Resistance welding method

Abstract

To provide a resistance welding method which prevents poor welding, by forming a desired melting part under an electrification condition of comparatively suppressing a heat input volume.SOLUTION: A resistance welding method for joining a first member 20 consisting of nonferrous metal, and a second member 30 consisting of ferrous metal, includes the steps of: abutting a shank 42 of an element 40 consisting of ferrous metal on the first member 20, and superposing the element 40, the first member 20, and the second member 30 on each other in this order; sandwiching and pressurizing the element 40, the first member 20, and the second member 30 using a pair of electrodes 50, and pressurizing at least either of the element 40 or the first member 20 by using an external pressurizing tool 60 disposed in the periphery of the electrodes 50; and melting the first member 20 according to electrification by the pair of electrodes 50, while maintaining the pressure according to the pair of electrodes 50 and the external pressurizing tool 60, and further, penetrating the element 40 into the first member 20 and welding the element 40 and the second member 30.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a resistance welding method, and more particularly to a resistance welding method for joining dissimilar metals, that is, a member made of a non-ferrous metal and a member made of an ferrous metal. [Background technology]

[0002] It is difficult to directly join non-ferrous metals such as aluminum and magnesium to ferrous metals using conventional spot welding, and a method of joining them by mechanical fastening with rivets such as SPR (Self-Piercing Riveted) is generally used. In recent years, a method has been proposed in which a part of the non-ferrous metal is replaced with ferrous metal using flanged steel rivets (hereinafter referred to as "elements"), and the elements and ferrous metal are resistance-welded to indirectly join dissimilar metals. In particular, from the viewpoint of productivity, a method of performing replacement with elements and joining with ferrous metal in a single process has attracted attention.

[0003] As a method of performing replacement with an element and joining with an iron-based metal in one step, for example, Patent Document 1 discloses a manufacturing method for a dissimilar joining member in which a rivet (corresponding to the above-mentioned "element") having a head, a shank with one end connected to the head, and a groove formed in the surface of the head on the shank side is protruded from a first member while applying pressure and current, and the shank is inserted into the first member while the first member that has been softened by heating or melted flows into the groove, thereby joining the rivet and a second member. This manufacturing method is said to be able to prevent the molten first member from flowing out around the rivet and to suppress the occurrence of burrs.

[0004] Patent Document 2 discloses a method for joining dissimilar materials, which involves overlapping a first member on a second member, placing a rivet on the first member, applying pressure and electricity to the rivet and the second member with an electrode tip, penetrating the rivet into the first member by resistance heating in a first step, and forming a molten part between the rivet and the second member in a second step. It is said that this joining method can prevent molten metal from spilling out of the rivet by blowing air during joining.

[0005] Furthermore, Patent Document 3 discloses a joining method in which a button part (corresponding to the above-mentioned "element") is pressed into a surface side of a second part made of a material different from steel without heating with a first pressure that is higher than a second pressure during welding, and then a second pressure is applied to weld the tip of the penetrated button part to the first part made of steel by resistance spot welding. It is said that this joining method can join a structure made of dissimilar metal materials such as aluminum to a structure made of steel with higher strength without increasing costs. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2018-43258 A [Patent Document 2] JP 2020-69499 A [Patent Document 3] JP 2018-61968 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, as a result of investigations by the present inventors, it was found that with the conventional methods such as those shown in Patent Documents 1 to 3, it is difficult to form a desired (i.e., high-strength) molten zone between the element and the iron-based metal, while a large heat input is required to form the desired molten zone, which may result in frequent welding defects.

[0008] Specifically, for example, the heterogeneous joining methods disclosed in Patent Documents 1 and 2 involve inserting a rivet having a groove into a first component that has been softened or melted by heating, and then inserting the shaft into the first component while allowing the first component that has been softened or melted by heating to flow into the groove, thereby spot welding the rivet and the second component. However, it has been found that the flow of the first component that has been softened or melted by heating into the groove causes the rivet to be pushed upward, which may hinder the formation of the desired molten part between the rivet and the second component.

[0009] Furthermore, it was found that the joining method disclosed in Patent Document 3 involves forcibly pressing the button part into the surface side of the second part, which is made of a material different from steel, in an unheated state, and therefore the second part around the button part tends to warp upward, causing the button part to be easily pushed upward during welding, which may hinder the formation of the desired molten joint between the button part and the first part.

[0010] The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide a resistance welding method capable of forming a desired molten zone between an element made of an iron-based metal and a member made of an iron-based metal under current flow conditions with a relatively reduced heat input, thereby preventing poor welding. [Means for solving the problem]

[0011] Therefore, the above object of the present invention is achieved by the resistance welding method having the following configuration [1] or [2].

