Method and device of resistance welding

Abstract

To provide a new method and device of resistance welding between dissimilar metals of an aluminum plate and a steel plate which do not need material and processing which are used between plates, such as bolts and brazing, and endure social implementation in terms of limitation of time and costs and practicability.SOLUTION: A resistance welding method between dissimilar metals of an aluminum plate and a steel plate, comprises a step in which welding is performed in a state that a periphery of a contact portion between the aluminum plate and a welding electrode is cooled with a fluid. Further, the method comprises a step in which the welding is performed in a state that the fluid is flowed out toward a periphery of a contact portion with the welding electrode in a direction parallel to an axis of the welding electrode and an entire part of the periphery of the contact portion is locally cooled.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a resistance welding method and apparatus, and more particularly to a resistance welding method and apparatus for welding dissimilar metals, such as an aluminum plate and a steel plate. [Background technology]

[0002] In recent years, the automotive industry has advocated the use of multi-materials using aluminum alloys in order to improve fuel efficiency by reducing the weight of vehicles, etc. This has led to an increasing demand for dissimilar metal joining technology between aluminum-based sheets (aluminum alloy sheets) and steel-based sheets (iron-based sheets).

[0003] On the other hand, resistance welding, especially resistance spot welding, which is a joining technique used in the automotive industry, is the most widely used joining method because it is easy to automate production lines and has low cost per welding point.

[0004] However, aluminum has a low melting point and very high thermal conductivity, making it inherently unsuitable for resistance welding. Furthermore, joining dissimilar metals between aluminum and steel plates is not only difficult due to the large difference in melting temperatures, but also because unstable intermetallic compounds (IMCs) such as Fe3Al, FeAl, FeAl2, Fe2Al5, and FeAl3 form at the joining interface, resulting in brittle properties and insufficient joint strength. Brazing also presents problems with controlling and ensuring high reliability at the joint.

[0005] In this context, several research results have been reported on dissimilar metal joining between aluminum and steel plates, and it is not impossible from a technical standpoint. However, for example, friction welding has limitations on the material shape and causes deformation during joining, while diffusion bonding has difficulties in pre-processing and control, and there are strict time and cost constraints, making it unsuitable for mass production.

[0006] In other words, the problem has not been solved from the viewpoints of time and cost limitations and practicality, and the reality is that physical joints such as bolt joints are still being used. [Prior art documents] [Patent documents]

[0007] [Non-Patent Document 1] Journal of the Japan Institute of Metals, Vol. 77, No. 7 (2013) 259-267 Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, the present invention aims to provide a new method and apparatus for resistance welding between dissimilar metals, i.e., aluminum-based plates and steel-based plates, which does not require inter-plate materials or processing such as bolts or brazing, and which is suitable for practical implementation in terms of time and cost constraints and practicality. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the resistance welding method of the present invention is a method for resistance welding between dissimilar metals, i.e., an aluminum-based plate and a steel-based plate, and comprises welding while cooling the periphery of a contact portion between the aluminum-based plate and a welding electrode with a fluid.

[0010] Furthermore, it is preferable that the fluid be caused to flow parallel to the axis of the welding electrode toward the periphery of the contact portion with the welding electrode, so that welding is performed while locally cooling the entire periphery of the contact portion.

[0011] Furthermore, the present invention provides an attachment for a spot welding electrode, comprising an outer peripheral wall, an inner peripheral wall, and an upper wall constituting a cylindrical body, and a flow passage provided between the outer peripheral wall and the inner peripheral wall, wherein the outer peripheral wall or the upper wall is provided with a fluid supply section to the flow passage section, and the attachment is capable of allowing fluid supplied from the fluid supply section to flow out of the attachment from the lower part, and the welding electrode is placed inside the cylindrical body using the attachment, and spot welding is performed while locally cooling the area around the contact portion.

[0012] It is also preferable that the inner wall of the attachment be in contact with the welding electrode.

[0013] Furthermore, the present invention provides a spot welding machine comprising a welding electrode, a fluid supply device, and an attachment for the welding electrode connected to the fluid supply device, the attachment comprising an outer peripheral wall, an inner peripheral wall, and an upper wall constituting a cylindrical body, and a cavity provided between the outer peripheral wall and the inner peripheral wall, the outer peripheral wall or the upper wall being provided with a fluid supply section to the cavity, the welding electrode being disposed within the cylindrical body, and the attachment being capable of causing fluid supplied from the fluid supply section to flow out of the attachment from a lower part thereof.

