JP2016059954A - Resistance spot welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resistance spot welding method with which spot welding can be carried out and sufficient joint characteristics are obtained irrespective of a material combination.SOLUTION: A spot welding method includes: a preparation step for preparing a plate set containing a lamination part 10 in which plate materials 1, 2, and 3 are stacked in three layers; and a welding step for sandwiching the lamination part 10 of the plate set between a pair of electrodes 20 and 20 and applying pressure to the lamination part 10 by using the electrodes 20 and 20 so that electric current is applied between the electrodes 20 and 20, and thereby subject the lamination part 10 to resistance spot welding. In the preparation step, as for the lamination part 10, the plate materials 1 and 3 of mutually the same steel-based material are disposed on the outermost layers, whereas the plate material 2 of an aluminium-based material having a through-hole 2a is disposed on an inner layer. In the welding step, resistance spot welding is applied in a state that a position of the through hole 2a in the plate material 2 of the inner layer coincides with positions of the electrodes 20 and 20.SELECTED DRAWING: Figure 1B

Description

  The present invention relates to a resistance spot welding method for joining plate materials together.

  Transportation machines such as automobiles, industrial machines, and the like are composed of a plurality of structural parts. In many cases, resistance spot welding (hereinafter, also simply referred to as “spot welding”) is used to manufacture structural parts.

  Usually, spot welding is performed as follows. Prepare a board as a material. The plate assembly has a stacked portion in which a plurality of metal plate materials are stacked. Next, the laminated portion of the plate assembly is sandwiched between the pair of electrodes. And an electric current is applied between electrodes, pressing the laminated part with the electrode. Thereby, the metal plate which adjoins the lamination | stacking part of a board assembly with the pressurization by an electrode, and an electric current flows into this contact area | region. The contact area is melted by heat generated by electric resistance, and this is solidified to form a nugget. By forming the nugget, the metal plates of the plate set are joined and joined together, and a structural component is manufactured.

  In recent years, especially in transportation machines, the weight reduction of the vehicle body has been promoted, and the weight reduction of the structural parts constituting the vehicle body has been strongly demanded. For this reason, structural parts are combined with different metal materials, such as steel-based materials (eg, ordinary steel (mild steel)) and aluminum (Al) -based materials (eg, Al, Al alloys). May be. In this case, a plurality of plate materials of different materials are laminated and joined by spot welding.

  For structural parts, the same or similar metals such as high-tensile steel (so-called high-tensile) and high-tensile steel, high-C (carbon) -containing steel and high-C steel, high-tensile steel and high-C steel, etc. A structure combining materials may be employed. In this case, a plurality of plate materials of the same material or the same material are laminated and joined by spot welding.

  As in the former case, when different materials are combined and joined by spot welding, there are the following problems. A brittle intermetallic compound is produced at the joint interface of the weld. In general, when the region where the intermetallic compound is generated becomes thick, fracture occurs in the intermetallic compound itself or at the interface between the intermetallic compound and the base material, and the quality of the welded joint decreases. For this reason, compared with a welded joint made of the same material (eg, welded joint of mild steel and mild steel, welded joint of Al and Al), the characteristics of the welded joint made of different materials are deteriorated. The joint characteristics here are tensile shear strength (TSS), cross tension strength (CTS), and the like.

  Moreover, like the latter, when combining the same material or the same kind of materials by spot welding, there are the following problems. The weld metal may harden and become brittle, and sufficient joint characteristics may not be obtained. This tendency is manifested particularly in spot welding between high-tensile steels containing a large amount of alloy elements, spot welding between high-C steels, or spot welding between high-tensile steels and high-C steels. In the future, it is expected that spot welding of a steel material containing more C will be required. In that case, the formation of a fragile structure accompanying the hardening of the weld metal is promoted, and the deterioration of the joint quality becomes more obvious.

