Conductor joining 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 method for joining conductors, and more particularly to a 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 society or a decarbonized society have been active, and in vehicles as well, research and development on electrification technologies have been conducted in order to reduce CO2 emissions and improve energy efficiency. In order to popularize electric vehicles, it is important to reduce the manufacturing cost of electric motors (motors and / or generators) and improve energy efficiency.

[0003] In order to reduce costs and improve energy efficiency, rectangular wires may be used for the coils wound around the stator core of an electric motor. In order to wind the rectangular wires around the teeth, the coatings on the tip portions of a pair of rectangular wires inserted into the slots between the teeth are peeled off, and the tip portions of the conductors of the pair of exposed rectangular wires are joined by laser welding using laser beam irradiation.

[0004] As such a joining method, Patent Document 1 discloses that when irradiating the end faces of the first and second rectangular wires with a laser beam, within the end face of the first rectangular wire, the laser beam is scanned in a loop shape to form a molten pool, and within the end face of the first rectangular wire, the diameter of the loop-shaped locus along which the laser beam is scanned is increased, and the molten pool is made to reach the butting surface between the end side faces. Thereby, the gap between the butting surfaces can be filled with the molten pool without irradiating the butting surface with the laser beam, and it is possible to suppress the laser beam from entering the gap and damaging the insulating coating of the rectangular wire.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] However, the method described in Patent Document 1 assumes that the end faces of the first and second rectangular wires to be joined are the same height and that the gap between the abutting surfaces of the end faces is small. On the other hand, since the first and second rectangular wires are bent to bring their ends closer together after being inserted into the corresponding slots, the heights of the end faces may be misaligned. High processing precision is required to make the heights of the end faces the same, which leads to increased 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 rectangular wires at low cost, even if there is a difference in height between the joining end faces of the two rectangular wires. [Means for solving the problem]

[0008] To solve the above problems, 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 step of irradiating the inner regions (31) of the end faces of the first conductor and the end faces of the second conductor with laser light to form a pair of molten pools (33) parallel to the end faces of both conductors such that the outer periphery of each end face forms a dike; an intermediate irradiation step of irradiating the joining-side regions (32) of the end faces of the first conductor and the end faces of the second conductor, which are close to each other, with laser light to connect the pair of molten pools; and a late irradiation step of irradiating the overall end face formed by the end faces of the first conductor and the end faces of the second conductor with laser light in a substantially circular shape to form the pair of molten pools connected to each other into a hemispherical molten ball (34).

[0009] According to this embodiment, the conductor joining method comprises an initial irradiation step, a mid-term irradiation step, and a late irradiation step. This allows the molten ball to grow to an appropriate size without falling, even if there is a height difference between the tips of the conductors of a pair of flat wires from which the coating has been removed. Therefore, it is possible to reliably join the two conductors at low cost.

[0010] In the above embodiment, it is preferable to irradiate the inner region with laser light while weaving it in a loop shape during the initial irradiation step.

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

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

[0013] According to this embodiment, by allowing the molten pool of the first conductor with the higher end face to flow into the molten pool of the second conductor with the lower end face, the flow of the molten pool into the gap between the two conductors is suppressed.

[0014] In the above embodiment, it is preferable to irradiate the molten ball with laser light in the later irradiation step such that the first conductor and the second conductor are obscured by the molten ball in a plan view.

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

[0016] According to the above embodiment, a conductor joining method can be provided 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 drawing]

[0017] [Figure 1] Cross-sectional view of a stator during the manufacturing process of a rotating electrical machine according to an embodiment [Figure 2] Perspective view of a pair of flat angle wires after bending [Figure 3] Diagram schematically showing the state of joining of flat angle wires [Figure 4] Explanatory diagram of the joining method according to an embodiment [Figure 5] Explanatory diagram of the end face of a flat angle wire [Figure 6] Diagram showing the irradiation trajectory of the first modification of the initial irradiation process [Figure 7] Diagram showing the irradiation trajectory of the second modification of the initial irradiation process [Figure 8] Diagram showing the irradiation trajectory of a modification of the intermediate process

MODE FOR CARRYING OUT 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 the manufacturing process of a rotating electrical machine according to an embodiment. The conductor joining method according to the present invention is carried out when manufacturing the rotating electrical machine shown in FIG. 1. The rotating electrical machine includes a stator 1 and a rotor (not shown) rotatably disposed 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, and this axis 2X coincides with the rotation axis of the rotor. That is, the rotor is rotatably provided around the axis 2X of the stator core 2.

