Method for joining metal components

Abstract

To provide a method and a structure for joining a metallic component, which can join a joined part by suppressing energization caused by burrs.SOLUTION: In a method for joining the metallic component, which joins an outer peripheral surface part 31 of an inner metallic member 3 and an inner peripheral surface part 21 of an outer metallic member 2 with heat generated through energization while pressurization of them is carried out in an axial direction, an insulation part 50 for blocking current flowing through burrs 62 generated when the outer peripheral surface part 31 of the inner metallic member 3 and the inner peripheral surface part 21 of the outer metallic member 2 are joined is disposed near a joined part 60 formed between a joined outer diameter part 32 of the inner metallic member 3 and a joined inner diameter prat 22 of the outer metallic member 2. The joining method forms the joined part 60 between the joined outer diameter part 32 and the joined inner diameter prat 22 with heat generated through energization while the joined outer diameter part 32 of the inner metallic member 3 and the joined inner diameter prat 22 of the outer metallic member 2 are pressurized from one end side in the axial direction toward the other end side in the axial direction.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for joining metal members. By law Regarding. [Background technology]

[0002] 2. Description of the Related Art A so-called FR (front engine, rear drive) based vehicle is known in which a drive source such as an engine and a transmission are arranged at the front of the vehicle body with their axes extending in the fore-and-aft direction of the vehicle body, and driving force transmitted from the transmission is transmitted from a rear wheel output shaft extending toward the rear of the vehicle body to the rear wheels as the main drive wheels, via a rear wheel propeller shaft and a rear wheel differential device.

[0003] The rear wheel differential device (hereinafter referred to as the differential device) installed in such a vehicle is configured to distribute the driving force transmitted from the rear wheel propeller shaft (hereinafter referred to as the propeller shaft) to the corresponding left and right drive wheels, for example, when the vehicle turns, thereby adjusting the difference in wheel rotation speed that occurs between the left and right drive wheels.

[0004] This differential device includes a ring gear to which driving force is transmitted from a propeller shaft, and a differential case that is joined to the ring gear and rotates together with the ring gear. The differential case is provided with a pair of left and right side gears that distribute the driving force transmitted from the ring gear to the left and right drive wheels, a pinion shaft that extends in a direction perpendicular to the ring gear, and a pinion gear that is provided on the pinion shaft and meshes with the pair of left and right side gears to adjust the difference in wheel rotation speed generated between the drive wheels.

[0005] As a method for joining a ring gear and a differential case, for example, ring mash joining is known, in which the inner metal member, the differential case, and the outer metal member, the ring gear, are pressurized in the axial direction while current is passed through them to soften the metal at the contact area by resistive heating, generating plastic flow and forming a diffusion bond.

[0006] For example, Patent Document 1 discloses a ring mash joining in which an outer diameter portion for joining and an inclined surface portion located on at least one of the axial sides of the outer diameter portion for joining are provided on the outer peripheral wall portion of an inner metal member, and an inner diameter portion for joining corresponding to the outer diameter portion for joining and an inclined surface portion corresponding to the inclined surface portion of the inner metal member are provided on the inner peripheral wall portion of an outer metal member, so that when the outer diameter portion for joining and the inner diameter portion for joining are joined to each other by resistance heating due to electrical current while the outer peripheral wall portion of the inner metal member and the inner peripheral wall portion of the outer metal member are pressurized in the axial direction to form a joining portion where the outer diameter portion for joining and the inner diameter portion for joining are joined to each other by resistance heating due to electrical current passing through them, a tapered fitting portion is formed where the inclined surface portion of the inner metal member and the inclined surface portion of the outer metal member fit together. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6119795 Summary of the Invention [Problem to be solved by the invention]

[0008] With the ring mash joining of Patent Document 1, the stress generated when an external force is applied to the outer metal member or the inner metal member is distributed to both the joint and the tapered mating portion, thereby preventing stress concentration at the joint and obtaining a joint structure that is resistant to repeated impacts.

[0009] On the other hand, in actual ring mash joining, burrs of softened metal extending from the joint may be formed. For example, in the case where the inner metal member is made of cast iron and the outer metal member is made of steel, when the outer peripheral surface of the inner metal member and the inner peripheral surface of the outer metal member are pressurized from the other axial end side toward the one axial end side while the joint outer diameter portion and the joint inner diameter portion are joined to each other by resistance heating due to current flow, if the outer metal member has an inner wall portion extending radially outward from the joint inner diameter portion on the axial one end side of the joint inner diameter portion, a burr may be formed extending radially outward from the one axial end side of the joint so as to abut against the inner wall portion. If a burr is formed abutting against the inner wall portion of the outer metal member, a current flows through the burr and is diverted toward both the joint and the burr, which may result in a poor joint.