  Japanese Patent Application Laid-Open No. 7-328774 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2003-236673 (Patent Document 2) disclose conventional techniques for joining dissimilar materials by spot welding. In the spot welding methods disclosed in these Patent Documents 1 and 2, steel materials, aluminum materials, and steel materials are sequentially stacked and stacked, and the stacked portions are sandwiched by electrodes and pressed strongly as they are. An electric current is applied between the electrodes. Thereby, in the contact area | region between board | plate materials, the Al type material of an inner layer melt | dissolves first, and the fuse | melted Al type material is discharged | emitted outside. As a result, the steel materials in the outermost layer come into contact with each other, and the steel materials are joined by spot welding in the contact region.

JP-A-7-328774 JP 2003-236673 A

  In the spot welding methods disclosed in Patent Documents 1 and 2, it is essential to first melt and discharge the inner layer material. For this reason, it is essential that a material having a melting point lower than that of the outer layer is disposed in the inner layer, and that the difference between the melting points is remarkably large. Therefore, combinations of materials used for the inner layer and the outer layer are limited.

  In the spot welding methods disclosed in Patent Documents 1 and 2, the material of the inner layer must be melted by resistance heat generation. For this reason, it is essential that the material of the inner layer has conductivity. Therefore, for example, it is difficult to join plate materials made of nonconductive materials such as plastics and ceramics. It is also difficult to join a conductive material plate having an insulating coating such as a painted metal plate.

The object of the present invention is to provide a resistance spot welding method having the following characteristics:
・ Spot welding is possible regardless of the combination of materials;
-Sufficient joint characteristics can be obtained.

A resistance spot welding method according to an embodiment of the present invention includes:
A spot welding method for joining plate materials,
A preparation step of preparing a plate assembly including a laminated portion in which plate materials are stacked in at least three layers;
A welding step of sandwiching the laminated portion of the plate assembly between a pair of electrodes, applying a current between the electrodes while pressing the laminated portion with the electrodes, and performing resistance spot welding on the laminated portion.
In the preparatory step, the same or the same kind of metal plate material is arranged in the outermost layer as the laminated portion, and the plate material of the material different from the material of the outermost layer plate material in the inner layer and having a through hole Place.
In the welding step, resistance spot welding is performed in a state where the position of the through hole and the position of the electrode in the inner layer plate material are matched.

  In the case of this spot welding method, the material of either one of the outermost plate material and the inner layer plate material is a steel material, and the other plate material is an aluminum material. it can.

  Any of the above spot welding methods may be configured such that the plate material of the inner layer is a non-conductive material or a conductive material having an insulating film.

  Any of the above spot welding methods may have a configuration in which any one of the outermost plate members is a contact plate.

  In any of the above spot welding methods, it is preferable that a contour shape of the through hole in the plate material of the inner layer is a circle or a square, and the diameter or the length of one side of the through hole is larger than a target nugget diameter.

  In any of the above spot welding methods, it is preferable that the thickness of the outermost layer plate material is 3.0 mm or less, and the total thickness of the inner layer plate material is 2.4 mm or less.

The resistance spot welding method of the present invention has the following significant effects:
・ Spot welding is possible regardless of the combination of materials;
-Sufficient joint characteristics can be obtained.

FIG. 1A is a cross-sectional view schematically showing a procedure of the resistance spot welding method of the present embodiment, and shows a plate material before being stacked. FIG. 1B is a cross-sectional view schematically showing a procedure of the resistance spot welding method of the present embodiment, and shows a state before welding of a laminated portion in which plate materials are stacked. FIG. 1C is a cross-sectional view schematically showing the procedure of the resistance spot welding method of the present embodiment, and shows a state in the middle of welding. FIG. 1D is a cross-sectional view schematically showing the procedure of the resistance spot welding method of the present embodiment, and shows a state at the end of welding. FIG. 1E is a cross-sectional view schematically showing a procedure of the resistance spot welding method of the present embodiment, and shows a laminated portion after welding is completed. FIG. 2 is a diagram showing test results of the examples.

