JPH07178563A - Joining method and joining structure by spot welding together with pressure welding - Google Patents

Abstract

PURPOSE:To improve the strength of a coupler by spot welding by drawing down a spot welding electrode and the periphery of contact part of a material to be welded by using an insulater indenter when a power is supplied. CONSTITUTION:When the spot welding is performed, the material 13 to be welded is drawn down by bringing into contact with the spot welding electrode 11. Press welding is performed by drawing down the spot welding electrode 11 and the periphery of contact part of the material 13 to be welded by using the insulator indenter 12 when the power is supplied. In such a case, the width of a corona bond part 14 in the periphery of a nugget 15 is set at a value between 20-100% of a nugget diameter 17. In this way, solid joining can be performed by the synergetic effect of temperature and pressure, and a large corona bond part can be formed in the periphery of the nugget on which the spot welding is performed. Therefore, the coupler strength of a joint can be increased to expand a joining area from only a nugget area to the one on which a corona bond area is added.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining structural materials used for automobiles, railway vehicles, ships, building structures, etc. and a joined structure.

[0002]

2. Description of the Related Art In spot welding, as shown in FIG. 3, electric current is applied between electrodes 11 adhered to both sides of superposed materials 13 to be welded to each other by resistance heat generation at the interface of the materials to be welded. Nugget 1 by melting and rolling down
5 is a method of forming and joining. This welding method is a method that is widely used industrially in the assembly of automobiles and railway vehicles as a method of joining iron-based materials and aluminum-based materials.

The strength of joints joined by spot welding depends on the nugget diameter 17 for both tensile shear strength and cross tensile strength, which are typical strengths of spot welded joints.
It is known that the joint strength increases as the nugget diameter increases. In addition, the nugget diameter is related to the value of the current that flows. Therefore, conventionally, as a method for improving the strength of the spot-welded joint, a method of forming a large nugget by passing a larger current has been performed. However, when an attempt is made to increase the diameter of the nugget above a certain level, melting due to heat generation at the interface of the material to be welded reaches the electrode-side surface of the material to be welded, and a phenomenon called so-called scattering occurs, so that the formation of a nugget occurs. It will be difficult. Therefore, conventionally, it was difficult to form a nugget having a diameter equal to or larger than a certain value with respect to the plate thickness of the material to be welded. This means that it is difficult to improve the strength of the spot-welded joint to a certain value or more by the conventional method.

Further, around the nugget 15 of the spot welded portion, there is a so-called corona bond portion 14 in which the materials to be welded are solid-layer joined by receiving heat and pressure although they are not melted. In "Iron and Steel," Vol. 68, No. 9, page 1444, "Improving the fatigue strength of spot welded joints in high tensile steel plates," it is said that the expansion of the corona bond portion is effective in improving the fatigue strength. It is known that size affects the strength of spot welded joints.
However, the width 16 of the corona bond portion formed by the conventional spot welding is usually 5 to 10% of the diameter of the nugget, although the width 16 of the corona bond portion varies depending on the material to be welded and the welding conditions, and the ratio to the joint area is as small as 30% or less. , The contribution to the strength of the welded joint is small.

Further, it is possible to perform spot welding not only on the same kind of materials such as iron-based materials and aluminum-based materials but also on different materials such as steel and aluminum alloys. However, when dissimilar metals such as steel and aluminum are welded, an intermetallic compound may be formed in the joint due to heat input, and an embrittlement layer may be generated. In particular, satisfactory weld strength may be obtained in the cross tension test. I can't. This is because the outer peripheral portion of the nugget, which becomes the stress concentration portion in the cross tension test, becomes an embrittlement layer. As one of such dissimilar metal joining methods, there is a method in which at least one side surface of an iron-based material is coated with an aluminum-based material, and the aluminum-based material is welded to the aluminum-coated surface side to be joined. It is disclosed in the official gazette. However, also in this method, since an intermetallic compound of iron and aluminum is generated, it is the same in that an embrittlement layer is generated, and it is difficult to express the cross tensile strength of the joint. Therefore, conventionally, when such materials are used in combination, mechanical fastening with bolts or the like has been used.

