JP2524094B2 - Spot welder and spot welding method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding machine for spot welding a member having a coating film on at least one outer surface of a welded member to be lap-welded, and a spot welding method using the spot welding machine.

[0002]

2. Description of the Related Art A conventional spot welding machine of this type is disclosed in Japanese Patent Laid-Open No. 5-92274, a welding power source, a cable drawn from one pole of the power source, and a first welding electrode connected to the cable end. A chip and at least two cables connected to the other pole of the power supply, one of which
To make a contact connection to the spot of the welded member that is superposed on the cable end of the book, and to the exposed surface area of the metal that is separated from the spot welding site of the superposed welded member to one of the cable ends With the provided contact member,
A second welding electrode tip connected to the other cable end of the two cables, a means for detecting a current flowing to the second welding electrode tip, and an output from the current detecting means. A device provided with a device for interrupting a current flowing to the contact member is known.

In this welding machine, a first welding electrode tip connected to a cable end drawn out from one pole of a welding power source is used to polish a metal on the upper surface of a spot welding site of one of the members to be welded by metalizing. The second welding electrode tip connected to one exposed end of one of the two cables connected to the other pole of the welding power source is connected to the first welding electrode tip. A metal surface facing away from the spot-welded portion of the member to be welded by contacting the outer coating film surface of the other member to be welded with the contact member provided at the other cable end of the two cables. Of the first welding electrode tip is heated by supplying an electric current from the welding power source between the first welding electrode tip and the contact member. Coating the coating film or the like present on the outer surface softening of the welding member, and molten or evaporated, a second welding electrode tip is electrically conductive contact with the metal surface has been pressed therein,
An electric current starts flowing from the first welding electrode tip to the second welding electrode tip. When the current to the second welding electrode tip is detected, the current flowing from the first welding electrode tip to the contact member is cut off based on the detection signal to cut off the first welding electrode tip and the second welding electrode tip. The original welding current flows due to the small spread of the spot welding area between the welding electrode tips, and the heat generation area or volume of the surroundings becomes small and the loss power also becomes small, but between the first welding electrode tip and the second welding electrode tip. When the welding current begins to flow in the first welding electrode tip and the current flowing between the first welding electrode tip and the contact member is instantaneously cut off, the first welding electrode tip
The current with the welding electrode tip of No. 1 turns on and off, a large surge voltage is generated, cracking and sparking occur at the time of welding, and good spot welding cannot be obtained.

The cause is, for example, in welding when repairing the body of an automobile, when the coating of the member to be welded which is in contact with the second welding electrode tip is close to that of a new vehicle, the coating is soft and does not cause much problems. However, in old automobiles, the paint has hardened due to aging, and the preheating current flowing between the first welding electrode tip and the contact member causes the paint to melt or not melt at the welding site, resulting in the second welding. This is because energization to the electrode tip is interrupted. In addition, when the paint adheres to the second welding electrode tip during the work, it sometimes sticks and the energization hinders energization until the adhered paint melts and disappears. Therefore, the original welding current is repeatedly turned on and off. The turn-off of this energization increases the surge voltage. Therefore, a spark is generated at the welded portion due to a high surge voltage and holes are formed.

[0005]

DISCLOSURE OF THE INVENTION The present invention overcomes the above-mentioned problems due to frequent on / off of energization at the initial stage of energization between the first welding electrode tip and the second welding electrode tip as described above. It is to be.

[0006]

According to the present invention to solve the above-mentioned problems, a welding power source, a cable drawn from one pole of the power source, and a first cable connected to the cable end are provided.
Welding electrode tip, at least two cables connected to the other pole of the power supply, and one of them, 0.5 to
A contact member provided for contact-connecting to an exposed surface region of the metal separated from the spot welding site of the overlapped members to be welded, at the end of the cable into which the parallel circuit of the low resistance of 10Ω and the switch is inserted and connected. A second welding electrode tip connected to the other cable end of the two cables, a means for detecting a current flowing to the second welding electrode tip, and an output from the current detecting means And a device for turning off the switch for parallel response of the low resistance and the switch.

Furthermore, the welding method according to the present invention includes a first welding method in which a welding end is connected to a cable end drawn from one pole of a welding power source.
The conductive electrode connection of the welding electrode tip of one of the first and second members to be welded on the upper surface of the spot welding site, and the two electrodes connected to the other pole of the power source. Pressing the second welding electrode tip connected to one cable end of the cable against the first welding electrode tip against the outer coating surface of the other member to be welded; The contact member provided at the end of the cable to which the parallel circuit of the low resistance of 0.5 to 10Ω and the switch of the two cables connected to the pole is inserted and connected is separated from the spot welding site of the member to be welded. A contact connection to the exposed surface area of the metal surface, supplying a current from the welding power source between the first welding electrode tip and the contact member, and the first welding electrode tip. The step of detecting a current flow between the second welding electrode tip and the detection result of the current flow between the first welding electrode tip and the second welding electrode tip A low resistance of 0.5 to 10 Ω inserted into a cable connecting the first welding electrode tip and the contact member, and a step of controlling a switch and a switch of a parallel circuit to be turned off.

