Laser Welding Method

Abstract

To provide a laser welding method capable of restraining a crack of a joining part and obtaining a welding structure when laser-welding a first annular member composed of cast iron and a second annular member composed of steel.SOLUTION: In a laser welding method for welding a first annular member 3 and a second annular member 2, the first annular member 3 and the second annular member 2 are rotated, and radiation of a laser and supply of a filler to a joining part 52 of the first annular member 3 and the second annular member 2 are started, and when output of the laser exceeds a prescribed value AH set between 0 and a half of a prescribed set value AD, the filler reaches a joining part 52, and afterwards, the first annular member 3 and the second annular member 2 make one round, and when a rotation angle of the first annular member 3 and the second annular member 2 reaches an output reduction starting rotation angle position θD larger than a filler arrival rotation angle position θR and smaller than an output maximum rotation angle position θM, output of irradiating laser is gradually reduced.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a laser welding method, and more particularly to a laser welding method for a differential ring gear and a differential case of a vehicle differential device. [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 differential ring gear to which driving force is transmitted from the propeller shaft, and a differential case that is joined to the differential ring gear by screwing or welding and rotates together with the differential ring gear. The differential case is provided with a pair of left and right side gears that distribute the driving force transmitted from the differential ring gear to the left and right drive wheels, a pinion shaft that extends in a direction perpendicular to the differential 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 differential ring gear and a differential case, for example, laser welding is known in which a laser is irradiated to the joint where a differential ring gear made of carbon steel and a differential case made of cast iron are welded to join the differential ring gear and the differential case.

[0006] A groove having a groove that opens toward the outside is provided at the joint where the differential ring gear and the differential case are in contact with each other. A space is provided between the differential ring gear and the differential case on the inside of the joint. When laser welding is performed, a filler is supplied from the outside to the groove while rotating the differential ring gear and the differential case, and a laser is irradiated to the groove. In this way, the molten metal forms a weld bead in the groove, and the differential ring gear and the differential case are welded together.

[0007] Generally, the differential ring gear is made of steel while the differential case is made of cast iron, so when the differential ring gear and the differential case, which are made of different materials, are welded together, there is a problem that cracks are likely to occur at the joint.

[0008] For example, Patent Document 1 discloses a method for determining whether or not a crack has occurred in the weld bead at the joint by checking the shape of the weld bead formed at the joint when welding a differential ring gear and a differential case. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 5252126 Summary of the Invention [Problem to be solved by the invention]

[0010] Fig. 4 is a graph showing the laser output and the travel distance of the filler relative to the rotation angle of the differential device in a conventional laser welding method. The horizontal axis of the graph in Fig. 4 shows the rotation angle position of the differential ring gear and the differential case relative to the reference position θ00. The vertical axis of the graph in Fig. 4 shows the output of the laser irradiated to the joint and the travel distance of the filler supplied to the joint.

[0011] In the graph of FIG. 4, the solid line AL10 and the dashed line AL20 show the magnitude of the laser output irradiated to the joint with respect to the rotation angle position of the differential ring gear and the differential case. In particular, the dashed line AL20 shows the magnitude of the laser output when the rotation of the differential ring gear and the differential case is completed. As shown by the solid line AL10, the laser starts to be irradiated at the same time as the rotation of the differential ring gear and the differential case starts from the reference position θ00. After that, the laser output gradually increases, and when the rotation of the differential ring gear and the differential case reaches a predetermined welding start rotation angle position θW0, it reaches a predetermined set value AD0. As shown by the dashed line AL20, when the rotation of the differential ring gear and the differential case is completed, the laser output gradually decreases. After that, when the rotation of the differential ring gear and the differential case reaches a predetermined laser stop rotation angle position θF0, the laser irradiation stops completely.

[0012] In addition, in the graph of FIG. 4, the solid line PL10 and the dashed line PL20 indicate the movement distance of the filler supplied to the joint with respect to the rotation angle of the differential ring gear and the differential case. In particular, the dashed line PL20 indicates the movement distance of the filler when the differential ring gear and the differential case rotate one revolution. As shown by the solid line PL10, the filler starts to be supplied when the rotation of the differential ring gear and the differential case reaches a predetermined filler supply start rotation angle position θS0 from the reference position θ00. After that, the filler gradually moves toward the joint between the differential ring gear and the differential case, and when the rotation of the differential ring gear and the differential case reaches the welding start rotation angle position θW0, it reaches the arrival position PD0 indicating that the filler has reached the joint between the differential ring gear and the differential case. As shown by the dashed dotted line PL20, when the differential ring gear and the differential case complete one revolution and reach the welding start rotational angle position θW0 again, the supply of filler stops.

