Bonding method and bonding apparatus

Abstract

[Problem] To improve shearing strength and peeling strength in bonding dissimilar metal members to each other. [Solution] Provided is a bonding method for resistance spot welding, using a pair of electrodes 10, a workpiece W in which an adhesive 3 is applied between a first metal member 1 and a second metal member 2 made of a metal different from that of the first metal member 1, the method comprising diffusion-bonding the first metal member 1 and the second metal member 2 in a state in which a preheated welding point P1 of the workpiece W, said preheated welding point P1 being separated from a welding point P2 between the first metal member 1 and the second metal member 2, is energized while being pressed to cause a prescribed amount of an adhesive 3 to be discharged from the energization path R of the welding point P1, and the welding point P2 is energized while being pressed to cause a prescribed amount of the adhesive 3 to be discharged from the energization path R of the welding point P2.

Description

Bonding Method and Bonding Apparatus

[0001] The present invention relates to a bonding method and a bonding apparatus for bonding members formed of different metals to each other.

[0002] For the purpose of improving fuel efficiency by reducing the weight of an automobile body, it is preferable to apply light metals such as aluminum alloys, which are lighter and have better energy absorption properties than the steel materials conventionally used. Unless the entire vehicle body is formed of an aluminum alloy material, a combination with a dissimilar metal material such as the steel material such as the steel plate originally used is essential. Therefore, in the manufacture of the vehicle body, bonding of different metals between an aluminum alloy material and a steel material (dissimilar material bonding) is required. However, dissimilar material bonding has problems such as galvanic corrosion and crevice corrosion occurring due to contact of different metals, and the corrosion resistance is inferior to that of welding of the same metal.

[0003] In Patent Document 1 below, in order to solve the above problems, in a dissimilar material bonding method by lap resistance welding using aluminum and iron, by sandwiching an adhesive for dissimilar material bonding at the interface of the joint portion using the weld bond method, galvanic corrosion and the like are prevented and bonding properties are ensured.

[0004] Japanese Patent Application Laid-Open No. 2007-136497

[0005] The bonding method of Patent Document 1 is a dissimilar material bonding method that employs the weld bond method and energizes electrodes in a state where an adhesive is applied between dissimilar metal members of a steel material and an aluminum alloy material to bond the members to each other. However, in such a conventional dissimilar material bonding method, the adhesive ignites and carbonizes due to energization during welding, and this carbide remains in the energization path of the weld nugget. Therefore, there is a problem that an intermetallic compound layer is formed unevenly between the steel material and the aluminum alloy material, and although the shear strength is sufficient, the peel strength is low.

[0006] Furthermore, in conventional dissimilar material joining methods, if plated steel with a plated surface is used, some of the adhesive may be discharged from the current path along with the molten plating material when current is applied. On the other hand, in conventional dissimilar metal joining methods, if unplated steel without a plated surface is used, there is no plating material to melt when current is applied, so the adhesive is less likely to be discharged. As mentioned above, in conventional dissimilar material joining methods, the adhesive remaining between the steel and the aluminum alloy can affect the formation of the intermetallic compound layer. Therefore, conventional dissimilar material joining methods also have the problem that the joint strength changes depending on whether or not the steel used is plated.

[0007] At least one embodiment of the present invention has been made in view of the above circumstances, and specifically aims to provide a joining method and joining apparatus that can improve the shear strength and peel strength between dissimilar metal members when joining them, regardless of whether or not they are plated.

[0008] The joining method according to this embodiment is a joining method in which a workpiece having an adhesive applied between a first metal member and a second metal member made of a different metal from the first metal member is resistance spot welded using a pair of electrodes, wherein a preheating point on the workpiece, away from the welding point between the first metal member and the second metal member, is energized while pressurizing to discharge a predetermined amount of the adhesive from the energizing path of the welding point, and the first metal member and the second metal member are diffusely joined together while the welding point is energized while pressurizing to discharge a predetermined amount of the adhesive from the energizing path of the welding point.

[0009] The joining apparatus according to this embodiment is a joining apparatus for resistance spot welding a workpiece in which an adhesive has been applied between a first metal member and a second metal member made of a different metal from the first metal member, and comprises a pair of electrodes that apply pressure to the workpiece while energizing it, a pressurizing mechanism that pressurizes and holds the workpiece with the pair of electrodes, a power supply unit that energizes the pair of electrodes with a predetermined current value, and a control unit that drives and controls at least the pressurizing mechanism and the power supply unit, wherein the control unit applies pressure to a preheating point on the workpiece that is away from the welding point between the first metal member and the second metal member, and controls the pressurizing mechanism and the power supply unit to discharge a predetermined amount of the adhesive from the energizing path of the welding point, and controls the pressurizing mechanism and the power supply unit to apply pressure to the welding point, and to form a joint in which the first metal member and the second metal member are diffusely bonded while the adhesive has been discharged from the energizing path of the welding point.

[0010] According to at least one embodiment of the present invention, a joining method and joining apparatus can be provided that can improve the shear strength and peel strength between dissimilar metal members when joining them, regardless of whether or not they are plated.

