Controlling plasma arc torches and related systems and methods

Patent metadata

Field	Value
Publication number	US-10722971-B2
Application number	US-201615287698-A
Country	US
Kind code	B2
Filing date	Oct 6, 2016
Priority date	Oct 6, 2015
Publication date	Jul 28, 2020
Grant date	Jul 28, 2020

Abstract

In some aspects, methods of initiating a plasma arc of a plasma arc torch to pierce a workpiece and detecting plasma piercing through the workpiece to begin a cutting sequence can include calculating a pulse width modulation characteristic of an electrical signal associated with a plasma arc between an electrode of a plasma arc torch and a workpiece to be processed; monitoring the characteristic during operation of the torch over a time period of a workpiece piercing sequence; comparing the characteristic to a threshold value; and responsive to determining that a calculated characteristic meets and/or exceeds the threshold value, ending the workpiece piercing sequence and beginning the cutting sequence and causing the plasma arc torch to move relative to the workpiece to form a cut.

First claim

What is claimed:

1. A method of detecting a plasma arc of a plasma arc torch has pierced through a workpiece during a piercing sequence in order to begin a cutting sequence, the method comprising:
calculating, by an at least one processor, a rate of change of a characteristic reflecting a pulse width modulation duty cycle associated with a plasma arc between an electrode of the plasma arc torch and the workpiece;
monitoring, by the at least one processor, the rate of change of the characteristic during an operation of the plasma arc torch over a time period of a piercing sequence;
comparing, by the at least one processor, the rate of change of the characteristic to a threshold value; and
ending the piercing sequence and commencing the cutting sequence by causing the plasma arc torch to move relative to the workpiece to form a cut, in response to determining, by the at least one processor, that the rate of change of the characteristic is equal to or greater than the threshold value, indicating that the plasma arc has pierced through the workpiece.

2. The method of claim 1 wherein the comparing the characteristic comprises referencing a lookup table of threshold values for a particular cutting process.

3. The method of claim 2 wherein the lookup table comprises multiple threshold values, each being associated with a set of cutting parameters.

4. The method of claim 1 further comprising, during the piercing sequence, delivering a gas mixture comprising an inert gas as a plasma gas and/or a shield gas to surround the plasma gas, the presence of the inert gas reducing a maximum plasma arc voltage required to break through the workpiece during the piercing sequence.

5. The method of claim 1 wherein the commencing the cutting sequence comprises changing at least one of a plasma gas or a shield gas from piercing gas mixture comprising an inert gas to a different gas mixture.

6. The method of claim 5 wherein the piercing gas mixture comprising the inert gas is a plasma gas.

7. The method of claim 5 wherein the piercing gas mixture comprising the inert gas is a shield gas and the different gas mixture comprising air of oxygen for the cutting sequence.

8. The method of claim 1 , wherein the beginning the cutting sequence and causing the plasma arc torch to move relative to the workpiece to form the cut comprises sending a signal, from a power supply to a gantry controller, to cause relative motion between the plasma arc torch and the workpiece.

9. A method of performing a piercing sequence to pierce a hole in a workpiece with a plasma arc torch, the method comprising:
initiating an arc between an electrode and a nozzle of the plasma arc torch during a pilot arc mode;
transferring the arc from the nozzle to a workpiece for piercing and cutting the workpiece;
beginning a workpiece piercing sequence;
estimating, by an at least one processor, a rate of change of a characteristic reflecting a pulse width modulation duty cycle being provided to a power module to maintain the arc between the plasma arc torch and the workpiece during the workpiece piercing sequence;
comparing, by the at least one processor, the rate of change of the characteristic to a predetermined value; and
ending the workpiece piercing sequence and initiating a cutting sequence in response to determining, by the at least one processor, that the rate of change of the characteristic is equal to or greater than the predetermined value, indicating that the arc has pierced through the workpiece.

10. The method of claim 9 , wherein the initiating the cutting sequence comprises initiating a relative movement between the workpiece and the plasma arc torch.

11. The method of claim 10 wherein the initiating relative movement between the workpiece and the plasma arc torch comprises sending a signal from a power supply in communication with the plasma arc torch to a movement controller mechanically coupled to the plasma arc torch.

12. The method of claim 10 wherein the initiating relative movement between the workpiece and the plasma arc torch is delayed by a predetermined time period.

13. The method of claim 12 wherein delaying the initiating relative movement opens a semi-conical pierced hole in the workpiece into a cylindrical pierced hole using plasma expelled from the plasma arc torch.

14. The method of claim 9 wherein the determining that the estimated rate of change of the characteristic meets and/or exceeds the predetermined value identifies that plasma from the plasma arc torch has broken through the workpiece.

15. A method for increasing a usable number of pierce operations for an electrode of a plasma arc torch, the method comprising:
initiating an arc between the electrode and a corresponding nozzle of the plasma arc torch during a pilot arc mode;
transferring the arc from the corresponding nozzle to a workpiece for piercing and cutting the workpiece;
increasing a current of the plasma arc;
delivering a gas mixture comprising an inert gas as at least one of a plasma gas or a shield gas to surround the arc and initiating a piercing sequence;
calculating, by an at least one processor, a rate of change of a characteristic reflecting a pulse width modulation duty cycle associated with a plasma arc between an electrode of the plasma arc torch and the workpiece;
responsive to determining that the piercing sequence has completed, beginning a cutting sequence and moving the plasma arc torch relative to the workpiece to form a cut, in response to determining, by the at least one processor, that the rate of change of the characteristic is equal to or greater than the threshold value, indicating that the plasma arc has pierced through the workpiece.

16. The method of claim 15 wherein the presence of the inert gas reduces a maximum plasma arc voltage required to break through the workpiece during the piercing sequence.

17. The method of claim 15 wherein the presence of the inert gas increases an arc attachment time during the piercing sequence.

18. The method of claim 15 wherein the presence of the inert gas increases a workpiece piercing time.

19. The method of claim 15 wherein the beginning a cutting sequence comprises providing a motion signal to a CNC controller to initiate relative motion between the torch and the workpiece.

20. The method of claim 15 wherein the beginning a cutting sequence comprises delivering a second gas mixture to surround the arc that is distinct from gas mixture delivered during the piercing sequence.

21. The method of claim 15 wherein the gas mixture comprises an inert gas as a plasma gas during the piercing sequence.

22. The method of claim 15 wherein the gas mixture delivered during the piercing sequence comprises a plasma gas comprising argon and a shield gas comprising oxygen, and the beginning a cutting sequence comprises delivering a second gas mixture to surround the arc comprising a plasma gas comprising nitrogen and a shield gas comprising argon.

23. The method of claim 15 wherein the gas mixture comprising the inert gas is delivered from a metering console located on or near the plasma arc torch.

24. The method of claim 15 wherein the determining that the piercing sequence has completed comprises:
estimating and monitoring a characteristic of an electrical signal associated with the arc between the electrode and the workpiece;
comparing the characteristic to a threshold value; and
determining that an estimated characteristic

Assignees

• Hypertherm Inc

Inventors

• Mitra Soumya
• Peters John

Classifications

• H05H1/34 Primary

  Details, e.g. electrodes, nozzles · CPC title

• H05H1/36 Primary

  Circuit arrangements (H05H1/38, H05H1/40 take precedence) · CPC title

• H05H1/3473

  Safety means · CPC title

• H05H1/3494

  Means for controlling discharge parameters · CPC title

• H05H1/3421

  Transferred arc or pilot arc mode · CPC title