[0013] As shown in FIG. 4, while the rotation angle of the differential ring gear and the differential case reaches the welding start rotation angle position θW0 from the reference position θ00, the laser is irradiated to the joint, but the filler does not reach the joint, so a blank firing area NA0 of the joint where the laser is irradiated without the filler reaching the joint is generated. In this blank firing area NA0, the steel differential ring gear and the cast iron differential case are substantially quenched, so that a brittle structure is formed at the interface of the weld bead of the joint. Thereafter, when the weld bead is cooled, it shrinks. The stress caused by this shrinkage destroys the brittle structure formed at the interface between the joint of the differential ring gear and the differential case and the weld bead, and there is a risk of cracks occurring at the interface between the joint of the differential ring gear and the differential case and the weld bead.

[0014] As shown in Fig. 4, after the differential ring gear and the differential case have completed one revolution, the laser continues to be irradiated to the joint from the welding start rotation angle position θW0 to the laser stop rotation angle position θF0, and the supply of the filler is stopped, so that a remelted region RA0 of the joint where the laser is irradiated again is generated after the laser welding is completed. In this remelted region RA0, the joint where the laser welding is completed is heated again by the laser, so the weld bead of the joint shrinks twice. These two shrinkages generate large stress in the center of the weld bead of the joint, which may cause cracks.

[0015] Therefore, an object of the present invention is to provide a laser welding method that can obtain a welded structure that can suppress cracking at the joint when laser welding a first annular member made of cast iron and a second annular member made of steel. [Means for solving the problem]

[0016] In order to solve the above problems, the present invention is characterized by having the following configuration.

[0017] First, the invention described in claim 1 of the present application is a laser welding method for welding the first annular member and the second annular member, by rotating a first annular member made of cast iron and attached to the rotation drive unit, and a second annular member made of steel and fitted to the first annular member, together by a rotation drive unit, while supplying a filler by a filler supply unit and irradiating a laser by a laser irradiation unit to a joint portion where the first annular member and the second annular member are butted together, a first step in which the rotation drive unit rotates the first annular member and the second annular member from a reference position, the laser irradiation unit starts irradiating the joint with a laser, and the filler supply unit starts supplying filler to the joint, and the output of the laser irradiated by the laser irradiation unit is gradually increased until the output of the laser exceeds a predetermined value set between 0 and half of a predetermined set value, at which point the rotation angle of the first annular member and the second annular member reaches a filler arrival rotation angle position and the filler supplied by the filler supply unit reaches the joint; a second step in which the output of the laser irradiated by the laser irradiation unit reaches the set value when the rotation angle of the first annular member and the second annular member reaches a maximum output rotation angle position that is greater than the filler reach rotation angle position; a third step of stopping the supply of filler by the filler supply unit when the first annular member and the second annular member complete one revolution and the rotation angles of the first annular member and the second annular member reach the filler arrival rotation angle position again; a fourth step of gradually reducing the output of the laser irradiated by the laser irradiation unit when the first annular member and the second annular member complete one revolution and the rotation angles of the first annular member and the second annular member pass the filler reach rotation angle position again and reach an output reduction start rotation angle position that is smaller than the output maximum rotation angle position; and a fifth step of stopping laser irradiation by the laser irradiation unit when the first annular member and the second annular member have completed one revolution and the rotation angles of the first annular member and the second annular member have passed the output reduction start rotation angle position and the maximum output rotation angle position, and then reached a laser stop rotation angle position that is greater than the maximum output rotation angle position.

[0018] The invention described in claim 2 is the invention described in claim 1, wherein an intermediate angle region is provided between the filler reach rotational angle position and the maximum output rotational angle position during a period from the first step to the second step, and during a period from the third step to the fourth step until the rotational angles of the first annular member and the second annular member reach the maximum output rotational angle position, The laser irradiation unit irradiates the laser twice in the intermediate angle region.

[0019] The invention described in claim 3 is characterized in that in the invention described in claim 1 or claim 2, the output reduction start rotational angle position is greater than the filler arrival rotational angle position.

