Conductor joining method

Abstract

To provide a conductor joining method that can form a weld bead with suppressed void formation by a simple method, even with conductors containing copper oxide. [Solution] A conductor joining method comprising: a molten pool formation step of irradiating a welding area between conductors containing copper oxide with laser light to form a molten pool at the welding area; and a welding bead formation step of solidifying the molten pool to form a welding bead, wherein in the molten pool formation step, laser light is irradiated to form a molten pool so that the temperature of the welding area is higher than the melting point of copper and lower than the melting point of copper oxide, and the molten pool is stirred by changing the irradiation position of the laser light on the molten pool.

Description

[Technical Field]

[0001] The present invention relates to a method for joining conductors. [Background technology]

[0002] When welding conductors other than oxygen-free copper to stators and other components of rotating electric machines, there is a problem of reduced strength in the weld bead due to hydrogen embrittlement. Hydrogen embrittlement of the weld bead is caused by the formation of voids (bubbles) due to water vapor when the molten pool solidifies. The voids in the weld bead are formed when hydrogen (hydrogen ions [H]) originates from moisture contained in the welding atmosphere into the molten pool where the conductor has molten. + As oxygen (oxygen ions [O) dissolves into the molten pool, the molten pool changes from a liquid phase to a solid phase, and the solubility decreases. 2- Hydrogen embrittlement occurs when it combines with ]) to form water (water vapor) and precipitates. In particular, when recycled copper or conductors with low CO2 emissions during manufacturing are used as winding materials for the purpose of sustainable resource procurement, the presence of copper oxide results in a higher oxygen content compared to oxygen-free copper, making the weld bead more susceptible to hydrogen embrittlement. Since hydrogen-embrittle weld beads reduce the mechanical strength of the joint, it is necessary to suppress the generation of voids due to hydrogen embrittlement of the weld bead in order to obtain the required joint strength.

[0003] Conventionally, a technique for preventing void formation in weld beads is known, which involves irradiating the target object with laser light comprising a main power region including a main beam and a sub-power region including a sub-beam with a lower power density than the main beam, so that voids in the molten pool are released outside the molten pool before the molten pool solidifies (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2022 / 085632 [Overview of the initiative] [Problems that the invention aims to solve]

[0005] However, conventional joining methods require the use of a special laser welding device configured to emit both a main beam and a sub-beam with a lower power density than the main beam, making them not versatile.

[0006] Furthermore, as a technique to prevent a decrease in joint strength due to void formation, it is known that in TIG welding, additives such as phosphorus, which react with oxygen or hydrogen and are released as molecules, are added to the molten part to suppress void formation. However, this method requires additives and equipment to supply them to the molten part, which not only complicates the equipment but also incurs additional costs, making it uneconomical.

[0007] The present invention aims to provide a conductor joining method that can form a weld bead with suppressed void formation by a simple method, even when using a conductor containing copper oxide. [Means for solving the problem]

[0008] (1) A conductor joining method comprising: a molten pool forming step of irradiating a welding location (e.g., welding location 310 described later) between conductors containing copper oxide (e.g., coil end 31 described later) with laser light (e.g., laser light LB described later) to form a molten pool (e.g., molten pool 32 described later) by melting the welding location; and a weld bead forming step of solidifying the molten pool to form a weld bead (e.g., weld bead 33 described later), wherein in the molten pool forming step, the laser light is irradiated to form the molten pool so that the temperature of the welding location is higher than the melting point of copper and lower than the melting point of copper oxide, and the molten pool is stirred by changing the irradiation position of the laser light to the molten pool.

[0009] According to (1) above, it is possible to join conductors containing copper oxide by simply changing the irradiation position of the laser beam to the molten pool, thereby forming a weld bead in which the generation of voids is suppressed.

[0010] (2) In the conductor bonding method according to (1) above, in the molten pool forming step, the welding location is irradiated with laser light in an atmospheric gas filled region.

[0011] According to (2) above, the amount of hydrogen dissolved into the molten pool from the periphery of the welding location can be suppressed.

[0012] (3) In the conductor bonding method according to any one of (1) or (2) above, the copper oxide is tough pitch copper equivalent to JIS C1100.

[0013] According to (3) above, the conductor is excellent in conductivity, and since the oxygen content in the copper oxide is low, the generation of voids in the weld bead can be further suppressed.

