JPH0910949A - Plasma arc machining equipment - Google Patents

Abstract

PURPOSE: To provide a plasma arc machining equipment with little noise trouble which is surely arc started by rectifying the pulse-shaped high voltage generated when the current is cut off, and charging the electrostatic capacity of a joined part. CONSTITUTION: A torch provided with a main electrode 4 and a tip electrode 5 is brought close to a work 6, and a starting switch 8 is pressed. A control circuit CL2 transmits the drive signal to an inverter circuit TR1 for starting, and the continuity and cut-off command signal having a prescribed time period and the repeated cycle is fed to a switching circuit TR2. The control circuit CL2 cuts off the continuity command signal to the switching circuit TR2 while the drive signal is added to the inverter circuit TR1 around the time when the current flowing to the series circuit of a primary winding L2(1/2) and the switching circuit TR2 reaches a prescribed value. The positive pulse-shaped high voltage is generated on the negative output terminal side of a secondary rectifying circuit DR2 of the primary winding L2(1/2) of a reactor L2, and induction in a magnetically coupled secondary winding L2(2/2) is caused to charge the electrostatic capacity of a joined part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a plasma arc processing apparatus used for plasma arc welding or cutting.

[0002]

2. Description of the Related Art FIG. 1 is a connection diagram showing an example of a conventional apparatus in the case of using a high DC voltage for starting a plasma arc in the case of plasma arc welding. In FIG. 1, 10
Are welding power sources, 1 to 3 are primary input lines, and 4 are main electrodes, which are held by a welding torch (not shown). Reference numeral 5 is a tip electrode, 6 is a workpiece, that is, a workpiece, 7a is a main electrode side cable, 7b is a workpiece side cable, 7c is a tip electrode side cable, 8 is a start switch, and 9 is an output regulator.
In the welding power source 10, DR1 is a primary rectifier circuit, C1 is a smoothing capacitor, TR1 is an inverter circuit, T1 is an inverter transformer, DR2 is a secondary rectifier circuit, L1 is a reactor, CT1 and CT2 are current detectors, and CL1 is a control circuit. , TR2 is a switching circuit, DR3 is a reverse blocking diode, Tm1 is a main electrode side output terminal, Tm2 is a workpiece side output terminal, and Tm3 is a tip electrode side output terminal. Also, R
Reference numeral 1 is a current limiting resistor for limiting the pilot arc current flowing through the tip electrode 5, and CR1 is a starting switch 8
Is a contact point that is closed from when the main circuit is closed until the main arc for machining is generated.

In FIG. 1, when the start switch 8 is pressed,
The control circuit CL1 drives a gas supply circuit (not shown) in response to the input of the start signal. The gas supply circuit releases the shield gas between the main electrode 4 and the tip electrode 5, and ejects it at high speed from the nozzle portion at the tip of the tip electrode. The control circuit CL1 detects the time when the shield gas is ejected from the nozzle portion at the tip of the tip electrode 5,
1 and the switching circuit TR2 are driven. The inverter circuit TR1 performs a switching operation at a frequency of several tens of kHz and induces a voltage necessary for generating a plasma arc on the secondary side of the inverter transformer T1. This voltage is rectified by the secondary rectifier circuit DR2, supplied to the main electrode side output terminal Tm1 and the workpiece side output terminal Tm2 via the reactor L1 and the reverse blocking diode DR3, and the main electrode 4 and the workpiece 6 are connected. Applied between. Further, the contact CR1 is closed by the command from the control circuit CL1 due to the closing of the start switch 8, and the positive output of the secondary rectifier circuit DR2 is also transmitted to the tip electrode side output terminal Tm3 through the resistor R1 and applied to the tip electrode 5. It The switching circuit TR2 conducts and shuts off, and intermittently supplies a current to the reactor L1 by the output of the secondary rectification circuit DR2. When the switching circuit TR2 tries to cut off from the conducting state, the current of the reactor L1 tends to suddenly change toward zero, but the presence of the reactor L1 prevents the sudden change, that is, the secondary rectification of the reactor L1. Positive to the terminal on the side of circuit DR2,
A negative pulsed high voltage is generated at the reverse blocking diode DR3 side terminal. This pulsed high voltage has a secondary side rectifying circuit DR2, a resistor R1 and a tip electrode side output terminal T on the positive side.
m3 and the tip electrode side cable 7c, the negative side through the reverse blocking diode DR3, the main electrode side output terminal Tm1 and the main electrode side cable 7a, the main electrode 4 and the tip electrode 5
Join between and.