[0011] This is a diagram schematically showing the configuration of the joining device according to this embodiment. This is a diagram showing the preheating point and welding point of the joining device according to this embodiment. This is a diagram showing the joining method according to this embodiment in order of steps. This is a diagram showing the joining method according to this embodiment in order of steps. This is a diagram showing the joining method according to this embodiment in order of steps. This is a diagram showing the joining method according to this embodiment in order of steps. This is a diagram showing the workpiece joined by the joining method according to this embodiment. This is a graph showing the test results of the example of Test 1. This is a graph showing the test results of the comparative example of Test 1. This is a graph showing the test results of Test 2.

[0012] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. The embodiments shown herein are illustrative examples for embodying the technical idea of ​​the present invention and do not limit the present invention. Furthermore, all other implementable forms, examples, and operational techniques that can be conceived by those skilled in the art without departing from the spirit of the present invention are included in the scope and spirit of the present invention, as well as in the claims and their equivalents.

[0013] Furthermore, the drawings attached to this specification may be schematically represented with changes to scale, aspect ratio, shape, etc., from the actual object for the sake of illustration and ease of understanding, but these are merely examples and do not limit the interpretation of the present invention.

[0014] The joining method according to this embodiment is a weld bond method using the joining device 100 described below, and is a dissimilar material joining method in which a workpiece W, which is a combination of dissimilar metals consisting of a first metal member 1 and a second metal member 2 with an adhesive 3 interposed between them, is joined by diffusion bonding.

[0015] The workpiece W to be joined by the joining device 100 is composed of a first metal member 1, a second metal member 2, and an adhesive 3 placed between the first metal member 1 and the second metal member 2. The workpiece W may also include other members.

[0016] The first metal member 1 is a member made of a different metal material than the second metal member 2. The first metal member 1 can be made of a material with higher electrical resistance than the second metal member 2.

[0017] The first metal member 1 can be made of steel with iron as the main component. As the steel material, bare steel materials such as mild steel or alloy steel such as high-tensile steel can be used. The first metal member 1 is used, for example, as the frame of a vehicle. The first metal member 1 may be a plate, an extruded member (pipe, hollow, solid, or irregularly shaped cross-section), or a forged material (plate, ribbed).

[0018] The first metal member 1 may be a plated member with a known plating treatment applied to the bonding surface 1a with the second metal member 2, or it may be an unplated member without any plating treatment. Examples of plated members include plated steel materials such as galvanized steel sheets (GI steel sheets) and alloyed galvanized steel sheets (GA steel sheets). Materials that can be used for plating treatment are materials with a melting point at least below the ignition point of the adhesive. For the unplated member, an unplated steel material or the like with no plating treatment applied to the bonding surface 1a with the second metal member 2 can be used.

[0019] The second metal member 2 is a member formed from a different metal material than the constituent material of the first metal member 1. The second metal member 2 can be made of a material with lower electrical resistance than the first metal member 1.

[0020] The second metal member 2 is used, for example, as a panel for a vehicle. The second metal member 2 is not limited to a sheet metal, but may also be an extruded member (pipe material, hollow, solid, or irregularly shaped cross-section material), or a forged material (sheet metal, or ribbed material). The second metal member 2 may be subjected to various surface treatments such as blasting, etching, or brush polishing.

[0021] The second metal member 2 can be made of an aluminum alloy with aluminum as the main component. Suitable aluminum alloys include those of the 2000, 3000, 4000, 5000, 6000, and 7000 series. From the viewpoint of weldability, 5000, 6000, and 7000 series aluminum alloys are particularly preferred. The second metal member 2 may be made of the same material, or a combination of the above materials. Furthermore, the second metal member 2 can be made of a wrought material of 1000 series pure aluminum.

[0022] Adhesive 3 is applied between the joining surface 1a of the first metal member 1 and the joining surface 2a of the second metal member 2. Adhesive 3 can be an epoxy adhesive or the like. For example, Sandine (manufactured by Parker Asahi Co., Ltd.) can be used as an epoxy adhesive. In addition to epoxy adhesives, mastic adhesives with a rubber-based main component can also be used as adhesive 3. Adhesive 3 has the characteristic of decreasing viscosity due to the heat generated when pressurizing and energizing at the preheating point P1, which is the first energizing point by the electrode 10, and when pressurizing and energizing at the welding point P2, which is the second energizing point.

[0023] The adhesive 3 is pressurized by the clamping of the electrode 10, and its viscosity decreases when current is passed to the preheating point P1, causing a predetermined amount to be discharged from the current path R of the welding point P2. Almost all of the adhesive 3 is discharged from the current path R of the welding point P2. In other words, in the joining method according to this embodiment, an amount of adhesive 3 sufficient for diffusion bonding of the first metal member 1 and the second metal member 2 may remain in the current path R of the welding point P2. However, since the amount of adhesive 3 remaining is minute, it does not affect the formation of a substantially uniform intermetallic compound layer 4.

