Tungsten inert gas arc striking device
United States Patent 1191 Hirasawa et a1.  
 [ 1 Apr. 8, 1975&#39; 1 1 TUNGSTENJNERT GAS ARC STRIKING DEVICE [75] Inventors: Kazushige ll-lirasawa, Toyonaka;  
 Takeshi Oku, Kawanishi; Yoshimitsu Matsumoto, Toyonaka, all of Japan [73] Assignee: Matsushita Electric Industrial Co.,  
 Ltd., Osaka, Japan [22] Filed: Feb. 14, 1973 [2]] Appl. N0.: 332,311  
 [30] Foreign Application Priority Data Nov. 8, 1972 Japan 47-112489 Feb. 18, 1972 Japan... 47-017585 Feb. 18, 1972 Japan 47-017586 Feb. 18, 1972 Japan 47-017587 Feb. 18, 1972 Japan 47-017588 Feb. 18, 1972 Japan 47-017589 Feb. 18, 1972 Japan 47-017590 Feb. 18, 1972 Japan 47-017591 Feb. 18, 1972 Japan 47-017592 152] U.S. Cl 219/131 R; 315/171; 315/172; 315/173 [51] Int. Cl 823k 9/10 [58] Field of Search 219/131, 135, 25, 137; 315/121, 172, 173, 174, 204, 209, 241; 328/146 [56] References Cited UNITED STATES PATENTS 2,235,385 3/1941 Rava 315/171 2,399,415 4/1946 White 315/173 2,659,036 11/1953 Needham et a1 315/171 3,154,719 10/1964 Sommeria 315/171 3,328,637 6/1967 Aldenhoff.... 219/131 R 3,444,431 5/1969 Goldberg 315/171 3,474,258 10/1969 Nagy 1 328/146 3,551,741 12/1970 Tajbl et 81.... 315/209 3,588,465 6/1971 Anderson 219/131 R 3,637,974 1/1972 Tajbl et a1 219/135 3,780,258 12/1973 Iceland et a1. 219/131 R FORElGN PATENTS OR APPLICATIONS 85,988 0/1957 Germany 219/131 F Primary E.\&#39;aminer-J. V. Truhe Assistant Examiner-Clifford C. Shaw Attorney, Agent, or FirmStevens, Davis, Miller &amp; Mosher [57] ABSTRACT A tungsten inert gas are striking device for welding stainless steels and nonferrous metals, e.g., aluminum is provided, in which when striking an are or restriking the arc, the charge stored in a capacitor is momentarily discharged through a discharge switch and a c0upling coil to produce a kick voltage and this kick voltage is then superimposed on a welding current to effect the are striking 0r restriking. Thus, welds of high quality can be produced and the occurrence of radio interferences can also be eliminated.  
 6 Claims, 15 Drawing Figures SMLU 1 OF 7 FIG I PRIOR ART Pmimmn&#39;ams 3,876,855 smear? FIG. 30 PRIOR ART 6 PIRTENTEBAPR 819. 5  
  si-zasrunn 2 1i i L L i.  
  1 TUNGSTEN INERT GAS ARC STRIKING DEVICE The present invention relates to improvements in or relating to tungsten inert gas arc striking devices. More particularly, the present invention relates to a tungsten inert gas are striking device of the type in which when striking or restriking the arc, a discharge switch having first and second electrodes disposed opposite to each other and a discharge starting electrode located near the first and second electrodes is used, and a trigger pulse voltage is applied across either one of the first and second electrodes and the discharge starting electrode to thereby momentarily discharge the charge stored in a capacitor across the first and second electrodes of the discharge switch and through a coil, whereby a kick voltage induced in the coil is superimposed on a welding current circuit to effect the striking or restriking of the arc.  
