Conductor joint method

Abstract

To provide a conductor joint method which can join conductors 11 in a low cost and an accurate manner when there is a difference Δh of height between joint end surfaces of two flat wires 8.SOLUTION: A conductor joint method comprises: an initial radiation process where laser beam is radiated to an inner region of an end face of a first conductor and an inner region of an end face of a second conductor to form a pair of molten pools in parallel with the end faces of both conductors so that outer periphery parts of the respective end faces become dikes; a middle radiation process where laser beam is radiated to a joint side region of the end face of the first conductor and a joint side region of the end face of the second conductor and both regions are adjacent to each other so as to connect the pair of molten pools with each other; and a latter radiation process where laser beam is radiated to the whole body end face consisting of the end face of the first conductor and the end face of the second conductor in an approximately circular shape to form the pair of molten pools connected to each other into a molten ball 34 in a semi-spherical shape.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a conductor joining method, and more particularly to a conductor joining method for joining a first conductor and a second conductor by laser welding. [Background technology]

[0002] In recent years, efforts to realize a low-carbon or carbon-free society have become more active, and research and development into electrification technologies is being conducted in order to reduce CO2 emissions and improve energy efficiency in vehicles. In order to popularize electric vehicles, it is important to reduce the manufacturing costs of electric motors (motors and / or generators) and improve their energy efficiency.

[0003] To reduce costs and improve energy efficiency, rectangular wires are sometimes used for the coils wound around the stator cores of electric motors. A known method for winding rectangular wires around teeth involves peeling off the coating at the tips of a pair of rectangular wires inserted into the slots between the teeth, and then laser welding the exposed tips of the conductors of the pair of rectangular wires by irradiating them with a laser beam.

[0004] As such a joining direction, Patent Document 1 discloses a joining method in which, when irradiating the end faces of the first and second rectangular wires with a laser beam, the laser beam is scanned in a loop within the end face of the first rectangular wire to form a molten pool, and the diameter of the loop-like trajectory along which the laser beam is scanned within the end face of the first rectangular wire is increased until the molten pool reaches the butting surface between the end side surfaces. This allows the molten pool to fill the gap between the butting surfaces without irradiating the butting surface with the laser beam, preventing the laser beam from penetrating the gap and damaging the insulating coating of the rectangular wires. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6390672 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method described in Patent Document 1 assumes that the heights of the end faces of the first and second rectangular wires to be joined are the same and that the gap between the butting surfaces of the end faces is small. However, after the first and second rectangular wires are inserted into the corresponding slots, they are bent to bring the ends closer together, which can cause the heights of both end faces to differ. Achieving the same height for both end faces requires high processing precision, which increases manufacturing costs.

[0007] In view of the above background, the present invention aims to provide a conductor joining method that can reliably join the conductors of two flat rectangular wires at low cost, even if there is a difference in height between the joining end surfaces of the two flat rectangular wires. [Means for solving the problem]

[0008] In order to solve the above problem, one aspect of the present invention is a conductor joining method for joining a first conductor (11A) and a second conductor (11B) by laser welding, comprising an initial irradiation process in which laser light is irradiated onto the inner regions (31) of each end face of the first conductor and the second conductor, forming a pair of molten pools (33) parallel to the end faces of both conductors so that the outer peripheries of each end face form embankments; a middle irradiation process in which laser light is irradiated onto the joining side regions (32) of each end face of the first conductor and the second conductor, which are close to each other, to connect the pair of molten pools; and a final irradiation process in which laser light is irradiated in an approximately circular shape onto the entire end face formed by the end faces of the first conductor and the second conductor, to form the pair of connected molten pools into a hemispherical molten ball (34).

[0009] According to this aspect, the conductor joining method includes an initial irradiation process, a middle irradiation process, and a final irradiation process, so that even if there is a difference in height between the tips of a pair of rectangular wire conductors after the coating has been peeled off, the molten ball can be grown to an appropriate size without falling, making it possible to reliably join the two conductors at low cost.

[0010] In the above aspect, in the initial irradiation step, the laser light may be irradiated onto the inner region while weaving in a loop shape.

[0011] According to this aspect, a molten pool can be efficiently formed in the inner region of the end face.

[0012] In the above aspect, the end face of the first conductor is positioned higher than the end face of the second conductor, and in the intermediate irradiation process, laser light is first irradiated onto the joining side region of the first conductor, causing the molten pool of the first conductor to flow into the molten pool of the second conductor.

[0013] According to this aspect, by causing the molten pool of the first conductor having the higher end face to flow into the molten pool of the second conductor having the lower end face, the molten pool is prevented from flowing into the gap between the two conductors.

