Finite element prediction of thermal stresses and deformations in layered manufacturing of metallic parts

Residual stress induced deformations are a major cause of loss in tolerances in Solid Freeform Fabrication processes employing direct metal deposition. In this paper, a 2D finite element thermo-mechanical model is presented to predict the residual stress induced deformations with application to processes where material is added using a distributed, moving heat source. A sequentially coupled thermo-mechanical analysis is performed using a kinematic thermal model and plane strain structural model. Temperature dependent material properties are used with the material modeled as elastic perfectly plastic. An interpass cooling between successive depositions is employed in accordance to the requirement of experiment. The simulation results are compared with experimental data for successive sections along deposition and it is found that, with the exception of deposition center and plate edges, the two are in very good agreement. The error at plate edges can be as high as 45%, and the reason is that a 2D model cannot capture the effect of plate bolting accurately. A case of continuous deposition, without interpass cooling, has been compared with the base case of employing interpass cooling. It has been found that continuous deposition results in higher preheating of the substrate which consequently reduces the deformation.