JPH07102457B2 - AC arc welding equipment - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC arc welding apparatus used for aluminum welding or the like in which a high frequency conversion circuit is provided on a primary side and an AC output is obtained by a low frequency conversion circuit on a secondary side. It is a thing.

Conventional technology AC arc welding has different welding characteristics depending on its polarity.For example, in the case of positive polarity in which the electrode is the cathode and the base metal is the anode, deep penetration can be obtained in the base metal, and the electrode is the anode and the base metal. In the case of the reverse polarity which serves as the cathode, the penetration is shallow, but there is an action (cleaning action) of removing the oxide film of the base material. Conventionally, when welding aluminum, an AC arc welding apparatus is used to remove an oxide film (aluminum oxide Al ₂ O ₂ ) generated on the aluminum surface by utilizing this cleaning action. Conventionally, as shown in FIG. 4, for example, an AC arc welding apparatus for obtaining an AC arc of this type obtains a sine wave or a rectangular wave from an AC input 1 to a secondary side of a transformer 2 to form an electrode 3 and a base metal. An arc was being generated between No.4 and No.4. However, in the case of an AC arc, the load impedance is lower in the positive polarity than in the reverse polarity due to the difference in electron emission function between the base material 4 and the electrode 3, and the load current is different between the positive polarity and the reverse polarity. Occurred, and therefore, the transformer 2 was biased.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the above-mentioned conventional technology, in order to maximize the effect of the welding characteristics depending on the polarity of the AC arc, it is necessary to reduce the magnetic bias of the transformer and prevent damage to the device. Nara Katsuta. Therefore, conventionally, there has been a problem that the capacity of the transformer must be made sufficiently larger than the maximum load current, the volume and weight of the transformer are large, and the price is expensive. Further, when the polarity is switched between the positive polarity and the reverse polarity, a counter electromotive voltage is generated by the inductive element connected to the load (for example, the load current smoothing reactor or the inductance of the cables connected to the base material and the electrodes). When a current control element such as a diode or a transistor is used on the secondary side of the transformer, the current control element may be damaged due to the back electromotive force caused by the back voltage. Therefore, conventionally, the withstand voltage of the current control element is increased more than necessary, and a surge absorption circuit for protecting the transistor including a resistor 6 and a capacitor 7 is provided at both ends of the transistor 5 which is the current control element as shown in FIG. It was provided. However, this protection method has a problem that it is not suitable for absorbing a large back electromotive force due to the reactor, although it can absorb a surge voltage having a very small power.

The present invention is to solve the above-mentioned conventional problems, to prevent the demagnetization of the transformer caused by the difference in polarity of the AC arc, and further to maximize the effect of the welding characteristics due to the polarity of the AC arc. It is an object of the present invention to provide an AC arc welding device which can be obtained and which can be obtained at low cost without increasing the capacity of the transformer.

Means for Solving the Problems In order to solve the above problems, an AC arc welding apparatus according to the present invention includes a first rectifier circuit for converting an AC input into a DC voltage, and a voltage rectified by the first rectifier circuit. A high frequency conversion circuit for converting a high frequency to a high frequency, a secondary winding having an intermediate tap, a transformer for converting the high frequency voltage, and two diode anodes at both ends of the secondary winding of the transformer. A second rectifier circuit in which one end of each diode is connected to each other, and cathodes on the other end side and anodes on the other end side of each diode are connected to each other, and the cathodes on the other end side and the anodes on the other end side to the above A low frequency circuit interposed between the center tap and the rectified output of the second rectifier circuit to alternately apply the rectified output of the second rectifier circuit to the base material and the electrode, respectively. Connect a capacitor between the intermediate tap of the wire and the cathode on the other end side of each diode and the anode on the other end side of each wire, and smooth between the connection point of this capacitor and the intermediate tap and the welding load. The AC arc welding device is connected to an induction element such as a power reactor that generates a back electromotive force.

