Numerical approach for a strongly coupled thermomechanical process with multi-phase transition and applications in additive manufacturing

Abstract

We propose a monolithic incremental Lagrangian framework based on the hot optimal transportation meshfree (HOTM) method for a strongly coupled thermomechanical process with multiphase transition. The HOTM method combines the optimal transportation meshfree method and the variational thermomechanical constitutive updates. This numerical approach is applied to conduct meshfree direct numerical simulations (DNS) for metal additive manufacturing. We present two kinds of simulations, the powder bed selective laser melting (SLM) and the laser material deposition technology referred to as extreme high-speed laser material deposition (EHLA) at the powder scale. In the simulations, the powder particles are modeled explicitly using the size distribution measured in experiments and discretized using nodes and material points. The governing equations, including the linear momentum conservation and energy conservation equations, are solved simultaneously in the meshfree framework to predict the deformation, temperature, and local state of the powder particles. A full-field constitutive model is developed to simulate multiphase flow with melting and solidification. The Lagrangian feature of the HOTM method overcomes various challenges in the DNS of melt pool thermodynamics in additive manufacturing. The proposed approach is used to quantify the influence of the main processing parameters, such as the powder size distribution, laser power, laser radius, deposition speed, powder mass flow, and axial feed on the layer thickness, surface roughness, and porosity of the bonding zone. It further enables an in-depth understanding of quality control in additive manufacturing.