  The spot welding method by one Embodiment of this invention is used in order to join plate materials, and includes a preparation process and a welding process. The preparation step is a step of preparing a plate set including a laminated portion in which plate materials are stacked in at least three layers. The welding step is a step of performing resistance spot welding on the laminated portion by sandwiching the laminated portion of the plate assembly with a pair of electrodes and applying a current between the electrodes while pressing the laminated portion with the electrodes. In the preparation step, the same or the same type of metal plate material is arranged in the outermost layer as the laminated portion of the plate assembly, and the plate material having a through hole is arranged in the inner layer. In the welding process, resistance spot welding is performed in a state in which the positions of the through holes and the positions of the electrodes in the inner layer plate material are matched.

  Below, a specific aspect is demonstrated about the resistance spot welding method by this embodiment.

  1A to 1E are cross-sectional views schematically showing the procedure of the resistance spot welding method of the present embodiment. In these drawings, FIG. 1A shows a plate material before being stacked. FIG. 1B shows a state before welding of the laminated portion in which the plate materials are stacked. FIG. 1C shows a state in the middle of welding. FIG. 1D shows a state at the end of welding. FIG. 1E shows the laminated portion after welding is completed.

  This embodiment is intended for the case where different materials are combined and joined by spot welding. In the following, a case where a steel material (eg, ordinary steel (soft steel)) and an Al material (eg, Al, Al alloy) are joined will be exemplified.

  Prepare a board as a material. As shown in FIGS. 1A and 1B, the plate assembly includes three plate members 1, 2, and 3, and includes a laminated portion 10 having a three-layer structure in which these plate members 1, 2, and 3 are sequentially stacked. In the laminated part 10, the materials of the first and third layer plate materials 1, 3 which are the outermost layers are the same and are metal steel-based materials. On the other hand, the material of the second-layer plate material 2 which is the inner layer is a metal Al-based material which is different from the materials (steel-based materials) of the first-layer and third-layer plate materials 1 and 3.

  That is, the plate material 2 of the second layer of Al-based material is sandwiched between the plate materials 1 and 3 of the first and third layers of steel-based material. The second layer plate 2 is provided with a through hole 2a in advance. The outline shape of the through hole 2a may be circular or square. Practically, the through hole 2a is circular.

  Of the first and third layer (outermost layer) plate materials 1 and 3 that are the same material (steel-based material), the third layer plate material 3 is a backing plate and forms the essential shape of the structural component. Not what you want. That is, the first-layer plate material 1 and the second-layer plate material 2 that are not backing plates form the essential shape of the structural component. In the preparation step, a plate set including the stacked portion 10 having such a configuration is prepared.

  After passing through the preparation process, the process proceeds to a welding process by spot welding. In the welding process, first, the laminated portion 10 of the plate assembly is sandwiched between the pair of electrodes 20 and 20. At that time, as shown in FIG. 1B, the positions of the through holes 2a provided in the plate material 2 of the second layer (inner layer) and the positions of the electrodes 20 and 20 are made to coincide with each other. Subsequently, the stacked portion 10 is pressurized by the electrodes 20 and 20. As a result, as shown in FIG. 1C, the plate materials 1 and 3 of the first layer and the third layer (outermost layer) are deformed and are in contact with each other in the region of the through hole 2a in the plate material 2 of the second layer (inner layer). become.

  Furthermore, a current is applied between the electrodes 20, 20 while pressing the laminated part 10 with the electrodes 20, 20. Thereby, an electric current flows into the contact area | region of the board | plate materials 1 and 3 of a 1st layer and a 3rd layer (outermost layer). The contact area is melted and solidified by resistance heat generation, and a nugget 4 is formed as shown in FIG. 1D. Around the nugget 4, the first and third layers (outermost layers) of the plate materials 1, 3 are in pressure contact with each other.

