Abstract:
A consumable electrode arc-welding machine comprising an arc resistance calculating part that calculates an arc resistance from a welding current and a welding voltage to develop an arc resistance signal, wherein the welding current and welding voltage are controlled by a short-circuit waveform control signal and an arc waveform control signal that vary in accordance with the arc resistance signal. In this way, the spatter control and the arc stability can be achieved. During an arc period, if the arc resistance signal exhibits a level greater than a predetermined level for a predetermined period, a constant current control signal is developed to perform a constant current control of the welding current by use of a predetermined current value that is higher than the current value developed during the development of the arc waveform control signal, thereby preventing the arc from going off.

Description:
[0001]    This application is a U.S. National Phase application of PCT International Application PCT/JP2006/304946 filed Mar. 14, 2006. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a consumable electrode type welding machine which makes an arc discharge between a welding wire (hereinafter referred to as wire) and a base metal of welding (base metal) for welding. 
       BACKGROUND ART 
       [0003]    It has been generally known that the conventional consumable electrode type welding machine, which makes use of an arc between wire and base metal, controls the voltage during arc period while it controls the current during short-circuit period. This type of technology has been disclosed in, for example, Japanese Patent Unexamined Publication No. H10-109163. 
         [0004]      FIG. 5  shows a schematic diagram of the conventional consumable electrode type arc welding machine. In the conventional consumable electrode type arc welding machine shown in  FIG. 5 , output of incoming power of three-phase AC  11  is rectified by diode rectifier circuit  12  into DC power. And then, the DC current is converted by switching element  13  into high frequency electricity of some several tens of thousand to several hundreds kHz, and transformer  14  lowers voltage thereof. The high frequency output of lowered voltage is rectified by diode rectifier circuit  15 . The rectified output is supplied to wire  18  through reactor  16  and torch  17 . Wire  18  is thus melted and welded to base metal  19 . 
         [0005]    Specifically, the consumable electrode type arc welding machine includes welding voltage detection circuit  5  which detects the welding voltage and outputs welding voltage detection signal S 1 , and welding current detection circuit  6  which detects the welding current via current detector  20  and outputs welding current detection signal S 2 . The welding machine also includes short-circuit arc judgment circuit  7  which accepts welding voltage detection signal S 1  and judges whether it is in a short-circuit state or in an arc state, and outputs short-circuit arc judgment signal S 3 . The welding machine further includes short-circuit waveform control circuit  108  for outputting short-circuit waveform control signal S 4  based on welding current detection signal S 2  inputted thereto, and arc waveform control circuit  109  for outputting arc waveform control signal S 5  for an arc period based on welding voltage detection signal S 1  inputted thereto. Still further, it includes also switching circuit  10  which selects arc waveform control signal S 5  for an arc period and short-circuit waveform control signal S 4  for a short-circuit period in accordance with short-circuit arc judgment signal S 3 , and outputs a selected control signal. Switching circuit  10  delivers short-circuit waveform control signal S 4  to switching element  13  in a short-circuit period, whereas when it is released from the short-circuit period and entered into an arc period it delivers arc waveform control signal S 5  to switching element  13 . 
         [0006]    It is a broadly practiced technology among the conventional consumable electrode type welding machines to control the voltage in an arc period and control the current in a short-circuit period, under certain given welding conditions. Especially during an arc period, the welding machine relies mostly on a self control of arc-length. In such a conventional method of welding control, however, a state that is uncontrollable by means of the voltage control in arc period, or the current control in short-circuit period, would occur; such a state can be caused for example by the emergence of a micro short-circuit during welding, fattening of drip at the tip-end of wire during arc period, etc. Thus, the conventional method of welding control can not totally prevent the occurrence of such uncertainty factors as arc instability, sputtering phenomenon, arc break, etc. 