[0024] The preheating point P1 set on the workpiece W is set at a predetermined distance from the welding point P2 and may coincide with the point where the first current C1 is applied by the electrode 10 (the clamping position of the workpiece W). The welding point P2 set on the workpiece W is set at the position where the first metal member 1 and the second metal member 2 are welded to form the joint 5 and may coincide with the point where the second current C2 is applied by the electrode 10 (the clamping position of the workpiece W). The distance (D2) between the preheating point P1 and the welding point P2 will be described in detail later.

[0025] Next, the joining device 100 according to this embodiment will be described.

[0026] As shown in Figure 1, the bonding device 100 is composed of an electrode 10, a pressurizing mechanism 20, a power supply unit 30, a moving mechanism 40, and a control unit 50. Note that the bonding device 100 shown in Figure 1 has many other components besides those shown in Figure 1, but their illustration and detailed description are omitted.

[0027] The electrode 10 is composed of a pair of electrodes: a first electrode 11 and a second electrode 12. The electrode 10 is configured to be movable relative to the workpiece W by a pressurizing mechanism 20, and can pressurize the workpiece W while holding it in place. The electrode 10 is energized by a predetermined current from a power supply unit 30. The electrode 10 can move at least between the preheating point P1 and the welding point P2 by a moving mechanism 40.

[0028] The first electrode 11 is a columnar electrode tip made of a conductive material such as metal. The first electrode 11 is energized while a predetermined pressure is applied to the first metal member 1. The shape of the tip of the first electrode 11 is not particularly limited, but it can be a dome radius type (DR type) as shown in Figure 1. As shown in Figure 1, the first electrode 11 has a first contact surface 11a with a diameter D1 that contacts the first metal member 1. The first electrode 11 is configured to be movable relative to the workpiece W by driving the pressurizing mechanism 20. Current is supplied to the first electrode 11 from the power supply unit 30 while the workpiece W is pressurized.

[0029] The second electrode 12 is a columnar electrode tip made of a conductive material such as metal. The second electrode 12 is energized while a predetermined pressure is applied to the second metal member 2. The shape of the tip of the second electrode 12 is not particularly limited, but it can be a radius type (R type) as shown in Figure 1. As shown in Figure 1, the second electrode 12 has a second contact surface 12a with a diameter D3 that contacts the second metal member 2. The second electrode 12 is configured to be movable relative to the workpiece W by driving the pressurizing mechanism 20. Current is supplied to the second electrode 12 from the power supply unit 30 while the workpiece W is pressurized.

[0030] By using a DR-type electrode for the first electrode 11 and an R-type electrode for the second electrode 12, the greatest pressure can be applied to the center of the joint 5 between the first metal member 1 and the second metal member 2. This makes it easier to discharge the adhesive 3 from the joint interface during joining, thereby improving the joint strength.

[0031] As shown in Figure 1, the contact area of ​​the first contact surface 11a of the first electrode 11 is smaller than that of the second contact surface 12a of the second electrode 12. In other words, the diameter D1 of the first contact surface 11a of the first electrode 11 is smaller than the diameter D3 of the second contact surface 12a of the second electrode 12. Therefore, when the electrode 10 is energized, the current density is relatively higher in the first metal member 1 that is in contact with the first electrode 11, and relatively lower in the second metal member 2 that is in contact with the second electrode 12. At this time, the amount of heat generated at the bonding interface between the first metal member 1 and the second metal member 2 and the amount of heat generated inside the second metal member 2 are greater in the first metal member 1. Consequently, the temperature inside the first metal member 1 is the highest compared to the temperature at the bonding interface between the first metal member 1 and the second metal member 2 and the temperature inside the second metal member 2.

[0032] For example, if the first metal member 1 is a bare steel plate and the second metal member 2 is an aluminum alloy plate, the maximum temperature of the first metal member 1 will be approximately 1500°C. The temperature at the interface between the first metal member 1 and the second metal member 2 will be approximately 700°C. At this time, eutectic melting (or diffusion melting) of iron and aluminum occurs at the joining interface due to the pressure and temperature rise, and the oxide film on the surface is melted and discharged outside the joining interface. Then, the newly formed surface of the steel plate and the newly formed surface of the aluminum alloy plate come into contact, forming an intermetallic compound layer 4, and the first metal member 1 and the second metal member 2 are diffusion-bonded. If the first metal member 1 is a GA steel plate or GI steel plate with a plating layer, the plating layer will also melt and be discharged outside the joining interface.

[0033] In this way, by making the diameter D1 of the first electrode 11 smaller than the diameter D3 of the second electrode 12, the contact area of ​​the first electrode 11 with the first metal member 1 can be reliably made smaller than the contact area of ​​the second electrode 12 with the second metal member 2. As a result, the current density inside the first metal member 1 can be made higher than the current density inside the second metal member 2. Also, since the diameter D3 of the second electrode 12 is relatively larger than the diameter D1 of the first electrode 11, the heat capacity of the second electrode 12 is also relatively larger. Therefore, because the second electrode 12 is in contact with the second metal member 2, the cooling performance of the second metal member 2 by the second electrode 12 can be improved, and the reduction in the thickness of the second metal member 2 can be suppressed.

