High-fidelity modelling of selective laser melting copper alloy: Laser reflection behavior and thermal-fluid dynamics

Abstract

Despite of the promising capabilities of selective laser melting (SLM), the poor formability of copper and its alloys is a critical challenge for industrial applications, which is widely-believed attributed to the high reflectivity of copper. Due to the difficulty of observing laser reflections, current understanding on the laser reflection mechanisms is still vague and unclear. This work constructs a high-fidelity CFD model coupled with a ray-tracing method to visualize the flow kinetics and reflection behavior during SLM Cu-Cr-Zr alloy. Considering the material specificity of copper, a temperature-dependent absorption rule is introduced to overcome the simulation deviation caused by the widely-used Fresnel absorption, showing good agreement with experiments in terms of track width and depth. The in-situ absorptivity measurement experiments are further conducted to compare with simulations with the error less than 2%. Additionally, different reflection mechanisms for continuous and distorted tracks are revealed. At relatively high linear energy density (LED), the global absorptivity undergoes a rise and a decrease in the initial stage, and finally gets stable. At low LED level, the surface tension drives the melt pool to form isolated balls and exposed plat surface, which is responsible for the intense absorptivity oscillation as the balling effect occurs.