This study develops a three-dimensional transient thermal model in COMSOL Multiphysics to investigate melt pool dynamics in Ti-6Al-4V during laser powder bed fusion (LPBF). The model implements a moving Gaussian surface heat source and temperature-dependent thermophysical properties using the equivalent heat capacity method, enabling accurate simulation of rapid phase changes and extreme thermal gradients characteristic of LPBF. The results reveal a highly localized temperature field, with a peak temperature of 3751.92 K, which exceeds the reported boiling point of Ti-6Al-4V (~3560 K at atmospheric pressure). This extremely high value may be partially attributed to the limitations of the continuum-based thermal model, which does not explicitly account for vaporization dynamics and recoil pressure effects. The melt pool exhibits an asymmetric “comet-like” morphology, and its dimensions are highly sensitive to process parameters. Increasing laser power from 200 W to 600 W expands melt pool depth from 22 μm to 39 μm, which enhances consolidation but raises the risk of keyhole instability, suggesting a transition from conduction-mode to keyhole-mode melting. Conversely, increasing scanning speed from 0.5 m/s to 1.0 m/s sharply reduces the laser–material interaction time, resulting in smaller melt pools and a higher propensity for lack-of-fusion defects. These findings provide a quantitative theoretical framework for optimizing LPBF parameters to enhance the structural integrity of additively manufactured Ti-6Al 4V components. The simulation results are in good agreement with previously reported studies, suggesting that the model can reasonably capture the dominant thermal behavior.

Laser Powder Bed Fusion (LPBF); Ti-6Al-4V alloy; COMSOL Multiphysics; Numerical simulation; Melt pool morphology; Thermal-physical behavior; Process optimization.