  Further, in the above-described welding process, before the first layer and the third layer (outermost layer) plate members 1 and 3 come into contact with each other, the current can be changed so as to be applied between the electrodes 20 and 20. In this case, first, the plate materials 1 and 3 of the first layer and the third layer (outermost layer) are in contact with the plate material 2 of the second layer in the annular region around the through hole 2a in the plate material 2 of the second layer (inner layer). It will be in the state. For this reason, an electric current flows into the annular contact area of the plate materials 1 and 3 of the first layer and the third layer and the plate material 2 of the second layer. Thereby, since the annular region generates heat, the plate materials 1 and 3 of the first layer and the third layer are softened in and around the annular region. Further, if the pressing of the laminated portion 10 by the electrodes 20 and 20 is continued while applying current between the electrodes 20 and 20, the softened first and third layer (outermost layer) plate materials 1 and 3 are deformed. Then, they are in contact with each other in the region of the through hole 2a in the plate material 2 of the second layer (inner layer) (see FIG. 1C). Thereby, an electric current flows also in the contact area | region of the board | plate materials 1 and 3 of a 1st layer and a 3rd layer (outermost layer), and the nugget 4 is finally formed (refer FIG. 1D).

  Thus, the laminated part 10 is joined by spot welding, and a structural component is manufactured (see FIG. 1E). In spot welding, the outermost layers (first and third layers) of the steel materials 1 and 3 are joined to each other through the through holes 2a in the inner material (second layer) of the aluminum material 2 (second layer). Is done. By this joining, the laminated portion 10 is in a state in which the inner-layer plate material 2 is strongly sandwiched between the outermost plate materials 1 and 3.

  Thus, according to the spot welding method of the present embodiment, it is possible to join by combining different materials such as a steel-based material and an Al-based material. Moreover, since substantial joining by spot welding is performed between the plate materials 1 and 3 of the outermost layers (first layer and third layer) that are the same steel material, no intermetallic compound is generated at the joining interface. . For this reason, since the fracture | rupture accompanying the production | generation of a weak intermetallic compound does not arise, sufficient joint characteristics can be acquired.

  In the spot welding method of the present embodiment described above, the materials of the first and third layer plate materials 1 and 3 that are the outermost layers and the material of the second layer plate material 2 that is the inner layer can be interchanged. . That is, the material of the first and third layer plate materials 1 and 3 can be Al-based material, and the material of the second layer plate material 2 can be steel-based material.

  Further, the materials of the outermost layer (first layer and third layer) plate materials 1, 3 are the same metal material, and the inner layer (second layer) plate material 2 is the material of the outermost layer plate materials 1, 3. As long as they are different from each other, these materials are not limited. However, the materials of the outermost plate members 1 and 3 are not limited to being the same, and may be the same type of metal material. Here, the same kind of metal material means a metal material having the same element with the highest content in the chemical composition. The heterogeneous material means a material having a different element with the highest content in chemical composition.

  For example, in terms of steel materials, mild steel, high-tensile steel, high C-containing steel, and the like are the same kind of metal material. In addition, α-based (ferritic) stainless steel, γ-based (austenitic) stainless steel, TWIP (Twinning-Induced Plasticity) steel, and the like are also the same type of metal material. In terms of Al-based materials, Al and Al alloys are the same kind of metal materials.

  The material of the inner layer (second layer) plate 2 may be a non-conductive material instead of the Al-based material. This is because the substantial joining by spot welding is performed between the outermost layers (first layer and third layer) of the plate materials 1 and 3 which are metal materials, and therefore conductivity is not essential as a characteristic of the inner layer plate material 2. . For example, a material such as a light-weight and high-strength carbon-fiber-reinforced plastic (CFRP) can be used for the inner layer plate material 2. In addition, ceramics or the like can be used.

  Table 1 below shows an example of a combination of the material of the plate material 1 of the first layer (outermost layer), the material of the plate material 2 of the inner layer, and the material of the plate material 3 of the third layer (outermost layer).

  In the spot welding method of the present embodiment described above, out of the outermost layer (first layer and third layer) plate members 1 and 3, the first layer plate member 1 is used as the backing plate instead of the third layer plate member 3. Also good. However, it is not always necessary to use one of the outermost plate materials 1 and 3 as the contact plate. That is, both the outermost plate materials 1 and 3 and the inner layer (second layer) plate material 2 may form the essential shape of the structural component.

