Arc efficiency of plasma arc welding

Arc efficiency was measured for variable polarity plasma arc welds on 6061 aluminum. It was found to vary from 0.48 to 0.66 and increased with arc voltage but decreased with arc current. The current and voltage dependence of the various mechanisms for heat transfer from the arc to a workpiece are critically examined. Calculations show that radiation from the optically thin arc contributes little to the transferred energy, but that heating of the shield gas by convection from the arc gas is a significant component of workpiece heating. Experimental values are compared to theory and show approximate agreement.