[0014] In the above aspect, in the latter irradiation step, the laser light may be irradiated onto the molten ball so that the first conductor and the second conductor are invisible in a plan view due to the molten ball.

[0015] According to this aspect, the two conductors can be reliably welded together by a molten ball larger than the cross sections of the two conductors. [Effects of the Invention]

[0016] According to the above-described embodiment, it is possible to provide a conductor joining method that can reliably join two conductors at low cost even if there is a difference in height between the joining end faces of two rectangular wires. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a cross-sectional view of a stator in the process of being manufactured for a rotating electric machine according to an embodiment; [Figure 2] A perspective view of a pair of rectangular wires after bending [Figure 3] A diagram showing the joining of rectangular wires [Figure 4] 1 is an explanatory diagram of a joining method according to an embodiment; [Figure 5] Illustration of the end face of a rectangular wire [Figure 6] FIG. 10 is a diagram showing an irradiation trajectory in a first modified example of the initial irradiation step. [Figure 7] FIG. 10 is a diagram showing an irradiation trajectory in a second modified example of the initial irradiation step. [Figure 8] FIG. 10 is a diagram showing the irradiation trajectory of a modified example of the intermediate step. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0019] FIG. 1 is a cross-sectional view of a stator 1 during manufacture of a rotating electric machine according to an embodiment. A conductor joining method according to the present invention is carried out when manufacturing the rotating electric machine shown in FIG. 1. The rotating electric machine includes the stator 1 and a rotor (not shown) rotatably arranged inside the stator 1. The stator 1 includes a stator core 2 and a coil 3. The stator core 2 has a cylindrical shape extending along an axis 2X, which coincides with the rotation axis of the rotor. In other words, the rotor is rotatably arranged around the axis 2X of the stator core 2.

[0020] The stator core 2 has a plurality of teeth 4 on the radial inside that extend in the axial direction (the up-and-down direction in FIG. 1). The teeth 4 are T-shaped with a wider tip than the base end, and are arranged at equal intervals in the circumferential direction. A plurality of slots 5 that penetrate the stator core 2 in the axial direction are formed at equal intervals in the circumferential direction between adjacent teeth 4. In addition, a plurality of slits 6 are formed on the inner peripheral surface of the stator core 2 by the tips of adjacent teeth 4. The slits 6 have a width smaller than the circumferential width of the slots 5. Each slot 5 extends radially outward in the radial direction from the slit 6 formed on the inner peripheral surface of the stator core 2, widening its width. However, the slits 6 are not essential.

[0021] The coil 3 is obtained by joining multiple segment coils 7 by laser welding. The segment coil 7 is obtained by bundling multiple coil elements (conductive wires) and forming them into a roughly U-shape. The coil elements use flat wire 8 with a rectangular cross-sectional shape. The flat wire 8 has a linear conductor portion 11 (Fig. 2) made of a conductor such as copper, and a coating 12 (Fig. 2) made of an insulator that covers the conductor portion 11. The multiple segment coils 7 are aligned in an annular shape while overlapping each other in the circumferential direction, and are inserted into the slots 5 along the axis 2X of the stator core 2.

[0022] FIG. 2 is a perspective view of a pair of rectangular wires 8 after bending. FIG. 2 shows the stator core 2 shown in FIG. 1 flipped axially to show the portion of the rectangular wire 8 protruding from the underside of the stator core 2. As shown in FIG. 2, the coating 12 is stripped from both ends of each rectangular wire 8 protruding from the slot 5 of the stator core 2, exposing the conductor portion 11. After the rectangular wire 8 is inserted into the slot 5, the ends are bent circumferentially to be joined to the corresponding other rectangular wire 8. As a result of the bending process, the portion of the rectangular wire 8 protruding from the slot 5 has an inclined portion 13 inclined circumferentially with respect to the axis 2X of the stator core 2, and a parallel portion 14 extending from the end of the inclined portion 13 parallel to the axis 2X of the stator core 2 and forming an end portion.

[0023] The ends of a pair of rectangular wires 8, arranged close to each other by bending, are parallel and close to each other. However, due to springback of the rectangular wires 8 after bending, the ends of the rectangular wires 8 may shift circumferentially from the desired position. If this continues, the ends of the two rectangular wires 8 to be joined will separate, making it impossible to join the two rectangular wires 8. Therefore, the two rectangular wires 8 are clamped by a clamping jig 16 having a pair of clamp bodies 15, and joined with the ends close to each other. The clamping jig 16 may be, for example, one described in Patent Publication No. 6483079 and Patent Publication No. 6680867 by the present applicant, or one with a similar configuration.