[0010] Therefore, the present invention provides a method for joining metal members that can suppress current flow due to burrs and can join joints well. Law The objective is to provide [Means for solving the problem]

[0011] In order to solve the above problems, the present invention is characterized by having the following configuration.

[0012] First, the present invention provides a method for joining metal members, in which an outer peripheral surface portion of an inner metal member and an inner peripheral surface portion of an outer metal member are joined by resistance heating due to electrical current while applying pressure in an axial direction, a joining outer diameter portion is formed on the outer circumferential surface portion of the inner metal member; a joining inner diameter portion corresponding to the joining outer diameter portion is formed on the inner circumferential surface portion of the outer metal member; an insulating portion is disposed in the vicinity of a joint formed between the outer diameter joint portion of the inner metal member and the inner diameter joint portion of the outer metal member, the insulating portion preventing a current from flowing through a burr generated when the outer peripheral surface portion of the inner metal member and the inner peripheral surface portion of the outer metal member are joined; the joining outer diameter portion of the inner metal member and the joining inner diameter portion of the outer metal member are pressurized from the other axial end side toward the one axial end side, while current is passed through the joining outer diameter portion and the joining inner diameter portion to generate resistance heat, thereby forming the joining portion between the joining outer diameter portion and the joining inner diameter portion. It is characterized by:

[0013] According to the present invention, by disposing an insulating portion near the joint formed between the joint outer diameter portion of the inner metal member and the joint inner diameter portion of the outer metal member, when the joint outer diameter portion of the inner metal member and the joint inner diameter portion of the outer metal member are pressurized from the other axial end side toward the one axial end side and a joint is formed between the joint outer diameter portion and the joint inner diameter portion by resistance heating due to current flow, if the outer metal member has an inner wall portion located on the one axial end side of the joint inner diameter portion and extending radially outward from the joint inner diameter portion, the insulating portion can prevent burrs extending radially outward from the one axial end side of the joint from abutting on the inner wall portion of the outer metal member. Therefore, current is prevented from flowing through the burrs and flows concentratedly at the joint, thereby allowing the joint to be well joined.

[0014] The joint may be heated again by resistance heating caused by passing current again between the joint outer diameter portion of the inner metal member and the joint inner diameter portion of the outer metal member.

[0015] According to this configuration, when the joint is reheated by resistance heating caused by passing current through the inner metal member and the outer metal member again, the current is prevented from flowing through the burrs and the current is concentrated in the joint. Therefore, the joint is heated by resistance heating, and the joint can be tempered, thereby improving the strength of the joint.

[0016] The outer metal member is provided with an inner wall portion located on one axial end side of the joining inner diameter portion and extending radially outward from the joining inner diameter portion, The insulating portion may be paint applied to the inner wall portion.

[0017] According to this configuration, the insulating portion is provided by applying paint, for example cathodic painting, to the inner wall portion of the outer metal member, so that the paint can prevent current from flowing through the burrs.

[0018] The outer metal member is provided with an inner wall portion located on one axial end side of the joining inner diameter portion and extending radially outward from the joining inner diameter portion, The insulating portion may be a paper sheet member disposed on the inner wall portion.

[0019] According to this configuration, an insulating portion is provided by disposing a paper sheet member on the inner wall portion of the outer metal member, and therefore the paper sheet member can prevent current from flowing through the burr.

[0020] a fitting tapered outer diameter portion is formed on the outer circumferential surface portion of the inner metal member and is located on one axial end side of the joining outer diameter portion, a fitting tapered inner diameter portion corresponding to the fitting tapered outer diameter portion is formed on the inner circumferential surface portion of the outer metal member; The outer metal member is provided with an inner wall portion located on one axial end side of the joining inner diameter portion and extending radially outward from the joining inner diameter portion, The insulating portion may be provided from the inner wall portion of the outer metal member to the fitting tapered inner diameter portion.

