Mechanics of Additive and Advanced Manufacturing, Volume 9

Additively Manufactured (AM) parts exhibit orthotropic behavior when loaded as a result of the layer-by-layer assembly commonly utilized. While previous authors have studied the effect of layer orientation on the tensile, flexural, and impact response of AM parts, the effect of layer orientation on the fracture response is not well established. Here we explore the effect of layer orientation on the fracture properties of Acrylonitrile-Butadiene-Styrene (ABS) materials fabricated through the Fused Filament Fabrication (FFF) process. Critical fracture toughness values of Single Edge Notch Bend (SENB) specimens with a pre-crack oriented either parallel or perpendicular to the direction of layer-by-layer assembly were compared. Results show that the inter-laminar fracture toughness (fracture between layers) is approximately one order of magnitude lower than the cross-laminar toughness (fracture through layers) of similarly manufactured parts. Contrasting brittle and ductile fracture behavior is observed for inter-laminar and cross-laminar crack propagation, respectively, demonstrating that the elastic-plastic response of AM ABS parts is governed by the orientation of the layers with respect to the direction of crack propagation.

3D printing technologies have made creating prototypes with complex geometries relatively simple thus it has become an increasingly popular method for creating prototypes in a research setting. Therefore, it is crucial to understand the properties of the materials being used. This paper examines the effects of printing direction and testing method type on the complex modulus of viscoelastic materials printed using the Objet Connex 3D Printer from Stratasys. Because of its ability to print multiple materials in a single print job, this printer is a popular choice to create models. Throughout these tests the sample material will be kept constant to isolate the effects of print direction and test performed. DM 8430 is produced by mixing VeroWhitePlus™ and TangoPlus™ in a specific ratio. Since the 3D printer threads and smooths the sample uniaxially, the print direction of the sample can be manipulated by changing the orientation at which the sample is placed on the printer. Two different print directions, that are perpendicular with respect to each other, will be examined. The two test methods that will be used to determine the complex modulus are the Dynamic Mechanical Analysis (DMA) test, which examines the tensile behavior of the material, and the vibrating beam test, which examines the bending behavior. The goal is to gain greater insight into the uncertainty in the complex modulus that results from changing the test and printing direction used to determine this value. This will be done by performing a total of four tests. For each testing method, DMA and vibrating beam, the complex modulus will be found for two samples of different print direction, vertical and horizontal. These results will permit a greater understanding of the amount of variability produced by print direction.

For simulating the geometry of melt pool’s cross section more accurately in Selective Laser Melting (SLM) process, modeling the volumetric heat source is considered as the key issue. In the present study, a three dimensional finite element heat transfer simulation with new volumetric heat source is proposed to simulate the geometry of melt pool’s cross section during SLM process. The approach to build up the volumetric heat source is based on the modified sequential addition method to simulate the powder bed and the Monte Carlo ray tracing simulation in Zemax to calculate the energy distribution along the depth of metal powder layer. For validating the proposed simulation model, the simulated result of the contact-width between melt pool and substrate is compared with experimental result presented in the existing literature.

Laser-based metal additive manufacturing technologies such as Selective Laser Sintering (SLS) and Selective Laser Melting (SLM) allow the fabrication of complex parts by selectively sintering or melting metallic powders layer by layer. Although elaborate features can be produced by these technologies, heat accumulation in overhangs leads to heat stress and warping, affecting the dimensional and geometrical accuracy of the part. This work introduces an approach to mitigate heat stress by minimizing the temperature gradient between the heat-accumulated zone in overhangs and the layers beneath. This is achieved by generating complex support structures that maintain the mechanical stability of the overhang and increase the heat conduction between these areas. The architecture of the complex support structures is obtained by maximizing heat conduction as an objective function to optimize the topology of support structure. This work examines the effect of various geometries on the objective function in order to select a suitable one to consume less material with almost same conduction. Ongoing work is the development of an experimental testbed for verification.

Carbon nanotube (CNT) reinforced acrylonitrile-butadiene-styrene (ABS) composites fabricated using a fused deposition modeling approach were characterized for mechanical strain energy storage and dissipation capabilities. Dynamic mechanical analysis (DMA) was performed to quantify loss factor as a function of applied dynamic strain. In addition, DMA was performed at varying temperatures to give insight into the molecular interactions present in these composites. Insight into the microstructure was provided by atomic force microscopy (AFM). The results are compared to neat ABS and ABS/CNT systems processed through an injection molding technique. Results show large energy dissipation, accompanied by permanent damage, in both injection molded and additively manufactured neat ABS samples. In contrast, the additively manufactured ABS/CNT nanocomposites exhibited strain energy dissipation but reduced the effect of cavitation and crazing by possible reinforcement. This result suggests CNT fillers have the potential to alter the dissipation mechanisms present in additively manufactured structures to control structural damping. This research provides insight into the design and additive manufacturing of materials where energy dissipation is essential to maintain structural stability and functionality under dynamic loading.