  The laminated portion 10 of the plate assembly may be any one in which plate materials are stacked in at least three layers. That is, the inner layer may have a configuration in which a plurality of plate materials are stacked. In this case, a through hole may be provided coaxially in all the inner layer plate materials.

  Here, in the above-described spot welding method of the present embodiment, the thicknesses of the plate materials 1 and 3 of the outermost layers (first layer and third layer) are set according to the design specifications of the structural parts. For example, the thicknesses of the outermost plate materials 1 and 3 are practically 0.3 mm to 3.0 mm. If the thickness is too thin, the strength cannot be ensured. For this reason, the minimum with the preferable thickness is 0.3 mm, More preferably, it is 0.5 mm. On the other hand, when the thickness is too thick, deformation due to pressurization from the electrodes during spot welding becomes difficult, and the contact between the outermost plate materials 1 and 3 becomes insufficient. For this reason, the upper limit with the preferable thickness is 3.0 mm, More preferably, it is 2.0 mm, More preferably, it is 1.6 mm.

  In addition, the thickness of the inner layer (second layer) plate 2 (the thickness of the entire inner layer when the inner layer is two or more) is related to the thickness of the outermost layers (first layer and third layer) of the plates 1 and 3. However, it is set according to the design specifications of the structural parts. For example, the entire thickness of the inner plate 2 is practically 0.3 mm to 2.4 mm. If the thickness is too thin, the strength cannot be ensured. For this reason, the minimum with the preferable thickness is 0.3 mm, More preferably, it is 0.5 mm. On the other hand, if the thickness is too thick, the deformation amount of the outermost plate materials 1 and 3 due to pressurization from the electrodes during spot welding becomes excessive, and the contact between the outermost plate materials 1 and 3 becomes insufficient. For this reason, the upper limit with the preferable thickness is 2.4 mm, More preferably, it is 1.8 mm, More preferably, it is 1.2 mm.

  Electrodes 20 and 20 used for spot welding may be any of a DR (dome radius) type, a CF (center flat) type, and an SR (single are) type. The DR-type electrode has a generally cylindrical shape with a tip portion protruding in a dome shape, and the tip surface is formed in a convex curved surface having a large radius of curvature. The CF-type electrode has a substantially cylindrical shape with a tip portion protruding in a truncated cone shape, and the tip surface is formed into a flat surface. The SR-type electrode has a generally cylindrical shape, and its tip surface is formed as a convex curved surface with a constant radius of curvature.

  Here, in the spot welding method of the present embodiment described above, the diameter of the through hole 2a provided in the inner layer (second layer) plate 2 is preferably larger than the target nugget diameter. The reason is as follows.

Generally, when manufacturing a structural part by spot welding, a target nugget diameter (nugget diameter) ND _aim is determined according to design specifications. That is, the nugget formed by spot welding is required to be not less than the target nugget diameter ND _aim . The target nugget diameter ND _aim is smaller than the diameter D of the electrode body.

Usually, the target nugget diameter ND _aim is represented by X√t [mm] with the thickness t [mm] of the plate material to be joined as an index. The coefficient X is determined by design specifications. The target nugget diameter ND _aim is, for example, 5√t.

On the other hand, in the spot welding method of this embodiment, the nugget 4 penetrates through the contact region of the outermost layer (first layer and third layer) plate materials 1 and 3, that is, the inner layer (second layer) plate material 2. It is formed in the region of the hole 2a. Therefore, in order to form a nugget 4 having a target nugget diameter ND _aim or larger, the diameter of the through hole 2a (when the through hole is circular) or the length of one side (when the through hole is square) is The nugget diameter needs to be larger than the ND _aim . More safely, the diameter or the length of one side of the through hole 2a may be greater than or equal to the diameter D of the electrode body.

  However, if the diameter or the length of one side of the through hole 2a is too large, the inner layer (second layer) plate material 2 is not sandwiched by joining the outer layer (first layer and third layer most) plate materials 1 and 3 together. It will be enough. For this reason, it is preferable that the diameter or the length of one side of the through-hole 2a is 2.5 times or less of the diameter D of the electrode body.

