Conductor joining method

Abstract

The invention relates to a conductor joining method. The conductor bonding method includes: an initial stage irradiation step of irradiating an inner region of an end surface of each of a first conductor and a second conductor with a laser to form a pair of molten pools arranged side by side on the end surfaces of the first conductor and the second conductor so that a bank is formed at an outer peripheral portion of each end surface; an intermediate-stage irradiation step of irradiating the joining-part-side regions of the end surfaces of the first conductor and the second conductor, which are close to each other, with laser light so that the pair of molten pools are joined to each other; and a post-stage irradiation step of irradiating the entire end surface jointly formed by the end surfaces of the first conductor and the second conductor with laser light in a substantially circular shape to form the pair of molten puddles into hemispherical molten balls.

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 Art

[0002] In recent years, efforts to achieve a low-carbon or carbon-neutral society have become more aggressive. As for vehicles, research and development of electrification technologies are underway to reduce CO2 emissions and improve energy efficiency. To promote the widespread adoption of electric vehicles, it is crucial to reduce the manufacturing cost of electric motors (motor and / or generator) and improve energy efficiency.

[0003] To reduce costs and improve energy efficiency, flat wires are used in coils wound around the stator core of electric motors. To wind the flat wires around the teeth, a known method involves stripping the insulation film from the distal ends of a pair of flat wires inserted into the slots between each pair of adjacent teeth and joining the exposed conductor ends of the pair of flat wires by laser welding using laser irradiation.

[0004] As one such joining method, JP6390672B2 discloses a joining method in which the end faces of a first flat wire and a second flat wire to be joined are irradiated with a laser beam. The joining method includes: applying a laser beam in a circular manner inside the end face of the first flat wire to form a molten pool; and applying the laser beam to the inside of the end face of the first flat wire while gradually increasing the diameter of the circular trajectory of the laser beam to allow the molten pool to reach the side faces of the end. This allows the gap (spacing) between the side faces to be filled with the molten pool without applying the laser beam between the side faces, thereby preventing the laser beam from entering the gap and damaging the insulating film of the flat wire.

[0005] However, the method described in Japanese Patent Application Laid-Open No. 6390672B2 assumes that the end faces of the first and second flat wires to be joined are at the same height, and that the gap between the side faces of the ends of the first and second flat wires is small. On the other hand, after inserting the first and second flat wires into their respective slots, the first and second flat wires are bent to bring the ends closer together, which can result in the end faces being at different heights. Ensuring that the end faces are at the same height requires high machining precision, which can increase manufacturing costs. Summary of the Invention

[0006] In view of the above background, a main object of the present invention is to provide a conductor joining method capable of joining conductors reliably and at low cost even when there is a height difference between end surfaces to be joined of two rectangular wires.

[0007] To achieve the above-mentioned objectives, one aspect of the present invention provides a conductor joining method for joining a first conductor 11A and a second conductor 11B by laser welding, the conductor joining method comprising: an initial-stage irradiation step of irradiating an inner region 31 of an end face of each of the first and second conductors with laser light to form a pair of molten pools 33 arranged side by side on the end faces of the first and second conductors so as to form a bank along the outer periphery of each end face; an intermediate-stage irradiation step of irradiating a joint-side region 32 of the end faces of the first and second conductors adjacent to each other with laser light to connect the pair of molten pools to each other; and a final-stage irradiation step of irradiating an entire end face constituted by the end faces of the first and second conductors with laser light in a substantially circular shape to form the connected pair of molten pools into a hemispherical molten ball 34.

[0008] According to this aspect, the conductor joining method includes an initial irradiation step, an intermediate irradiation step, and a final irradiation step. Therefore, even when there is a height difference between the distal ends of the conductors of a pair of flat wires after the film has been peeled off, the molten ball can be grown to an appropriate size without falling. Consequently, conductors can be joined reliably and at low cost.

[0009] In the above aspect, preferably, in the initial stage irradiation step, the inner area is irradiated with the laser light while the laser light is caused to weave in a circular manner.

[0010] According to this aspect, a molten pool can be efficiently formed in the inner region of the end surface.

[0011] In the above aspect, preferably, when the end face of the first conductor is located at a higher position than the end face of the second conductor, in the intermediate-stage irradiation step, the joint side region of the first conductor is irradiated with the laser earlier than the joint side region of the second conductor, so that the molten pool of the first conductor flows toward the molten pool of the second conductor.

[0012] According to this aspect, the molten pool of the first conductor having a higher end surface flows toward the molten pool of the second conductor having a lower end surface, and thus it is possible to suppress the molten pool from flowing into the gap between the conductors.

