Selective laser melting (SLM) technique is a widely adopted fabrication procedure in metal additive manufacturing. One of the reasons for the extensive usage of SLM is the material freedom which it offers; therefore, Nickel alloy IN718 metal components were fabricated for this study. However, like in any manufacturing process, physical defects are evident in SLM fabricated parts. The origin of these defects can be attributed to the variation in the process parameters. For any physical components fabricated using the SLM technique, various stresses are developed due to the thermal gradients during the fabrication process. The developed stresses are hence termed as residual stresses. These stresses can be detrimental to the mechanical properties of the part. Residual stresses lead to warping of the part during the fabrication process, thereby leading to failure of the component. Therefore, it is necessary to investigate the effect of change in process parameters on the residual stresses. Although each process parameter has its effect on the overall properties and residual stresses, to limit the scope of the study, the scan strategy is the only parameter that is varied. Scan strategies adopted here are checkered, stripes scan strategy, FO1, and customized scan strategy, where the angle between the consecutive layers has been changed consistently at an angle of 67° . In this study, the residual stresses are measured using the contour deflection method. Based on the results, various levels of residual stresses were observed for different scan strategies. It was concluded that a more uniform scan strategy results in less residual stress.
Post-process heat treatments are conventional methods used to minimize porosities and improve the microstructure of metallic parts. It can also increase the hardness value and help tailor the mechanical properties of the part. On the other hand, the heat treatment process includes several steps and can be a costly and time-consuming procedure. The different variables and parameters in heat treatment can make this process even more complicated. Utilizing optimal heat treatment parameters decreases the cost and operation time and results in higher finish quality and better device performance. This study investigates the influence of heat treatment parameters on microstructure and metallurgical properties of NiTi shape memory alloys to find the optimum values for post-processing. The samples were cut in equally sized dimensions, and they were treated using the same equipment. Various ranges of heating duration and temperature were considered for the experiments. It was revealed that, regardless of parameters, the heat treatment process can bring about better compositional characteristics and hardness properties of NiTi. However, some particular sets of heat treatment parameters resulted in higher quality and more favorable final properties.
Selective laser melting (SLM) is an additive manufacturing technique designed to use a high power-density laser to melt and fuse metallic powder to fabricate complex parts with high accuracy. The accuracy and the functional properties of the fabricated part are greatly dependent on the process parameters. Thus, depending on the desired properties and the material, the parameters need to be optimized before fabrication. The processing parameters that control the SLM process comprise of the laser power, scan speed, hatch spacing, layer thickness and scan strategy. These process parameters are dependent on each other and therefore make the task of optimizing the process parameters an important one. This research is concerned with the optimization of several process parameters as well as the development of a model to predict the best properties for Inconel 718 superalloy. This study uses the Design of Experiment (DOE) system coupled with the full factorial Composite Central Design (CCD) of the Response Surface Methodology (RSM) to perform the regression analysis on laser power, scanning speed, and hatch spacing in order to predict the CAD model deviation, hardness values, and, variation in the phase composition using X-ray Diffraction (XRD). The simulated models obtained using the RSM technique were then analyzed. These results provided valuable information and helped us in controlling the functional properties of the fabricated part.
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