[0014] (4) In the conductor bonding method according to any one of (1) to (3) above, the laser beam has an energy density of 33.8kW / cm 2 or more near-infrared wavelength light, and an energy density of 1.41kW / cm 2 or more visible wavelength light.

[0015] According to (4) above, convection can be effectively generated in the molten pool by the keyhole formed in the molten pool by laser beam irradiation. This promotes the discharge of hydrogen dissolved in the molten pool, and can further suppress the generation of voids in the weld bead.

[0016] (5) In the conductor bonding method according to any one of (1) to (4) above, the conductor is a coil (e.g., a segment coil 3 described later) protruding from a slot (e.g., a slot 22 described later) of a stator core (e.g., a stator core 2 described later) in a rotary electric machine.

[0017] According to (5) above, a rotary electric machine including a stator in which a conductor joint having high bonding strength is formed can be manufactured by a simple method.

Effects of the Invention

[0018] According to the present invention, there can be provided a conductor bonding method capable of forming a weld bead in which the occurrence of voids is suppressed by a simple method even for a conductor containing copper oxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] [Figure 1] FIG. 1 is a schematic diagram illustrating a schematic configuration of a laser welding apparatus according to an embodiment. [Figure 2] FIG. 2 is a perspective view showing a plurality of coil ends protruding from respective slots of a stator core. [Figure 3] FIG. 3 is a perspective view showing an assist gas injection unit and a wall member of the laser welding apparatus. [Figure 4] FIG. 4 is an enlarged view of part A in FIG. 1. [Figure 5] FIG. 5 is a longitudinal sectional view taken along line C-C in FIG. 4. [Figure 6] FIG. 6 is an enlarged view of part B in FIG. 1. [Figure 7] FIG. 7 is a longitudinal sectional view taken along line D-D in FIG. 6. [Figure 8] FIG. 8 is a plan view showing a state before a plurality of coil ends are clamped by a clamp jig of the laser welding apparatus. [Figure 9] FIG. 9 is a plan view showing a state after a plurality of coil ends are clamped by the clamp jig of the laser welding apparatus. [Figure 10] FIG. 10 is a flowchart for explaining an embodiment of a conductor bonding method using the laser welding apparatus. [Figure 11] FIG. 11 is a perspective view showing a state where the assist gas injection unit and the wall member of the laser welding apparatus are positioned with respect to a plurality of coil ends to be laser-welded. [Figure 12] FIG. 12 is a plan view showing a state where the assist gas injection unit and the wall member of the laser welding apparatus are positioned with respect to a plurality of coil ends to be laser-welded. [Figure 13] FIG. 13 is a longitudinal sectional view taken along line E-E in FIG. 12. [Figure 14]This is a schematic diagram showing the state in which a molten pool is formed at the end of a coil by irradiation with laser light. [Figure 15] This is a schematic diagram illustrating the behavior of hydrogen in a molten pool when irradiated with laser light. [Figure 16] This is a longitudinal cross-sectional view along the FF line in Figure 12. [Figure 17] This is a plan view showing the coil end where the weld bead has been formed. [Modes for carrying out the invention]

[0020] Embodiments of the present invention will be described in detail below with reference to the drawings. Figure 1 schematically shows one embodiment of a laser welding apparatus that can be used when carrying out the conductor joining method according to the present invention. The laser welding apparatus 1 laser-welds the coil ends 31 of a plurality of segment coils 3 that protrude from a stator core 2 used in a rotating electric machine (not shown). The plurality of coil ends 31 protrude from one end face 2a in the axial direction Z of the stator core 2.

[0021] Here, we define the directions indicated by the arrows at both ends in each figure. X indicates the circumferential direction of the stator core 2. Direction X1 indicates one side of the circumferential direction X, and direction X2 indicates the other side of the circumferential direction X. Y indicates the radial direction of the stator core 2. Direction Y1 indicates the outside of the radial direction Y, and direction Y2 indicates the inside of the radial direction Y. Z indicates the axial direction of the stator core 2. Direction Z1 indicates one side of the axial direction Z, and direction Z2 indicates the other side of the axial direction Z. Z is not necessarily limited to the direction along the vertical direction, but in this embodiment, we will describe the case where it is arranged along the vertical direction. Therefore, direction Z1 indicates the upward direction in the vertical direction, and direction Z2 indicates the downward direction in the vertical direction.