[0034] When the pressurizing mechanism 20 energizes the workpiece W, it moves the first electrode 11 and the second electrode 12 relative to the workpiece W, and clamps the workpiece W with a predetermined pressure. The pressurizing mechanism 20 may apply the same pressure to the first electrode 11 and the second electrode 12, or it may apply different pressures to each electrode.

[0035] The power supply unit 30 is, for example, a power supply circuit, and is configured to supply a current of a predetermined value between the first electrode 11 and the second electrode 12. The power supply unit 30 supplies a first current C1 to the electrode 10 for supplying power to the preheating point P1 and a second current C2 to supply power to the welding point P2, under the control of the control unit 50. The first current C1 has a lower current value than the second current C2.

[0036] When the power supply unit 30 energizes the preheating point P1, it energizes the electrode 10 with a current (first current C1) that reduces the viscosity of the adhesive 3 and generates heat in the workpiece W without causing ignition. The current energized through the electrode 10 energizes the workpiece W, generating heat (Joule heat), which is then transferred to the welding point P2 through the first metal member 1 and the second metal member 2. The heat transferred to the vicinity of the welding point P2 reduces the viscosity of the adhesive 3 applied to the energizing path R of the welding point P2. The current value energized through the electrode 10 reduces the viscosity of the adhesive 3, but is controlled so that the adhesive 3 does not ignite. Therefore, the adhesive 3 in and around the energizing path R of the welding point P2 reduces in viscosity without carbonizing, and a predetermined amount is discharged from the energizing path R of the welding point P2 by the pressure applied by the electrode 10.

[0037] When the power supply unit 30 energizes the welding point P2, it energizes the workpiece W with a current (second current C2) to the electrode 10 so that an intermetallic compound layer 4 is formed at the joining interface between the first metal member 1 and the second metal member 2, and a diffusion-bonded joint 5 is formed. As a result, the temperature of the first metal member 1 (steel) and the second metal member 2 (aluminum alloy) rises to the diffusion temperature, and impurities on the surface of the first metal member 1 and the second metal member 2, along with a predetermined amount of adhesive, are discharged through the energizing path R by pressurization. Then, at the joining interface where the first metal member 1 and the second metal member 2 come into contact, a substantially uniform intermetallic compound layer 4 controlled to be 1 to 2 μm is formed and the two metal members are diffuse-bonded. The workpiece W is diffuse-bonded, forming a joint 5 with excellent shear strength and peel strength (see Figure 7).

[0038] The moving mechanism 40 can move the electrodes 10 to a desired position relative to the workpiece W. When energizing the preheating point P1 of the workpiece W, the moving mechanism 40 moves the first electrode 11 and the second electrode 12 to the position of the preheating point P1. When energizing the welding point P2 of the workpiece W, the moving mechanism 40 moves the first electrode 11 and the second electrode 12 to the position of the welding point P2.

[0039] The control unit 50 is configured with various processors and memory devices such as a CPU, ROM, and RAM, and comprehensively controls the driving of each part of the joining device 100 and various controls related to the joining process. The control unit 50 controls the pressurizing mechanism 20 to clamp and pressurize the workpiece W with the electrode 10, and controls the power supply unit 30 to control the current value supplied to the electrode 10 to either the first current C1 or the second current C2. The control unit 50 controls the moving mechanism 40 to move the electrode 10 to the preheating point P1 and the welding point P2.

[0040] Next, the positional relationship between the preheating point P1 and the welding point P2, which are energized by the electrode 10, will be described in the joining apparatus 100 according to this embodiment.

[0041] The positional relationship between the preheating dot P1 and the welding dot P2 is derived from the following formulas (1) and (2). As shown in FIG. 1, the diameter of the first contact surface 11a of the first electrode 11 with respect to the first metal member 1 is denoted as "D1". As shown in FIG. 2, the distance between the preheating dot P1 and the welding dot P2 is denoted as "D2". The "distance between welding dots" means the distance between the center positions of each welding point of the preheating dot P1 and the welding dot P2. At this time, the shortest distance of D2 satisfies the relationship of formula (1): D2 ≥ 1 / 2 × (D1), and the longest distance of D2 satisfies the relationship of formula (2): D2 ≤ 5 × (D1). That is, D2 is set within the range of 1 / 2 × (D1) ≤ D2 ≤ 5 × (D1).

[0042] The shortest distance of the above D2 is a distance at which the combustion product (carbide) of the adhesive 3 generated by the heat generated by energization when energized at the preheating dot P1 does not affect the welding dot P2. On the other hand, the longest distance of the above D2 is a distance at which the viscosity of the adhesive 3 applied to the energization path R of the welding dot P2 is reduced by the heat generated by energization when energized at the preheating dot P1, and the adhesive 3 with reduced viscosity can be extruded from the energization path R of the welding dot P2 by the pressing force of the electrode 10. Therefore, if the distance D2 between the preheating dot P1 and the welding dot P2 is outside the above range, the viscosity of the adhesive 3 will not decrease or it will be affected by carbides, and the workpiece W will not be properly diffusion-bonded.

[0043] Next, the bonding method according to the present embodiment will be described. FIGS. 3 to 7 show the operation when bonding the workpiece W using the above-described bonding apparatus 100 and the bonded workpiece W.

