Behaviors of Cathode Spot in Alternative Current Helium TIG Welding of Aluminum

Abstract

Alternative current TIG welding is a common way to joint aluminum for the use of the oxide cleaning action by cathode spots. In order to improve the efficiency of the oxide cleaning through the control of the cathode spot, the cathode spot behaviors should be clarified in detail. For this purpose, an observation of the oxide cleaning action in helium TIG welding was carried out by a highspeed camera. Here, the behaviors of cathode spots were elucidated by tracking the movement of them in the observation. As a result, the new cathode spots were found to be generated only from the division of the old cathode spot. This division took place continuously around the radial distance of 3.5mm from the center of weld pool. Most of the cathode spots generated there tended to move outward at average velocity decreasing from 200 m/s to 20 m/s with the radial distance. Arriving at the white zone, they suddenly decelerated around the radial distance of 5.5 mm to become gradually weak and then finally disappear. The probability of the generation of the cathode spot except for in the vicinity of the weld pool center was hence seen to be very low. Consequently, the general tendency of the life cycle of the cathode spot from the generation to the disappearance was clarified through the quantitative evaluation of the distribution and velocity of the cathode spot.