JPH06179082A - Double action type resistance spot welding electrodes - Google Patents

Abstract

PURPOSE:To improve the service life of the electrodes to perform spot welding on a plated steel sheet, aluminum and an aluminum alloy or material with aluminum and the aluminum alloy plated. CONSTITUTION:The double acting type resistance spot welding electrodes are composed of inside electrodes 10 and 12 with electric conduction of a core part as a main purpose and outside electrodes 11 and 13 with pressurization as a main purpose formed around those and the inside electrodes are made of metal having electric conductivity >=75 (IACS%). Further, the diameter thereof is made 2.5sq. rt. t (wherein (t) = thickness mm of materials to be welded), the outside electrodes are made of metal having electric conductivity lower by >=40 (IACS%) than the inside electrodes and having the melting point higher than the materials to be welded and gaps are provided between the inside electrodes and the outside electrodes and these are made movable mutually.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a compound for dramatically improving the electrode life when a plated steel sheet having a shorter electrode life than a rolled steel sheet, aluminum and an aluminum alloy and its metal plated material are used as the materials to be welded. The present invention relates to a dynamic resistance spot welding electrode.

[0002]

2. Description of the Related Art Electrode materials conventionally used for resistance spot welding of plated steel sheets, aluminum and aluminum alloys and their metal plating materials have relatively high high-temperature strength, good electrical conductivity, and good thermal conductivity. Chrome copper, chromium-zirconium copper, and alumina-dispersed copper, which are relatively low in cost, are used. Further, as the electrode shape for spot welding, R type, DR type, CF type, pimple type, etc. are often used. All of these electrodes perform the function of supplying electricity necessary for welding and the function of pressurizing with one electrode.

When two electrodes are overlapped and resistance spot welded using these electrodes under proper welding conditions, as shown in FIG. 4, the nugget 5 (two plates are melted by resistance heat generation and added The part joined by pressure) is in the shape of a go stone,
It is formed within the range of the diameter of 2, there is no dust generation, and the strength of the joint is high, but when the electrode and the material to be welded are alloyed and the tip of the electrode is consumed, the nugget 5 becomes uneven as shown in FIG. Then, it melts to the outside of the electrode diameter, and middle dust 8 and outer dust 7 are generated,
In a remarkable case, most of the molten metal in the nugget becomes dust and scatters to form cavities 9, which lowers the strength of the joint and extends the life of the electrode.

In the initial stage of welding, since the electrodes are not consumed, electricity is applied at the center of the electrodes, and resistance heating between the plates directly below the electrodes melts the materials to form a gobstone-shaped nugget. The molten nugget is a ring-shaped corona bond region 6 (diffusion-bonded that prevents molten metal from leaking outside) formed near the outer circumference of the electrode between the two plates directly below the electrode by pressing the electrode. It is surrounded by () and forms a good nugget without jumping out.

However, when the electrode is consumed and current is applied to the outer periphery of the electrode, a nugget is formed outside the corona bond region, so that the function of covering the molten metal with the corona bond is lost and dust is generated and the nugget is hollow. And the strength decreases. With conventional electrodes, the electrode life is
It is said that the number is 3000 to 5000 points, about 30 to 1000 points in the case of aluminum and aluminum alloys, and the number of the metal-plated materials is less than that. In the automobile industry, spot welding is performed using rolled steel sheets, and the electrode life is 10,000 points or more. Compared with that, the electrode life of the conventional plated steel sheet is 3
000 to 5,000 points, aluminum and aluminum alloys have 30 to 1,000 points, and the metal plating material has less than that, which is extremely inferior.

[0006] As a method for improving the life of the electrode, many studies have hitherto been made. Among them, the one proposed by many researchers is to use a material having a high melting point and hardness as a core material and to have conductivity outside. This is a method of using a good material or a material having relatively high strength and toughness. For example, JP-A-47-
No. 23426, JP-A-49-106456 and other publications. However, even when spot welding was performed using these electrodes, the heat generated during welding of the core material was large, and the core material was alloyed with the material to be welded and welded. In addition, since electricity is applied where the conductivity of the outer periphery of the electrode is good, a nugget is formed outside the corona bond, and dust is generated, and the life shortening effect is actually small.

Contrary to the above method, a method of obtaining a stable weld portion by using a material having good conductivity as a core material and using a non-conductive or wear resistant material on the outside has been considered. For example, there are Japanese Patent Publication No. 45-30580 and Japanese Patent Publication No. 46-900. In this case, it is considered that the effect of covering the molten metal of the nugget is obtained by applying current at the core material and forming a corona bond by applying pressure with the non-conductive or wear-resistant material of the outer peripheral portion, Had a small effect of improving the life because the non-conductive ceramic and the wear-resistant cemented carbide were cracked when pressed.