[0014] It is also preferable that the fluid cooling device is connected to the fluid supply device, the attachment is connected to the fluid cooling device, and the fluid supply device and the attachment are connected via the fluid cooling device.

[0015] Although it is known that aluminum sheets can develop microcracks if they are rapidly cooled after welding, the inventors investigated the intermetallic compounds and joint characteristics of Fe / Al dissimilar resistance spot welded joints using external cooling and discovered that IMC can be reduced by welding while cooling the periphery of the contact area between the aluminum sheet and the electrode, i.e., the area around the electrode, which is the contact area, with a fluid, preferably gas. In the method of the present invention, the increase in the cooling rate in the aluminum alloy molten zone reduces the atomic diffusion time, thereby selectively suppressing Al-rich IMC (FeAl2, Fe2Al5, FeAl3, etc.). Suppressing this Al-rich IMC allows for favorable welding between dissimilar metals, such as aluminum and steel sheets.

[0016] Therefore, theoretically, it is sufficient that the temperature is lower than the welding temperature, and there is no lower limit. Also, as long as it is possible to cool the area around the contacting electrode in a concentrated manner, the means of cooling is not necessarily important, and a configuration in which a fluid is sprayed from multiple nozzles around the periphery is also acceptable. The fluid can be liquid or gas, and any type is acceptable as long as welding is possible.

[0017] In practice, since it is important to suppress IMC of Alrich at the welded portion, affecting areas distant from the welded portion would be inefficient and cause uncertainties, so it is preferable to cool only the periphery of the welded portion entirely and locally without any gaps. Therefore, it is preferable to flow a fluid parallel to the electrode axis toward the periphery of the contact portion with the welding electrode, and to perform welding while locally cooling the entire periphery of the contact portion.

[0018] Furthermore, the inventors discovered that the method of the present invention can be realized in a highly practical and efficient manner by improving and using the attachment configuration of Japanese Patent Application Laid-Open No. 2023-107002, which was developed to prevent oxidation of the heat-affected zone of the weld. Specifically, as described below, the attachment configuration required a straightening section, but by adopting a hollow configuration, the area around the weld is cooled globally and locally without gaps, resulting in a more significant welding effect. Furthermore, this configuration has the effect of cooling the electrode itself by having the inner wall contact the electrode.

[0019] Theoretically, the fluid can be a liquid. However, the benefits of the present invention cannot be fully utilized with a liquid due to the uncertain effects on the welded area, the equipment required for material preparation and post-processing, the time and cost involved, and other factors. In other words, a gas is preferable because it is easy to handle and does not require pre- or post-processing. While well-known gases such as argon gas and nitrogen gas can also be used, the present invention is extremely advantageous in that it can use the air available at the work site as is, and in terms of effectiveness, it overcomes cost and practical issues.

[0020] As mentioned above, theoretically, the temperature should be below the welding temperature, and there is no lower limit. However, since the cooling effect is greater at lower temperatures, a temperature of 15°C or less, or even 10°C or less, is preferable. From the viewpoints of equipment, temperature control, and cooling efficiency, gas is preferable, and air is particularly preferable because low temperatures can be easily achieved using a known small cooling device. For this reason, in a configuration using this attachment, air cooled to 10°C or less is preferably ejected via a cooling device. Furthermore, since the attachment can be easily attached around the electrode in this invention, a supply device and a cooling device can easily be added externally to a conventional spot welding machine.

[0021] The amount and flow rate of the fluid are not limited, but it is preferable to flow a larger amount and faster in order to lower the temperature around the electrodes. From this viewpoint, a gas is preferable, and since air can be used, problems of cost and practicality can be overcome.

[0022] In the present invention, aluminum-based sheets broadly include aluminum alloy sheets. Pure aluminum lacks strength, so it is often alloyed by adding additional elements during the manufacturing process. Among aluminum alloy sheets for automobiles, the 1000 series, 3000 series, 4000 series, and 5000 series are non-heat-treatable alloys. On the other hand, the 2000 series, 6000 series, and 7000 series are heat-treatable alloys. Regarding steel-based sheets, the JIS defines iron with a carbon content of less than 0.02% as "pure iron," iron with a carbon content of 0.02% to 2.14% as "steel," and cast iron with a carbon content of more than that as "iron." Of these, "steel" is divided into carbon steel and alloy steel, but this term includes both.

