This paper reviews aspects of the plastic behavior common in metals and alloys. Macroscopic and microscopic phenomena occurring during plastic deformation are described succinctly. Constitutive models of plasticity at the micro- and macro-scales, suitable for applications to forming, are discussed in a very broad fashion. Approaches to plastic anisotropy are reviewed in a more detailed manner.
An automotive project is now based on numerical validation to reduce the development time between the project preparation and the start of production. That is particularly true to predict the formability of materials and solve dimensioning problems. But some problems remain and we will give examples of limitations in the case of steel sheet stamping, of tubes or profile bending, of polymer injection. We will also show that the main difficulty relates to constitutive equations that require to be more and more representative of the real behaviour of materials.
The lack of accuracy of numerical results is still nowadays one of the main drawbacks of sheet metal forming process simulation. One of the main reasons for such a lack of accuracy is the constitutive models used to describe the real material’s mechanical behavior. The most widely used phenomenological constitutive model is based on the classical Hill 1948 yield criterion. In the last decade several new yield criteria have been proposed, with the constraint that a parameter identification procedure has not always been clearly set. This study presents a general approach to optimize anisotropic plastic description. A weight-based optimization procedure is presented in order to perform the optimization of several constitutive models based on experimental results. Using this procedure is expected to improve the plastic description with a global optimum solution.
B.M. Chaparro, J.L. Alves, L.F. Menezes, J.V. Fernandes
Cost saving and product improvement have always been important goals in the metal forming industry. To achieve these goals, metal forming processes need to be optimised. During the last decades, simulation software based on the Finite Element Method (FEM) has significantly contributed to designing feasible processes more easily. More recently, the possibility of coupling FEM to mathematical optimisation algorithms is offering a very promising opportunity to design optimal metal forming processes instead of only feasible ones. However, which optimisation algorithm to use is still not clear.
In this paper, an optimisation algorithm based on metamodelling techniques is proposed for optimising metal forming processes. The algorithm incorporates nonlinear FEM simulations which can be very time consuming to execute. As an illustration of its capabilities, the proposed algorithm is applied to optimise the internal pressure and axial feeding load paths of a hydroforming process. The product formed by the optimised process outperforms products produced by other, arbitrarily selected load paths. These results indicate the high potential of the proposed algorithm for optimising metal forming processes using time consuming FEM simulations.
A continuous model for the non-isothermal flow in a non-isotropic porous medium is presented and a mechanical dispersion model is proposed. An experimental device is set up in order to measure the permeability and mechanical dispersion components in a typical transversely isotropic cubic block consisting of polymeric needles. Finally, a micro-macro model for the flow of a Newtonian fluid in a porous medium is developed. The micro-model consists of a geometrical network of connectors and junctions. Integration and assembly of the equations provides a macroscopic model which obeys the Darcy or Forchheimer model depending on the dimensionless flow rate. Some peculiarities of the Brinkman model are addressed.
The paper shows a number of investigation results about three- dimensional-bending of profiles. The investigations concentrated on two-dimensional bending using a conventional three-roll-bending machine with a simultaneous deflection of the profiles towards the third axis by means of a special device. The special device consists of a hydraulic cylinder giving the motion and the required force for bending in the third axis coupled with a guiding tool to guide the profile in the 3D-space. The most important aspect of these tools is the use of the previous plastic deformation in the 2D-bending zone for an easier bending in the 3D-space through the superposition of lateral forces. By means of this machine set-up both symmetrical and asymmetrical profiles can be bent three-dimensionally and the unwanted torsion of asymmetrical profiles can be prevented through a compensation moment.
Although in times of highest significance of process modelling and numerical simulation yield loci get more and more important, these characteristic values do only exist for a few materials primarily at room temperature. In this paper a novel concept of an experimental setup is introduced, with which plastic yielding of sheet metal can be examined also at elevated temperatures. The design of specimen is of great importance for the quality of experimental results, because stress conditions and with it forming behaviour are constituted. Thus, it must be optimized in consideration of stress singularities at corners and for achieving stress states, which are comparable to those of previous yield locus examinations. Most information and details can be obtained from finite element simulation.
In this paper the predictive capabilities of a recently proposed yield criterion, CB2001, are assessed. Also, a numerical scheme for identifying the material coefficients is presented. It is shown that although convexity is not a default property of the criterion, it can be achieved numerically. Applications to two sheet forming operations are presented. Using the commercial FE code ABAQUS, simulations of the deep-drawing of a cylindrical cup and springback analysis for unconstrained bending are performed. Two aluminum alloys were considered and modelled with Hill’48 (ABAQUS) and CB2001 (UMAT). The results are also compared with another popular criterion, Yld’96. We conclude that for sheet forming operations were large plastic deformations are involved, accurate fit of the initial plastic anisotropy is a basic condition for successful FE simulations.
