Pipe seam tack welding methods and apparatus using modified series arc welding

• US 7,495,193 B2
• Filed: 03/15/2005
• Issued: 02/24/2009
• Est. Priority Date: 03/15/2005
• Status: Active Grant

• Current Assignee: Lincoln Global Incorporated (Lincoln Electric Holdings Incorporated)
• Original Assignee: Lincoln Global Incorporated (Lincoln Electric Holdings Incorporated)
• Inventors: Myers, Russ K., O'Donnell, Timothy M., Rosiek, Timothy P.
• Primary Examiner(s): Hoang; Tu B
• Assistant Examiner(s): Ralis; Stephen J
• Application Number:
  US11/081,059
• Publication Number:
  US 20060207983A1
• Time in Patent Office: 1,442 Days
• Field of Search: 219/54, 219/60.2, 219/61, 219/60.A, 219/130.51, 219/137.R, 219/137.PS, 219/76.13, 219/76.14
• US Class Current: 219/130.51
• CPC Class Codes: B23K 2101/06 Tubes
• CPC Class Codes: B23K 9/092 characterised by the shape of the pulses produced

Abstract

Welders and methods are presented for short-circuit arc welding a workpiece using a modified series arc welding configuration with two electrodes via a sequence of welding cycles, in which each cycle includes an arc condition a short-circuit condition, wherein one or both electrode currents are selectively reversed during a reverse boost portion of the welding cycle to transfer molten metal from the second electrode to the first electrode prior to a short-circuit condition of a subsequent welding cycle.

Claims

1. A modified series arc welder for depositing weld metal along a groove proximate two edges of a metal workpiece using a plurality of welding cycles having a short-circuit condition and an arc condition, said welder comprising:

first and second wire feeders respectively adapted to direct first and second electrodes toward a point proximate said workpiece;

a first power source having a first output terminal coupled with said first electrode to provide a first current thereto according to a selected first waveform in a welding cycle; and

a second power source having a first output terminal coupled with said second electrode to provide a second current thereto according to a selected second waveform in said welding cycle;

said power sources and said electrodes being coupled in a series circuit to provide electrical power to said electrodes as a plurality of said welding cycles for depositing molten metal in the form of a pool along said groove during a welding operation, each of said welding cycles including an arc condition during which said first electrode is spaced from said pool and energy applied to said first electrode causes a first molten metal to form on an end of said first electrode and a short-circuit condition during which said first molten metal on said end of said first electrode contacts said pool and then transfers from said first electrode to said pool by a necking action;

wherein said first power source provides said first current having a first polarity during said arc condition and at least a portion of said short-circuit condition, and provides said first current having a second opposite polarity during a reverse boost portion of said welding cycle according to said first waveform to transfer molten metal from said second electrode to said first electrode prior to a short-circuit condition of a subsequent welding cycle.

2. A modified series arc welder as defined in claim 1, wherein current flows from said first output terminal of said first power source to said first electrode when said first current has said first polarity, and wherein current flows from said first electrode to said first output terminal of said first power source when said first current has said second opposite polarity.

3. A modified series arc welder as defined in claim 2, wherein said second power source provides said second current having a first polarity during said arc condition and at least a portion of said short-circuit condition, and provides said second current having a second opposite polarity during said reverse boost portion of said welding cycle according to said second waveform to transfer said molten metal from said second electrode to said first electrode prior to a short-circuit condition of a subsequent welding cycle.

4. A modified series arc welder as defined in claim 3, wherein current flows from said second electrode to said first output terminal of said second power source when said second current has said first polarity, and wherein current flows from said first output terminal of said second power source to said second electrode when said second current has said second polarity.

5. A modified series arc welder as defined in claim 1, wherein said second power source provides said second current having a first polarity during said arc condition and at least a portion of said short-circuit condition, and provides said second current having a second opposite polarity during said reverse boost portion of said welding cycle according to said second waveform to transfer said molten metal from said second electrode to said first electrode prior to a short-circuit condition of a subsequent welding cycle, wherein current flows from said second electrode to said first output terminal of said second power source when said second current has said first polarity, and wherein current flows from said first output terminal of said second power source to said second electrode when said second current has said second polarity.