       SUMMARY OF THE INVENTION 
       [0007]    A consumable electrode type arc welding machine of the present invention supplies wire for generating an arc between the wire and base metal of welding. The welding machine includes a welding voltage detection circuit for detecting a welding voltage and outputting a welding voltage detection signal, a welding current detection circuit for detecting a welding current and outputting a welding current detection signal, a short-circuit arc judgment circuit for judging whether it is in a short-circuit state or in an arc state and outputting a short-circuit arc judgment signal after accepting the welding voltage detection signal, a short-circuit waveform control circuit for outputting a short-circuit waveform control signal after accepting the welding current detection signal, an arc waveform control circuit for outputting an arc waveform control signal for arc period after accepting the welding voltage detection signal, and a switching circuit for selectively outputting the arc waveform control signal in an arc period or the short-circuit waveform control signal in a short-circuit period in accordance with the short-circuit arc judgment signal after accepting the short-circuit waveform control signal and the arc waveform control signal. The welding power is controlled by an output from the switching circuit. The welding machine further includes an arc resistance calculator for calculating and outputting an arc resistance signal after accepting the welding voltage detection signal and the welding current detection signal. The arc resistance signal is inputted to at least either one of the short-circuit waveform control circuit and the arc waveform control circuit, for controlling the welding power. 
         [0008]    Another consumable electrode type arc welding machine in the present invention supplies wire for generating an arc between the wire and base metal of welding. The welding machine includes a welding voltage detection circuit for detecting the welding voltage and outputting a welding voltage detection signal, a welding current detection circuit for detecting a welding current and outputting a welding current detection signal, a short-circuit arc judgment circuit for judging whether it is in a short-circuit state or in an arc state and outputting a short-circuit arc judgment signal after accepting the welding voltage detection signal, a short-circuit waveform control circuit for outputting a short-circuit waveform control signal after accepting the welding current detection signal, an arc waveform control circuit for outputting an arc waveform control signal in an arc period after accepting the welding voltage detection signal, and a first switching circuit for selectively outputting the arc waveform control signal in an arc period or the short-circuit waveform control signal in a short-circuit period in accordance with the short-circuit arc judgment signal after accepting the short-circuit waveform control signal and the arc waveform control signal. The output from first switching circuit controls the welding power. The welding machine further includes an arc resistance calculator for calculating an arc resistance signal after accepting the welding voltage detection signal and the welding current detection signal and outputting the calculated signal, a constant-current control period setting unit for accepting the arc resistance signal and outputting a constant-current control period signal which indicates a period of constant-current control when the arc resistance signal continuously shows a certain value that is higher than a certain specific value, a constant-current circuit for accepting the welding current detection signal and outputting, based on the inputted detection signal, a constant-current signal for controlling the current to be staying constant at a certain specific value, and a second switching circuit for selecting a constant-current signal in a constant-current control period or an output signal from the first switching circuit in a period other than the constant-current control period in accordance with the constant-current control period signal and outputting a selected signal. In the period other than the constant-current control period, the arc resistance signal is delivered to at least one of the short-circuit waveform control circuit and the arc waveform control circuit, and the welding power is controlled based on the output from second switching circuit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a block diagram showing the outline structure of a consumable electrode type arc welding machine in accordance with a first exemplary embodiment of the present invention. 
           [0010]      FIG. 2  is a relationship chart of welding voltage, welding current and arc resistance signal in the first through third embodiments of the present invention. 
           [0011]      FIG. 3  is a block diagram showing the outline structure of a consumable electrode type arc welding machine in accordance with a second exemplary embodiment of the present invention. 
           [0012]      FIG. 4  is a block diagram showing the outline structure of a consumable electrode type arc welding machine in accordance with a third exemplary embodiment of the present invention. 
           [0013]      FIG. 5  is a block diagram showing the outline structure of a conventional consumable electrode type arc welding machine. 
