Laser welding method and method for manufacturing rotary electrical machine

Abstract

A laser welding method according to an embodiment comprises: a step for irradiating alternately an end portion of a first linear member and an end portion of a second linear member adjacent to the first linear member with laser light to form a first molten pool spreading over the end portion of the first linear member and the end portion of the second linear member; and a step for irradiating the first molten pool with the laser light. In the step for irradiating the first molten pool with the laser light, the center side of the first molten pool is set as a starting point of the irradiation of the laser light, and, as the irradiation position of the laser light rotates around the starting point, the irradiation position of the laser light gradually moves away from the starting point, or moves away from the starting point step-by-step.

Description

Laser welding method and manufacturing method for rotating electric machine

[0001] An embodiment of the present invention relates to a laser welding method and a method for manufacturing a rotating electric machine.

[0002] For example, a technique has been proposed in which two linear members are arranged side by side and an end of one linear member and an end of the other linear member adjacent thereto are irradiated with laser light to weld the ends of the two linear members. In this case, if there is a gap between the ends of the two linear members, the laser light may leak from the gap. If the laser light leaks from the gap between the ends, the laser light may be incident on, for example, a coating provided on the side of the linear member or on a member provided near the linear member. If the laser light is incident on the coating or the member, the laser light may damage them.

[0003] Therefore, a technique has been proposed in which the ends of the two linear members are individually irradiated with laser light, which prevents the laser light from entering the coating or the member through the gap between the ends of the linear members.

[0004] However, it was found that this laser beam trajectory was not very effective in suppressing the occurrence of blowholes in welded parts. When blowholes occur, the tensile strength of the welded part decreases, thereby reducing the reliability of the joint. Furthermore, because blowholes are not formed intentionally, the size, number, and location of the blowholes are random. This tends to lead to large variations in the quality of the welded parts. Therefore, there was a need for the development of technology that can suppress the occurrence of blowholes in welded parts.

[0005] JP 2018-20340 A International Publication No. 2019 / 159737

[0006] An object of the present invention is to provide a laser welding method and a method for manufacturing a rotating electric machine that can suppress the occurrence of blowholes in a welded portion.

[0007] The present invention relates to a laser welding method, and more particularly to a method for welding a welded portion of a weld metal, the method comprising: a step of alternately irradiating an end of a first linear member and an end of a second linear member adjacent to the first linear member with a laser beam to form a first molten pool spanning the end of the first linear member and the end of the second linear member; and a step of irradiating the first molten pool with the laser beam. In the step of irradiating the first molten pool with the laser beam, the center of the first molten pool is set as a starting point for irradiation with the laser beam, and the irradiation position of the laser beam moves gradually away from the starting point as it revolves around the starting point, or moves away in stages from the starting point.

[0008] FIG. 1 is a schematic perspective view illustrating a stator. FIG. 2 is a schematic view illustrating a segment before being attached to a core. FIG. 3 is a schematic view illustrating a coil attached to a core. FIG. 4 is a schematic view illustrating the formation of a molten pool. FIG. 5 is a schematic view illustrating the movement path of the irradiation position of laser light. FIG. 6 is a schematic view illustrating the movement path of the irradiation position of laser light. FIG. 7 is a schematic view illustrating the movement path of the irradiation position of laser light according to another embodiment. FIG. 8 is a schematic view illustrating the movement path of the irradiation position of laser light according to another embodiment. (a) and (b) are photographs of the cut surface of the boundary between the ends of two conductor portions and the welded portion. (b) are photographs of the cut surface of the boundary between the ends of two conductor portions and the welded portion.

[0009] The laser welding method according to this embodiment can be used to weld together the ends of linear members arranged side by side. For example, a rotating electric machine such as a motor or a generator has a coil wound around a core. In recent years, after inserting multiple segments into a slot, a laser beam is irradiated onto the end of one segment and the end of an adjacent segment to weld them together, thereby forming a coil wound around the core. Therefore, the following describes, as an example, a method for manufacturing a stator, along with the laser welding method according to this embodiment. That is, the present invention can be applied to a method for manufacturing a rotating electric machine. Furthermore, to illustrate a method for manufacturing a stator, a linear member having a rectangular cross-sectional shape is exemplified. However, the present invention can also be applied to, for example, a linear member having a polygonal cross-sectional shape.