[0021] According to this configuration, by providing the insulating portion from the inner wall portion of the outer metal member to the fitting taper inner diameter portion, when a joint is formed between the joint outer diameter portion and the joint inner diameter portion by resistance heating caused by current flow while pressing the joint outer diameter portion of the inner metal member and the joint inner diameter portion of the outer metal member from the other axial end side toward the one axial end side, the insulating portion can prevent burrs from contacting the inner wall portion of the outer metal member, and the joint can be joined well. In addition, when stress acts between the inner metal member and the outer metal member, the tapered fitting portion can prevent stress concentration at the joint. Furthermore, since the insulating portion is disposed between the fitting taper outer diameter portion and the fitting taper inner diameter portion, when the joint is heated again by resistance heating caused by current flow again between the inner metal member and the outer metal member, the current does not flow through the tapered fitting portion. Therefore, when current is passed again, the current flows concentratedly at the joint, and the joint is heated by resistance heating, so that the joint can be tempered and the strength of the joint can be improved.

[0022] Further, a first fitting tapered outer diameter portion is formed on the outer circumferential surface portion of the inner metal member, the first fitting tapered outer diameter portion being located on one axial end side with respect to the joining outer diameter portion, and a second fitting tapered outer diameter portion being located on the other axial end side with respect to the joining outer diameter portion, a first fitting tapered inner diameter portion corresponding to the first fitting tapered outer diameter portion and a second fitting tapered inner diameter portion corresponding to the second fitting tapered outer diameter portion are formed on the inner peripheral surface portion of the outer metal member; The outer metal member is provided with an inner wall portion located on one axial end side of the joining inner diameter portion and extending radially outward from the joining inner diameter portion, The insulating portion is provided on the inner wall portion, When the joint outer diameter portion of the inner metal member and the joint inner diameter portion of the outer metal member are axially pressurized while current is passed through them to generate resistance heating to form the joint between the joint outer diameter portion and the joint inner diameter portion, the first fitting tapered outer diameter portion and the second fitting tapered outer diameter portion of the inner metal member may fit with the first fitting tapered inner diameter portion and the second fitting tapered inner diameter portion of the outer metal member to form a first tapered fitting portion and a second tapered fitting portion.

[0023] According to this configuration, when a joint is formed between the joint outer diameter portion of the inner metal member and the joint inner diameter portion of the outer metal member by resistance heating caused by current flow while pressurizing the joint outer diameter portion and the joint inner diameter portion from the other axial end side toward the one axial end side, a first tapered fitting portion and a second tapered fitting portion are provided on both axial sides of the joint. The first tapered fitting portion and the second tapered fitting portion provided on both axial sides of the joint can further suppress stress concentration at the joint.

[0024] The inner metal member may be a differential case, and the outer metal member may be a ring gear.

[0025] According to this configuration, since the inner metal member is the differential case and the outer metal member is the ring gear, the joint between the differential case and the ring gear can be satisfactorily joined. Effect of the Invention

[0028] Therefore, the method for joining metal members according to the present invention By law This makes it possible to suppress current flow due to burrs and to achieve good joining of the joint. [Brief description of the drawings]

[0029] [Figure 1] 1 is a schematic diagram showing a differential device including a joint structure for metal members according to an embodiment of the present invention; [Diagram 2] 2 is a partial enlarged view of the area surrounded by the dashed-dotted circle II in FIG. 1. [Diagram 3] 1A to 1C are explanatory diagrams illustrating a method for joining metal members. [Figure 4] 4 is a partial enlarged view of the area surrounded by a dashed-dotted circle IV in FIG. 3. [Diagram 5] 5 is a schematic diagram showing a transition in current output when metal members are joined. FIG. [Figure 6] FIG. 13 is a schematic diagram showing an insulating portion in another embodiment. [Figure 7]11 is a schematic diagram showing a differential device including a joint structure for metal members according to another embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0031] Fig. 1 is a schematic diagram showing a differential device having a joint structure for metal members according to an embodiment of the present invention. As shown in Fig. 1, the differential device having the joint structure for metal members according to an embodiment of the present invention is configured as a differential device 1 for rear wheels of a front engine, rear drive vehicle.

[0032] The differential device 1 includes a ring gear 2 configured as an outer metal member of the differential device 1, and a differential case 3 configured as an inner metal member of the differential device 1. The ring gear 2 is a bevel gear made of carbon steel. The differential case 3 is a substantially cylindrical part made of cast iron.

[0033] The ring gear 2 has a substantially cylindrical inner circumferential surface portion 21. A joint inner diameter portion 22 extending in the axial direction of the ring gear 2 is formed on this inner circumferential surface portion 21. In addition, bevel teeth 25 that incline toward one axial end of the ring gear 2 as they extend outward are provided on the outer periphery of the other axial end side of the ring gear 2.