The pulsed high voltage is applied to the main electrode 4
When it is higher than the dielectric breakdown voltage between the chip electrode 5 and
During this time, a spark discharge is generated, a pilot arc is generated by this spark discharge, and a plasma arc discharge for welding is induced by this pilot arc. On the other hand, when the pulse voltage at this time is insufficient to break the insulation between the main electrode 4 and the tip electrode 5, this pulse voltage is applied to the main electrode side cable 7a and the tip electrode side cable 7c. Charge stray capacitance between and. This charging voltage is prevented and maintained by being blocked by the reverse blocking diode DR3 and flowing back to the secondary rectifier circuit DR2. When the plasma arc has not occurred due to the interruption of the previous switching circuit, the control circuit CL1 conducts the switching circuit TR2 again for a certain period of time after a certain period of time, and again interrupts it. The reactor L1 again generates a pulsed high voltage due to the conduction and interruption of the switching circuit again. Since this high voltage has the same polarity as the voltage charged in the stray capacitance between the main electrode side cable 7a and the tip electrode side cable 7c, this voltage is further increased. Even if the insulation between the main electrode 4 and the chip electrode 5 is not destroyed by this result, the switching circuit T
R2 repeats conduction and interruption. As a result, charging of the stray capacitance between the main electrode side cable 7a and the tip electrode side cable 7c progresses, and finally the insulation between the main electrode 4 and the tip electrode 5 is destroyed, causing spark discharge. However, this will induce a pilot arc.

[0005]

In the above-mentioned conventional device, the reverse blocking diode DR3 has the main electrode side cable 7
The charge stored in the stray capacitance between the a and the chip electrode side cable 7c is blocked to prevent it from flowing back to the secondary rectifier circuit DR2, but before the reverse blocking operation starts, the reverse blocking diode DR3 It is necessary to charge the electrostatic capacitance at the junction of the above with the electric charge charged in the floating capacitance between the main electrode side cable 7a and the tip electrode side cable 7c. However, since the welding current is generally large, the electrostatic capacitance at the junction of the reverse blocking diode DR3 is large on the cable 7 on the main electrode side.
Far from being negligible to the stray capacitance between a and the tip electrode side cable 7c, the capacitance at the junction of the reverse blocking diode DR3 is the stray capacitance between the main electrode side cable 7a and the tip electrode side cable 7c. It may become larger. Similarly, the secondary rectifier circuit DR2 also has a large capacitance at the junction. For example, the secondary rectifier circuit D
Each capacitance at the junction of R2 and reverse blocking diode DR3 is 5,000 to 20,000 pF, whereas the stray capacitance of the cable is at most 100 to 250.
It is about pF.

Therefore, when the pulse voltage of the reactor L1 generated when the switching circuit TR2 is cut off disappears, the stray capacitance between the main electrode side cable 7a and the tip electrode side cable 7c is charged through the reactor L1. The electric charge is supplied to the series circuit of the electrostatic capacities of the respective junctions of the secondary rectifier circuit DR2 and the reverse blocking diode DR3 to charge them. Here, assuming that the capacitance of the secondary rectifier circuit DR2 is C2, the capacitance of the reverse blocking diode DR3 is C3, and the stray capacitance between the cables is Cs, the switching circuit TR2 cuts off the pulse generated by the reactor L1. Assuming that the voltage Vcs charged in the stray capacitance between the cables by the constant voltage charges the electrostatic capacitance of each junction when the pulse voltage disappears, it is assumed that no charge is consumed in the middle. Since the sum of the charges at the time point is equal, Cs.Vcs = (Cj + Cs) .Vs However, since Cj = C2.C3 / (C2 + C3), Vs = {Cs / (Cj + Cs)}. Vcs. As mentioned above, C2 and C3 are Cs 2
If it is about 0 to 200 times, Cj is also C2 and C
Since it is about 10 to 100 times that of 3, Vs = (1/11) Vcs to (1/101) Vcs, and Vs is greatly reduced from the initial voltage Vcs. Moreover, the electric charge charged at these junctions is discharged when the switching circuit TR2 is turned on next time. For this reason, in order to break the insulation between the main electrode 4 and the tip electrode 5, the switching circuit TR2 requires a very large number of conduction / interruption operations, or the main electrode 4
The voltage for breaking the insulation between the chip electrode 5 and the chip electrode 5 will not be reached. Further, the repeated operation of the switching circuit TR2 diminishes the noise reduction effect of this system. This tendency becomes more remarkable as the cable becomes shorter, and changes greatly depending on the size of the stray capacitance between the cables.

