Effect of overlap rate and pattern on residual stress in selective laser melting

Selective laser melting (SLM) can be directly used to fabricate high-performance three-dimensional (3D) parts with complex structures. However, the high residual stress caused by the extremely uneven temperature distribution is detrimental to formability during the process. A 3D finite element model based on the sequentially coupled thermal-structural method was developed to predict the effect of an overlap region on the residual stress induced by the island scanning strategy. The existence of the overlap region had the most influence on the X-component of stress in comparison with the Y and Z components of stress when using the unidirectional pattern. The X-component of stress and equivalent stress decreased first and then increased with the increase of the overlap rate, which primarily relied on the combined action of the laser re-scanning, pre-heating effect from the previous island and scanning length. In terms of the maximum X-component of stress and equivalent stress, an overlap rate of 25%-50% was recommended for the generally utilized island size. The laser vertical re-scanning the overlap region with a short scanning length was beneficial in reducing the residual stress. The simulated results were in good agreement with the experimental data, including the molten pool dimension, residual stress distribution and the effect of overlap rate on the residual stress. The findings of this study will improve the understanding of stress distribution during the SLM process and provide effective methods to reduce residual stress.