[0034] FIG. 2 is a partial enlarged view of the area surrounded by a dashed-dotted circle II in FIG.

[0035] An inner circumferential surface portion 21 of the ring gear 2 is provided with an inner wall portion 24 located on one axial end side of the inner diameter joining portion 22 and extending radially outward in a substantially straight line.

[0036] Returning to FIG. 1, the differential case 3 has a substantially cylindrical outer peripheral surface portion 31. A substantially cylindrical joint outer diameter portion 32 is formed on the outer peripheral surface portion 31 so as to fit with the joint inner diameter portion 22 of the ring gear 2 and extend in the axial direction of the differential case 3. The differential case 3 also has a substantially spherical internal space 33 formed inside the outer peripheral surface portion 31. In addition, the outer peripheral surface portion 31 of the differential case 3 is provided with a substantially circular flange 34 located on one axial end side of the joint outer diameter portion 32 and extending radially outward.

[0037] A fitting tapered outer diameter portion 35 is formed at the radially outer end of the flange 34 of the outer peripheral surface portion 31 of the differential case 3, located at one axial end side with respect to the joint outer diameter portion 32, and inclined toward the axial one end side of the differential case 3 as it moves outward. On the other hand, a fitting tapered inner diameter portion 23 is formed at the inner peripheral surface portion 21 of the ring gear 2, located at one axial end side with respect to the joint inner diameter portion 22 and the inner wall portion 24, and inclined toward the axial one end side of the ring gear 2 as it moves outward. The fitting tapered outer diameter portion 35 and the fitting tapered inner diameter portion 23 are formed to be inclined at the same angle so that they can be fitted together.

[0038] Further, in the differential case 3, a shaft hole 41 is disposed inside the outer circumferential surface portion 31, the shaft hole 41 extending in a direction perpendicular to the axis of the outer circumferential surface portion 31 so as to pass through the internal space 33, and a pinion shaft 42 is attached so as to extend through the shaft hole 41. A pinion gear (not shown) housed in the internal space 33 is connected to the pinion shaft 42.

[0039] In this embodiment, paint 50 configured as an insulating part that prevents current from flowing through burrs 62 generated when joining the outer peripheral surface portion 31 of the differential case 3 and the inner peripheral surface portion 21 of the ring gear 2 is provided on the inner wall portion 24 of the ring gear 2 located near the joint portion 60 formed between the joint outer diameter portion 32 of the differential case 3 and the joint inner diameter portion 22 of the ring gear 2. Paint 50 configured as an insulating part is also provided on the fitting tapered inner diameter portion 23. This paint 50 is applied to the surfaces of the inner wall portion 24 and the fitting tapered inner diameter portion 23 by cathodic painting.

[0040] Next, a method for joining the ring gear 2 and the differential case 3 will be described.

[0041] FIG. 3 is an explanatory diagram illustrating a method for joining metal members.

[0042] As the first current application step, first, a differential case 3 is prepared in which a joint outer diameter portion 32 and a fitting tapered outer diameter portion 35 located on one axial end side of the joint outer diameter portion 32 are formed on an outer peripheral surface portion 31. Next, a ring gear 2 is prepared in which a joint inner diameter portion 22 corresponding to the joint outer diameter portion 32 and a fitting tapered inner diameter portion 23 corresponding to the fitting tapered outer diameter portion 35 are formed on an inner peripheral surface portion 21. Paint 50 is applied to the inner wall portion 24 and the fitting tapered inner diameter portion 23 of the ring gear 2 at the same time. The above-mentioned differential case 3 is inserted into the ring gear 2, and the other axial end side of the joint outer diameter portion 32 of the differential case 3 and the one axial end side of the joint inner diameter portion 22 of the ring gear 2 are abutted over the entire circumference. As a result, the ring gear 2 and the differential case 3 are in a coaxial state.

[0043] FIG. 4 is a partial enlarged view of the area surrounded by a dashed-dotted circle IV in FIG.

[0044] In practice, the outer diameter joint portion 32 of the differential case 3 is formed to have a larger diameter than the inner diameter joint portion 22 of the ring gear 2 so as to overlap radially with the inner diameter joint portion 22, with an overlapping margin of, for example, 0.6 mm.