[0007]

The present invention effectively utilizes the capacitance of the junction portion of the reverse blocking diode, which has been disadvantageous in the prior art, in order to solve the problems of the above-mentioned conventional device. There is an auxiliary reactor having primary and secondary windings, and a switching circuit for forcibly flowing a DC current in the primary winding of the auxiliary reactor repeatedly at a predetermined time width and interval when the arc is started. Provide the secondary winding of the auxiliary reactor in series with the auxiliary rectifier circuit that has a polarity that is in the forward direction with respect to the voltage generated in the secondary winding when the switching circuit is cut off, and has the same polarity as the output polarity of the DC power supply. It is connected between the main electrode side output terminal and the tip electrode side output terminal or the work piece side output terminal, and is connected in parallel to the series circuit consisting of the reverse blocking diode, the auxiliary rectifier circuit and the secondary winding of the auxiliary reactor. As a structure in which a capacitor is connected, the current flowing in the primary winding of this auxiliary reactor is interrupted, and the pulsed high voltage generated when the current is cut off is rectified through the secondary winding of the reactor and this capacitor and reverse Applying reverse polarity to the blocking diode to charge the junction capacitance,
A stable direct high voltage is applied between the main electrode and the tip electrode so as to obtain a stable pilot arc start with low noise.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 2 is a connection diagram showing an embodiment of the present invention. In FIG. 2, L2 is an auxiliary reactor, and the primary winding L2
(1/2) and the secondary winding L2 (2/2). The switching circuit TR2 is the primary winding L of the auxiliary reactor L2.
A switching circuit for short-circuiting the output of the secondary rectifier circuit DR2 via 2 (1/2) and forcibly flowing a direct current to the primary winding L2 (1/2) of the auxiliary reactor L2. A self-extinguishing type switching element such as a switching transistor or a gate turn-off thyristor (GTO), a thyristor provided with an appropriate commutation circuit, or a high withstand voltage mechanical switch such as a vacuum switch can be used. DR4 is the secondary winding L2 of the auxiliary reactor L2 (2 /
2) is an auxiliary rectifier circuit that is connected in series with the secondary winding L of the reactor L2 by shutting off the switching circuit TR2.
It is connected in a forward polarity with respect to the voltage generated at 2 (2/2). R1 is a pilot arc current limiting resistor, R2 is a discharge resistor connected between the main electrode side output terminal Tm1 and the tip electrode side output terminal Tm3, and CL2.
Is a control circuit, which controls the switching circuit TR2 together with the inverter circuit TR1. C2 is a capacitor, which is connected between the connection point of the reactor L1 and the reverse blocking diode DR3 and the auxiliary rectification circuit DR4, and is connected to the auxiliary rectification circuit DR4 and the secondary winding L2 (2 /
2) and the reverse blocking diode DR3 are connected in parallel to a series circuit. In the figure, the other parts and assemblies having the same functions as those of the conventional device of FIG.

In FIG. 2, at the start of welding, an operator puts a torch having a main electrode 4 and a tip electrode 5 on a workpiece 5.
And press the start switch 8. The control circuit CL2 receives the start signal from the start switch 8 and sends a drive signal to the inverter circuit TR1 to start the drive signal, and also supplies the switching circuit TR2 with a conduction / cutoff command signal having a constant time width and a repeating cycle. . Inverter circuit T
When R1 is started, a voltage of several tens of kHz is applied to the primary side of the inverter transformer T1 and converted to a voltage value necessary for plasma arc welding on the secondary side, and the secondary rectifier circuit DR2
Is converted into direct current by and is added to the series connection circuit of the primary winding L2 (1/2) of the auxiliary reactor L2 and the switching circuit TR2. When the switching circuit TR2 is turned on, the output of the secondary rectifier circuit DR2 is the primary winding L2 (1/2).
Therefore, the current flowing through the series circuit of the primary winding L2 (1/2) of the reactor L2 and the switching circuit TR2 increases with the passage of time. The control circuit CL2 keeps applying the drive signal to the inverter circuit TR1 when the current flowing through the series circuit of the primary winding L2 (1/2) and the switching circuit TR2 reaches a certain value. The conduction command signal to the switching circuit TR2 is cut off and cut off.