Laser Engineered Net Shaping (LENS) and Powder Bed Fusion (PBF) are 3-D additive manufacturing (AM) processes. They are capable of printing metal parts with complex geometries and dimensions effectively. Studies have shown that AM processes create metals with distinctive microstructure features and material properties, which are highly dependent on the processing parameters. The mechanical properties of an AM material may appear to be similar to the corresponding wrought material in some way. This investigation focuses on the relationships among AM process, microstructure features, and material properties. The study involves several AM SS316L components made from 3D LENS and PBF printing. Specimens were taken from different locations and orientations of AM components to obtain the associated tensile properties, including yield, strength, and ductility, and to conduct microstructure analyses.

A significant drop in the hardness values have been achieved in the friction stir welded dissimilar titanium alloys after post weld heat treatment. A closer look at the microstructural evolution suggests that the heat treatment at 933 °C changes the microstructure in the weld nugget from globular blocky grains to distinct microstructure with β flakes distributed uniformly in the α phase. With Ti-6242 FG (β transus = 996 °C), and Ti-54 M (β transus = 966 °C) being on the retreating and advancing side respectively, a series of microstructure evolves from retreating to advancing side. With a difference in the composition of the alloys, difference in the diffusion of elements is also responsible for the corresponding microstructure. Diffraction patterns were measured by X-ray diffraction method. Diffraction peaks for ADV side were slightly shifted towards left in comparison with retreating, and center of the weld along with significant difference in the preferred crystal orientation between as welded and post weld heat-treated conditions.

Plastic injection molding industry uses traditionally machined tools and dies to manufacture various sizes and shapes of plastic products. With the advent of advanced manufacturing technology and expanding global competition in business, it is necessary to provide innovative solutions to the injection molding industry to sustain their business. Typically, the cooling time comprises more than half of the overall injection molding cycle time. The application of additive manufacturing technique can provide a solution to reduce the cooling time in injection molding process. The potential of 3D printing technology to produce any size and shape of products using metal powders provides an opportunity to design and produce innovative injection molding tools, which is unattainable by traditional machining process. Though the conformal cooling channels are capable of reducing the cooling time significantly, the cost of manufacturing the injection molds by 3D printing is quite high and hence a crucial decision making factor for the mold designers about whether or not to go for the 3D printed molds. By making the molds porous, it is possible to reduce the cost of additive manufacturing, thus creating a positive impact on the use of 3D printed molds in injection molding business. In this paper, the effect of mold porosity on the thermal performance of the injection molds are studied. The properties of 3D printed mold material and traditional mold material is quite different and have been considered for the analysis. An optimization study has been conducted to identify the best possible design solution in terms of thermal and printing cost perspectives.

New generation of turbine blade coating using additive manufacturing (AM) technique to coat a layer of oxide dispersion strengthening (ODS) alloy on superalloy substrate is presented. A novel combined mechanochemical bonding (MCB) plus ball milling process is utilized to produce near spherical and uniform alloyed ODS powders. AM-assisted ODS coating by direct energy deposition (DED) method on MAR-247 substrate, with laser powers of 100 W, 150 W and 200 W were carried out. The ODS coated samples were then subjected to cyclic thermal loadings for over 1280 cycles. Corresponding Young’s modulus measurements of ODS coating at various thermal loading cycles were conducted using a unique non-destructive micro-indentation testing method. Correlation of the measured Young’s modulus with evolution of the ODS microstructures are studied. In particular, the presence of secondary gamma prime phase in the ODS coating after thermal cycles is noted. Test results revealed a thin steady durable alpha alumina oxide layer on the 200 W ODS sample. After 1280 thermal cycles, strong bonding at ODS/substrate interface is maintained for the 200 W ODS coated sample. Test results also showed stable substrate microstructures due to the protective ODS coating.

Ti64 titanium alloy sheets and AZ31 magnesium alloy sheets were stacked in an alternating order and rolled to form three types of roll-bonded multilayered materials. The microstructure of these roll-bonded samples was observed using optical microscope, and the Vickers hardness data were also obtained. The thickness of the AZ31 layers was severely reduced, while the thickness of Ti64 layers was only slightly changed. Compared with the as-received Ti64 titanium alloy and AZ31 magnesium alloy, the Vickers hardness of Ti64 layers only slightly deviated from that of the as-received state, while AZ31 layers was refined equiaxed grains had higher hardness than that of the as-received state.

