Numerical Study of Liquid Metal 3D Printing Process: Shape Morphology Evolution, Solidification, and Formation of Defects

The utilization of uniformly deposited metal droplets has attracted significant attention for diverse applications, such as rapid prototyping and manufacturing. Achieving flawless aluminum structures through droplet-based liquid metal 3D printing (LM3DP) is critical in aerospace and electronics. However, challenges persist in eliminating defects during deposition due to constrained temperature ranges and complex impact dynamics. This study introduces a 3D computational model using a volume of fluid technique to analyze the consecutive deposition of molten aluminum droplets on a heated substrate, protected by nitrogen gas. Simulations reproduce droplet shapes in agreement with experimental results. Molten aluminum droplets solidify layer by layer continuously in an upward direction due to high thermal conductivity, forming surface ripples. L-shaped ripples emerge on neighboring droplets due to combined effects of solidification and oscillation, which involve alternating spreading and recoiling of the droplets leading to defects like cold laps, whereas bottom-hole defects occur due to inadequate metal filling with the substrate. This investigation systematically explores shape, defect formation, temperature, solid fraction, and velocity evolution during continuous deposition. Insights establish a fundamental basis for LM3DP technology.