As a result, the primary winding L2 of the reactor L2
Since the current of (1/2) suddenly changes toward zero,
Direction to prevent the sudden change, namely 1 of reactor L2
A positive pulsed high voltage is generated on the negative output terminal side of the secondary rectification circuit DR2 of the secondary winding L2 (1/2). This pulsed high voltage is also induced in the secondary winding L2 (2/2) of the reactor L2 that is magnetically coupled, and is generated as a positive voltage on the side connected to the auxiliary rectifier circuit DR4. This voltage is applied to the secondary winding L2 (2/2) of the reactor L2, the auxiliary rectifier circuit DR4, the capacitor C2, the reverse blocking diode DR.
3 is applied to the circuit of the secondary winding L2 (2/2) of the electrostatic capacitance of the junction portion of the capacitor C2 and the reverse blocking diode D.
Charge the junction capacitance of R3.

At the same time, this voltage is also applied to the circuit of the resistor R1, the tip electrode side cable 7c, the tip electrode 5, the main electrode 4, and the main electrode side cable 7a, so that the tip electrode side cable 7c and the main electrode side cable 7a are connected to each other. The stray capacitance between is also charged. However, the electrostatic capacitance at the junction of the reverse blocking diode DR3 is sufficiently larger than the stray capacitance between the main electrode side cable 7a and the tip electrode side cable 7c as described in the conventional device of FIG. Most of the energy stored in the reverse blocking diode DR3
The electrostatic capacity of the junction and the capacitor C2 are charged. The voltage of the capacitor C2 is the secondary rectifier circuit DR2.
Since it has the same polarity as that of the output voltage of, the secondary rectifier circuit DR2 is destroyed when the contact CR1 is closed when the voltage of the capacitor C2 becomes excessive. However, since the voltage generated in the secondary winding L2 (2/2) of the reactor L2 is applied to the series circuit of the capacitor C2 and the reverse blocking diode DR3, it is distributed in inverse proportion to the respective capacitances. Therefore, if the capacitance of the capacitor C2 is set sufficiently larger than the junction capacitance of the reverse blocking diode DR3, for example, about 10 times, the terminal voltage of the capacitor C2 becomes low, and the secondary rectification circuit DR2 becomes It can be prevented from being destroyed. That is, the capacitance of the capacitor C2 is Co,
Let C3 be the junction capacitance of the reverse blocking diode DR3,
Assuming that the generated voltage of the secondary winding L2 (2/2) of the reactor L2 is Vso, the terminal voltage Vco of the capacitor C2 is Vco = Vso.C3 / (Co + C3). Therefore, if Co = 10.C3 is selected. , Vco = Vso
It becomes 1/11, and it is not necessary to use a special high withstand voltage for the secondary rectifier circuit DR2.

The sum of the charging voltage at the junction of the reverse blocking diode DR3 and the terminal voltage of the capacitor C2 rises as the switching circuit TR2 repeats conduction and interruption, and the positive side is the tip electrode side output terminal Tm3. And the tip electrode side cable 7c, and the negative side is applied between the electrode 4 and the tip electrode 5 via the main electrode side output terminal Tm1 and the main electrode side cable 7a.

As described above, most of the electromagnetic energy held by the reactor L2 is charged in the capacitor C2 and the junction capacitance of the reverse blocking diode DR3, and the charging voltages of both are added to add the main electrode 4 and the chip. Since it is applied between the electrode 5 and the electrode side cable 7a and the tip electrode side cable 7c, the stray capacitance is charged by a voltage which is the sum of both voltages. When the voltage between the two rises rapidly and the insulation between them is broken, a pilot arc is generated between the two. When the output current detector CT2 detects the occurrence of a pilot arc,
The control circuit CL2 stops the repeated operation of the conduction / interruption of the switching circuit TR2 and maintains the cutoff state. As a result,
The number of times of charging / discharging the stray capacitance is reduced, and the generation of noise accompanying this is also reduced. When a pilot arc is generated, it is induced by this and a main arc for machining is established between the main electrode 5 and the workpiece 6. When the current detector CT1 detects the occurrence of the main arc, the control circuit CL2 compares the detected value with the set value of the output adjuster 9 and controls the inverter circuit TR1 so that the output current becomes the set value. At the same time, the contact CR1 is opened by the output signal of the current detector CT1 to stop the pilot arc.

The resistor R2 discharges the electric charge charged in the junction capacitance between the capacitor C2 and the reverse blocking diode DR3 and the floating capacitance between the main electrode side cable 7a and the tip electrode side cable 7c when not needed. It is for doing. This resistance value corresponds to the capacitor C2 and the reverse blocking diode DR with respect to the intermittent period of the switching circuit TR2.
It may be selected so that the time constant of the discharge circuit constituted by each capacitance of No. 3 and the resistor R2 becomes sufficiently long.