  The tungsten inert gas arc welding process (TIG arc welding process) is extensively used for welding stainless steels and nonferrous metals such as aluminum. In the TIG arc welding process, an arc is struck or restruck between a base metal and an electrode with no contact therebetween and therefore a high-voltage high-frequency is employed. The high frequency generator for producing such a high-voltage high-frequency is of a so-called spark oscillation type and one form of this type of high frequency generator is shown in FIG. 1. In the figure, numeral 1 designates power supply terminals, 2 a welding power supply terminal, 3 a welding torch terminal. Symbol H designates a high frequency generating portion, T a high frequency transformer, G and G spark gaps&#39;consisting of tungsten electrodes, C an oscillating capacitor, L an oscillating coil, C.C a coupling coil for superimposing a high frequency on a welding current circuit, F a noise suppressing filter. This type of high frequency generator is strong and is thus used extensively, but has the following disadvantages. The generated high frequency includes frequency components ranging over a wide band with the center frequency being in the range 1-3 MHz and consequently, even if the filter is provided between the power source and the device, there occurs the propagation of noise to the power supply line and this noise further results in radiant waves, causing considerable interference in radio equipments, e.g., radio and television receivers and in radio communications as well.  
  It is therefore an object of the present invention to provide a novel method of striking an arc and device therefor which eliminate the foregoing drawbacks of the prior art device of the above-described type, i.e., a novel method and device therefor which eliminate radio interference and ensure welds of high quality.  
  The advantages attributable to the use of the are striking device according to the present invention are summarized as follows:  
  1. Due to the kick voltage superimposing system of this invention, when used for welding aluminum, no failure to strike an arc during a negative going half cycle of the welding current can take place and welds of high quality with a wide cleaning area can be produced, thereby showing considerable advantages over the prior art devices of the spark oscillation type.  
  2. As will be seen from FIG. 13 of the accompanying drawing showing the noise field intensity caused by the use of the arc striking device according tothe present invention and the noise field intensity due to the prior art device of the spark oscillation type, particularly over a frequency band ranging from 1 to 3 MHZ, the noise field density due to the device of the present invention is lower by 45 decibels than that due to the known spark oscillation type device and it is about the same as the ambient noise.  
  3. The welding arc starting characteristic of the arc striking device according to the present invention is excellent as compared with that of the known spark oscillation type device.  
  Many other objects and advantages of the present invention will become apparent from considering the following detailed description in conjunction with the accompanying drawings, in which:  
  FIG. 1 is an electric circuit diagram of a tungsten inert gas are striking device (TIG arc device) of the type known in the art;  
  FIG. 2 is an electric circuit diagram of a TIG arc device according to the present invention;  
  FIG. 3a is a diagram showing the welding current waveform when striking or restriking the arc in the prior art TIG arc device of FIG. 1;  
  FIG. 3b is a diagram showing the welding current waveform when striking or restriking the arc in the TIG arc device according to the present invention;  
  FIG. 4 is a waveform diagram of the rise portion of the welding voltage in the TIG arc device according to the present invention;  
  FIGS. 50 and 5b show welding arc voltage waveforms in the TIG arc device according to the present invention;  
  FIG. 6 is a block diagram of the pulse signal generating circuit employed in the TIG arc device of the present invention;  
  FIG. 7 shows the welding power supply voltage waveform and the trigger pulse voltage waveform for gener ating a kick voltage in the device of the present invention;  
  FIG. 8 shows the welding power supply voltage waveform and the pulse waveform in the device of the present invention;  
  FIG. 9 shows the welding current waveform in the prior art device;  
  FIGS. 10 to 12 are electric circuit diagrams of other different embodiments of the tungsten inert gas arc striking device according to the present invention; and  
  FIG. 13 is a graph showing the noise field intensity characteristic curves of the prior art device and the device of the present invention, respectively.  