[0022] The stator core 2 is annular in shape and has a central shaft hole 21 in which a rotor (not shown) is rotatably housed. The stator core 2 has a plurality of slots 22 arranged radially along the circumferential direction X. The slots 22 penetrate the stator core 2 in the axial direction Z. A plurality of segment coils 3, each of which are electrical conductors, are inserted into each slot 22. The segment coils 3 are U-shaped and have a pair of legs. The pair of legs of the segment coils 3 are inserted into different slots 22, 22 along the axial direction Z of the stator core 2. As a result, a pair of legs from each segment coil 3 protrudes from one end face 2a of the stator core 2, which is positioned facing upward Z1 in Figure 1.

[0023] As shown in Figures 1 and 2, each pair of legs protruding from each slot 22 is bent along the circumferential direction X of the stator core 2. The coil ends 31, which are the tips of the pair of legs of each segment coil 3, are each raised substantially perpendicular to one end face 2a of the stator core 2. The coil ends 31 of the multiple segment coils 3 inserted into the slots 22 are arranged in a row along the radial direction Y of the stator core 2. In the example shown in Figure 2, eight coil ends 31 are arranged in a row along the radial direction Y for each slot 22, forming a coil end row 30. The number of coil end rows 30 is the same as the number of slots 22 in the stator core 2, and they are arranged radially along the circumferential direction X of the stator core 2.

[0024] Although the surface of the segment coil 3 is covered with an insulating coating, the insulating coating is removed from each coil end 31 for laser welding, exposing the metal portion of the segment coil 3. The laser welding apparatus 1 uses the tips of two adjacent coil ends 31, 31 along the radial direction Y within the slot 22 as welding points 310 (see Figures 9 and 11), and joins the coil ends 31, 31 together by irradiating these welding points 310 with laser light.

[0025] The metal constituting the segment coil 3 contains copper oxide. Since recycled materials can be used for the segment coil 3, an inexpensive rotating electric machine can be constructed. The copper oxide is preferably of a grade equivalent to JIS C1100. Such copper oxide is generally called tough pitch copper and has excellent conductivity. Tough pitch copper is a eutectic of copper and copper(I) oxide, and although it is copper oxide, it has a low oxygen content, making it effective in suppressing voids in the weld bead. In this embodiment, the case in which tough pitch copper is used for the segment coil 3 will be described.

[0026] The laser welding apparatus 1 comprises a laser irradiation device 4, an assist gas injection device 5, a wall member 6, a clamp jig 7, and a fixing jig 8.

[0027] The laser irradiation device 4 comprises a laser irradiation unit 41 that irradiates laser light onto the welding locations 310 of multiple coil ends 31, and a laser oscillator 42 that generates laser light. The laser irradiation device 4 irradiates the welding locations 310 of the two coil ends 31, 31 to be welded from the laser irradiation unit 41 using laser light generated by the laser oscillator 42.

[0028] As shown in Figure 1, the laser irradiation unit 41 is positioned above Z1 on one end face 2a of the stator core 2 and contains an optical system for focusing laser light and a scanning means, such as a galvanometer mirror, that can scan and move the laser light over the welding area 310. The laser oscillator 42 is not particularly limited, but for example, it can be capable of generating laser light including near-infrared wavelengths (1020 nm to 1120 nm) and visible light wavelengths (400 nm to 500 nm). In this case, it is preferable that the laser irradiation unit 41 is provided to emit near-infrared laser light and visible light laser light simultaneously and coaxially. For such a laser irradiation device 4, for example, a fiber laser device can be used. Specifically, for example, the Brace-X manufactured by Furukawa Electric Co., Ltd. can be used.

[0029] The assist gas injection device 5 comprises an assist gas injection unit 51 having a piping structure and an assist gas supply source 52 that generates assist gas and circulates it to the assist gas injection unit 51 at a predetermined pressure. As shown in Figure 1, the assist gas injection unit 51 is positioned between the laser irradiation unit 41 and one end face 2a of the stator core 2. The assist gas injection unit 51 has an injection nozzle 511 at its tip. The assist gas injection unit 51 injects assist gas from the injection nozzle 511 toward the welding locations 310 of the multiple coil ends 31 that are to be welded.