[0020] The invention described in claim 4 is the invention described in any one of claims 1 to 3, wherein the first annular member is a differential case of a differential device, The second annular member is a differential ring gear of a differential device. Effect of the Invention

[0021] According to the invention described in claim 1 of the present application, when the laser output exceeds a predetermined value set between 0 and half of a predetermined set value by starting the laser irradiation unit to irradiate the joint with a laser and starting the filler supply unit to supply the filler, the filler supplied by the filler supply unit reaches the joint in the first step, whereby the blank firing region of the joint where the laser is irradiated without the filler reaching the joint is reduced. In addition, when the first and second annular members make one revolution and the rotation angle of the first and second annular members passes the filler arrival rotation angle position again and reaches the output reduction start rotation angle position which is smaller than the output maximum rotation angle position, the output of the laser irradiated by the laser irradiation unit is gradually reduced in the fifth step, whereby the remelted region of the joint where the laser is irradiated again after the laser welding is completed is reduced. By reducing the blank firing region and the remelted region as described above, a welded structure capable of suppressing cracks in the joint can be obtained.

[0022] In addition, according to the invention described in claim 2 of the present application, a laser is irradiated twice in an intermediate angle region between the filler arrival rotation angle position and the maximum output rotation angle position through which the rotation angles of the first annular member and the second annular member pass, between the first step and the second step, and from the third step to the fourth step until the rotation angle of the first annular member and the second annular member reaches the maximum output rotation angle position, so that the filler supplied to the joint can be melted at a sufficient temperature, thereby improving the quality of the welded structure in the intermediate angle region.

[0023] Furthermore, according to the invention described in claim 3 of the present application, in the region between the filler arrival rotational angle position and the power reduction start rotational angle position where a laser having an output smaller than a set value is irradiated to the joint from the first step to the second step, a laser having an output equal to the set value is irradiated to the joint from the third step to the fourth step, thereby completing laser welding, and the filler supplied to the joint is melted at a sufficient temperature, thereby improving the quality of the welded structure.

[0024] Furthermore, according to the invention described in claim 4 of the present application, when the joint between the differential case and the differential ring gear of the differential device is laser welded, the blind area and re-melted area of ​​the joint are reduced, thereby obtaining a welded structure that can suppress cracking of the joint. [Brief description of the drawings]

[0025] [Figure 1] 1 is a schematic diagram showing a laser welding device according to an embodiment of the present invention. [Diagram 2] 2 is a schematic cross-sectional view of the laser welding apparatus taken along line II-II in FIG. 1. [Diagram 3] 2 is a graph showing the laser output and the travel distance of a filler relative to the rotation angle of the differential ring gear and the differential case in FIG. 1. [Figure 4] 1 is a graph showing the laser output and the filler travel distance relative to the rotation angle of a differential ring gear and a differential case in a conventional laser welding method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0027] Fig. 1 is a schematic diagram showing a laser welding apparatus according to an embodiment of the present invention. As shown in Fig. 1, a laser welding apparatus 100 according to the embodiment of the present invention laser-welds a differential ring gear 2 and a differential case 3 of a differential device 1 configured as a rear wheel differential device of a front engine / rear drive vehicle.

[0028] The differential device 1 includes a differential ring gear 2 configured as a bevel gear made of carbon steel, and a differential case 3 made of cast iron. The differential ring gear 2 includes a substantially cylindrical inner peripheral side surface 21 and an annular bottom surface 22 provided on one axial end side of the inner peripheral side surface 21 of the differential ring gear 2. In addition, on the other axial end side of the differential ring gear 2, bevel teeth 25 are provided that incline toward the one axial end side of the differential ring gear 2 as they move outward. On the other hand, the differential case 3 includes a substantially cylindrical outer peripheral side surface 31 having an outer diameter equivalent to that of the inner peripheral side surface 21 so as to fit with the inner peripheral side surface 21 of the differential ring gear 2, and an approximately spherical internal space 32 formed inside the outer peripheral side surface 31. In addition, on one axial end side of the outer peripheral side surface 31 of the differential case 3, a substantially circular flange 33 having a diameter equivalent to that of the bottom surface 22 of the differential ring gear 2 and a substantially cylindrical shaft portion 34 having a diameter smaller than that of the outer peripheral side surface 31 are provided.

[0029] A case-side inclined portion 35 is provided at a radial end of the flange 33 of the differential case 3, inclining toward one axial end of the differential case 3 as it moves outward. Meanwhile, a gear-side inclined portion 23 is provided at a radial end of the bottom surface 22 of the differential ring gear 2, inclining toward the opposite side to the case-side inclined portion 35 of the differential case 3 as it moves outward, and having a radial width equivalent to that of the case-side inclined portion 35.