[0044] In carrying out the bonding method, a workpiece W is prepared. The workpiece W is set in the bonding apparatus 100. Then, as shown in FIG. 3, the bonding apparatus 100 moves the electrode 10 to the preheating dot P1 and sandwiches the workpiece W with the electrode 10.

[0045] As shown in Figure 4, the bonding device 100 drives the power supply unit 30 to supply a first current C1 to the electrode 10. The applied pressure at this time is not particularly limited, but can be 4kN to 8kN. The squeeze time is not particularly limited, but can be 50msec to 200msec. The energizing time is not particularly limited, but can be 30msec to 100msec.

[0046] The heat generated by the current supplied from the electrode 10 is transferred to the welding point P2 through the first metal member 1 and the second metal member 2. The viscosity of the adhesive 3 applied to the welding point P2 decreases due to the heat transferred from the preheating point P1. As shown in Figure 4, the reduced viscosity adhesive 3 is discharged in a predetermined amount from the current supply path R at the welding point P2 by the pressurization of the electrode 10. In addition, some of the adhesive 3 near the preheating point P1 may burn, but this does not affect the joining of the welding point P2.

[0047] As shown in Figure 5, the joining device 100 moves the electrode 10 from the preheating point P1 to the welding point P2, clamps the workpiece W with the electrode 10, and drives the power supply unit 30 to supply a second current C2 to the electrode 10. When the workpiece W is supplied with current to the welding point P2, the welding point P2 is pressurized by the electrode 10, causing a predetermined amount of adhesive 3 with reduced viscosity to be discharged from the current supply path R at the welding point P2. The applied pressure at this time is not particularly limited, but can be 4kN to 8kN. The squeeze time is not particularly limited, but can be 50msec to 200msec. The energizing time is not particularly limited, but can be 150msec to 350msec. The hold time is not particularly limited, but can be 1500msec to 2500msec.

[0048] As described above, as shown in Figure 7, the joint surface between the first metal member 1 and the second metal member 2 of the workpiece W is heated by the current supplied from the electrode 10, forming an intermetallic compound layer 4 of substantially uniform thickness and causing diffusion bonding. As a result, the workpiece W has a joint portion 5 formed at the joint interface between the first metal member 1 and the second metal member 2 through diffusion bonding. The workpiece W is firmly bonded by the diffusion bonding of the first metal member 1 and the second metal member 2 to form the joint portion 5, which can improve shear strength and peel strength.

[0049] Note that the work W joined by the joining method according to the present embodiment may be a combination of dissimilar metals such as, for example, an aluminum alloy and a plated steel material, or a combination of an aluminum alloy and a non-plated steel material. Further, in the joining method using the joining device 100, the shear strength and the peel strength can be improved by diffusion joining of dissimilar metals regardless of the presence or absence of plating. Further, the joining method according to the present embodiment is also applicable to joining of other dissimilar metal members other than the combination of a steel material and an aluminum alloy.

[0050] [Operation and Effect] As described above, the joining method according to the present embodiment is a joining method in which a work W coated with an adhesive 3 is subjected to resistance spot welding using a pair of electrodes 10 between a first metal member 1 and a second metal member 2 made of a metal different from the first metal member 1. While pressurizing a preheating spot P1 separated from the welding spot P2 between the first metal member 1 and the second metal member 2 of the work W, electric current is passed to discharge a predetermined amount of the adhesive 3 from the current conduction path R of the welding spot P2. The first metal member 1 and the second metal member 2 are diffusion joined to form a joined portion 5 in a state where a predetermined amount of the adhesive 3 is discharged from the current conduction path R of the welding spot P2 while pressurizing the welding spot P2 and passing an electric current.

[0051] Thereby, the heat generated by pressurization and energization with respect to the preheating spot P1 is transferred to the adhesive 3 applied to the current conduction path R of the welding spot P2 through the first metal member 1 and the second metal member 2, and the viscosity of the adhesive 3 decreases. The adhesive 3 with reduced viscosity is discharged in a predetermined amount from the current conduction path R of the welding spot P2 by the pressurization of the electrode 10. Since the appropriate amount of the adhesive 3 is discharged from the current conduction path R of the welding spot P2 for diffusion joining in the work W, an intermetallic compound layer 4 is formed at the joining interface between the first metal member 1 and the second metal member 2, and a joined portion 5 joined by diffusion joining can be formed. Therefore, the joining method according to the present embodiment can produce a joined product having excellent shear strength and peel strength regardless of the presence or absence of plating.

[0052] Furthermore, in the joining method according to this embodiment, the electrode 10 is composed of a first electrode 11 having a first contact surface 11a that contacts the first metal member 1, and a second electrode 12 having a second contact surface 12a that contacts the second metal member 2. When the diameter of the first contact surface 11a is D1 and the distance between the welding points P1 and P2 is D2, the shortest distance of D2 satisfies the relationship D2 ≥ 1 / 2 × (D1), and the longest distance of D2 satisfies the relationship D2 ≤ 5 × (D1).

