mechanical forming process was higher than that of simple hydro-mechanical forming and that of simple tailor heat treated blanks.

It is necessary to prevent the surface oxide film peeling caused by sliding between workpiece and die material with high surface pressure for reducing punch load and preventing fracture. Hence, we have focused on the method to prevent the titanium surface oxide film peeling during press forming to prevent the adhesion. The workpieces with surface oxide film by atmospheric oxidation were utilized to demonstrate the effect of titanium surface oxide film on formability in deep drawing process. Additionally, the method to prevent adhesion during deep drawing process was developed. In this study, the compressed air was applied to the die and the blank holder force (BHF) with vibration technique was utilized during circular-cup deep-drawing of TP340 sheetsTP340 titanium sheets. As a result, the occurrence of adhesion was prevented significantly by the application of developed methods.

Because of the low ductility of Ti–6Al–4V alloyTi-6Al-4V alloy at the temperatures between room temperature and 600 °C, fracture easily occurs during press forming. Hence, a method of press forming of Ti–6Al–4V alloy sheets at 300 °C was developed. In this method, the punch motion and blank holding force were applied separately to prevent fracture at the punch radius until the maximum punch load was reached, and the deep drawing process was demonstrated from the maximum punch load until finish forming to prevent the fracture at end of the flange. In addition, by applying the developed method, we were able to prevent the decrease in wall thickness at the punch shoulder, compared with that in press forming. As a result, warm press formingWarm forming of Ti–6Al–4V alloyTi-6Al-4V alloy sheets at 300 °C was achieved without fracture of the formed cup or local decrease in the wall thickness by applying the developed method.

Hot stamping technology is widely used to produce car body components with more complex shape, higher strength, and less springback. A pair of optimal hot stamping toolHot stamping tool should have a long service life, low manufacturing cost, and good cooling performance simultaneously. Consequently, a new manufacturing method of hot stamping toolHot stamping tool with CCC (conformal cooling channels) is introduced in this study. Besides, CuCrZr and Fe-based alloy were welded on the specimens as intermediateIntermediate layer layer and surface layerSurface layer respectively, high-temperature compressive yield strength, the heat conductivity, and thermal expansion coefficient of welding materials were measured. The whole stamping process of the new hot stamping toolHot stamping tool is simulated and discussed. The simulation results indicate the maximum stress in each area of the new tool was less than the yield strength of the corresponding welding materials, which demonstrated that the new tool manufactured by surfacing technologySurfacing technology could meet the strength requirement and deserve further research.

The environmental concerns to save energy are currently driving the attention toward alternative ways to produce lightweight components, matching the most promising light alloys (as in the case of aluminium alloys) with new and innovative manufacturing trends. To address these new requirements the use of tubular structures has increased as a solution to reduce weight. Parallel to the need to increase the material formability local heat treatment of metal sheets has gained some relevance in the last years. The present work is focused on the evaluation of the formability at room temperature of thin-walled aluminium alloy tubes previously overaged in specific zones by laser. The formability limitsFormability limits of the thin-walled tubeThin-walled tubes material in the ‘as-received’ condition were preliminarily determined by means of tensile tests and tube expansion with elastomer. An initial numerical analysis was performed in order to define laser heating parameters to effectively overage the material. The experimental work (tensile and tube expansion tests) was assisted by the Digital Image Correlation (DIC). On the other hand, the laser treatment to obtain Locally Overaged Tubes (LOTs) was investigated according to the results of the preliminary numerical simulations and such LOTs were subjected to experimental tensile and tube expansion tests. The strain paths and failure strains obtained on LOTs were assessed and compared to the formability limitsFormability limits of the ‘as-received’ tube, thus allowing to evaluate the effect of the local modification of the material properties on the formability of the tube.

Experimental study of sheet material flow curves was performed using combined methods of cold rolling for prestraining material to targeted strain and then tensile testing. Experimental studies revealed that aluminum alloys show a tendency for flow curves saturation which substantially lowers work hardeningWork hardening of the sheet material. Performed numerical simulations of cup drawing illustrated that this effect leads to earlier material wrinklingWrinkling compared to power law approximation of the flow curve. Examples of numerical simulation with Autoform software comparing the result of cup drawing for various cases of flow curve approximation are discussed in this paper. Analysis of fracture strainsFracture strain was performed by combined gridding and paint spraying on the sheet surface. This approach enabled measurements of local strains in the area closely adjacent to fracture without having continuous access to this area by video camera. This approach was used for sheet hole expansion, sheared edge stretchability along straight cut, hemming, and self-piercing riveting for high-strength steels and aluminum alloys.