Further, in the AC arc welding apparatus of the present invention, one end of the reactor is connected to the intermediate tap of the secondary winding of the transformer, and the other end of the reactor and the cathodes on the other end side of each diode and the anode on the other end side are connected. Capacitors are connected between each other, and an inductive element such as a smoothing reactor that generates a counter electromotive voltage is connected between a connection point between the capacitors and the reactor and a welding load.

Action With the above configuration, one potential is always positive (positive polarity side) and the other is positive with respect to the intermediate tap of the transformer secondary winding by the second rectifying circuits connected to both ends of the secondary winding. Of the transformer secondary winding depends on the direction in which the transformed high-frequency current flows, even when supplying a positive or negative potential. Since the same current always flows by alternately using the windings of and, the occurrence of magnetic bias in the transformer is eliminated, and the polarity effect can be selected by the low frequency conversion circuit to arbitrarily select the positive polarity and reverse polarity. Can be maximized.

In addition, the counter electromotive voltage generated when the polarity is switched by the inductive element that generates the counter electromotive force, such as a smoothing reactor, is generated between the diode of the second rectifier circuit and the diode of the second rectifier circuit between both ends of the transformer secondary winding and the intermediate tap. A closed loop consisting of a capacitor connected via a reactor, a low-frequency conversion circuit that switches the polarity, a base metal, an arc load, and an electrode acts to absorb and remove the back electromotive force before the next polarity switching, and Prevents damage to current control elements such as switching elements.

The reactor connected to the intermediate tap of the secondary winding of the transformer acts to limit the inrush current of the back electromotive force bypass capacitor.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the AC arc welding apparatus of the present invention. In FIG. 1, 11 is a three-phase AC power supply,
It is connected to the first rectifier circuit 12 which is composed of six diodes. A capacitor 13 is connected in parallel to the first rectifier circuit 12 for smoothing. The smoothed DC voltage is supplied to the high frequency conversion circuit 14, converted into a high frequency voltage, and applied to the primary winding 15a of the transformer 15. High frequency conversion circuit 1
4 is transistors 14a and 14b and capacitors 14c and 14
the collector of the transistor 14a and the capacitor 14c on the positive side of the DC voltage, and the transistor 1 on the negative side of the DC voltage.
The emitter of 4b and the capacitor 14d are connected.
Transistor 14a is connected to one terminal of primary winding 15a of transformer 15.
And the collector of the transistor 14b, and the capacitors 14c and 14d are connected to the other terminal of the primary winding 15a.
The other terminal of is connected. High frequency conversion control circuit 16
By alternately turning on and off the transistors 14a and 14b, when the transistor 14a is ON, the emitter of the transistor 14a is connected to the primary winding 15a and the capacitor 14d, and when the transistor 14b is ON. The capacitor 14c is connected to the primary winding 15a and the transistor 14b, and a high frequency voltage is applied to the primary winding 15a. The frequency of the high frequency voltage can be arbitrarily set by the high frequency conversion control circuit 16 from several KHz to several tens KHz. Further, when the balance of the load currents alternately flowing in the primary winding 15a of the transformer 15 is lost, the capacitors 14c and 14d may cause a sudden load change, for example.
Alternatively, it acts to prevent magnetic bias in the transformer due to variations in the ON periods of the transistors 14a and 14b. The transformer 15 has a secondary winding having an intermediate tap, and is constituted by secondary windings 15b and 15c on both sides of the intermediate tap. Secondary winding 15
Positive and negative potentials are applied to both ends of b and 15c with respect to the intermediate tap, and they are alternately inverted in synchronization with the high frequency voltage of the primary winding 15a. A second rectifying circuit 17 including diodes 17a and 17b and 18a and 18b is provided on both ends of the secondary windings 15b and 15c.
And 18 are connected. With respect to the intermediate tap of the secondary winding, the cathode sides of the diodes 17a and 18a always have a positive potential, and the anode sides of the diodes 17b and 18b always have a negative potential. One terminal of the reactor 19 is connected to the intermediate tap of the secondary winding, and the other terminal of the reactor 19 is connected to the cathode side of the diodes 17a and 18a and the anode side of the diodes 17b and 18b, respectively. It is connected to the other end of 21.
Further, one terminal of the high frequency voltage ripple smoothing reactor 22 as an inductive element is the reactor 19 and the capacitor 20.
And 21 and the other terminal of the reactor 22 is connected to the electrode 23. The outputs of the second rectifier circuits 17 and 18 are connected to a low frequency conversion circuit 24 composed of a pair of transistors 24a and 24b and free wheel diodes 24c and 24d connected to both ends of the transistors, respectively. The emitter of the transistor 24a that opens and closes and the collector of the transistor 24b that opens and closes on the opposite polarity side are connected to the base material 25. The transistors 24a and 24b are alternately turned on and off by the low frequency conversion control circuit 26 for an arbitrary time,
When the transistor 24a is ON, the base material 25 is positive (positive potential) and the electrode 23 is negative (negative potential), and when the transistor 24b is ON, the electrode 23 is positive (positive potential),
An AC output can be obtained when the base material 25 has the opposite polarity to the anode (negative potential). Further, the frequency of the AC output can be arbitrarily set by the low frequency conversion control circuit 26 from several Hz to several 100 Hz.