[0008]

According to the present invention, the first welding electrode tip connected to the cable end drawn out from one pole of the welding power source is used as a metal by polishing the upper surface of the spot welding site of one of the members to be welded. Conductive contact connection to the exposed part of
The second welding electrode tip connected to one cable end of the two cables connected to the other pole of the welding power source is placed outside the other member to be welded so as to face the first welding electrode tip. The contact member provided at the end of the other cable of the two cables in which the parallel circuit of the low resistance of 0.5 to 10 Ω and the switch is inserted and connected is placed in contact with the coating surface. First, by contact-connecting to an exposed region of a metal surface of the welding member, which is remote from the spot welding site, and first supplying a current from the welding power source between the first welding electrode tip and the contact member with the switch closed. Of the welding electrode tip of No. 2 is heated and the coating such as a coating film on the outer surface of the other member to be welded below is softened, melted or evaporated, and the second welding is pressed against it. Metal electrode tip To conductively contact, current flows from the first welding electrode tip to the second welding electrode tip. When the current to the second welding electrode tip is detected, the switch connected in parallel to the low resistance is turned off based on the detection signal to flow between the first welding electrode tip and the contact member. Since the current flows through the low resistance, the current flowing therethrough becomes small, and the original welding current flows with a small spread in the spot welding site between the first welding electrode tip and the second welding electrode tip. Therefore, even if energization is turned on / off at the initial stage of energization between the first welding electrode tip and the second welding electrode tip, the resistance inserted and connected between the first welding electrode and the contact member in the cable is Since a current is flowing therethrough, a large surge voltage is not generated, welding quality is improved, and holes are not formed.

[0009]

Embodiments of the present invention will now be described in detail with reference to FIGS. The parts corresponding to those in FIGS. 1 and 2 are denoted by the same reference numerals and have the same functions.

In FIG. 1, a plus side cable 1 is connected to a plus terminal of a welding power source, and a first welding electrode tip 2 attached to an end of the plus side cable 1 is pressed onto an exposed metal surface of a member 3 to be welded. Make a contact connection. If there is a coating such as paint on not only the inner side surface of the member to be welded to be welded but also the outer side surface to be contact-connected, it must be removed. Cables 4a and 4 to the negative terminal of the welding power source
b are two cables 4 individually or in the middle
The branched cables are connected to a and 4b. A contact clamper 5 is connected to the tip of the cable 4a. The contact clamper 5 is connected to the exposed portion of at least one metal of the members to be welded 3 and 6 at a position relatively distant from the spot welding portion, and the other cable 4b is connected. A second welding electrode tip 7 is attached to the tip, and the second welding electrode tip 7 faces the first welding electrode tip 2 on the coating film 6a of the member 6 to be welded so that both members to be welded are attached. It is pinched and pressed. A relay coil 8 is provided in the current path of the cable 4b, a contact 9 corresponding to the relay coil 8 is provided in the current path of the cable 4a, and this contact 9
A low resistance 10 of 0.5 to 10 Ω is connected in parallel with.

First, from the positive pole of the welding power source to the cable 1,
Pre-heating current to the negative pole through the first welding electrode tip 2, the contact clamper 5 through the welded members 3 or 3, 6 and the cable 4a and the normally closed contact 9 that short-circuits the low resistance 10. Flows. Due to this preheating current, heat is generated in the vicinity of the pressure contact point between the first welding electrode tip and the member to be welded, and the heat causes the second portion of the member to be welded 6 to be heated.
When the coating of the coating film or the like at the portion where the welding electrode tip of is abutted is softened, melted or evaporated, and the second welding electrode tip makes conductive contact with the metal surface of the member to be welded, the current to the second welding electrode tip Current begins to flow in the path and the relay coil 8 is excited to open the corresponding contact 9 to the position shown by the broken line. Therefore, the current path to the negative terminal via the first welding electrode tip 1, the members to be welded 3, 6, the contact clamper 5, and the low resistance 10, and the welding current is the first welding electrode tip 2, the members to be welded 3, 6. , The second welding electrode tip 33, and the original welding current path to the minus terminal via the time limit circuit 11 and the relay 8 flows separately. The time circuit 11 is intended to allow the current used for the original welding to flow only for a predetermined time period, and the original welding time can be kept constant by adjusting the setting of the energizing time of the time circuit. Can perform strong welding efficiently. In this original welding process, since the preheating current flowing through the low resistance 10 becomes low due to the opening of the contact 9, a large welding current flows in the original spot welding portion. The welding power supply current is, for example, 500
If 0A, the current flowing through the low resistance is 20A or less, and the current flowing through the original welded portion is 4980A. Therefore, it is possible to reduce the area or volume of the heat-generating portion expanded from the original welded portion, and the power loss is reduced. In addition, since the preheating current is not interrupted after the start of energization to the first welding electrode tip 7 and the second welding electrode tip of the original welding portion and is allowed to flow slightly through the low resistance, the current of the original welding portion is maintained. The surge voltage will not increase excessively even if the power is turned on / off due to the remaining paint. Therefore, there is no hole in the welded part.