[0024] By using the clamping jig 16, the ends of the pair of rectangular wires 8 are aligned circumferentially and positioned close to each other so as to face each other radially around the stator core 2. However, because the coating 12 is provided on the lower part of the parallel portion 14 and the inclined portion 13 of the ends of the pair of rectangular wires 8, a small gap g (FIG. 3) exists between the conductor portions 11. The end faces of the pair of rectangular wires 8 are preferably positioned at the same height (the distance from the end face of the stator core 2 along the axis 2X of the stator core 2). However, because the clamping jig 16 cannot adjust the height position of the conductor portion 11, the end faces of the pair of rectangular wires 8 are positioned at different heights with a slight difference Δh (FIG. 3). The ends of the two rectangular wires 8 positioned in this manner are reliably joined by joining them using the conductor joining method described below.

[0025] Next, an embodiment of a specific method for laser welding the ends of the conductor portions 11 of the rectangular wires 8 will be described. FIG. 3 is a diagram schematically illustrating the joining of the rectangular wires 8. The conductor joining method according to this embodiment is performed using a laser welding device 20 shown in FIG. 3, with a pair of rectangular wires 8 arranged closely together with the end faces of the conductor portions 11 facing upward. Specifically, the pair of conductor portions 11 are joined to each other by laser welding, in which the laser welding device 20 irradiates the end faces (end faces of the conductor portions 11) of the pair of rectangular wires 8 with laser light 21. The conductor joining method includes an initial irradiation process, a middle irradiation process, a joining process, and a final irradiation process.

[0026] The laser welding device 20 includes a laser oscillator 22 with high focusing ability capable of emitting a laser beam with a wavelength of, for example, 100 μm or less, and a galvano-scanning laser head 23 capable of scanning the laser light 21 emitted by the laser oscillator 22 at a speed of, for example, 500 mm / sec or more. The type of laser light 21 is not limited, and may be a fiber laser, YAG laser, CO2 laser, semiconductor pumped laser, or the like. In the illustrated example, the laser welding device 20 includes one laser oscillator 22 and one laser head 23, and sequentially irradiates the end faces of a pair of rectangular wires 8 with the laser light 21. In other embodiments, the laser welding device 20 may include two laser oscillators 22 and two laser heads 23, and simultaneously irradiate the end faces of a pair of rectangular wires 8 with the laser light 21.

[0027] Fig. 4 is an explanatory diagram of a joining method according to an embodiment. Fig. 4 shows a side view, a plan view, and a planar image for each of (A) before irradiation, (B) an initial irradiation step, (C) a middle irradiation step, and (D) a late irradiation step. The conductor joining method is performed in the order of the initial irradiation step, the middle irradiation step, and the late irradiation step. These steps will be described in order below. Note that the plan view of each irradiation step in Fig. 4 shows the trajectory of the laser light 21.

[0028] As shown in Figure 4(A), before irradiation, a pair of conductors 11 at the ends of the rectangular wire 8 are arranged close to each other with a gap g roughly equivalent to twice the thickness of the coating 12 and with their upper end faces at different heights. Hereinafter, the conductor 11 of the rectangular wire 8 on the right side of the figure will be referred to as the first conductor 11A, and the conductor 11 of the rectangular wire 8 on the left side will be referred to as the second conductor 11B. When there is no need to distinguish between the two, they may simply be referred to as the conductor 11 or both conductors 11. The end face of the first conductor 11A is higher than the end face of the second conductor 11B.

[0029] Here, the end face of the conductor portion 11 of the rectangular wire 8 will be described with reference to Fig. 5. Fig. 5 is an explanatory diagram of the end face of the conductor portion 11 of the rectangular wire 8. As shown in the figure, the conductor portion 11 of the rectangular wire 8 has a substantially rectangular shape in a plan view. In this specification, the inner region (the region surrounded by imaginary lines) of the end face of each conductor portion 11 is referred to as the inner region 31. The inner region 31 need not extend to the outer edge of the end face. The proportion of the area of ​​the inner region 31 in the end face of the conductor portion 11 is not limited, but may be, for example, 30% to 70%.

[0030] In this specification, the region of the end face of each conductor 11 that faces the other conductor 11 to be joined (the region hatched and separated by imaginary lines) is referred to as the joining-side region 32. The joining-side region 32 need not include a region on the opposite side to the other conductor 11 to be joined. The proportion of the area of ​​the joining-side region 32 in the area of ​​the end face of the conductor 11 is not limited, but may be, for example, 20% to 60%. Furthermore, the joining-side region 32 may or may not have a portion overlapping with the inner region 31.