[0020] The stator core 2 has multiple teeth 4 extending axially (up and down in Figure 1) and facing radially inward. The teeth 4 have a T-shape, with the tip wider than the base, and are arranged at equal intervals in the circumferential direction. Between adjacent teeth 4, multiple slots 5 are formed at equal intervals in the circumferential direction, penetrating the stator core 2 in the axial direction. In addition, multiple slits 6 are formed on the inner circumferential 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 from the slits 6 formed on the inner circumferential surface of the stator core 2, widening as it goes. However, the slits 6 are not essential.

[0021] Coil 3 is obtained by joining multiple segment coils 7 by laser welding. Segment coils 7 are obtained by bundling multiple coil elements (conductive wires) and forming them into a roughly U-shape. Flat rectangular wires 8 with a rectangular cross-section are used for the coil elements. The flat rectangular wire 8 comprises a linear conductor portion 11 (Figure 2) made of a conductor such as copper, and a coating 12 (Figure 2) made of an insulator that covers the conductor portion 11. Multiple segment coils 7 are inserted into slots 5 along the axis 2X of the stator core 2 in a ring-shaped arrangement while overlapping in the circumferential direction.

[0022] Figure 2 is a perspective view of a pair of rectangular wires 8 after bending. Note that Figure 2 shows the portion of the rectangular wires 8 protruding from the underside of the stator core 2, with the stator core 2 shown in Figure 1 inverted axially. As shown in Figure 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 being inserted into the slot 5, the ends of the rectangular wires 8 are bent circumferentially in order to be joined to the corresponding rectangular wires 8. Due to the bending process, the portion of the rectangular wire 8 protruding from the slot 5 has an inclined portion 13 that is inclined circumferentially with respect to the axis 2X of the stator core 2, and a parallel portion 14 that extends parallel to the axis 2X of the stator core 2 from the end of the inclined portion 13 and forms the end.

[0023] The ends of a pair of rectangular wires 8, which are positioned close to each other by bending, are positioned parallel and close to each other. However, due to springback in the rectangular wires 8 after bending, the ends of the rectangular wires 8 may shift circumferentially from the desired position. If left as is, the ends of the two rectangular wires 8 to be joined will be separated, making it impossible to join the two rectangular wires 8. Therefore, the two rectangular wires 8 are clamped between a clamping jig 16 having a pair of clamping bodies 15, and joined with their ends close together. For the clamping jig 16, for example, those described in the applicant's Japanese Patent Publication No. 6483079 and Japanese Patent Publication No. 6680867, or those having a similar configuration, can be used.

[0024] By using the clamping jig 16, the ends of a pair of rectangular wires 8 are aligned in the circumferential direction and positioned close to each other so as to face each other in the radial direction of the stator core 2. However, since the ends of the pair of rectangular wires 8 have a coating 12 on the lower part of the parallel section 14 and the inclined section 13, there is a small gap g (Figure 3) between the conductor sections 11. It is preferable that the end faces of the pair of rectangular wires 8 be positioned at the same height (distance from the end face of the stator core 2 along the axis 2X of the stator core 2). However, since the clamping jig 16 cannot adjust the height position of the conductor section 11, the end faces of the pair of rectangular wires 8 will be positioned at different heights with a slight difference Δh (Figure 3). The ends of the two rectangular wires 8 positioned in this way are reliably joined by joining them using the conductor joining method described later.

