A novel electrode-arc-weld pool model for studying the keyhole formation in the keyhole plasma arc welding process

Abstract

A novel electrode-arc-weld pool model considering the influence of the backside keyhole deviation on the heat source distribution, the influence of the keyhole constraint on the arc pressure and the keyhole geometry dependent plasma shear stress, is developed to study the keyhole formation in the KPAW process. The numerical and experimental results show that: the keyhole depth increases very quickly at first, then smoothly, and then quickly again. In the blind keyhole stage, the arc pressure deepens the keyhole. The plasma shear stress facilitates the fluid flow along the rear keyhole wall and decreases the curvature of the keyhole. The process between the weld pool penetration and the keyhole penetration is defined as the blasting penetration stage, in which the molten bridge under the arc is quickly broken. The pressure balance and mass conservation mechanisms are proposed to be responsible for the blasting penetration. The low melting temperature, low surface tension and bottom surface deformation promote the blasting penetration, while the high thermal conductivity suppresses the blasting penetration. In the penetrated keyhole stage, two contrary convective eddies are found inside the weld pool. At the top surface of the weld pool, the molten metal flows upward and backward near the keyhole, but obviously flows forward at the rear part of the weld pool. At the bottom surface of the weld pool, the molten metal flows downward and backward.