Key Engineering Materials Vol. 969

Abstract: The joining of metals and polymer-based materials has a very high interest for many industrial sectors, as it allows to achieve components combining the specific characteristics of each material class. Additive manufacturing technologies could boost the production of these joints, allowing the controlled deposition of a polymeric material over the metal substrate. The present research is aimed to study the feasibility of a joint concept that can be used to produce aluminium/polymer-based material joints through a 3D printing-supported technique. The innovative joint concept, which is based on an interlocking mechanism promoted by a deposited pin, was compared to two conventional concepts. The innovative joint concept allows the production of samples with good mechanical behaviour, in which the failure occurs outside the material overlapping zone. This design is very suitable to be tested for the production of dissimilar material joints.

Abstract: This paper serves as basis for subsequent studies investigating a potential material and manufacturing method selection for producing lattice structures to be used as energy absorption device, such as in novel wearable protective gear. Four additively manufactured plastics from two additive manufacturing methods are examined in detail. Polyamide 12 specimens produced on two Powder Bed Fusion (PBF) machines are compared against specimens produced on a stereolithography (SLA) printer using a standard and an engineering-grade resin. A comprehensive analysis of their mechanical properties is presented by measuring their densities as well as tensile, fatigue, and impact properties. In addition, Poisson’s ratio of the resin materials is estimated using Digital Image Correlation (DIC).

Abstract: Most design-to-manufacturing frameworks combining topology optimization (TO) and additive manufacturing (AM) integrate mesh smoothing methods as post-processing techniques to remove discrete irregularities of optimized topologies. Notably, a design framework is proposed incorporating all the CAD development stages within the design phase providing smooth and ready-to-print topologies. The Laplacian-based smoothing algorithms have demonstrated a high capacity in removing surface noise. This study focuses on investigating the smoothing capacity of both HC Laplacian and Taubin methods using mesh quality metrics to assess on their performance in terms of geometric preservation and volume shrinkage. Taubin method was found to produce high-quality smooth meshes with less volume shrinkage compared to HC Laplacian. The Taubin model exhibited an increase of 15.06% in mesh volume whereas the HC Laplacian model had a volume shrinkage of 28.14%. Additionally, finite element analyses of the three-point bending test using ANSYS is set to measure the flexural stiffness of an optimized MBB beam under both HC Laplacian and Taubin smoothing methods. Overall, the flexural stiffness of Taubin is nearly two times the original model with a surplus of 46.91% whereas HC Laplacian exhibited a flexural stiffness that is less with 72.07% than the original model.

Abstract: Additively manufactured continuous fibers reinforced composite materials parts have huge potential to replace existing plastics and metal parts in a wide range of industrial applications. However, the continuous fibers reinforced 3D printing technology is still in nascent stages, and commercial 3D printers and raw materials available in the market are less cost effective. In this work, continuous glass fibers reinforced PLA filaments are manufactured through a cost-effective melt impregnation method. The experimental set up for manufacturing the filaments consisting of impregnation mold and yarn spreading mechanism was designed and fabricated in-house. Parametric study was carried out to understand the effect of process parameters on the quality and mechanical properties of the filaments. The input process parameters in this study are impregnation temperature and yarn spreading. While the output parameters are impregnation, fiber-volume fraction, and tensile and flexural behavior of filament. A novel method is proposed for quantitative analysis of impregnation of the filament. The optical images of the filament are used to quantify the impregnation of PLA resin in the glass fiber yarn. It was observed that the yarn spreading has major influence on impregnation, tensile strength, and flexural strength of the filaments. Lastly, finite element-based simulation study was carried out to interpret the experimental results and thus to understand the effect of fibers spreading on tensile and flexural strength of the filament. The simulation results agreed very well with the experimental results.

Abstract: A multiphysics numerical approach based on a coupling of heat conduction equation, mechanical field (effect of gravity), and phase-field equations is proposed as an alternative to predict the microstructure evolution of 316L stainless steel during the pressureless solid-state sintering process. In this context, a numerical model based on the finite element method has shown to be suitable for evaluating the impact of the thermal field, as the activation force of the sintering process, on the microstructure field evolution and, in turn, the impact of the evolution of phase field variables on the material properties. The model was validated by comparison with literature results and applied to simulate the microstructure evolution for different sintering temperatures and particle sizes to evaluate the influence of these parameters on microstructure evolution. The results proved that model can be used to analyze the microstructure evolution, both from a quantitative and quality point of view, which makes it suitable for evaluating the impact of sintering parameters on material properties.

