Research on dynamic behavior of molten pool in adaptive laser welding of TC4 titanium alloy with unequal gap structure

To address the problem of uneven pre-welding assembly gaps widely existing in the laser welding process of complex thin-walled aviation components, adaptive laser welding experiments were conducted on 1.2 mm thick TC4 titanium alloy plates with unequal gaps. A three-dimensional transient thermal-fluid coupling model of the welding process was established to analyze the influence of different welding gaps on the dynamic behavior of the molten pool. The results indicate that to balance welding quality with the linearly increasing weld gap, the laser energy density shows a gradually decreasing trend while matching the corresponding laser spot radius. As the welding gap increases, and the laser energy density decreases, the surface tension and recoil pressure acting on the inner wall of the keyhole decrease significantly, making it difficult to maintain the high-temperature and high-speed Marangoni circulation required for a long conical molten pool. The fluid velocity at the keyhole tip decreases markedly, and the keyhole shape transforms from a long conical shape to a flat gyroscope-like shape, which fails to exert a strong impact on the molten pool bottom. Consequently, the vortex at the molten pool bottom disappears, and the weld profile transitions from an X-shape at the initial section to a Y-shape at the final section.