Shear cuttingShear cutting induces high strains and work hardeningWork hardening into the shear-affected zone, thus reducing the formability of the sheet metal material during subsequent forming operations. A common method for increasing the residual formability of shear-cut component edges is to shave the surfaces. The shaving process allows for the removal of highly hardened areas from a pre-cut contour, resulting in a comparatively high residual formability of the cutting surface. However, as known from conventional cutting, a burr remains on the shear surface when shaving. Such burr formation is undesirable and therefore usually has to be removed afterward. For this reason, a new process has been developed which combines two processes within the same stroke of punch, the counter-cutting, and shaving process, enabling the production of burr-free shear surfaces showing a high portion of clean-cut proportions and significantly 1.6 times higher hole expansion ratios than conventional cutting surfaces. The present paper deals with numerical and experimental investigations carried out in the course of the process development with the high-strength sheet metal material DP600.

Femtosecond laser trimming procedure was optimized to reduce the edge curvature of diamond-coated WC (Co) punch as possible and to decrease the maximum roughness of diamond coatings. Bare diamond-coated WC (Co) punches with normal grain size were prepared to have an original film thickness of 9 μm. Through two laser machining steps, the edge width of diamond coating was reduced down to 2 μm. By using the core die with the clearance of 4%, fine piercingPiercing experiments were performed to measure the load–stroke relationship and to describe the affected zone formation by shearing. The affected zone area as well as the fractured surface ratio significantly decreased with a reduction of the edge width down to 2 μm.

In the hot stamping process, the sheet will lose a lot of heat which results in poor formabilityFormability of the sheet. So, a novel hot stamping process for the three-layer sheet is proposed in this paper, which uses two steel sheets to clamp the titanium alloyTitanium alloy sheet for transferring and stamping. In this paper, the hot stamping depth is studied by experiments and simulation under the single/three-layer sheet hot stampingThree-layer sheet hot stamping condition. The results show that the temperature of the titanium alloyTitanium alloy sheet can be controlled effectively by using the three-layer sheet hot stampingThree-layer sheet hot stamping process, and the stamping depth can be improved. Compared with the single-layer sheet hot stamping process, the depth of the titanium alloyTitanium alloy parts can be increased by 135.7% under the three-layer sheet hot stamping process at 900 °C, and the thickness distribution of titanium alloyTitanium alloy parts obtained by three-layer sheet hot stampingThree-layer sheet hot stamping process is more uniform. The finite element analysis results show that the temperature and stress distribution of titanium alloyTitanium alloy sheet by three-layer sheet stamping process is more uniform, and the temperature difference is small through the sheet. The distribution of thickness obtained by simulation has good consistency with the experimental results. Under the three-layer sheet hot stampingThree-layer sheet hot stamping process, the titanium alloyTitanium alloy sheet has good deep drawing.

Utilizing a servo pressServo press for sheet metal forming provides benefits for users such as a fully adjustable slide motion and blank holder force control during the stroke. These allow users to program unique motion profiles of press slide and cushion based on position and velocity. This paper will discuss how unique servo pressServo press motion profiles can avoid various strain path failures that may occur in final formed parts. Standard crank motion, variable blank holder force, and attach-detach slide motion were used to evaluate biaxial and plane strain failures of 980GEN-3980Gen-3 steel. It was determined that different strain failure paths require different servo press programs to improve the overall part quality.

Due to the ease in calibration from simple tests and the reliability of the parameter identification, generally von Mises isotropic criterion and Hill orthotropic criterion are used in industry. While more advanced 3-D yield criteria have been developed, generally such criteria are written in terms of eigenvalues of transformed stress tensors, and as such the anisotropy coefficients are not directly related to mechanical properties. Therefore, the quality of the F.E. simulations depends on the experience of the analyst in calibrating these parameters. Very recently, it was shown that all advanced non-quadratic yield criteria are in fact polynomials in terms of stress components (see [1]). Moreover, for the 3-D orthotropic criteria involving one linear transformation (e.g. Yld91), the anisotropy coefficients can be determined using analytical formulas, involving only four yield points or three Lankford coefficients, respectively (see [2, 3]). In this paper, the predictive capabilities of the orthotropic criteria of Hill [4], Yld91 [5], and Cazacu [6] calibrated using both analytical and numerical minimization procedures are discussed. Moreover, simulation results of deep drawing of steel alloy DC06 are presented. The influence of the choice of the criterion, the procedure used for identification (analytical vs. numerical), and the type/extent of the data used for identification are analyzed in detail.