[0045] Returning to FIG. 3, annular electrodes 51, 52 are installed on the other axial end side of the inner peripheral surface portion 21 of the ring gear 2 and on one axial end side of the flange 34 of the differential case 3, respectively. The electrodes 51, 52 are arranged so as to sandwich the joint inner diameter portion 22 of the ring gear 2 and the joint outer diameter portion 32 of the differential case 3 in the axial direction and to be as close to each other as possible in the radial direction. The electrodes 51, 52 are electrically connected to a controller 53 so that the output of the current is controlled. In addition, a motor 54 that moves the electrode 51 in the axial direction is disposed between the electrode 51 and the controller 53. The motor 54 is configured to apply pressure to the ring gear 2 and the differential case 3 in the axial direction by moving the electrode 51 toward the one axial end side.

[0046] Next, the ring gear 2 and the differential case 3 are pressed in the axial direction via the electrodes 51 and 52 while current is applied by the controller 53 to perform ring mash joining. The current supplied from the controller 53 shown by the dashed line in Fig. 3 flows from the electrode 51 on the ring gear 2 side through the contact portion between one axial end side of the joint inner diameter portion 22 of the ring gear 2 and the other axial end side of the joint outer diameter portion 32 of the differential case 3 to the electrode 52 on the differential case 3 side. This current application causes the radially overlapping portion of the joint outer diameter portion 32 and the joint inner diameter portion 22 to heat up to about 900°C by resistance heating, soften, and plastically flow.

[0047] 5 is a schematic diagram showing a transition in the output of current flow during joining of metal members. As shown in Fig. 5, the controller 53 maintains the output of the current flowing from the electrode 51 on the ring gear 2 side to the electrode 52 on the differential case 3 side at a constant output P1 from the start of current flow until time T1 as described above.

[0048] Since the differential case 3 and the ring gear 2 are pressurized in the axial direction, as the heat generation, softening, and plastic flow of the overlapping portion between the above-mentioned joint outer diameter portion 32 and the joint inner diameter portion 22 progress in the pressure direction, the ring gear 2 is pressed into the differential case 3 until the fitting tapered inner diameter portion 23 of the ring gear 2 abuts against the fitting tapered outer diameter portion 35 of the differential case 3 via the paint 50, as shown in Fig. 1. At this time, in the overlapping portion between the joint outer diameter portion 32 and the joint inner diameter portion 22, softened metal burrs are formed so as to gradually extend from one axial end side along the radially outward direction.

[0049] When time T1 has elapsed since the start of energization, the fitting tapered inner diameter portion 23 of the ring gear 2 comes into contact with the fitting tapered outer diameter portion 35 of the differential case 3 via the paint 50. At this time, the controller 53 temporarily reduces the output of the current flowing from the electrode 51 on the ring gear 2 side to the electrode 52 on the differential case 3 side to zero.

[0050] The joint inner diameter portion 22 of the ring gear 2 and the joint outer diameter portion 32 of the differential case 3 form a joint portion 60 by ring mash joining. The fitting tapered inner diameter portion 23 of the ring gear 2 fits into the fitting tapered outer diameter portion 35 of the differential case 3 via the paint 50 to form a tapered fitting portion 61. In addition, a burr 62 that curves in an arc shape toward the axial one end side is formed along the radial outside on the axial one end side of the joint portion 60. This burr 62 extends toward the inner wall portion 24 of the ring gear 2, and when the burr 62 becomes large and approaches the inner wall portion 24 of the ring gear 2, it abuts against the inner wall portion 24 of the ring gear 2 via the paint 50.

[0051] Returning to Figure 5, in the first current flow step described above, when time T1 is reached after the start of current flow and the output of the current flowing from electrode 51 on the ring gear 2 side to electrode 52 on the differential case 3 side temporarily becomes 0, a certain time passes and then the second current flow step is started.

[0052] In this embodiment, the second current application step is started at time T2, which is 3 to 4 seconds after time T1.

[0053] In the second current application step, the joint 60 between the ring gear 2 and the differential case 3 is heated by resistance heating caused by the second current application using the electrodes 51, 52. At this time, it is preferable that the output of the current flowing from the electrode 51 on the ring gear 2 side to the electrode 52 on the differential case 3 side is maintained at an output P2 that is 120 to 130% larger than the output P1, since the joint 60 formed between the joint inner diameter portion 22 and the joint outer diameter portion 32 has become larger.

