Gravity effects on horizontal variable polarity plasma arc welding

Welding defects easily appear in variable polarity plasma arc (VPPA) horizontal welding of aluminum alloy. The influence of gravity on the molten metal flow plays a critical role. Thus, the effect of the dip angle of the torch and the position of the feed wire were investigated. The stable keyhole of the dip angle torch along the welding direction was easily achieved compared to that of the right-angle torch. The distribution of thermal-force input to the keyhole was changed and the effect of gravity on the molten metal flow decreased. The melting metal bridging between the upper and the lower side became uniform by adjusting the position of the feed wire, the metal liquid state was then adjusted to ensure that gravity is a beneficial force on the molten metal flow. By introducing these optimizing methods, stable keyholes process and acceptable weld quality were obtained in VPPA horizontal welding.