Patent ID: 8354609

Claim:
A method for cutting a part from a workpiece according to a cutting program, the part having a hole and a contour, wherein the hole is within a perimeter of the part, the method comprising: providing a plasma arc torch having a nozzle and an electrode that define a plasma chamber, a plasma arc generated in the plasma chamber, a shield gas supply line for providing a shield gas flow to the plasma arc torch, and a control unit for controlling cutting parameters including shield gas composition; using the plasma arc torch to (i) pierce the workpiece and cut the hole in the part and (ii) pierce the workpiece and cut the contour without changing the nozzle and electrode; controlling the cutting parameters such that when the contour is cut the shield gas comprises a first shield gas composition and when the hole is cut the shield gas comprises a second shield gas composition, wherein the first shield gas composition is different than the second shield gas composition; and controlling an amount of nitrogen in the shield gas flow such that the second shield gas composition contains less nitrogen as a percentage of a total shield gas volume than the first shield gas composition whereby a cylindricity of the hole is substantially reduced.