Abstract
There is no unified understanding about the mechanism of hump weld bead. Research on the internal relationship between humping formation and the viscosity of molten pool is still lack of study. The numerical simulation method is used to study the mechanism quantitatively by considering the changing viscosity, which is mainly determined by temperature and the content of alloy elements. The results show that viscosity is an important factor affecting temperature and pressure fields. In addition, temperature field determines the existence of hump, pressure field determines the size of the hump. Four weld parameters like boundary temperature, welding moving speed, welding power and alloy element content in molten pool have significant effects on humping formation, which are discussed emphatically. All effects are positive. Finally, an experiment is designed to verify the simulation well.