JPH0910958A - Transformer for resistance welding machine and resistance welding machine - Google Patents

Abstract

PURPOSE: To reduce an electric power to be consumed by a secondary wiring supplying the electric power from a transformer to a stud gun, and also, to miniaturize the transformer. CONSTITUTION: By arranging a transformer 22 near a stud gun 18, a secondary wiring is shortened. Especially, by arranging the transformer 22 so that it moves as one body with a movable electrode 26, a secondary cable of a consumable is abolished. Consequently, the impedance of the secondary wiring is reduced, and its loss is reduced. Also, since an induced voltage can be lowered by the loss reduced, the cross-sectional area of the iron core of the transformer 22 is reduced, and making the transformer 22 light in weight and miniaturizing it are achieved. Further, by calculating a transformer capacity corresponding to the actual duty cycle of an apparatus, the transformer 22 with a minimum capacity is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transformer used in a resistance welding machine to apply a voltage to electrodes, and more particularly to a technique for downsizing the transformer. Furthermore, it relates to a welding machine using this transformer.

[0002]

2. Description of the Related Art Resistance welding is a welding method in which a large current is directly applied to an object to be welded, Joule heat generated thereby is used to heat the joint, and at the same time, a pressure is applied to join the metals. This resistance welding is used in all industrial fields because of its characteristics such as good mass productivity.
In particular, in order to further promote mass productivity, there is a multi-spot welder that welds a plurality of spots at the same time.

This multi-spot welder employs a method of supplying electric power from a single transformer to a plurality of electrodes. Since this transformer is heavy, it is fixedly installed on the outer periphery of the spot welding machine so that it can be easily repaired and replaced if a failure occurs. The transformer and the electrodes are connected to the bus bar by a secondary wiring including a flexible cable (secondary cable), and electric power is supplied through the secondary wiring.

[0004]

In the above-mentioned multi-spot welding machine, the secondary wiring from the transformer to the electrodes becomes long, and the power loss due to the impedance at this portion becomes large. Due to this loss, there has been a problem that the capacity of the transformer has to be increased, which causes a reduction in energy efficiency. Also, the secondary cable is consumed by the large current flowing during welding,
There was also a problem that it would be necessary to replace it regularly.

The present invention has been made to solve the above-mentioned problems, and provides a miniaturized transformer, and by using the transformer, the workability is good and the energy efficiency is high. The purpose is to provide a spot welder.

[0006]

In order to achieve the above object, a transformer for a resistance welding machine according to the present invention has an induced voltage of 6 times or less of the voltage between the welding electrodes, and an iron core of the transformer. The cross-sectional area is the minimum value required to generate the induced voltage.

Furthermore, in a transformer for a resistance welding machine according to another invention, the number of windings of a secondary coil is increased, and the cross-sectional area of the iron core of the transformer is set to a minimum value required to generate the induced voltage. There is.

Furthermore, in a transformer for a resistance welding machine according to another invention, a maximum usage rate is set based on the usage conditions of a welding machine in which the transformer is used, and the heat radiation amount per unit time of the coil of the transformer is set. The ratio of the heat generation amount per hour of the coil at the time of welding is the maximum utilization rate of the coil.

Further, a multi-spot welding machine according to another invention includes an electrode capable of advancing and retreating with respect to a welding object, and a transformer which advances and retracts integrally with the electrode and is connected to the electrode by a rigid wiring. have.

[0010]

The present invention has the above-mentioned structure, and reduces the induced voltage to reduce the cross-sectional area of the iron core of the transformer, thereby making the transformer compact and lightweight.

Further, by increasing the number of turns of the secondary coil as compared with the conventional one, the cross-sectional area of the iron core of the transformer is reduced,
The transformer is small and lightweight.

Further, the maximum usage rate is determined based on the actual usage conditions, and the heat dissipation capacity of the coil is determined so that the heat generation amount and the heat dissipation amount of the coil are balanced at this maximum usage rate, thereby making the transformer compact and lightweight. It can be anything.

Further, by disposing the transformer so as to advance and retreat together with the electrode, the secondary wiring can be shortened and the power loss can be reduced. Also, by maintaining the secondary wiring as a rigid wiring and eliminating the cable, maintenance of the cable becomes unnecessary.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the structure of a multi-spot welding machine according to this embodiment. A copper chip 12 is placed on the copper base 10, and a work piece 14,
16 are mounted. A stud gun 18 is fixedly installed on the gun bracket 20 above the copper base 10. The illustrated device is provided with four stud guns 18. Further, behind the stud gun 18, a transformer 22 for generating a welding voltage is installed.