[0031] As shown in FIG. 4(B), in the initial irradiation step, the laser beam 21 is irradiated onto the inner regions 31 (see FIG. 5) of the end faces of both conductors 11. For example, the laser welding device 20 irradiates the inner region 31 of the end face of the first conductor 11A with the laser beam 21, and then irradiates the inner region 31 of the end face of the second conductor 11B with the laser beam 21. In the example shown in FIG. 4(B), the laser welding device 20 irradiates the inner regions 31 of the end faces of each conductor 11 with the laser beam 21 so as to draw successive spiral circles of different sizes. The laser welding device 20 may irradiate the end face of the first conductor 11A and the end face of the second conductor 11B with the laser beam 21 once each, or may irradiate each of the end faces of the first conductor 11A and the second conductor 11B with the laser beam 21 once, twice, or three times.

[0032] As shown in the side view of Fig. 4(B), by the irradiation of the laser beam 21 in the initial irradiation step, the end of the first conductor 11A and the end of the second conductor 11B are melted in the inner region 31 but not in the outer region. In other words, the outer region of each conductor 11 acts as a bank, and a molten pool 33 is formed in the inner region 31. In this way, a pair of molten pools 33 are formed side by side on the end faces of both conductors 11.

[0033] Fig. 6 is a diagram showing the irradiation trajectory of a first modified example of the initial irradiation step. In Fig. 6, the starting point of the trajectory of the laser beam 21 is indicated by a circle, and the direction of the trajectory is indicated by an arrow. As shown in Fig. 6, the laser welding device 20 may irradiate the inner region 31 of the end face of each conductor 11 with the laser beam 21 so as to draw successive circles of the same size while shifting the circles. In this way, the laser welding device 20 irradiates the inner region 31 with the laser beam 21 while weaving it in a loop shape, thereby efficiently forming a molten pool 33 in the inner region 31 of the end face.

[0034] Fig. 7 shows the irradiation trajectory of a second modified example of the initial irradiation step. As shown in Fig. 7, the laser welding device 20 may irradiate the laser beam 21 so as to draw circles of the same size successively on the inner region 31 of the end face of each conductor 11 while shifting the circles in one direction, and then draw circles of the same size successively while shifting the circles in the other direction. By irradiating the inner region 31 with the laser beam 21 in this way, the laser welding device 20 can also efficiently form a molten pool 33 in the inner region 31 of the end face.

[0035] Next, as shown in FIG. 4(C), in the intermediate irradiation step, the laser beam 21 is irradiated onto the joint-side regions 32 (see FIG. 5) of the end faces of both conductors 11. The joint-side region 32 of the first conductor 11A is the portion of the outer periphery of the end face of the first conductor 11A that is closer to the second conductor 11B. The joint-side region 32 of the second conductor 11B is the portion of the outer periphery of the end face of the second conductor 11B that is closer to the first conductor 11A. The laser welding device 20, for example, irradiates the laser beam 21 onto the joint-side region 32 of the end face of the first conductor 11A, and then irradiates the laser beam 21 onto the joint-side region 32 of the end face of the second conductor 11B.

[0036] 4(C), the laser welding device 20 irradiates the joining side region 32 of the end face of each conductor 11 with the laser beam 21 so as to draw an oval. The oval may be single, double, or triple. The laser welding device 20 may irradiate the end face of the first conductor 11A and the end face of the second conductor 11B with the laser beam 21 once each, or may irradiate each of the end faces of the first conductor 11A and the second conductor 11B with the laser beam 21 twice or three times.

[0037] The bank portion of the first conductor 11A on the second conductor 11B side and the bank portion of the second conductor 11B on the first conductor 11A side are melted by the irradiation of the laser beam 21 in the middle irradiation step, whereby the pair of molten pools 33 are joined to form one large molten pool 33.

[0038] Fig. 8 shows the irradiation trajectory of a modified example of the intermediate irradiation step. As shown in Fig. 8, the laser welding device 20 may irradiate the joining side region 32 of the end face of each conductor 11 with the laser beam 21 so as to draw successive circles of the same size while shifting the circles. In this way, the laser welding device 20 irradiates the joining side region 32 with the laser beam 21 while weaving it in a loop shape, thereby efficiently melting the bank portion of the joining side region 32 of the end face.