On the other hand, in recent years, new proposals have been made regarding the bonding of such dissimilar metals. For example, in Japanese Patent Publication No. 4-127973, as shown in FIG. 4, an iron-based material 22 is provided between an iron-based material 21 and an aluminum-based material 24.
And a two-layer clad material 29 made of aluminum-based material 23 are inserted so that the same materials face each other,
A method of joining an iron-based material and an aluminum-based material by conducting electricity for a time of 10 ms or less is disclosed.

[0007] Dissimilar metal joining consisting of two layers of multi-layer steel sheets in which the iron-based material plate and the aluminum-based material plate are laminated and joined between the iron-based material plate and the aluminum-based material plate. The strength of the joints joined by the dissimilar metal joining method of inserting the materials so that the same kind of materials face each other and spot welding the plate of the iron-based material and the plate of the aluminum-based material is the typical strength of the spot-welded joint. Both tensile shear strength and cross tensile strength improve as the nugget diameter increases. To increase the nugget diameter,
The amount of current to be applied is increased, but if the amount of current is increased too much, the amount of heat generated will increase, and an intermetallic compound of iron and aluminum will form to form an embrittlement layer, which in turn causes a decrease in strength. In some cases, this tendency is remarkable especially in the cross tensile strength. Therefore, it is difficult to increase the strength of such a joint to a certain value or more by the method of increasing the amount of current to be applied.

In such a joint, the nugget 26 formed at the interface between the aluminum-based materials or its periphery is broken in both the tensile shear test and the cross tensile test. Therefore, in order to improve the strength of such a joint, it is not necessary to change the nugget diameter of the nugget 25 formed at the interface between the iron-based materials, and the nugget diameter of the nugget 26 formed at the interface between the aluminum-based materials. Should be increased.

[0009]

DISCLOSURE OF THE INVENTION The present invention provides a joining method and a joining structure by spot welding in which a joint having high strength can be obtained by enlarging a corona bond portion existing around a nugget and having an influence on the joint strength. The purpose is to do.

[0010]

The summary of the present invention is as follows.
(1) In the welding method by spot welding, the welding method is characterized in that the periphery of the contact portion between the spot welding electrode 11 and the material 13 to be welded is pressed down by using an insulator indenter 12 during energization to perform pressure welding. . And (2) a two-layer multi-layer steel plate 29 in which a plate 22 made of an iron material and a plate 23 made of an aluminum material are laminated and joined between a plate 21 made of an iron material and a plate 24 made of an aluminum material. In a dissimilar metal joining method in which the same kind of material is inserted so as to face each other and the iron-based material plate 21 and the aluminum-based material plate 24 are spot-welded, the spot welding electrode 11 and the iron-based material plate 21 and aluminum are energized when energized. A joining method by spot welding of dissimilar metals, characterized in that the periphery of a contact portion of a plate 24 made of a system material is pressure-welded by pressing down with an insulator indenter 12. In addition, (3) the width of the corona bond portion 14 around the nugget 15 is set to the nugget diameter 1
20% or more and 100% or less of 7 were joined structures by spot welding. And (4) a two-layer multi-layer steel plate 29 in which the iron-based material plate 22 and the aluminum-based material plate 23 are laminated and joined between the iron-based material plate 21 and the aluminum-based material plate 24. Spot welding, in which a width of a corona bond portion 27 around a nugget 26 of aluminum-based materials is 20% or more and 100% or less of a nugget diameter 28 in a joined structure in which materials of the same kind are joined to face each other. It is in a bonded structure.

Here, the nugget diameter is the arithmetic average of the lengths of the long diameter 71 and the short diameter 72 of the nugget 75 in two directions, as shown in FIG. The width of the corona bond portion is a value obtained by subtracting the nugget diameter from the arithmetic mean of the lengths in two directions of the long diameter 73 and the short diameter 74 around the corona bond portion and dividing by 2.

[0012]

The vicinity of the nugget formed by spot welding is heated to a high temperature close to the melting temperature of the material to be welded, although it does not melt when energized. In the conventional spot welding method in which only the electrode is pressed, almost no pressure is applied to this portion, so that the corona bond portion solid-bonded is hardly formed. However, by pressing down this portion using the indenter of the insulator by the method of the present invention, solid layer bonding is performed by the synergistic effect of temperature and pressure, and a large corona bond portion is formed. Forming a large corona bond expands the bonding area from just the nugget area to the nugget area plus the area of the corona bond, thus producing the same effect as expanding the nugget diameter. The joint strength of can be increased.

