Influence of Admixture of Oxygen into Shielding Gas on Cathode Spot Behavior

Abstract

The cleaning action with AC Tungsten Inert Gas (TIG) welding is attributed to the removal process of oxide film caused by cathode spots. In this study, a double shielding gas torch, which used the internal shielding gas of helium and the external shielding gas of helium or helium with 5.0 % oxygen, was employed to investigate influence of admixture of oxygen into the shielding gas on the cathode spot behavior in AC TIG welding. The cathode spots were photographed by a high-speed video camera and their distribution and velocity are discussed. Consequently, it was found that when the oxygen was mixed into the shielding gas, the number of cathode spots seemed to increase. Furthermore, the average velocity of cathode spots was considerably decreased to approximately 50 m/s near the center of the weld pool compared with 100m/s in case of pure helium shielding gas.