6. A modified series arc welder as defined in claim 1, wherein said first power source comprises a second output terminal coupled with at least one of said second power source and said workpiece;

and a high speed switching output stage coupled with said first and second output terminals for creating said first current according to said selected first waveform, said first waveform being generated by a waveform generator controlling a pulse width modulator circuit to determine the current operation of said output stage.

7. A modified series arc welder as defined in claim 6, wherein said first power source further comprises a short-circuit detection circuit coupled with at least one of said first and second output terminals of said first power source, said short-circuit detection circuit detecting a beginning of said short-circuit condition and providing a short-circuit signal to said waveform generator in response to said beginning of said short-circuit condition.

8. A modified series arc welder as defined in claim 7, wherein said short-circuit detection circuit comprises a first comparator receiving a first current signal indicative of said first current and a first reference signal, said first comparator providing said short-circuit signal when said first current signal is greater than said first reference signal.

9. A modified series arc welder as defined in claim 8, wherein said first power source further comprises a premonition circuit coupled with at least one of said first and second output terminals of said first power source, said premonition circuit detecting an imminent fuse condition in which said first molten metal separates from said first electrode, and said premonition circuit providing a premonition signal to said waveform generator in response to said imminent fuse condition.

10. A modified series arc welder as defined in claim 9, wherein said premonition circuit comprises a dv/dt circuit receiving a signal indicative of a first voltage between said first and second output terminals of said first power source and providing a dv/dt signal indicative of a rate of change of said first voltage, and a second comparator receiving said dv/dt signal from said dv/dt circuit and a second reference signal, said second comparator providing said premonition signal when said dv/dt signal is greater than said second reference signal.

11. A welder as defined in claim 10, wherein current flows from said first output terminal of said first power source to said first electrode when said first current has said first polarity, and wherein current flows from said first electrode to said first output terminal of said first power source when said first current has said second opposite polarity.

12. A modified series arc welder as defined in claim 10, wherein said second power source provides said second current having a first polarity during said arc condition and at least a portion of said short-circuit condition, and provides said second current having a second opposite polarity during said reverse boost portion of said welding cycle according to said second waveform to transfer said molten metal from said second electrode to said first electrode prior to a short-circuit condition of a subsequent welding cycle, wherein current flows from said second electrode to said first output terminal of said second power source when said second current has said first polarity, and wherein current flows from said first output terminal of said second power source to said second electrode when said second current has said second polarity.

13. A modified series arc welder as defined in claim 6, wherein said first power source further comprises a premonition circuit coupled with at least one of said first and second output terminals of said first power source, said premonition circuit detecting an imminent fuse condition in which said first molten metal separates from said first electrode and said premonition circuit providing a premonition signal to said waveform generator in response to said imminent fuse condition, wherein said premonition circuit comprises a dv/dt circuit receiving a signal indicative of a first voltage between said first and second output terminals of said first power source and providing a dv/dt signal indicative of a rate of change of said first voltage, and a second comparator receiving said dv/dt signal from said dv/dt circuit and a second reference signal, said second comparator providing said premonition signal when said dv/dt signal is greater than said second reference signal.

14. A modified series arc welder as defined in claim 13, wherein current flows from said first output terminal of said first power source to said first electrode when said first current has said first polarity, and wherein current flows from said first electrode to said first output terminal of said first power source when said first current has said second opposite polarity.

15. A modified series arc welder as defined in claim 13, wherein said second power source provides said second current having a first polarity during said arc condition and at least a portion of said short-circuit condition, and provides said second current having a second opposite polarity during said reverse boost portion of said welding cycle according to said second waveform to transfer said molten metal from said second electrode to said first electrode prior to a short-circuit condition of a subsequent welding cycle, wherein current flows from said second electrode to said first output terminal of said second power source when said second current has said first polarity, and wherein current flows from said first output terminal of said second power source to said second electrode when said second current has said second polarity.

16. A modified series arc welder as defined in claim 6, wherein said second power source comprises a second output terminal coupled with at least one of said first power source and said workpiece;

and a high speed switching output stage coupled with said first and second output terminals of said second power source for creating said second current according to said selected second waveform, said second waveform being generated by a waveform generator in said second power source controlling a pulse width modulator circuit to determine the current operation of said output stage of said second power source.

17. A modified series arc welder as defined in claim 16, wherein current flows from said first output terminal of said first power source to said first electrode when said first current has said first polarity, and wherein current flows from said first electrode to said first output terminal of said first power source when said first current has said second opposite polarity.