  The present invention will now be explained with reference to the accompanying drawings. Referring first to FIG. 2, numeral 2 designates a welding power supply terminal, 3 a welding torch terminal. Symbol C designates a capacitor, E, a DC power source for charging the capacitor C to a high voltage, SW a discharge switch according to the present invention. The discharge switch SW consists of a discharge starting electrode P for operating the discharge switch SW, a first electrode 4 and a second electrode 5, and these electrodes are made of metal, e.g., tungsten. If necessary, an inert gas, e.g., an argon gas is continuously supplied into the discharge switch SW. When a pulse-type trigger voltage indicated at Pu is applied across the discharge starting electrode P and the second electrode 5, a pulse discharge is momentarily caused across the discharge starting electrode P and the second electrode 5 and consequently the gap formed between the first and second electrodes 4 and 5 is conditioned to readily start a discharge. Symbol CC designates a coupling coil for superimposing a kick voltage induced in a coil L on the welding current circuit. The operation of this circuit will now be explained with reference to FIG. 2. If, when striking or restriking the arc, a pulse-type trigger voltage is applied across the discharge starting electrode P and the second electrode 5 in the discharge switch SW, this creates a condition in the gap between the first and second electrodes 4 and 5 which tends to readily start a discharge. Consequently, the charge stored in the capacitor C is discharged momentarily across the gap between the first and second electrodes in the discharge switch SW and through the coil L. As a result, a kick voltage is induced in the coil L and this high-tension kick voltage is then superimposed on the welding current circuit through the coupling coil C.C, thereby effecting the arc strike or are restriking. The high frequency generated in the prior art device of FIG. 1 and the kick voltage generated in the device of this invention&#39;when striking or restriking the welding arc, are shown respectively in FIGS. 3a and 3b in comparison with each other.  
  In FIG. 3, numeral 6 designates the welding current waveform, 7 the welding arc striking time, 8 the welding arc restriking time. Numeral 9 designates the high frequency which is generated at the welding arc striking time 7 and the restriking times 8, and numeral 10 designates the high-tension kick voltage generated at the welding arc striking time 7 and the restriking times 8. As will be seen from FIG. 3, in the prior art device the high frequency 9 is substantially generated continuously, whereas in the device of the present invention the kick voltage 10 is generated only momentarily at the welding arc striking time 7 and the restriking time 8. This results ina considerable decrease in the noise field intensity. In this case, it is to be noted that the phase at which the kick voltage will be generated is very important and has an important bearing on the stability of the welding arc.  
  In other words, a welding arc which ensures welds of high quality can be continuously provided only if the kick voltage is generated across the torch electrode and the base metal to be welded at a properly selected phase when striking or restriking the welding arc. Different methods have been conceived for generating a kick voltage at a suitable phase. FIGS. 4, 6, 7 and 8 illustrate such methods of operation.  
  FIG. 4 relates to a method in which the kick voltage is generated in synchronism with the rise portion of the welding voltage waveform. In the figure, the voltage across the terminals of the welding machine rises as shown by the waveform designated by the numeral 11 after the welding current flow is reduced to zero. Numeral 12 designates the phase at which a trigger pulse voltage Pue is generated at a voltage value e of the rise portion of the welding voltage waveform. 13 designates the phase at which a trigger pulse voltage Pue is generated at a voltage value 2 of the rise portion of the welding voltage waveform. At the point 12 in FIG. 4 where the voltage value of the rise portion of the welding voltage waveform is e, the trigger pulse voltage Pue is generated and applied to the discharge starting electrode P in the discharge switch SW shown in FIG. 2, actuating the discharge switch SW&#39;and. thus inducing a kick voltage. F IG. 5 illustrates the welding arc voltage waveforms resulting from the kick voltages generated by the method of FIG. 4. FIG. 5a shows the voltage waveform of the welding are obtained when the discharge switch SW was actuated by the trigger pulse voltage Pue in FIG. 4, and FIG. 5b shows the voltage waveform of the welding are obtained when the discharge switch SW was actuated by the trigger pulse voltage Pue in FIG. 4.  
