Apparatus and method for short circuit welding with ac waveform

Abstract

A system and method is provided in which a surface tension transfer welding function is employed where the welding waveform switches polarity during welding when a short circuit event is detected.

1 - 22 . (canceled) 
     
     
         23 . A method of short arc welding:
 providing a welding current waveform to at least one workpiece to be welded, where said welding current waveform comprises a plurality of welding cycles and each of said welding cycles comprises at least an arc portion and a shorting portion; and   controlling said welding current waveform such that said welding current waveform comprises a plurality of first waveform portions and a plurality of second waveform portions; and   switching between said first and second polarities only when a short circuit event is detected during welding,   wherein each of said first and second waveform portions of said welding current waveform comprises a plurality of said welding cycles,   wherein all of the current during said first portions has a first polarity, and all of the current during said second portions has a second polarity, which is opposite of said first polarity,   wherein said switching between said first and second polarities occurs before said short circuit event is cleared, and   wherein at least one of said plurality of first waveform portions and said plurality of second waveform portions has a duration defined by a number of detected events or a duration defined by time.   
     
     
         24 . The method of  claim 23 , wherein at least one of said plurality of first waveform portions and said plurality of second waveform portions has said duration defined by a number of detected events and said detected events are events occurring during welding cycles. 
     
     
         25 . The method of  claim 24 , wherein said detected events are either of said arc portion or said shorting portion of said cycles. 
     
     
         26 . The method of  claim 24 , wherein said duration is at least 5 of said detected events. 
     
     
         27 . The method of  claim 24 , wherein said duration is in the range of 5 to 40 of said detected events. 
     
     
         28 . The method of  claim 23 , wherein said plurality of first waveform portions has said duration defined by a number of detected events or said duration defined by time,
 wherein said plurality of second waveform portions has said duration defined by a number of detected events or said duration defined by time, and   wherein said duration for said first waveform portions is different from said duration for said second waveform portions.   
     
     
         29 . The method of  claim 23 , wherein said plurality of first waveform portions and said plurality of second waveform portions have said duration defined by time, and
 wherein at least one of said durations of said first and second waveform portions is at least 300 μs.   
     
     
         30 . The method of  claim 23 , wherein said plurality of first waveform portions and said plurality of second waveform portions have said duration defined by time, and
 wherein at least one of said durations of said first and second waveform portions is in the range of 300 μs to 600 ms.   
     
     
         31 . The method of  claim 28 , wherein said duration defined by said detected events is in the range of 5 to 40 detected events, and said duration defined by time is in the range of 100 to 600 ms. 
     
     
         32 . The method of  claim 23 , wherein at least one of said first waveform portions and said second waveform portions has a duration defined by the shorter of a time or a number of detected events. 
     
     
         33 . A Method of short circuit welding, comprising:
 providing a welding current waveform to at least one workpiece to be welded, where said welding current waveform comprises a plurality of welding cycles and each of said welding cycles comprises at least a short circuit transfer portion and a plasma arc melting portion;   controlling said welding current waveform such that said welding current waveform comprises a plurality of first waveform portions and a plurality of second waveform portions; and   switching between said first and second polarities when a short circuit event is detected during welding,   wherein each of said first and second waveform portions of said welding current waveform comprises a plurality of said welding cycles,   wherein all of the current during said first portions has a first polarity, and all of the current during said second portions has a second polarity, which is opposite of said first polarity, and   wherein said switching between said first and second polarities occurs before said short circuit event is cleared.   
     
     
         34 . The method of  claim 33 , wherein at least one of said plurality of first waveform portions and said plurality of second waveform portions has a duration defined by a number of detected events, where said detected events are events occurring during welding cycles. 
     
     
         35 . The method of  claim 34 , wherein said detected events are either of a short circuit event or a peak current event occurring during each of said welding cycles. 
     
     
         36 . The method of  claim 34 , wherein said duration is at least 5 of said detected events. 
     
     
         37 . The method of  claim 34 , wherein said duration is in the range of 5 to 40 of said detected events. 
     
     
         38 . The method of  claim 33 , wherein said first waveform portions have a first duration and said second waveform portions have a second duration, and said first duration is different from said second duration. 
     
     
         39 . The method of  claim 33 , wherein said first waveform portions have a first duration and said second waveform portions have a second duration, and at least one of said first and second durations is up to 1 second. 
     
     
         40 . The method of  claim 33 , wherein said first waveform portions have a first duration and said second waveform portions have a second duration, and at least one of said first and second durations is in the range of 300 μs to 600 ms. 
     
     
         41 . The method of  claim 34 , wherein the other of said at least one of said plurality of first waveform portions and said plurality of second waveform portions has a duration defined by time. 
     
     
         42 . The method of  claim 41 , wherein said duration defined by said detected events is in the range of 5 to 40 detected events, and said duration defined by time is in the range of 100 to 600 ms. 
     
     
         43 . The method of  claim 33 , wherein at least one of said first waveform portions and said second waveform portions has a duration defined by the shorter of a time or a number of detected events. 
     
     
         44 . A method of short arc welding:
 providing a welding current waveform to at least one workpiece to be welded, where said welding current waveform comprises a plurality of welding cycles and each of said welding cycles comprises at least an arc portion and a shorting portion which is initiated after the detection of a short circuit between an electrode and said at least one workpiece;   controlling said welding current waveform such that said welding current waveform comprises a plurality of first waveform portions and a plurality of second waveform portions; and   switching between said first and second polarities only when a short circuit event is detected during welding,   wherein each of said first and second waveform portions of said welding current waveform comprises a plurality of said welding cycles,   wherein all of the current during said first portions has a first polarity, and all of the current during said second portions has a second polarity, which is opposite of said first polarity, and   wherein said switching between said first and second polarities occurs before said short circuit event is cleared by the shorting portion of the cycle which immediately follows the short circuit detection event.