[0053] With this configuration, when joining workpieces W, if the welding point D2, which is the distance between the preheating point P1 and the welding point P2, is controlled to satisfy the aforementioned relationship, the adhesive 3 is appropriately discharged from the current path R of the welding point P2, forming an intermetallic compound layer 4 with substantially uniform thickness and achieving diffusion bonding. Therefore, the workpiece W has sufficient bonding strength and becomes a joined product with excellent shear strength and peel strength.

[0054] Furthermore, in the joining method according to this embodiment, the first metal member 1 may be made of steel, and the second metal member 2 may be made of an aluminum alloy.

[0055] With this configuration, the workpiece W, which consists of a first metal member 1 made of steel and a second metal member 2 made of aluminum alloy, is diffusion-bonded with the adhesive 3 applied to the current-carrying path R of the welding point P2 being discharged. As a result, the workpiece W, which consists of the first metal member 1 made of steel and the second metal member 2 made of aluminum alloy, becomes a joint with excellent shear strength and peel strength.

[0056] Furthermore, in the joining method according to this embodiment, the first metal member 1 may be formed from plated steel with plating treatment applied to at least a portion of the joining surface 1a, or from unplated steel with no plating treatment applied to the joining surface 1a, and the second metal member 2 may be formed from an aluminum alloy.

[0057] With this configuration, a workpiece W made of a first metal member 1 formed from plated or unplated steel and a second metal member 2 formed from an aluminum alloy is diffusion-bonded with the adhesive 3 applied to the current-carrying path R of the welding point P2 being discharged. Therefore, a workpiece W made of a first metal member 1 formed from plated or unplated steel and a second metal member 2 formed from an aluminum alloy becomes a joined product with excellent shear strength and peel strength, regardless of whether or not it is plated.

[0058] Furthermore, in the joining method according to this embodiment, the pair of electrodes 10 consists of a first electrode 11 having a first contact surface 11a that contacts the first metal member 1, and a second electrode 12 having a second contact surface 12a that contacts the second metal member 2, and the contact area of ​​the first contact surface 11a with the first metal member 1 may be smaller than the contact area of ​​the second contact surface 12a with the second metal member 2.

[0059] With this configuration, the current density inside the first metal member 1 can be made higher than the current density inside the second metal member 2. Also, since the diameter D3 of the second electrode 12 is relatively larger than the diameter D1 of the first electrode 11, the heat capacity of the second electrode 12 is also relatively larger. Therefore, because the second electrode 12 is in contact with the second metal member 2, the cooling performance of the second metal member 2 by the second electrode 12 can be improved, and the reduction in the thickness of the second metal member 2 can be suppressed.

[0060] Furthermore, in the joining method according to this embodiment, the current supplied to the pair of electrodes 10 includes a first current C1 supplied at the preheating point P1 and a second current C2 supplied at the welding point P2. The first current C1 is set to a value that reduces the viscosity of the adhesive 3 and generates heat to prevent the adhesive 3 from burning, and the second current C2 is set to a value that generates heat to enable the formation of a diffusion-bonded joint 5 by forming an intermetallic compound layer 4 between the joining surface 1a of the first metal member 1 and the joining surface 2a of the second metal member 2.

[0061] The first current C1 supplied to electrode 10 reduces the viscosity of the adhesive 3, but is controlled to prevent the adhesive 3 from igniting. Therefore, the first current C1 reduces the viscosity of the adhesive 3 in the current path R of the welding point P2 and its surroundings without carbonizing it or with minimal carbonization, and a predetermined amount can be discharged from the current path R of the welding point P2 by pressurizing electrode 10. In addition, the second current C2 supplied to electrode 10 is controlled to form an intermetallic compound layer 4 at the bonding interface between the first metal member 1 and the second metal member 2, enabling diffusion bonding. The second current C2 raises the temperature of the first metal member 1 and the second metal member 2 to the diffusion temperature, and by pressurizing, impurities on the surface of the first metal member 1 and the second metal member 2, along with a predetermined amount of adhesive 3, can be discharged from the current path R. Therefore, when a first current C1 is applied to the preheating point P1 and a second current C2 is applied to the welding point P2 of the first metal member 1 and the second metal member 2, an intermetallic compound layer 4 is formed at the joint interface where the two come into contact, resulting in diffusion bonding and a joint with excellent shear strength and peel strength.

[0062] Furthermore, the joining apparatus 100 according to this embodiment is a joining apparatus 100 for resistance spot welding a workpiece W to which adhesive 3 has been applied between a first metal member 1 and a second metal member 2 made of a different metal from the first metal member 1, and comprises a pair of electrodes 10 that conduct current while applying pressure to the workpiece W, a pressurizing mechanism 20 that pressurizes and holds the workpiece W with the pair of electrodes 10, a power supply unit 30 that conducts a current of a predetermined value to the pair of electrodes 10, and a control unit 50 that drives and controls at least the pressurizing mechanism 20 and the power supply unit 30. The control unit 50 applies pressure to a preheating point P1 located away from the welding point P2 between the first metal member 1 and the second metal member 2 of the workpiece W, and controls the pressurizing mechanism 20 and the power supply unit 30 to discharge a predetermined amount of adhesive 3 from the current path R of the welding point P2. The control unit 50 applies pressure to the welding point P2, and controls the pressurizing mechanism 20 and the power supply unit 30 to form a joint 5 by diffusion bonding between the first metal member 1 and the second metal member 2 while applying pressure to the welding point P2 and discharging a predetermined amount of adhesive 3 from the current path R of the welding point P2.

