JPH0322265B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field The present invention relates to a power supply device for an AC arc welding machine, and particularly relates to improving arc transferability.

(b) Summary of the Invention The power supply device for an AC arc welding machine according to the present invention supplies each half-wave of AC from a separate secondary winding, and at the start of each half-wave, the power supply device for an AC arc welding machine supplies the power to the AC arc welding machine. The back electromotive force thus generated is superimposed and applied to the welding electrode to facilitate arc migration.

(c) Prior art and its disadvantages Power supplies for AC arc welding machines are generally used when welding aluminum. This is an oxide film (aluminum oxide) that forms on the aluminum surface.
This is to utilize the effect (cleaning effect) of removing Al ₂ O ₃ ) by an arc flow caused by a welding current of opposite polarity (negative electrode on the base metal side, positive electrode on the welding electrode side). However, since the alternating current has a point where the current becomes 0 during alternation, the arc tends to become unstable, and there is a drawback that arc failure occurs frequently, especially when transitioning from positive polarity to reverse polarity.

Therefore, conventionally, at the start of welding, a high-frequency voltage generation circuit that assists arc ignition was operated every time the welding voltage polarity changed, and the high-frequency voltage was applied superimposed on the arc welding voltage in order to stabilize the arc transition. .
However, frequent generation of high frequencies generates a large amount of high frequency noise, which may cause equipment to malfunction if there is equipment using ICs or the like on the power supply side.

In addition, in the case of an AC arc, the impedance of the arc load differs between positive polarity and reverse polarity, causing current distortion on the input side, which may cause biased magnetization in the transformer. In order to prevent damage to the transformer, conventionally the transformer had to have a sufficiently large capacity compared to the maximum load current. As a result, it has the drawbacks of being large in volume and weight, and becoming expensive.

(d) Purpose of the Invention In view of the above-mentioned drawbacks, the present invention aims to provide a power supply device for AC arc welding that does not easily cause biased magnetism and can maintain a stable AC arc without using a stable high-frequency voltage generation circuit. purpose.

(e) Structure and effect of the invention This invention provides a transformer for transforming high frequency voltage.
It is equipped with two secondary windings having intermediate taps on both sides, and a low frequency conversion circuit that converts the transformed high frequency output to a low frequency is connected to the terminals at both ends of each of the two secondary windings. The circuit consists of a full-wave rectifier circuit including a diode, and an open/close circuit that applies the rectified outputs of these two rectifier circuits to the base metal and the welding electrode alternately in positive and reverse polarity, respectively, and the polarity of the applied voltage is an inductive element that produces a back emf when the inductive element switches, and an arc forcing that applies the voltage generated by this inductive element to the base material or wire electrode at the beginning of the next half-wave with the same polarity as that half-wave. It is characterized by having a transition circuit.

According to the above configuration, the following effects can be achieved according to the present invention.

(1) The voltage due to the back electromotive force generated in the inductive element at the time of polarity transition is applied in a superimposed manner with the same polarity at the start of the transition half-wave, so the superimposed voltage becomes sufficient for arc ignition. By setting as follows, arc transition can be performed smoothly.

(2) As described above, since arc transition during polarity transition is easy, there is no need to superimpose high-frequency current during arc transition as in the past, and high-frequency noise can be reduced.

(3) Each half wave of the low frequency is assigned to each of the two secondary windings, and the polarity is set between the intermediate tap and both electrodes, so the magnetic flux due to the current cancels out and becomes 0. . Therefore, even if the currents of positive and reverse polarity are different, almost no biased magnetization occurs, and there is no risk of damaging the transformer. There is no risk of damaging the high frequency conversion circuit that supplies high frequency voltage to the transformer.

(4) The induced back electromotive force generated when the polarity switches is used to facilitate arc transition.
There is no need to increase the welding voltage itself. Therefore, it is not necessary to increase the withstand voltage of the rectifying element, etc., and it is possible to improve the arc transfer positive while maintaining the safety of preventing electric shock.

(5) The arc forced transition circuit is composed of diodes, switch elements, etc., and contains some electrostatic capacitance and induction coefficient. Therefore, it is possible to prevent the low frequency conversion circuit from being damaged due to the kick voltage generated at the time of polarity switching.

