JPH0756135Y2 - Resistance welder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a resistance welding machine having a circuit for supplying electric power for preheating and postheating.

[Conventional technology]

Welding of the metal plate A and the metal pipe B shown in FIGS. 6 (A) and (B) is sufficiently possible only by the pulse welding current flowing by discharging the electric energy charged in the capacitor in a short time. When the material to be welded contains carbon in an amount of 0.2% or more, even the impulse-shaped welding current waveform causes rapid heating and cooling, and the joint is hardened and the strength decreases. Therefore, when welding such an object to be welded, as shown in FIG. 5 (A), an alternating current i is passed after the impulse welding current I to perform a post heat treatment to improve the joint structure. There is.

Further, as an example of welding in which preheat treatment is performed, FIG.
As shown in (B), the convex portion D ₁ of the other metal plate D is inserted into the hole C ₁ of the one metal plate C and combined in a T-shape to form a space between the upper electrode E and the lower electrode (not shown). Preliminary heating is performed by passing an alternating current i in a state of being arranged and pressurized. As a result, the convex portion B ₁ is crushed in advance, and then the crimp welding is completed with the impulse welding current I. Note that both of these post heat treatments may be performed as necessary, and P is a pressure waveform.

As described above, in resistance welding, melting and crushing occur at the joint of the objects to be welded by heating and pressing, so after the welding is completed, the initial dimensions l and d in the figure should be shorter. The size of the swaging amount corresponding to the shortened size may have a great influence on the accuracy of the product, and the product may be accepted or rejected or its value may be determined.

Such resistance welding has been performed by a circuit as shown in FIG. In the figure, 1 and 1 ′ are AC input terminals for receiving commercial AC power, 2 is a normal charging circuit for charging the charging / discharging capacitor 3 to a set voltage, and 4 is a discharging circuit for discharging the charged charge of the capacitor 3. A thyristor 5 used as a discharge switch is a first primary winding 6 and a second thyristor 2.
A welding transformer having a secondary winding 7 and a secondary winding 8, and 9 is a bidirectional switch for selectively passing an alternating current to the second primary winding 7 of the welding transformer 5. Since the operation of such a conventional circuit is well known, a detailed description thereof will be omitted. However, the electric energy of the capacitor 3 charged to the set voltage by the operation of the charging circuit 2 turns on the thyristor 4 to turn on the welding transformer 5. Is discharged through the primary winding 6 of 1,
Impulse welding current I shown in FIGS. 4A and 4B flows through the secondary winding 8. By switching the bidirectional switch 9 before and after that, the preheating AC current i and the postheating AC current i as shown in FIGS.

[Problems to be solved by the device]

In such resistance welding, the heat input condition of the workpiece changes due to fluctuations in the magnitude of the alternating current for preheating or postheating, so the swaging amount also changes, and the uniformity of the welding results is significantly increased. It turned out to make it worse. The cause of the fluctuations in the preheating and post-heating AC currents is that the AC input terminals 1, 1'of FIG. 8 are directly connected to the commercial AC power supply, and therefore are directly affected by the power supply environment of the factory. I found out. Another reason is that the AC current was flowing at any time without being synchronized, so the current flowing through the windings of the welding transformer in one direction is larger than the current flowing in the other direction. There is a possibility that a phenomenon of strong excitation in a certain direction, that is, biased excitation may occur, and inrush current may flow due to this biased excitation, which further deteriorates the accuracy of the final finished size of the welded product. .

[Means for Solving Problems] In order to solve the above problems, the AC power supplied from the AC input terminal is stabilized to provide either stabilized preheating power or postheating power. It is characterized in that it is provided with a stabilizing device for supplying one or both of them to the welding transformer.

[Action]

According to the present invention, since the electric power in the factory is supplied to the AC winding of the welding transformer through the stabilizer, it is not adversely affected by the power fluctuation and the fluctuation of the heat input due to the irregular inrush current. Since it can be suppressed, it is possible to obtain a welded product with an extremely accurate finish size.

〔Example〕

The first embodiment of the present invention will be described with reference to FIG.
The same symbols as those shown in the figures indicate corresponding circuit components. In the figure, 10 is a stabilizing device, which is an input voltage detector 11, a normal voltage stabilizing circuit for stabilizing an input AC voltage by a detection signal from the detector.
12, an evaluation circuit 13 for detecting the zero point of the detection signal from the input AC voltage detector 11 and discriminating between positive and negative polarities, a signal having the same polarity as the AC input voltage and a predetermined polarity based on the signal from the circuit 13. And a firing circuit 15 that receives a signal from the drive circuit 14 and applies a signal of a predetermined magnitude to the gate of the bidirectional switch 9.

Next, the operation of this circuit will be described.

The voltage stabilizing circuit 12 operates according to the change of the detection signal from the input AC voltage detecting circuit 11 and controls so that its output voltage becomes constant. On the other hand, the evaluation circuit 13 receives the detection signal from the input AC voltage detection circuit 11, generates a zero-point detection signal each time the waveform passes through the zero point, and at the same time determines the polarity of the waveform of the detection signal to determine that A polarity indicating signal indicating the polarity is generated. The drive circuit 14 responds to these two types of signals,
A drive signal to be given to the anti-parallel thyristors 9A and 9B forming the bidirectional switch 9 is output to the ignition circuit 15 at a time substantially corresponding to the zero point. Regarding this point, FIG. 4 (A),
An explanation will also be given using (B).