[0063] With this configuration, the heat generated by pressurizing and energizing the preheating point P1 of the workpiece W is transferred to the adhesive 3 applied to the energizing path R of the welding point P2 through the first metal member 1 and the second metal member 2, causing the viscosity of the adhesive 3 to decrease. The adhesive 3 with reduced viscosity is discharged in a predetermined amount from the energizing path R of the welding point P2 by pressurizing the electrode 10. Because an appropriate amount of adhesive 3 for diffusion bonding is discharged from the energizing path R of the welding point P2 of the workpiece W, an intermetallic compound layer 4 is formed at the bonding interface between the first metal member 1 and the second metal member 2, and a diffusion-bonded joint 5 is formed. Therefore, the bonding apparatus 100 according to this embodiment can produce a bonded product with excellent shear strength and peel strength, regardless of whether or not it is plated.

[0064] The following embodiments are also included in the scope of the present invention: the joining method according to claim 1 having the features of claim 2; the joining method according to claim 1 or 2 having the features of claim 3; the joining method according to claim 1 or 2 having the features of claim 4; the joining method according to any one of claims 1 to 4 having the features of claim 5; the joining method according to any one of claims 1 to 5 having the features of claim 6. A joining device that diffuse-bonds a first metal member and a second metal member by the joining method according to any one of claims 1 to 6 to form a joint at the welding point.

[0065] The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited to the following examples.

[0066] [Test 1] In Test 1, samples A1 to A5 were prepared as examples, and samples B1 to B5 were prepared as comparative examples. Peel strength tests were conducted according to the following test procedures to compare the peel strength of each sample.

[0067] Samples A1 to A5 and Samples B1 to B5 all had the same specifications. For each sample, the first metal component was an unplated steel sheet measuring 150 mm in length, 50 mm in width, and 0.7 mm in thickness. The second metal component was a 6000 series aluminum alloy measuring 150 mm in length, 50 mm in width, and 1.1 mm in thickness.

[0068] Each sample in the examples was joined using a servo-type inverter spot welding machine, with current applied to both the preheating point and the welding point. The welding point spacing (D2) between the preheating point and the welding point was set to 0 mm to 20 mm. Note that the time it takes for the electrode to move from the preheating point to the welding point is omitted. Preheating point: Pressurized force 7000 N, squeeze time 100 msec, first current applied (current value: 12 kA, application time: 60 msec) Welding point: Pressurized force 7000 N, squeeze time 100 msec, second current applied (current value: 22 kA, application time: 240 msec).

[0069] Each sample in the comparative example was prepared using a servo-type inverter spot welding machine, and the welding point was energized twice. • Welding point: Pressurized force 7000N, squeeze time 100msec, first energization (current value: 10kA, energization time: 20msec), cooling time 300msec, second energization (current value: 22kA, energization time: 240msec), holding time 2000msec.

[0070] The peel strength of each sample was measured using a tensile and compression testing machine (model: SDW-5003, manufactured by Imada Seisakusho Co., Ltd.) by performing a cross tensile test as specified in JIS Z 3137. The tensile speed was set to 10 mm / min.

[0071] Figure 8 shows the peel strength results for Samples A1 to A5, which are examples. Figure 9 shows the peel strength results for Samples B1 to B5, which are comparative examples. In the tables in Figures 8 and 9, the vertical axis is CTS (Cross Tensile Strength), and the CTS for each sample is graphed. As shown in Figures 8 and 9, when comparing Samples A1 to A5 of the examples with Samples B1 to B5 of the comparative examples, the peel strength of the examples all exceeded that of the comparative examples. From this, it was confirmed that when joining workpieces, applying current to the preheating point and the welding point separately, as in the examples, allows the adhesive to be discharged from the current path of the welding point, resulting in a stronger bond between the workpieces, rather than applying current to the welding point multiple times, as in the comparative examples.

[0072] [Test 2] In Test 2, the same samples used in Test 1 were prepared, and peel strength tests were conducted by changing the distance (D2) between the preheating point and the welding point, and the peel strength of each sample was measured and compared.

[0073] <Test Details> Test 2 was conducted using a servo-type inverter spot welding machine, varying the welding point spacing (D2) between the preheating point and the welding point to 0 mm, 2 mm, 4 mm, 6 mm, 8 mm, 12 mm, 15 mm, 18 mm, and 20 mm, and performing the same test as in the example of Test 1. The diameter (D1) of the contact surface of the first electrode constituting the electrode was set to 6 mm. The peel strength of the sample was measured using a tensile and compression testing machine (model: SDW-5003, manufactured by Imada Seisakusho Co., Ltd.) and performing a cross tensile test as specified in JIS Z 3137. The tensile speed was set to 10 mm / min. Fifteen samples were prepared from the samples of Test 1, with one each of 0 mm, 2 mm, and 20 mm tested, and two each of the other distances tested. In the table shown in Figure 10, the vertical axis represents CTS (cross-tensile strength), and the horizontal axis represents the distance D2. In the table, "○" indicates a sample in which an improvement in peel strength was confirmed, and "×" indicates a sample in which no improvement in peel strength was confirmed or the peel strength did not meet the standard.