[0013] In the above aspect, preferably, in the later-stage irradiation step, the molten sphere is irradiated with the laser light to such an extent that the first conductor and the second conductor are hidden by the molten sphere in a plan view.

[0014] According to this aspect, the conductors can be reliably welded using the molten ball that is larger than the cross-section of the conductors.

[0015] According to the above aspect, it is possible to provide a conductor joining method capable of joining conductors reliably and at low cost even when there is a height difference between end surfaces to be joined of two rectangular wires. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a cross-sectional view of a stator of a rotating electric machine according to an embodiment, wherein the stator is in the middle of manufacturing;

[0017] Figure 2 This is a three-dimensional image of a pair of flat wires after bending.

[0018] Figure 3 is a diagram schematically showing how flat wires are joined;

[0019] Figure 4 is an explanatory diagram of a joining method according to an embodiment;

[0020] Figure 5 This is an illustration of the end face of a flat wire;

[0021] Figure 6 is a diagram showing an irradiation trajectory according to a first variation of the initial stage irradiation step;

[0022] Figure 7 is a diagram showing an irradiation trajectory according to a second variation of the initial-stage irradiation step; and

[0023] Figure 8 is a diagram showing an irradiation trajectory according to a modification of the intermediate stage irradiation step. DETAILED DESCRIPTION

[0024] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0025] Figure 1 1 is a cross-sectional view of a stator 1 of a rotating electrical machine according to an embodiment, wherein the stator 1 is in the middle of manufacturing. Figure 1 The rotating electric machine shown in FIG. The rotating electric machine includes a stator 1 and a rotor (not shown) rotatably disposed within the stator 1. The stator 1 comprises a stator core 2 and coils 3. The stator core 2 has a cylindrical shape extending along an axis 2X, which coincides with the rotor's rotational axis. Specifically, the rotor is rotatable about the stator core 2's axis 2X.

[0026] The stator core 2 is provided with a plurality of axially extending ( Figure 1A plurality of teeth 4 extending in the stator core 2 (in the up and down directions) are provided. Each tooth 4 is T-shaped in such a manner that the distal end is wider than the base end, and the teeth 4 are arranged at equal intervals in the circumferential direction. Between mutually adjacent teeth 4, a plurality of slots 5 penetrating the stator core 2 in the axial direction are arranged at equal intervals in the circumferential direction. In addition, on the inner circumferential surface of the stator core 2, a plurality of slits 6 are formed through the distal ends of mutually adjacent teeth 4. The circumferential width of the slits 6 is smaller than the circumferential width of the slots 5. Each slot 5 extends radially outward from the slit 6 formed on the inner circumferential surface of the stator core 2, so that the width of the slot 5 increases as the slot 5 extends radially outward. However, it should be noted that the slit 6 is not indispensable.

[0027] The coil 3 is obtained by joining a plurality of segment coils 7 by laser welding. Each segment coil 7 is obtained by bundling a plurality of coil elements (conducting wires) and forming them into a substantially U-shape. As the coil element, a flat wire 8 having a rectangular cross-sectional shape is used. Each flat wire 8 includes a linear conductor portion 11 ( Figure 2 ) and a film 12 ( Figure 2 A plurality of segment coils 7 are annularly arranged so as to overlap in the circumferential direction, and in this state are inserted into the slots 5 along the axis 2X of the stator core 2 .

[0028] Figure 2 This is a perspective view of a pair of flat wires 8 after bending. Figure 2 Shown by making Figure 1 The stator core 2 is shown as being reversed in the axial direction and a portion of the flat wire 8 protrudes from the lower side of the stator core 2. Figure 2 As shown, at both ends of each flat wire 8 protruding from the slot 5 of the stator core 2, film 12 is peeled off to expose the conductor portion 11. After being inserted into the slot 5, each end of each flat wire 8 is bent in the circumferential direction to join with another corresponding flat wire 8. As a result of the bending, the portion of each flat wire 8 protruding from the slot 5 has an inclined portion 13 that is inclined in the circumferential direction relative to the axis 2X of the stator core 2, and a parallel portion 14 that extends from the end of the inclined portion 13 parallel to the axis 2X of the stator core 2 and forms an end.