18. A modified series arc welder as defined in claim 16, wherein said second power source provides said second current having a first polarity during said arc condition and at least a portion of said short-circuit condition, and provides said second current having a second opposite polarity during said reverse boost portion of said welding cycle according to said second waveform to transfer said molten metal from said second electrode to said first electrode prior to a short-circuit condition of a subsequent welding cycle, wherein current flows from said second electrode to said first output terminal of said second power source when said second current has said first polarity, and wherein current flows from said first output terminal of said second power source to said second electrode when said second current has said second polarity.

19. A modified series arc welder as defined in claim 1, wherein said first power source comprises a second output terminal coupled with said first terminal of said second power source, wherein said second power source comprises a second output terminal coupled with said workpiece, wherein return currents associated with said first and second power sources flow through said workpiece, and wherein current flowing through said pool of molten metal during said arc and short-circuit conditions is about equal to a sum of said first and second currents.

20. A modified series arc welder as defined in claim 1, wherein said second current at least partially causes formation of a second arc between said second electrode and said first electrode.

21. A welder as defined in claim 20, wherein current of said second arc flows from said first electrode to said second electrode during said arc condition and said portion of said short-circuit condition, and wherein said current of said second arc flows from said second electrode to said first electrode during said reverse boost portion of said welding cycle.

22. A method of short-circuit arc welding a workpiece, the method comprising:

(a) directing first and second electrodes toward a point proximate a workpiece;

(b) providing first and second currents to said first and second electrodes according to selected first and second waveforms, respectively, to deposit molten metal from at least one of said electrodes onto said workpiece in a sequence of welding cycles, each of said welding cycles including an arc condition during which said first electrode is spaced from said workpiece and energy applied to said first electrode causes a first molten metal to form on an end of said first electrode and a short-circuit condition during which said first molten metal on said end of said first electrode contacts said workpiece and then transfers from said first electrode to said workpiece; and

(c) selectively reversing an electrical polarity of said first current during said welding cycle such that said first current has a first polarity during said arc condition and at least a portion of said short-circuit condition, and a second opposite polarity during a reverse boost portion of said welding cycle according to said first waveform to transfer molten metal from said second electrode to said first electrode prior to a short-circuit condition of a subsequent welding cycle.

23. A method as defined in claim 22, wherein current flows from said first electrode to said workpiece when said first current has said first polarity, and wherein current flows from said workpiece to said first electrode when said first current has said second opposite polarity.

24. A method as defined in claim 23, further comprising:

(d) selectively reversing an electrical polarity of said second current during said welding cycle such that said second current has a first polarity during said arc condition and at least a portion of said short-circuit condition, and a second opposite polarity during a reverse boost portion of said welding cycle according to said second waveform prior to a short-circuit condition of a subsequent welding cycle.

25. A method as defined in claim 24, wherein current flows from said first electrode to said second electrode when said second current has said first polarity, and wherein current flows from said second electrode to said first electrode when said second current has said second polarity.

26. A method as defined in claim 22, further comprising:

(d) selectively reversing an electrical polarity of said second current during said welding cycle such that said second current has a first polarity during said arc condition and at least a portion of said short-circuit condition, and a second opposite polarity during a reverse boost portion of said welding cycle according to said second waveform prior to a short-circuit condition of a subsequent welding cycle.

27. A method as defined in claim 26, wherein current flows from said first electrode to said second electrode when said second current has said first polarity, and wherein current flows from said second electrode to said first electrode when said second current has said second polarity.

28. A method for welding a pipe seam, the method comprising:

engaging two pipe seam edges to one another to form a cylindrical pipe structure having an inside and an outside, said cylindrical pipe structure having a seam at the two engaged seam edges with an outer groove and an inner groove;

welding a portion of the outer groove using a series welding process to tack the two seam edges together, said series welding process comprising a plurality of welding cycles individually having a short-circuit condition and an arc condition;

welding the inner groove after the two seam edges have been tacked together to essentially fill the inner groove and form an inner seam; and

welding the outer groove after welding the inner groove to essentially fill the outer groove and form an outer seam;

wherein each of said welding cycles includes an arc condition during which a first electrode is spaced from said workpiece and energy applied to said first electrode causes a first molten metal to form on an end of said first electrode and a short-circuit condition during which said first molten metal contacts said workpiece and then transfers from said first electrode to said workpiece by a necking action;

