Numerical simulation of melt pool evolution and interlayer bonding in LPBF process

Laser powder bed fusion (LPBF) involves rapid melting, solidification, and repeated layer deposition, making melt-pool evolution and interlayer bonding highly sensitive to powder-bed morphology and process parameters. In this study, a mesoscopic CFD–DEM model coupled with the VOF method was developed to simulate single-track single-layer and double-layer LPBF of Inconel 718 with a non-uniform powder size distribution. The model was validated by comparing simulated and experimental melt-track morphologies, with the maximum relative error in melt-track width remaining within 6%. The results show that laser power and scanning speed exert opposite effects on melt-pool morphology. Increasing laser power enlarges the melt-pool width and depth and improves melt continuity, whereas increasing scanning speed reduces the effective energy input and promotes discontinuous or fractured tracks. The morphology of the first-layer track strongly affects second-layer powder re-spreading and remelting. Smooth and continuous underlying tracks promote uniform powder coverage, sufficient remelting, and dense metallurgical bonding, whereas fractured tracks cause local powder accumulation, insufficient heat penetration, and interlayer lack-of-fusion voids. The parameter set of 200 W and 1000 mm/s provides a balanced energy input and produces the best interlayer bonding quality among the tested cases. In contrast, 250 W and 1500 mm/s leads to fractured tracks and severe interlayer defects. This work clarifies the coupling mechanism among underlying track morphology, secondary powder re-spreading, and interlayer defect evolution in LPBF.