(f) Embodiment FIG. 1 is a circuit diagram of an AC arc welding power supply device which is an embodiment of the present invention.

The rectifier circuit 2 is a three-phase AC full-wave rectifier circuit using six diodes, and is connected to the three-phase AC power source 1. A smoothing capacitor 3 is included in the rectifier circuit 2.
are connected in parallel to absorb the pulsating current components of the rectified power supply. The smoothed DC voltage is supplied to the high frequency conversion circuit 4. The high frequency conversion circuit 4 includes a transistor 4a that connects the positive pole of the DC voltage to one terminal of the primary winding 5a of the transformer 5 to be connected next;
A transistor 4b to which the negative electrode is connected, a transistor 4c to which the positive electrode of the DC voltage is connected to the other terminal of the primary winding, and a transistor 4 to which the negative electrode is connected.
It is composed of d. These transistors are turned on and off by the high frequency conversion circuit control section 13,
Two sets of transistors, transistor 4a and transistor 4d, and transistor 4b and transistor 4c, are alternately turned on and off. Its frequency is several kHz. The transformer 5 is wound with two similar secondary windings 5b, 5c, each winding having an intermediate tap. The intermediate tap of the secondary winding 5b is connected to a welding electrode 20 via a reactor 10, and a diode 6 is connected to the terminals at both ends of the winding.
A positive current rectifier 6 composed of a and 6b is connected. The positive current rectifier 6 has a secondary winding 5b.
This is a full-wave rectifier circuit in which the anodes of diodes 6a and 6b are connected to terminals at both ends of the rectifier, and the output of this rectifier is a positive pole, and the intermediate tap is a negative pole. The rectified output is supplied to the base material 21 via the switching transistor 8. On the other hand, the intermediate tap of the secondary winding 5c is connected to the base material 21 via the switching transistor 9, and the terminals at both ends of the winding are connected to diodes 7a and 7b.
A reverse polarity current rectifier 7 consisting of the following is connected. The negative polarity current rectifier 7 is a full-wave rectifier circuit in which the anodes of diodes 7a and 7b are connected to terminals at both ends of the secondary winding 5c, and the output of this rectifier is a positive pole and the intermediate tap is a negative pole. It is configured. The rectified output is supplied to the welding electrode 20 via the reactor 10. Here, when the switching transistors 8 and 9 are alternately turned on and off at a frequency of several tens of Hz, positive and negative voltages are alternately applied to the welding electrode 20 and the base material 21. On/off control of the switching transistors 8 and 9 is performed by a switching transistor control section 23. Reactor 10 as above
is connected between the secondary winding of the transformer 5 and the welding electrode 20, the anode of the diode 12 is connected to the transformer 5 side of the reactor 10, and the positive electrode of the capacitor 18 is connected to the cathode of the diode 12. is connected. The negative electrode of the capacitor 18 is the base material 2
Connected to 1. Further, the positive electrode of the capacitor 18 is connected to the electrode 20 via the thyristor 14 and the resistor 16.
It is connected to the. Similarly, smooth reactor 10
The cathode of a diode 13 is connected to the transformer 5 side, and the negative electrode of a capacitor 19 is connected to the anode of the diode 13. The positive electrode of capacitor 19 is connected to base material 21 . Further, the negative electrode of the capacitor 19 is connected to the electrode 20 via the thyristor 15 and the resistor 17. Thyristor 1
The on/off of 4 and 15 controls the thyristor control section 24.

With the above connection, when the load resistance is low and the current value is approximately constant during arc ignition, the capacitor 1
The voltage between terminals 8 and 19 is also low and charging hardly occurs, but when the polarity of the welding voltage changes, reactor 10
The electric charge due to the induced electromotive force generated in the capacitor 18
Or it will be stored in the capacitor 19. That is, when the half wave of positive polarity ends (transistor 8
capacitor 18 is charged by the induced voltage (immediately after transistor 9 switches from on to off), and when a half-wave of opposite polarity flows (immediately after transistor 9 switches from on to off), capacitor 18 is charged by the induced voltage. capacitor 19
is charged. Furthermore, the thyristors 14 and 15 are controlled to be turned on for a short time at the start of a half-wave of opposite polarity (when transistor 9 is turned on) and at the beginning of a half-wave of positive polarity (when transistor 8 is turned on), respectively. Since the capacitors 18 and 19 are charged when these thyristors 14 and 15 are turned on, the charges are discharged and superimposed on the welding voltage. These diodes 12 and 13, thyristors 14 and 15, resistors 16 and 17, and capacitors 18 and 19 constitute an arc forced transition circuit 11.