[0010] In addition, in this specification, the movement path of the laser beam irradiation position is the movement path along which the center of the laser spot moves when the laser beam is irradiated, and is the movement path along which the center of the laser spot moves when the laser beam irradiation is stopped, assuming that the laser spot is formed. For example, the movement path of the laser beam irradiation position can be determined in advance. Data on the predetermined movement path is stored, for example, in a controller of the laser welding device, and is used when executing the laser welding method described below. The movement path of the laser beam irradiation position will be described later.

[0011] Hereinafter, an embodiment will be illustrated with reference to the drawings. In each drawing, similar components are denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate. First, a stator 1 will be illustrated. FIG. 1 is a schematic perspective view illustrating the stator 1. As shown in FIG. 1, the stator 1 is provided with a core 2 and a coil 3.

[0012] The core 2 is, for example, formed by stacking multiple annular magnetic members in the axial direction of the stator 1 (Z direction in FIG. 1 ). The magnetic members are formed, for example, from electromagnetic steel plates (silicon steel plates). The core 2 includes a yoke 21 and multiple teeth 22. The yoke 21 is cylindrical and located on the outer periphery of the core 2. The multiple teeth 22 are provided at equal intervals on the inner circumferential surface of the yoke 21. Each of the multiple teeth 22 protrudes from the inner circumferential surface of the yoke 21 toward the center of the core 2 and extends in the axial direction of the stator 1. Grooves provided between the teeth 22 serve as slots 23. The shape, number, and size of the teeth 22 are not limited to those illustrated and can be changed as appropriate depending on the application, size, specifications, etc. of the rotating electric machine in which the stator 1 is installed.

[0013] The coil 3 includes a plurality of segments 31. FIG. 2 is a schematic diagram illustrating the segments 31 before they are attached to the core 2. As shown in FIG. 2, the segments 31 include a conductor portion 31a (which corresponds to an example of a first linear member and a second linear member) and an insulating film 31b. The conductor portion 31a before being attached to the core 2 may have a generally U-shaped appearance. The conductor portion 31a is formed from a material with high conductivity. The conductor portion 31a is formed from, for example, so-called pure copper or a material primarily composed of copper. The conductor portion 31a may also be formed from a rectangular wire. The rectangular wire is a linear member with a square cross section. The cross-sectional dimensions of the rectangular wire may be, for example, approximately 1 mm to 4 mm.

[0014] The insulating film 31b covers the outer surface of the conductor portion 31a. However, the insulating film 31b is not provided near both ends of the conductor portion 31a, so that the conductor portion 31a is exposed. The insulating film 31b includes, for example, enamel.

[0015] Fig. 3 is a schematic diagram illustrating the coil 3 attached to the core 2. As shown in Fig. 3, the segment 31 is provided inside the slot 23. Both ends of the segment 31 protrude from one end of the core 2. The portion of the segment 31 protruding from one end of the core 2 extends in a direction approaching the adjacent segment 31.

[0016] Furthermore, the vicinity of the portion of the conductor portion 31a exposed from the insulating film 31b extends in the axial direction (Z direction in FIG. 3 ) of the core 2. In the circumferential direction of the core 2 (direction around the central axis of the core 2), the portion of the conductor portion 31a exposed from the insulating film 31b overlaps the portion of the adjacent conductor portion 31a exposed from the insulating film 31b.

[0017] The ends of adjacent conductor portions 31 a are laser-welded to each other. A single coil 3 is formed by connecting a plurality of segments 31 via welds 31 c.

[0018] In this case, multiple coils 3 can be arranged side by side in the radial direction of the core 2 (a direction passing through the central axis of the core 2 and perpendicular to the Z direction). For example, three coils 3 can be provided, one for the U phase, one for the V phase, and one for the W phase. The external shape, number, size, etc. of the coils 3 and the segments 31 are not limited to those shown as examples, and can be changed as appropriate depending on the application, size, specifications, etc. of the rotating electrical machine in which the stator 1 is installed. For example, four coils 3 can be arranged side by side in the radial direction of the core 2.

[0019] Next, an example of a manufacturing method for the stator 1 will be described. First, the core 2 is formed. For example, a plurality of plate-shaped magnetic members each having a yoke 21 and portions that will become a plurality of teeth 22 are formed. For example, the magnetic members are formed by punching electromagnetic steel sheets with a thickness of approximately 0.05 mm to 1.0 mm. Then, the plurality of magnetic members are stacked, and the core 2 is formed by, for example, welding or crimping the plurality of magnetic members. The core 2 can also be formed by pressure-molding a magnetic material powder and a resin binder.

