JPH01317687A - Spot welding method for laminated steel plate - Google Patents

Abstract

PURPOSE:To improve joining strength of spot welding of a laminated steel plate by vibrating pressing electrodes by ultrasonic waves at the time of preheating to remove a resin layer of a welding point and pressing and electrifying said welding point by the electrodes to perform welding thereon. CONSTITUTION:The laminated steel plate 1 formed by laminating the resin layer 1a between a couple of steel plates 1b and 1c and an ordinary steel plate 2 are held between the upper electrode 3a and the lower electrode 3b. These are pressed and electrified by both electrodes 3a and 3b. At a first stage, at the time of preheating, the upper electrode 3a is vibrated by an ultrasonic oscillator 6 and a vibrator 7 and the resin layer of the spot welding point is softened and removed. At a second stage, the welding point where the resin layer is removed is pressed and electrified by both electrodes 3a and 3b and welded and joined together. By this method, the joining strength of spot welding of the laminated steel plate can be improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a laminated steel plate in which a resin layer is laminated between a pair of steel plates, or a laminated steel plate and a normal steel plate, which are laminated and subjected to resistance welding. This invention relates to improvements in spot welding methods for steel plates.

[Conventional technology]

Laminated steel plates with a resin layer sandwiched between them are widely used as vibration damping steel plates. When performing spot welding, in which such laminated steel plates, or a laminated Mll plate and a regular steel plate are stacked on top of each other and are held and pressed between a pair of electrodes while a current is applied to melt and join them by the resistance heat generation of the welded parts, the laminated steel plates Top and bottom 2
Since the layers are electrically insulated by an intermediate resin layer, they cannot be welded by normal methods, so welding is carried out by a branch welding method as shown in FIG.

In the figure, two steel plates lb and l are sandwiched between resin layer 1a.
A laminated steel plate 1 formed by laminating the 1X layered steel plate 1 and a normal steel plate 2 are stacked on top of each other, and the 1X layered steel plate 1 and the normal steel plate 2 are held between a pair of electrodes 3a and 3b. Further, the outer steel plate 1b of the laminated steel plate 1 and the normal steel plate 2 are connected to the short-circuiting fitting 4.
electrically connected by.

By applying a voltage to the electrodes 3a and 3b, the current flows between the electrode 3a and the steel plate 1 as shown by arrow A at the initial stage of energization.
b. Short circuit fitting 41 normal steel plate 2. It flows in the order of the electrode 3b, the thin steel plate 1b generates heat due to volume resistance, and then the temperature of the resin layer 1a in contact with it rises.

As a result, the resin in this part softens and the electrode 3a.

The electrode 3a is removed to the surroundings by the pressing force of the electrode 3b.

The steel plates 1b and lc between the steel plates 3b are in direct contact with each other. From then on, electrode 3
Ordinary spot welding is performed by applying current and pressure through a and 3b. Once the −degree welding point is formed, it is not necessary to attach the shorting fitting 4 for welding from the second point onwards. The same applies to spot welding between laminated steel plates.

Also, as a conventional proposal related to this technology.

As described in Japanese Patent Application Laid-Open No. 55-139188,
In the first step, the object to be welded is held and pressurized while applying ultrasonic vibrations to the electrodes to remove the coating from the welding area, and in the second step, welding current is passed between the electrodes to perform welding. Welding methods, such as those described in Japanese Unexamined Patent Publication No. 62-248577, are known in which the electrodes are vibrated by ultrasonic waves during welding to achieve stable quality welding with low current. be.

[Problem to be solved by the invention]

However, according to the conventional method shown in FIG. 3, the shunt path through which the shunt current for preheating the laminated steel plate 1 passes is long and its resistance is large, so a high voltage must be applied between the electrodes 3a and 3b. It won't happen.

For this reason, if total bending particles are mixed in the resin layer 1a, current will concentrate there, and the steel plate 1b will be heated.

There was a problem in that a pinhole-like defect occurred through 1c.

In addition, the preheating time using the shunt current must be appropriately set according to the shunt current value and the thickness of the laminated steel plate 1.1. If the second preheating time is insufficient, the removal of the resin layer 1a will be insufficient, resulting in a problem of poor conductivity.

In addition, the former of the above two publications applies pressure with an electrode and vibrates the electrode with ultrasonic waves without applying a welding current.
This method removes the coating on the surface of the workpiece, and the latter removes the oxide film on the surface of the workpiece by vibrating the electrode with ultrasonic waves during the actual spot welding.
In both cases, no consideration was given to the fact that the intermediate resin layer of the laminated steel plate is removed by ultrasonic waves during preheating for spot welding.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for spot welding laminated steel plates that can shorten preheating time during welding of laminated steel plates and improve joint strength.

[Means to solve the problem]

In order to achieve the above-mentioned object, the present invention includes a pair of laminated steel plates in which a resin layer is laminated between each other, or a laminated steel plate and a normal steel plate, which are sandwiched between a pair of electrodes and energized under pressure. In a spot welding method for laminated steel plates to be joined, a first step of applying ultrasonic vibration to at least one electrode during preheating by applying pressure and electricity through the electrode, and softening the resin layer by the frictional heat caused by the vibration and removing it from the welding point. This is a spot welding method comprising the following steps: and a second step of welding and joining by applying pressure and current through the pair of electrodes disposed at the welding point from which the resin layer has been removed.