In FIG. 2, the stud gun 18 and the transformer 22 are shown.
A schematic perspective view of is shown. The stud gun 18 includes an air cylinder 24 having an outer cylinder 24a and an inner cylinder 24b, the outer cylinder 24a being fixed to the gun bracket 20, and an electrode 26 provided at the tip of the inner cylinder 24b. .
Therefore, the expansion and contraction of the air cylinder 24 causes the electrode 26
Can move back and forth with respect to the workpieces 14 and 16. Further, a transformer bracket 28 is provided near the base of the electrode 26 in a direction substantially orthogonal to the electrode axis direction. The transformer 22 is mounted on one end of the transformer bracket 28. Therefore, the transformer 22 and the electrode 26
Move forward and backward as the air cylinder 24 expands and contracts. Further, as shown in FIG. 1, in this device, one transformer 22 is provided for two stud guns 18.
Is arranged, and one end of the secondary coil of the transformer has one electrode 2
6, the other end of the secondary coil is connected to the other electrode 26. The transformer bracket 28 is a part of the secondary wiring and is entirely made of copper or copper alloy. Even when the whole is not made of copper or the like, the electrode 26
It is preferable to use a material having a low impedance such as copper for the portion connecting the and transformer mounting portion.

The operation during welding is as follows. Workpieces 14 and 16 are mounted on the copper chip 12.
Then, the air cylinder 24 extends and the workpiece 1
The electrodes 26 are lowered from above the electrodes 4 and 16 and pressed with a predetermined pressure. This state is the state shown by the two left stud guns in FIG. Almost at the same time as this pressing operation, a voltage is applied between the two electrodes by the transformer 22. As a result, the two workpieces 1 are separated from the one electrode 26.
4 and 16 through the copper tip 12 and the copper base 10 and again through the workpieces 14 and 16 and the other electrode 26.
Current flows through. This current causes the workpiece 1
The joint portions 4 and 16 are melted, and the work piece is joined by the pressing force of the electrode 26.

According to this apparatus, the stud gun 24 and the transformer 22 are integrated to shorten the secondary wiring,
A reduction in loss is achieved. However, since the transformer 22 is a movable element, the transformer 22 needs to be small and lightweight. In this device, the size and weight of the transformer are reduced by the method described below.

In this device, a buzz bar and a secondary cable that connect the transformer and the electrode in the conventional device are used.
The next wiring is only the transformer bracket 28. Therefore, the impedance of the secondary wiring can be made very small, and therefore the induced voltage of the transformer can be made small accordingly. Although it depends on the scale of the equipment, in a device for spot welding a body frame of a passenger car or the like, the impedance of the conventional secondary wiring is 500 to 150 μm while the impedance of the workpiece is 100 to 200 μΩ.
It is 0 μΩ. That is, of the induced voltage of the transformer, the voltage applied to the workpiece was about 1/15 to 1/5, and the energy efficiency was low. In other words, in the conventional device, the induced voltage of the transformer needs to be 5 to 15 times the voltage applied to the workpiece.

In this device, the impedance of the secondary wiring is about 100 to 200 μΩ, which is much smaller than that of the conventional device. Therefore, it is understood that the loss in the secondary wiring is reduced and the induced voltage of the transformer is 1/2 or less of the conventional voltage. Furthermore, the internal impedance of the transformer is 100-200μΩ, and the overall impedance is 600μΩ.
It is necessary to generate an induced voltage corresponding to Further, since the minimum value of the impedance of the work piece is approximately 100 μΩ, it can be seen that the induced voltage is 6 times or less the voltage between the welding electrodes.

The induced voltage of the transformer is generally represented by the following equation.

## EQU1 ## V = 4.44 × f × N × B × S (1) At this time, f is frequency (Hz), B is magnetic flux density (Wb /
m ² ), N is the total number of turns, and S is the iron core cross-sectional area (m ² ).
Among these, the most effective factor for downsizing and weight reduction of the transformer is the iron core cross-sectional area S that accounts for about 80% of the total weight of the transformer.
It is. That is, if the iron core cross-sectional area S can be reduced, the weight of the transformer can be reduced and the outer dimensions can be reduced. Transforming equation (1),

## EQU00002 ## S = V / (4.44.times.f.times.N.times.B) (2) As described above, since the loss in the secondary wiring is reduced, the required induced voltage V becomes smaller, and the expression (2)
It can be seen that the coil cross-sectional area S can be made smaller. Therefore, the iron core can be made smaller, and the size and weight of the transformer can be reduced.
And the electrode 26 are easily integrated. Further, from the formula (2), the coil cross-sectional area S can be reduced even if the number of windings N is increased, and it is also preferable that the number of windings is usually two but three.