[0054] Returning to FIG. 1, the current supplied from the controller 53 shown by the dashed line in FIG. 1 flows from the electrode 51 on the ring gear 2 side through the joint 60 between the joint inner diameter portion 22 of the ring gear 2 and the joint outer diameter portion 32 of the differential case 3 to the electrode 52 on the differential case 3 side. On the other hand, since the paint 50 is arranged as an insulating portion between the fitting tapered inner diameter portion 23 of the ring gear 2 and the fitting tapered outer diameter portion 35 of the differential case 3, the current does not flow through the tapered fitting portion 61 between the fitting tapered inner diameter portion 23 and the fitting tapered outer diameter portion 35. Also, even when the burr 62 extending from the joint portion 60 abuts against the inner wall portion 24 of the ring gear 2 via the paint 50, the paint 50 is arranged as an insulating portion between the inner wall portion 24 of the ring gear 2 and the burr 62, so that the current does not flow from the inner wall portion 24 to the burr 62. Therefore, the current is not divided into three directions, that is, the joint 60, the tapered fitting portion 61, and the burr 62, and the joint 60 can be heated again to a tempering temperature of about 700°C. After the current is passed for a set time, such as 2 seconds, from time T2 shown in FIG. 5, the current is stopped. This causes the joint 60 to be tempered.

[0055] In this embodiment, the first current application step and the second current application step are performed, but it is also possible to perform only the first current application step.

[0056] In this manner, in the joining structure of metal components according to an embodiment of the present invention, paint 50 configured as an insulating portion that prevents electric current is applied to the inner wall portion 24 and the mating tapered inner diameter portion 23 of the ring gear 2.

[0057] In the joining of metals according to an embodiment of the present invention, a paint 50 for preventing current flowing through burrs 62 generated when joining the outer peripheral surface 31 of the differential case 3 and the inner peripheral surface 21 of the ring gear 2 is disposed near the joint 60 formed between the joint outer diameter portion 32 of the differential case 3 and the joint inner diameter portion 22 of the ring gear 2, and a first current application step is performed in which the joint outer diameter portion 32 of the differential case 3 and the joint inner diameter portion 22 of the ring gear 2 are pressurized from the other axial end side toward the one axial end side while current is passed through them to form the joint 60 between them by resistance heating; and a second current application step is performed in which current is passed again between the joint outer diameter portion 32 of the differential case 3 and the joint inner diameter portion 22 of the ring gear 2 to heat the joint 60 again by resistance heating.

[0058] By disposing the paint 50 near the joint 60 formed between the joint outer diameter portion 32 of the differential case 3 and the joint inner diameter portion 22 of the ring gear 2, when the joint outer diameter portion 32 of the differential case 3 and the joint inner diameter portion 22 of the ring gear 2 are pressurized from the other axial end side toward the one axial end side and the joint 60 is formed between the joint outer diameter portion 32 and the joint inner diameter portion 22 by resistance heating due to current flow, in the case where the ring gear 2 has an inner wall portion 24 located on the one axial end side with respect to the joint inner diameter portion 22 and extending radially outward from the joint inner diameter portion 22, the paint 50 can prevent the burr 62 extending along the radial outside from the one axial end side of the joint 60 from abutting against the inner wall portion 24 of the ring gear 2. Therefore, the current is prevented from flowing through the burr 62, and the current flows concentratedly in the joint 60, so that the joint 60 can be well joined.

[0059] Furthermore, in the second current application step, the joint 60 is reheated by resistance heating caused by passing current again between the joint outer diameter portion 32 of the differential case 3 and the joint inner diameter portion 22 of the ring gear 2. This prevents current from flowing through the burrs 62 and causes the current to flow concentratedly at the joint 60. As a result, the joint 60 is heated by resistance heating, and the joint 60 can be tempered, thereby improving the strength of the joint 60.

[0060] In addition, by providing the paint 50 from the inner wall portion 24 of the ring gear 2 to the fitting tapered inner diameter portion 23, when a joint is formed between the joint outer diameter portion 32 of the differential case 3 and the joint inner diameter portion 22 of the ring gear 2 by resistance heating caused by current flow while pressurizing the joint outer diameter portion 32 of the differential case 3 and the joint inner diameter portion 22 of the ring gear 2 from the other axial end side toward the one axial end side, the paint 50 can suppress the burrs 62 from contacting the inner wall portion 24 of the ring gear 2, and the joint 60 can be joined well. In addition, when stress acts between the differential case 3 and the ring gear 2, the tapered fitting portion 61 can suppress stress concentration on the joint 60. Furthermore, since the paint 50 is disposed between the fitting tapered outer diameter portion 35 and the fitting tapered inner diameter portion 23, when the joint 60 is heated again by resistance heating caused by current flow between the differential case 3 and the ring gear 2, no current flows through the tapered fitting portion 61. Therefore, when current is passed again, the current flows concentratedly through joint 60, and joint 60 is heated by resistance heating, thereby tempering joint 60 and improving the strength of joint 60.

