Temperature-dependent modified inherent strain method for predicting residual stress and distortion of Ti6Al4V walls manufactured by wire-arc directed energy deposition

As an additive manufacturing (AM) process, wire-arc directed energy deposition (DED) has drawn increasing attention due to its ability to print large metal parts. However, the heat accumulation during the deposition may result in significant residual stress and distortion in the as-built part. Although post heat treatment can relieve the residual stress, most of the distortion remains, thus making post-processing such as machining and cutting more difficult. As a numerical modeling approach, the modified inherent strain (MIS) method has been proven effective for predicting residual stress and distortion of small parts manufactured by the laser powder bed fusion (L-PBF) and powder DED process. In this work, the MIS method is extended to include the effect of heat accumulation so that it can be applied to large parts built by wire-arc DED. Instead of loading constant inherent strains layer-by-layer, the extended method divides each layer into several segments according to the deposition path and sequentially loads temperature-dependent inherent strains based on the interpass temperature of the build. A flash heating simulation involving transient thermal analysis is added to obtain the interpass temperature. The proposed temperature-dependent MIS method has been experimentally validated. Compared with the constant MIS method, the new method reduces the stress prediction error from 46.5 % to 8.7 % for a 112 mm small wall and from 19.5 % to 6.9 % for a 250 mm large wall. The maximum distortion error is reduced from 29.7 % to 7.9 % for the large wall.