[0029] The ends of each pair of flat wires 8 that are arranged close to each other as a result of the bending process are arranged parallel to each other. However, it should be noted that due to the springback caused in the flat wires 8 after the bending process, the ends of the flat wires 8 may deviate from the desired position in the circumferential direction. This will cause the ends of the two flat wires 8 to be joined to separate, and the flat wires 8 cannot be joined. In order to solve this problem, the two flat wires 8 are clamped by a clamping fixture 16 including a pair of clamping bodies 15, and are joined to each other while the ends are kept close to each other. As the clamping fixture 16, for example, the clamping fixture disclosed in JP6483079B2 and JP6680867B2 submitted by the applicant or a clamping fixture having a similar configuration thereto can be used.

[0030] By using the clamping jig 16, the ends of the pair of flat wires 8 are aligned in the circumferential direction and arranged close to each other so as to face each other in the radial direction of the stator core 2. However, it is noted that since the ends of the pair of flat wires 8 are each provided with the film 12 on the lower part of the parallel portion 14 and the inclined portion 13, a small gap g ( Figure 3 ). Preferably, the end faces of the pair of flat wires 8 are arranged at the same height (separated by a certain distance from the end faces of the stator core 2 along the axis 2X of the stator core 2). However, since the holding fixture 16 cannot adjust the position of the conductor portion 11 in the height direction, the end faces of the pair of flat wires 8 may be arranged at different heights with a slight difference ΔH ( Figure 3 The ends of the rectangular wires 8 arranged in this manner are reliably joined by using a conductor joining method described later.

[0031] Next, one embodiment of a specific method of laser welding the end portions of the conductor portion 11 of the rectangular wire 8 will be described. Figure 3 The diagram schematically shows how the flat wires 8 are joined. In a state where the end faces of the conductors 11 are facing upward and a pair of flat wires 8 are arranged close to each other, the flat wires 8 are joined by using Figure 3 The illustrated laser welding device 20 performs the conductor joining method according to this embodiment. Specifically, a pair of conductor portions 11 are joined together by laser welding, in which the laser welding device 20 irradiates the end faces of a pair of flat wires 8 (the end faces of the conductor portions 11) with laser light 21. The conductor joining method includes an initial irradiation step, an intermediate irradiation step, and a final irradiation step.

[0032] The laser welding device 20 includes a laser oscillator 22, which can emit a laser beam with a wavelength of, for example, less than or equal to 100 μm and high light-concentrating properties, and a current scanning laser head 23. The current scanning laser head 23 can scan the laser light 21 emitted from the laser oscillator 22 at a rate of, for example, 500 mm / s or greater. The type of laser oscillator 22 is not particularly limited and can be a fiber laser, a YAG laser, a CO2 laser, a semiconductor pump 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 flat wires 8 with the laser light 21. In another embodiment, the laser welding device 20 can include two laser oscillators 22 and two laser heads 23, and simultaneously irradiates the end faces of a pair of flat wires 8 with the laser light 21.

[0033] Figure 4 It is an explanatory diagram of the bonding method according to this embodiment. Figure 4 The side view, plan view and plan image of each of (A) before irradiation, (B) initial stage irradiation step, (C) intermediate stage irradiation step and (D) later stage irradiation step are shown. The conductor bonding method is performed in the order of the initial stage irradiation step, the intermediate stage irradiation step and the later stage irradiation step. Hereinafter, these steps are described in order. Note that in Figure 4 In the plan view of each irradiation step in FIG. 1 , the trajectory of the laser light 21 is shown.

[0034] like Figure 4 As shown in (A), before irradiation, the conductor portions 11 at the ends of a pair of flat wires 8 are positioned close to each other, separated by a gap g approximately equal to twice the thickness of the film 12, with their upper end surfaces located at different heights. Hereinafter, the conductor portion 11 of the right-hand flat wire 8 in the figure will be referred to as the first conductor portion 11A, and the conductor portion 11 of the left-hand flat wire 8 will be referred to as the second conductor portion 11B. When no distinction is made, these may be simply referred to as the conductor portion 11, the two conductor portions 11, or the like. The end surface of the first conductor portion 11A is located at a higher position than the end surface of the second conductor portion 11B.

[0035] Here, refer to Figure 5 , the end surface of the conductor portion 11 of the rectangular wire 8 will be described. Figure 5 This is an explanatory diagram of the end surface of the conductor portion 11 of the flat wire 8. As shown in the figure, the conductor portion 11 of each flat wire 8 has a generally rectangular shape when viewed from above. In this specification, the inner region of the end surface of each conductor portion 11 (the region surrounded by an imaginary line) is referred to as the inner region 31. The inner region 31 does not extend to the outer edge of the end surface. The ratio of the area of the inner region 31 to the area of the end surface of the conductor portion 11 can be, for example, 30% to 70%, but is not limited thereto.

