Towards the simulation of Selective Laser Melting processes via phase transformation models

Abstract

Selective Laser Melting (SLM) – as one of a number of additive manufacturing techniques – is a promising method for the manufacturing of complex structures and may bring about significant improvements in the context of custom-made designs and lightweight constructions. However, the complex multiphysical processes occurring during SLM necessitates the establishment of appropriate constitutive and process models in order to quantitatively predict the properties of the final workpiece. In particular, the accurate determination of process-induced eigenstresses is a challenging yet important task. In this work, a constitutive modelling framework stemming from phase transformations in shape memory alloys is adopted to the modelling of the changes of state during SLM. This model is based on energy densities and energy minimisation in general and specifically serves as a basis for further enhancements such as the consideration of multiple solid phases of the underlying material. This is particularly considered important due to the fact that the cooling rates during SLM are heterogeneously distributed and that thus different solid phases may form out of the molten material pool. As a first step, the present overall model comprises three phases of the material, namely powder, molten, and re-solidified material. The thermomechanically fully coupled Finite-Element-based process model incorporates approaches for, e.g., the laser beam impact zone and the layer construction model.