PLASMA CUTTING METHOD AND NC PLASMA CUTTING APPARATUS

The present invention relates to a plasma cutting method and a NC plasma cutting apparatus in which an improvement can be made in the quality of a bore-cut product obtained by using a transferred plasma arc, and the productive efficiency can also be enhanced. In order to achieve the above-described advantages, the transferred plasma arc is switched to a non-transferred plasma arc in a position immediately before a cutting finishing point and in the vicinity of a position in which cutting lines cross each other. Simultaneously with this switching operation, the moving speed of a plasma torch is varied in accordance with a change in the plasma arc current. Additionally, the transferred plasma arc current is reduced in a position immediately before the cutting finishing point and in the vicinity of a position in which cutting lines cross each other. The moving speed of the plasma torch may be varied in accordance with the reduction in the arc current. Further, the above-described voltage detecting function is kept in the off state during a cutting operation, and it is actuated in a position immediately before the cutting finishing point and in the vicinity of a position in which cutting lines cross each other.