PROBLEM TO BE SOLVED: To provide a plasma keyhole welding method and a plasma keyhole welding system, capable of forming a more beautiful bead.;SOLUTION: Between a plasma electrode 112 and a base material W, there are provided an output circuit 31 for outputting the pulse current of the set frequency Ffr, a keyhole size detection unit for detecting the size of a keyhole formed in the base material W, and a frequency calculation circuit 38 for calculating the set frequency Ffr based on the change of the size of the keyhole detected by the keyhole size detection unit. In this constitution, the size of the keyhole can be adjusted by adjusting the frequency of the pulse current. Thus, the more beautiful bead can be formed.;COPYRIGHT: (C)2013,JPO&INPIT
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