[0030] The nozzle 511 of the assist gas injection unit 51 is positioned on one end side in the arrangement direction of the coil end row 30, which consists of multiple coil ends 31. More specifically, the nozzle 511 of the assist gas injection unit 51 is positioned on the inside Y2 of the radial direction Y of the stator core 2 in the coil end row 30 and opens toward the outside Y1 of the radial direction Y of the stator core 2. More specifically, the assist gas injection unit 51 is positioned obliquely to one end face 2a of the stator core 2, from the inside Y2 of the radial direction Y of the stator core 2 in the coil end row 30 toward the outside Y1 of the radial direction Y. That is, the central axis 511a of the nozzle 511 of the assist gas injection unit 51 is positioned to intersect one end face 2a of the stator core 2 at an angle θ less than 90° (see Figure 16). The specific angle θ is not particularly limited, but can be, for example, 30° to 45°.

[0031] The assist gas injection unit 51 injects assist gas supplied from the assist gas supply source 52 from the injection nozzle 511 toward the welding area 310 at a predetermined pressure. This blows away impurities such as fumes, dust, and spatter generated during laser welding due to the gas injection pressure. The injected assist gas forms an atmosphere gas-filled area around the welding area 310. Inert gases such as argon, neon, nitrogen, and helium can be used as assist gas.

[0032] As shown in Figure 1, the wall member 6 is positioned between one end face 2a of the stator core 2 and the nozzle 511 of the assist gas injection unit 51. As shown in Figure 3, the wall member 6 has a pair of plate portions 61, 61. The pair of plate portions 61, 61 extend substantially parallel to the radial direction Y of the stator core 2, with a constant distance between them in the circumferential direction X of the stator core 2. The surface direction of each plate portion 61, 61 is aligned with the radial direction Y and the axial direction Z of the stator core 2, respectively.

[0033] The lengths of each plate portion 61, 61 along the radial direction Y of the stator core 2 are the same. The length of each plate portion 61, 61 can be, for example, greater than or equal to the length of the coil end row 30 protruding from the slot 22 along the radial direction Y. The height of each plate portion 61, 61 along the axial direction Z of the stator core 2 is constant along the radial direction Y of the stator core 2. The height of each plate portion 61, 61 can be, for example, greater than or equal to the protruding height of the multiple coil ends 31 protruding from the clamp jig 7 described later. The wall member 6, with its pair of plate portions 61, 61, sandwiches a row of coil end rows 30 protruding from the stator core 2 from both sides in the circumferential direction X of the stator core 2, and houses the entire row of coil end rows 30 inside. A pair of plate sections 61, 61 sandwiching a row of coil end sections 30 form gas regulating plates on both sides of the row of coil end sections 30 in the circumferential direction X, which regulate the flow of assist gas injected from the nozzle 511. This makes it easy to form an atmosphere gas-filled area between the pair of plate sections 61, 61 by the assist gas injected from the nozzle 511.

[0034] One end of each of the pair of plate portions 61, 61 is overlapped with the other. Specifically, as shown in Figure 3, the inner ends 61a, 61a of the pair of plate portions 61, 61 in the radial direction Y2 of the stator core 2 are bent and overlapped with each other to form an attachment portion 62 to the assist gas injection unit 51. The attachment portion 62 is fixed to an attachment pipe 63 attached to the outer circumference of the tip of the assist gas injection unit 51 by a fixing member 64 consisting of a bolt and nut. In this way, the wall member 6 is integrally attached to the tip of the assist gas injection unit 51.

[0035] The pair of plate portions 61, 61 of the wall member 6, when attached to the assist gas injection unit 51, extend from the injection nozzle 511 toward the outer side Y1 in the radial direction Y of the stator core 2, substantially parallel to one end face 2a of the stator core 2. The extension direction of the pair of plate portions 61, 61 is arranged to intersect the central axis 511a of the injection nozzle 511 of the assist gas injection unit 51 at an angle θ (see Figure 16). When the one end face 2a of the stator core 2 is viewed from above, the extension direction of the pair of plate portions 61, 61 is arranged along the central axis 511a of the injection nozzle 511 of the assist gas injection unit 51 (see Figure 12).

[0036] The inner ends 61b, 61b of the pair of plate portions 61, 61 of the wall member 6, on the inner side Y2 in the radial direction Y of the stator core 2, are separated in the circumferential direction X of the stator core 2 while maintaining a predetermined distance. The space between the pair of plate portions 61, 61 is open to the outer side Y1 in the radial direction Y of the stator core 2, as shown in Figures 3, 11, and 12. Therefore, the assist gas injected from the nozzle 511 of the assist gas injection unit 51 flows between the pair of plate portions 61, 61 while being restricted by them, and is then smoothly discharged to the outer side Y1 in the radial direction Y of the stator core 2.

