Numerical investigation of thermal dynamics and local dry region evolution during shallow water laser welding

Abstract

Shallow water laser welding (SWLW), a process in the critical transition regime between dry and deep-water techniques, offers significant potential for high-precision joining and cladding in thin water layers. However, the complex multiphysics governing this process, particularly the thermal dynamics and evolution mechanism of the local dry region (LDR), remain poorly understood. In this study, a 3D computational fluid dynamics (CFD) model is proposed to predict the SWLW process of 304 stainless steel at water depths ≤4 mm. The results reveal that the LDR provides an effective thermal shield for SWLW to achieve deep penetration welding similar to that of the conventional laser welding (CLW) case. The LDR boundaries simultaneously serve as sites for intense phase-change-driven heat transfer, which dominates the thermal balance of the process. Furthermore, the LDR is identified as a thermal buffer zone, creating a sharp and discontinuous drop in thermal gradients at its interface with the surrounding water. It demonstrates that increasing the water depth from 2 mm to 4 mm results in a 20.8 % reduction in the LDR's area, a direct consequence of the delicate thermal-hydrodynamic balance governing the process. The findings provide a fundamental understanding of the laser-water/metal interactions, which is significant for optimizing any laser-based process conducted in the presence of thin liquid layers.