[0030] Further, a bottom surface 22 of the differential ring gear 2 is provided with a recess 24 that is recessed in an annular shape toward the other axial end side of the differential ring gear 2, on the inside of the gear side inclined portion 23.

[0031] Further, in the differential case 3, on the inside of the outer peripheral side surface 31, a shaft hole 41 extending in a direction perpendicular to the axis of the outer peripheral side surface 31 so as to pass through the internal space 32, a pinion shaft 42 attached to extend through the shaft hole 41 and having a pin insertion hole 43 on the radial end side of the differential case 3, an insertion hole 44 extending and connecting with the pin insertion hole 43 so as to intersect with the pinion shaft 42 and communicate with the outside, and a hollow pinion shaft fixing pin 60 extending through the insertion hole 44 so as to penetrate the pinion shaft 42 through the pin insertion hole 43 at the radial end side of the differential case 3 in order to fix the pinion shaft 42 are provided. A pinion gear (not shown) housed in the internal space 32 is connected to this pinion shaft 42.

[0032] When the differential ring gear 2 and the differential case 3 are joined, the inner peripheral side surface 21 of the differential ring gear 2 is press-fitted into the outer peripheral side surface 31 of the differential case 3 to form a fitting portion 51. In addition, the bottom surface 22 of the differential ring gear 2 abuts against the flange 33 of the differential case 3 to form a joint portion 52 having a groove that opens outward and is welded between the gear side inclined portion 23 and the case side inclined portion 35, and a space portion 53 that is surrounded by the recess 24, the outer peripheral side surface 31, and the flange 33 and expands in an annular shape between the fitting portion 51 and the joint portion 52.

[0033] In addition, when the inner peripheral side surface 21 of the differential ring gear 2 and the outer peripheral side surface 31 of the differential case 3 are press-fitted and fitted to each other, the bevel teeth 25 of the differential ring gear 2 overlap with the shaft hole 41 and the pinion shaft 42 of the differential case 3 in the axial direction of the differential ring gear 2 and the differential case 3. Therefore, before the inner peripheral side surface 21 of the differential ring gear 2 and the outer peripheral side surface 31 of the differential case 3 are press-fitted and fitted to each other, the pinion shaft 42 is attached to the shaft hole 41 of the differential case 3, and the pinion shaft fixing pin 60 is attached to the insertion hole 44 via the pin insertion hole 43. Thereafter, in a state in which the inner peripheral side surface 21 of the differential ring gear 2 and the outer peripheral side surface 31 of the differential case 3 are press-fitted and fitted to each other, laser welding is performed on the joint portion 52 of the differential ring gear 2 and the differential case 3.

[0034] Further, the differential case 3 is provided with a communication passage 54, one end of which opens into the space 53 and the other end of which opens into the insertion hole 44. The communication passage 54 has a cylindrical shape with a diameter of 1.5 mm to 2 mm, although this is not limited thereto.

[0035] The pinion shaft fixing pin 60, which is disposed so as to pass through the insertion hole 44, is provided at the same position as the other end of the communicating passage 54 in the axial direction of the differential ring gear 2 and the differential case 3, and has a communicating passage facing portion 61 on its side that faces the other end of the communicating passage 54. In the embodiment, the pinion shaft fixing pin 60 is configured in a cylindrical shape. In the cylindrical pinion shaft fixing pin 60, a plurality of through holes 63 are provided around the entire circumference of the communicating passage facing portion 61.

[0036] The laser welding apparatus 100 that performs laser welding on the above-mentioned differential device 1 will be described below.

[0037] When the differential ring gear 2 and the differential case 3 are welded together, the shaft portion 34 of the differential case 3 is fixed to a fixture 102 that is rotationally driven by a motor 101. The motor 101 is electrically connected to an externally disposed controller 103 so that the rotational drive is controlled.

[0038] A pinion shaft 42 inserted into the shaft hole 41 and a pinion shaft fixing pin 60 inserted into the insertion hole 44 are attached to the differential case 3. At this time, the pinion shaft fixing pin 60 is appropriately positioned in the axial direction of the differential ring gear 2 and the differential case 3 so that a communication passage facing portion 61 of the pinion shaft fixing pin 60 faces the other end of the communication passage 54.