[0023] The attachment specifically comprises an outer peripheral wall and an inner peripheral wall that form a cylindrical body, and a flow channel provided between the outer peripheral wall and the inner peripheral wall. The flow channel may be configured as a straightening section with a lattice structure or the like, but is preferably a hollow section. The attachment has an overall cylindrical or columnar shape, and the internal space defined by the outer peripheral wall and the inner peripheral wall serves as a fluid flow path. Therefore, the upper portion is blocked by an upper wall (including when it is configured as part of the outer wall) to prevent the fluid from flowing out, and a fluid supply section is provided on the outer peripheral wall or the upper wall. Typically and preferably, the fluid supply section is a nozzle integral with the body, which receives the fluid and supplies the inflowing fluid to the internal space defined by the outer peripheral wall and the inner peripheral wall. The fluid supply section is not limited to a nozzle shape and may be configured as an opening provided in the outer peripheral wall. Other forms, such as inserting a separate tube or the like into the opening, are not excluded. The fluid supply portion is preferably provided at the upper portion of the attachment, specifically at the top or above the central position in the longitudinal direction of the outer peripheral wall, in order to reduce the effect on the space and mobility of the spot welding device.

[0024] The outer peripheral wall preferably has no protruding parts facing outward other than the fluid supply part. This configuration is important for ensuring space and mobility while also ensuring ease of attachment and detachment and versatility. The inner peripheral wall is also configured without any protruding parts facing the internal space, similarly ensuring space and mobility while also ensuring ease of attachment and detachment, avoiding contact with electrodes, and ensuring quality.

[0025] Furthermore, an opening for inserting a fixing member is provided, penetrating from the outer peripheral wall to the inner peripheral wall, making it possible to fix the attachment to the electrode. While known members and means can be used to fix the attachment without any particular limitations, it is preferable to use a member that can be fixed by inserting it into the opening, such as a screw. This configuration, which allows for fixation by simply inserting it into the opening, further improves ease of operation, efficiency, and cost-effectiveness, while minimizing restrictions on space and mobility. It is preferable that the opening of the hollow portion be surrounded by a sealed wall to prevent fluid leakage.

[0026] The attachment is not limited to a specific diameter because the suitable diameter is determined by the electrode diameter. However, if the outer diameter is 30 mm or less, especially 24 mm or less, and the thickness of the outer and inner walls is 1 mm or less, especially 0.5 mm or less, and the thickness of the flow straightening portion is 5 mm, especially 3 mm or less, it can be used with most electrodes and can achieve high effectiveness while minimizing restrictions on the space and mobility of the welding equipment.

[0027] Another possible attachment configuration is one with a single fluid supply unit. The attachment can be formed in the shape of a beveled cylinder, with the upper part serving as a space and the lower part as a flow passage, and the fluid supply unit located at the top.

[0028] In use, the attachment is attached to the electrode, and a fluid cooling device is connected to the fluid supply unit. The fluid cooling device is connected to a fluid supply device, such as an air tank. A known control device, etc., is used to discharge the fluid at the appropriate time, and the spot welding is performed while cooling the periphery of the aluminum-based plate and the electrode. Since the inner wall portion is in contact with the electrode, further cooling of the electrode can be achieved.

[0029] Although the electrode shape is not limited, it is preferable to use a general cylindrical rod electrode in consideration of ease of attachment of the attachment and the need to completely cover the periphery of the electrode with fluid. In theory, the present invention can be applied not only to spot welding but also to other resistance welding methods such as seam welding, by cooling the periphery of the electrode contact. [Effects of the Invention]

[0030] The present invention provides a new method and apparatus for resistance welding between dissimilar metals, i.e., aluminum-based sheets and steel-based sheets, which does not require inter-sheet materials or processing such as bolts or brazing, and which is suitable for practical implementation in terms of time and cost constraints and practicality. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a perspective view showing an example of an attachment used in the present invention. [Figure 2] FIG. 2 is a front view of the attachment of FIG. 1. [Figure 3] FIG. 2 is a plan view of the attachment of FIG. 1. [Figure 4] FIG. 2 is a bottom view of the attachment of FIG. 1. [Figure 5] FIG. 2 is a cross-sectional view of the attachment of FIG. 1. [Figure 6] FIG. 10 is a perspective view showing another example of the attachment of the present invention. [Figure 7] FIG. 1 shows the amount of IMC produced by Alrich and Ferich. [Figure 8] FIG. 1 is a diagram showing test piece dimensions. [Figure 9] FIG. 10 is a diagram showing a state in which a cooling device is attached. DETAILED DESCRIPTION OF THE INVENTION