[0036] In this specification, the area of the end face of each conductor portion 11 on the side that joins with the other conductor portion 11 (the area divided by an imaginary line and shaded) is referred to as the joint side area 32. The joint side area 32 of each conductor portion 11 does not include the area on the opposite side of the other conductor portion 11 to be joined. The ratio of the area of the joint side area 32 to the area of the end face of the conductor portion 11 can be, for example, 20% to 60%, but is not limited to this. Furthermore, the joint side area 32 may or may not overlap with the inner area 31.

[0037] like Figure 4 As shown in (B), in the initial stage irradiation step, the inner region 31 of the end face of the two conductor parts 11 is irradiated with the laser 21 (refer to Figure 5 For example, the laser welding device 20 irradiates the inner region 31 of the end face of the first conductor portion 11A with the laser beam 21 and then irradiates the inner region 31 of the end face of the second conductor portion 11B with the laser beam 21. Figure 4 In the example shown in (B), the laser welding device 20 irradiates the inner region 31 of the end face of each conductor portion 11 with laser light 21 in a spiral pattern, continuously drawing circles of varying sizes. The laser welding device 20 may irradiate the end face of the first conductor portion 11A and the end face of the second conductor portion 11B with laser light 21 once, twice, or three times.

[0038] Since the laser 21 is irradiated in the initial stage irradiation step, as Figure 4 As shown in the side view of FIG. 1 (B), the end portions of first conductor portion 11A and second conductor portion 11B are each melted within inner region 31, but not melted in the outer region. In other words, the outer region of each conductor portion 11 forms a bank, while a molten pool 33 is formed in inner region 31. Thus, a pair of molten pools 33 are formed side by side on the end surface of conductor portion 11.

[0039] Figure 6 is a diagram showing an irradiation trajectory according to a first variation of the initial stage irradiation step. Figure 6 In FIG, a circle represents the starting point of the trajectory of the laser 21, and an arrow represents the direction of the trajectory. Figure 6 As shown, the laser welding device 20 can irradiate the inner region 31 of the end face of each conductor portion 11 with the laser light 21 so as to continuously draw circles of the same size while moving in one direction. In this way, the laser welding device 20 irradiates the inner region 31 of the end face with the laser light 21 while weaving the laser light 21 in a circular shape, thereby efficiently forming a molten pool 33 in the inner region 31 of the end face.

[0040] Figure 7 FIG. 4 shows an irradiation trajectory according to a second variation of the irradiation step in the initial stage. Figure 7 As shown, the laser welding device 20 can irradiate the inner region 31 of the end face of each conductor portion 11 with the laser 21 so as to continuously draw circles of the same size while moving in one direction, and further continuously draw circles of the same size while moving in the opposite direction. In this case, the molten pool 33 can also be efficiently formed in the inner region 31 of the end face.

[0041] Then, if Figure 4 As shown in (C), in the intermediate stage irradiation step, the joint side region 32 (refer to Figure 5 The joint-side region 32 of the first conductor portion 11A is a portion of the end surface of the first conductor portion 11A located on the second conductor portion 11B side. The joint-side region 32 of the second conductor portion 11B is a portion of the end surface of the second conductor portion 11B located on the first conductor portion 11A side. For example, the laser welding device 20 irradiates the joint-side region 32 of the end surface of the first conductor portion 11A with the laser beam 21, and then irradiates the joint-side region 32 of the end surface of the second conductor portion 11B with the laser beam 21.

[0042] exist Figure 4 In the example shown in (C), the laser welding apparatus 20 irradiates the joint-side region 32 of the end face of each conductor portion 11 with laser light 21 to draw one or more elongated circles. The one or more elongated circles may consist of a single elongated circle or a nested combination of two or three elongated circles. Furthermore, the laser welding apparatus 20 may irradiate the end face of the first conductor portion 11A and the end face of the second conductor portion 11B with laser light 21 once, twice, or three times.

[0043] The laser beam 21 irradiation in the intermediate irradiation step melts the bank portion of the first conductor portion 11A on the second conductor portion 11B side and the bank portion of the second conductor portion 11B on the first conductor portion 11A side, thereby connecting the pair of molten pools 33 to form a single molten pool 33 .

[0044] Figure 8 FIG shows an irradiation trajectory according to a variation of the intermediate stage irradiation step. Figure 8 As shown, the laser welding device 20 can irradiate the joint-side region 32 of the end face of each conductor portion 11 with laser light 21, thereby continuously drawing circles of the same size while moving in one direction. In this way, the laser welding device 20 irradiates the joint-side region 32 with laser light 21 while weaving the laser light 21 in a circular shape, which can effectively melt the bank portion of the end face joint-side region 32.