In the present invention, the reason why the width of the corona bond portion is set to 20% or more of the nugget diameter is that the corona bond portion accounts for about 50% or more of the joint area, and the influence of the corona bond portion on the joint strength. Because it appears significantly. Set the width of the corona bond to 10 of the nugget diameter.
The reason for setting it to 0% or less is that heat and pressure are required for pressure welding, but when the residual heat of spot welding is used, it seems to contribute to the improvement of the strength of a joint having a width of more than 100% of the nugget diameter. This is because it is difficult to form a large corona bond portion.

The same applies to the joining of the iron-based material and the aluminum-based material, and the strength of the dissimilar joint can be improved by thus improving the strength of the joining portion on the aluminum-based material side. . In dissimilar material bonding in which an embrittlement layer due to an intermetallic compound is likely to occur during bonding, the corona bond portion generated on the outer peripheral portion of the joint due to the above action becomes a stress concentration portion, and the embrittlement layer due to the intermetallic compound causes a stress concentration portion. Therefore, the cross tensile strength is significantly improved by the synergistic effect of the above-mentioned expansion of the joint area. As the indenter, in addition to ceramics, any indenter such as glass or plastic may be used as long as it is a material that is an insulator and can withstand pressure reduction in the operating temperature range and has a hardness of at least 30 Hv or more in the operating temperature range. May be. In addition, FIG.
It is also possible to use such an electrode. Further, as for the pressing force of the indenter, it is sufficient to select a pressing force with which good bonding strength can be obtained within a range of 20% to 500% of the pressing force per unit area by the electrode.

[0015]

【Example】

Example 1 Using a 5000 mm aluminum alloy plate having a thickness of 1 mm as a material to be welded, a conventional spot welding joint and a joint according to the method of the present invention shown in FIG. 1 were manufactured.
A tensile shear test was performed. A conventional spot-welded joint is manufactured with an electrode diameter of 5 mm and a pressing force of 1.8 kN. With the method of the present invention, when performing spot welding under the same conditions, at the same time, the electrode and unit area per unit area are surrounded by a ceramic indenter. It was manufactured by the method of pressurizing so that the applied pressure of the same becomes the same. As a result, the average nugget diameter of the joint by spot welding was 4.9 mm on average, and the average tensile shear strength was 2.7 kN, but the joint diameter of the joint manufactured by the method of the present invention was 7.3 mm on average. That is, the width of the corona bond portion was about 1.2 mm, which was 24% of the nugget diameter, the average tensile shear strength was 3.5 kN, and a strength improvement of 30% was observed.

[Embodiment 2] As shown in FIG. 5, a 0.7 mm-thick SPCC steel plate having an aluminum plate on one side and a 1 mm-thick 50
The method of the present invention was applied to the joining of 00-series aluminum alloy plates, and the joint strength by cross tension was compared with that of spot-welded joints using the conventional method. The conventional spot-welded joint is manufactured with an electrode diameter of 6 mm and a pressing force of 2 kN. With the method of the present invention, when performing spot welding under the same conditions, at the same time, the electrode and the unit area per unit area are applied by a ceramic indenter around the electrode. It was manufactured by a method of pressurizing so that the pressure becomes the same.
As a result, although the average nugget diameter of the joint by spot welding was 5.6 mm and the average tensile shear strength was 0.3 kN, the joint diameter of the joint manufactured by the method of the present invention was 8.4 mm on average. That is, the width of the corona bond portion was about 1.4 mm, which was 25% of the nugget diameter, the average tensile shear strength was 0.6 kN, and a 100% strength improvement was observed.

[Embodiment 3] A 0.8 mm thick SPCC steel plate having a thickness of 0.8 mm as an iron-based material, an SPCC steel plate having a thickness of 0.4 mm as an aluminum clad steel plate, and a pure aluminum having a thickness of 0.4 mm are joined in FIG. Using a 5000 series aluminum alloy having a thickness of 1.0 mm as an aluminum-based material, a joint by conventional spot welding and a joint by the method of the present invention were manufactured, and a tensile shear test was performed to compare the strengths.