[0037] As shown in Figure 1, the clamping jig 7 is positioned between one end face 2a of the stator core 2 and the wall member 6. The clamping jig 7 consists of an upper clamping jig 71 and a lower clamping jig 72. The upper clamping jig 71 and the lower clamping jig 72 are made of annular plate members having the same outer diameter and the same inner diameter.

[0038] As shown in Figures 4 and 5, the upper clamp jig 71 has an annular upper clamp jig body 711. The upper clamp jig body 711 is divided into an annular inner ring portion 711a and an outer ring portion 711b. Clamp halves 712 are provided to connect the inner ring portion 711a and the outer ring portion 711b of the upper clamp jig body 711. The same number of clamp halves 712 are provided between the inner ring portion 711a and the outer ring portion 711b as the number of slots 22 of the stator core 2 (i.e., the number of coil end rows 30), and are arranged at predetermined intervals along the circumferential direction X of the upper clamp jig body 711. The clamp halves 712 are positioned and fixed to the inner ring portion 711a by pins 713, and fixed to the outer ring portion 711b by bolts 714 that are screwed in from the outside Y1 in the radial direction Y of the outer ring portion 711b.

[0039] As shown in Figure 4, the clamp half 712 has three mountain-shaped guide projections 712a formed on one side X1 in the circumferential direction X of the upper clamp jig 71, at predetermined intervals in the radial direction Y of the upper clamp jig 71. As a result, the clamp half 712 has four end-receiving recesses 712b along the radial direction Y on one side X1 in the circumferential direction X of the upper clamp jig 71, which accommodate two coil ends 31, 31 each. The clamp half 712 has the same axial thickness Z as the inner circumferential ring portion 711a and outer circumferential ring portion 711b of the upper clamp jig body 711, but as shown in Figure 4, a recess 712c is formed in the region where the guide projections 712a and end-receiving recesses 712b are formed, which is recessed toward one side X1 in the circumferential direction X of the upper clamp jig 71.

[0040] As shown in Figures 6 and 7, the lower clamp jig 72 has an annular lower clamp jig body 721. The lower clamp jig body 721 is divided into an annular inner ring portion 721a and an outer ring portion 721b. Clamp halves 722 are provided to connect the inner ring portion 721a and the outer ring portion 721b of the lower clamp jig body 721. The same number of clamp halves 722 are provided between the inner ring portion 721a and the outer ring portion 721b as the number of slots 22 of the stator core 2 (i.e., the number of coil end rows 30), and are arranged at predetermined intervals along the circumferential direction X of the lower clamp jig body 721. The clamp halves 722 are positioned and fixed to the inner ring portion 721a by pins 723 and fixed to the outer ring portion 721b by bolts 724 that are screwed in from the outside Y1 in the radial direction Y of the outer ring portion 721b.

[0041] As shown in Figure 6, the clamp half 722 has three mountain-shaped guide protrusions 722a formed on the other side X2 of the lower clamp jig 72 in the circumferential direction X, at predetermined intervals in the radial direction Y of the lower clamp jig 72. As a result, the clamp half 722 has four end-receiving recesses 722b formed along the radial direction Y on the other side X2 of the lower clamp jig 72 in the circumferential direction X, which accommodate two coil ends 31, 31 each. The ends of the clamp half 722 in the radial direction Y have the same axial thickness Z as the inner circumferential ring portion 721a and outer circumferential ring portion 721b of the lower clamp jig body 721, but as shown in Figures 6 and 7, a protruding wall portion 722c is formed in the region where the guide protrusions 722a and end-receiving recesses 722b are formed, projecting upward Z1. The protruding wall portion 722c is positioned on one side X1 in the circumferential direction X of the clamp half 722 and forms a recessed shape 722d that is recessed toward the other side X2 in the circumferential direction X.

[0042] The upper clamping jig 71 and the lower clamping jig 72 are stacked on top of each other so that the upper clamping jig 71 is positioned above Z1 in the axial direction Z, thereby forming the clamping jig 7. Each clamping half 722 of the lower clamping jig 72 is housed between adjacent clamping halves 712, 712 of the upper clamping jig 71 in the circumferential direction X. The guide projections 712a and end-receiving recesses 712b of the clamping halves 712 of the upper clamping jig 71 and the guide projections 722a and end-receiving recesses 722b of the clamping halves 722 of the lower clamping jig 72 are arranged to face each other, as shown in Figures 8 and 9.