Wire-arc additive manufacturingWire-Arc Additive Manufacturing (WAAM) (WAAM) complex components can be built-up layer by layer from metallic construction materials. In this investigation two different WAAM processes with high built-up rates (CMTCold Metal Transfer (CMT) and pulsed GMAWPulsed GMAW) were compared in terms of geometry formation and component properties. The reference is a rectangular thin-walled geometry made of the austenitic stainless steel 316LSi (1.4430). During the welding process, the temperature development in the weld layer was measured. The experimental comparison of CMT ( $${\text{R}}_{\text{m}}=630 {\text{MPa}}$$ R m = 630 MPa ) and pulsed GMAW ( $${\text{R}}_{\text{m}}=605 {\text{MPa}}$$ R m = 605 MPa ) is completed by the determination of the mechanical properties using micro-tensile tests. Furthermore, the additive-manufactured walls were cold rolled with a subsequent heat treatment or hot rolled to provide proof of formability and forming induced property improvement.

To increase the economic efficiency in the production of geometrically complicated forgingsForging, material efficiency is a determining factor. In this study, a method is being validated to automatically design a multi-staged forgingForging sequence initially based on the CADCAD file of the forging. The method is intended to generate material-efficient forging sequences and reduce development time and dependence on reference processes in the design of forging sequences. Artificial neural networks are used to analyze the geometry of the forging and classify it into a shape class. Result of the analysis is information on component characteristics, such as bending and holes. From this, special operations such as a bending process in the forging sequence can be derived. A slicer algorithm is used to divide the CADCAD file of the forgingForging into cutting planes and calculate the mass distribution around the center of gravity line of the forging. An algorithm approaches the mass distribution and cross-sectional contour step by step from the forging to the semi-finished product. Each intermediate form is exported as a CAD file. The algorithm takes less than 10 min to design a four-stage forgingForging sequence. The designed forging sequences are checked by FE simulations. Quality criteria that are evaluated and investigated are form filling and folds. First FE simulations show that the automatically generated forgingForging sequences allow the production of different forgings. In an iterative adaptation process, the results of the FE simulations are used to adjust the method to ensure material-efficient and process-reliable forgingForging sequences.

Technologies for forming and fabricating tubes have been contributing to the development of society, and should evolve and have great roles in the future societies, considering the problems on environment and population. Global warming is a critical problem and the average temperature in the world is still increasing. The world population number is stopping rapid increase accompanying with decreasing birthrate, resulting in aging society. Tubes have advantages of high rigidity for a unit weight and could manufacture light-weightLight-weight components for transport equipment. The technologies are utilized for forming parts in medical devices. The technologies on tubes should contribute for solving these problems and realizing sustainable societies. This paper introduces the author’s technologies and reviews others’ recent technologies on tubes. The technologies include hydro and air forming, rotary forming, bending, micro forming and so on. These technologies are qualitatively evaluated in terms of conflicting characteristics, such as formabilityFormability, strengthStrength, productivityProductivity, flexibilityFlexibility and miniaturization. Some technologies are emerging to improve some of the conflicting characteristics at the same time for realizing excellent performances of the formed products.

The kinematics and dynamics characteristics of driving mechanism will directly affect the processing quality and efficiency of multi-link die mechanical press. Based on the structural parameters of a certain type of cold forging pressForging press, the dynamic optimal model of elbow-bar driving mechanism is established. Several performance indexes both in the respect of kinematics and dynamics were put forward which were took as the objective functions and constraint functions. Based on virtual prototyping, this paper proposed an improved algorithm method for an elbow-bar driving mechanism, which can also be applied to optimal synthesis of multi-link mechanism. And with this, we find an optimized dimension of elbow-bar driving mechanism. Theoretical and simulation results examine the performance of the optimized mechanism, and demonstrate that its performance parameters are improved obviously.

