PURPOSE: To suppress the generation of weld defects and the degradation in welding efficiency by fixing the operating polarity of a polarity changing means and outputting only the DC when a positive polarity period falls to a prescribed value or below.
CONSTITUTION: The output of a DC power source 1 is set at two levels of large and small currents by output current setting means 13, 14. The DC is converted to AC by the polarity changing means 8. The reverse polarity and positive polarity periods are set by polarity period setting means 12, 15, 16. The output of the welding current is controlled by increasing and decreasing the positive polarity period by welding current control means 2, 6. The operating polarity of the polarity changing means 8 is fixed and only the DC output is outputted when the positive polarity period falls to the prescribed value or below. The unstability of the arc form is prevented in this way.
KASHIMA TAKAYUKI
SHINADA TSUNEO
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