       
    
    
     REFERENCE MARKS IN THE DRAWINGS 
       [0000]    
       
           1  Arc Resistance Calculator 
           2  Constant-Current Control Circuit 
           3  Constant-Current Control Period Setting Unit 
           4  Second Switching Circuit 
           5  Welding Voltage Detection Circuit 
           6  Welding Current Detection Circuit 
           7  Short-Circuit Arc Judgment Circuit 
           8 ,  108  Short-Circuit Waveform Control Circuit 
           9 ,  109  Arc Waveform Control Circuit 
           10  Switching Circuit (First Switching Circuit) 
           11  Incoming power of three-phase AC 
           12  Diode Rectifier Circuit 
           13  Switching Element 
           14  Transformer 
           15  Diode Rectifier Circuit 
           16  Reactor 
           17  Torch 
           18  Wire 
           19  Base metal of welding 
           20  Current Detector 
           21  Short-Circuit Period 
           22  Arc Period 
           23  Welding Voltage 
           24  Welding Current 
           25  Arc Resistance Signal 
         S 1  Welding Voltage Detection Signal 
         S 2  Welding Current Detection Signal 
         S 3  Short-Circuit Arc Judgment Signal 
         S 4 , S 7  Short-Circuit Waveform Control Signal 
         S 5 , S 9  Arc Waveform Control Signal 
         S 6  Arc Resistance Signal 
         S 8 , S 12  Switching Element Control Signal 
         S 10  Constant-Current Control Period Signal 
         S 11  Constant-Current Signal 
       
     
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     First Exemplary Embodiment 
       [0048]    A consumable electrode type arc welding machine in accordance with a first exemplary embodiment of the present invention is described referring to  FIGS. 1 and 2 . Those constituent portions identical to those of the conventional consumable electrode type arc welding machine described in the above referring to  FIG. 5  are designated by using the same symbols, and detailed description of these portions are eliminated. The main point of difference of the arc welding machine in the first embodiment as compared with the conventional counterpart is in short-circuit waveform control circuit  8 , and that arc resistance calculator  1 , which will be described later, is added. 
         [0049]    In  FIG. 1 , welding voltage detection circuit  5  detects the welding voltage, and outputs welding voltage detection signal S 1 . Welding current detection circuit  6  detects the welding current, and outputs welding current detection signal S 2 . Arc resistance calculator  1  treats welding voltage detection signal S 1  and welding current detection signal S 2  as input signals. Based on these input signals, calculator  1  calculates an arc resistance value (for example, it calculates an arc resistance value by dividing welding voltage detection signal S 1  with welding current detection signal S 2 ). Arc resistance calculator  1  outputs the result of calculation as arc resistance signal S 6 , to short-circuit waveform control circuit  8 . Short-circuit arc judgment circuit  7  accepts welding voltage detection signal S 1  as an input signal, judges whether it is in a short-circuit state or in an arc state based on the input signal, and conveys short-circuit arc judgment signal S 3  to switching circuit  10 . Short-circuit waveform control circuit  8  accepts arc resistance signal S 6  and welding current detection signal S 2  as input signals, outputs short-circuit waveform control signal S 7  in accordance with these input signals, and delivers the output signal to switching circuit  10 . In short-circuit period, the short-circuit current waveform is controlled by means of changing the tilting curve of short-circuit current waveform due to short-circuit waveform control signal S 7 . Arc waveform control circuit  109  accepts welding voltage detection signal S 1  as an input signal, outputs arc waveform control signal S 5  based on the input signal, and delivers it to switching circuit  10 . Switching circuit  10  accepts short-circuit arc judgment signal S 3 , arc waveform control signal S 5  and short-circuit waveform control signal S 7  as input signals. Switching circuit  10  selects short-circuit waveform control signal S 7  when short-circuit arc judgment signal S 3  indicates a short-circuit state, or arc waveform control signal S 5  when an arc state is indicated, and outputs switching element control signal S 8  to switching element  13 . 
         [0050]      FIG. 2  shows an exemplary relationship among welding current  24 , welding voltage  23  and arc resistance signal  25  in the consuming electrode type arc welding machine in the first embodiment. As shown in  FIG. 2 , during short-circuit period  21 , welding voltage  23  stays at a low level, while welding current  24  increases at a certain inclination in accordance with short-circuit waveform control signal S 7 . In the conventional consuming electrode type arc welding machine shown in  FIG. 5 , the welding current in short-circuit state is controlled in accordance with short-circuit waveform control signal S 4 , but the welding voltage in that state is left out of control. However, the tip-end shape of wire  18  and the state of contact made between base metal  19  and wire  18  are unstable, thus the welding voltage always changes. When the welding voltage becomes too high, it sometimes causes a sputtering phenomenon. 
