The second is, when steel is welded by means of VPTIG of argon, the changes in current, voltage and arc shape.

第二部分研究了在氩气作保护气体的情况下，用变极性TIG焊方法焊钢时，焊接电流、电压的变化情况和电弧形态的变化。

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The third is, when Al is welded by means of VPTIG method of helium, the changes in current, voltage and arc shape.

第三部分研究了在氦气作保护气体的情况下，用变极性TIG焊方法焊铝时，焊接电流、电弧电压的变化情况和电弧形态的变化。

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The third is, when Al is welded by means of VPTIG method of helium, the changes in current, voltage and arc shape.

第三部分研究了在氦气作保护气体的情况下，用变极性TIG焊方法焊铝时，焊接电流、电弧电压的变化情况和电弧形态的变化。

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