Due to the strong heating effect and arc force

plasma arc welding (PAW) can instantly melt metal material and then penetrate through the molten metal

forming a vapor-filled cavity called as "keyhole". The arc temperature is extremely high in keyhole

and thus a large percentage of heat is able to be transferred to the bottom metal through the keyhole. With respect to the moving PAW

a keyhole-tracking heat source was developed to reflect the nonuniform heat transfer due to welding movement. It consists of a double-elliptical heat flux on top surface and a lower developing conical heat source proportional to the keyhole growth. The volume of fluid (VOF) method was applied to track keyhole interface

and the heat source was auto-controlled according to keyhole depth. By numerical simulation

heat transfer during the keyholing process was revealed and corresponding temperature field was calculated to display the thermal-physical mechanism in moving PAW. Moreover

keyhole evolution and molten metal flow in weld pool were also investigated to exhibit how the keyhole promotes deep penetration welding. Finally

experiment was carried out on stainless steel plate of thickness 8 mm

and the measured weld geometry and size coincide with simulation results.