  FIG. 6 illustrates in block diagram form another method in which the voltage waveform across the terminals of the welding machine subjected to full-wave rectification is compared with a DC reference voltage so that the kick voltage is generated at that phase near which the rectified voltage waveform across the terminals of the welding machine and the DC reference voltage join. In FIG. 6, numeral 14 designates an AC welding arc voltage waveform, 15 a rectifier circuit in which the voltage waveform across the terminals of the welding machine is subjected to full-wave rectification, 16 a DC reference voltage, 17 a comparison circuit for comparing the rectified voltage waveform across the terminals of the welding machine with the DC reference voltage, 18 a pulse generating circuit.  
  The operation of the arrangement shown in FIG. 6 is as follows: The are voltage waveform 14 across the terminals of the welding machine, is subjected to full-wave rectification through the rectifier circuit 15 and the resultant rectified voltage waveform across the terminals of the welding machine is compared with the DC reference voltage 16 in the comparator circuit 17. As a result, the pulse generating circuit 18 is operated at that phase near which the voltage waveform across the terminals of the welding machine and the DC reference voltage join, producing a trigger pulse voltage 19 which is applied to the discharge starting electrode P of the discharge switch SW in FIG. 2. Consequently, the discharge switch SW is operated thereby inducing a kick voltage.  
  FIG. 7 illustrates another method for generating the kick voltage in synchronization with the welding power supply frequency. In FIG. 7, numeral 20 designates a welding power supply input voltage waveform, and numeral 22 designates a trigger pulse voltage synchronized with the welding power supply frequency and generated at a point 21 which is in advance of the welding power supply input voltage phase by a time T. The pulse 22 synchronized with the welding power supply frequency and generated at the point 21 which is in advance, by time T, of the welding voltage supply input voltage phase, is applied to the discharge starting electrode P of the discharge switch SW in FIG. 2, whereby the discharge switch SW is operated to thereby induce the kick voltage.  
  FIG. 8 illustrates a still further method in which the phase at which the kick voltage will be generated, is selected so that both the positive and negative half cycles of the welding current have practically the same effective current value.  
  When the TIG arc welding process is employed for welding metals, e.g., aluminum or the like using an AC arc, as will be seen from the welding current waveform indicated as 23 in FIG. 9, there is in fact a flow of unbalanced current containing a considerable DC component, giving rise to such inconveniences as an overloading of the welding power supply and an adverse effect on thecleaning action. The method of FIG. 8 is contemplated to overcome these difficulties.  
  In FIG. 8, numeral 23 designates a welding current waveform containing a DC component, 24 negative half cycles of the welding current, 25 positive half cycles of the welding current having the same effective value as that of the negative half cycles 24. Numeral 26 designatesa trigger pulse voltage generated at that phasewhich is so selected that both the positive and negative half cycles of the welding current have practically the same effective value. The trigger pulse voltage 26 generated at the phase selected to provide practically the same effective value for both the positive and negative half cycles of the welding current, is applied to the discharge starting electrode P of the discharge switch SW in FIG. 2 so that the discharge switch SW is operated thus inducing the kick voltage. Upon generation of the kick voltage, an arc is struck or restruck, thereby providing a welding current waveform containing no DC component as indicated by numeral 27 in FIG. 8.  
  As will be seen from the welding current waveform 27 in FIG. 8, there are times when the welding arc is not produced, but the welding arc is extremely stable, is capable of performing high quality welding on aluminum, for example, and eliminates any adverse effect on the welding power supply.  
  While the methods for effecting the production of kick voltage at a properly selected phase have been explained by way of specific arrangements therefor, it should be understood that the present invention is not limited to these methods and specific arrangements.  
  Next, the proper value of a kick voltage used when striking or restriking the welding arc will be explained.  