[0061] Furthermore, since the inner metal member is the differential case 3 and the outer metal member is the ring gear 2, the joint 60 between the differential case 3 and the ring gear 2 can be joined well.

[0062] Further, the paint 50 is applied to the inner wall portion 24 of the ring gear 2 by, for example, cathodic painting. Therefore, the paint 50 can prevent a current from flowing through the burrs 62.

[0063] FIG. 6 is a schematic diagram showing an insulating portion in another embodiment.

[0064] In the embodiment described above, the paint 50 configured as an insulating portion is disposed on the inner wall portion 24 and the fitting tapered inner diameter portion 23 of the ring gear 2, but an annular paper sheet member 150 shown in Fig. 4 may be disposed as an insulating portion by being attached to the inner wall portion 24 and the fitting tapered inner diameter portion 23, for example, by an adhesive. Hereinafter, this paper sheet member 150 is referred to as a paper packing. The paper packing 150 has a substantially conical shape and has an upper surface portion 151 extending in the radial direction substantially perpendicular to the axial direction, and an inclined side surface portion 152 inclined toward one axial end side of the ring gear 2 as it goes outward.

[0065] An upper surface portion 151 of the paper packing 150 is attached to the inner wall portion 24 of the ring gear 2, and an inclined side surface portion 152 of the paper packing 150 is attached to the fitting tapered inner diameter portion 23 of the ring gear 2. Therefore, the paper packing 150 can prevent a current from flowing through the burrs 62.

[0066] FIG. 7 is a schematic diagram showing a differential gear including a joint structure for metal members according to another embodiment of the present invention.

[0067] In the above-described embodiment, the ring gear 2 is provided with one mating tapered inner diameter portion 23, and the differential case 3 is provided with one mating tapered outer diameter portion 35, but a first mating tapered inner diameter portion 223a and a second mating tapered inner diameter portion 223b, and a first mating tapered outer diameter portion 235a and a second mating tapered outer diameter portion 235b shown in FIG. 7 may be provided on the ring gear 202 and the differential case 203, respectively.

[0068] As shown in FIG. 7, a first fitting tapered outer diameter portion 235a is formed at the radially outer end of the flange 234 of the outer peripheral surface portion 231 of the differential case 203, which is located at one axial end side with respect to the joint outer diameter portion 232 and inclined toward the axial one end side of the differential case 203 as it moves outward. Also, a second fitting tapered outer diameter portion 235b is formed at the outer peripheral surface portion 231 of the differential case 203, which is located at the other axial end side with respect to the joint outer diameter portion 232 and inclined toward the axial one end side of the differential case 203 as it moves outward. Meanwhile, a first fitting tapered inner diameter portion 223a is formed at the inner peripheral surface portion 221 of the ring gear 202, which is located at one axial end side with respect to the joint inner diameter portion 222 and inclined toward the axial one end side of the ring gear 202 as it moves outward. Further, a second fitting tapered inner diameter portion 223b is formed on the inner circumferential surface portion 221 of the ring gear 202, located on the other axial end side of the joining inner diameter portion 222 and inclined toward one axial end side of the ring gear 202 as it extends outward.

[0069] The first and second fitting tapered outer diameter portions 235a and 235b, and the first and second fitting tapered inner diameter portions 223a and 223b are inclined at the same angle so that they can fit together. In addition, paints 250a and 250b, which are configured as insulating parts, are provided on the inner wall portion 224 and the first and second fitting tapered inner diameter portions 223a and 223b, respectively.

[0070] In this embodiment, when the joint outer diameter portion 32 of the differential case 3 and the joint inner diameter portion 22 of the ring gear 2 are pressurized from the other axial end side toward the one axial end side and a joint portion 60 is formed between the joint outer diameter portion 32 and the joint inner diameter portion 22 by resistance heating due to current flow, the first fitting tapered outer diameter portion 235a and the second fitting tapered outer diameter portion 235b of the differential case 203 and the first fitting tapered inner diameter portion 223a and the second fitting tapered inner diameter portion 223b of the ring gear 202 are fitted together to form the first tapered fitting portion 261a and the second tapered fitting portion 261b. This makes it possible to further suppress stress concentration on the joint portion 260.