Abstract: The ability of direct metal deposition (DMD) to fabricate complex geometries is still limited. Especially in thin-walled structures heat accumulation can lead to intolerable geometric deviation and which has to be avoided. Combining thin walls and massive sections in one layer requires parameter adapting for each section within a layer. An existing semi-empirical model predicts the optimal process parameters for the austenitic steel 1.4404. This study demonstrates the validity of the model for martensitic steel 1.4313 by an experimental campaign. The demonstrators are characterized by a massive inner part attached to a thin-walled rib. They were fabricated by DMD using constant and adapted heat input and were qualified by visual inspection, geometrical accuracy, Vickers hardness, and microstructure analysis. The demonstrators built with the adapted laser power showed enhanced geometrical accuracy which is essential for post-processing. The hardness along the symmetry plane was significantly increased, especially in the thin wall section. The study confirms the applicability of the model for martensitic steel in terms of geometrical accuracy but identifies perspectives to integrate microstructural aspects into the model.

Abstract: The quality of the finished product is affected by a number of factors during the plastic injection molding process. Two crucial process variables in the creation of products are melted and mold temperature. The study uses the Design of Experiments tool in Autodesk Moldflow to look at the impact of melt and mold temperatures on injection molding technology. Analytical items are specifically made of polypropylene (PP) using kids' chair mold. According to simulation analysis results, there is a remarkable effect of the melt temperature on both time at end of packing as well as deflection in the range of the analytical temperature at t_mold of [40, 80]°C and t_melt of [180, 220]°C. Melt temperature also shows a notable influence not only on deflection but also on sink mark depth and volumetric shrinkage, along with the criteria to evaluate the expense of a product (time at end of packing, total part weight).

Abstract: Multiple-input multiple-output (MIMO) antenna technology owes its low weight and energy-saving electronic applications to the use of polymer substrates. Applying metallization to obtain conductive substrates involves spraying untreated molds with a gel to form a temporary protective coating. The coating is then partially removed with a laser to expose areas for metallization. After that, the exposed areas are modified with a palladium-tin (Pd-Sn) colloidal catalyst to enhance the adhesion between the insulating surface and copper deposition. It’s with these three steps that the modified areas become selective to metallization. It’s observed that copper deposited incessantly at a high speed of 5 μm/hr after above treatment, and formed a dense layer with a low resistivity. The conductive patterns plated on the 3D substrate render the MIMO antenna system applicable to wireless local area network (WLAN) with two switchable frequencies, as evidenced by the simulation tests in which the antennae had ECC values below 0.2, a VSWR of 3 to 1, and a radiation efficiency around 50% at 2.4 GHz and 37% at 5.8 GHz. The electroless plating technology used above adds to a duplicable MIMO-antenna manufacturing process of low temperature and cost.

Abstract: This study is concerned with the post-heat treatment of rotational friction welds. AISI 1030 carbon steel parts are welded by rotational friction welding (RFW). The welding process parameters include friction pressure (P1), friction time (T1); Forging pressure (P2), forging time (T2). During the friction phase, the rotational speed is 1450 rpm; after that, the welding parts is stopped immediately and pressed together. The weld samples will be annealed at 650 °C for 4 hours. The change in the properties of the material of a RFW weld joint such as hardness, tensile strength, bending strength as well as grain size when undergone a heat treatment process was investigated. The obtained results show that the annealing process strongly changes the mechanical properties through altering the microstructure of the weld. Particularly, the weld hardness and tensile strength decrease significantly while the bending strength and elongation increase as a result of the increase in grain size and uniformity of the phase distribution. The annealed weld has a hardness reduction of nearly 20% and a tensile strength reduction of about 24% compared to the original weld. The elongation in the tensile test increases from 1.1% for weld specimens to 2.54% for post-heat-treated welds. In the bending test, the maximum load before the appearance of cracks on the specimen increased by about 42% when comparing the post-heat and original weld specimens.