Reduction of blowholes by vibration of the molten pool in arc welding of galvanised carbon steel sheet

Summary

This paper examines measures to reduce the number of blowholes formed through vaporised zinc gas bubbles infiltrating into the molten pool through the weld gap in pulsed arc welding of galvanised carbon steel sheet with consumable electrodes by the hot metal being induced to flow along the molten pool base. Longitudinal vibration of the base metal by 1 mm during the welding process in such a way as to produce back and forth flow of the hot metal along the molten pool base leads to a significant reduction in the number of blowholes. The optimum vibration frequency giving the minimum number of blowholes is 30 Hz. This frequency is assumed to correspond to the natural vibration frequency depending on the size and physical properties of the molten pool, etc. To exert the same effect as described above by welding current control, the paper also describes an investigation of the molten pool being vibrated longitudinally by a repetitive current waveform sequence of a high peak/short time pulsed waveform group and a low peak/long time pulsed waveform group. The molten pool can also be arranged to vibrate longitudinally by control of the arc force, with blowhole generation being significantly reduced by such vibration. Vibration of the molten pool is effective for promoting the removal not only of blowholes due to the generation of vaporised zinc gas bubbles, but also supersaturation blowholes due to nitrogen formed at the solidification front.