[0039] The inner peripheral side surface 21 of the differential ring gear 2 is press-fitted into the outer peripheral side surface 31 of the differential case 3 fixed to the fixing tool 102, forming a fitting portion 51. At this time, the bottom surface 22 of the differential ring gear 2 abuts against the flange 33 of the differential case 3, forming a joint portion 52 having a groove that opens outward between the gear side inclined portion 23 and the case side inclined portion 35. In addition, between the fitting portion 51 and the joint portion 52, a space portion 53 is formed that is surrounded by the recess 24 of the differential ring gear 2 and the outer peripheral side surface 31 and flange 33 of the differential case 3 and expands in an annular shape.

[0040] A laser torch 104 is disposed outside the joint 52 as a laser irradiation unit so that a laser can be incident straight on the groove of the joint 52. This laser torch 104 is electrically connected to a controller 103 so that the irradiation of the laser on the joint 52 is controlled. In addition, a filler supply unit 105 is disposed near the laser torch 104 so that a filler can be supplied to the groove of the joint 52. This filler supply unit 105 is electrically connected to the controller 103 so that the supply of filler to the joint 52 is controlled.

[0041] When the differential ring gear 2 and the differential case 3 arranged as described above are welded together, the motor 101 is rotationally driven based on an electrical signal transmitted from the controller 103. At this time, the differential case 3 fixed to the fixture 102 via the shaft portion 34 and the differential ring gear 2 fitted to the differential case 3 at the fitting portion 51 rotate together with the fixture 102 rotated by the motor 101.

[0042] Based on an electrical signal transmitted from the controller 103, filler is supplied from the filler supply unit 105 to the joint 52 between the rotating differential ring gear 2 and the differential case 3, and a laser is irradiated from the laser torch 104. The filler is melted by the laser irradiated by the laser torch 104 to form a weld bead at the joint 52, thereby welding the differential ring gear 2 and the differential case 3. As the differential ring gear 2 and the differential case 3 rotate, the rotational angle position of the joint 52 to which the laser is irradiated moves in the circumferential direction, and laser welding is performed over the entire circumference of the differential ring gear 2 and the differential case 3.

[0043] Fig. 2 is a schematic cross-sectional view of the laser welding apparatus 100 as seen from line II-II in Fig. 1. In the embodiment, although not limited thereto, the differential ring gear 2 and the differential case 3 are initially arranged at a rotation angle position where the pinion shaft fixing pin 60 inserted into the insertion hole 44 faces the laser torch 104 in the radial direction of the differential ring gear 2 and the differential case 3. This rotation angle position is determined as a reference position θ0 when the differential ring gear 2 and the differential case 3 start to rotate.

[0044] From the above-mentioned initial state, the controller 103 transmits electrical signals to the motor 101, the laser torch 104, and the filler supply unit 105, whereby the motor 101 starts to rotate, the laser torch 104 starts to irradiate the laser, and the filler supply unit 105 starts to supply the filler. As the motor 101 starts to rotate, the differential ring gear 2 and the differential case 3 start to rotate counterclockwise in FIG. 2 around the axes of the differential ring gear 2 and the differential case 3. At this time, the rotational angle position of the joint 52 irradiated with the laser by the laser torch 104 shifts in the clockwise direction in FIG. 2.

[0045] FIG. 3 is a graph showing the laser output and the travel distance of the filler with respect to the rotation angle of the differential ring gear 2 and the differential case 3 in FIG. 1. The horizontal axis of the graph in FIG. 3 indicates the rotation angle position of the differential ring gear 2 and the differential case 3 with respect to the reference position θ0, with the reference position θ0 being defined as 0°. In particular, the region to the right of the reference position θ0 indicates a rotation angle position in the positive direction as viewed from the reference position θ0, with the clockwise direction in which the rotation angle position of the joint 52 irradiated with the laser by the laser torch 104 changes being positive. On the other hand, the region to the left of the reference position θ0 indicates a rotation angle position in the negative direction as viewed from the reference position θ0, with the direction opposite to the positive direction being negative, and indicates the rotation angle position before the rotation of the differential ring gear 2 and the differential case 3 reaches the reference position θ0 again when the rotation of the differential ring gear 2 and the differential case 3 goes around once. The vertical axis of the graph in FIG. 3 indicates the output of the laser irradiated by the laser torch 104 and the travel distance of the filler supplied by the filler supply unit 105.

