The Arc Physical Characteristics and Molten Pool Dynamic Behaviors in Conduction Plasma ArcWelding

Conduction plasma arc welding is widely used to weld thin stainless-steel plates in a liquefied natural gas carrier, in which high arc energy density can be achieved through the constraint effects of the constricting nozzle. However, the welding current is relatively low, such that a keyhole is not formed inside the molten pool in conduction plasma arc welding, causing significantly different arc physical characteristics and molten pool dynamic behaviors from those of keyhole plasma arc welding. In this study, a one-way coupled electrode-arc-molten pool model was developed, and spectral analysis, infrared thermography, and particle tracing methods were used to investigate the arc physical characteristics and molten pool dynamic behaviors in conduction plasma arc welding. In conduction plasma arc welding, numerical and experimental results show that plasma impinges on the surface and flows toward the edge of the molten pool. Two contrary convective eddies were found inside the molten pool. The counterclockwise eddy at the center of the molten pool is driven by arc pressure, Marangoni forces, and Lorentz forces, and the clockwise eddy at the rear part of the molten pool is driven by plasma shear stress, Marangoni forces, and buoyancy forces. Additionally, the maximum temperature of the molten pool in conduction plasma arc welding is higher than that in keyhole plasma arc welding due to higher arc energy density and weaker convection.