JPH08681U - Spot welder - Google Patents

Abstract

(57) [Summary] [Purpose] Even if there is a bad conductor such as a coating film at a part of the welded spot, spot welding can be performed without removing it, especially when the coating film is destroyed. To prevent excessive heat generation at the welded portion, which tends to occur, and to eliminate insufficient welding strength. [Structure] A large current circuit 16 for flowing a positive current ia is provided between a positive electrode 13a and a negative electrode 13b which are in contact with each other so as to sandwich two metal plates 12a and 12b.
A low current circuit 15 for flowing a low current ib is provided between the negative electrode 13b and the second positive electrode 14 in contact with the metal plate 12b in the vicinity thereof. In the SW element 20, the welding spot portion is heated by the low current ia, and the metal plate 1
When the coating film or the like interposed in 2a or the like is destroyed and the main current ia starts to flow between the positive electrode 13a and the negative electrode 13b, it is turned off by the drive circuit 21 under the control of the control circuit 22.
Then, the low current circuit 15 is opened.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a spot welder, and more particularly to a spot welder having an improved structure for supplying a welding current supplied to a welding spot portion and its circuit.

[0002]

[Prior art]

 Conventionally, this type of spot welder stacks two metal plates, presses them with a round bar electrode to energize them, heats the metal with Joule heat to bring it into a molten state, and applies pressure to form dots. Pressed. Particularly recently, economical three-phase commutation type spot welders that use an average load from a three-phase power source have been used. This three-phase rectifying spot welder uses, for example, a transformer wound with three primary coils and three secondary coils and is controlled by six ignitrons to generate a low-frequency single-phase alternating current. Is configured to get.

Specifically, as shown in FIG. 4, two metal plates 1a and 1b to be welded are superposed and sandwiched by the electrodes 3a and 3b of the clamp 2, and a weld metal is used. Instead, they are pressed and welded. At this time, it is desirable to polish the welding spots of the metal plates 1a and 1b to remove the coating film, rust, surfacer, etc., but as proposed in Japanese Utility Model Publication No. 49-123330. However, even if a thin coating film, rust, or a surfacer is mixed in, good spot welding has become possible.

That is, in Japanese Utility Model Laid-Open No. 49-123330, the metal plate B is superposed on the other surface of the metal plate A, one surface of which is covered with an electric insulator, and the superposed portions are opposed to each other from above and below. It is sandwiched by first and second electrodes, one first electrode is provided so as to move along the overlapping portion of the metal plates A and B, and the second electrode moves the first electrode. A plate-shaped sub-electrode, which is formed in a rod shape along the direction and is arranged in close contact with the metal plate A so as to be electrically conductive, is arranged on one side or both sides of the first electrode side. The first electrode and the sub-electrode are energized to destroy the insulating material of the metal plate A directly below the first electrode by resistance heating, and the first electrode is passed through this portion. Welding current is applied between the electrode of No. 2 and the electrode of No. 2 and then along the overlapping portion of the metal plates A and B in order. In the one in which the nugget is generated to join the two metal plates A and B, a rod-shaped electrode in which the facing surface of the second electrode is formed into a convex or arc-shaped or uneven surface is used. A resistance welding device is described.

In the resistance welding apparatus described in the above publication having such a structure, for example, when the rod-shaped second electrode is used, the insulating material of the metal plate A is softened by resistance heating and the second electrode Since only the softened portion is surely pressed by the arcuate surface and comes into contact with the metal plate A, a welding current is passed under a sufficient pressing force with the first electrode, and good welding can be performed.

[0006]

[Problems to be solved by the device]

 However, in such a welding method, even after the electric current starts to flow between the first electrode and the second electrode, the plate-shaped sub-electrode is transferred from the first electrode to the plate-shaped sub-electrode through the site where spot welding should be originally performed. Welding current continues to flow. Therefore, it is heated up to the peripheral area that should not be welded originally, and for example, if it is a thin metal plate, or if the welding time is lengthened, there are holes in the welded part, or in the part where the welding current is wide. Since it spreads, there is a shortcoming that the welding current at the essential spot welding site is insufficient and the strength of the welded member is insufficient.

The present invention has been made in view of the above-mentioned circumstances, and even if a defective conductor such as a coating film is present at a welding location, spot welding can be performed without removing all of the defective conductors. To provide a spot welding machine capable of preventing excessive heat generation at a spot welding portion which tends to occur due to destruction of the coating film or the like by preheating, eliminating insufficient welding strength, and suppressing unnecessary power consumption. It is in.