[0012] [1] A resistance welding method for joining a first member made of a non-ferrous metal and a second member made of an iron-based metal using an element having a head and a shaft and made of an iron-based metal, comprising: a step of abutting the shaft portion against the first member, and stacking the element, the first member, and the second member in this order; a step of clamping and pressurizing the element, the first member, and the second member with a pair of electrodes, and pressurizing at least one of the element and the first member with an external pressurizing tool disposed around at least one of the pair of electrodes that is closer to the element; a step of melting the first member by energizing the pair of electrodes while maintaining pressure applied by the pair of electrodes and the external pressure jig, and further penetrating the element into the first member to weld the element and the second member; A resistance welding method comprising:

[0013] [2] A resistance welding method for joining a first member made of a non-ferrous metal, a second member made of an iron-based metal, and a third member made of an iron-based metal using an element having a head and a shaft and made of an iron-based metal, comprising: a step of abutting the shaft portion against the first member, and stacking the element, the first member, the second member, and the third member in this order; a step of clamping and pressurizing the element, the first member, the second member, and the third member with a pair of electrodes, and pressurizing at least one of the element and the first member with an external pressurizing tool disposed around at least one of the pair of electrodes that is closer to the element; a step of melting the first member by energizing the pair of electrodes while maintaining pressure applied by the pair of electrodes and the external pressure jig, and further penetrating the element into the first member to weld the element, the second member, and the third member; A resistance welding method comprising: Effect of the Invention

[0014] According to the resistance welding method of the present invention, by applying pressure to at least one of the element and the non-ferrous metal member using an external pressure jig arranged around the electrode during welding, the non-ferrous metal member is prevented from pushing up the element due to the molten non-ferrous metal member during welding. This makes it possible to form a desired molten zone between the ferrous metal element and the ferrous metal member under current flow conditions with a relatively low heat input, thereby preventing poor welding. [Brief description of the drawings]

[0015] [Figure 1] Fig. 1 is a schematic cross-sectional view showing a process of forming a dissimilar material welded joint by a resistance welding method according to a first embodiment. Fig. 1(a) is a schematic cross-sectional view showing a state in which an element, a first member, and a second member are stacked in this order, and the element, the first member, and the second member are clamped and pressed by a pair of electrodes, and the element is pressed by an external pressing jig arranged around each of the pair of electrodes. Fig. 1(b) is a schematic cross-sectional view showing a state in which the element and the second member are welded by passing a current between the pair of electrodes. [Diagram 2] FIG. 2 is a perspective view of an example element. [Figure 3A] FIG. 3A is a perspective view showing a first example of the configuration of an external pressure jig. [Figure 3B] FIG. 3B is a perspective view showing a second example of the configuration of the external pressure jig. [Figure 4] FIG. 4 is a graph showing an example of the relationship between the welding pressure and the welding current with respect to the elapsed time during welding. [Diagram 5] Fig. 5 is a schematic cross-sectional view showing a process of forming a dissimilar material welded joint by a resistance welding method according to a second embodiment. Fig. 5(a) is a schematic cross-sectional view showing a state in which an element, a first member, and a second member are overlapped in this order, and the element, the first member, and the second member are clamped and pressed by a pair of electrodes, and the element is pressed by an external pressing jig arranged only around the electrode of the pair of electrodes that is closer to the element. Fig. 5(b) is a schematic cross-sectional view showing a state in which the element and the second member are welded by passing a current between the pair of electrodes. [Figure 6] Fig. 6 is a schematic cross-sectional view showing a process of forming a dissimilar material welded joint by a resistance welding method according to a third embodiment. Fig. 6(a) is a schematic cross-sectional view showing a state in which an element, a first member, and a second member are stacked in this order, and the element, the first member, and the second member are clamped and pressed by a pair of electrodes, and the first member is pressed around the head of the element by an external pressing jig arranged around each of the pair of electrodes. Fig. 6(b) is a schematic cross-sectional view showing a state in which the element and the second member are welded by passing a current between the pair of electrodes. [Figure 7] Fig. 7 is a schematic cross-sectional view showing a process of forming a dissimilar material welded joint by a resistance welding method according to a fourth embodiment. Fig. 7(a) is a schematic cross-sectional view showing a state in which an element, a first member, and a second member are stacked in this order, and the element, the first member, and the second member are clamped and pressed by a pair of electrodes, and both the element and the first member around the head of the element are pressed by external pressing jigs arranged around each of the pair of electrodes. Fig. 7(b) is a schematic cross-sectional view showing a state in which the element and the second member are welded by passing current between the pair of electrodes. [Figure 8] Fig. 8 is a schematic cross-sectional view showing a process of forming a dissimilar material welded joint by a resistance welding method according to a fifth embodiment. Fig. 8(a) is a schematic cross-sectional view showing a state in which an element, a first member, a second member, and a third member are stacked in this order, and the element, the first member, the second member, and the third member are clamped and pressed by a pair of electrodes, and the element is pressed by an external pressing jig arranged around each of the pair of electrodes. Fig. 8(b) is a schematic cross-sectional view showing a state in which the element, the second member, and the third member are welded by passing current between the pair of electrodes. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, embodiments of a resistance welding method according to the present invention will be described in detail with reference to the drawings.

[0017] (First embodiment) A resistance welding method according to a first embodiment of the present invention will be described with reference to Figures 1 to 4. Figure 1 is a schematic cross-sectional view showing a process of forming a dissimilar material welded joint by the resistance welding method according to the first embodiment.

[0018] 1, the resistance welding method according to this embodiment is a resistance welding method in which a first member 20 made of a non-ferrous metal such as aluminum or magnesium and a second member 30 made of an iron-based metal are overlapped with each other and joined using an element 40 made of an iron-based metal to form a dissimilar welded joint 10. In the following description, in a laminate in which the element 40, the first member 20, and the second member 30 are overlapped in this order, the element 40 side is referred to as the "upper side" and the second member 30 side is referred to as the "lower side."

