Parameters optimization for the generation of a keyhole weld pool during the start-up segment in variable-polarity plasma arc welding of aluminium alloys

Stable weld formation is still one of the goals pursued in variable-polarit y plasma are welding (VPPAW) of aluminium alloys. Basically, VPPAW is divid ed into three segments: the startup segment, during which the keyhole is ge nerated, the main body segment, during which the keyhole is dynamically mai ntained, and the terminal segment, during which the keyhole collapses and t he crater is filled. Very often? a smooth transition cannot be made from th e start-up segment to the main body segment, and the weld easily fails beca use the keyhole weld pool is not properly generated. This paper explores fo ur different combinations of plasma gas and welding current for generating a smooth transition from the start-up segment to the main body segment in V PPAW. The keyhole weld pool is categorized as one of three types: heat cond uction mode, strong force mode or heat and force mode. The heat and force m ode of the keyhole weld pool can be generated by raising the gas flowrate, raising the current or by raising both the gas and current. An increase in the plasma gas flowrate accompanied with an increase in the welding current is the best combination for generating a smooth transition during the star t-up segment, which results in only a few double arcs and no short circuiti ng between the nozzle and the workpiece. The quality of the initial weld be ad can be guaranteed using this approach.