With the above configuration, even when the ON period of the transistor 24a is lengthened and the ON period of the transistor 24b is shortened to obtain the positive polarity effect as shown in FIG. And 18a supply alternating positive potentials and diodes 17b and 18b alternately supply opposite polarity potentials so that the secondary windings 15b and 15c of the transformer always have equal currents regardless of the direction of the high frequency. Flowing. Also,
As shown in FIG. 2 (b), the same is true when trying to obtain the reverse polarity effect, and the occurrence of bias magnetization due to the difference in transformer load current is eliminated, and the positive polarity and reverse polarity effects are obtained. Can be maximized.

Further, the counter electromotive voltage generated by the inductive element associated with the polarity switching, such as the reactor 22, is absorbed as follows. First, when the transistor 24a is ON, the base material 25 and the electrode 2
The current flowing in the arc load generated between 3 is 2 of the transformer.
Diodes 17a and 18 from both ends of the secondary windings 15b and 15c
a, the transistor 24a, the base material 25, the electrode 23, and the reactors 22 and 19 to the intermediate tap of the secondary winding of the transformer.
When the transistor 24a is turned off, the counter electromotive voltage e'as shown in FIG. This back electromotive force e ′
, Capacitor 21, free wheel diode 24d, base material 2
5. Due to the arc load and the closed loop of the electrode 23, the transistor 24b is absorbed by the capacitor 21 before the transistor 24b is turned on and the polarity is switched, and the transistor 24a is protected from the damage of the counter electromotive voltage by the reactor 22.

FIG. 3 (a) is a waveform diagram showing the switching timing of the transistors 24a and 24b of the low frequency conversion circuit 24.
FIG. 6B shows the emitter-collector voltage of the transistor 24a. In the figure, the timing T ₁ (dead time) at which the transistor 24a is switched to the transistor 24b is several to several tens of microseconds, and the counter electromotive voltage generated in the reactor 22 during this period is absorbed by the capacitor 21. In addition, E ₀ in FIG. 3 (b) is a steady voltage when the transistor 24a is OFF, and E _{1 is}
Is the voltage after absorbing the back electromotive force at the time of polarity switching by the protection circuit, E ₂ is the back electromotive voltage without the protection circuit, and when E ₂ exceeds the allowable voltage E ₃ between the emitter and collector of the transistor, Will be damaged. Also, the transistor 24
Similarly, when b is switched from ON to OFF, a closed circuit is created by the capacitor 20 and the free wheel diode 24c, and the counter electromotive voltage of the reactor 22 is absorbed by the capacitor 20 to protect the transistor 24b. Since the reactor 19 acts to limit the inrush current of the capacitors 20 and 21, it is not necessary to increase the capacitance of each diode of the second rectifier circuits 17 and 18 and the transistor of the high frequency conversion circuit 14 more than necessary.

Although the present invention has been described for the case where the AC input is three-phase, the same effect can be obtained even if the AC input is three-phase, and, as can be seen from the examples, there is no bias magnetization, so only the positive polarity is obtained. Alternatively, it can be used as a DC arc welding device using only reverse polarity.