[0043] During laser welding, the clamping jig 7 is positioned to be close to one end face 2a of the stator core 2 by a moving mechanism (not shown). As a result, as shown in Figure 8, each coil end row 30 protruding from the stator core 2 is housed between the clamp halves 712 and 722 of the clamping jig 7. Between each pair of clamp halves 712 and 722, there is a coil end row 30 consisting of eight coil ends 31. The eight coil ends 31 of the coil end row 30 are housed in pairs of two adjacent coil ends 31, 31 between the four end-receiving recesses 712b of the clamp half 712 of the upper clamping jig 71 and the four end-receiving recesses 722b of the clamp half 722 of the lower clamping jig 72. The upper end faces of the eight coil ends 31 between the end-receiving recesses 712b and 722b are positioned substantially flush with the upper surfaces of the upper clamping jig 71 and the lower clamping jig 72.

[0044] At least one of the upper clamp fixture 71 and the lower clamp fixture 72 is connected to a rotation mechanism (not shown). The rotation mechanism rotates at least one of the upper clamp fixture 71 and the lower clamp fixture 72 along the circumferential direction X. Specifically, when only the upper clamp fixture 71 is connected to the rotation mechanism, the upper clamp fixture 71 rotates to one side X1 of the circumferential direction X relative to the lower clamp fixture 72, which remains in a fixed position. When only the lower clamp fixture 72 is connected to the rotation mechanism, the lower clamp fixture 72 rotates to the other side X2 of the circumferential direction X relative to the upper clamp fixture 71, which remains in a fixed position. When both the upper clamp fixture 71 and the lower clamp fixture 72 are connected to the rotation mechanism, the upper clamp fixture 71 rotates to one side X1 of the circumferential direction X, and the lower clamp fixture 72 rotates to the other side X2 of the circumferential direction X. As a result, the clamping half 712 of the upper clamping jig 71 and the clamping half 722 of the lower clamping jig 72 move closer to each other, and as shown in Figure 9, the two coil ends 31, 31 positioned between the end receiving recesses 712b, 722b are clamped from both sides in the circumferential direction X. The two clamped coil ends 31, 31 are guided by the inclined surfaces of the guide projections 712a, 722a, bringing them into close contact with each other in the circumferential direction X to form a welding area 310, and the device enters a laser welding standby state.

[0045] As shown in Figure 1, the fixing jig 8 is positioned below Z2 in the axial direction Z of the stator core 2, and supports and fixes the stator core 2 on it. The fixing jig 8 rotates around the central axis of the stator core 2 at a predetermined pitch (for example, the arrangement pitch of the slots 22) by the drive of the motor 81. In this way, the fixing jig 8 rotates the stator core 2 that it fixes and moves along the circumferential direction X. In this case, the fixing jig 8 and the motor 81 constitute a moving device that moves the stator core 2 relative to the laser irradiation unit 41, the assist gas injection unit 51, and the wall member 6.

[0046] As shown in Figure 1, the laser welding apparatus 1 has a controller 100. The controller 100 is electrically connected to the laser irradiation unit 41 of the laser irradiation device 4, the laser oscillator 42, the assist gas supply source 52 of the assist gas injection device 5, the moving mechanism and rotation mechanism of the clamp jig 7, and the motor 81, respectively, and performs laser welding on each welding location 310 consisting of two coil ends 31, 31 by controlling the operation of these components. The controller 100 operates according to a predetermined program for performing laser welding. The controller 100 includes a memory and a processor for storing the program. The processor controls the operation of the laser oscillator 42, the assist gas supply source 52, the moving mechanism and rotation mechanism of the clamp jig 7, and the motor 81, respectively, according to the predetermined program for laser welding read from the memory. The controller 100 may be provided exclusively for the laser welding apparatus 1. Alternatively, the functions of the controller 100 may be realized by an external terminal such as a PC (personal computer) or tablet terminal connected to the laser welding apparatus 1.

[0047] Next, a conductor joining method for joining the welding points 310 using a laser welding apparatus 1 will be explained with reference to Figures 10 to 17. Figure 10 is a flowchart of the laser welding process performed under the control of the controller 100.

