A mechanical model in wire + Arc additive manufacturing process

Abstract

Material properties are dependent upon the microstructural characteristics of the part. Developing an accurate and sufficient representation of the microstructure obtained in metal additive manufacturing (AM) is critical to precisely estimate material properties. Since the material properties for AM parts are an important function of the welding processing parameters, a fundamental understanding of how AM components behave in load-bearing applications depends on understanding the evolution of thermal cycles and residual stresses during component fabrication. In this work, a finite-element thermo-plasticity procedure in wire + arc AM process was developed in a three-dimensional domain using the finite-element (FE) code ABAQUS. The proposed research aims to establish a methodology for characterizing directed energy deposited metals by linking processing variables to the resulting plastic strains and residual stresses. The effect of multi-layer deposition on the prediction and validation of local plastic strains and thermally induced stresses was investigated. It was found that the thermal (residual) stresses increase with either the increase of weld speed or the increase of the heat distribution parameter. On the other hand, local plastic strains increase with the increase of welding speed, but not necessarily with the increase of the heat distribution parameter. Similarly, the level of thermal stresses and local plastic strains is lower in each new successive AM layer. As a new layer is deposited over a previously heated one, the relief of thermal stresses and plastic strains occurs by preheating; the more preheated the previous layer, the less the level of thermal stresses and plastic strains in the successive deposited layer. Furthermore, the lowest level of stresses and strains observed in the last deposited AM layer, it can be solely caused by the hotter previous layer, even though the top unrestrained weldment surface is free to expand. Numerically predicted thermal stresses at different welding layers are presented for further experimental comparison. A firm foundation for thermo-mechanical modelling in wire + arc additive manufacturing process is established.