For example, when the capacitance of the junction portion of the reverse blocking diode DR3 is the above-mentioned capacitance and the capacitance of the capacitor C2 is selected to be about 10 times as large as this, the resistance value of the resistor R1 is several. It may be MΩ or several tens of MΩ. By connecting the resistor R2 thus selected, the high voltage charged between the electrode side cable 6 and the workpiece side cable 7 will operate even if the start of the arc should fail. After the discontinuation, the electric discharge is reduced in a relatively short time and the electric potential is lowered, so that the risk of electric shock is eliminated even if the electrode is accidentally touched. However, when the leakage resistance value of the circuit viewed from the output terminals Tm1 and Tm3 is the resistance value of the above-mentioned degree, the discharging resistor R2 may not be particularly provided.

The discharge resistor R2 may be connected between the output terminals Tm1 and Tm3, as shown in FIG. 2, or may be connected between the output terminals Tm1 and Tm2. it can. Furthermore, for the sake of safety, the output terminal T
Similar resistors may be connected between m1 and Tm2, between output terminals Tm1 and Tm3, or between output terminals Tm1 and Tm2 and between output terminals Tm2 and Tm3, respectively. .

FIG. 3 shows another embodiment. In the figure, the connection point between the capacitor C2 and the auxiliary rectification circuit DR4 is connected to the workpiece side output terminal Tm2 instead of being connected to the chip electrode side output terminal Tm3 via the resistor R1. In the embodiment shown in the figure, the sum of the voltages charged in the junction capacitance of the capacitor C2 and the reverse blocking diode DR3 by the conduction / interruption operation of the switching circuit TR2 is
Since it is supplied from the tip electrode side output terminal Tm3 to the tip electrode 5 through the contact point CR1 and the resistor R1, the operation is substantially the same as that of the embodiment shown in FIG. In the embodiment of FIG. 3, the discharging resistor R2 is connected between the main electrode side output terminal Tm1 and the work piece side output terminal Tm2.

FIG. 4 shows still another embodiment. 2 is different from FIG. 2 in that an auxiliary winding T1a of an inverter transformer T1 insulated from a welding output circuit and a rectifying circuit DR5 thereof are separately provided as a power source for a current flowing through a reactor L2 (1/2). And the others are shown in Figure 2.
Since it is similar to the above, detailed description will be omitted. In the embodiment shown in the figure, since the switching circuit TR2 is insulated from the welding circuit, the control circuit is easily insulated from the welding circuit.

Also in the embodiment shown in FIG. 3, the primary winding L2 (1 of the reactor L2 is similar to the embodiment shown in FIG.
/ 2) as a power source for the DC current supplied to the secondary rectifier circuit D
It may be supplied from another power source that is insulated from R2.

Further, when the starting operation is performed, normally, when the switching circuit TR2 is turned on and off once or several times, the pilot arc is normally started and the switching circuit is stopped. is there. However, there are times when the pilot arc cannot be activated for some reason. In such a case, the switching circuit TR2
The repetition of the conduction interruption operation of is useless, and since the high voltage is continuously applied to the main electrode and the chip electrode,
In order to prevent this and protect the equipment, the number of operations is limited so that the switching circuit stops after several to ten or more times, or the main electrode side output terminal Tm1 and the chip electrode side output are output. When the voltage between the terminal Tm3 (or the workpiece side output terminal Tm2) reaches a constant value, or the main electrode side output terminal Tm1 and the tip electrode side output terminal T
It is desirable to stop when the voltage between m3 (or the work-side output terminal Tm2) reaches a certain value and to repeat conduction and interruption for a certain number of times. To this end, when the voltage between the main electrode side output terminal Tm1 and the tip electrode side output terminal Tm3 (or the workpiece side output terminal Tm2) exceeds a set value, or the switching circuit TR2 of the control circuit CL2. It suffices to have a function of counting the number of operations and stopping the device as an abnormality when the number of repetitions reaches a set number.

In each of the above embodiments, the pilot arc current is limited by the limiting resistor R1. However, the pilot arc current may be limited by other methods. For example, instead of a resistor, the output of the pilot arc current detector CT2 is compared with a reference value and a difference signal is used to limit the output of the inverter circuit TR1 to a predetermined value by feedback control. The current may be limited to a predetermined value by such an analog control element or a method of chopper control by switching. In these cases, connecting a DC reactor in series with the pilot arc circuit is effective in smoothing the pilot arc current and preventing overshoot at the time of starting.