[0046] In the graph of FIG. 3, the solid line AL1 and the dashed line AL2 indicate the magnitude of the laser output irradiated by the laser torch 104 with respect to the rotation angle of the differential ring gear 2 and the differential case 3. In particular, the dashed line AL2 indicates the magnitude of the laser output when the rotation of the differential ring gear 2 and the differential case 3 completes one revolution. As shown by the solid line AL1, the laser torch 104 starts irradiating the laser at the same time as the rotation of the differential ring gear 2 and the differential case 3 starts from the reference position θ0. After that, the laser torch 104 gradually increases the laser output, and when the rotation of the differential ring gear 2 and the differential case 3 reaches a predetermined maximum output rotation angle position θM, the laser torch 104 reaches a predetermined set value AD. As shown by the dashed line AL2, when the rotation of the differential ring gear 2 and the differential case 3 completes one revolution and reaches the output reduction start rotation angle position θD, the laser torch 104 gradually reduces the laser output. Thereafter, when the rotation of the differential ring gear 2 and the differential case 3 reaches a predetermined laser stop rotation angle position θF, the laser torch 104 completely stops outputting the laser.

[0047] In the laser welding method of the present invention, the power reduction start rotational angle position θD is set to an angle that is larger than the reference position θ0 and smaller than the maximum output rotational angle position θM.

[0048] In the embodiment, the maximum output rotation angle position θM is set to, but is not limited to, about 13.4° relative to the reference position θ0 defined as 0°. The output reduction start rotation angle position θD is set to, but is not limited to, about 8.0° relative to the reference position θ0 defined as 0°. The laser stop rotation angle position θF is set to, but is not limited to, about 21.4° relative to the reference position θ0 defined as 0°.

[0049] In addition, in the graph of FIG. 3, the solid line PL1 and the dashed line PL2 indicate the moving distance of the filler supplied by the filler supply unit 105 with respect to the rotation angle of the differential ring gear 2 and the differential case 3. In particular, the dashed line PL2 indicates the moving distance of the filler when the rotation of the differential ring gear 2 and the differential case 3 is completed. As shown by the solid line PL1, the filler supply unit 105 starts supplying the filler at the same time that the rotation of the differential ring gear 2 and the differential case 3 starts from the reference position θ0 and the laser torch 104 starts irradiating the laser. Thereafter, the filler gradually moves toward the joint 52 of the differential ring gear 2 and the differential case 3, and when the rotation of the differential ring gear 2 and the differential case 3 reaches the filler reaching rotation angle position θR, it reaches the reaching position PD indicating that the filler has reached the joint 52 of the differential ring gear 2 and the differential case 3. As indicated by the dashed dotted line PL2, when the rotation of the differential ring gear 2 and the differential case 3 completes one revolution and reaches the filler arrival rotational angle position θR again, the filler supply unit 105 stops supplying the filler.

[0050] In an embodiment, the feeler arrival rotational angular position θR is set to about 5.4° with respect to a reference position θ0 defined as 0°, although this is not limited thereto.

[0051] The method of laser welding the differential ring gear 2 and the differential case 3 using the laser welding apparatus 100 will be described in more detail below.

[0052] In the laser welding method of the present invention, as described above, the differential ring gear 2 and the differential case 3 are, although not limited to this, in the initial state, the pinion shaft fixing pin 60 inserted into the insertion hole 44 is positioned at an angle in the rotational direction opposite the laser torch 104 in the radial direction of the differential ring gear 2 and the differential case 3, i.e., at the reference position θ0.

[0053] In the first step of the laser welding method, from the above-mentioned initial state, the controller 103 of the laser welding apparatus 100 transmits an electrical signal to the motor 101, the laser torch 104, and the filler supply unit 105, so that the motor 101 starts to rotate, the laser torch 104 starts to irradiate the laser, and the filler supply unit 105 starts to supply the filler. When the motor 101 starts to rotate, the differential ring gear 2 and the differential case 3 start to rotate from the reference position θ0 in the counterclockwise direction in FIG. 2 around the axis of the differential ring gear 2 and the differential case 3. Also, as shown in FIG. 3, when the differential ring gear 2 and the differential case 3 start to rotate from the reference position θ0, the output of the laser irradiated by the laser torch 104 starts to increase toward the set value AD, and the filler supplied by the filler supply unit 105 starts to move toward the arrival position PD.

[0054] Next, when the gradually increasing laser output exceeds a predetermined value AH, the rotation angle of the differential ring gear 2 and the differential case 3 reaches the filler reaching rotation angle position θR. Also, when the rotation angle of the differential ring gear 2 and the differential case 3 reaches the filler reaching rotation angle position θR, the filler supplied by the filler supply unit 105 reaches the reaching position PD, that is, reaches the joint 52 of the differential ring gear 2 and the differential case 3. The above-mentioned predetermined value AH is set to a value smaller than half the set value AD of the laser output. In particular, in the embodiment, the predetermined value AH is set to a value between one-third and one-half of the set value AD, although it is not limited thereto.