[0071] In this case as well, instead of using paint as the insulating portion, an insulating portion such as a paper packing may be provided.

[0072] The present invention is not limited to the exemplified embodiments, and various improvements and design modifications are possible without departing from the gist of the present invention.

[0073] INDUSTRIAL APPLICABILITY As described above, according to the present invention, it is possible to suppress electrical conduction due to burrs and to achieve good joining of joints, and therefore the present invention may be suitably used in the technical field of joining metal members. [Explanation of symbols]

[0074] 2 Outer metal part (ring gear) 3 Inner metal parts (differential case) 21 Inner peripheral surface section 22 Joint inner diameter part 31 Outer peripheral surface section 32 Joint outer diameter part 50 Insulation (paint) 60 Joint 62 Bali

Claims

1. A method for joining metal members, in which an outer peripheral surface portion of an inner metal member and an inner peripheral surface portion of an outer metal member are joined by resistance heating due to electrical current flow while applying pressure to each other in an axial direction, comprising the steps of: a joining outer diameter portion is formed on the outer circumferential surface portion of the inner metal member; a joining inner diameter portion corresponding to the joining outer diameter portion is formed on the inner circumferential surface portion of the outer metal member; an insulating portion is disposed in the vicinity of a joint formed between the outer diameter joint portion of the inner metal member and the inner diameter joint portion of the outer metal member, the insulating portion preventing a current from flowing through a burr generated when the outer peripheral surface portion of the inner metal member and the inner peripheral surface portion of the outer metal member are joined; the joining outer diameter portion of the inner metal member and the joining inner diameter portion of the outer metal member are pressurized from the other axial end side toward the one axial end side, while current is passed through the joining outer diameter portion and the joining inner diameter portion to generate resistance heat, thereby forming the joining portion between the joining outer diameter portion and the joining inner diameter portion. A method for joining metal members comprising the steps of:

2. 2. The method for joining metal members according to claim 1, further comprising the step of: again passing an electric current through the outer diameter portion of the inner metal member and the inner diameter portion of the outer metal member to generate resistance heating, thereby reheating the joint.

3. The outer metal member is provided with an inner wall portion located on one axial end side of the joining inner diameter portion and extending radially outward from the joining inner diameter portion, 3. The method for joining metal members according to claim 1, wherein the insulating portion is a paint applied to the inner wall portion.

4. The outer metal member is provided with an inner wall portion located on one axial end side of the joining inner diameter portion and extending radially outward from the joining inner diameter portion, 3. The method for joining metal members according to claim 1, wherein the insulating portion is a paper sheet member disposed on the inner wall portion.

5. a fitting tapered outer diameter portion is formed on the outer circumferential surface portion of the inner metal member and is located on one axial end side of the joining outer diameter portion; a fitting tapered inner diameter portion corresponding to the fitting tapered outer diameter portion is formed on the inner circumferential surface portion of the outer metal member; The outer metal member is provided with an inner wall portion located on one axial end side of the joining inner diameter portion and extending radially outward from the joining inner diameter portion, 5. The method for joining metal members according to claim 1, wherein the insulating portion is provided from the inner wall portion of the outer metal member to the fitting taper inner diameter portion.

6. a first fitting tapered outer diameter portion located on one axial end side of the joint outer diameter portion and a second fitting tapered outer diameter portion located on the other axial end side of the joint outer diameter portion are formed on the outer circumferential surface portion of the inner metal member; a first fitting taper inner diameter portion corresponding to the first fitting taper outer diameter portion and a second fitting taper inner diameter portion corresponding to the second fitting taper outer diameter portion are formed on the inner peripheral surface portion of the outer metal member; The outer metal member is provided with an inner wall portion located on one axial end side of the joining inner diameter portion and extending radially outward from the joining inner diameter portion, The insulating portion is provided on the inner wall portion, 5. The method for joining metal members according to claim 1, wherein when the joining outer diameter portion of the inner metal member and the joining inner diameter portion of the outer metal member are axially pressurized and resistance heating is generated by passing an electric current between the joining outer diameter portion and the joining inner diameter portion, the first fitting tapered outer diameter portion and the second fitting tapered outer diameter portion of the inner metal member fit together with the first fitting tapered inner diameter portion and the second fitting tapered inner diameter portion of the outer metal member to form a first tapered fitting portion and a second tapered fitting portion.

7. 7. The method for joining metal members according to claim 1, wherein the inner metal member is a differential case, and the outer metal member is a ring gear.

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