[0008]

[Means for Solving the Problems]

 In order to achieve the above-mentioned object, the present invention makes one of the two stacked metal plates contact the first electrode of either the positive electrode or the negative electrode, and the other of the metal plates. In a spot welding machine in which a second electrode having a polarity different from that of the first electrode is brought into contact, and these are pressed and welded, the second electrode is brought into contact with the vicinity of the welding spot of the metal plate. For generating a current between the third electrode and a third electrode having the same polarity as the first electrode, which is different from the first electrode for A first current circuit, a second current circuit that is turned on together with the first current circuit to generate a current between the first electrode and the second electrode, and the second current circuit. A current sensor for detecting a current flowing from the first electrode to the second electrode via Sa and is characterized in that it comprises a control circuit for controlling to turn OFF the switch element inserted in the current circuit when it is detected that the current flows through this current sensor.

Further, in the current sensor, for example, even if a coating film or the like is present on the surface of the metal plate that contacts the first electrode and / or the contact surface of the two metal plates, The current flowing between the third electrode and the second electrode preheats the vicinity of the two electrodes, thereby destroying the coating film and the like, and between the first electrode and the second electrode. When the current sensor detects that the current starts flowing, it is desirable that the control circuit receiving the detection signal turns off the current. Further, it is desirable to use a semiconductor switch such as a thyristor for the switch element.

[0010]

[Action]

 The spot welding machine configured as described above is different from the first electrode in which the first electrode having either the positive electrode or the negative electrode is in contact with one of the two metal plates. The polar second electrode is brought into contact with the other metal plate. Further, a third electrode, which is different from the first electrode and has the same polarity as the first electrode, is brought into contact with the vicinity of the welding spot portion of the metal plate with which the second electrode contacts. A second current circuit that generates a current between the first electrode and the second electrode during welding, and a first current circuit that generates a current between the second electrode and the third electrode. And both are turned on.

For example, in the case where a bad conductor such as a coating does not exist on the surface of one metal plate with which the first electrode contacts and the contact surface of the two metal plates and they are in conductive contact with each other. , The current flows from the first current circuit between the third electrode and the second electrode, but the current also flows from the second current circuit between the first electrode and the second electrode. Then, the current sensor detects the current, and the control circuit which receives the detection signal turns off the switch element inserted in the first current circuit to open the first current circuit, and the subsequent current Since the supply is stopped, the portion of the metal plate where the second electrode and the third electrode come into contact with each other is not heated excessively, the spread of the region where the welding current flows is prevented, and reliable spot welding is performed. Realize it and reduce unnecessary power consumption.

Further, for example, when a defective conductor such as a coating film is present on either the surface of one metal plate with which the first electrode contacts and / or the contact surface of two metal plates, No current initially flows between the second electrode and the second electrode, but a current flows between the third electrode and the second electrode due to the first current circuit, and in the vicinity of the spot welding spot. When the is heated, the coating film on the metal plate is destroyed, and the first electrode and one metal plate and both metal plates come into conductive contact with each other, and the second current circuit causes the first electrode and the first metal plate to come into contact with each other. An electric current begins to flow between the two electrodes.

Then, the current sensor detects that this current has flowed, and the control circuit receiving the detection signal turns off the switch element inserted in the first current circuit to turn on the first current circuit. Since it is opened and the supply of electric current is stopped thereafter, there is no extra force that may hinder the spot welding of the two metal plates sandwiched between the first electrode and the second electrode, which are originally to be welded. It does not cause excessive heating or insufficient welding current.

[0014]

【Example】

 Hereinafter, a preferred embodiment of a spot welding machine according to the present invention will be described in detail with reference to the accompanying drawings. As shown in FIG. 1, the clamp 11 of the spot welding machine 10 of the present embodiment clamps two metal plates 12a and 12b which are superposed on each other, and presses and welds these metal plates 12a and 12b. A positive electrode 13a as one electrode and a negative electrode 13b as a second electrode are provided. The positive electrode 13a contacts one metal plate 12a, and the negative electrode 13b contacts the other metal plate 12b.