[0025] Next, an embodiment of a specific method for laser welding the ends of the conductor portions 11 of the rectangular wire 8 will be described. Figure 3 is a schematic diagram showing the joining of the rectangular wires 8. In this embodiment, the conductor joining method is performed using the laser welding apparatus 20 shown in Figure 3, with a pair of rectangular wires 8 placed close together with the end faces of the conductor portions 11 facing upwards. Specifically, the pair of conductor portions 11 are joined to each other by laser welding, in which the laser welding apparatus 20 irradiates the end faces of the pair of rectangular wires 8 (end faces of the conductor portions 11) with laser light 21. The conductor joining method comprises an initial irradiation step, a mid-term irradiation step, a joining step, and a final irradiation step.

[0026] The laser welding apparatus 20 includes a highly focused laser oscillator 22 capable of emitting a laser beam with a wavelength of, for example, 100 μm or less, and a galvanoscanning type laser head 23 capable of scanning the laser light 21 emitted by the laser oscillator 22 at, for example, 500 mm / second or more. The type of laser light 21 is not limited and may be a fiber laser, YAG laser, CO2 laser, semiconductor-pumped laser, etc. In the illustrated example, the laser welding apparatus 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 other embodiments, the laser welding apparatus 20 may include two laser oscillators 22 and two laser heads 23, and simultaneously irradiate the end faces of a pair of flat wires 8 with the laser light 21.

[0027] Figure 4 is an explanatory diagram of the joining method according to the embodiment. Figure 4 shows a side view, a top view, and a top image for each of the following stages: (A) before irradiation, (B) initial irradiation process, (C) mid-term irradiation process, and (D) late irradiation process. The conductor joining method is performed in the order of initial irradiation process, mid-term irradiation process, and late irradiation process. These will be explained in order below. Note that the trajectory of the laser beam 21 is shown in the top view of each irradiation process in Figure 4.

[0028] As shown in Figure 4(A), before irradiation, a pair of conductor sections 11 at the ends of the rectangular wire 8 are positioned close to each other with a gap g approximately twice the thickness of the coating 12, and with different heights of their upper end faces. Hereinafter, the conductor section 11 of the rectangular wire 8 on the right in the figure will be referred to as the first conductor section 11A, and the conductor section 11 of the rectangular wire 8 on the left will be referred to as the second conductor section 11B. When not distinguishing between the two, they may simply be referred to as conductor section 11 or both conductor sections 11, etc. The end face of the first conductor section 11A is at a higher position than the end face of the second conductor section 11B.

[0029] Now, with reference to Figure 5, the end faces of the conductor portions 11 of the rectangular wire 8 will be described. Figure 5 is an explanatory diagram of the end faces of the conductor portions 11 of the rectangular wire 8. As shown in the figure, the conductor portions 11 of the rectangular wire 8 are roughly rectangular in plan view. The inner region of each end face of the conductor portion 11 (the region enclosed by the dashed lines) is referred to as the inner region 31 in this specification. The inner region 31 does not need to extend to the outer edge of the end face. The ratio of the inner region 31 to the area of ​​the end face of the conductor portion 11 is not limited, but may be, for example, 30% to 70%.

[0030] In this specification, the area of ​​the end face of each conductor portion 11 that is to be joined to the other conductor portion 11 (the area demarcated by dashed lines and marked with hatching) is referred to as the joining-side region 32. The joining-side region 32 does not need to include the area on the opposite side of the other conductor portion 11 that is to be joined. The ratio of the joining-side region 32 to the area of ​​the end face of the conductor portion 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 that overlaps with the inner region 31.

[0031] As shown in Figure 4(B), in the initial irradiation process, the laser beam 21 is irradiated onto the inner region 31 (see Figure 5) of the end faces of both conductor portions 11. The laser welding apparatus 20, for example, 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. In the example shown in Figure 4(B), the laser welding apparatus 20 irradiates the inner region 31 of the end face of each conductor portion 11 with the laser beam 21 in a manner that continuously draws a spiral of circles of different sizes. 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 the laser beam 21 once each, or it may irradiate them two or three times each.

[0032] As a result of the irradiation by the laser beam 21 during the initial irradiation process, as shown in the side view of Figure 4(B), the ends of the first conductor portion 11A and the ends of the second conductor portion 11B melt in the inner region 31 but not in the outer region. In other words, the outer region of each conductor portion 11 acts as a barrier, and a molten pool 33 is formed in the inner region 31. In this way, a pair of molten pools 33 are formed in parallel on the end faces of both conductor portions 11.

