A modified method for estimating inherent strains from detailed process simulation for fast residual distortion prediction of single-walled structures fabricated by directed energy deposition

Predicting residual distortion in metal additive manufacturing (AM) is important to ensure quality of the fabricated component. The inherent strain method is ideal for this purpose, but has not been well developed for AM parts yet. In this paper, a modified inherent strain model is proposed to estimate the inherent strains from detailed AM process simulation of single line depositions on top of each other. The obtained inherent strains are employed in a layer-by-layer static equilibrium analysis to simulate residual distortion of the AM part efficiently. To validate the model, depositions of a single wall and a rectangular contour wall models with different number of layers deposited by a representative directed energy deposition (DED) process are studied. The proposed model is demonstrated to be accurate by comparing with full-scale detailed process simulation and experimental results. To make the method practical, a small-scale detailed simulation model is proposed to extract the mean inherent strains. Based on this approach, simulation results applied to the rectangular contour wall structures of different heights show that the modified inherent strain method is quite efficient, while the residual distortion of AM parts can be accurately computed within a short time. The improvement of the computational efficiency can be up to 80 times in some specific cases.