Keyhole thermal behavior in GTAW welding process

GTAW was found to be able to conduct keyhole mode welding when the applied welding current is high enough with a special-modified torch. GTAW uses free-burning arc as the heat source, the keyhole thermal behavior should differ to that in plasma arc welding. In this paper, to understand the keyhole process in the novel keyhole welding process, a vision observation system was applied to capture the keyhole exit image during the welding process. Keyhole process was imaged in real time in the keyhole GTAW process. Keyhole exit dimensional and positional parameters were calculated from the processed keyhole images. Influence of the welding current and welding speed to the keyhole parameters were visualized through the vision system. A contrast of the GTAW keyhole parameters to the PAW keyhole parameters was drawn. The ratio of the arc pressure to the current in GTAW arc is much lower than that in PAW arc. Estimation model was developed to correlate the backside keyhole exit diameter to the front side arc jet diameter. It suggests that the coupling behavior between the free-burning arc and the keyhole in GTAW differs to that in PAW. It lays a solid foundation for keyhole stability control and process optimization in keyhole GTAW process. (C) 2017 Elsevier Masson SAS. All rights reserved.