Effects of welding procedures on resistance projection welding of nuts to sheets

Abstract

In this study, experiments were conducted to investigate the effects of welding current, welding time, electrode force and types of nuts on resistance projection welding of nuts to sheets. The microstructures and welded joint size of welded joints in different welding procedures have been analyzed. The failure mode of welded joints was also discussed. It is found the microhardness distribution of the fusion zone gradually becomes homogeneous with the increase of the welding current or the welding time. Lower electrode force causes the occurrence of splash and large fluctuations of the microhardness in fusion zone. Different types of nuts lead to different heat distribution in the projection welding process. The welded joint in nut is deeper than that in base metal for welding nut with higher electrical resistivity. Button pull fracture, partial thickness fracture and interfacial fracture are the three failure modes of nut projection welded joints. The interfacial fracture is brittle rupture and the partial thickness fracture is ductile rupture.