[0019] The first member 20 and the second member 30 used in this embodiment are flat plate members having thicknesses t1 and t2, respectively, and have not been subjected to pre-processing such as drilling or riveting. The material of the first member 20 is not particularly limited as long as it is an iron-based material including pure iron and iron alloys, and examples thereof include mild steel, carbon steel, stainless steel, etc. The material of the second member 30 is not particularly limited as long as it is a non-ferrous metal having a lower melting point than the above iron-based metals, and examples thereof include pure aluminum, pure magnesium, aluminum alloys, magnesium alloys, etc.

[0020] Element 40 is made of an iron-based metal, and as shown in FIG. 2 as an example, comprises a substantially disk-shaped head 41, a substantially truncated cone-shaped shaft portion 42 formed to protrude from one side of head 41, an annular protrusion portion 43 provided near the outer edge portion on one side of head 41, and an annular groove portion 44 formed between shaft portion 42 and annular protrusion portion 43.

[0021] As shown in FIG. 2, the head 41 has a diameter D h is the diameter D of the base of the shaft portion 42 sIn this manner, by forming the element 40 into a substantially T-shape in cross section (see element 40 shown in FIG. 1), it is possible to increase the restraining force on the first member 20 that is sandwiched between the second member 30 and the head 41 of the element 40 after welding is completed.

[0022] The shaft portion 42 has a generally truncated cone shape tapering from the base to the tip, which makes it easier for the element 40 to enter the first member 20 during resistance welding, which will be described later. Furthermore, the groove 44 acts as a reservoir into which the molten first member 20 flows during resistance welding. As shown in Fig. 1, the length L from the lower surface of the annular protrusion 43 to the tip of the shaft 42 is designed to be equal to or greater than the thickness t1 of the first member 20. This allows the shaft 42 of the element 40 and the second member 30 to come into contact with each other while the first member 20 is being clamped, as will be described later, and ensures that welding can be performed between these members.

[0023] The shape of the head 41 is not particularly limited, and may be a round head, a flat head, a countersunk head, or even a polygonal shape as necessary. The shape of the shaft 42 is also not limited to a truncated cone shape as shown in Fig. 2, and may be a cylindrical shape, a conical shape, or the like.

[0024] The material of the element 40 is not particularly limited as long as it is an iron-based material including pure iron and iron alloys, and examples thereof include mild steel, carbon steel, and stainless steel.

[0025] The pair of electrodes 50 are electrodes for resistance spot welding, and include an upper electrode 51 and a lower electrode 52 disposed opposite to each other with the element 40, the first member 20, and the second member 30 interposed therebetween.

[0026] Furthermore, a pair of external pressure tools 60 are disposed around each of the pair of electrodes 50, facing each other vertically via the element 40, the first member 20, and the second member 30. The external pressure tools 60 include a substantially annular upper external pressure tool 61 disposed around the upper electrode 51, and a substantially annular lower external pressure tool 62 disposed around the lower electrode 52. The upper external pressurizing jig 61 is not limited to a configuration in which the entire circumference is pressed as an annular shape (for example, a pipe with a concentric cross section) as shown in Fig. 3A, and may be configured, for example, as divided into a plurality of parts in the circumferential direction to apply pressure at multiple points (not shown), or may be configured in the form of an arm as shown in Fig. 3B. The lower external pressurizing jig 62 is similar to the upper external pressurizing jig 61 described above.

[0027] Next, a method for resistance welding the dissimilar material welded joint 10 will be described with reference to FIGS.

[0028] In the resistance welding method according to this embodiment, first, as shown in FIG. 1(a), a first member 20 and a second member 30, which are components of a dissimilar material welded joint 10, are overlapped, and then the shaft portion 42 of an element 40 is abutted against the first member 20 to obtain a pre-welding state.

[0029] Next, the upper electrode 51 and the upper external pressure jig 61 are each abutted against the upper surface of the head 41 of the element 40, and the lower electrode 52 and the lower external pressure jig 62 are each abutted against the lower surface of the second member 30, so that the pair of electrodes 50 and the pair of external pressure jig 60 clamp the element 40 and the second member 30 via the first member 20. It is preferable that the portion of the upper external pressure jig 61 that comes into contact with the element 40 is a portion radially outward of the shaft portion 42 of the element 40, in other words, a portion that corresponds to the annular protrusion portion 43 or the groove portion 44. This makes it possible to press the annular protrusion portion 43 or the groove portion 44 of the element 40 from above, and as described below, when the element 40 enters the first member 20, the element 40 can be more effectively prevented from being pushed up by the action of a repulsive force caused by deformation of the first member 20 and the action of droplets caused by melting of the first member 20 entering the groove portion 44 of the element 40.

[0030] Next, the upper electrode 51 is pressed with a pressure F1, and in this embodiment, the upper external pressing jig 61 is pressed with a pressure F2 larger than the pressure F1, thereby pressing the element 40, the first member 20 and the second member 30.

[0031] In this embodiment, the pressing force F2 of the upper external pressing jig 61 is described as being greater than the pressing force F1 of the upper electrode 51, but the magnitudes of the pressing forces F1 and F2 can be changed according to the welding conditions, and the pressing force F1 may be greater than the pressing force F2, or may be the same as the pressing force F2. Note that Fig. 4 shows an example in which the pressing force F1 = the pressing force F2.