Further, in this apparatus, the cooling capacity of the transformer 22 is determined based on the actual usage state (maximum usage rate) of the transformer 22. That is, if the ratio of the energization time is small, the cross-sectional area of the winding in the transformer 22 can be reduced accordingly, and the transformer can be downsized.

In spot welding, since a short-time energization and a relatively long down time are repeated, it is necessary to consider the usage rate when setting the capacity of the transformer. The usage rate α is

[Expression 3] α = t _a / (t _a + t _b ) ... (3) Here, t _a is the energization time and t _b is the rest time. In such a case, the cooling capacity can be reduced when the usage rate α is low, even if the amount of current flowing during energization is equal. The cooling capacity is sufficient if it has the ability to radiate the amount of heat generated during the energization time by the next energization time. In this way, the temperature rise of the secondary coil does not occur.
If you show it with a formula,

## EQU4 ## q _G × t _a = q _R × (t _a + t _b ) ... (4) Here, q _G is the amount of heat generated per unit time during energization, and q _R is the amount of heat released per unit time. By transforming equation (4),

[Equation 5] q _R / q _G = t _a / (t _a + t _b ) = α (5), and the cooling capacity is set so that the ratio of the heat radiation amount q _R and the heat generation amount q _G becomes the usage rate α. do it. Therefore, if the usage rate α is low, the cooling capacity can be lowered. Therefore, as described above, it is possible to reduce the cross-sectional area of the winding in the transformer and to downsize the transformer.

Since the calculation of the heat radiation amount and the heat generation amount described above may be difficult in an actual device, consideration will be made below in terms of capacity. As the rated capacity of the transformer, the capacity when the usage rate is 50% is adopted according to JIS (Japanese Industrial Standard). When the equivalent current is 12000A at this usage rate, if the usage rate is 10%, the equivalent current is approximately 5367A because it is proportional to the square root of the usage rate α, and if the usage rate is 2%, it is approximately 2400A. . Therefore, if the usage rate is limited to 2% and a transformer is used, the rated value is 24
A 00A transformer can be used, and the external dimensions do not become larger than necessary.

3 and 4 show another embodiment according to the present invention. A lower transformer 132 having a lower electrode 130 is placed below the workpieces 114 and 116. On the other hand, above the workpieces 114 and 116, the upper electrode 1 facing the lower electrode 130 is provided.
A stud gun 118 with 26 is provided. The stud gun 118 is fixedly arranged on the gun bracket 120. The illustrated device includes a stud gun 118.
Is equipped with four. Further, behind the stud gun 118 is an upper transformer 12 for generating a voltage for welding.
2 are installed.

The stud gun 118 is an air cylinder 124.
The air cylinder 124 has the same structure as the air cylinder 24 of the above-described embodiment. The electrode 126 is arranged at the tip of the air cylinder 124. Therefore, the electrode 126 can advance and retract with respect to the workpieces 114 and 116 by the expansion and contraction of the air cylinder 124. Furthermore, near the base of the electrode 126,
The transformer bracket 128 is provided in a direction substantially orthogonal to the electrode axis direction. The upper transformer 122 is mounted on one end of the transformer bracket 128. Therefore, the upper transformer 122 and the electrode 126 are connected to the air cylinder 1
By the expansion and contraction of 24, it moves back and forth as a unit. Further, as shown in the figure, in this apparatus, one upper transformer 122 is arranged for two stud guns 118, and one end of the secondary coil of the transformer has one electrode 126-1.
The other end of the secondary coil is connected to the other electrode 126-2. The transformer bracket 128 is a part of the secondary wiring, and is entirely made of copper or copper alloy. Even when the whole is not made of copper or the like, it is preferable to use a material having a low impedance such as copper for the portion connecting the electrode 126 and the transformer mounting portion.

The lower electrode 130 and the lower transformer 132 are fixedly arranged, and no air cylinder such as the stud gun 118 is provided. Further, one transformer 132 is provided for each of the two lower electrodes 130.
One end of the secondary coil in 32 is one lower electrode 130-1
The other end of the secondary coil is connected to the other lower electrode 130-2.

The upper and lower electrode polarities are wired so that the opposite electrodes have different signs. That is, if the upper electrode 126-1 is positive and 126-2 is negative, the lower electrode 13
0-1 is negative and 130-2 is positive. This electrode structure is a so-called push-pull type.