         [0051]    The consumable electrode type arc welding machine in the present first embodiment is provided with arc resistance calculator  1  as shown in  FIG. 1 . Arc resistance calculator  1  calculates arc resistance signal S 6  based on welding voltage detection signal S 1  and welding current detection signal S 2 , and outputs the results of calculation. If welding voltage  23  changes during short-circuit period  21 , it outputs arc resistance signal S 6  according to the changing to short-circuit waveform control circuit  8 . Namely, it outputs arc resistance signal S 6  in which the welding voltage is also taken into consideration, besides the welding current. Short-circuit waveform control circuit  8  accepts arc resistance signal S 6  as well as welding current detection signal S 2 ; thereby, it outputs short-circuit waveform control signal S 7  which corresponds to the change in welding voltage in addition to the change in welding current. Switching circuit  10  accepts short-circuit waveform control signal S 7 , and outputs switching element control signal S 8  based on the input signal. Switching element control signal S 8  is input to switching element  13  to control the welding power. Short-circuit waveform control circuit  8  can be formed of, for example, an arithmetic circuit which processes adding welding current detection signal S 2  and arc resistance signal S 6 . Arc resistance signal S 6  reflects changes in the tip-end shape of the wire, state of contact between base metal  19  and wire  18  during short-circuit period  21 , as well as change in the arc resistance value due to droplet transfer or the like. In a case when the arc resistance value becomes too-high causing a too-high welding voltage, the welding voltage is lowered to prevent sputtering phenomenon. Or, when the arc resistance value happened to turn out to be too-small causing a too-low welding voltage, the welding voltage is raised and the short-circuit period is shortened, which helps shifting to arc period earlier. Thus it can prevent possible troubles, such as buckling of the wire. As described in the above, the consumable electrode type arc welding machine in accordance with the present first embodiment can control the welding power properly. 
       Second Exemplary Embodiment 
       [0052]      FIG. 3  is a block diagram showing the outline structure of a consumable electrode type arc welding machine in accordance with a second exemplary embodiment of the present invention. In  FIG. 3 , those portions having identical structure as those in the first embodiment are identified by designating with the same marks, and their detailed descriptions are eliminated. The point of difference as compared with the first embodiment is in short-circuit waveform control circuit  108  and arc waveform control circuit  9 , and that the output of arc resistance calculator  1  is delivered to arc waveform control circuit  9 , instead of short-circuit waveform control circuit  108 . 
         [0053]    In  FIG. 3 , arc resistance calculator  1  accepts welding voltage detection signal S 1  from welding voltage detection circuit  5  and welding current detection signal S 2  from welding current detection circuit  6  as input signals. Arc resistance calculator  1  calculates an arc resistance value from these input signals, and delivers the result of calculation as arc resistance signal S 6  to arc waveform control circuit  9 . Arc waveform control circuit  9  accepts arc resistance signal S 6  and welding voltage detection signal S 1  as input signals, outputs arc waveform control signal S 9  based on these input signals, and delivers the signal to switching circuit  10 . Arc waveform control signal S 9  outputs a control signal for changing the tilt of welding voltage waveform in an arc period. Thus it can control the welding voltage waveform in arc period. Short-circuit waveform control circuit  108  accepts welding current detection signal S 2  as an input signal, and outputs short-circuit waveform control signal S 4  to switching circuit  10 . Switching circuit  10  accepts short-circuit arc judgment signal S 3 , arc waveform control signal S 9  and short-circuit waveform control signal S 4  as input signals. When short-circuit arc judgment signal S 3  indicates a short-circuit state, switching circuit  10  selects short-circuit waveform control signal S 4 , or selects arc waveform control signal S 9  when signal S 3  indicates an arc state, and outputs a selected signal to switching element  13 . 
         [0054]    During arc period  22 , welding voltage  23  goes lower at a certain inclination, as shown in  FIG. 2 , in accordance with arc waveform control signal S 9 . Welding current  24  is also decreased. In the welding control performed by the conventional consumable electrode type arc welding machine shown in  FIG. 5 , the welding voltage is controlled on the basis of arc waveform control signal S 5 , but the welding current is left to be out of control. However, the welding current is always fluctuating due to conditions of base metal  19  and other factors. The instability of arcing can not help ill-affecting the appearance of welding beads. So, it is always requested to have a stable arc discharge. Fluctuation of welding current at the end of arc period may cause an arc break, which may well lead to a defect of welding. 
