JPH0234286A - Spot welding method - Google Patents

Abstract

PURPOSE:To stabilize welding quality and to reduce the number of shapings and replacements of electrodes by measuring tip areas of the electrodes before starting welding and during welding and regulating electric current concentration based on said measured areas to maintain it constant. CONSTITUTION:A holding tool 7 is provided to a rotation axis 6 and the same material piece 8 as a work is fixed thereon. Pieces of carbon paper 9 and transfer paper 10 are arranged on both surfaces of the material piece 8 which is made insertable between the electrodes 4 and 5. After welding is finished once, the electrodes 4 and 5 of a welding gun 1 sandwich and press the laminated pieces of transfer paper 10 and carbon paper 9 and material piece 8. At this time, the electrode tip shape areas are transferred to the pieces of paper 10 and the areas are calculated by cameras 11 and 12, a picture processor 13 and an arithmetic unit 14. The welding current concentration is then regulated based on the measured area and its value is always maintained constant. Accordingly, welding quality is stabilized and the number of shapings and replacements of the electrodes are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a spot welding method, and more particularly to a spot welding method in which stable welding strength can always be obtained using the same electrode.

[Prior art J] When spot welding is performed by holding a workpiece between a pair of electrodes and applying pressure and current, the number of welding points increases and the area of the tip of the electrode in contact with the workpiece increases, resulting in the current density of the welding current. decreases and welding quality deteriorates.

For this reason, in the past, deterioration in welding quality was prevented by frequently shaping the electrode tip or replacing the electrode. For this reason, there was a problem in that the welding work had to be stopped each time, resulting in a decrease in productivity. Particularly in a processing line that uses a large number of welding machines, electrode shaping and replacement must be carried out at the same time even though each electrode has a different degree of wear, resulting in a lot of wasted time and materials.

As a means to solve this problem,
As described in Japanese Patent No. 7034, a method is known in which welding is performed by measuring the number of welding times and linearly changing the welding current according to the number of welding times as shown in FIG.

[Problem to be solved by the invention]

In recent years, galvanized steel sheets have been increasingly used in automobile bodies, but when spot welding is performed on such galvanized steel sheets, the electrode tip area increases with the number of welding points due to the crushing of the electrode. This is due to the fact that a brittle alloy layer of copper and zinc is formed at the tip of the electrode, and this alloy layer falls off during welding.Since this falling off of the alloy metal generally occurs aperiodically, the area of the tip of the electrode does not change at a constant rate.

Therefore, with the method of changing the welding current value linearly with the number of welding points as described in the above publication, it is not always possible to obtain the current density necessary for welding, and there is a problem that sufficient welding quality cannot be obtained. was there.

The present invention has been made in view of the above circumstances, and provides a spot welding method that can obtain the current density necessary for welding by following changes in the electrode tip area, and can always obtain stable welding quality. The purpose is to

[Means to solve the problem]

In order to achieve the above object, the present invention measures the electrode tip area with a TV camera at any time before starting spot welding and during welding, and adjusts the welding current to a predetermined current density each time based on the measured area. It is characterized by being able to perform welding by adjusting it.

[Effect]

According to the above method, even if the electrode tip area changes discontinuously, this area is measured each time with a TV camera and the welding current is adjusted to obtain the required current density, so it is always stable. It is possible to obtain high quality welding.

〔Example〕

An embodiment of the spot welding method according to the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of the apparatus used in this example.

In the figure, electrodes 4 and 5 are attached to the tips of a pair of arms 2 and 3 of a welding gun 1 attached to a welding robot (not shown), respectively.

On the other hand, one end of a piece of material 8, which is the same as the workpiece to be welded by the welding gun 1, is attached to a holder 7 on a rotating shaft 6 which is rotationally driven by a perturbation source (not shown), and is perpendicular to the rotating shaft 6. Fixed in direction. Further, carbon paper 9 and transfer paper 10, each of which has one end held by the holder 7, are laminated on both ends of this material piece 8. The carbon calendar of the carbon paper 9 is formed on the surface opposite to the surface facing the material piece 8, and the transfer paper 10 is made of translucent paper such as tracing paper. The transfer paper 10 and the material piece 8 are inserted integrally between the electrodes 4 and 5, and when they are pressed by the electrodes 4 and 5, the tips of the electrodes 4 and 5 The shape is transferred to the transfer paper 10 as a suppression.

On the other hand, the depressions transferred onto the transfer paper 10 at the tips of these electrodes 4 and 5 are detected by small television cameras 11 and 12, respectively.
This small television camera 11.12 is equipped with an image processing device 13. Arithmetic device 14
．． A welding current control device 15 is connected in sequence, and this welding current control device 15 is connected to a welding power source 16.

Next, a method of performing spot welding using the apparatus configured as described above will be described below.

After one welding is completed, the welding gun 1 is positioned by the taught robot at the predetermined position shown in FIG. 1, and the transfer paper 10.5 on which five layers of electrodes 4.5 are laminated is applied using the same pressure as during welding. carbon paper.

The material piece 8 is held and pressed. At this time, the shapes of the tips of the electrodes 4 and 5 are transferred from the carbon paper 9 to the transfer paper 10.

Then, this shape is imaged by a television camera 11.degree. 12, and the area is determined by performing image processing by an image processing device 13. At this time, if the wear of the electrodes 4 and 5 is different and the areas of the tips are different, the areas are compared and the larger one is taken as the area measurement value.

Then, the arithmetic unit 14 multiplies this area measurement value by the current density during the first welding and sets it as the next welding current value. The current density during this initial welding is the initial welding current divided by the initial electrode tip area, and can be determined in advance. By repeating these operations, a constant welding current density can always be obtained via the welding current control device 15, and stable welding quality can be ensured.

Note that since the transfer paper 10 is made of semi-transparent paper, the suppression can be read from the back side of the transfer surface, and since the carbon paper 9 cannot be transferred continuously at the same position, the holder 7 is attached. By rotating the rotating shaft 6, pressure transfer can always be performed on a new surface.

It is most desirable to measure the area of the electrode tip and change the welding current as described above each time weld.

In practice, it may be performed every several to ten-odd welds.

According to this embodiment, the welding current is changed in accordance with the change in the area of the tips of the electrodes 4, 5, so that a constant current density can always be obtained. 5, it is possible to obtain stable welding quality over a long period of time. As a result, the number of times of electrode shaping and replacement is greatly reduced, and time and material waste can be reduced.

In the above embodiment, a case has been described in which the shapes of the tips of the electrodes 4 and 5 are imaged by the television camera 11.12 using the transfer paper 10 and the carbon paper 9.
12 may directly image the tip shapes of the electrodes 4 and 5.

〔Effect of the invention〕

As described above, according to the spot welding method according to the present invention, the electrode tip area is measured at any time using a television camera, and the welding current is always adjusted to a predetermined current density, so that a pair of electrodes can be It is possible to obtain stable welding quality over a long period of time. Moreover, the number of times of electrode shaping and replacement can be greatly reduced, which saves time and waste of materials.

[Brief explanation of the drawing]

FIG. 1 is a system configuration diagram showing an embodiment of the spot welding method according to the present invention, and FIG. 2 is a graph showing the relationship between the number of welds and welding current in a conventional spot welding method. 4.5... Electrode, 11.12... Television camera. 13... Image processing device. 15...Welding current control device. 16...Welding power source.

Claims (1)

[Claims] (1) Before starting spot welding and during welding, the area of the electrode tip is measured at any time using a TV camera, and the welding current is adjusted each time based on the measured area so that the current density is always the specified value. Characteristic spot welding method.