In the embodiment of FIG. 2, a current sensor 12 is provided around the cable 4b in order to detect the current in the current path of the cable 4b. After the output of this current sensor is amplified and processed by the control circuit 13, The electronic switch provided in the current path of the cable 4a is controlled to be turned off. As the electronic switch, a bipolar power transistor, a power MOSFET, a semiconductor switch such as a thyristor for a static induction transistor, a GTO thyristor, a static induction thyristor can be used.

A low resistance 10 is provided in parallel with the electronic switch so that a reduced preheating current flows after the start of the energization of the welding current that originally flows through the welding site is detected by the current sensor and the electronic switch is turned off. ing. The low resistance 10 may be an adjustable variable type, or a plurality of low resistances may be arranged in parallel and selectively used. As the current detecting means, a current transformer may be connected to the current path of the cable 4b, and the secondary coil current may be processed by the control circuit and then the gate of the thyristor or the base of the transistor may be controlled. A Hall element can be used as the current detecting means. Even in the embodiment, since the preheating current continues to flow through the low resistance 10 even after the original welding current is applied, the generation of excessive surge voltage in the welding electrode tip can be avoided and the occurrence of welding failure can be prevented.

In the above description, two cables of the negative pole of the welding power source are used, but it is also possible to connect the cable 1 to the negative side and connect the cables 4a and 4b to the positive side. An alternating current power source may be used as the welding power source, in which case the cable 1 may be connected to one terminal of the alternating current power source and the cables 4a and 4b may be connected to the other terminals.

[0015]

According to the present invention, first, a molten preheating current flows between the first welding electrode tip, the member to be welded and the contact member, so that the first welding electrode tip and the member to be welded are brought into contact with each other in the vicinity of the contact point. The second welding electrode tip is preheated and softened, melted, or evaporated to a coating such as a coating film on the member to be welded, which is in contact with the second welding electrode tip facing the first welding electrode tip. Is conductively contacted with the member to be welded, and when a current starts to flow between the first and second welding electrode tips, the current between the first welding electrode tip and the contact member flows through low resistance and is reduced to a low value, First and second
Since the original welding is performed with a large welding current between the parts to be welded, the area of heat generation is narrow, the occurrence of excessive surge voltage at the welding electrode tip can be prevented, the quality of welding is uniform, and the power loss is reduced. It has the effect of increasing the ability.

[Brief description of drawings]

1 is a schematic circuit diagram of a spot welder of the present invention.

FIG. 2 is a schematic circuit diagram of the spot welder of the present invention.

[Explanation of symbols]

 2 Welding electrode tip 3 Welding member 5 Contact clamper 6 Welding member 7 Welding electrode tip 8 Relay coil 9 Relay contact 10 Low resistance 12 Current sensor 14 Electronic switch

Claims (5)

(57) [Claims] 1. A welding power source, a cable drawn from one pole of the power source, a first welding electrode tip connected to the cable end, and at least two wires connected to the other pole of the power source. Cable and one of them, 0.5
A contact member provided to make a contact connection to the exposed surface region of the metal separated from the spot-welded portion of the overlapped members to be welded to the cable end to which the parallel circuit of the low resistance of 10Ω and the switch is inserted and connected. A second welding electrode tip connected to the other cable end of the two cables, a means for detecting a current flowing through the second welding electrode tip, and an output from the current detecting means. And a device for turning off a switch of a parallel circuit of the low resistance and the switch. 2. A relay coil inserted in a current path to the second welding electrode tip is used as the current detecting means,
The spot welding machine according to claim 1, wherein a contact of the relay is used as the switch. 3. The spot welding machine according to claim 1, wherein a Hall element is used as the current detecting device, and an output of the Hall element is used to turn off an electronic switch via a control circuit. 4. The spot welding machine according to claim 1, wherein a semiconductor switch such as a bipolar power transistor, a power MOSFET, a thyristor, a GTO thyristor, a static induction type thyristor, or a static induction type thyristor is used as the switch. 5. A spot welding portion of one of the first and second members to be welded, on which the first welding electrode tip connected to the cable end drawn from one pole of the welding power source is superposed. A conductive contact connection on the upper surface, b a second welding electrode tip connected to one cable end of one of the two cables connected to the other pole of the power source, a first welding electrode. A step of pressing against the outer coating surface of the other member to be welded, facing the tip; and a switch having a low resistance of 0.5 to 10 Ω and a switch of the two cables connected to the other pole. A step of contact-connecting a contact member provided at an end of a cable in which a parallel circuit is inserted and connected to an exposed surface area of a metal surface of a member to be welded, which is away from a spot welding site; and d) the first welding electrode tip The contact A current from the welding power source between the first welding electrode tip and the second welding electrode tip; and a step of detecting a current flow between the first welding electrode tip and the second welding electrode tip; Based on the detection result of the current flow between the welding electrode tip of No. 1 and the second welding electrode tip, 0.5 inserted and connected to the cable connecting the first welding electrode tip and the contact member. A spot welding method comprising a low resistance of -10Ω and a step of controlling a switch and a switch of a parallel circuit to be turned off.