[0055] Next, in the second step of the laser welding method, when the rotation angle of the differential ring gear 2 and the differential case 3 reaches the maximum output rotation angle position θM, the gradually increasing laser output reaches the set value AD. Thereafter, the controller 103 changes the electrical signal sent to the laser torch 104 so that the output of the irradiated laser is maintained at the set value AD. As a result, the output of the laser irradiated by the laser torch 104 is maintained at the set value AD.

[0056] Next, in a third step of the laser welding method, when the rotation of the differential ring gear 2 and the differential case 3 completes one revolution and the rotation angle of the differential ring gear 2 and the differential case 3 again reaches the filler arrival rotation angle position θR, the controller 103 changes the electrical signal sent to the filler supply unit 105 so as to stop supplying the filler. This causes the filler supply unit 105 to stop supplying the filler.

[0057] In a fourth step of the laser welding method, when the rotation of the differential ring gear 2 and the differential case 3 completes one revolution and the rotation angle of the differential ring gear 2 and the differential case 3 reaches the output reduction start rotation angle position θD that is larger than the filler reach rotation angle position θR and smaller than the output maximum rotation angle position θM, the controller 103 changes the electrical signal sent to the laser torch 104 so that the output of the irradiated laser gradually decreases. As a result, the output of the laser irradiated by the laser torch 104 gradually decreases.

[0058] Finally, in the fifth step of the laser welding method, when the rotation angle of the differential ring gear 2 and the differential case 3 reaches the laser stop rotation angle position θF, the laser torch 104 completely stops outputting the laser.

[0059] As shown in FIG. 3, in the first step, that is, until the rotational angle of the differential ring gear 2 and the differential case 3 reaches the filler arrival rotational angle position θR from the reference position θ0, the laser output by the laser torch 104 is irradiated to the joint 52, while the filler supplied by the filler supply unit 105 has not reached the joint 52 between the differential ring gear 2 and the differential case 3, an empty striking area NA of the joint 52 where the laser is irradiated is created in a state in which the filler has not reached.

[0060] In addition, between the fourth step and the fifth step, that is, until the rotation of the differential ring gear 2 and the differential case 3 has completed one rotation and the rotational angle of the differential ring gear 2 and the differential case 3 has passed the output reduction start rotational angle position θD and reached the laser stop rotational angle position θF that is greater than the output maximum rotational angle position θM, the laser output by the laser torch 104 continues to be irradiated to the joint 52 after the filler supply unit 105 stops supplying filler, so that after the laser welding is completed, a re-melted area RA of the joint 52 where the laser is irradiated again is generated.

[0061] Furthermore, between the first step and the second step, and between the third step and the fourth step until the rotation angle of the differential ring gear 2 and the differential case 3 reaches the maximum output rotation angle position θM, an intermediate angle region MA is provided between the filler reach rotation angle position θR and the maximum output rotation angle position θM. In this intermediate angle region MA, the laser output by the laser torch 104 is irradiated to the joint 52 twice.

[0062] According to the laser welding method of the present invention, by the first step of starting to irradiate a laser with laser torch 104 and to supply filler with filler supply unit 105, the blank shot area NA of joint 52 where the laser is irradiated before the filler has arrived becomes smaller than the blank shot area NA0 produced by the conventional laser welding method shown in FIG. 4.

[0063] In addition, when the differential ring gear 2 and the differential case 3 have completed one rotation and the rotational angle of the differential ring gear 2 and the differential case 3 reaches the output reduction start rotational angle position θD that is greater than the filler reach rotational angle position θR and less than the maximum output rotational angle position θM, a fourth step is performed to gradually reduce the output of the laser irradiated by the laser torch 104, so that after the laser welding is completed, the re-melted area RA of the joint 52 where the laser is irradiated again becomes smaller than the re-melted area RA0 produced by the conventional laser welding method shown in Figure 4.

[0064] As described above, by reducing the blank area NA and the remelted area RA, a welded structure capable of suppressing cracking of the joint 52 can be obtained.

[0065] In addition, by irradiating the laser twice in the intermediate angle region MA between the filler arrival rotational angle position θR and the maximum output rotational angle position θM, through which the rotational angles of the differential ring gear 2 and the differential case 3 pass, the filler supplied to the joint 52 is melted at a sufficient temperature, thereby improving the quality of the welding structure in the intermediate angle region.