In the automobile industry, from the viewpoint of energy saving and global environment, weight reduction of automobiles is desired, and aluminum and aluminum alloys and materials obtained by metal plating of these are attracting attention as automobile materials. As described above, the electrode life of these materials is remarkably inferior to that of the rolled steel sheet, which is a bottleneck. At least an electrode life of 4000 to 5000 points, which is about the current electrode life of plated steel sheets, is desired. In addition, a plated steel sheet is used for the outer plate in order to improve the corrosion resistance of automobiles and increase in quality. However, since the electrode life is still inferior to that of the rolled steel sheet, an electrode life of 10,000 points or more comparable to that of the rolled steel sheet is desired. It was However, it has been difficult for the conventional electrodes to improve their service lives as described above.

[0009]

DISCLOSURE OF THE INVENTION The present invention has been made as a result of studies on the above-mentioned problems, and in resistance spot welding of plated steel sheets, aluminum and aluminum alloys and their metal-plated materials, We have developed an electrode that dramatically improves the life of the electrode.

[0010]

According to the present invention, an inner electrode whose main purpose is electric conduction of a core and an outer electrode whose main purpose is pressurization are formed around the inner electrode, and the inner electrode has a conductivity of 75.
(IACS%) or more, and its diameter is 2.5√t (where t = plate thickness mm of the material to be welded), and the conductivity of the outer electrode is 40 (IAC) than that of the inner electrode.
For double-acting resistance spot welding, characterized by being made of a metal having a melting point higher than that of the material to be welded, having a gap between the inner electrode and the outer electrode, and being movable with respect to each other. The electrode is claim 1, and the material of the inner electrode is
99.9% Cu, Cu-1% Cr, Cu-1% Cr-
0.2Zr, 1% alumina dispersed copper, Cu-2% Be, 9
The double-acting resistance spot welding electrode according to claim 1, wherein the outer electrode is made of 99.9% Fe, 18-8 stainless steel, 99.9% Ti, 99.9% Ni, Ni alloy (alumel), 99.9% Mo, 99.9% W, Cu-10%
The double-action resistance spot welding electrode according to claim 1 is Zn. That is, the present invention, the electrode has a double structure, the inner electrode is a highly conductive material, the outer electrode is a low conductive material,
In addition, a gap is provided between the inner electrode and the outer electrode so that the inner electrode and the outer electrode are movable with respect to each other.

[0011]

[Function] The reason why the electrode is the double-acting type is that the conventional core material is a conductive material and the outer periphery is made of a material with poor electrical conductivity. The material to be welded is consumed by alloying with the aluminum alloy, and only the material on the outer periphery remains, and finally the tip has a concave shape, which makes it difficult to conduct electricity and makes it impossible to weld. The electrode of the present invention separates the inner electrode that is consumed and the outer electrode that is less likely to be worn, and by moving them separately, the material to be welded is always in contact with the inner electrode and the outer electrode, and the functions of both are The life of the electrode is improved by always making it the same as when welding was started. In the present invention, the conductivity of the inner electrode is 75 (IAC
S%) or more, the reason is that if it is less than that, the electrode is easily heated and alloyed, and the effect of improving the life of the electrode is small. The conductivity of the outer electrode is 40 (IAC
The reason why the nugget must be made lower than the S%) is that when the conductivity is higher than that value, the nugget is formed outside the electrode contact part by energizing at the outer peripheral part of the coating material during welding, and the nugget is pressed by the electrode. This is because the corona bond area that holds the molten metal inside is broken, and the molten metal jumps out from there and becomes dust, causing the nugget to become hollow, reducing the strength, and shortening the electrode life.

The reason why the melting point of the outer electrode is set higher than that of the material to be welded is that if the melting point is lower than these, it is likely to melt and alloy. When the material to be welded is a plating material, it is higher than the melting point of the plating material. Furthermore, the reason for setting the tip diameter of the inner electrode to 2.5√t (where t = plate thickness mm of the material to be welded) or more is that if it is less than that, the nugget diameter will be small if welding is performed under suitable welding conditions, and the electrode life will be reduced. This is because when the welding is performed under welding conditions such that the length becomes short and the nugget diameter is made large, the electrode is consumed greatly.