[0032] Experiment 1: The effects of spray shape and spray gas temperature on the IMC formation state were investigated. Test material Positive electrode: 980MPa class high strength steel plate thickness t=1.2mm Negative electrode: A6061 plate thickness t=1.0mm Welding conditions Power supply characteristics: DC inverter type Power supply frequency: 50 Hz Electrode material: Alumina dispersion strengthened copper (Al2O3Cu) JPEG2025119364000002.jpg1173 Trial gas Ar gas (temperature: 15-25°C) and air (temperature: 0°C, super-cooled) Trial configuration (attachment) Control (Base), Nost (with a hollow flow section), and Lattice (with a rectifying (lattice) structure in the flow section

[0033] evaluation IMC thickness distribution: IMC thickness is measured at five points every 200 μm to obtain the IMC thickness distribution. IMC composition analysis: Using a scanning electron microscope (SEM), the IMC thickness was measured at five random locations (N=3) in the center, edge, and half sections for each cooling condition. The results are shown in Table 1 below.

[0034] [Table 1]

[0035] Consideration In both welding methods, IMC was suppressed compared to the control (Base). Regarding the spray gas temperature, IMC thickness was significantly suppressed when air (approximately 0°C) was used. This suggests that cooling with lower temperature gas is more effective. Furthermore, regarding the attachment configuration, IMC thickness was significantly suppressed when air (approximately 0°C) was used with a hollow configuration without a flow straightening section. This suggests that a spray configuration using an attachment that does not require flow straightening and sprays without reducing speed is more effective. Furthermore, Figure 7 shows the results of a comparison of IMC amounts between Al-rich (FeAl2, Fe2Al5, FeAl3) and Fe-rich (Fe3Al, FeAl). These results indicate that the cooling effect has a small effect on the IMC of Fe-rich, but significantly suppresses the IMC of Al-rich.

[0036] Experiment 2 The effect of external cooling using a gas spray device on the joint characteristics was investigated. Cross tension tests were conducted in accordance with JIS Z 3137 for the hollow attachment and 0°C air welds in Experiment 1 (tensile speed: 5 mm / min). Interfacial fracture and partial plug fracture were recorded separately. The test specimen dimensions are shown in Figure 8. The results are shown in Table 2 below.

[0037] [Table 2]

[0038] As is clear from the table above, regardless of the welding current value, strength was significantly improved in all cases. Furthermore, observation of the fracture surface showed a decrease in interfacial fractures and an increase in partial plug fractures. These changes indicate that a change in crack propagation behavior led to a shift to partial plug fractures, improving strength. In other words, with regard to IMC, Fe-rich IMCs have high strength, while Al-rich IMCs have low strength. However, by selectively suppressing Al-rich IMCs according to the present invention, cracks are less likely to propagate through the IMCs, and the fracture morphology changes to one in which the crack propagates through the aluminum alloy plate, such as partial plug or plug fracture, improving strength.

[0039] 1 to 5 are perspective views showing an example of an attachment of the present invention.

[0040] The attachment 1 shown in Fig. 1 is integrally formed entirely from a copper alloy, and is configured in a cylindrical and columnar shape, including an outer peripheral wall 2, an inner peripheral wall 3, an upper wall 4, and a cavity 5 provided between the outer peripheral wall 2 and the inner peripheral wall 3. Nozzles 6 and 7 are provided on the outer peripheral wall 2. The outer peripheral wall 2 does not have any outwardly protruding portions, and the inner peripheral wall 3 does not have any inwardly protruding portions.

[0041] The nozzles 6 and 7 each have a first portion 8 facing outward and a second portion 9 parallel to the axis 10 of the attachment 1, ensuring space and movability when installed. In addition, the nozzles 6 and 7 are provided at positions 180 degrees apart on the outer peripheral wall 2, ensuring movability and the introduction of uniform gas into the flow straightening section 5.