Further, the spot welding machine 10 of the present embodiment has a second positive electrode 14 as a third electrode different from the positive electrode 13a. The second positive electrode 14 is attached to the clamp 11 or is formed separately from the clamp 11. The second positive electrode 14 is provided in contact with the vicinity of the welding spot 12c of the metal plate 12b with which the negative electrode 13b is in contact. Therefore, when the second positive electrode 14 is attached to the clamp 11, the second positive electrode 14 is located near the negative electrode 13b.

In this embodiment, the metal plate 12b where the negative electrode 13b and the second positive electrode 14 are in contact with each other has conductivity by removing the coating film and the like, but the positive electrode 13a is in contact with the metal plate 12b. The description will be made assuming that a coating film or the like is interposed between the portion of the metal plate 12a and the contact surface between the metal plates 12a and 12b. Further, as shown in FIG. 2, the spot welding machine 10 of the present embodiment is provided with a first current circuit for generating a low current ib between the second positive electrode 14 and the negative electrode 13b. And a large current circuit 16 as a second current circuit for generating the main current ia between the positive electrode 13a and the negative electrode 13b.

Specifically, for example, a phase control power element 17 is connected to a three-phase 200v power source, and a power transformer 18 and a rectifier circuit 19 are sequentially connected to the phase control power element 17. The large current circuit 16 is connected to the rectifier circuit 19 and is energized by a positive electrode 13a and a negative electrode 13b that sandwich the two metal plates 12a and 12b. The low current circuit 15 is branched on the positive electrode 13a side of the large current circuit 16, and the second positive electrode 14 is provided at the tip end thereof via a SW element (switch element) 20. The SW element 20 is connected via a drive circuit 21 to a control circuit 22 composed of a microprocessor or the like. Further, a current sensor 23 is provided on the positive electrode 13a side of the branch portion of the large current circuit 16, and the current sensor 23 is connected to the control circuit 22. The control circuit 22 is connected to an input side 24 such as an operation switch, and its output side 25 is connected to the phase control power element 17.

In the spot welding machine 10 of the present embodiment configured as described above, the main current ia is output from the large current circuit 16 and the low current ib is output from the low current circuit 15. . First, when the phase control power element 17 and the SW element 20 are turned on, the large current circuit 16 in this embodiment causes the positive electrode 13a to contact the surface of the metal plate 12a (or two sheets of the metal plate 12a). Since a defective conductor such as a coating film is present on both or one of the contact surfaces of the metal plates 12a and 12b), the current flow does not flow because the energization condition is not satisfied, Only the low current ib flows through the low current circuit 15.

Next, the effect of the low current ib, that is, the low current ib output from the low current circuit 15 flows between the second positive electrode 14 and the negative electrode 13b, and the vicinity of the portion to be spot-welded is detected. Between the positive electrode 13a and the negative electrode 13b due to destruction (melting, softening, vaporization, carbonization, etc.) of the coating film that has been applied to both sides or one side of the metal plate 12a and one side of the metal plate 12b by heating. This current starts to flow to. Then, the current sensor 23 provided in the large current circuit 16 detects this and inputs it to the control circuit 22. Then, the control circuit 22 drives the drive circuit 21 to turn off the SW element 20.

FIG. 3 shows an ON / OFF principle circuit of the SW element 20 provided in the low current circuit 15. That is, a semiconductor switch (thyristor SCR1) is interposed in the low current circuit 15, the anode side of the thyristor SCR1 is connected to the rectifier circuit 19, and the cathode side thereof is the second positive electrode. It is connected to 14. The thyristor SCR1 is provided with a constant voltage circuit to which a constant voltage is applied by the capacitor 26 and a current ic flows. Further, a semiconductor switch (thyristor SCR2) is provided on the positive side of the constant voltage circuit. The drive circuits 21 are connected to the gates of the thyristors SCR 1 and SCR 2, respectively, and the control circuit 22 is connected to the drive circuits 21 via an interface 28.

The ON / OFF principle circuit of the low current circuit 15 configured as above operates as follows. That is, first, the thyristor SCR1 is turned on by the operation of the drive circuit 21. Next, when the SCR2 is turned on by the operation of the drive circuit 21, the above thyristor SCR1 is reverse biased and turned off. When the thyristor SCR1 is turned off, the reverse bias current ic of the thyristor SCR2 also becomes 0 and the SCR2 is also turned off. By repeating such an operation, the thyristor SCR1 provided in the low current circuit 15 can be turned ON / OFF.

