THE EFFECT OF WELD GAS-FLOW RATE ON AL-LI WELDABILITY

Adequate shield and plasma gas flow rate during plasma arc welding are crucial factors in achieving high quality welds. Too low a shield gas flow rate lets atmosphere enter into the arc and too high a rate wast es weld gas and may cause turbulence and entrain atmosphere. Sufficien t plasma gas flow is required for keyhole welding and, as shown in thi s paper, can reduce hydrogen contamination in the weld. In-situ optica l spectroscopy used to detect oxygen and hydrogen in the welding arc d uring variable polarity plasma arc (VPPA) welding of aluminum 2090 rev ealed that there is an easily detected critical shield gas flow rate n eeded to exclude atmosphere and that this critical rate can be used to automatically control gas flow rates during welding.