  In order to confirm the effects of the present invention, the spot welding method of the present embodiment shown in FIGS. 1A to 1E was applied, and a welding test was performed. Non-plated mild steel plate material (hereinafter also referred to as “steel plate”) having a thickness of 0.6 mm and a 6000 series (Al—Mg—Si based) Al alloy plate material having a thickness of 1.2 mm as test plate materials (Hereinafter also referred to as “Al plate”). In some of the steel plates and Al plates, through holes having a diameter of 16 mm were formed using a crank press.

  As Example 1 of the present invention, a plate assembly having a three-layer structure in which a holeless Al plate, a holed steel plate, and a holeless Al plate were sequentially stacked was prepared, and spot welding was performed. As Invention Example 2, a plate assembly having a three-layer structure in which a steel plate without holes, an Al plate with holes, and a steel plate without holes was sequentially stacked was prepared, and spot welding was performed. As a comparative example, a plate assembly having a two-layer structure in which a holeless Al plate and a holeless steel plate were sequentially stacked was prepared, and spot welding was performed.

In each spot welding, the welding current was changed variously. Common welding conditions are as follows.
・ Welding machine: Air pressure spot welding machine with single-phase AC power source ・ Electrode: DR type electrode (tip surface diameter: φ6 mm, radius of curvature of tip surface: R40 mm, body diameter: φ16 mm)
・ Pressure: 400kgf (= 3.92kN)
Energizing time: 14 cycles (1 cycle means 1/60 second)

  Joint characteristics were evaluated for each plate assembly after spot welding. Evaluation of joint characteristics was performed by tensile shear strength (TSS) based on JIS Z3136. Table 2 below shows test conditions and test results.

  FIG. 2 is a diagram showing test results of the examples. From the results shown in Table 2 and FIG. 2, it was found that Examples 1 and 2 of the present invention can secure TSS stably as compared with the comparative example. In Invention Examples 1 and 2, no welding occurred between the electrode and the plate during spot welding. For this reason, according to the welding conditions of Examples 1 and 2 of the present invention, it was found that troubles such as the electrode falling off during actual operation did not occur and smooth operation could be performed.

  The present invention can be effectively used for spot welding of all materials.

1: plate material of the first layer (outermost layer), 2: plate material of the second layer (inner layer),
2a: through hole, 3: plate material of third layer (outermost layer), 4: nugget,
10: Laminate part of plate assembly, 20: Electrode

Claims (6)

A resistance spot welding method for joining plate materials,
A preparation step of preparing a plate assembly including a laminated portion in which plate materials are stacked in at least three layers;
A welding step of sandwiching the laminated portion of the plate set by a pair of electrodes, applying a current between the electrodes while pressing the laminated portion with the electrodes, and performing resistance spot welding on the laminated portion,
In the preparation step, the same or the same kind of metal plate material is disposed in the outermost layer as the laminated portion, and a plate material of a material different from the material of the outermost layer plate material in the inner layer and having a through hole And place
A resistance spot welding method in which, in the welding step, resistance spot welding is performed in a state where the position of the through hole and the position of the electrode in the inner layer plate material are matched. The resistance spot welding method according to claim 2,
A resistance spot welding method in which one of the plate material of the outermost layer and the plate material of the inner layer is a steel material, and the material of the other plate material is an aluminum material. The resistance spot welding method according to claim 1 or 2,
The resistance spot welding method, wherein the material of the inner layer plate material is a non-conductive material or a conductive material having an insulating film. The resistance spot welding method according to any one of claims 1 to 3,
The resistance spot welding method, wherein any one of the outermost plate members is a contact plate. The resistance spot welding method according to any one of claims 1 to 4,
The resistance spot welding method, wherein a contour shape of the through hole in the inner layer plate is circular or square, and a diameter or a side length of the through hole is larger than a target nugget diameter. A resistance spot welding method according to any one of claims 1 to 5,
The resistance spot welding method in which each thickness of the plate material of the outermost layer is 3.0 mm or less, and the total thickness of the plate material of the inner layer is 2.4 mm or less.

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