  When the welding arc is struck, a high kick voltage must be provided to ensure a satisfactory arc strike, whereas when restriking the arc, a satisfactory arc restriking can be accomplished by simply applying a relatively low kick voltage across the torch electrode and the base metal, since the torch electrode and the base metal have been heated to an elevated temperature. When restriking the welding arc, the kick voltage value may be reduced to a relatively low value, if the voltage on the capacitor C in FIG. 2 is decreased following the starting of the&#39;welding arc. This is a great advantage, since the reduction of the capacitor voltage reduces the value of the voltage applied to the discharge switch SW and hence has, for example, a good effect on the life of the first and second electrodes 4 and 5 constituting the discharge switch SW.  
  In this case, however, variation in the value of the kick voltage applied across the welding torch electrode and the base metal electrode or variation in the value of the voltage on the capacitor C in FIG. 2 tends to produce an unstable momentary arc between the respective electrodes constituting the discharge switch SW. This problem has been considered and it is now found that depending on the value of the voltage on the capacitor C there is a certain proper value for the power of trigger pulse voltage Pu which is necessary for starting a discharge in the discharge switch SW. In  
 other words, when the value of the voltage on the capacitor C is high, a lower value for the power of the trigger pulse voltage Pu applied across the second electrode 5 and the discharge starting electrode P in the discharge switch SW may produce a better result, whereas when the value of the voltage on the capacitor C, is low, a higher value for the power of the trigger pulse voltage Pu may produce a better result. Namely,  
 there is an inverse correlation between the two values.  
  In the embodiment shown in FIG. 10, symbol SW designates a switching element for changing the voltage on the capacitor C Ca designates a capacitor for generating the trigger pulse voltage Pu across the second electrode 5 and the&#39;discharge starting electrode P in the discharge switch SW, E a power supply for charging the capacitor C A switching element SW is an element whose internal impedance decreases considerably upon application of an electric pulse thereto and it may consist of a thyristor or the like. Symbol SW designates a switching element for changing the capacity of the capacitor C The operation of the embodiment shown in FIG. 10 will now be explained. When an electric pulse Sg is applied to the switching element SW the internal impedance of the switching element SW, decreases considerably so that the&#39;charge stored in the capacitor C is discharged momentarily through the switching element SW and a coil I.C. Consequently, a trigger pulse voltage is generated at the secondary side terminal of the coil I.C, i.e., across the second electrode 5 and the discharge starting electrode P of the discharge switch SW, causing a momentary discharge therebetween. This creates a condition between the first and second electrodes 4 and 5 so that a discharge may be readily started, whereby the discharge switch SW is actuated.  
  When striking a welding arc, the switching element SW is connected to a high voltage terminal 28, that is, the capacitor C is charged to a high voltage and the contacts of the switching element SW are opened, i.e., the total capacitance of the capacitor C is reduced. In other words, the power value of the trigger pulse voltage Pu is reduced to thereby operate the discharge switch SW. On the other hand, for restriking the welding arc, the switching element SW is connected to a low voltage terminal 29, i.e., the capacitor C, is charged to a low voltage and the contacts of the switching element SW are closed, i.e., the capacitor of the capacitor C is increased. In other words, the discharge switch Sw is operated with the trigger pulse voltage Pu having an increased power value. In this way, the kick voltage is generated to accomplish the striking and restriking of the welding arc. In this embodiment, a very stable arc can be established between the respective electrodes constituting the discharge switch SW and hence quality welds can be obtained.  
  FIG. 11 illustrates another embodiment of the present invention in which the value of the voltage on the capacitor C is varied as a means of varying the power value of trigger pulse voltage Pu. Pu.  
