Since it is indispensable to remove oxide layer on aluminum for realizing high quality weld joint in arc welding of aluminum plates, AC TIG welding is generally employed. In periods of EP (Electrode Positive) of AC TIG welding, the oxide layer is removed by cleaning action of cathode spots. In this paper, results on experimental observations of the cleaning action of the oxide layer by cathode spots in AC TIG welding of the aluminum plate with a high speed video camera will be reported. As a result, it was found that cathode spots moved slowly on the oxide layer and their averaged velocity was 26.1m/s. On the other hand, cathode spots near the center of the weld pool, where the oxide layer had been mostly removed, moved at high speed and their averaged velocity reached 121.9 m/s. Furthermore, the velocity greatly changed depending on the position of the cathode spot and exceeded 1 km/s at the maximum.
TIG pulsed-arc welding is suitable for back-bead welding, thin plate welding and so on, because the heat source properties can be controlled by current waveform. The heat flux onto the base metal is affected mainly by thermal conduction and electron condensation from the arc. Both factors strongly depend on the temperature distribution and current path in the arc. In order to clarify the heat source properties of TIG pulsed-arc, dynamic variation in two-dimensional temperature distribution of TIG pulsed-arc was measured through Fowler-Milne method with a high speed video camera as a first step of the study. As a result, it was found that the arc column was expanded in radial direction and the maximum arc temperature was 20,000K during the peak current of 200A. On the other hand, the width of the arc column decreased especially in the downstream region of the arc and the maximum arc temperature fell to 17,500K during the base current of 50A.
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