[0042] An opening 11 is provided in the outer peripheral wall of the attachment 1. The attachment can be attached by fastening it to the electrode with a screw via the opening 11. The opening 11 penetrates from the outer peripheral wall 2 to the inner peripheral wall 3, and the area around the penetration is made up of a sealed wall and has a screw receiving groove, ensuring ease of attachment and detachment and preventing unexpected gas leakage.

[0043] The attachment 1 is fixed around the electrode with screws through the opening 11. As shown in Fig. 9, an air tank (not shown) is connected to the nozzles 6 and 7 via a cooling device and a hose, and is configured to be able to supply cooling gas.

[0044] 6 is a perspective view showing another example of the attachment of the present invention. The main configuration is the same as in Example 1, but the outer wall 2' of the attachment 1' covers the entire top, and there is only one nozzle 6'. [Explanation of symbols]

[0045] 1 Attachment 2 Outer wall 3 Inner wall 4 Upper wall 5 Cavity 6 nozzles 7 nozzles 8. First Part 9 Second Part 10 axes 11 Aperture

Claims

1. A resistance welding method for dissimilar metals, i.e., an aluminum plate and a steel plate, comprising: The periphery of the contact portion between the aluminum plate and the welding electrode is A resistance welding method characterized by welding while cooling with a fluid.

2. 2. The resistance welding method according to claim 1, wherein the fluid is caused to flow parallel to the axis of the welding electrode toward the periphery of the contact portion with the welding electrode, thereby performing welding while locally cooling the entire periphery of the contact portion.

3. An attachment for a spot welding electrode, The device includes an outer peripheral wall, an inner peripheral wall, and an upper wall that form a cylindrical body, and a flow passage provided between the outer peripheral wall and the inner peripheral wall, a fluid supply portion for the flow passage portion is provided on the outer peripheral wall or the upper wall; 2. The resistance welding method according to claim 1, wherein a welding electrode is placed inside the cylindrical body using an attachment that allows the fluid supplied from the fluid supply part to flow out of the attachment from a lower part thereof, and spot welding is performed while locally cooling the periphery of the contact portion.

4. 4. The resistance welding method according to claim 3, wherein the inner wall of the attachment is in contact with the welding electrode.

5. 3. The resistance welding method according to claim 2, wherein the fluid is a gas cooled to 15 degrees or less by a cooling device.

6. 4. The resistance welding method according to claim 3, wherein the fluid is a gas cooled to 15 degrees or less by a cooling device.

7. 6. The resistance welding method according to claim 5, wherein the gas is cooled by the cooling device to a temperature of 10 degrees or less.

8. 7. The resistance welding method according to claim 6, wherein the gas is cooled by the cooling device to a temperature of 10 degrees or less.

9. 9. The resistance welding method according to claim 1, wherein the fluid is air.

10. 10. The resistance welding method according to claim 9, wherein the welding electrode and the periphery of the contact portion with the welding electrode are cooled simultaneously.

11. A spot welding machine a welding electrode; a fluid supply device; an attachment for the welding electrode connected to the fluid supply device, The cylindrical body includes an outer peripheral wall, an inner peripheral wall, and an upper wall, and a cavity portion provided between the outer peripheral wall and the inner peripheral wall, a fluid supply portion for supplying fluid to the cavity portion is provided on the outer peripheral wall or the upper wall; A welding electrode is disposed within the cylindrical body, an attachment that allows the fluid supplied from the fluid supply unit to flow out of the attachment from a lower portion thereof; A spot welding machine characterized by comprising:

12. the fluid cooling device is connected to the fluid supply device; the attachment is connected to the fluid cooling device; the fluid supply device and the attachment are connected via the fluid cooling device; Spot welding machine.

13. The spot welder according to claim 12, wherein the inner wall of the attachment is in contact with the welding electrode.

14. 14. The spot welder according to claim 13, wherein the attachment is integrally formed from the same material.

15. A spot welding electrode attachment that can be used in the method of any one of claims 1 to 10, The cylindrical body includes an outer peripheral wall, an inner peripheral wall, and an upper wall, and a cavity portion provided between the outer peripheral wall and the inner peripheral wall, a fluid supply portion for supplying fluid to the cavity portion is provided on the outer peripheral wall or the upper wall; A welding electrode can be placed inside the cylindrical body, An attachment that allows the fluid supplied from the fluid supply unit to flow out of the attachment from a lower portion thereof.

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