Materials that can be welded using the electrode of the present invention include aluminum or aluminum alloys, for example, aluminum alloys such as Al--Cu type, Al--Mn type, and A type.
1-Si type, Al-Mg type, Al-Mg-Cu type, Al
-Mg-Si system, Al-Zn-Mg system, Al-Zn-M
Zn, Zn-Fe, Zn- on the surface of the above aluminum or aluminum alloy, including alloy materials such as g-Cu
Materials plated with metals such as Ni, Fe, Fe-Zn, and Fe-Ni, Zn, Zn-Fe, Zn-Ni, and Fe-
It can be applied to resistance spot welding of plated steel sheets such as P.

The welding machine used for the resistance spot welding is a conventionally used single-phase AC welding machine, single-phase rectification welding machine, three-phase low-frequency welding machine, three-phase rectification welding machine, and inverter welding machine. , A condenser type welding machine or the like may be used.
Further, the electrode shape may be any of R type, DR type, CF type, pimple type and the like.

[0015]

EXAMPLES An example of the present invention will be described below. Example 1 FIG. 1 is a schematic diagram showing Example 1. That is, the electrode is R
Shape, the inner electrodes 10 and 12 are Φ2.5 to 5.5 mm, the outer electrodes 11 and 13 are Φ16 mm, the gap 14 is 0.1 mm, and R = 8.
It was set to 0 mm. A5182P-0 material with a plate thickness (t) of 1 mm was used as the materials 3 and 4 to be welded. The width of the test piece is 30m
The length was set to m and the length was set to 200 mm, two of them were stacked and used, and the electrode conditions were changed as shown in Table 1 for welding. The welding conditions are as follows.・ Welding equipment: Single-phase AC welding machine ・ Pressure force: Inner electrode 270kgf Outer electrode 300kgf ・ Electrification time: 5 cycles ・ Welding current: Appropriate welding current value at each electrode (25000)
± 1000 A) ・ Welding pitch: 30 mm ・ Spotting speed: 1 point / 2 seconds The electrode life was evaluated by nugget diameter = 4√t × 90% = 3.
6 mm was set as the maximum number of welding points until it could not be secured, and when electrode cracking or electrode welding occurred on the way, the test was terminated at that point. Table 1 shows the electrode life test results. In addition, the judgment in the table indicates that the electrode life is 5000 points or more.
Mark, 4000 to less than 5000 points, ○ mark, 1000 to 40
Less than 00 points were marked with Δ, and less than 1000 points were marked with X.

[0016]

[Table 1]

As is clear from Table 1, when the electrode of the present invention was used, the electrode life of 5000 points or more was exhibited in all cases. On the other hand, the reference electrode No. No. 8 has a small inner electrode diameter, so No. No. 9 has a low conductivity, and No. No. 10 has a small difference in conductivity between the inner and outer electrodes. In No. 11, since the melting point of the outer electrode is low, the electrode life is less than 1000 points. In addition, the conventional electrode No. 12-No. 18 was also less than 1000 points.

Example 2 As shown in FIG. 2, the electrodes are DR type and the inner electrodes 10 and 12 are
Is Φ3-6mm, outer electrodes 11 and 13 are Φ16mm, tip Φ
7 mm, the gap 14 was 0.3 mm, and R = 40 mmR. As a material to be welded, a material having a plate thickness (t) of 1.2 mm, which was plated with Zn, Zn-15% Fe, and Zn-10% Ni on both sides of 20 g / m ² was used. The dimensions of the test piece were 30 mm in width and 200 mm in length. Two pieces of the test piece were used in piles, and the electrode conditions were changed as shown in Table 2 to perform welding. The welding conditions are as follows.・ Welding equipment: Single-phase rectification welding machine ・ Pressure force: Inner electrode 300kgf Outer electrode 325kgf ・ Electrification time: 5 cycles ・ Welding current: Appropriate welding current value at each electrode (25000)
± 1000 A) ・ Welding pitch: 30 mm ・ Spotting speed: 1 point / 2 seconds The electrode life was evaluated by nugget diameter = 4√t × 90% = 3.
9 mm was set as the maximum number of welding points until it could not be secured, and when electrode cracking or electrode welding occurred on the way, the test was terminated at that point. Table 2 shows the electrode life test results. The judgments in the table are the same as in Example 1.

[0019]

[Table 2]

As is apparent from Table 2, when the electrode of the present invention was used, the electrode life was 4000 points or more. On the other hand, the reference electrode No. No. 8 has a small inner electrode diameter, so No. No. 9 has a low electrical conductivity, so No. 10 is inside,
Since the difference in conductivity of the outer electrode is small, No. In No. 11, since the melting point of the outer electrode is low, the electrode life is less than 1000 points.
In addition, the conventional electrodes No. 12 to No. 18 was also less than 1000 points.

