A Review of the Evolution of Residual Stresses in Additive Manufacturing During Selective Laser Melting Technology.

Residual stress (RS) is one of the main reasons for component failure during an additive manufacturing (AM) process, especially using selective laser melting (SLM) technology. This paper reviews RS's investigation methods, formation mechanisms and regularities of distribution. When considering recent research progress, studies indicate that the dominant stress is primarily attributed to thermal stress induced by significant laser temperature gradients during the rapid melting and forming process, which subsequently transforms into RS upon cooling to room temperature, as verified by simulation and experiments. Then, the distribution regularities of RS are analyzed. SLM RS gradually increases when it is measured from the surface layer to the substrate. In the plane direction, at the center and edge of the part, tensile stresses are found; as for the middle area, which is the transition area of compressive stress, the whole plane stress remains in an equilibrium state. Based on the forementioned conclusions, the three-dimensional distribution diagram of RS on the sample was constructed. Finally, the strategic approaches for stress mitigation are briefly discussed. The excessive stress in forming can be reduced by process parameter matching, and the RS can be greatly remitted by pre-treatment/post-treatment, so as to improve the quality of formed parts. This review provides a valuable theoretical basis for practical applications of SLM.