Simulation of keyhole plasma arc welding with electro-magneto-thermo-hydrodynamic interactions

Keyhole-mode welding is an advantage of plasma arc welding (PAW), and much research has been conducted on keyhole formation and weld pool geometry. However, researchers usually constructed equivalent heat source models to represent the actual thermal arc energy. A unified keyhole PAW model was constructed to make a comprehensive analysis of the keyhole-mode heat transfer originating from the electro-magneto-thermo conversion within the plasma arc. The magnetic vector potential formulation was applied to obtain a more accurate electromagnetic field. Joule heating, electron energy transfer, and electromagnetic force were all taken into account. Temperature field and velocity field in arc region and workpiece were simultaneously predicted. It is found that the radial heat conduction flux is about two times of that in the axis direction along the keyhole wall. All heat fluxes jump dramatically near the joint of keyhole wall and top metal surface. Current density and electromagnetic force distributions revealed that there are highest Joule heating and electromagnetic effects near the electrode tip, and they decrease sharply along the radial direction. The experimental test was carried out on the 304 stainless steel, and the experimental images agree well with the calculated results. The orthogonal test shows that distance from torch to the workpiece, shrinkage of tungsten electrode, and orifice diameter are of the primary effect on the weld bead geometry, and the shielding gas flow rate has the least impact.