Embodiment 3 As shown in FIG. 3, the electrodes are CF type, and the inner electrodes 10 and 12 are
Is Φ2.5-5.5 mm, the outer electrodes 11, 13 are Φ16 m
m, the gap 14 was 0.5 mm, and the tip was 6 mm. Zn, Zn-15% F with a plate thickness (t) of 0.8 mm as the material to be welded
e, a plated steel sheet having Zn-10% Ni plating of 20 g / m ² was used. The width of the test piece is 30 mm and the length is 20
The thickness was set to 0 mm, two of them were stacked, and the electrode conditions were changed as shown in Table 3 and welding was performed. The welding conditions are as follows.・ Welding equipment: Inverter welding machine ・ Pressure force: Inner electrode 270kgf Outer electrode 300kgf ・ Electrification time: 5 cycles ・ Welding current: Proper welding current value at each electrode (8000 ±
1000 A) ・ Welding pitch: 30 mm ・ Spotting speed: 1 point / 2 seconds The electrode life was evaluated by nugget diameter = 4√t × 90% = 3.
The maximum number of welding points until 2 mm cannot be secured was reached, and when electrode cracking or electrode welding occurred during the test, the test was terminated at that point. Table 3 shows the electrode life test results. The judgments in the table are the same as in Example 1.

[0022]

[Table 3]

As is clear from Table 3, when the electrode of the present invention was used, the electrode life was 10,000 points or more. On the other hand, the reference electrode No. No. 8 has a small diameter for the inner and outer electrodes, so No. 8 No. 9 has a low electrical conductivity, so No. No. 10 has a small difference in conductivity of the inner electrode, so No. In No. 11, since the melting point of the outer electrode is low, the electrode life is less than 5000 points.
In addition, the conventional electrode No. 12-No. 18 was also less than 5000 points.

[0024]

INDUSTRIAL APPLICABILITY As described above, the present invention can remarkably improve the electrode life when resistance spot welding aluminum and aluminum alloys and materials having metal plating on the surface thereof or plated steel sheets. Therefore, it greatly contributes to the improvement of resistance spot welding and the improvement of the electrode life of the plated steel sheet, which have been the biggest bottleneck of aluminum in mass production of automobiles and the like.

[Brief description of drawings]

FIG. 1 is a sectional view of a welded portion by spot welding using the electrode of the present invention.

FIG. 2 is a cross-sectional view of another example of a welded portion by spot welding using the electrode of the present invention.

FIG. 3 is a sectional view of yet another example of a welded portion by spot welding using the electrode of the present invention.

FIG. 4 is a sectional view of a welded portion at the beginning of welding by spot welding using a conventional electrode.

FIG. 5 is a cross-sectional view of a welded portion when the electrode is consumed by spot welding using a conventional electrode.

[Explanation of symbols]

 1 Upper electrode 2 Lower electrode 3 Upper welded material 4 Lower welded material 5 Nugget 6 Corona bond area 7 Outer dust 8 Middle dust 9 Cavity inside nugget 10 Upper inner electrode 11 Upper outer electrode 12 Lower inner electrode 13 Lower outer electrode 14 Gap

Claims (3)

[Claims] 1. An inner electrode whose main purpose is electric conduction of a core, and an outer electrode whose main purpose is pressurization are formed around the inner electrode.
The inner electrode is made of a metal having a conductivity of 75 (IACS%) or more, its diameter is 2.5√t (where t = the plate thickness mm of the material to be welded), and the outer electrode has a conductivity of It is composed of a metal whose melting point is 40 (IACS%) or more lower than that of the inner electrode and whose melting point is higher than that of the material to be welded, and has a gap between the inner electrode and the outer electrode, and is movable mutually. Electrode for dynamic resistance spot welding. 2. The material of the inner electrode is 99.9% C
u, Cu-1% Cr, Cu-1% Cr-0.2% Zr,
1% alumina dispersed copper, Cu-2% Be, 99.9% Ti
The double-acting resistance spot welding electrode according to claim 1, wherein 3. The material of the outer electrode is 99.9% F
e, 18-8 stainless steel, 99.9% Ti, 99.9%
Ni, Ni alloy (alumel), 99.9% Mo, 99.
The double acting resistance spot welding electrode according to claim 1, wherein the electrode is 9% W and Cu-10% Zn.