Further, in each of the above-mentioned embodiments, the main circuit of the welding power source has been described by using the inverter control type, but the main circuit system of the welding power source is not limited to the inverter control type in implementing the present invention. . That is, thyristor control or DC chopper control on the secondary side of the transformer may be used. Further, it is needless to say that the output form thereof may include a component including a periodically pulsating component or a pulse waveform other than the direct current described above.

Further, although the above-mentioned embodiments have been described only for the case where the present invention is applied to the plasma arc welding,
The present invention can be applied to anything that processes using plasma arc discharge, and can be applied to, for example, plasma arc cutting, thermal spraying, heating, melting, etc. other than welding.

[0024]

As described above, the present invention does not use the high frequency generated by the high frequency generator and repeats conduction and interruption of the current flowing in the reactor, and the high voltage generated at the time of interruption is temporarily connected to the capacitor and the reverse blocking diode. Since it is used to start the pilot arc by charging using the electrostatic capacity of the part and converting it into a DC high voltage with less pulsation, a large and expensive high-frequency generator is not required and the cable length is increased. Regardless of the size of the stray capacitance between the sheaths, reliable arc starting is possible, and noise interference can be almost eliminated.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing an example of a conventional plasma arc processing apparatus.

FIG. 2 is a connection diagram showing an embodiment when the present invention is applied to plasma arc welding.

FIG. 3 is a connection diagram showing another embodiment when the present invention is applied to plasma arc welding.

FIG. 4 is a connection diagram showing another embodiment when the present invention is applied to plasma arc welding.

[Explanation of symbols]

 4 Main electrode 5 Chip electrode 6 Workpiece 7a Electrode side cable 7b Workpiece side cable 7c Chip electrode side cable 8 Start switch 9 Output regulator 10 Welding power supply DR1 Primary rectification circuit DR2 Secondary rectification circuit DR3 Reverse blocking diode DR4 Auxiliary rectifier circuit DR5 Rectifier circuit TR1 Inverter circuit TR2 Switching circuit T1 Inverter transformer T1a Inverter transformer T1 auxiliary winding L1 Reactor L2 (1/2) Auxiliary reactor primary winding L2 (2/2) Auxiliary reactor secondary winding Line C2 Capacitor CT1 Processing main current detector CT2 Pilot arc current detector CL1 Control circuit CL2 Control circuit Tm1 Electrode side output terminal Tm2 Workpiece side output terminal Tm3 Chip electrode side output terminal R1 Pilot arc current limiting resistor R2 Discharge Resistor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Nakamura 2-1-1 Tagawa, Yodogawa-ku, Osaka City Daihen Stock Company

Claims (5)

[Claims] 1. A plasma arc machining apparatus for supplying electric power from a negative output of a DC power supply to a main electrode side terminal and from a positive output to a workpiece side terminal and a tip electrode side output terminal for a pilot arc, respectively. A reverse blocking diode connected in series between the negative output of the main electrode and the output terminal on the main electrode side, and an auxiliary reactor having primary and secondary windings and a primary winding of the auxiliary reactor when the arc is started. A switching circuit for repeatedly and intermittently flowing a DC current at a predetermined time width and interval, and a voltage generated in the secondary winding of the auxiliary reactor when the switching circuit cuts off the secondary winding of the auxiliary reactor. To the main electrode side output terminal and the output voltage of the DC power supply and the same polarity as the output voltage of the DC power supply A capacitor connected in parallel to a series circuit composed of the reverse blocking diode, the auxiliary rectifier circuit, and the secondary winding of the auxiliary reactor. Plasma arc processing equipment. 2. A high resistance resistor forming a discharge circuit is connected in parallel between the main electrode side output terminal and the chip electrode side output terminal or the workpiece side output terminal. The plasma arc processing apparatus described in. 3. The switching circuit comprises a DC power source and a switching element, which are insulated from the main circuit.
Or the plasma arc processing apparatus according to any one of 2. 4. The switching circuit is a circuit which detects the occurrence of a pilot arc and stops its operation.
The plasma arc processing apparatus according to any one of 1 to 3. 5. The switching circuit is a circuit which stops its operation when the occurrence of a pilot arc is detected or when conduction and interruption are repeated a predetermined number of times, whichever comes first. 3. The plasma arc processing device according to any one of 3 above.