wherein said high current series welding process comprises providing first and second currents to said first and second electrodes to deposit molten metal from at least one of said electrodes onto said workpiece in a sequence of welding cycles, and wherein welding a portion of the outer groove using a series welding process comprises selectively reversing an electrical polarity of said first current during said welding cycle such that said first current has a first polarity during said arc condition and at least a portion of said short-circuit condition, and a second opposite polarity during a reverse boost portion of said welding cycle to transfer molten metal from said second electrode to said first electrode prior to a short-circuit condition of a subsequent welding cycle.

29. A method as defined in claim 28, further comprising grinding the outer seam.

30. A method as defined in claim 28, wherein said series welding process comprises providing first and second currents to said first and second electrodes to deposit molten metal from at least one of said electrodes onto said workpiece in a sequence of welding cycles, and wherein welding a portion of the outer groove using a high current series welding process comprises selectively reversing an electrical polarity of one of said currents during said welding cycles.

31. A modified series arc welder for depositing weld metal along a groove proximate a pipe seam using a plurality of welding cycles individually having a short-circuit condition and an arc condition, said welder comprising:

first and second wire feeders respectively adapted to direct first and second electrodes toward a point proximate said workpiece;

a first power source providing a first current to said first electrode;

a second power source providing a second current to said second electrode, said power sources and said electrodes being connected in a series circuit;

a short-circuit detection; and

wherein said first power source provides said first current having a first polarity during said arc condition and at least a portion of said short-circuit condition, and provides said first current having a second opposite polarity during a reverse boost portion of said welding cycle to transfer molten metal from said second electrode to said first electrode prior to a short- circuit condition of a subsequent welding cycle.

32. A modified series arc welder as defined in claim 31, wherein said at least one of said power sources is adapted to selectively reverse an electrical polarity of one of said currents during said welding cycles.

33. A modified series arc welder as defined in claim 31, wherein said short-circuit detection circuit comprises a first comparator receiving a first current signal indicative of said first current and a first reference signal, said first comparator providing said short-circuit signal when said first current signal is greater than said first reference signal.

34. A modified series arc welder as defined in claim 31, wherein said premonition circuit comprises a dv/dt circuit receiving a signal indicative of a first voltage and providing a dv/dt signal indicative of a rate of change of said first voltage, and a second comparator receiving said dv/dt signal from said dv/dt circuit and a second reference signal, said second comparator providing said premonition signal when said dv/dt signal is greater than said second reference signal.

35. An arc welding system, comprising:

a wire feeding system adapted to direct first and second electrodes toward a workpiece, said first and second electrodes being connected in a series circuit; and

a source of electrical power providing a first current to said first electrode and a second current to said second electrode to deposit material from said first and second electrodes in a short-circuit arc welding process having an arc condition and a short-circuit condition in each of a plurality of welding cycles; and

wherein said source of electrical power provides said first current having a first polarity during said arc condition and at least a portion of said short-circuit condition, and provides said first current having a second opposite polarity during a reverse boost portion of said welding cycle to transfer material from said second electrode to said first electrode prior to a short-circuit condition of a subsequent welding cycle.

36. An arc welding system as defined in claim 35, wherein said wire feeding system comprises a first wire feeder adapted to direct said first electrode toward said workpiece and a second feeder adapted to direct said second electrode toward said workpiece.

37. An arc welding system as defined in claim 36, wherein said source of electrical power comprises a first power source providing said first current to said first electrode and a second power source providing said second current to said second electrode.

38. An arc welding system as defined in claim 37, wherein said source of electrical power provides said first and second currents such that a first arc is established between said first electrode and said workpiece and a second arc is established between said first and second electrodes during said arc condition of said welding cycles.

39. An arc welding system as defined in claim 38, further comprising a short-circuit detection circuit adapted to detect a beginning of said short-circuit condition and a premonition circuit adapted to detect an imminent metal breaking fuse condition at an end of said short-circuit condition, wherein said source of electrical power provides said first and second currents according to said detected beginning of said short-circuit condition, and according to said detected imminent metal breaking fuse condition, and wherein said source of electrical power provides a power boost to said first electrode during the arc condition to form molten metal on said first electrode.