[0033] Figure 6 shows the irradiation trajectory of the first modified example of the initial irradiation process. In Figure 6, the starting point of the laser beam 21 trajectory is indicated by a circle, and the direction of the trajectory is indicated by an arrow. As shown in Figure 6, the laser welding apparatus 20 may irradiate the inner region 31 of the end face of each conductor part 11 with the laser beam 21 so as to continuously draw circles of the same size with a slight offset. By irradiating the inner region 31 with the laser beam 21 while weaving in a loop shape, the laser welding apparatus 20 can efficiently form a molten pool 33 in the inner region 31 of the end face.

[0034] Figure 7 shows the irradiation trajectory of a second modified example of the initial irradiation process. As shown in Figure 7, the laser welding apparatus 20 may irradiate the inner region 31 of each conductor portion 11 with laser light 21 so as to continuously draw circles of the same size shifted in one direction, and then continuously draw circles of the same size shifted in the other direction. By irradiating the inner region 31 with laser light 21 in this way, the molten pool 33 can be efficiently formed in the inner region 31 of the end face.

[0035] Next, as shown in Figure 4(C), in the intermediate irradiation process, the laser beam 21 is irradiated onto the joining-side region 32 (see Figure 5) of the end faces of both conductor portions 11. The joining-side region 32 of the first conductor portion 11A is the portion of the outer periphery of the end face of the first conductor portion 11A that is on the side of the second conductor portion 11B. The joining-side region 32 of the second conductor portion 11B is the portion of the outer periphery of the end face of the second conductor portion 11B that is on the side of the first conductor portion 11A. For example, the laser welding apparatus 20 irradiates the joining-side region 32 of the end face of the first conductor portion 11A with the laser beam 21, and then irradiates the joining-side region 32 of the end face of the second conductor portion 11B with the laser beam 21.

[0036] In the example shown in Figure 4(C), the laser welding apparatus 20 irradiates the joining-side region 32 of the end face of each conductor portion 11 with laser light 21 in the manner of drawing an oval. The oval may be single, double, or triple. The laser welding apparatus 20 may also 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 each, or it may irradiate them two or three times each.

[0037] During the intermediate irradiation process, the irradiation of laser light 21 causes the embankment portion of the first conductor portion 11A on the second conductor portion 11B side and the embankment portion of the second conductor portion 11B on the first conductor portion 11A side to melt. As a result, a pair of molten pools 33 are connected to form one large molten pool 33.

[0038] Figure 8 shows the irradiation trajectory of a modified example of the mid-term irradiation process. As shown in Figure 8, the laser welding apparatus 20 may irradiate the joining-side region 32 of the end face of each conductor portion 11 with laser light 21 so as to continuously draw circles of the same size with a slight offset. By irradiating the joining-side region 32 with laser light 21 while weaving the laser light 21 in a loop shape, the dam portion of the joining-side region 32 of the end face can be efficiently melted.

[0039] As shown in Figure 3, in this embodiment, the laser welding apparatus 20 first irradiates the end face of the first conductor section 11A, which has a higher end face, with the laser beam 21. As a result, as shown in Figure 4(C), the embankment of the first conductor section 11A melts first, and the molten pool 33 of the first conductor section 11A flows into the molten pool 33 of the second conductor section 11B. In this way, during the intermediate irradiation process, by allowing the molten pool 33 of the first conductor section 11A, which has a higher end face, to flow into the molten pool 33 of the second conductor section 11B, which has a lower end face, the flow of the molten pool 33 into the gap g between the conductor sections 11 is suppressed.

[0040] As shown in Figure 4(D), in the later irradiation process, the laser welding apparatus 20 irradiates the entire end surface, which is formed by the end face of the first conductor portion 11A and the end face of the second conductor portion 11B, with laser light 21 in a substantially circular shape, forming a pair of interconnected molten pools 33 into a hemispherical molten sphere 34. As the molten sphere cools and solidifies, the first conductor portion 11A and the second conductor portion 11B are joined together.