[0032] Then, as shown in FIG. 4, after maintaining the predetermined squeeze time T1, while maintaining pressure from the pair of electrodes 50 (upper electrode 51 and lower electrode 52) and the pair of external pressure jigs 60 (upper external pressure jig 61 and lower external pressure jig 62), a first current I1 smaller than the second current I2 during actual welding is passed between the pair of electrodes 50 (first current flow), thereby melting the first member 20, which has a lower melting temperature than the element 40 and the second member 30, and forming a molten pool (not shown).

[0033] As a result, the element 40, which is pressed by the combined force of the pressing forces F1 and F2, has its shaft 42 enter the molten pool of the first member 20 and move downward until it penetrates the first member 20, and the tip of the shaft 42 abuts against the second member 30. As shown in Fig. 4, the reason why a small first current I1 is initially applied is that if a large current is applied from the beginning, the first member 20 may melt all at once and liquid droplets may scatter around. In addition, by the shaft 42 of the element 40 entering the molten pool of the first member 20, liquid droplets spilling over from the molten pool are contained in the annular groove 44 of the element 40, and the generation of burrs is suppressed.

[0034] Here, when the element 40 advances into the first member 20, a force acts in a direction in which the tip of the shaft portion 42 moves away from the second member 30 (i.e., upward in FIG. 1) due to the action of a repulsive force generated by the deformation of the first member 20 and the action of droplets due to the melting of the first member 20 entering the groove portion 44 of the element 40. That is, a force acts to push up the element by the first member 20 melted during welding. However, since the element 40 is not only sandwiched and pressurized by the upper electrode 51 and the lower electrode 52, but also sandwiched and pressurized by the upper external pressurizing jig 61 and the lower external pressurizing jig 62 arranged around it, the element 40 is suppressed from being pushed up, and the abutting state between the tip of the shaft portion 42 and the second member 30 is well maintained during welding. In particular, in this embodiment, the upper external pressure application tool 61 applies pressure to a portion of the element 40 radially outward of the shaft portion 42, thereby more effectively suppressing the upward movement of the element 40 and making it possible to more reliably ensure the contact state between the tip of the shaft portion 42 and the second member 30.

[0035] 1(b) and 4, while maintaining pressure from the pair of electrodes 50 and the pair of external pressure jigs 60, a second current I2, which is a main welding current, is passed between the upper electrode 51 and the lower electrode 52 (second current flow), and a molten zone 22 is formed between the tip of the shaft portion 42 and the second member 30 by a normal spot welding method, thereby welding the element 40 and the second member 30 together, thereby joining the iron-based metals together. Finally, the state is held for a predetermined hold time T2, and the welding is completed.

[0036] As described above, according to the resistance welding method of the first embodiment, the element 40 and the second member 30 are welded with the first member 20 sandwiched therebetween under the pressure of the pair of electrodes 50 as well as the pressure of the pair of external pressure jigs 60 arranged therearound, and compared to the conventional case where only the pressure of the pair of electrodes 50 is applied, the above-mentioned action effectively prevents the element 40 from being pushed up when the element 40 enters the first member 20, making it possible to form a desired high-strength molten part without applying a large heat input. Therefore, a desired molten part can be formed under current conditions with a relatively low heat input, and welding defects can also be prevented.

[0037] Furthermore, as described in this embodiment, if the pressure force F2 of the upper external pressure jig 61 is greater than the pressure force F1 of the upper electrode 51, this is particularly preferable because it can more effectively suppress the action of the element 40 being pushed up when the element 40 enters the first member 20.

[0038] In addition, when the droplets of the melted first member 20 enter the groove 44 of the element 40, the welding current may be diverted to the droplets in the groove 44, making it difficult to form the molten part 22. Therefore, in order to prevent the welding current from being diverted to the droplets in the groove 44, the diameter D u is the diameter D of the base of the shaft portion 42 s It is preferable that the diameter D of the lower electrode 52 is approximately equal to the diameter D of the lower electrode 52. In addition, this problem can be solved by applying, for example, an adhesive to the contact surface between the element 40 and the first member 20 to suppress the shunt current. dAlthough not particularly limited, the diameter D of the upper electrode 51 is set to 1 / 100 mm in order to prevent interference with the lower external pressure jig 62. u It is preferable that it is approximately equal to

[0039] Furthermore, as described above, when the element 40 is pressurized by the external pressure application tool 60, it is preferable that the external pressure application tool 60 apply pressure to a portion of the head 41 of the element 40 that is radially outward of the shaft portion 42. This makes it possible to press the annular protrusion portion 43 or the groove portion 44 of the element 40 from above, and more effectively prevents the molten first member 20 from flowing into the groove portion 44 during welding and pushing up the element 40.

[0040] Second embodiment Next, a resistance welding method according to a second embodiment of the present invention will be described with reference to Fig. 5. Fig. 5 is a schematic cross-sectional view showing a process of forming a dissimilar material welded joint by the resistance welding method according to the second embodiment.

