Method for starting a multi-gas plasma arc torch
A method of starting a multi-gas plasma arc torch for cutting a workpiece is provided that includes directing a pre-flow gas within the plasma arc torch and switching the pre-flow gas to a plasma gas before a pilot arc is transferred to the workpiece. The plasma gas is supplied initially at a first gas pressure when the pre-flow gas is switched to the plasma gas. The gas pressure is switched to a second gas pressure that is different than the first gas pressure after the pilot arc is transferred. The method provides a smooth transition from the pre-flow gas to the plasma gas and reduces the time delay in replacing the pre-flow gas with the plasma gas in the plasma arc torch, thereby improving cut or marking quality.
1. A method of starting a plasma arc torch for operating on a workpiece, the method comprising:
providing a pre-flow gas supply and a plasma gas supply from two different gas sources;
directing the pre-flow gas supply within the plasma arc torch;
initiating a pilot arc within the plasma arc torch;
switching to the plasma gas supply to reduce a time delay when the pre-flow gas is completely replaced with the plasma gas within the plasma arc torch;
transferring a pilot arc to the workpiece after the pre-flow gas supply is switched to the plasma gas supply; and
adjusting the pressure of the plasma gas supply after the pilot arc is transferred to the workpiece.
2. The method according to claim 1 , wherein the pressure is increased after the pilot arc is transferred to the workpiece.
3. The method according to claim 1 , wherein the pressure is decreased after the pilot arc is transferred to the workpiece.
4. The method according to claim 1 , wherein the pilot arc is generated within the plasma arc torch after switching from the pre-flow gas supply to the plasma gas supply.
5. The method according to claim 1 , wherein the pilot arc is generated within the plasma arc torch before switching from the pre-flow gas supply to the plasma gas supply.
6. The method according to claim 1 further comprising directing the pre-flow gas at a first pressure and directing the plasma gas at the first pressure when the pre-flow gas is switched to the plasma gas.
7. The method according to claim 6 further comprising switching the plasma gas from the first pressure to a second pressure after the pilot arc is transferred to the workpiece.
8. The method according to claim 7 wherein the second pressure is higher than the first pressure.
9. The method according to claim 1 further comprising increasing an arc current to a first set value to transfer the pilot arc to the workpiece.
10. The method according to claim 9 further comprising ramping up the arc current from the first set value.
11. The method according to claim 10 further comprising switching the plasma gas from a first pressure to a second pressure when the arc current reaches a second set value that is higher than the first set value.
12. The method according to claim 1 , wherein the pre-flow gas is switched to the plasma gas approximately 10 ms-1000 ms before the pilot arc is transferred to the workpiece.
13. The method according to claim 1 , wherein the plasma arc torch has a tip orifice smaller than about 0.040 inches.
14. The method according to claim 1 , wherein the pre-flow gas is directed at a pressure greater than about 50 psi.
15. The method according to claim 1 , further comprising operating the plasma arc torch at a value of between about 4 amps to about 150 amps.
16. The method according to claim 1 , wherein the pre-flow gas is selected from a group consisting of argon, nitrogen and air.
17. The method according to claim 1 , wherein the plasma gas is oxygen.
18. A method of starting a plasma arc torch for cutting a workpiece, the method comprising:
providing a pre-flow gas supply and a plasma gas supply from two different gas sources;
directing the pre-flow gas supply;
initiating a pilot arc within the plasma arc torch;
switching from the pre-flow gas supply to the plasma gas supply;
supplying the plasma gas at a first gas pressure to reduce a time delay when the pre-flow gas is completely replaced with the plasma gas within the plasma arc torch;
transferring the pilot arc to the workpiece after the pre-flow gas supply is switched to the plasma gas supply; and
switching the plasma gas from the first gas pressure to a second gas pressure that is higher than the first gas pressure after the pilot arc is transferred to the workpiece.