Patent ID: 8354610

Claim:
A method for cutting a hole and a contour in a workpiece, the method comprising: providing a plasma arc torch having a nozzle and an electrode that define a plasma chamber in which a plasma arc is generated, a shield gas supply source for providing a shield gas flow to the plasma arc torch, and a control unit for controlling cutting parameters including shield gas composition and a cutting speed; cutting the hole with the plasma arc torch while using the control unit to control the cutting parameters for a second shield gas composition and a second cutting speed changing the shield gas composition from the second shield gas composition to a first shield gas composition, the second shield gas composition containing less nitrogen as a percentage of a total shield gas volume than the first shield gas composition; and cutting the contour with the plasma arc torch at a first cutting speed without changing the nozzle and electrode by using the control unit to control the first shield gas composition and the first cutting speed, the second cutting speed being slower than the first cutting speed.