JPH0592276A - Resistance welding equipment - Google Patents

Abstract

PURPOSE:To mutually equalize wear of a couple of welding electrodes. CONSTITUTION:Thyristors 12 and 13, and 14 and 15 of antiparallel, connection to carry out switching operation are provided on a secondary side circuit to join a welding transformer 1 to the couple of welding electrodes 8 and 9. The thyristors 12 and 14, and the thyristors 13 and 15 are subjected to ON-OFF operation alternately by a controller 16 for every welding operation and the flowing direction of a welding current is changed over for every welding operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance welding apparatus represented by a spot welding apparatus.

[0002]

2. Description of the Related Art As one of spot welding apparatuses, there is a so-called DC type apparatus in which a welding current is directly rectified in a secondary side circuit of a welding transformer. In this system, for example, as shown in FIG. 4, a pair of diodes 4 and 5 are connected as a rectifier 3 to a secondary coil 2 of a welding transformer 1 connected to an AC welding power source to directly rectify a secondary current to generate a direct current. It is intended to obtain a predetermined welding current by converting the material into a different material. In addition, 6 is a primary coil of the welding transformer 1, 7 is a spot welding gun having a pair of welding electrodes 8 and 9, and W is an object to be welded.

[0003]

In the conventional spot welding apparatus as described above, it is assumed that the integrated terminal portions 10 on the output side of the diodes 4 and 5 are connected to one welding electrode 8. Assuming that the terminal portion 11 from which the intermediate portion of the next coil 2 is pulled out is connected to the other welding electrode 9, the welding current is always from one welding electrode 8 to the other welding electrode due to the rectifying action of the diodes 4 and 5. 9 side (arrow e
Direction) and the welding current flow direction remains constant. As a result, the wear of the welding electrodes 8 and 9 is concentrated on one of the welding electrodes, and the life of the welding electrodes 8 and 9 is shortened.

The present invention has been made in view of the above problems, and it is an object of the present invention to equalize the wear of both welding electrodes by switching the flow direction of the welding current for each welding operation. And

[0005]

According to the present invention, there are provided two sets of antiparallel connection rectifying elements that perform switching operation in a secondary side circuit connecting a welding transformer of a resistance welding apparatus and a pair of welding electrodes. A welding current switching control means for selectively turning on and off the plurality of rectifying elements for each welding operation to switch the flow direction of the welding current for each welding operation. There is.

[0006]

According to this structure, the flow direction of the welding current is switched for each welding operation, which is opposite to the flow direction of the welding current at the previous welding. As a result, the wear of the pair of welding electrodes is equalized.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing an embodiment of the present invention, in which parts common to those in FIG. As shown in FIG. 1, in the present embodiment, the structure of the rectifier 3 is different from that of the conventional one, and both ends of the secondary coil 2 of the welding transformer 1 are in antiparallel with each other as rectifying elements that perform switching operation. A pair of thyristors 12, 13 and 14,
Both ends of the secondary coil 2, to which the thyristors 12, 13 and 14, 15 are connected, are gathered at the terminal portion 10 and the spot welding gun 7 is provided.
It is connected to one of the welding electrodes 8. The gate electrodes of the thyristors 12, 13 and 14, 15 are connected to the control device 16 as the welding current switching control means.

In the spot welding apparatus constructed as described above, as shown in the simplified circuits of FIGS.
When a welding voltage is applied to the welding transformer 1 and a welding current flows through the welding transformer 1 in response to a welding command at a specific welding point position, the control device 16 sends a gate signal to the thyristors 12 and 14 to cause the thyristors 12 and 14 to operate. Turn it on. As a result, does the welding current (secondary current) i flow from one welding electrode 8 of the spot welding gun 7 to the other welding electrode 9 side through the terminal portion 10 as shown by the arrow a in FIG. , Or thyristor 1 as shown by arrow b
4 through the terminal portion 10 to flow from one welding electrode 8 of the spot welding gun 7 to the other welding electrode 9 side in the same manner as described above, and the workpiece W is subjected to predetermined welding. At this time, since the other thyristors 13 and 15 are both in the OFF state, the welding current i does not flow except through the above path.

When the welding of the specific welding spot is completed, the control device 16 receives the welding completion signal and the control device 16 receives the thyristors 12, 14.
Of the thyristors 12 and 14 are turned off when the electric current to the welding transformer 1 is cut off and the anode current (anode voltage) of the thyristors 12 and 14 becomes less than the holding current.

On the other hand, when the welding current flows through the welding transformer 1 again at the time of welding the next welding point, the control device 16 sends a gate signal to the thyristors 13 and 15 in the opposite manner to turn on the thyristors 13 and 15. As a result, the welding current i flows from the thyristor 13 through the terminal portion 11 to one welding electrode 9 of the spot welding gun 7 to the other welding electrode 8 side as shown by an arrow c in FIG. From the thyristor 15 to the terminal portion 11 as shown by the arrow d.
Similarly, the welding current flows from one welding electrode 9 of the spot welding gun 7 to the other welding electrode 8 side, and the object W to be welded is subjected to predetermined welding. Then, the above operation is repeated thereafter.

As described above, the thyristors 12, 14 and 13, 15 are alternately turned ON for each welding operation, whereby the flow direction of the welding current is switched each time. Needless to say, the present invention can be applied to resistance welding other than spot welding.

[0012]

As described above, according to the present invention, by changing the flow direction of the welding current flowing between the pair of welding electrodes for each welding operation, the wear of the welding electrodes as in the prior art is eliminated. The wear of the pair of welding electrodes can be equalized without being biased to one of the electrodes, and thus the life of the welding electrodes can be extended.

Further, when welding is continuously performed using the same electrode, the welding current is gradually increased until dressing (polishing) of the welding electrode is required in anticipation of wear of the welding electrode. However, by equalizing the wear of the pair of welding electrodes and prolonging their service life as described above, it is possible to reduce the current increase rate when the welding current is stepped up. Therefore, energy saving can also be achieved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a circuit configuration of a spot welding apparatus showing an embodiment of the present invention.

FIG. 2 is an operation explanatory view of a circuit which is a simplified version of FIG.

FIG. 3 is an operation explanatory diagram of a circuit obtained by simplifying FIG. 1.

FIG. 4 is a structural explanatory view showing an example of a conventional DC spot welding apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Welding transformer 2 ... Secondary coil 7 ... Spot welding gun 8, 9 ... Welding electrode 12, 13, 14, 15 ... Thyristor as a rectifying element 16 ... Control device a, b, c as a welding current switching control means. d ... Welding current flow direction i ... Welding current (secondary current)

Claims (1)

[Claims] 1. A pair of anti-parallel connection rectifying elements that perform switching operation are provided in a secondary side circuit connecting a welding transformer of a resistance welding device and a pair of welding electrodes, and two sets are provided for each welding operation. ON-OF selectively selecting the plurality of rectifying elements
A resistance welding apparatus characterized by comprising welding current switching control means for performing F operation and switching the flow direction of welding current for each welding operation.