Prediction of spatiotemporal variations of deposit profiles and inter-track voids during laser directed energy deposition

Abstract

The spatiotemporal variations of the molten pool and deposit profiles during laser Directed Energy Deposition (DED) largely affect the formation of printing defects and the build quality. Quantitative assessment of the dependencies of molten pool characteristics on critical process variables is helpful to reveal the evolution of the depositing tracks. To this end, a novel 3D transient phenomenological model was developed in this work to explore the evolution of the temperature and velocity fields and the molten pool dimensions for both single-track and multi-track laser DED deposits. The influences of laser scanning speed, mass feed rate, laser power, Mass per Unit Length (MUL, g/mm) and Energy per Unit Mass (EUM, J/g) intensities on the deposit characteristics were comprehensively examined. The 3D profiles of the deposited tracks were sectioned, reconstructed and visualized. The computed deposit profiles showed that the contact angles of the single-tracks increased significantly with higher MUL intensity. In contrast, the contact angle decreased with higher EUM intensity. The formation of highly convex deposits was carefully examined in particular, and a prominent bulge was found near the beginning of the deposit with local contact angle larger than 100°. The simulation results showed that convex deposit profiles obtained at high MUL intensity further caused inter-track voids during multi-track deposition.