Proceedings of the
9th International Conference of Asian Society for Precision Engineering and Nanotechnology (ASPEN2022)
15 – 18 November 2022, Singapore

The Development of an Effective and Comprehensive Modeling Technique for Thermomechanical Analysis of Selective Laser Melting Process

Nitesh Ananda, Yu-Bin Chen and Ming-Tsang Lee

Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu City, 30013, Taiwan R.O.C


Selective laser melting (SLM) is an additive manufacturing process that can be used to digitally fabricate three dimensional products by selectively sintering material powders in a powder bed layer by layer. The heat transfer with melting and solidification, the flow in the melting pool, and the transient thermomechanical behavior of the material during the process are critical for the properties of workpieces fabricated via SLM process. The typically high heat input along with rapid heating and cooling of the material in SLM lead to high thermal stresses in fabricated specimen, which in turn leads to distortion, cracks, and fatigue failure of the workpiece. In this study, a new modeling technique coupled heat transfer, melting pool flow, and thermomechanical analysis was developed to investigate temperature and thermal stress during the SLM process. Inconel 718 powders were used as the material in the experiment. The proposed two-stage quasi-transient model composes a transient thermal analysis followed by a transient thermomechanical analysis by using a hopping heat source to approximate the continuously moving laser heating. The thermomechanical analysis employed element birth and death technique. Material phase change, such as the melting and solidification of the powder, and the formed metal layer as well as the re-melting of the solidified layer were all considered. In a representative case, it was demonstrated that this novel quasi-transient model significantly reduces the computation cost by 99% as compared to the conventional simulation of SLM with a reasonable accuracy on the molding shape. Including the re-melting process in the analysis enabled accurate prediction of stress release in the overlapped laser scanned region of the specimen. The residual stress distributions obtained from the developed two-stage quasi-transient thermomechanical model were compared with measurement results from electron back scatter diffraction (EBSD) analysis. It is shown that the quasi-transient thermomechanical model provides important characteristics of residual stress consistent with that from a conventional full transient model in 68% less computation time. The dynamic stress release due to re-heating and re-melting in overlapped laser scanned regions was in close confirmation with experimental results. This efficient quasi-transient model is useful for rapid analysis and optimization of SLM processing parameters

Keywords: Additive Manufacturing, Residual Stress, Selective Laser Melting, Thermomechanical Model.

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