         [0055]    On the other hand, the consumable electrode type arc welding machine in accordance with the present second embodiment is provided with arc resistance calculator  1 , which calculates arc resistance signal S 6  based on welding voltage detection signal S 1  and welding current detection signal S 2 , and outputs it. When welding current  24  changes during arc period  22 , it outputs arc resistance signal S 6  according to the change in welding current  24  to arc waveform control circuit  9 . Namely, arc resistance signal S 6  taking the welding current into consideration as well as the welding voltage is output. Receiving arc resistance signal S 6  in addition to welding voltage detection signal S 1 , arc waveform control circuit  9  outputs arc waveform control signal S 9  reflecting the change in the welding current. The output controls the welding power via switching circuit  10  and switching element  13 . In this way, the instability of arcing can be prevented for an appropriate control of welding. If, for example, arc current goes lower at the end of arc period  22 , and the arc resistance value is increased to exceed a certain specific level, arc waveform control circuit  9  outputs arc waveform control signal S 9  based on arc resistance signal S 6  at that moment. Based on the output, switching element  13  controls the welding power with a certain specific constant-current value that is higher than that output at the normal constant-voltage control in arc period. Thereby, an arc break can be prevented. 
         [0056]    Although the above descriptions in the first and the second embodiments have been based on an exemplary case where an output from arc resistance calculator  1 , viz. arc resistance signal S 6 , is delivered to either one of short-circuit waveform control circuit  8  and arc waveform control circuit  9 , the signal may of course be delivered to both of the short-circuit waveform control circuit and the arc waveform control circuit. 
         [0057]    Besides the above-described control structure, other configurations can be considered; namely, instead of providing an independent arc resistance calculator  1 , inputting welding voltage detection signal S 1  to short-circuit waveform control circuit  8  in addition to welding current detection signal S 2 , or inputting welding current detection signal S 2  besides welding voltage detection signal S 1  to arc waveform control circuit  9 . These configurations, however, make it necessary to provide a circuit that is equivalent to arc resistance calculator  1  in short-circuit waveform control circuit  8  and arc waveform control circuit  9 , respectively. So, it seems advantageous in terms of the economy and the space to provide an independent arc resistance calculator  1 , like the configuration in the first and the second embodiments above, and deliver the output S 6  to short-circuit waveform control circuit  8  and arc waveform control circuit  9 . 
       Third Exemplary Embodiment 
       [0058]    Those constituent portions of the present embodiment having identical structure as those in the first and the second embodiments are designated with the same marks, and the detailed description of such portions are eliminated. The main point of difference from the first and the second embodiments is that the present embodiment is further provided with constant-current control circuit  2 , constant-current control period setting unit  3  and second switching circuit  4 ; aiming to prevent an arc break by introducing a constant-current control when the welding current dropped in an arc period. Description on these portions will come later. 
         [0059]    In  FIG. 4 , arc resistance calculator  1  calculates arc resistance value from welding voltage detection signal S 1  and welding current detection signal S 2 , and outputs the result of calculation result as arc resistance signal S 6 , to constant-current control period setting unit  3 , short-circuit waveform control circuit  8  and arc waveform control circuit  9 . Short-circuit waveform control circuit  8  outputs, responding to arc resistance signal S 6  and welding current detection signal S 2 , short-circuit waveform control signal S 7  to first switching circuit  10  for controlling the welding current waveform in a short-circuit period. Short-circuit waveform control signal S 7  is a control signal which can control, for example, an inclination of welding current waveform in the short-circuit period. Arc waveform control circuit  9  outputs, responding to arc resistance signal S 6  and welding voltage detection signal S 1 , arc waveform control signal S 9  to first switching circuit  10  for controlling the welding voltage waveform in the arc period. Arc waveform control signal S 9  is a control signal which can change, for example, an inclination of welding voltage waveform in an arc period. First switching circuit  10  accepts short-circuit arc judgment signal S 3 , short-circuit waveform control signal S 7  and arc waveform control signal S 9  as input signals. First switching circuit  10  selects short-circuit waveform control signal S 7  when short-circuit arc judgment signal S 3  a short-circuit state, or arc waveform control signal S 9  when signal S 3  indicates an arc state, and outputs switching element control signal S 8  to second switching circuit  4 . 
         [0060]    Constant-current control period setting unit  3  accepts arc resistance signal S 6  and short-circuit arc judgment signal S 3  and outputs constant-current control period signal S 10  to second switching circuit  4 . Constant-current control circuit  2  outputs constant-current signal S 11  to second switching circuit  4  based on welding current detection signal S 2 . Second switching circuit  4  selects switching element control signal S 8  or constant-current signal S 11  in accordance with constant-current control period signal S 10 , and outputs the selected signal as switching element control signal S 12  to switching element  13 . Second switching circuit  4  selects constant-current signal S 11  when constant-current control period signal S 10  indicates that it is in a constant-current control period, or switching element control signal S 8  in a period other than the constant-current control period. Constant-current control period signal S 10  exhibits a constant-current control period if arc resistance signal S 6  continued showing a certain value that is higher than a certain specific level for a certain length of time in arc period  22 . 