Assuming that the black dots indicating the winding start of the first and second primary windings 6 and 7 of the welding transformer 5 are in the same direction, the charge of the charging / discharging capacitor 3 causes the first primary winding 6 to reach the black dots. Since the current flows in from the side, the drive circuit 14 first passes through the ignition circuit 15 so that the current flowing through the second primary winding 7 first comes in from the side opposite to the black point and flows out from the black point. Thyristor
Turn on 9B at almost zero. Then, in the next half cycle, the thyristor 9A is turned on at a substantially zero point, thereafter the thyristors 9B and 9A are alternately turned on, and the thyristor 9B is turned on in the last half cycle.

By driving the bidirectional switch 9 in this way,
The AC voltage stabilized by the voltage stabilizing circuit 12 is applied to the second primary winding 7 by approximately 180 ° in each half cycle, and the AC current i and the impulse welding current I flowing through the welding transformer 5 are Looking at the polarity, the currents flow alternately. Therefore, a stable AC current flows through the welding transformer regardless of fluctuations in the AC input voltage, and because the polarity of the current is taken into consideration, the current flowing through the windings of the welding transformer in the positive and negative directions is almost balanced. And therefore,
Since an irregular rush current does not flow, it is possible to obtain a welded product having a very accurate weld finish size.

Next, a second embodiment of the present invention will be described with reference to FIG.

In the first embodiment, a voltage stabilizing circuit is separately provided and the bidirectional switch 9 is used as a mere discharge switch without controlling the phase, but in this embodiment, the bidirectional switch element 9'is controlled in phase. ing. The phase control circuit 16 compares the detection signal from the AC input voltage detector 11 and the reference voltage, and gives an error signal to the drive circuit 14 so that they are equal, and the drive circuit 14 sets the phase corresponding to the error signal. The drive signal which it has is given to the bidirectional switch element 9 ′ via the ignition circuit 15. Therefore, the bidirectional switch element 9 ′ is phase-controlled so that a stable AC voltage is applied between the second primary windings 7.

Next, a third embodiment of the present invention will be described with reference to FIG.

The stabilizing device 10 includes a full-wave rectifying circuit 17, an inductor 18 and a capacitor 19 which form an LC filter, and a second primary winding 7
And an inverter circuit 20 having a bridge configuration or a half bridge configuration. The inverter circuit 20 is
The pulse width is controlled according to the value of the DC input voltage, and the stabilized AC voltage having a predetermined frequency is supplied to the second primary winding 7
Give to. In addition to this embodiment, in the second embodiment as well, the relationship with the impulse welding current I is the fourth.
An alternating current i as shown in FIGS. (A) and (B) flows through the welding transformer.

[Effect of device]

As described above, according to the present invention, in a resistance welding machine in which an alternating current is passed before, after, or before and after the impulse welding current obtained by discharging the electric charge charged in the capacitor, the alternating current with respect to the impulse welding current is used. In consideration of the positive and negative polarities of the above, only the AC voltage for flowing the AC current into the welding transformer is stabilized, so the size of the finish is extremely accurate with a relatively small stabilizer regardless of fluctuations in the input voltage. It is possible to obtain weldments of.

[Brief description of drawings]

1 to 3 are views showing first, second and third embodiments of the resistance welding machine according to the present invention, and FIGS. 4 (A) and 4 (B) are welding currents for explaining the present invention. Waveforms, FIGS. 5 (A) and 5 (B) show welding current waveforms by a conventional one, and FIGS. 6 (A) and 6 (B) show butt welding of a metal plate and a metal pipe. Drawing 7, Drawing 7 (A), and (B) are figures showing crimp welding of metal plates, and Drawing 8 is a figure showing the conventional resistance welding machine. 1, 1 '... AC input terminal, 2 ... Charging circuit 3 ... Charging / discharging capacitor, 4 ... Discharging switch 5 ... Welding transformer, 6 ... First primary winding 7 ... Second Primary winding, 8 ... Secondary winding 9 ... Bidirectional switch 9 '... Bidirectional switch element, 10 ... Stabilizer 11 ... AC voltage detector, 12 ... Voltage stabilization Circuit 13 …… Evaluation circuit, 14 …… Drive circuit 15 …… Ignition circuit, 16 …… Phase control circuit 20 …… Inverter circuit

Claims (2)

[Scope of utility model registration request] 1. A charging circuit connected to an input terminal, a charging / discharging capacitor charged by the charging circuit, and a first primary winding for receiving energy from the charging / discharging capacitor via a discharging switch. A welding transformer having a second primary winding connected to the input terminal for supplying one or both of preheating power and postheating power, and a secondary winding for supplying a welding current to a workpiece. In the resistance welding machine, a stabilizing device is connected to the second primary winding to supply stabilized one or both of preheating power and postheating power to the object to be welded. Resistance welding machine. 2. The stabilizer comprises a half cycle having a polarity opposite to that of a voltage induced by a current flowing through a first primary winding of the welding transformer due to discharge of a charged load of the charging / discharging capacitor. The resistance welding machine according to claim 1, wherein an alternating current voltage that starts and ends in a half cycle of reverse polarity is caused to flow a current that induces in the second primary winding.