Modeling Thermal Behavior and Residual Stress for Layer-by-Layer Rotated Scan Direction in Laser Powder Bed Fusion Process

Abstract

Abstract Laser powder bed fusion (LPBF) is an Additive Manufacturing (AM) process that uses a laser beam to solidify powder particles following a predefined pattern on a powder bed to build a part layer-by-layer as per a CAD model. In LPBF, the moving heat source and the rapid solidification cause nonuniform variations in temperature along the build part. This transient and moving heating and cooling process causes uneven expansion and shrinkage of the part that leads to the development of residual stresses in the part. The residual stresses depend on the thermal history of the part and may eventually lead to part distortion, crack initiation, warpage, etc. The present study represents the effect of altering the scan pattern layer-by-layer on the residual stress. Furthermore, a novel alternating double pass spiral scan pattern is introduced and compared with alternating island zigzag, alternating zigzag, regular zigzag, and spiral out-center patterns on the basis of thermal distribution and residual stress. Numerical approach is used to solve the governing equations. It is observed that residual stress greatly depends on thermal distribution. The variation in inherent residual stress is found to be lower for alternating zigzag pattern than regular zigzag pattern due to more even thermal distribution. Furthermore, the novel pattern also effectively distributes the heat which contributes to the reduction of inherent residual stress from the first layer. On the other hand, it is found that the alternating island zigzag scan pattern increases island temperature that can prevent rapid solidification. Overall, the findings of this study can be helpful in understanding the effects of altering scan directions layer-by-layer and in identifying a scan strategy that can enhance the usability of the powder bed fusion additive manufacturing technology.