Natural vibration frequency of objects fabricated by Additive Manufacturing (AM) is experimentally investigated. In this paper, several beam structures consisting of square unit cells are fabricated by material extrusion type AM, which is usually called Fused Deposition Modeling (FDM). The target object is oscillated by a magnetic motor and the amplitude of vibration is measured with a laser vibrometer. The effects of deposition direction and material composition on the primary natural frequency are discussed. These factors can be controlled by using AM. The experimental results showed that the frequency obviously depends on both deposition direction and material composition. The possibility of a vibration design method in product design was indicated.

Additive Manufacturing (AM) is a process that is based on manufacturing parts layer by layer in order to avoid any geometric limitation in terms of creating the desired design. In the early stages of AM development, the goal was just creating some prototypes to decrease the time of manufacturing assessment. But with metal-based AM, it is now possible to produce end-use parts. In powder-based AM, a designed part can be produced directly from the STL file (Standard Tessellation Language/ stereolithography) layer by layer by exerting a laser beam on a layer of powder with thickness between 20 μm and 100 μm to create a section of the part. The Achilles’ heel of this process is generation of some defects, which weaken the mechanical properties and in some cases, these defects may even lead to part failure under manufacturing. This prevents metal-based AM technology from spreading widely while limiting the repeatability and precision of the process. Online monitoring (OM) and intelligent control, which has been investigated prevalently in contemporary research, presents a feasible solution to the aformentioned issues, insofar as it monitors the generated defects during the process and eliminates them in real-time. In this regard, this paper reveals the most frequent and traceable defects which significantly affect quality matrices of the produced part in powder-based AM, predominately focusing on the Selective Laser Sintering (SLS) process. These defects are classified into “Geometry and Dimensions,” “Surface Quality (Finishing),” “Microstructure” and the defects leading to “Weak Mechanical Properties.” In addition, we introduce and classify the most important parameters, which can be monitored and controlled to avoid those defects. Furthermore, these parameters may be employed in some error handling strategies to remove the generated defects. We also introduce some signatures that can be monitored for adjusting the parameters into their optimum value instead of monitoring the defects directly.

Tensile tests were conducted following the ASTM Standard D3039 for different specimens produced using additive manufacturing. In the expansion of the 3D printing market, different methods of three-dimensional printing and materials have been developed. Different specimens ranging in materials and infill were printed with a consumer grade PLA FDM printer without heated bed, a consumer grade SLA printer, and an industrial manufacturing grade ABS FDM printer with heated bed. The specimens included Polylactic Acid (PLA), Tough PLA, Acrylonitrile Butadiene Styrene (ABS), and black resin. The PLA and tough PLA specimens were printed at infill intervals of 20% and at 0/90 and ±45^° with respect to the longitudinal axis. The ABS material was also printed at the same angles with respect to the longitudinal axis at solid (SO), sparse double density (DD), sparse high density (HD), and sparse low density (LO) infill values. The consumer grade SLA printer was used to print specimens using black resin and was divided into two sets. The first set includes specimens that were cured under an ultraviolet light while the second set contained those that were not cured after printing. The overall result showed that the infill and print orientation of ±45° performed better for the PLA and Tough PLA material. However, the orientation did not influence the ABS material which may have been the result of using an industrial grade 3D printer. In resins, the increase in resolution resulted in a higher ultimate stress while curing normalized the ductility of the material.

Titanium alloys are mainly utilized in the aerospace, biomedical, power generation, automotive and marine sectors due to their high hot hardness, ability to operate at higher operating temperatures and resistance against corrosion. Alpha-beta titanium alloy (Ti6Al4V) is the most frequently used titanium alloy, mainly preferred for the applications such as blades, discs, jet engine airframes and biomedical implants. TiAlN coating is highly favored for the metal cutting applications due to its superior cutting performance. The high cutting performance of TiAlN coating is linked with the addition of aluminum to the traditional TiN coating. The addition of aluminum results in the formation of aluminum oxide on the cutting tool surface resulting in ability to sustain high cutting temperatures. In this study a series of machining experiments were conducted to evaluate the machinability of difficult-to-cut titanium alloy (Ti6Al4V) by using PVD-TiAlN coated carbide tools under vegetable oil assisted minimum quantity cooling lubrication (MQCL). The cutting insert consists of substrate based on tungsten carbide with 6% cobalt to maintain high hot hardness and fracture resistance. Thin PVD-TiAlN coating on the substrate provides excellent adhesion resistance to prolong the cutting edge sharpness and results in enhanced tool life. In this study the influences of vegetable oil flow rate was taken into consideration to evaluate machinability. The study incorporated two different oil flow rates of 60 and 80 ml/h using a specially designed tool holder with internal coolant delivery channels for MQCL arrangement. The MQCL based results were also compared with the dry cutting. Detailed study on micro-wear mechanisms at the cutting edge was conducted by utilizing scanning electron microscopy (SEM). The study revealed adhesion, micro-edge chipping, abrasion and attrition as major wear mechanisms when using PVD-TiAlN coated tools for machining Ti6Al4V.