[0041] The resistance welding method according to this embodiment differs from the resistance welding method according to the first embodiment in that the diameter D d The diameter D of the head 41 of the element 40 h and does not include a lower external pressure jig 62. That is, the lower electrode 53 has the functions of both the lower electrode 52 and the lower external pressure jig 62 in the first embodiment.

[0042] In the resistance welding method according to this embodiment, first, as shown in FIG. 5(a), the first member 20 and the second member 30, which are components of the dissimilar material welded joint 10, are overlapped, and then the shaft portion 42 of the element 40 is abutted against the first member 20 to obtain a pre-welding state.

[0043] Next, the upper electrode 51 and the upper external pressure jig 61 are respectively abutted against the upper surface of the head 41 of the element 40, and the lower electrode 53 is abutted against the lower surface of the second member 30, so that the element 40 and the second member 30 are clamped via the first member 20 by the pair of electrodes 50 (upper electrode 51 and lower electrode 53) and external pressure jig 60 (upper external pressure jig 61). In this embodiment, as in the first embodiment, the contact portion of the upper external pressure application jig 61 with the element 40 is a portion radially outward of the shaft portion 42 of the element 40, in other words, a portion corresponding to the annular protrusion portion 43 or the groove portion 44.

[0044] Then, the upper electrode 51 and the upper external pressing jig 61 are pressed with pressure forces F1 and F2, respectively.

[0045] Next, while maintaining pressure applied by the pair of electrodes 50 and the external pressure jig 60, a first current I1 and a second current I2 are sequentially passed between the pair of electrodes 50, as in the first embodiment, to ultimately form a molten zone 22 between the tip of the shaft portion 42 and the second member 30, thereby welding the element 40 and the second member 30 together, thereby joining the iron-based metals together.

[0046] The other parts are similar to those in the resistance welding method of the first embodiment, so the same or corresponding reference numerals are used for the same parts, and the description thereof will be simplified or omitted.

[0047] As described above, according to the resistance welding method of the second embodiment, as in the first embodiment, the element 40 and the second member 30 are welded with the first member 20 sandwiched therebetween under the pressure of the pair of electrodes 50 as well as the pressure of the pair of external pressure jigs 60 arranged therearound. Compared to the conventional case where only the pressure of the pair of electrodes 50 is applied, the above-mentioned action, specifically, the repulsive force caused by the deformation of the first member 20 when the element 40 enters the groove portion 44 of the element 40, effectively suppresses the element 40 from being pushed up when the element 40 enters the first member 20, so that it is possible to form a desired high-strength molten part without applying a large heat input. Therefore, a desired molten part can be formed under current conditions with a relatively low heat input, and poor welding can be prevented.

[0048] The lower electrode 53 receives both the pressure F1 from the upper electrode 51 and the pressure F2 from the upper external pressure jig 61, and plays the role of both the lower electrode 52 and the lower external pressure jig 62 in the first embodiment. Since the resistance welding method according to the present embodiment does not include the lower external pressure jig 62, it is possible to simplify the resistance welding mechanism and reduce costs.

[0049] Meanwhile, in the resistance welding method according to the first embodiment described above, the external pressure jig 60 is arranged not only around the electrode (i.e., upper electrode 51) of the pair of electrodes 50 that is closer to the element 40, but also around the electrode (i.e., lower electrode 52) of the pair of electrodes 50 that is farther from the element 40. With this configuration, the tip diameter of the lower electrode 52 can be made substantially equal to the tip diameter of the upper electrode 51 while receiving the pressure force F1 from the upper electrode 51 and the pressure force F2 from the upper external pressure jig 61. This makes it possible to minimize an increase in the current carrying area during resistance welding due to the difference in electrode size between the upper and lower electrodes in the pair of electrodes 50, and makes it possible to reduce the current value required to ensure a sufficient nugget diameter.

[0050] Third embodiment Next, a resistance welding method according to a third embodiment of the present invention will be described with reference to Fig. 6. Fig. 6 is a schematic cross-sectional view showing a process of forming a dissimilar material welded joint by the resistance welding method according to the third embodiment.

[0051] The resistance welding method according to this embodiment differs from the resistance welding method according to the first embodiment in that the external pressure jig 60 presses the first member 20 instead of the element 40 .

[0052] In the resistance welding method according to this embodiment, first, as shown in FIG. 6(a), the first member 20 and the second member 30, which are components of the dissimilar material welded joint 10, are overlapped, and then the shaft portion 42 of the element 40 is abutted against the first member 20 to obtain a pre-welding state.

[0053] Next, the upper electrode 51 is abutted against the upper surface of the head 41 of the element 40, and the upper external pressure application tool 61 is abutted against the upper surface of the first member 20, while the lower electrode 52 and the lower external pressure application tool 62 are abutted against the lower surface of the second member 30, respectively, so that the element 40 and the second member 30 are clamped via the first member 20 by the pair of electrodes 50 (upper electrode 51 and lower electrode 52) and the pair of external pressure application tools 60 (upper external pressure application tool 61 and lower external pressure application tool 62). In addition, since the upper external pressure jig 61 applies pressure to the first member 20, not to the element 40, the inner diameter of the annular upper external pressure jig 61 is set to be equal to or larger than the diameter D of the head 41. h The inner diameter of the lower external pressurizing jig 62 disposed opposite the upper external pressurizing jig 61 is also formed to be substantially the same as the inner diameter of the upper external pressurizing jig 61.