[0020] Next, a plurality of segments 31 are formed as components of the coil 3. First, a paint containing enamel or the like is applied to the outer surface of the rectangular wire to form the insulating film 31b. Alternatively, rectangular wire already coated with enamel or the like may be purchased.

[0021] Next, the insulating film 31b near both ends of the conductor portion 31a is peeled off to expose the conductor portion 31a. Thereafter, the conductor portion 31a is cut to a predetermined length where the conductor portion 31a is exposed. Note that after the conductor portion 31a on which the insulating film 31b is formed is cut to a predetermined length, the insulating film 31b near both ends of the cut portion may be peeled off. Alternatively, peeling off the insulating film 31b and cutting the conductor portion 31a may be performed simultaneously.

[0022] 2, the conductor portion 31a, the vicinity of both ends of which are exposed from the insulating film 31b, is bent into a substantially U-shape to form the conductor portion 31a. In this manner, a plurality of segments 31 can be formed.

[0023] Next, as shown in Fig. 3, each of the multiple segments 31 is mounted in a predetermined slot 23 of the core 2. For example, each of the multiple segments 31 is inserted into a predetermined slot 23 from the axial direction of the core 2 (Z direction in Fig. 1). At this time, one segment 31 is inserted across multiple slots 23. The coil 3 according to this embodiment can be a so-called distributed winding coil. The coil 3 according to this embodiment can also be a so-called wave winding coil.

[0024] Next, as shown in Figure 3, the portion of each segment 31 protruding from the core 2 is bent toward the adjacent segment 31. The conductor portion 31a is then bent in the axial direction of the core 2 (the Z direction in Figure 3) near the portion exposed from the insulating film 31b. In the circumferential direction of the core 2, the portion of the conductor portion 31a exposed from the insulating film 31b is made to overlap the portion of the adjacent conductor portion 31a exposed from the insulating film 31b. By repeating the above procedure, multiple sets of segments 31 lined up in the circumferential direction of the core 2 are provided in the radial direction of the core 2.

[0025] Although the above example illustrates a case where the bending process is performed after the multiple segments 31 are installed in the slots 23, the present invention is not limited to this. For example, the multiple segments 31 can be bent and then each of the multiple bent segments 31 can be installed in a predetermined slot 23. In this case, the bent segments 31 can be installed from the inside to the outside of the core 2. Also, a cylindrical insulating cover can be provided inside the core 2 in which the multiple segments 31 are installed to close the openings of the slots 23.

[0026] Next, the ends of adjacent segments 31 (conductor portions 31 a) are welded together to form multiple coils 3 mounted in the slots 23. When welding, a jig can be used to bring the ends of adjacent conductor portions 31 a closer to each other. For example, a jig can be used that includes an annular member provided on the inside of multiple segments 31 arranged circumferentially around the core 2 and an annular member provided on the outside of the multiple segments 31. When the annular member provided on the inside of the multiple segments 31 is attached, one end of each of the multiple conductor portions 31 a is pressed toward the outside of the core 2. When the annular member provided on the outside of the multiple segments 31 is attached, the other end of each of the multiple conductor portions 31 a is pressed toward the inside of the core 2. Therefore, the jig moves the ends of adjacent conductor portions 31 a toward each other. The jig also holds the multiple conductor portions 31 a.

[0027] The configuration of the jig is not limited to the example shown. Any jig may be used as long as it can bring the ends of adjacent conductor portions 31a close to each other. Welding can also be performed without using a jig. However, using a jig can improve the quality of the welded portion 31c and the workability of the welding work.

[0028] The ends of adjacent conductor portions 31a can be welded together by irradiating the ends of the conductor portions 31a with laser light. That is, the ends of adjacent conductor portions 31a can be laser-welded together.

[0029] Laser welding can be performed using laser light in the infrared region or shorter wavelengths in the blue to green range. Laser light with a wavelength in the infrared region makes it easy to irradiate with a relatively high output. For example, the output of the laser light can be about 4 kW.

[0030] The laser welding device used to weld the end of the conductor portion 31a may be, for example, a fiber laser welding device or a disk laser welding device. The laser welding device is preferably a continuous wave laser (CW) welding device capable of continuously emitting laser light. The laser welding device is also capable of moving the irradiation position of the laser light. For example, the laser welding device may be equipped with a galvanometer mirror or the like.

