Real-time observation of cathodic cleaning during variable-polarity gas tungsten arc welding of aluminium alloy

Abstract

Online observation is expected to provide a better understanding of the cathodic cleaning of oxides from the molten pool during variable-polarity gas tungsten arc welding (VP GTAW) of aluminium alloys. In this paper, a machine-vision system with appropriate illumination and filtering is used to monitor in real time the effect of different process parameters on the cleaning of oxides from the molten pool during VP GTAW of Al 6061. Based on the observations, the process conditions under which a clean molten pool can be achieved are determined. In addition, the control of the welding process to maintain the consistency of cathodic cleaning is discussed. The results showed that in order to have an oxide-free molten pool, the solid surface in front of the molten pool should be cleaned from oxides by the electric arc. The choice of process parameters to satisfy this condition has been discussed. It was found that the percentage of direct current electrode positive (DCEP) polarity in the cycle of current has the highest impact on the cathodic cleaning, with the arc current having less influence, and the welding speed showing the least effect. Furthermore, in order to keep the consistency of oxide cleaning, process parameters should be set or controlled to maintain the cleaned zone larger than the molten pool.

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

“…The oxide layer can be cleaned during the EP polarity by a large number of cathode spots occurring on the surface of the base metal to be cathode 6), 7) . The cathode spot is known to have greatly high current density and also travel randomly on the surface at very large velocity.…”

“…Therefore, in this study, behaviors of the cathode spot are further investigated in AC TIG welding process with helium shielding gas by using the highspeed camera which has the maximum frame rate of 1,000,000 fps. The increase of the DCEP duration is known to enlarge the clean zone 7) . It means the cathode spot has enough time to move far toward the oxide layer in that condition.…”

Improvement of Arc Properties in GTAW of Aluminium Alloys

“…Studies of this welding method have been continued for more than half a century [2]. However, the number of papers on its optimization is not decreasing nowadays [3][4][5][6][7][8][9][10][11][12][13]. For example, simulation [14,15] and experimental studies [15][16][17][18][19][20] are used for deeper understanding of physical processes taking place in a welding arc.…”