[0054] Then, the upper electrode 51 and the upper external pressing jig 61 are pressed with pressure forces F1 and F2, respectively.

[0055] Next, while maintaining pressure applied by the pair of electrodes 50 and the pair of external pressure jigs 60, a first current I1 and a second current I2 are sequentially passed between the pair of electrodes 50, as in the first embodiment, to ultimately form a molten zone 22 between the tip of the shaft portion 42 and the second member 30, thereby welding the element 40 and the second member 30 together, thereby joining the iron-based metals together.

[0056] The other parts are similar to those in the resistance welding method of the first embodiment, so the same or corresponding reference numerals are used for the same parts, and the description thereof will be simplified or omitted.

[0057] As described above, according to the resistance welding method of the third embodiment, the element 40 and the second member 30 are welded with the first member 20 sandwiched therebetween, in the same manner as in the first embodiment, in addition to the pressing force of the pair of electrodes 50, the pressing force of the pair of external pressing jigs 60 arranged around them is also applied, and compared to the conventional case where only the pressing force of the pair of electrodes 50 is applied, the above-mentioned action, specifically, the repulsive force caused by the deformation of the first member 20 when the element 40 enters the first member 20, and the action of the liquid droplets caused by the melting of the first member 20 entering the groove portion 44 of the element 40, effectively suppress the element 40 from being pushed up when the element 40 enters the first member 20, so that it is possible to form a desired high-strength molten part without applying a large heat input. Therefore, a desired molten part can be formed under current conditions with a relatively low heat input, and poor welding can also be prevented.

[0058] (Fourth embodiment) Next, a resistance welding method according to a fourth embodiment of the present invention will be described with reference to Fig. 7. Fig. 7 is a schematic cross-sectional view showing a process of forming a dissimilar material welded joint by the resistance welding method according to the fourth embodiment.

[0059] The resistance welding method according to this embodiment is a welding method that combines the resistance welding method according to the first embodiment and the resistance welding method according to the third embodiment. As in the first and third embodiments, the method includes an upper electrode 51 and a lower electrode 52 that clamp and weld the element 40, the first member 20, and the second member 30 while applying pressure. The shapes and functions of the upper electrode 51 and the lower electrode 52 are the same as those in the resistance welding method of the first embodiment.

[0060] Further, external pressure applying jigs 60 formed in a substantially annular shape are provided on the radially outer sides of the upper electrode 51 and the lower electrode 52. The external pressure applying jig 60 is composed of an upper external pressure applying jig 61 and a lower external pressure applying jig 62. Furthermore, the upper external pressurizing jig 61 includes a first upper external pressurizing jig 61a that comes into contact with a portion of the element 40 that is radially outer than the shaft portion 42 to pressurize the element 40, and a second upper external pressurizing jig 61b that pressurizes the first member 20 around the head portion 41 of the element 40. That is, the upper external pressurizing jig 61 includes the first upper external pressurizing jig 61a and the second upper external pressurizing jig 61b that are arranged in two layers in a substantially concentric manner.

[0061] The lower external pressure application jig 62 is formed in an approximately circular ring shape radially outwardly surrounding the lower electrode 52, and has a large contact area with the second member 30 so as to face the first upper external pressure application jig 61a and the second upper external pressure application jig 61b.

[0062] In the resistance welding method according to the present embodiment, the element 40, the first member 20, and the second member 30 are clamped by the upper electrode 51, the first upper external pressing jig 61a, the second upper external pressing jig 61b, and the lower electrode 52 and the lower external pressing jig 62. Then, the upper electrode 51 is pressed with a pressing force F1, the first upper external pressing jig 61a with a pressing force F2, and the second upper external pressing jig 61b with a pressing force F4, and while maintaining the pressure by the pair of electrodes 50 and the pair of external pressing jigs 60, a first current I1 and then a second current I2 are passed between the upper electrode 51 and the lower electrode 52 in this order, thereby melting the first member 20 and forming a molten portion 22 between the shaft portion 42 of the element 40 and the second member 30, thereby welding the element 40 and the second member 30.

[0063] The other parts are similar to those in the resistance welding method of the first embodiment, so the same or corresponding reference numerals are used for the same parts, and the description thereof will be simplified or omitted.

[0064] As described above, according to the resistance welding method of the fourth embodiment, as in the first and third embodiments, the element 40 and the second member 30 are welded with the first member 20 sandwiched therebetween under the pressure of the pair of electrodes 50 as well as the pressure of the pair of external pressure jigs 60 arranged therearound. Compared to the conventional case where only the pressure of the pair of electrodes 50 is applied, the above-mentioned action, specifically, the repulsive force caused by the deformation of the first member 20 when the element 40 enters the groove portion 44 of the element 40, effectively suppresses the element 40 from being pushed up when the element 40 enters the first member 20, so that it is possible to form a desired high-strength molten part without applying a large heat input. Therefore, a desired molten part can be formed under current conditions with a relatively low heat input, and poor welding can be prevented.

[0065] In particular, in the third embodiment, the external pressure application tool 60 applies pressure to both the element 40 and the first member 20, thereby making it possible to particularly effectively suppress the action of the element 40 being pushed up when the element 40 enters the first member 20.