40. An arc welding system as defined in claim 37, further comprising a short-circuit detection circuit adapted to detect a beginning of said short-circuit condition and a premonition circuit adapted to detect an imminent metal breaking fuse condition at an end of said short-circuit condition, wherein said source of electrical power provides said first and second currents according to said detected beginning of said short-circuit condition, and according to said detected imminent metal breaking fuse condition, and wherein said source of electrical power provides a power boost to said first electrode during the arc condition to form molten metal on said first electrode.

41. An arc welding system as defined in claim 36, wherein said source of electrical power provides said first and second currents such that a first arc is established between said first electrode and said workpiece and a second arc is established between said first and second electrodes during said arc condition of said welding cycles.

42. An arc welding system as defined in claim 41, further comprising a short-circuit detection circuit adapted to detect a beginning of said short-circuit condition and a premonition circuit adapted to detect an imminent metal breaking fuse condition at an end of said short-circuit condition, wherein said source of electrical power provides said first and second currents according to said detected beginning of said short-circuit condition, and according to said detected imminent metal breaking fuse condition, and wherein said source of electrical power provides a power boost to said first electrode during the arc condition to form molten metal on said first electrode.

43. An arc welding system as defined in claim 36, further comprising a short-circuit detection circuit adapted to detect a beginning of said short-circuit condition and a premonition circuit adapted to detect an imminent metal breaking fuse condition at an end of said short-circuit condition, wherein said source of electrical power provides said first and second currents according to said detected beginning of said short-circuit condition, and according to said detected imminent metal breaking fuse condition, and wherein said source of electrical power provides a power boost to said first electrode during the arc condition to form molten metal on said first electrode.

44. An arc welding system as defined in claim 35, wherein said source of electrical power comprises a first power source providing said first current to said first electrode and a second power source providing said second current to said second electrode.

45. An arc welding system as defined in claim 44, wherein said source of electrical power provides said first and second currents such that a first arc is established between said first electrode and said workpiece and a second arc is established between said first and second electrodes during said arc condition of said welding cycles.

46. An arc welding system as defined in claim 45, further comprising a short-circuit detection circuit adapted to detect a beginning of said short-circuit condition and a premonition circuit adapted to detect an imminent metal breaking fuse condition at an end of said short-circuit condition, wherein said source of electrical power provides said first and second currents according to said detected beginning of said short-circuit condition, and according to said detected imminent metal breaking fuse condition, and wherein said source of electrical power provides a power boost to said first electrode during the arc condition to form molten metal on said first electrode.

47. An arc welding system as defined in claim 44, further comprising a short-circuit detection circuit adapted to detect a beginning of said short-circuit condition and a premonition circuit adapted to detect an imminent metal breaking fuse condition at an end of said short-circuit condition, wherein said source of electrical power provides said first and second currents according to said detected beginning of said short-circuit condition, and according to said detected imminent metal breaking fuse condition, and wherein said source of electrical power provides a power boost to said first electrode during the arc condition to form molten metal on said first electrode.

48. An arc welding system as defined in claim 35, wherein said source of electrical power provides said first and second currents such that a first arc is established between said first electrode and said workpiece and a second arc is established between said first and second electrodes during said arc condition of said welding cycles.

49. An arc welding system as defined in claim 48, further comprising a short-circuit detection circuit adapted to detect a beginning of said short-circuit condition and a premonition circuit adapted to detect an imminent metal breaking fuse condition at an end of said short-circuit condition, wherein said source of electrical power provides said first and second currents according to said detected beginning of said short-circuit condition, and according to said detected imminent metal breaking fuse condition, and wherein said source of electrical power provides a power boost to said first electrode during the arc condition to form molten metal on said first electrode.

50. An arc welding system as defined in claim 35, further comprising a short-circuit detection circuit adapted to detect a beginning of said short-circuit condition and a premonition circuit adapted to detect an imminent metal breaking fuse condition at an end of said short-circuit condition, wherein said source of electrical power provides said first and second currents according to said detected beginning of said short-circuit condition, and according to said detected imminent metal breaking fuse condition, and wherein said source of electrical power provides a power boost to said first electrode during the arc condition to form molten metal on said first electrode.