[0031] 1 and 3 are formed by welding the ends of adjacent conductor portions 31a together. Furthermore, a single coil 3 is formed by connecting a plurality of segments 31 (conductor portions 31a) in series. Furthermore, a plurality of coils 3 are formed that are arranged in the radial direction of the core 2. For example, three coils 3, one for a U phase, one for a V phase, and one for a W phase, can be formed.

[0032] Next, resin or the like is applied to the exposed portions of the coils 3 where the conductor portions 31a are exposed to insulate them. Next, the multiple coils 3 are fixed to the core 2. For example, varnish is dripped into the gaps between the slots 23 and the coils 3, and the varnish is allowed to harden to fix the coils 3 to the core 2. In this manner, the stator 1 can be manufactured.

[0033] If there is a gap between the ends of adjacent conductor portions 31a, the laser light may pass through the gap and be incident on the insulating film 31b of the segment 31 or on a member provided near the segment 31. If the laser light is incident on the insulating film 31b or the member, the insulating film 31b or the member may be damaged by the laser light.

[0034] In this case, the use of the aforementioned jig can reduce the gap between the ends of adjacent conductor portions 31 a. However, the ends of the conductor portions 31 a have variations in size, shape, and deformation. Therefore, even if the jig is used, it is difficult to eliminate the gap between the ends of adjacent conductor portions 31 a.

[0035] Furthermore, if the laser beam is irradiated separately onto each of the two ends of the adjacent conductors 31 a, it is possible to prevent the laser beam from passing through the gap and entering the insulating film 31 b or the other components. However, this increases the likelihood of blowholes occurring in the welded portion 31 c and also increases the welding time.

[0036] Therefore, in the laser welding method according to the present embodiment, the ends of adjacent conductor portions 31a are welded together as follows.

[0037] First, laser light is alternately irradiated onto the end of the conductor portion 31a and the end of the conductor portion 31a adjacent to the conductor portion 31a, to form a molten pool 101 (corresponding to an example of a first molten pool) spanning the end of one conductor portion 31a and the end of the other conductor portion 31a.

[0038] 4 is a schematic diagram illustrating the formation of the molten pool 101. While Fig. 4 illustrates the case where the gap 31a1 is formed between the ends of the conductors 31a, the same can be achieved when the ends of the conductors 31a are in contact with each other (when there is no gap 31a1) by using the jig described above, for example.

[0039] As shown in Figure 4, a laser beam is alternately irradiated onto an end of one conductor portion 31a and an adjacent end of the other conductor portion 31a. By alternately irradiating the laser beam, the ends of the two conductor portions 31a are melted, forming two molten pools 101a and 101b (which correspond to examples of a second molten pool and a third molten pool). As the melting of the ends of the two conductor portions 31a progresses, the molten pools 101a and 101b gradually increase in size. As the molten pools 101a and 101b increase in size, they merge to form a molten pool 101 spanning the two ends. At this time, the opening of the gap 31a1 is covered by the molten pool 101.

[0040] In this case, the laser beam can be irradiated, for example, by the following procedure. First, as shown in Fig. 4, the end of one of the conductor portions 31a is irradiated with laser beam along a loop-shaped movement path 100 of the laser beam irradiation position. Next, the laser beam irradiation is stopped, and the laser beam irradiation position is moved from the end of one of the conductor portions 31a to the end of the other conductor portion 31a along a linear movement path 100b of the laser beam irradiation position.

[0041] Next, the irradiation of the laser light is resumed at the end of the other conductor portion 31a, and the laser light is irradiated along the loop-shaped movement path 100 of the laser light irradiation position. Next, the irradiation of the laser light is stopped, and the laser light irradiation position is moved from the end of the other conductor portion 31a to the end of one conductor portion 31a along the linear movement path 100b of the laser light irradiation position. The movement of the laser light irradiation position can be performed, for example, by a galvanometer mirror provided in the laser welding device.

[0042] As described above, in the process of forming the molten pool 101 spanning the two ends, the laser beam irradiation is stopped when the laser beam irradiation position is moved from one end to the other end. Therefore, even if a gap 31 a 1 is formed between the ends, the laser beam can be prevented from entering the insulating film 31 b or the component through the gap 31 a 1.