2A, B, and C are graphs showing the load current flowing between the welding electrode 20 and the base material 21, the voltage between the terminals of the capacitor 18, and the voltage between the terminals of the capacitor 19, respectively. The operation of the forced arc transition circuit 11 will be explained with reference to this figure.

First, in A and B of the same figure, when the switching transistor 8 is on and the switching transistor 9 is off, the secondary winding 5 of the transformer 5
b, a current in the positive polarity direction flows through the diode 6b of the positive current rectifier 6, the positive current supply switching transistor 8, the base material 21, the welding electrode 20, the reactor 10, and the intermediate tap of the secondary winding in this order.
Next, when the switching transistor 8 is turned off, the supply of the current in the positive polarity direction is stopped, so a voltage of -e is generated in the reactor 10 in the direction of the dotted arrow to prevent this, and this -e The current due to the back electromotive force flows from the reactor 10 to the capacitor 1.
8 Capacitor 1 via charging diode 12
8, the battery is charged to the polarity shown in FIG. This charging lasts for a time t ₁ after the switching transistor 8 is turned off and the switching transistor 9 is turned on.
When the thyristor 14 is turned on for a time t ₂ ((t ₁ + t ₂ ) is about several μs to several tens of μs), the voltage generated by charging the first capacitor 18 is transferred to the thyristor 14 and the resistor. electrode 2 through 16
0, applied between the base material 21. At this time, since the reverse polarity current switching transistor 9 is turned on at the same time, the applied voltage is superimposed on the rectified voltage supplied by the reverse polarity current rectifier 7. The polarity of the superimposed voltage at this time is the same as the polarity of the superimposed voltage. The capacitance of the capacitor 18 is set to be sufficiently large so that the discharge of the charge instantaneously generates an arc between the electrode 20 and the base material 21. Therefore, this instantaneous arc is forced to be instantaneously shifted.

FIG. 2C shows the charging voltage of capacitor 19.
The circuit on the capacitor 19 side, which is composed of the diode 13 for charging the capacitor 19, the thyristor 15, the resistor 17, and the capacitor 19, operates in the same way as the circuit on the capacitor 18 side described above, but arcing due to current in the opposite polarity direction Capacitor 1
9. Even if the charging diode 13, thyristor 15, resistor 17, and capacitor 9 are omitted, substantially the same effect can be obtained.

Although not shown, a high frequency oscillator is installed on the welding electrode 20 side or on the base material 21 to facilitate arc ignition at the start of arc welding.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a power supply device for an AC arc welding machine which is an embodiment of the present invention, and Figs. 5 is a diagram showing the applied voltage, the voltage between the terminals of the capacitor 18, and the voltage between the terminals of the capacitor 19. FIG. DESCRIPTION OF SYMBOLS 10... Smoothing reactor, 11... Arc forced transition circuit, 12, 13... Diode, 14, 15... Thyristor, 16, 17... Resistor, 18, 19... Capacitor, 24... Thyristor control part.

Claims (1)

[Scope of Claims] 1. A first rectifier circuit that once converts an AC power source into a DC voltage, a high frequency conversion circuit that converts the DC voltage to a high frequency voltage, and a transformer that transforms the high frequency voltage.
In an AC arc welding power supply device having a low frequency conversion circuit that converts a transformed high frequency into a low frequency and applies the converted high frequency to a base metal and a welding electrode, the transformer is provided with two double taps each having an intermediate tap on both sides. A full-wave rectifier circuit including a secondary winding and a full-wave rectifier circuit including diodes connected to terminals at both ends of the two secondary windings, and a rectified output of these two rectifier circuits. It consists of a switching circuit that applies voltage to the base material and welding electrode alternately with positive and reverse polarity, and an inductive element that generates a back electromotive force when the polarity of the applied voltage switches, and an inductive element that generates a back electromotive force. and an arc forced transition circuit that applies a voltage with the same polarity as that of the next half wave between the base material and the welding electrode at the start of the next half wave.