Next, the operation of the above embodiment will be described. As described above, the spot welding machine 10 of the present embodiment has the second positive electrode 14 in addition to the positive electrode 13a, and the second positive electrode 14 contacts the negative electrode 13b. The metal plate 12b is brought into contact with the vicinity 12c of the welding spot portion. At this time, at least the portion of the metal plate 12b where the negative electrode 13b and the second positive electrode 14 are in contact with each other has the coating film or the like removed or the coating film or the like has not been applied from the beginning. When performing spot welding, a large current circuit 16 for generating a main current ia between the positive electrode 13a and the negative electrode 13b, and a low current for generating a low current ib between the second positive electrode 14 and the negative electrode 13b. Both the circuit 15 and the circuit 15 are turned on.

First, it is assumed that neither the contact surfaces of the two metal plates 12a and 12b nor the surfaces of the metal plates 12a that contact the positive electrode 13a are in conductive contact with no coating film or the like. The operation when there is a relationship will be described. In this case, a low current ib flows from the low current circuit 15 between the second positive electrode 14 and the negative electrode 13b, but the main current circuit 16 and the positive electrode 13a and the negative electrode 13b are connected to each other. The current ia flows. Then, the current sensor 23 detects the main current ia, and the control circuit 22 receiving the detection signal drives the drive circuit 21 to turn off the SW element 20 to open the low current circuit 15. .

Therefore, after the main current ia starts to flow, the portion of the metal plate 12b where the second positive electrode 14 and the negative electrode 13b are in contact with each other may be overheated to make a hole at the welding site. It is possible to prevent the spread of the region where the welding current flows and to realize reliable spot welding.

Next, for example, the second positive electrode 14 and the negative electrode 13b contact the surface other than one surface (the lower surface in FIG. 1) of the metal plate 12b, that is, the positive electrode 13a. In the case where a defective conductor such as a coating film is present on one surface side (the upper surface side in FIG. 1) of the metal plate 12a and all the contact surfaces of the metal plates 12a and 12b, or at least one of them, the positive electrode 13a Between the negative electrode 13b and the negative electrode 13b is in an insulating state or in a state where the contact resistance is extremely high, so that no current initially flows or only a very weak current flows.

However, when the low current ib flows between the second positive electrode 14 and the negative electrode 13b by the low current circuit 15 and the vicinity of the spot welding spot is preheated, the metal plates 12a and 12b are heated. The upper coating film or the like is destroyed, and the positive electrode 13a and the two metal plates 12a and 12b are all brought into a conductive contact state, and the large current circuit 16 causes the positive electrode 13a and the two metal plates 12a and 12b. , And the current ia starts to flow via the negative electrode 13b.

Then, the current sensor 23 inserted in the large current circuit 16 detects that the main current ia flows, and outputs the detection signal to the control circuit 22. The control circuit 22 receiving this detection signal sets the switching element 20 inserted in the low current circuit 15 to OF F to open the low current circuit 15 and stops the supply of the low current ib thereafter, so that the welding process is not performed. There is no extra heating or insufficient welding current that would hinder spot welding of the two metal plates 12a and 12b sandwiched between the positive electrode 13a and the negative electrode 13b to be performed.

According to the spot welding machine of the present embodiment configured as described above, the second positive electrode 14 is brought into contact with the vicinity of the welding spot 12c of the metal plate 12b with which the negative electrode 13b is brought into contact. When a low current ib is generated between the second positive electrode 14 and the negative electrode 13b, the low current ib preheats the portions of the metal plates 12a and 12b to be welded. The positive electrode 13a and the metal plate are destroyed by breaking (softening, melting, evaporation, carbonization, etc.) of the coating film or the like applied to the upper surface of the metal plate 12a and / or the contact surface of the metal plates 12a and 12b that come into contact with 13a. Since the conductive contact is made between 12a and the metal plate 12b, the main current ia flows between the positive electrode 13a and the negative electrode 13b.