[0043] Furthermore, by repeating the above-described procedure multiple times, molten pools 101a and 101b are formed at each of the two ends. As the melting of the two ends progresses, the molten pools 101a and 101b gradually increase in size, and the molten pools 101a and 101b combine to form the molten pool 101 that spans the two ends. At this time, the opening of the gap 31a1 is covered by the molten pool 101.

[0044] In this case, the loop-shaped movement path 100 of the irradiation position may have the same shape and size, or may have different shapes and / or sizes.

[0045] For example, if the cross-sectional shapes and cross-sectional dimensions of adjacent linear members (conductor portions 31 a) are the same, the shape and size of the movement path 100 can be the same. For example, if the cross-sectional shapes and / or cross-sectional dimensions of adjacent linear members are different, the shape and / or size of the movement path 100 can be different.

[0046] Furthermore, there are no particular limitations on the shape of the movement path 100. The shape of the movement path 100 can be a shape composed of curves such as a circle or an ellipse, a shape composed of curves and straight lines as exemplified in FIG. 4, or a shape composed of straight lines such as a polygon such as a rectangle. However, if the shape of the movement path 100 has corners, sputtering is likely to occur when the corners of the movement path 100 are irradiated with laser light. Therefore, it is preferable that the shape of the movement path 100 be a shape composed of curves or a shape composed of curves and straight lines.

[0047] There is no particular limitation on the size of the movement path 100 of the loop-shaped irradiation position. However, as illustrated in Fig. 4, it is preferable that the shortest distance L between the outer edge of the laser spot 100a and the outer edge of the end of one conductor 31a is constant at the end of one conductor 31a. It is also preferable that the shortest distance L between the outer edge of the laser spot 100a and the outer edge of the end of the other conductor 31a is constant at the end of the other conductor 31a.

[0048] Furthermore, when moving from the loop-shaped movement path 100 of the irradiation position at the end of one conductor portion 31a to the loop-shaped movement path 100 of the irradiation position at the end of the other conductor portion 31a, for example, as shown in Fig. 4, a pair of linear movement paths 100b of the irradiation position can be provided that connect the loop-shaped movement path 100 of the irradiation position at the end of one conductor portion 31a and the loop-shaped movement path 100 of the irradiation position at the end of the other conductor portion 31a in the direction in which the ends of adjacent conductor portions 31a are aligned. The movement path 100b can be a straight line (common circumtangent) that is tangent to the two loop-shaped movement paths 100. The irradiation of the laser light is stopped at the movement path 100b of the irradiation position.

[0049] Furthermore, the heating of the end of the conductor portion 31a is performed along the movement path 100. Therefore, even if the laser light irradiation is stopped and then resumed at a position away from the outer edge of the end of the conductor portion 31a in the direction in which the ends of adjacent conductor portions 31a are aligned, heating of the end of the conductor portion 31a is not suppressed. For example, in the direction in which the ends of adjacent conductor portions 31a are aligned, the position at which the laser light irradiation is stopped can be approximately the center of the end of one conductor portion 31a, and the position at which the laser light irradiation is resumed can be approximately the center of the end of the other conductor portion 31a. Therefore, even if the ends of the conductor portions 31a have dimensional variations, shape variations, or deformations, or even if the dimensions of the gap 31a1 vary, irradiation of the laser light into the gap 31a1 can be effectively suppressed.

[0050] Furthermore, as shown in Figure 4, if the shortest distance L between the outer edge of the laser spot 100a and the outer edge of the end of the conductor portion 31a is made constant, irradiation of the gap 31a1 with laser light can be more effectively suppressed.

[0051] Furthermore, if the loop-shaped movement path 100 of the irradiation position has the same shape and size at each end of adjacent conductor portions 31a, the control program for irradiating the laser light can be simplified.

[0052] Furthermore, if the movement path 100b of the irradiation position is a straight line (common external tangent) tangent to the two loop-shaped movement paths 100 of the irradiation position, linear movement is possible from one movement path 100 of the irradiation position to the other movement path 100 of the irradiation position. Therefore, it is possible to shorten the movement time from one movement path 100 of the irradiation position to the other movement path 100 of the irradiation position, and ultimately to shorten the takt time.

