Abstract: It is discovered the inherent rules between weld pool oscillation frequency and weld penetration though study of weld pool oscillation behavior in the case of variable polarity plasma arc perforated vertical welding of aluminum alloy 3003. During welding, the weld pool is brought into oscillation by variable polarity current, and the oscillation frequency is measured by spectral analysis of arc voltage. The weld pool models of partial penetration and full penetration are established. It is found that variation of welding current has only a small effect on the weld pool oscillation frequency, so its impact can be neglected. In order to test accuracy of the models, it is performed the analysis of theory and measurement, and the results show that two values coincide. The weld pool natural oscillation frequency is dominated by weld pool depth, width and material density and not associated with welding parameters directly. Thus, weld pool oscillation frequency indirectly reflects weld pool penetration, which provides a theoretical support for automatic control of welding quality.

Key words: variable polarity plasma arc, weld pool model, weld pool oscillation