[0039] As shown in Fig. 3, in this embodiment, the laser welding device 20 first irradiates the end face of the first conductor 11A, which has a higher end face, with the laser beam 21. As a result, as shown in Fig. 4(C), the bank of the first conductor 11A melts first, and the molten pool 33 of the first conductor 11A flows into the molten pool 33 of the second conductor 11B. In this way, in the middle irradiation step, the molten pool 33 of the first conductor 11A, which has a higher end face, flows into the molten pool 33 of the second conductor 11B, which has a lower end face, thereby preventing the molten pool 33 from flowing into the gap g between the conductors 11.

[0040] 4(D), in the latter irradiation step, the laser welding device 20 irradiates the entire end surface formed by the end surface of the first conductor 11A and the end surface of the second conductor 11B with laser light 21 in a substantially circular pattern, and forms a pair of molten pools 33 connected to each other into a hemispherical molten ball 34. The molten ball cools and solidifies, thereby joining the first conductor 11A and the second conductor 11B to each other.

[0041] In the latter irradiation step, the laser welding device 20 irradiates the molten ball 34 with the laser beam 21 so that the first conductor 11A and the second conductor 11B are hidden from view in a plan view by the molten ball 34. This ensures that the conductors 11 are reliably welded together by the molten ball 34, which is larger than the cross sections of the conductors 11.

[0042] As described above, the conductor joining method of this embodiment includes an initial irradiation process, a middle irradiation process, and a final irradiation process. This allows the molten ball 34 to grow to an appropriate size without falling, even if a gap g and a height difference Δh exist between the tips of the conductor portions 11 of a pair of rectangular wires 8 from which the coating 12 has been peeled. Therefore, the conductor portions 11 can be joined reliably at low cost.

[0043] Although the description of specific embodiments has been completed above, the present invention is not limited to the above-described embodiments and modifications, and can be widely modified and implemented. For example, in the above-described embodiments, during the initial irradiation process and the middle irradiation process, the laser welding device 20 irradiates the end face of the first conductor 11A with the laser beam 21 and then irradiates the end face of the second conductor 11B with the laser beam 21. In other embodiments, during at least one of the initial irradiation process and the middle irradiation process, the laser welding device 20 may first irradiate the end face of the second conductor 11B with the laser beam 21. Alternatively, the laser welding device 20 may include two laser heads 23, and simultaneously irradiate the end face of the first conductor 11A and the end face of the second conductor 11B with the laser beam 21. Furthermore, the specific configuration, arrangement, quantity, and material of each component and part, as well as the specific method, numerical values, and trajectory shape of each step, can be appropriately modified within the scope of the present invention. Furthermore, some or all of the configurations of the above-described embodiments and modifications thereof can be combined with each other. Meanwhile, not all of the components shown in the above-described embodiments are necessarily required and can be selected appropriately. [Explanation of symbols]

[0044] 1: Stator 2: Stator core 2X: Axis 3: Coil 4: Teeth 5: Slot 6: Slit 7: Segment coil 8: Rectangular wire (coil element, example of conductive wire) 11: Conductor part (conductor) 11A: First conductor part 11B: Second conductor part 12:Coating 13: Inclined part 14: Parallel section 20: Laser welding equipment 21: Laser light 22: Laser oscillator 23: Laser head 31: Inner area 32: Junction side area 33: Weld pool 34: Molten ball g: gap

Claims

1. A conductor joining method for joining a first conductor and a second conductor by laser welding, comprising: an initial irradiation step of irradiating inner regions of the end face of the first conductor and the end face of the second conductor with laser light to form a pair of molten pools parallel to the end faces of both conductors so that the outer peripheries of the end faces form banks; a middle-stage irradiation step of irradiating a laser beam onto joining-side regions of the end faces of the first conductor and the second conductor, which are adjacent to each other, to connect the pair of molten pools; a later irradiation step of irradiating the entire end surface formed by the end surface of the first conductor and the end surface of the second conductor with laser light in an approximately circular shape, thereby forming the pair of molten pools connected to each other into a hemispherical molten ball.

2. 2. The conductor joining method according to claim 1, wherein in the initial irradiation step, the laser light is irradiated onto the inner region while weaving in a loop shape.

3. 3. The conductor joining method according to claim 1, wherein the end face of the first conductor is positioned higher than the end face of the second conductor, and in the intermediate irradiation process, the laser light is first irradiated onto the joining side region of the first conductor, causing the molten pool of the first conductor to flow into the molten pool of the second conductor.

4. 3. The conductor joining method according to claim 1, wherein in the latter irradiation step, the molten ball is irradiated with laser light so that the first conductor and the second conductor are hidden by the molten ball in a plan view.

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