Three-Dimensional Finite-Element Modelling of Deformation in Weld-Based Rapid Prototyping

Abstract

Residual stress-induced deformations are a major cause of tolerance loss in solid freeform fabrication process employing direct metal deposition. In this article, a three-dimensional finite-element (FE) 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, e.g. gas metal arc welding (GMAW). A sequentially coupled thermo-mechanical analysis is performed simulating buildup of a single layer on a bolted rectangular substrate. The material used in the present study is mild steel, with temperature-dependent material properties and the material modelled as elastic perfectly plastic. The numerical results are compared with experimental data by manufacturing plate-shaped single-layered specimen, using an indigenously developed semi-automatic deposition system. The fusion zone and temperatures predicted by numerical model show good agreement with experimental data, and the deformations of the substrate in bolted and unbolted conditions are also in good agreement. It has been observed that the heat transfer conditions vary during deposition; therefore, any assumption of thermal symmetry is not valid. Thermal cycling during deposition is the main cause of deformations. The effect of bolting is also very important.