51. An arc welding system, comprising:

a wire feeding system adapted to direct first and second electrodes toward a workpiece; and

a source of electrical power energizing said electrodes to deposit material from said electrodes in a short-circuit arc welding process having an arc condition and a short-circuit condition in each of a plurality of welding cycles, said source of electrical power providing a first current to said first electrode and a second current to said second electrode to establish a first arc between said first electrode and said workpiece and a second arc between said first and second electrodes; and

wherein said source of electrical power provides said first current having a first polarity during said arc condition and at least a portion of said short-circuit condition, and provides said first current having a second opposite polarity during a reverse boost portion of said welding cycle to transfer material from said second electrode to said first electrode prior to a short-circuit condition of a subsequent welding cycle.

52. An arc welding system as defined in claim 51, wherein said wire feeding system comprises a first wire feeder adapted to direct said first electrode toward said workpiece and a second feeder adapted to direct said second electrode toward said workpiece.

53. An arc welding system as defined in claim 52, wherein said source of electrical power comprises a first power source providing said first current to said first electrode and a second power source providing said second current to said second electrode.

54. An arc welding system as defined in claim 53, further comprising a short-circuit detection circuit adapted to detect a beginning of said short-circuit condition and a premonition circuit adapted to detect an imminent metal breaking fuse condition at an end of said short-circuit condition, wherein said source of electrical power provides said first and second currents according to said detected beginning of said short-circuit condition, and according to said detected imminent metal breaking fuse condition, and wherein said source of electrical power provides a power boost to said first electrode during the arc condition to form molten metal on said first electrode.

55. An arc welding system as defined in claim 51, further comprising a short-circuit detection circuit adapted to detect a beginning of said short-circuit condition and a premonition circuit adapted to detect an imminent metal breaking fuse condition at an end of said short-circuit condition, wherein said source of electrical power provides said first and second currents according to said detected beginning of said short-circuit condition, and according to said detected imminent metal breaking fuse condition, and wherein said source of electrical power provides a power boost to said first electrode during the arc condition to form molten metal on said first electrode.

56. An arc welding system as defined in claim 51, wherein said source of electrical power comprises a first power source providing said first current to said first electrode and a second power source providing said second current to said second electrode.

57. An arc welding system as defined in claim 56, further comprising a short-circuit detection circuit adapted to detect a beginning of said short-circuit condition and a premonition circuit adapted to detect an imminent metal breaking fuse condition at an end of said short-circuit condition, wherein said source of electrical power provides said first and second currents according to said detected beginning of said short-circuit condition, and according to said detected imminent metal breaking fuse condition, and wherein said source of electrical power provides a power boost to said first electrode during the arc condition to form molten metal on said first electrode.

58. An arc welding system as defined in claim 51, further comprising a short-circuit detection circuit adapted to detect a beginning of said short-circuit condition and a premonition circuit adapted to detect an imminent metal breaking fuse condition at an end of said short-circuit condition, wherein said source of electrical power provides said first and second currents according to said detected beginning of said short-circuit condition, and according to said detected imminent metal breaking fuse condition, and wherein said source of electrical power provides a power boost to said first electrode during the arc condition to form molten metal on said first electrode.

59. A method for welding a workpiece, said method comprising:

(a) directing first and second electrodes toward a point; and

(b) providing first and second currents to said first and second electrodes, respectively, to establish a first arc between said first electrode and a workpiece and a second arc between said first and second electrodes in order to transfer material from said electrodes to said workpiece in a plurality of welding cycles, each welding cycle including an arc condition and a short-circuit condition;

selectively reversing an electrical polarity of said first current during said welding cycle such that said first current has a first polarity during said arc condition and at least a portion of said short-circuit condition, and a second opposite polarity during a reverse boost portion of said welding cycle; and

transferring material from said second electrode to said first electrode by reversing a polarity of at least one of said currents during said arc condition prior to a short-circuit condition of a subsequent welding cycle.

60. A method as defined in claim 59, further comprising:

detecting a beginning of said short-circuit condition;

detecting an imminent metal breaking fuse condition at an end of said short-circuit condition, and controlling said first and second currents according to said detected beginning of said short-circuit condition and said detected imminent metal breaking fuse condition.

61. A method as defined in claim 60, further comprising providing a power boost to said first electrode during said arc condition to form molten metal on said first electrode.

62. A method as defined in claim 59, further comprising providing a power boost to said first electrode during said arc condition to form molten metal on said first electrode.