Mechanism study of flow characteristics of molten pool and keyhole dynamic behavior of K-TIG welding

The stability and reliability of K-TIG welding depend on the flow characteristics of molten pool and the dynamic behavior of keyhole. This work built a mathematical model of K-TIG welding in order to describe the variation mechanism between the flow behavior of liquid metal and the dynamic behavior of the keyhole while taking electromagnetic force, surface tension, buoyancy, etc., into consideration. The simulation results of the keyhole exit were compared with images of the keyhole exit taken by the high-speed CCD camera and the keyhole exit characteristic parameters, the deviation of keyhole outlet parameters (length along the welding direction XL and length perpendicular to the welding direction YL) under each group of process parameters was less than 0.2 mm, and the deviation of SA was less than 0.4 mm². The flow trend of molten metal in keyhole formation was mainly from the center of keyhole to the surrounding of the keyhole under the consideration of electromagnetic force, surface tension, etc. The trend of melt pool distribution decreased along the perimeter of the keyhole and the thickness of the workpiece, and the overall flow field was stepped. Moreover, the keyhole exit was in a dynamic equilibrium state under the action of gravity, surface tension, and arc pressure. The reduction in welding speed accelerated the formation of the keyhole exit and increased the maximum flow velocity of molten metal under the influence of Marangoni forces.