High quality hole cutting using variable shield gas compositions

1. 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.

2. The method of claim 1 wherein controlling the cutting parameters further comprises controlling the second shield gas composition according to a ratio of the diameter of the hole to the thickness of the workpiece.

3. The method of claim 2 wherein the ratio is less than or equal to 2.5.

4. The method of claim 1 further comprising:

providing a computer readable product tangibly embodied in an information carrier, operable on a CNC for use with a plasma torch system, the computer readable product containing cutting information for the plasma arc torch including instructions that select the first shield gas composition when cutting the contour and select the second shield gas composition when cutting the hole.

5. The method of claim 4 further comprising selecting the second shield gas composition according to a ratio of the diameter of the hole to the thickness of a workpiece.

6. A method for improving the cutting characteristics of a part from a workpiece according to a plasma torch cutting program, the part having a small internal feature and a contour, wherein the small internal feature is within a perimeter of the part, the method comprising:

piercing the workpiece;

cutting the small internal feature using a second shield gas composition, the small internal feature positioned on the workpiece within an anticipated contour cut of the workpiece; and

cutting the contour corresponding to the anticipated contour cut using a first shield gas composition, wherein the second shield gas composition comprises less nitrogen than the first shield gas composition, such that a bevel of an edge of the small internal feature is substantially eliminated.

7. A method for cutting a part from a workpiece using a plasma arc torch according to a cutting program, the part having a hole and a contour, wherein the hole is within a perimeter of the part, the plasma arc torch including a nozzle and electrode that define a plasma chamber, such that a plasma arc generated in the plasma chamber is used to cut the workpiece, and a shield gas supply line that delivers a shield gas flow to the plasma torch, the method comprising:

piercing the workpiece and cutting the hole in the part, wherein the shield gas flow comprises a second shield gas composition to cut the hole, the second shield gas composition selected such that a bevel of an edge of the hole is substantially eliminated;

piercing the workpiece and cutting the contour wherein the shield gas flow comprises a first shield gas composition to cut the contour; and

controlling the first shield gas composition and the second shield gas composition such that while cutting the hole the second shield gas composition comprises less nitrogen than the first shield gas composition.

8. The method of claim 7 , further comprising:

providing a computer readable product tangibly embodied in an information carrier, operable on a CNC for use with a plasma torch system, the computer readable product containing cutting information for the plasma arc torch including instructions that select the first shield gas composition when cutting the contour and select the second shield gas composition when cutting the hole.

9. The method of claim 8 further comprising selecting the second shield gas composition according to a ratio of a diameter of the hole to the thickness of a workpiece.

10. A method of cutting a part from a workpiece using a plasma arc torch according to a cutting program, the part having a hole and a contour, wherein the hole is within a perimeter of the part, the plasma arc torch including high-current consumables, the high-current consumables including a nozzle and electrode that define a plasma chamber, the method comprising:

generating a plasma arc in the plasma chamber using an arc current above 50 amps to pierce the workpiece;

controlling a shield gas composition of a shield gas flow such that when the hole is being cut, the shield gas composition comprises a second shield gas composition comprising a second amount of nitrogen such that a bevel of an edge of the hole is substantially eliminated; and

controlling the shield gas composition of the shield gas flow such that when the contour is being cut, the shield gas composition comprises a first shield gas composition comprising a first amount of nitrogen that substantially eliminates a bevel of an edge of the contour.

11. In the process of plasma arc 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, and wherein, while cutting the workpiece, a plasma arc torch that produces a plasma arc of ionized gas between an electrode and a nozzle mounted within the torch using a plasma gas and a shield gas, the improvement comprising:

piercing the workpiece and cutting the contour in the workpiece, the shield gas having a first shield gas composition while cutting the contour;

changing the shield gas from the first shield gas composition to a second gas composition; and

piercing the workpiece and cutting the hole in the part without changing the nozzle and electrode using the second shield gas composition while cutting the hole, wherein the second shield gas composition comprises less nitrogen than the first shield gas composition such that use of the second shield gas composition reduces a bevel of the hole cut.

12. In the process of plasma arc 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, and wherein, while cutting the workpiece, a plasma arc torch produces a plasma arc of ionized gas between an electrode and a nozzle mounted within the torch using a plasma gas and a shield gas, the improvement comprising:

piercing the workpiece and cutting the hole in the part, the shield gas having a second shield gas composition while cutting the hole;

changing the shield gas from the second shield gas composition to a first gas composition while cutting the contour; and

piercing the workpiece and cutting the contour in the workpiece without changing the nozzle and electrode using the first shield gas composition, wherein the second shield gas composition comprises less nitrogen than the first shield gas composition such that use of the second shield gas composition reduces a bevel of the hole cut.

13. 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 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;

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; and

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.

14. A method for improving the cutting characteristics of a part in a workpiece according to a plasma torch cutting program, the part having a small internal feature and a contour, wherein the small internal feature is within the perimeter of the part, the method comprising:

piercing the workpiece;

cutting the small internal feature using a second shield gas composition, the small internal feature positioned on a workpiece within an anticipated contour cut of a workpiece; and

cutting the contour corresponding to the anticipated contour cut using a first shield gas composition, wherein the first shield gas composition is different than the second shield gas composition.

15. In the process of plasma arc cutting of a part from a workpiece according to a cutting program, the part having a contour and a hole, wherein the hole is within a perimeter of the part, and wherein, while cutting the workpiece, a plasma arc torch produces a plasma arc of ionized gas between an electrode and a nozzle mounted within the torch using a plasma gas and a shield gas, the improvement comprising:

cutting the contour in the workpiece, the shield gas having a first shield gas composition;

changing the shield gas from the first shield gas composition to a second gas composition;

piercing the workpiece; and

cutting the hole in the part without changing the nozzle and electrode using the second shield gas composition, such that use of the second shield gas composition reduces a bevel of the hole cut.

16. In the process of plasma arc cutting of a part from a workpiece according to a cutting program, the part having a contour and a hole, wherein the hole is within a perimeter of the part, and wherein, while cutting the workpiece, a plasma arc torch produces a plasma arc of ionized gas between an electrode and a nozzle mounted within the torch using a plasma gas and a shield gas, the improvement comprising:

piercing the workpiece;

cutting the hole in the part, the shield gas having a second shield gas composition;

changing the shield gas from the second shield gas composition to a different first gas composition; and

cutting the contour in the workpiece without changing the nozzle and electrode using the first shield gas composition, such that use of the second shield gas composition reduces a bevel of the hole cut.