Computational analysis of the ultrasonic effects on resistance spot welding process

Ultrasonic resistance welding (URW) is a hybrid welding process that utilizes in situ ultrasonic vibration during resistance spot welding (RSW) process to increase nugget size, enhance weld mechanical properties, and refine microstructure. Despite the promising experimental results, the underlying mechanisms of acoustic effects on the RSW process are elusive as the involved interacting physical phenomena can hardly be revealed with direct experimental methods. In this study, a three-dimensional fully coupled electro-thermo-mechanical model of the URW process for aluminum alloys has been developed and validated, where the ultrasonic effect on nugget formation and evolution is simulated from different perspectives based on a RSW model. It shows that the enlarged nugget in URW welds is a result of coupling interactions among multiple ultrasonic effects on contact resistance and molten metal thermophysical properties, which are based on the ultrasonically assisted fracture of surface oxides, acoustic softening, cavitation and streaming physical phenomena.