Modified Inherent Strain Method for Predicting Residual Deformation and Stress in Metal Additive Manufacturing

Additive manufacturing (AM) has been widely employed to produce various metal parts with complex geometries. However, the large thermal gradient caused by the fast, intense, and repeated laser scanning brings significant residual deformation and stress to the as-built metal parts, increasing manufacturing difficulty and geometrical inaccuracy as a result. A modified inherent strain (MIS) method incorporating multiscale finite element (FE) simulation has been proposed to enable efficient prediction of the residual stress and deformation. The accurate inherent strains (ISs) are extracted from a small-scale detailed process simulation within a representative volume of the part. Then the extracted ISs are applied to a layer-by-layer quasi-static FE model to simulate the part-scale residual stress and deformation field. Both numerical and experimental studies are conducted to validate the MIS method. The comparisons show that the MIS-based simulation can provide accurate prediction of residual deformation and stress for the as-built metal parts. The MIS method opens the opportunity to control the residual stress and deformation induced in the AM process through numerical optimization. Three simulation-driven design solutions are presented, including support structure design for cracking prevention, topology optimization of support structures, and scanning path optimization for residual deformation and stress mitigation.