Modeling Forming Limit Diagrams (FLD) using the finite element method is a quite new approach. The article presents the prediction of both branches of an FLD, based on Hutchinson – Neale model, taking into account the strain rate sensitivity. Abaqus/Standard package has been used to perform the simulations. A numerical algorithm to describe the material behavior has been implemented as a user-subroutine UMAT. The plastic anisotropy of the sheet metal is described by the BBC2003 and Cazacu – Barlat yield criteria. The numerical results have been compared with experimental data for AA3103-0 aluminum alloy. The authors also present the experimental strategy to determine the FLD’s.
The paper is concentrated on the last developments related to process design for sheet and tube hydroforming. The paper first analysis the ways to properly account flow movements and pressure drops occurring in sheet and tube hydroforming that can interact with sheet or tube deformation during hydroforming described with a flow-structural approach, based on an ALE approach accounting well the structural interactions. Then different optimization strategies for process parameters are presented on the basis of cost functions associated to final geometry of sheet or tubular components, based on gradient approaches as well as stochastic ones, depending on the number of parameters and on the sensitivity of parameters relatively to the response functions. Finally an integrated design approach based on control of processes is described combining optimization and continuous adjustment of process parameters to get the required parts accounting the machine tool limits and the material ones. Different applications are given related to typical components that are used in automotive industry.
In many forming operations, due to the severe forging loads, the press frame deflects elastically and, consequently, upper and lower dies deviate from the nominal relative position. These conditions produce skewed surfaces that, in a too stiff press, can have detrimental effects on the service life of the machine and the tooling as well. This paper presents a new method to evaluate the stiffness of presses for forming operations where realistic loading systems are utilised. To this aim, a special testing and calibration apparatus was developed that consists of (i) a loading device capable of generating and at the same time measuring forces and torques in different directions and (ii) a special transducer that measures the relative displacement between the ram and the bed of the press. The paper describes the application of the method to the evaluation of the stiffness of a screw press.
The theory of fast material forming starts with the application of the Bingham model to the metal forming. It started with wire drawing, with drawing of tubes either free or with a floating plug, or with a fixed plug. The extrusion of cylindrical bars at increased temperatures, with floating glass as a lubricant, was also considered. The theory was done with several mathematical approaches, either direct or with applied.
A way of increasing productivity of Equal Channel Angular Pressing (ECAP) by increasing the number of channel turns in the die is being explored. Unlike in other proposals of this type, the channel passages are not in one plane. This leads to a new concept of 3D-ECAP and a possibility of realising the most desirable deformation route B_C in the die. The paper explains the above concept in detail and discusses the tool design issues. The laboratory trials of the new process are described and results presented. The structure of commercially pure aluminium 1070 subjected to 3D-ECAP is revealed. Basic mechanical properties are specified and conclusions formulated.
Asymmetric Incremental Sheet Forming (AISF) is a new sheet metal forming process for small batch production and prototyping. In AISF, a blank is shaped by the CNC movements of a simple tool. The standard forming strategies in AISF lead to severe thinning and an inhomogeneous wall thickness distribution. In this paper, several new types of forming strategies are presented that aim at a more homogeneous distribution of material. A forming strategy suitable for computer-aided optimization was identified by finite element analyses. A “metamodel” was constructed by 162 finite element calculations in order to test different optimization algorithms off-line for their performance: a Genetic Algorithm (GA), a Particle Swarm Optimization (PSO) algorithm and the simplex search method. The GA was found to be better at detecting the global optimum but lagged behind the PSO in terms of speed.
M. Bambach, M. Cannamela, M. Azaouzi, G. Hirt, J.L. Batoz
Single-Point Incremental Forming (SPIF) is a sheet metal forming technique that is gradually evolving towards industrial applicability. As recent market analysis studies have shown, accuracy is one of the most important limiting factors for the deployment of SPIF in industrial applications.
The case studies described in this paper aim to illustrate the state-of-the-art in achievable accuracy for a number of realistic parts having different geometric complexity and produced by different tool path strategies. A secondary goal of this study is to demonstrate the applicability of SPIF for prototyping or small batch production. The results of the different strategies were measured and compared to the geometric specifications. The achieved accuracy for the respective parts and process strategies are reported.
