Numerical analysis of heat transfer and fluid flow characteristics and their influence on bead defects formation in oscillating laser-GMA hybrid welding of lap joints

In this study, the accuracy of the model developed for oscillating laser-GMA hybrid welding has been improved by integrating more experimentally measured parameters, such as the droplet velocity, transient arc power, and fusion area on sheets at the transverse cross-section. The effects of lateral distance of hybrid heat source relative to the top sheet edge on heat transfer and fluid flow in weld pool are numerically simulated. It is found that with more offset of the hybrid heat source to the top sheet, a larger depression and stronger lateral flow occur in weld pool, which leads to a delayed and weak backwards flow. These characteristics of heat transfer and fluid flow play a great role in the formation of weld bead defects of lap joint configuration, such as irregularity, discontinuity, lack of fusion at the top sheet. Compared to the experimental investigation, the numerical simulation provides not only quantitative description of the occurrence of those weld bead defects but also a deep physical insight into the whole process. Thus, it is useful for the parameter optimizations and further applications of this hybrid welding process.