Shielding gas and heat transfer effeciency in plasma arc welding

Variable polarity plasma arc welding is widely used in the aerospace industry for producing high-quality welds on aluminum. In plasma welding the arc is produced in a narrow stream of plasma gas while workpiece shielding is accomplished by a lower velocity but higher flow rate stream of shielding gas that surrounds the arc. This paper will show that on aluminum welds both the melt zone and the heat-affected zone are appreciably decreased by this flow of shielding gas. Moreover, the amount of cooling is changed by the detailed shape of this flow as well as the flow rate. On the other hand, it will be shown that excessively high shielding flow rates can cause undercutting from contamination in the shielding gas.