[0066] Furthermore, according to the invention described in claim 3 of the present application, in the region between the filler arrival rotational angle position θR and the power reduction start rotational angle position θD, where a laser having an output smaller than the set value AD is irradiated to the joint 52 from the first step to the second step, a laser having an output equal to the set value AD is irradiated to the joint 52 from the third step to the fourth step, thereby completing laser welding, so that the filler supplied to the joint 52 is melted at a sufficient temperature, thereby improving the quality of the welded structure.

[0067] In addition, when laser welding the joint 52 between the differential ring gear 2 and the differential case 3 of the differential device 1, by reducing the blind area NA and the re-melted area RA of the joint 52, a welded structure can be obtained that can suppress cracking of the joint 52.

[0068] In this embodiment, the differential device 1 having a differential ring gear 2 and a differential case 3 welded by laser welding is configured as a rear wheel differential device of a front engine, rear drive vehicle, but for example, the differential ring gear and the differential case of a front wheel differential device of a front engine, front drive vehicle may also be laser welded.

[0069] 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.

[0070] As described above, according to the present invention, by reducing the blind area and remelted area of ​​the joint, a welded structure can be obtained that can suppress cracking of the joint, and therefore the present invention may be suitably used in the field of manufacturing vehicles equipped with differential devices. [Explanation of symbols]

[0071] 2 Differential ring gear (second annular member) 3 Differential case (first annular member) 52 Joint 101 Motor (rotary drive unit) 103 Controller 104 Laser torch (laser irradiation part) 105 Filler supply section θ0 Reference position θD Output reduction start rotation angle position θM Output maximum rotation angle position θR Filler reaching rotation angle position θF Laser stop rotation angle position AD setting value AH Predetermined value

Claims

1. a laser welding method for welding the first annular member and the second annular member, the method comprising: rotating a first annular member made of cast iron and attached to the rotation drive unit, and a second annular member made of steel and fitted to the first annular member, together with the first annular member and welding the first annular member and the second annular member, the method comprising: supplying a filler to a joint where the first annular member and the second annular member are butted together with a filler supplying unit and irradiating a laser with a laser irradiation unit, the method comprising: a first step in which the rotation drive unit rotates the first annular member and the second annular member from a reference position, the laser irradiation unit starts irradiating the joint with a laser, and the filler supply unit starts supplying filler to the joint, and the output of the laser irradiated by the laser irradiation unit is gradually increased until the output of the laser exceeds a predetermined value set between 0 and half of a predetermined set value, at which point the rotation angle of the first annular member and the second annular member reaches a filler arrival rotation angle position and the filler supplied by the filler supply unit reaches the joint; a second step in which the output of the laser irradiated by the laser irradiation unit reaches the set value when a rotation angle of the first annular member and the second annular member reaches a maximum output rotation angle position that is greater than the filler reach rotation angle position; a third step of stopping the supply of filler by the filler supply unit when the first annular member and the second annular member complete one revolution and the rotation angles of the first annular member and the second annular member reach the filler arrival rotation angle position again; a fourth step of gradually reducing the output of the laser irradiated by the laser irradiation unit when the first annular member and the second annular member complete one revolution and the rotation angles of the first annular member and the second annular member pass the filler reach rotation angle position again and reach an output reduction start rotation angle position that is smaller than the output maximum rotation angle position; a fifth step of stopping the laser irradiation by the laser irradiation unit when the first annular member and the second annular member complete one revolution and the rotation angles of the first annular member and the second annular member pass through the output reduction start rotation angle position and the maximum output rotation angle position and then reach a laser stop rotation angle position that is greater than the maximum output rotation angle position.

1. A laser welding method comprising:

2. an intermediate angle region is provided between the filler reach rotational angle position and the maximum output rotational angle position during a period from after the first step to the second step, and during a period from the third step to after the fourth step until the rotational angles of the first annular member and the second annular member reach the maximum output rotational angle position; The laser welding method according to claim 1 , wherein the laser irradiation unit irradiates the laser twice in the intermediate angle region.

3. 3. The laser welding method according to claim 1, wherein the output reduction start rotational angle position is greater than the filler arrival rotational angle position.

4. the first annular member is a differential case of a differential device, 4. The laser welding method according to claim 1, wherein the second annular member is a differential ring gear of a differential device.

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