Modelling of keyhole dynamics and porosity formation considering the adaptive keyhole shape and three-phase coupling during deep-penetration laser welding

The joint quality of deep-penetration laser beam welding is related to the keyhole behaviour, e.g. keyhole-induced porosities. In this paper, a model which considered the existence of three phases, including plasma gas, liquid metal and solid metal, was proposed to describe the keyhole phenomena of laser welding. The forces of interaction of fluid dynamics in the keyhole and molten pool were modelled using the CFD software, and an adaptive heat source model was proposed for the absorption of laser energy. The molten pool and keyhole phenomena of laser beam welding were simulated using the developed model, as well as the formation of keyhole-induced porosities. It was found that the keyhole depth self-fluctuates in continuous laser welding, and the bubbles formed from keyhole collapse and shrinkage are the cause of keyhole-induced porosity.