For a forging with complex shape, it is necessary to design one or more pre-forgingPre-forging shapes before the final forging to avoid forging defects and improve forging performance. In this paper, a novel method of using conformal mappingConformal mapping to design the pre-forgingPre-forging shape is proposed to achieve a reasonable three-dimensional (3D) shape of the pre-forging. Firstly, the 3D final forging was two-dimensionally (2D) sliced to simplify the design problem. The new profile of each slice was calculated based on the conformal mappingConformal mapping method. Then, the discrete points on all new profiles were combined into a 3D point cloud for surface reconstruction to obtain 3D model of the pre-forgingPre-forging. Next, four parameters (conformal factor and triaxle scaling factors) were applied to describe the pre-forging shape. Finite element analysisFinite element analysis was used to simulate the forging process of the designed pre-forgingPre-forging. Finally, this method was applied to design the pre-forging shapes of different forgings. Through reasonable parameter values, a satisfactory pre-forgingPre-forging shape can be obtained. This method is effective, easy to implement, and has universal adaptation.

Constitutive lawsConstitutive law for hot forming typically consider the effects of strain, strain rate, and temperature. Their parameter identificationIdentification requires experiments performed on wide ranges of these three factors. Usually, specialized equipment is utilized to ensure uniform strain, strain rate, and temperature. Alternatively, parameter databases provide parameter sets for various materials and constitutive laws at a low cost. This work explores the potential of using compression experiments on industrial presses for parameter identification of such constitutive models, in order to balance the cost and accuracy of these two existing alternatives. The results are compared with the reference results produced on specialized large temperature/strain rate compression equipment. Two materials are used to prove the usefulness of the proposed methodology.

For a given sheet material and thickness, the cutting conditions (punch/die clearance, punch shape, tool corner radii, lubrication, cutting speed, tool wear, and elastic deflection of tool and press) affect the cut edge and the quality of the subsequent forming or flanging operations. Factors such as friction and tool wear are becoming more important as the use of stronger alloys is increasing. This study uses the finite element method to evaluate the effect of these parameters on the edge characteristics and the cutting forces involved (vertical and horizontal). AluminumAluminum 5182-O and CP-W 800 with different sheet thicknesses (1.2 mm and 4.0 mm) were considered. The results indicated that both tool wear and coefficient of friction play a role on the analysis of piercingPiercing and trimming and should be accounted for. The effect of each of these variables changes with sheet thickness, material, and process type. This study also illustrates the difficulties and limitations of FE analysis in predicting piercing/trimming Trimmingvariables.

The finite element methodFinite element method has been widely used because of its powerful calculation since it was proposed. The method has been well developed in many different fields such as civil engineering and the aerospace industry. FEM was also used to simulate the deformation performance of materials in the metal forming process. But one of the critical problems of the conventional FEM is the termination of simulation caused by large deformation of mesh. Many studies are focused on the geographic technical method to solve the problem such as re-mesh. But the method is limited and time consumed. An element called space meshSpace mesh is proposed for the large deformation simulationLarge deformation simulation in this paper. The shape of the space mesh used in the simulation is not changed when the calculation is progressed. And the large deformation can be simulated without termination caused by the shape irregularity of the mesh.

Transferring insights from simulationsSimulation to an industrial application is a state-of-the-art procedure. The knowledge of how to design a manufacturing process, e.g. for Radial-Axial Ring RollingRadial-Axial Ring Rolling, is mainly taken from two sources: the machine operator’s experience and experiments, which are time- and cost-intensive. Therefore, creating results by using finite element method is a valuable alternative. This paper focusses on the shape deviations in the domain of Radial-Axial Ring RollingRadial-Axial Ring Rolling. It is a hot forming process to produce, e.g. steel rings, used as blanks for the manufacturing of huge bearings or gear rims. Real Radial-Axial rolled disk-shaped rings will be compared to data of a FEM SimulationSimulation Software (QForm 3D) with a focus on the height deviation of the ring. Regarding disk-shaped rings, the production of a constant height is of high importance to save effort and costs of rework.

A PID controllerPID control was implemented in FEMFEM platform as a user subroutine instead of a sophisticated and expensive control system implemented in a tube hydroforming machine to numerically generate the required boundary conditions, axial feed, and pressure profiles, based on proportional strain path at the pole of the bulging tube in the FEMFEM simulations. The generated boundary conditions can directly be used in free tube bulging experiments to generate different deformation modes for tubular materialTubular materials characterizationCharacterization based on accumulated plastic work equivalency. It was also shown that the numerical algorithm developed works accurately for isotropic and anisotropic yield functions. In this study von-Mises and Hill’s 1948 were used as the material models.