Machining processes are frequently investigated by numerical simulations. Usually 2D analyses are carried out in order to reduce CPU times, considering orthogonal cutting conditions. In this way, the computational time sharply reduces and many process variables may be calculated (i.e. forces, chip morphology, shear angle, contact length). On the other hand, the analysis of thermal aspects involved in machining, for instance the temperature distribution reached in tool, still represents an open problem. Finite element codes are able to simulate a very short process time that is not sufficient to reach steady state conditions. Several approaches have been proposed to overcome this problem: in the paper some of them are applied and critically discussed.
Numerical simulation of the wire-coating process is undertaken for non-Newtonian pseudoplastic and viscoplastic fluids. The Herschel-Bulkley model of viscoplasticity is used, which reduces with appropriate modifications to the Bingham, power-law and Newtonian models. The analysis is based both on the Lubrication Approximation Theory (LAT), which regards locally a fully developed shear flow, and on a two-dimensional axisymmetric Finite Element Method (FEM). For a given die design the results give distributions of important variables, such as pressure, shear stresses along the die walls and the wire, and the wire tension due to the shearing forces of the fluids on the moving wire. These results are obtained from a full parametric study of the dimensionless power-law index (in the case of pseudoplasticity) and the dimensionless yield stress or Bingham number (in the case of viscoplasticity). Increasing the power-law index or the Bingham number leads to an increase in dimensionless pressure and stresses. In the case of viscoplastic fluids, LAT predicts interesting yielded/unyielded zones, which are however erroneous, as a consequence of using the lubrication approximation. The full 2-D analysis based on FEM shows that such zones exist only after the die exit, where the coating fluid moves on the wire as a rigid body.
Possessing high specific strength and stiffness, woven composites have received great amount of attention as a potential alternative to sheet metals in aerospace and automobile industries. To successfully simulate the manufacturing process, predict the performance of the end products and provide information to aid design of manufacturing processes, the material model should take consideration of various length scales, dynamic characteristics and material properties under different temperatures. Bias extension and tensile tests are among the most important experiments that provide crucial modeling parameters for material characterizations. This paper focuses on experiments under different temperature trajectories, as the forming process itself is often conducted under such conditions.
This paper presents experimental results on steel thixoforming. The influence of thermal exchanges with tools and environment on the semi-solid response is analysed.
Several rheological experiments such as compression, extrusion or radial filling test were developed to understand the semi-solid steel behaviour and determine the parameters that have a major influence on thixoforming.
Actually, the temperature of the slug and probably the solid fraction was found a first order parameter while the morphology of the solid phase plays a minor role in our experiments.
The thixoforming of steels is so complex that it requires more investigations regarding both the materials and the technical tools dedicated to the elaboration of the process. In this paper we will show the experimental determination of appropriate solidus-liquidus interval on eight different steel compositions. This critical parameter was obtained using Differential Scanning Calorimetry. The paper also presents the results of thermophysical property determination. These parameters are important for the inductive heating phase of a semi-solid forming (SSF) process. Thanks to the simulations of the inductive heating process, the other main results consist on the developments of the heating techniques that are suitable for the achieving of the sine qua none condition to the semi-solid process, which is the uniform temperature distribution in the reheated billet.
J. Lecomte-Beckers, A. Rassili, M. Carton, M. Robelet, R. Koeune
This paper introduces recent advances for the calculation of secondary operations and springback by means of the FEA program AutoForm. A special feature of AutoForm is that the entire forming process including all forming operations, secondary operations and even springback, is calculated with an implicit shell, i.e. with equilibrium control. The advantages of the implicit shell are discussed here. Additionally, the significances of a high quality contact algorithm and of ahead refinement are analyzed, for their effect on the accuracy of springback calculations, and various AutoForm solutions are presented. Finally, these advances in sheet metal forming theory are evaluated, by comparison between theoretical results and actual sheet metal parts.
É. Schönbach, G. Glanzer, W. Kubli, M. Selig
Backmatter
Metadaten
Titel
Advanced Methods in Material Forming
verfasst von
Prof. Dorel Banabic
Copyright-Jahr
2007
Verlag
Springer Berlin Heidelberg
Electronic ISBN
978-3-540-69845-6
Print ISBN
978-3-540-69844-9
DOI
https://doi.org/10.1007/3-540-69845-0
Premium Partner
Marktübersichten
Die im Laufe eines Jahres in der „adhäsion“ veröffentlichten Marktübersichten helfen Anwendern verschiedenster Branchen, sich einen gezielten Überblick über Lieferantenangebote zu verschaffen.