[0041] In the later irradiation process, the laser welding apparatus 20 irradiates the molten ball 34 with laser light 21 so that the first conductor portion 11A and the second conductor portion 11B are obscured by the molten ball 34 in a plan view. As a result, both conductor portions 11 are reliably welded together by the molten ball 34, which is larger than the cross-section of both conductor portions 11.

[0042] Thus, the conductor joining method of this embodiment comprises an initial irradiation step, a mid-term irradiation step, and a late irradiation step. As a result, even if a gap g and a height difference Δh occur between the tips of the two conductor portions 11 of a pair of flat wires 8 from which the coating 12 has been peeled off, it is possible to grow the molten ball 34 to an appropriate size without causing it to fall. Therefore, it is possible to reliably join the two conductor portions 11 at low cost.

[0043] This concludes the description of specific embodiments. However, the present invention is not limited to the above embodiments or modifications and can be broadly modified and implemented. For example, in the above embodiment, in the initial irradiation process and the intermediate irradiation process, the laser welding apparatus 20 irradiates the end face of the first conductor part 11A with laser light 21, and then irradiates the end face of the second conductor part 11B with laser light 21. In other embodiments, in at least one of the initial irradiation process and the intermediate irradiation process, the laser welding apparatus 20 may irradiate the end face of the second conductor part 11B with laser light 21 first. Alternatively, the laser welding apparatus 20 may be equipped with two laser heads 23, and the laser light 21 may be irradiated simultaneously to the end face of the first conductor part 11A and the end face of the second conductor part 11B. In addition, the specific configuration, arrangement, quantity, material, etc. of each member or part, as well as the specific methods, numerical values, trajectory shapes, etc. of each procedure, can be changed as appropriate without departing from the spirit of the present invention. Furthermore, some or all of the configurations of the above embodiments and their modifications can be combined with each other. On the other hand, all of the components shown in the above embodiments are not necessarily essential and can be selected as appropriate. [Explanation of symbols]

[0044] 1: Status 2: Stator core 2X: Axis 3: Coil 4: Teeth 5: Slot 6: Slit 7: Segment coil 8: Flat rectangular wire (an example of a coil element or conductive wire) 11: Conductor part (conductor) 11A: First conductor section 11B: Second conductor section 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: Melting pool 34: Molten Ball g: gap

Claims

1. A conductor joining method in which a first conductor and a second conductor are joined by laser welding, An initial irradiation step involves irradiating the inner regions of the end faces of the first conductor and the end faces of the second conductor with laser light to form a pair of molten pools parallel to the end faces of both conductors, such that the outer periphery of each end face forms a dike. A medium-term irradiation step involves irradiating the joint-side regions of the end faces of the first conductor and the end faces of the second conductor, which are adjacent to each other, with laser light to connect a pair of molten pools, The process includes a later irradiation step in which a laser beam is irradiated in a substantially circular manner onto the overall end surface formed by the end surface of the first conductor and the end surface of the second conductor, thereby forming a pair of interconnected molten pools into a hemispherical molten ball. A conductor joining method comprising irradiating the inner region with laser light while weaving it in a loop shape during the initial irradiation step.

2. A conductor joining method in which a first conductor and a second conductor are joined by laser welding, An initial irradiation step involves irradiating the inner regions of the end faces of the first conductor and the end faces of the second conductor with laser light to form a pair of molten pools parallel to the end faces of both conductors, such that the outer periphery of each end face forms a dike. A medium-term irradiation step involves irradiating the joint-side regions of the end faces of the first conductor and the end faces of the second conductor, which are adjacent to each other, with laser light to connect a pair of molten pools, The process includes a later irradiation step in which a laser beam is irradiated in a substantially circular manner onto the overall end surface formed by the end surface of the first conductor and the end surface of the second conductor, thereby forming a pair of interconnected molten pools into a hemispherical molten ball. A conductor joining method in which the end face of the first conductor is located higher than the end face of the second conductor, and in the intermediate irradiation step, 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.

3. The conductor joining method according to claim 1 or 2, wherein in the later irradiation step, laser light is irradiated onto the molten ball such that the first conductor and the second conductor are obscured by the molten ball in a plan view.

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