[0066] Fifth embodiment Next, a resistance welding method according to a fifth embodiment of the present invention will be described with reference to Fig. 8. Fig. 8 is a schematic cross-sectional view showing a process of forming a dissimilar material welded joint by the resistance welding method according to the fifth embodiment.

[0067] The resistance welding method according to this embodiment is a welding method similar to the resistance welding method of the first embodiment, but is a resistance welding method in which a first member 20 made of a non-ferrous metal such as an aluminum alloy or a magnesium alloy, a second member 30 made of an iron-based metal, and a third member 35 made of an iron-based metal are overlapped and joined using an element 40 made of an iron-based metal to form a dissimilar welded joint 10. Note that the difference is that while the dissimilar welded joint 10 of the first embodiment is two-ply, the dissimilar welded joint 10 of this embodiment is three-ply.

[0068] In the resistance welding method according to the present embodiment, the element 40, the first member 20, the second member 30, and the third member 35 are clamped by an upper electrode 51 and an upper external pressure jig 61, and a lower electrode 52 and a lower external pressure jig 62. Then, the upper electrode 51 is pressurized with a pressure force F1, and the upper external pressure jig 61 is pressurized with a pressure force F2. While maintaining the pressure by the pair of electrodes 50 and the pair of external pressure jigs 60, a first current I1 and then a second current I2 are applied between the upper electrode 51 and the lower electrode 52 in this order, thereby melting the first member 20 and forming a molten portion 22 between the shaft portion 42 of the element 40, the second member 30, and the third member 35, thereby welding the element 40, the second member 30, and the third member 35.

[0069] The other parts are similar to those in the resistance welding method of the first embodiment, so the same or corresponding reference numerals are used for the same parts, and the description thereof will be simplified or omitted.

[0070] As described above, according to the resistance welding method of the fifth embodiment, the element 40, the second member 30, and the third member 35 are welded with the first member 20 sandwiched therebetween, in the same manner as in the first embodiment, in addition to the pressing force of the pair of electrodes 50, the pressing force of the pair of external pressing jigs 60 arranged around them is also applied. Compared to the conventional case where only the pressing force of the pair of electrodes 50 is applied, the above-mentioned action, specifically, the repulsive force caused by the deformation of the first member 20 when the element 40 enters the groove portion 44 of the element 40, effectively suppresses the element 40 from being pushed up when the element 40 enters the first member 20, so that it is possible to form a desired high-strength molten part without applying a large heat input. Therefore, a desired molten part can be formed under current conditions with a relatively low heat input, and poor welding can also be prevented.

[0071] In the above description, the second member 30 is made of an iron-based metal, but it may be made of a non-ferrous metal. That is, both the first member 20 and the second member 30 are made of a non-ferrous metal. In this case, the length L from the lower surface of the annular protrusion 43 of the element 40 to the tip of the shaft portion 42 is designed to be the total thickness of the thickness t1 of the first member 20 and the thickness t2 of the second member 30. This allows the shaft portion 42 of the element 40 to come into contact with the third member 35 while the first member 20 and the second member 30 are sandwiched, and welding can be performed reliably between these members.

[0072] In this embodiment, the dissimilar metal welded joint 10 is three-ply, but it can be more than three plies, i.e., four plies or more. In the case of four plies, the dissimilar metal welded joint 10 has, from the top, a non-ferrous metal, an iron-based metal, an iron-based metal, and an iron-based metal in that order, or from the top, a non-ferrous metal, a non-ferrous metal, and an iron-based metal.

[0073] Although the first to fifth embodiments have been described in detail above, the present invention is not limited to the above-described embodiments, and suitable modifications and improvements are possible.

[0074] As described above, the present specification discloses the following:

[0075] (1) A resistance welding method for joining a first member made of a non-ferrous metal and a second member made of an ferrous metal by using an element having a head and a shaft and made of an ferrous metal, comprising: a step of abutting the shaft portion against the first member, and stacking the element, the first member, and the second member in this order; a step of clamping and pressurizing the element, the first member, and the second member with a pair of electrodes, and pressurizing at least one of the element and the first member with an external pressurizing tool disposed around at least one of the pair of electrodes that is closer to the element; a step of melting the first member by energizing the pair of electrodes while maintaining pressure applied by the pair of electrodes and the external pressure jig, and further penetrating the element into the first member to weld the element and the second member; A resistance welding method comprising: According to this configuration, by applying pressure to at least one of the element 40 and the first member 20 made of a non-ferrous metal using the external pressure jig 60 arranged around the electrode 50 during welding, the first member 20 that melts during welding is prevented from pushing up the element 40, so that a desired molten portion can be formed between the element 40 made of an iron-based metal and the second member 30 made of an iron-based metal under current flow conditions with a relatively low heat input, thereby preventing poor welding.

[0076] (2) The resistance welding method described in (1) above, wherein the pressure applied by the external pressure jig to the element or the first member is greater than the pressure applied by the pair of electrodes to clamp and press the element, the first member and the second member. According to this configuration, the action of the element 40 being pushed up when the element 40 enters the first member 20 can be more effectively suppressed.