[Effect]

According to the above method, in the preheating process in which the object to be welded is held between a pair of electrodes, pressurized, and energized, at least one of these electrodes is vibrated by ultrasonic waves. Frictional heat is generated between the welding point and the welding point, and this frictional heat causes the resin layer in this area to heat up and soften, and is removed from the welding point to the surrounding area by the pressure and vibration of the electrode, and the steel plate in the area held between the electrodes is removed. comes into direct contact.

At this time, a voltage is applied between the electrodes, and the temperature of the welding point rises due to the contact resistance of the current flowing between the electrode and the steel plate, so the resin layer can be reliably removed in a short time, and the preheating time can be reduced. Can be shortened. After that, normal spot welding is performed.

〔Example〕

Hereinafter, one embodiment of the method for spot welding laminated steel plates according to the present invention will be described with reference to the drawings.

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

In the figure, parts that are the same or equivalent to those of the conventional device shown in FIG. 3 are designated by the same reference numerals, and their explanation will be omitted.

The device used in this example is characterized in that a vibrator 7 vibrated by an ultrasonic oscillator 6 is fixed to a shank 5 that supports an upper electrode 3a.

Next, a spot welding method according to this embodiment will be explained. In the first step, the laminated steel plate 1 and the normal steel plate 2 are overlapped to form a pair of electrodes 3a.

3b, and supplying current from a power source (not shown), the upper electrode 3a, @plate 1b, shorting fitting 4, normal steel plate 2,
A current is applied to the lower electrode 3b in this order. At the same time, while the upper electrode 3a is vibrated by the ultrasonic oscillator 6 via the shank 5 and the vibrator 7, the steel plate 1 and the ordinary steel plate 2 are pressurized between the upper electrode 3a and the lower electrode 3b. In this state, this portion generates heat due to the contact resistance between the upper electrode 3a and the steel plate 1b, and between the lower electrode 3b and the steel plate 1c, and this heat is transmitted to the resin layer 1a. At the same time, as the upper electrode 38 vibrates in the direction of arrow B, the laminated steel plate 1 and the ordinary steel plate 2 slide, and the frictional heat generated mainly between the steel plate IC and the ordinary steel plate 2 is transferred to the resin layer 1.
given to a. As a result, the resin in that area softens,
This resin is removed to the surroundings by the pressure applied by the electrodes 3a and 3b, and the 1wJ plates lb and lc come into direct contact.

Next, in a second step, spot welding as normal lap resistance welding is performed by supplying a predetermined welding current while applying pressure to the laminated steel plate 1 and the normal steel plate 2 using the electrodes 3a and 3b. - Once the weld point is formed, 2
For welding after the point, the shorting fitting 4 is not required, and normal spot welding is possible.

Figure 2 shows that when spot welding the laminated steel plate 1 and the normal steel plate 2 by the above method, the amplitude is 60 μm and the frequency is 15.
An experimental example of the relationship between the pressing force and vibration time of the electrodes 3a and 3b that can remove the resin when KHz ultrasonic vibration is applied will be shown.

According to this embodiment, heat generated by volume resistance and frictional heat generated by ultrasonic vibration are used together during preheating for resin removal, so it is possible to significantly shorten the energization time for preheating, and to ensure that Conductivity of the laminated steel plate 1 is obtained. Further, since the voltage applied for preheating can be small, even if metal particles are mixed in the resin, the occurrence of pinhole-like defects can be minimized.

In the above embodiment, the case where the laminated steel plates 1 and the normal steel plates 2 are spot welded is explained, but it can also be applied to the case where the laminated steel plates 1 are spot welded together, and the same effect can be obtained. Further, the vibrator 7 may be provided on the lower electrode 3b or the surface electrodes 3a, 3b instead of being fixed on the upper electrode 3a. Furthermore, the present invention can also be applied to a case where the intermediate layer of the laminated steel plate 1 is a weld bond in which an adhesive is present. Further, the conduction of the laminated steel plate 1 may be achieved by omitting the preheating by energization and using only the frictional heat caused by vibration.

〔Effect of the invention〕

As explained above, according to the present invention, the pressure electrode is vibrated by ultrasonic waves during preheating for spot welding laminated steel plates together or a laminated steel plate and an ordinary steel plate. The resin layer can be softened and removed by the frictional heat, and electrical conductivity can be quickly obtained between the laminated steel plates and the joint strength can be improved.

In addition, it is possible to shorten the energization time for preheating, reduce the voltage, and shorten the welding takt.
Moreover, the occurrence of pinholes can also be suppressed.

[Brief explanation of the drawing]

FIG. 1 is a front view of the main parts of a welding device used in an embodiment of the spot welding method for laminated steel plates according to the present invention, and FIG. A graph showing the relationship, and FIG. 3 is a front view of main parts showing a conventional spot welding device. DESCRIPTION OF SYMBOLS 1... Laminated steel plate, 1a... Resin layer, lb, lc... Steel plate, 2... Ordinary steel plate, 3a... Upper electrode, 3b... Lower electrode, 5... Shank, 6 ... Ultrasonic oscillator, 7... Vibrator.

Claims (1)

[Claims] (1) In a spot welding method for laminated steel plates in which a resin layer is laminated between a pair of steel plates, or a laminated steel plate and a normal steel plate, which are sandwiched between a pair of electrodes and joined by applying pressure and current. , a first step of applying ultrasonic vibration to at least one electrode during preheating by applying pressure and electricity through the electrode, and softening the resin layer by frictional heat caused by the vibration and removing it from the welding point; A method for spot welding laminated steel plates, comprising the step of welding and joining by applying pressure and current using the pair of electrodes disposed at the welding points.