Numerical analysis of undercut defect mechanism in high speed gas tungsten arc welding

A computational fluid dynamics model is developed to investigate undercut defect formation in high speed gas tungsten arc welding (GTAW) process. Double-ellipse arc shear stress model and modified double-ellipse arc heat source and arc pressure models are used, which are self-adaptive to weld pool surface evolution. The heat and mass transfer in weld pool and solidified weld bead profile are simulated and the undercut mechanism are discussed. The prematurely solidified periphery part at maximum width of weld pool is the initiation of undercut defect and the inward velocity component at trailing periphery due to teardrop-shaped weld pool profile promotes subsequent undercut formation, which provides an explanation to the high tendency of undercut formation during high current and high speed welding. The undercut morphology is unremarkably influenced by Marangoni force and the capillary pressure hinders undercut formation to some extent. The developed model is validated by comparing undercut morphology and gouging region profile from both simulation and experiment.