Numerical investigation of the mechanism of interfacial dynamics of the melt pool and defects during laser powder bed fusion

Abstract

The occurrence of structural defects during laser powder bed fusion (LPBF) impairs the mechanical properties of components fabricated by the technique. Therefore, having a good grasp of the mechanism of various structural defects is useful for guiding process maps. However, investigating melt-pool dynamics and corresponding defects using experiments is challenging. Numerical simulation thus represents a promising and visual way to reproduce these phenomena. In this study, predicated to first ensure accuracy, a two-dimensional (2D) model was numerically implemented by a phase field with a finite element method (FEM). Our model emphasises the interaction between neighbouring powders during heat duration with time-varying maximum intensity under different deposition parameters. Our simulation results indicate that the reinforcement of liquidity can significantly enhance the wettability of the neighbouring powder to release gas bubbles and extend the melt pool. Similarly, the remelting process also effectively eliminates porosity, which yields a smooth surface deposited in the previous layers to improve deposit densification. Our simulation also provided detailed insights into the evolution of liquid metal droplets away from “the elongated neck” and investigated the effect of scanning speed on the width of the melt pool of single tracks. Additionally, our model implemented a discrete FEM method with extremely refined free-triangle elements, which was accompanied by a decrease in computational cost and expressed good agreement with the experiments.