The current sensor 23 detects the main current ia and inputs it to the control circuit 22, and the control circuit 22 drives the drive circuit 21 to turn off the SW element 20. The spread of the area is prevented, the two metal plates 12a and 12b are satisfactorily pressed and welded, and the power loss can be reduced, and the welding work efficiency can be improved. . The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

For example, even if the positive electrode and the negative electrode are replaced with each other, there is no difference in action and effect. For example, in FIG. 1, 13a is a negative electrode, 13b is a positive electrode, and 14 is a second negative electrode. In this case, the negative electrode 13a serves as the first electrode, the positive electrode 13b serves as the second electrode, and the second negative electrode 14 serves as the third electrode. Further, in the above-described embodiment, the low current ib is described as being small with respect to the main current ia, but it is not always necessary to do so. For example, the value of the current ib is the same as the current ia. It is arbitrary whether or not the current ib is set larger than the current ia. For example, when the current ib is set larger than the current ia, the SW element 20 responds in a shorter time and the energization time of the current ib becomes shorter. That is. Therefore, here, the circuit for passing the current ib is referred to as the first current circuit, and the circuit for passing the current i a is referred to as the second current circuit.

[0031]

[Effect of device]

 As described above, according to the spot welding machine of the present invention, one of the positive and negative electrodes of the positive electrode is contacted with one of the two stacked metal plates, and the metal is In a spot welding machine in which a second electrode having a polarity different from that of the first electrode is brought into contact with the other of the plates, and these are pressed and welded, in the vicinity of a welding spot portion of a metal plate with which the second electrode comes into contact Between the third electrode and the second electrode, which is different from the first electrode and has the same polarity as the first electrode. And a second current circuit that is turned on together with the first current circuit to generate a current between the first electrode and the second electrode. Even if there is a coating film etc. on the welded part, it is inevitably removed all because it has been done Without Rukoto, Ki de be reliably spot welded to two metal plates, it can significantly increase the welding work efficiency.

Further, according to the spot welding machine of the present invention, a current sensor for detecting a current flowing from the first electrode to the second electrode via the second current circuit, and And a control circuit for controlling to turn off the switch element inserted in the first current circuit when the current sensor detects that a current has flowed. The energization between the electrodes of 3 is suppressed to the minimum necessary to destroy the coating film, etc., and the expansion of the area where excess heat generation and welding current flow is suppressed, making it the first of the two metal plates superposed. The original welding can be performed more efficiently and reliably between the portion sandwiched between the electrode and the second electrode, and unnecessary power consumption can be suppressed.

[Brief description of drawings]

FIG. 1 is a schematic view showing the vicinity of a clamp in an embodiment of a spot welding machine according to the present invention.

FIG. 2 is a block diagram showing a system circuit in an embodiment of a spot welding machine according to the present invention.

FIG. 3 is a circuit diagram showing an ON / OFF principle of a low current circuit in an embodiment of the spot welding machine according to the present invention.

FIG. 4 is a schematic view showing a clamp in an example of a conventional spot welder.

[Explanation of symbols]

 10 Spot Welder 12a, 12b Metal Plate 12c Weld Spot 13a Positive Electrode 13b Negative Electrode 14 Second Positive Electrode 15 Low Current Circuit 16 Large Current Circuit ia Main Current ib Low Current 17 Phase Control Power Element 18 Power Transformer 19 Rectifier Circuit 20 SW element SCR1, SCR2 Thyristor 21 Drive circuit 22 Control circuit 23 Current sensor 26 Capacitor 28 Interface

Claims (3)

[Scope of utility model registration request] 1. A first electrode having either one of a positive electrode and a negative electrode in contact with one of two stacked metal plates, and the other of the metal plates is different from the first electrode. In a spot welding machine in which polar second electrodes are brought into contact with each other to pressurize and weld them, the first for contacting the vicinity of a welding spot portion of a metal plate with which the second electrode comes into contact
A third electrode having a polarity different from that of the first electrode and having the same polarity as the first electrode, and a first current circuit for generating a current between the third electrode and the second electrode. A second current circuit that is turned on together with the first current circuit to generate a current between the first electrode and the second electrode; and the first current circuit through the second current circuit. A current sensor for detecting a current flowing from the second electrode to the second electrode, and turning off the switch element inserted in the first current circuit when the current sensor detects a current flowing. A spot welding machine, comprising: 2. The switch element is, for example, the first
Even if a coating film or the like is present on the surface of the metal plate that comes into contact with the electrode and / or the contact surface of the two metal plates,
The vicinity of both electrodes is preheated by the current flowing between the first electrode and the second electrode, so that the coating film and the like are destroyed and the current flows between the first electrode and the second electrode. 2. The spot welding machine according to claim 1, wherein when the current sensor detects that the current has started to flow, the control circuit receives the detection signal to turn off the current. 3. The spot welding machine according to claim 1, wherein a semiconductor switch such as a thyristor is used as the switch element.