The operation during welding is as follows. The workpieces 114 and 116 are placed on the lower electrode 130. Then, the air cylinder 124 is extended to lower the electrode 126 from above the workpieces 114 and 116,
Press with a predetermined pressure. This state is the state shown by the two stud guns on the left side of FIG. Almost at the same time as this pressing operation, a voltage is applied between the electrodes by the upper transformer 122 and the lower transformer 132. As a result, the upper electrode 126-1 and the lower electrode 130-1, and the upper electrode 126-2
114, 116 between the lower electrode and the lower electrode 130-2
An electric current flows through. This current causes the joints of the workpieces 114, 116 to melt, and the electrode 126
The workpieces are joined by the pressing force of. In the case of this push-pull type, the electric current flowing to other than the welded portion can be reduced, so that the electric current can be effectively used. Also,
Similar to the device described above, the stud gun 124 and the transformer 12
2, and by integrating the lower electrode 130 and the lower transformer 132, the secondary wiring can be shortened and the loss can be reduced.

In the apparatus shown in FIG. 3 and the like, the lower electrode 130 and the lower transformer 132 are fixed, but a transformer-integrated stud gun having the same structure as the stud gun 118 is placed upside down. It is also possible to sandwich the work piece from above and below, and in this case also, the same effect as that of the above-mentioned device is obtained.

Further, although each of the above-mentioned devices is a device for welding on a horizontal surface of a workpiece, it is possible to perform welding work on a vertical surface or a slope by tilting the illustrated device as it is.

[0032]

As described above, according to the present invention, by reducing the induced voltage, the cross-sectional area of the iron core of the transformer is reduced, and the transformer is made compact and lightweight.

By increasing the number of turns of the secondary coil, the cross-sectional area of the iron core of the transformer is reduced, and the transformer is made compact and lightweight.

Further, the maximum usage rate is determined based on the actual usage conditions, and at this maximum usage rate, the heat dissipation capacity of the coil is determined so that the heat generation amount of the coil and the heat dissipation amount of the coil are balanced. It can be anything.

Further, by disposing the transformer so as to advance and retreat together with the electrodes, it is possible to shorten the secondary wiring and reduce the power loss. Also, by maintaining the secondary wiring as a rigid wiring and eliminating the cable, maintenance of the cable becomes unnecessary. In addition, the compact and lightweight transformer makes maintenance and replacement work easier.

[Brief description of the drawings]

FIG. 1 is a schematic view of a multi-spot welding machine according to the present invention.

FIG. 2 is a detailed view of a stud gun and a transformer of the welding machine shown in FIG.

FIG. 3 is a schematic view of another multi-spot welding machine according to the present invention.

FIG. 4 is a diagram showing a transformer integrated stud gun of the welding machine shown in FIG. 3 and a transformer integrated electrode arranged to face the stud gun.

[Explanation of symbols]

18 Stud gun, 22 Transformer, 26 Electrode, 28
Transformer bracket, 118 stud gun, 122
Upper transformer, 126 upper electrode, 128 transformer bracket, 130 lower electrode, 132 lower transformer.

Claims (4)

[Claims] 1. A resistance welding machine transformer for stepping down a primary voltage to a predetermined induced voltage to obtain a desired voltage between welding electrodes, wherein the induced voltage is 6 times or less of the voltage between welding electrodes. The transformer for a resistance welding machine is characterized in that the cross-sectional area of the iron core of the transformer is set to a minimum value necessary for generating the induced voltage. 2. A resistance welding machine transformer for stepping down a primary voltage to a predetermined induced voltage to obtain a desired voltage between welding electrodes, wherein the number of windings of a secondary coil is increased, A transformer for a resistance welding machine, wherein a cross-sectional area of an iron core of the container is set to a minimum value necessary for generating the induced voltage. 3. A transformer for a resistance welding machine for stepping down a primary voltage to a predetermined induced voltage in order to obtain a desired welding electrode voltage, which is based on the usage conditions of a welding machine in which the transformer is used. A resistor having a coil in which a maximum usage rate is set, and a ratio of a heat radiation amount per unit time of the coil of the transformer to a heat generation amount per hour of the coil during welding is the maximum usage rate. Welder transformer. 4. A multi-spot welding machine capable of simultaneously welding a plurality of points, wherein an electrode capable of advancing and retreating with respect to an object to be welded, advancing and retracting integrally with the electrode, and being connected to the electrode by a rigid wiring. A multi-spot welding machine.