[0045] like Figure 3As shown in FIG. 1 , in this embodiment, the laser welding device 20 irradiates the end face of the first conductor portion 11A with the laser beam 21 earlier than the end face of the second conductor portion 11B, which is located at a higher position than the end face of the second conductor portion 11B. Figure 4 As shown in (C), the bank of the first conductor portion 11A melts earlier than the bank of the second conductor portion 11B, and the molten pool 33 of the first conductor portion 11A flows toward the molten pool 33 of the second conductor portion 11B. Thus, during the intermediate irradiation step, the molten pool 33 of the first conductor portion 11A, which has a higher end surface, flows toward the molten pool 33 of the second conductor portion 11B, which has a lower end surface. This prevents the molten pool 33 from flowing into the gap g between the conductor portions 11.

[0046] like Figure 4 As shown in (D), in the later stage irradiation step, the laser welding device 20 irradiates the entire end surface composed of the end surface of the first conductor portion 11A and the end surface of the second conductor portion 11B with laser light 21 in a substantially circular shape, thereby forming the pair of connected molten pools 33 into a hemispherical molten ball 34. When the molten ball 34 cools and solidifies, the first conductor portion 11A and the second conductor portion 11B are joined to each other.

[0047] In the later stage irradiation step, the laser welding device 20 irradiates the molten ball 34 with laser light 21 to such an extent that the first conductor portion 11A and the second conductor portion 11B are hidden by the molten ball 34 when viewed from above. Therefore, the conductor portion 11 is reliably welded by the molten ball 34, which is larger than the cross-section of the conductor portion 11.

[0048] As described above, the conductor joining method of this embodiment includes an initial irradiation step, an intermediate irradiation step, and a final irradiation step. Therefore, even when a gap g and a height difference ΔH exist between the distal ends of the conductor portions 11 of a pair of flat wires 8 after the film 12 has been peeled off, the molten ball 34 can be grown to an appropriate size without falling. This allows for reliable and cost-effective joining of the conductor portions 11.

[0049] While specific embodiments have been described above, the present invention is not limited to the above embodiments or variations and is capable of various modifications. For example, in the above embodiment, in both the initial irradiation step and the intermediate irradiation step, the laser welding device 20 irradiates the end face of the first conductor portion 11A with laser light 21 before irradiating the end face of the second conductor portion 11B with laser light 21. In another embodiment, in at least one of the initial irradiation step and the intermediate irradiation step, the laser welding device 20 may irradiate the end face of the second conductor portion 11B with laser light 21 earlier. Furthermore, the laser welding device 20 may be equipped with two laser heads 23 to simultaneously irradiate the end faces of the first conductor portion 11A and the second conductor portion 11B with laser light 21. Furthermore, the structure, arrangement, number, and materials of various components or parts, as well as the specific methods, numerical values, and trajectory shapes of various steps, may be appropriately modified without departing from the spirit of the present invention. Furthermore, some or all of the structures of the above embodiments and their variations may be combined. Furthermore, not all of the components shown in the above embodiments are required and may be selectively employed as appropriate.

Claims

1. A conductor joining method for joining a first conductor and a second conductor by laser welding, the conductor joining method comprising: an initial stage irradiation step of irradiating an inner region of an end face of each of the first conductor and the second conductor with a laser to form a pair of molten pools arranged side by side on the end faces of the first conductor and the second conductor in such a manner that a bank is formed on the outer periphery of each end face; an intermediate stage irradiation step of irradiating the end surfaces of the first conductor and the second conductor with the laser light so that the pair of molten pools are connected to each other at a side of a joint portion close to each other; and In the later-stage irradiation step, the laser is irradiated in a substantially circular shape onto the entire end surface composed of the end surfaces of the first conductor and the second conductor to form the pair of connected molten pools into a hemispherical molten ball.

2. The conductor bonding method according to claim 1, wherein: In the initial stage irradiation step, the inner area is irradiated with the laser light while weaving the laser light in a circular manner.

3. The conductor bonding method according to claim 1 or 2, wherein: When the end face of the first conductor is located at a higher position than the end face of the second conductor, in the intermediate-stage irradiation step, the joint-side region of the first conductor is irradiated with the laser earlier than the joint-side region of the second conductor, so that the molten pool of the first conductor flows toward the molten pool of the second conductor.

4. The conductor bonding method according to claim 1 or 2, wherein: In the later-stage irradiation step, the molten sphere is irradiated with the laser light to such an extent that the first conductor and the second conductor are hidden by the molten sphere in a plan view.

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