         [0061]    Those portions identical to those in  FIG. 1  or  FIG. 3  are designated using the same symbols, and description on which portions are eliminated. 
         [0062]      FIG. 2  shows an exemplary relationship among waveforms of welding current  24 , welding voltage  23  and arc resistance signal  25  of a consuming electrode type arc welding machine in accordance with the present third embodiment. 
         [0063]    As shown in  FIG. 2 , during short-circuit period  21 , welding voltage  23  goes to a low level, while welding current  24  increases at a certain inclination in accordance with short-circuit waveform control signal S 7 . If welding voltage  23  is changed in short-circuit period  21 , short-circuit waveform control circuit  8  outputs short-circuit waveform control signal S 7  in accordance with the change, after accepting arc resistance signal S 6  in accordance with the change together with welding current detection signal S 2 . Since constant-current control period setting unit  3  doesn&#39;t output constant-current control period signal S 10  in short-circuit period, second switching circuit  4  selects switching element control signal S 8 , which is the output from switching circuit  10 . Therefore, short-circuit waveform control signal S 7  is delivered to switching element  13  via switching circuit  10  and second switching circuit  4 . Thus, it helps implementing an appropriate control of welding, in which a sputtering phenomenon due to an over voltage and buckling of wire caused due to a too-low voltage are eliminated. 
         [0064]    During arc period  22 , welding voltage  23  goes lower at a certain inclination in accordance with arc waveform control signal S 9 , as shown in  FIG. 2 . Welding current  24  also decreases. By inputting arc resistance signal S 6  according to the change of welding current  24 , to arc waveform control circuit  9 , arc waveform control signal S 9  according to the change is output. In this case, since constant-current control period setting unit  3  doesn&#39;t output constant-current control period signal S 10 , second switching circuit  4  selects the output from switching circuit  10 , viz. switching element control signal S 8 . Therefore, arc waveform control signal S 9  is delivered to switching element  13  via switching circuit  10  and second switching circuit  4 . In this way, instability of the arc is prevented and an appropriate control can be achieved as described in the second embodiment of the present invention. 
         [0065]    Constant-current control period setting unit  3  accepts arc resistance signal S 6  and short-circuit arc judgment signal S 3 . If arc resistance signal S 6  continues exhibiting a value that is higher than a certain specific value for a certain time in arc period  22 , for example, unit  3  outputs constant-current control period signal S 10  to second switching circuit  4  indicating that it is in a constant-current control period. Upon receiving constant-current control period signal S 10 , second switching circuit  4  selects constant-current signal S 11  and delivers the signal to switching element  13  as switching element control signal S 12 . In this way, constant-current signal S 11  is delivered to switching element  13 , thus welding current  24  is controlled to be a constant-current. The constant-current control of welding current  24  is performed with a certain specific current value that is greater than the welding current value output at the moment when arc waveform control signal S 9  is output. Therefore, if welding current  24  goes smaller at a point close to the end of arc period  22 , or arc resistance signal S 6  exhibits a value that is higher than a certain specific value for a certain time, for example, the constant-current control of welding current  24  is conducted with a certain specific current value that is greater than the welding current value output at the moment when arc waveform control signal S 9  is output. Namely, since the process changed to short-circuit state while welding current  24  is kept in a substantial current value, an arc break can be avoided to achieve a stable arc welding operation. 
         [0066]    Although the present third embodiment is described that arc resistance signal S 6  is delivered to both short-circuit waveform control circuit  8  and arc waveform control circuit  9 , other configuration may of course be contrived in which signal S 6  is delivered to either one of the two circuits. 
       INDUSTRIAL APPLICABILITY 
       [0067]    A consumable electrode type arc welding machine in the present invention offers a stable welding operation, by controlling the welding power based on an arc resistance signal derived from the welding voltage and the welding current. Thus it would bring about a certain advantage in the welding industry which makes use of an arc discharge generated between a welding wire and a base metal of welding.