[0077] (3) A resistance welding method for joining a first member made of a non-ferrous metal, a second member made of an iron-based metal, and a third member made of an iron-based metal using an element having a head and a shaft and made of an iron-based metal, comprising: a step of abutting the shaft portion against the first member, and stacking the element, the first member, the second member, and the third member in this order; a step of clamping and pressurizing the element, the first member, the second member, and the third member with a pair of electrodes, and pressurizing at least one of the element and the first member with an external pressurizing tool disposed around at least one of the pair of electrodes that is closer to the element; a step of melting the first member by energizing the pair of electrodes while maintaining pressure applied by the pair of electrodes and the external pressure jig, and further penetrating the element into the first member to weld the element, the second member, and the third member; A resistance welding method comprising: According to this configuration, by applying pressure to at least one of the element 40 and the first member 20 made of a non-ferrous metal using the external pressure jig 60 arranged around the electrode 50 during welding, the first member 20 that melts during welding is prevented from pushing up the element 40, so that a desired molten portion can be formed between the element 40 made of an iron-based metal and the second member 30 and third member 35 made of an iron-based metal under current flow conditions with a relatively low heat input, thereby preventing poor welding.

[0078] (4) The resistance welding method described in (3) above, wherein the pressure applied by the external pressure jig to the element or the first member is greater than the pressure applied by the pair of electrodes to clamp and press the element, the first member, the second member and the third member. According to this configuration, the action of the element 40 being pushed up when the element 40 enters the first member 20 can be more effectively suppressed.

[0079] (5) The resistance welding method according to any one of (1) to (4) above, wherein the external pressure jigs are disposed around each of the pair of electrodes. According to this configuration, while receiving the pressure F1 from the upper electrode 51 and the pressure F2 from the upper external pressure jig 61, the tip diameter of the lower electrode 52 can be made approximately equal to the tip diameter of the upper electrode 51. This makes it possible to minimize the increase in the current carrying area during resistance welding due to the difference in electrode size between the upper and lower electrodes in the pair of electrodes 50, and makes it possible to reduce the current value required to ensure the nugget diameter.

[0080] (6) The resistance welding method according to any one of (1) to (5) above, wherein both the element and the first member are pressed by the external pressing jig. According to this configuration, the action of the element 40 being pushed up when the element 40 enters the first member 20 can be particularly effectively suppressed.

[0081] (7) When the element is pressurized by the external pressurizing tool, The resistance welding method according to any one of (1) to (6) above, wherein the external pressure jig applies pressure to a portion of the head of the element that is radially outward from the shaft portion. According to this configuration, the annular protrusion 43 or groove 44 of the element 40 can be pressed from above, and when the element 40 enters the first member 20, the element 40 can be more effectively prevented from being pushed up by the action of a repulsive force generated by deformation of the first member 20 and the action of droplets caused by melting of the first member 20 entering the groove 44 of the element 40. [Explanation of symbols]

[0082] 10 Dissimilar material welded joints 20 First member 30 Second member 35 Third member 40 Elements 41 Head 42 Shaft 50 Pair of Electrodes 51 Upper electrode (electrode closer to the element) 60 Pair of external pressure jigs F1 electrode pressure F2, F4 pressure of external pressure fixture

Claims

1. A resistance welding method for joining a first member made of a non-ferrous metal and a second member made of an iron-based metal using an element having a head and a shaft and made of an iron-based metal, the method comprising: a step of bringing the shaft portion into contact with the first member, stacking the element, the first member, and the second member in this order; a step of clamping and pressurizing the element, the first member, and the second member with a pair of electrodes, and pressurizing the element with an external pressurizing tool disposed around at least one of the pair of electrodes that is closer to the element; a step of melting the first member by energizing the pair of electrodes while maintaining pressure applied by the pair of electrodes and the external pressure jig, and further penetrating the element into the first member to weld the element and the second member; A resistance welding method comprising:

2. 2. The resistance welding method according to claim 1, wherein a pressure applied to the element by the external pressure jig is greater than a pressure applied to the element, the first member, and the second member by the pair of electrodes while clamping and applying pressure thereto.

3. A resistance welding method for joining a first member made of a non-ferrous metal, a second member made of an iron-based metal, and a third member made of an iron-based metal using an element having a head and a shaft portion and made of an iron-based metal, the method comprising: a step of abutting the shaft portion against the first member, and stacking the element, the first member, the second member, and the third member in this order; a step of clamping and pressurizing the element, the first member, the second member, and the third member with a pair of electrodes, and pressurizing the element with an external pressurizing tool disposed around at least one of the pair of electrodes that is closer to the element; a step of melting the first member by energizing the pair of electrodes while maintaining pressure applied by the pair of electrodes and the external pressure jig, and further penetrating the element into the first member to weld the element, the second member, and the third member; A resistance welding method comprising:

4. 4. The resistance welding method according to claim 3, wherein a pressure applied by the external pressure jig to the element is greater than a pressure applied by the pair of electrodes to clamp and press the element, the first member, the second member, and the third member.

5. The resistance welding method according to any one of claims 1 to 4, wherein the external pressure jigs are disposed around each of the pair of electrodes.

6. The resistance welding method according to any one of claims 1 to 5, wherein both the element and the first member are pressurized by the external pressure jig.

7. A resistance welding method described in any one of claims 1 to 6, wherein the external pressure jig applies pressure to a portion of the head of the element that is radially outer than the shaft portion.

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