[0053] When laser light is applied to form the two molten pools 101a and 101b, gas (e.g., air) near the ends of the conductor 31a is entrained within the molten pools 101a and 101b. Even if the molten pools 101a and 101b merge to form a molten pool 101 spanning the two ends, the entrained gas remains within the molten pool 101. If gas remains within the molten pool 101, blowholes will form within the welded portion 31c when the molten pool 101 cools and the welded portion 31c is formed. The occurrence of blowholes reduces the tensile strength of the welded portion 31c, thereby reducing the reliability of the joint. Furthermore, because blowholes are not formed intentionally, the size, number, and location of the blowholes are random. This can lead to significant variations in the quality of the welded portion 31c.

[0054] Next, the molten pool 101 is irradiated with a laser beam to expel the gas contained within the molten pool 101 to the outside. Figures 5 and 6 are schematic diagrams illustrating the movement path of the laser beam irradiation position. First, as shown in Figures 5 and 6, the center of the molten pool 101 is set as the starting point 31d of the laser beam irradiation. The starting point 31d of the laser beam irradiation can be set at a position between the end of one conductor portion 31a and the end of the other conductor portion 31a (e.g., the center of the gap 31a1). As described above, the opening of the gap 31a1 is covered by the molten pool 101. Therefore, since the laser beam is irradiated onto the molten pool 101, even if the starting point 31d is located above the gap 31a1, the laser beam can be prevented from irradiating the insulating film 31b, etc., through the gap 31a1. The end point of the laser light irradiation can be set to the position of an end of one of the conductor portions 31a or the position of an end of the other conductor portion 31a.

[0055] Next, the laser beam irradiation position is moved. In this case, as shown in Fig. 5 , the laser beam irradiation position can be configured to gradually move away from the starting point 31d as it revolves around the starting point 31d. In this case, the shape of the movement path 102 of the laser beam irradiation position can be configured to be a shape composed of a curve that gradually moves away from the starting point 31d as it revolves around the starting point 31d. For example, as shown in Fig. 5 , the shape of the movement path 102 of the laser beam irradiation position can be configured to be a spiral line.

[0056] 6, the shape of the movement path 102a of the laser beam irradiation position can be a shape made up of straight lines that gradually move away from the starting point 31d as the laser beam rotates around the starting point 31d. For example, as shown in FIG. 6, the shape of the movement path 102a of the laser beam irradiation position can be a square spiral line.

[0057] The shape of the path of movement of the laser light irradiation position may also be a shape made up of curves and straight lines that gradually moves away from the starting point 31d as it circles around the starting point 31d.

[0058] That is, the irradiation position of the laser beam may be gradually moved away from the starting point 31d as the laser beam rotates around the starting point 31d. However, as described above, if the shape of the movement path has corners, spattering is likely to occur when the laser beam is irradiated at the corners of the movement path. Therefore, it is preferable that the shape of the movement path be a shape consisting of curves or a shape consisting of curves and straight lines.

[0059] Furthermore, there is no particular limitation on the direction of rotation of the movement path, and the direction of rotation may be, for example, clockwise or counterclockwise.

[0060] If the shape of the path of movement of the laser beam irradiation position is such that it gradually moves away from the starting point 31d as it revolves around the starting point 31d, a flow can be formed inside the molten pool 101 that moves from the center to the periphery. This allows the gas contained inside the molten pool 101 to be discharged to the outside of the molten pool 101.

[0061] Furthermore, the flow inside the molten pool 101 (flow from the center to the periphery) and the impact of the incident laser beam can push the molten pool 101 outward, so that the molten pool 101, and thus the welded portion 31c, can be formed over almost the entire area of ​​the ends of the two conductors 31a.

[0062] 7 and 8 are schematic diagrams illustrating movement paths of the laser beam irradiation position according to another embodiment. As shown in FIG. 7, the shape of the movement path 102b of the laser beam irradiation position can be a plurality of circles whose size increases stepwise. For example, the shape of the movement path 102b can be concentric circles centered on the starting point 31d. In this case, the irradiation position is moved sequentially from the movement path 102b closest to the starting point 31d to the movement path 102b adjacent to the movement path 102b on the outside of the movement path 102b.

[0063] As shown in Fig. 8, the shape of the movement path 102c of the laser light irradiation position can be a plurality of polygons whose size increases stepwise. For example, the shape of the movement path 102b can be a concentric polygon centered on the starting point 31d. The shape of the movement path 102c illustrated in Fig. 8 is a concentric quadrilateral centered on the starting point 31d. In this case, the irradiation position is moved sequentially from the movement path 102c closest to the starting point 31d to the movement path 102c adjacent to the movement path 102c on the outside of the movement path 102c.