The conventional spot-welded joint has an electrode diameter of 6 m.
In the method of the present invention, when the spot welding is performed under the same conditions, the electrode periphery is simultaneously pressed by the ceramic indenter so that the pressing force per unit area is the same as the electrode. Made by the method. As a result, the average nugget diameter of the joint by spot welding was 5.9 mm, the corona bond width was 0.3 mm, and the average tensile shear strength was 3.1 kN. The nugget diameter of the aluminum-based material joint is 5.8 mm on average, the width of the corona bond is about 1.3 mm, which is 22% of the nugget diameter, and the average tensile shear strength is 3.9 kN, showing a 26% strength improvement. Was given.

[0019]

As described above, according to the present invention, a large corona bond portion can be formed around the spot welding nugget, and the strength of the spot welding joint can be improved. Further, when spot welding of iron and aluminum or the like is performed, the strength is remarkably improved in the joining of dissimilar materials which causes an embrittlement layer due to the intermetallic compound. In addition, a dissimilar metal bonding material composed of two layers of multi-layer steel plates in which a plate made of an iron material and a plate made of an aluminum material are laminated and joined between a plate made of an iron material and a plate made of an aluminum material It has become possible to obtain a dissimilar metal joined body having a high joint strength by inserting the materials so that the materials face each other and spot-welding the iron-based material plate and the aluminum-based material plate.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of the present invention.

FIG. 2 is a conceptual diagram of the present invention.

FIG. 3 is a conventional spot welding method.

FIG. 4 is a conceptual diagram of a conventional dissimilar material joining method.

FIG. 5 is a conceptual diagram of Example 2;

FIG. 6 shows a combination example of an electrode and an indenter.

FIG. 7 is a nugget diameter and a width of a corona bond portion.

[Explanation of symbols]

11 Electrode 12 Indenter 13 Welding Material 14 Corona Bond Part 15 Nugget 16 Width of Corona Bond Part 17 Nugget Diameter 21 Iron-based Material 22 Iron-based Material of Multi-layer Steel Sheet 23 Aluminum-based Material of Multi-layer Steel Sheet 24 Aluminum-based Material 25 Iron-based Material Nugget generated at the interface between materials 26 Nugget generated at the interface between aluminum-based materials 27 Corona bond part 28 Nugget diameter of nugget generated at the interface between aluminum-based materials 29 Aluminum clad steel plate 51 Aluminum plated steel plate 52 Aluminum alloy plate 53 Aluminum plating layer 61 Insulator coating 62 Electrode material 71 Nugget major axis 72 Nugget minor axis 73 Corona bond major axis 74 Corona bond minor axis 75 Nugget (melt bonding part) 76 Corona bond part (pressure bonding part)

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area B23K 103: 20

Claims (4)

[Claims] 1. A joining method by spot welding, comprising:
A joining method by spot welding, characterized in that the periphery of the contact portion of the spot welding electrode 11 and the material 13 to be welded is pressed down by using an insulator indenter 12 when energized to perform pressure welding. 2. A two-layered multi-layer steel plate 29 in which a plate 22 made of an iron material and a plate 23 made of an aluminum material are laminated and joined between a plate 21 made of an iron material and a plate 24 made of an aluminum material.
In a dissimilar metal joining method in which the same kind of material is inserted so as to face each other and the iron-based material plate 21 and the aluminum-based material plate 24 are spot-welded, and the spot welding electrode 11 and the iron-based material plate 21 and A joining method by spot welding of dissimilar metals, characterized in that the periphery of a contact portion of a plate 24 made of an aluminum-based material is pressed by using an insulator indenter 12 to perform pressure welding. 3. A corona bond portion 14 around a nugget 15.
Is 20% or more and 100% or less of the diameter of the nugget 17, a joined structure by spot welding. 4. A two-layer multi-layer steel plate 29 in which a plate 22 made of an iron material and a plate 23 made of an aluminum material are laminated and joined between a plate 21 made of an iron material and a plate 24 made of an aluminum material.
In a bonded structure in which materials of the same kind are bonded so as to face each other, the width of the corona bond portion 27 around the nugget 26 of aluminum-based materials is 20 of the nugget diameter 28.
% To 100% or less, a joined structure by spot welding.