EFFECTS OF THE INVENTION As described above, according to the AC arc welding apparatus of the present invention, the polarity is changed between the electrode and the base material and the voltage is alternately applied to obtain the positive polarity and the reverse polarity welding characteristics. In this case, it is possible to prevent the occurrence of transformer bias magnetism due to the difference in the transformer load current that occurs due to the difference in polarity, which can prevent damage to the equipment and, in addition, the welding characteristics due to the polarity of the AC arc. The effect can be maximized, and it can be provided at a small size and at a low cost.

In addition, when the polarity is switched, the counter electromotive voltage generated by the inductive element is absorbed and removed by the capacitor before the start of the next polarity, thereby damaging the diode, transistor, etc. of the current control element used on the secondary side of the transformer. It is possible to realize a safe, highly reliable, and inexpensive AC arc welding device.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an AC arc welding apparatus showing an embodiment of the present invention, FIGS. 2 (a) and 2 (b) are output waveform diagrams of the AC arc welding apparatus, and FIG. FIG. 3 is a waveform diagram showing switching timings of the transistors 24a and 24b in the arc welding device. FIG. 3 (b) is a surge absorption waveform diagram of the voltage between the emitter and collector of the transistor 24a at the time of switching, and FIG. FIG. 5 is a circuit diagram showing an arc welding device, and FIG. 5 is a surge absorbing circuit of a conventional arc welding device mounted between the emitter and collector of a transistor. 11 …… Three-phase AC power supply, 12 …… First rectifier circuit, 14 …… High-frequency converter circuit, 15 …… Transformer, 17,18 …… Second rectifier circuit, 19 …… Reactor, 20,21… … Capacitor, 22 ……
Reactor (inductive element), 23 ... Electrode, 24 ... Low frequency conversion circuit, 25 ... Base material.

Claims (2)

[Claims] 1. A first rectifier circuit for converting an alternating current input to a direct current,
A high-frequency conversion circuit that converts the voltage converted to DC by the first rectifier circuit into a high-frequency wave, a secondary winding having an intermediate tap, and a transformer that transforms the high-frequency voltage, and a secondary of the transformer. A second rectifier circuit in which anodes and cathodes of two diodes are respectively connected to both ends of the winding, and cathodes and anodes of the other ends of the diodes are respectively connected to the second rectifier circuit and the other end side. Of a low frequency, which is interposed between the cathodes of the other and the anodes of the other end and the intermediate tap, and alternately applies the rectified output of the second rectifier circuit to the base material and the electrode with positive polarity or reverse polarity, respectively. A conversion circuit, and capacitors are respectively connected between the intermediate tap of the secondary winding of the transformer and the cathodes on the other end side and the anodes on the other end side of each diode. , AC arc welder inductive element to produce a counter electromotive voltage, such as the smoothing reactor is connected between the welding load and a connection point between the intermediate tap and the capacitor. 2. A first rectifying circuit for converting an alternating current input to a direct current,
A high-frequency conversion circuit that converts the voltage converted to DC by the first rectifier circuit into a high-frequency wave, a secondary winding having an intermediate tap, and a transformer that transforms the high-frequency voltage, and a secondary of the transformer. A second rectifier circuit in which the anode and cathode of two diodes are connected to both ends of the winding, respectively, and the cathode and the anode of the other end of each diode are connected, respectively, and the other end of the second rectifier circuit. Of a low frequency, which is interposed between the cathodes of the other and the anodes of the other end and the intermediate tap, and alternately applies the rectified output of the second rectifier circuit to the base material and the electrode with positive polarity or reverse polarity, respectively. A conversion circuit, wherein one end of the reactor is connected to the intermediate tap of the secondary winding of the transformer, the other end of the reactor and the cathodes on the other end side of each diode, and the other end side. AC arc welding apparatus in which capacitors are respectively connected between the anodes, and an induction element such as a smoothing reactor that causes a counter electromotive voltage is connected between a connection point between the capacitors and the reactor and a welding load. .