[0064] Although the movement path has been exemplified as having multiple circles and multiple polygons, the shape of the movement path may be a shape consisting of curves, a shape consisting of straight lines, or a shape consisting of curves and straight lines. However, as mentioned above, in order to suppress the generation of spatter, it is preferable that the shape of the movement path has no corners. Furthermore, there is no particular limitation on the rotation direction of the movement path. The rotation direction may be, for example, clockwise or counterclockwise.

[0065] As described above, the irradiation position of the laser beam may be gradually moved away from the starting point 31d as it rotates around the starting point 31d. This configuration can also achieve the same effects as those described above. That is, a flow from the center to the periphery can be formed within the molten pool 101, allowing gas contained within the molten pool 101 to be expelled to the outside. Furthermore, the molten pool 101 can be expanded outward, allowing the molten pool 101, and therefore the welded portion 31c, to be formed over almost the entire area of ​​the ends of the two conductors 31a.

[0066] 9(a) and 9(b) are photographs of the cross section of the boundary between the ends of the two conductors 31a and the weld 31c. Figures 9(a) and 9(b) show the case where, after the molten pool 101 was formed, the process of venting the gas contained within the molten pool 101 to the outside of the molten pool 101 was not performed. As can be seen from Figures 9(a) and 9(b), blowholes have occurred within the weld 31c. This reduces the tensile strength of the weld 31c, thereby reducing the reliability of the joint. Furthermore, the size, number, and location of the blowholes are random. This tends to result in significant variation in the quality of the weld 31c.

[0067] Figure 10 is a photograph of a cross section of the boundary between the ends of the two conductors 31a and the weld 31c. Figure 10 shows a case where, after the formation of the molten pool 101, a process of discharging gas contained within the molten pool 101 to the outside of the molten pool 101 is performed. As can be seen from Figure 10, by performing the process of discharging gas contained within the molten pool 101 to the outside of the molten pool 101, the occurrence of blowholes within the weld 31c can be suppressed. This suppresses a decrease in the tensile strength of the weld 31c, thereby improving the reliability of the joint. Furthermore, it also reduces variation in the quality of the weld 31c.

[0068] Although several embodiments of the present invention have been described above, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other.

[0069] REFERENCE SIGNS LIST 1 stator 2 core 3 coil 31 segment 31a conductor portion 31a1 gap 31b insulating film 31c welded portion 31d starting point of irradiation 100 movement path 100b movement path 102 movement path 102a movement path 102b movement path 102c movement path 101 molten pool 101a molten pool 101b molten pool

Claims

1. A laser welding method comprising the steps of: alternately irradiating an end of a first linear member and an end of a second linear member adjacent to the first linear member with laser light to form a first molten pool spanning the end of the first linear member and the end of the second linear member; and irradiating the first molten pool with the laser light, wherein, in the step of irradiating the first molten pool with the laser light, the center side of the first molten pool is set as a starting point for irradiation with the laser light, and the irradiation position of the laser light gradually moves away from the starting point as it revolves around the starting point, or moves away from the starting point in stages.

2. A laser welding method as described in claim 1, wherein in the process of forming the first molten pool, a second molten pool formed at the end of the first linear member and a third molten pool formed at the end of the second linear member combine to form the first molten pool.

3. A laser welding method as described in claim 1 or 2, wherein in the process of irradiating the first molten pool with the laser light, the shape of the movement path of the irradiation position of the laser light is a spiral line.

4. A laser welding method as described in claim 1 or 2, wherein, in the process of irradiating the first molten pool with the laser light, the shape of the movement path of the irradiation position of the laser light is a plurality of circles whose size increases stepwise, or a plurality of polygons whose size increases stepwise.

5. A laser welding method as described in claim 1 or 2, wherein in the process of irradiating the first molten pool with the laser light, the starting point of the irradiation of the laser light is a position between an end of the first linear member and an end of the second linear member, and the end point of the irradiation of the laser light is the position of the end of the first linear member or the position of the end of the second linear member.

6. A laser welding method as described in claim 1 or 2, wherein in the process of irradiating the first molten pool with the laser light, gas contained in the first molten pool is discharged to the outside of the first molten pool.

7. A method for manufacturing a rotating electric machine, comprising the step of providing a coil in a plurality of slots, the coil including a plurality of segments, and in the step of providing the coil, ends of conductor portions of the plurality of segments are welded by the laser welding method described in claim 1 or 2.

Images