  While, in the embodiments of the invention so far described, the charge stored in the capacitor C has been momentarily discharged through the discharge switch SW and the coil L and a kick voltage thus induced in the coil L has been superimposed on the welding current circuit through the coupling coil CC to effect the welding arc strike or restriking, the present invention is not limited to the use of the discharge switch SW as a switching device for momentarily discharging the charge stored in the capacitor C FIG. 12 illustrates another embodiment of this invention in which the discharge switch SW is replaced by a gas discharge tube having two electrodes disposed in opposite positions and a trigger electrode disposed near the oppose electrodes. The operating principle of this embodiment is identical with the previously described embodiments employing the discharge switch SW. In other words, when an electric pulse Sg is applied to the switching element SW a high-tension trigger pulse voltage is induced between the secondary side terminal of the coil IC and a trigger winding G P and an electrode terminal G thereby momentarily ionizing the gas in the gas discharge tube G As a result, the state is reached where a discharge may be readily started between the electrodes G A and G of the gas discharge tube G and thus the charge stored in the capacitor C is discharged momentarily through the coil L and the gap between the electrodes G A and G of the gas discharge tube G thereby&#39;inducing a kick voltage in the coil L.  
  Further, the use of a thyristor as a switching device for momentarily discharging the charge on the capacitor C may be considered. In fact, however, when the charge stored in the capacitor C is momentarily discharged, the current change rate, i.e., di/dt and the change rate of a voltage applied to the thyristor, i.e., dv/dt tend to assume very high values due to the fact that it is impossible to increase the impedance of the coil L owing to the welding current directly flowing into the coupling coil CC and that the charge on the capacitor C, charged to a high voltage must be discharged momentarily to provide a high kick voltage of several thousand volts when striking a welding arc. Thus, it is impossible to prevent the breaking down of the thyristor. The breaking down of the thyristor may not be prevented even if an external additional circuit consisting principally of a capacitor and resistor is connected to the thyristor. However, it is needless to mention that if, in the future, a new thyristor having excellent characteristics with respect to both di/dt and dv/dt has been developed, it may be used as a switching device for discharging the charge stored in&#39;the capacitor C].  
 What we claim is:  
  1. Apparatus including an alternating current welding power supply for striking and restriking a tungsten inert gas arc to produce an AC welding arc voltage across a pair of welding electrodes comprising a. rectifier means for rectifying said arc voltage,  
 b. comparator means for comparing the rectified arc voltage with a reference voltage,  
 c. trigger pulse generator means coupled to said comparator means for producing a trigger pulse when said rectified arc voltage corresponds to said reference voltage,  
 d. a kick voltage generating circuit including l. a discharge switch having first and second electrodes opposing each other and a discharge starting electrode disposed adjacent said first and second electrodes,  
 2. a capacitor, and  
 3. first and second electromagnetically coupled coils; said first and second discharge switch electrodes, said capacitor and said first coil constituting a closed circuit, and  
 4. means for charging said capacitor;  
 e. means for applying said trigger pulse between said discharge starting electrode and one of said first and second discharge switch electrodes, the charge in said capacitor being discharged through said first and second electrodes of said discharge switch and said first coil to induce a kick voltage across said first coil, and  
 f. means connecting said second coil in series with said welding power supply and said welding electrodes, the kick voltage induced across said first coil being superimposed on the welding power supply voltage through said second coil for striking and restriking said welding arc.  
  2. Apparatus as defined by claim 1 wherein said trigger pulse is applied by said trigger pulse applying means in synchronism with the frequency of said alternating current welding power supply.  
  3. Apparatus as defined by claim 1 wherein the phase of the kick voltage is such that the effective values of the positive half cycles and the negative half cycles of the welding current are substantially equal.  
  4. Apparatus as defined in claim 1, wherein said means for charging said capacitor provides a first charge voltage for striking said arc and a charge voltage of lower magnitude to produce a kick voltage of sufficient magnitude to assure restriking.  
  5. Apparatus as defined by claim 4 wherein said means for applying said trigger pulse between the discharge starting electrode and one of the first and second discharge switch electrodes generate a trigger pulse having a relatively low power level when said discharge switch is actuated to strike a welding arc, said means further generating a trigger pulse having a relatively high power level after said welding arc has been struck to maintain stable operation of said discharge switch.  
 6. Apparatus as defined by claim 1 wherein an inert