[0074] Figure 10 shows the evaluation results of the peel strength for each welding point spacing (D2) between the preheating point and the welding point. As shown in Figure 10, the peel strength improved when D2 was set to 4 mm to 18 mm. On the other hand, the peel strength did not improve when D2 was set to 0 mm, 2 mm, or 20 mm. From these results, it was suggested that when the diameter of the contact surface of the first electrode with respect to the first metal member is "D1" and the distance between the preheating point and the welding point is "D2", the shortest distance of D2 satisfies the relationship D2 ≥ 1 / 2 × (D1), and the longest distance of D2 satisfies the relationship D2 ≤ 5 × (D1). In other words, setting D2 within the range of 1 / 2 × (D1) ≤ D2 ≤ 5 × (D1) suggests that the peel strength is improved by appropriately diffusion bonding the first metal member and the second metal member.

[0075] 1 First metal member, 1a Joining surface of the first metal member, 2 Second metal member, 2a Joining surface of the second metal member, 3 Adhesive, 4 Intermetallic compound layer, 5 Joint, 10 Electrode, 11 First electrode, 11a Contact surface with the first metal member, 12 Second electrode, 12a Contact surface with the second metal member, 20 Pressurizing mechanism, 30 Power supply unit, 40 Moving mechanism, 50 Control unit, 100 Joining device, C1 First current adjusted to the current value when energizing the preheating point, C2 Second current adjusted to the current value when energizing the welding point, D1 Diameter of the first contact surface of the first electrode, D2 Distance that becomes the welding point spacing between the preheating point and the welding point, D3 Diameter of the second contact surface of the second electrode, P1 Preheating point, P2 Welding point, W Workpiece.

Claims

1. A joining method for resistance spot welding a workpiece in which an adhesive has been applied between a first metal member and a second metal member made of a different metal from the first metal member, using a pair of electrodes, wherein the joining method involves applying pressure to a preheating point on the workpiece, which is located away from the welding point between the first and second metal members, and energizing it to discharge a predetermined amount of the adhesive from the energizing path of the welding point, and forming a joint by diffusion bonding between the first and second metal members while applying pressure to the welding point and energizing it to discharge a predetermined amount of the adhesive from the energizing path of the welding point.

2. The joining method according to claim 1, wherein the electrode comprises a first electrode having a first contact surface that contacts the first metal member, and a second electrode having a second contact surface that contacts the second metal member, and the diameter of the first contact surface is D1, and the distance between the preheating point and the welding point is D2, the longest distance of D2 satisfies the relationship D2 ≥ 1 / 2 × (D1), and the shortest distance of D2 satisfies the relationship D2 ≤ 5 × (D1).

3. The joining method according to claim 1, wherein the first metal member is made of steel and the second metal member is made of an aluminum alloy.

4. The joining method according to claim 1, wherein the first metal member is made of plated steel with a plating treatment applied to the joining surface or unplated steel with no plating treatment applied to the joining surface, and the second metal member is made of an aluminum alloy.

5. The joining method according to claim 3 or 4, wherein the pair of electrodes comprises a first electrode having a first contact surface that contacts the first metal member, and a second electrode having a second contact surface that contacts the second metal member, and the contact area of ​​the first contact surface with the first metal member is smaller than the contact area of ​​the second contact surface with the second metal member.

6. The joining method according to claim 1 or 2, wherein the current supplied to the pair of electrodes includes a first current supplied at the preheating point and a second current supplied at the welding point, the first current being a current value that reduces the viscosity of the adhesive and generates heat to prevent the adhesive from burning, and the second current being a current value that generates heat to enable the formation of a diffusion-bonded joint by forming an intermetallic compound layer at the bonding interface between the first metal member and the second metal member.

7. A joining device for resistance spot welding a workpiece in which an adhesive has been applied between a first metal member and a second metal member made of a different metal from the first metal member, comprising: a pair of electrodes that apply pressure to the workpiece while energizing it; a pressurizing mechanism that pressurizes and holds the workpiece with the pair of electrodes; a power supply unit that energizes the pair of electrodes with a predetermined current value; and a control unit that drives and controls at least the pressurizing mechanism and the power supply unit, wherein the control unit energizes a preheating point on the workpiece, away from the welding point between the first metal member and the second metal member, while applying pressure, and controls the pressurizing mechanism and the power supply unit to discharge a predetermined amount of the adhesive from the energizing path of the welding point; and energizes the welding point while applying pressure, and controls the pressurizing mechanism and the power supply unit to form a joint in which the first metal member and the second metal member are diffusely bonded while a predetermined amount of the adhesive is discharged from the energizing path of the welding point.

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