[0048] In the laser welding apparatus 1 in the laser welding standby state, the assist gas injection unit 51 and the wall member 6 are positioned above the clamp jig 7. The clamp halves 712 and 722 of the clamp jig 7 clamp the coil ends 31. The wall member 6 is positioned in contact with or close to the surface of the clamp jig 7. In this laser welding standby state, the controller 100 rotates the fixing jig 8 by driving the motor 81, and rotates the stator core 2 around its central axis so that the position of the wall member 6 matches the phase of one coil end row 30 consisting of multiple coil ends 31 to be welded on the stator core 2, and stops at a predetermined rotation position (step S1).

[0049] At this time, as shown in Figures 11 to 13, the wall member 6 is arranged to accommodate a row of coil end sections 30 between a pair of plate sections 61, 61, and the space S above the eight coil end sections 31 is sandwiched between the pair of plate sections 61, 61 from both sides in the circumferential direction X of the stator core 2. The laser irradiation section 41 is positioned above the wall member 6, i.e., above the row of coil end sections 30. The assist gas injection section 51, which is integrated with the wall member 6, is positioned inward Y2 in the radial direction Y of the stator core 2 relative to the row of coil end sections 30, and its injection nozzle 511 is directed toward the row of coil end sections 30.

[0050] Next, the controller 100 drives the laser oscillator 42 and the assist gas supply source 52 to irradiate the welding points 310 at the tips of the two coil ends 31, 31 in the slot 22 sandwiched between the pair of plate portions 61, 61 with laser light LB, and simultaneously injects assist gas from the nozzle 511 of the assist gas injection unit 51 to perform welding (step S2).

[0051] The process of welding by irradiating the welding area 310 with laser light LB consists of two main steps: a molten pool formation step and a weld bead formation step. The molten pool formation step involves irradiating the welding area 310 with laser light LB to form a molten pool 32, as shown in Figure 14. The weld bead formation step involves ending the irradiation of laser light LB and forming a roughly spherical weld bead 33 at the welding area 310 using the solidified molten pool 32, as shown in Figure 17, thereby completing the joining of the welding area 310. Details of each step will be explained further later.

[0052] In step S2, the laser irradiation unit 41, using a scanning means controlled by the controller 100, scans the laser beam LB over the welding area 310, which consists of pairs of coil ends 31, 31, as shown in Figure 16, and sequentially welds the two coil ends 31, 31 at a time. Simultaneously, the assist gas injection device 5 injects assist gas from the injection port 511 at a predetermined injection pressure.

[0053] The assist gas injected from the nozzle 511 through the assist gas injection unit 51 flows between the pair of plate portions 61, 61 of the wall member 6, as shown by the white arrows in Figure 16, forming an atmosphere gas-filled area consisting of the assist gas around the welding location 310. Furthermore, the assist gas that flows between the pair of plate portions 61, 61 flows outward Y1 in the radial direction Y of the stator core 2, blowing away impurities such as fumes, dust, dirt, and spatter generated during laser welding, and is discharged from between the pair of plate portions 61, 61. The wall member 6 restricts the flow of assist gas in the circumferential direction X of the stator core 2 with the pair of plate portions 61, 61. Therefore, the blown-away impurities are quickly discharged outward Y1 in the radial direction Y of the stator core 2, and the risk of impurities adhering to the coil ends 31 of other coil end rows 30 that are not being welded is reduced.

[0054] Furthermore, the distance between the pair of plate sections 61, 61 of the wall member 6 is greater than the diameter of the nozzle 511 of the assist gas injection unit 51. Therefore, the area filled with the assist gas atmosphere extends around the wall member 6. Since the assist gas is in a laminar flow state immediately after being injected from the nozzle 511, the assist gas flowing on both sides of the pair of plate sections 61, 61 does not affect the blowing away of impurities.

[0055] The irradiation of the laser beam LB and the injection of assist gas are continued until laser welding is completed to all coil ends 31 of one coil end row 30 within the wall member 6 (step S3). That is, for each of the four welding locations 310 within the wall member 6, a molten pool formation process and a weld bead formation process are performed, and finally, a weld bead 33 is formed at the welding location 310 as shown in Figure 17. Once laser welding is completed to all welding locations 310 within the wall member 6 (step S3; YES), the controller 100 determines whether the welding work to all welding locations 310 on the stator core 2 has been completed (step S4). Whether the welding work has been completed is determined, for example, by the controller 100 detecting the rotation angle of the stator core 2, the number of rotational movements, etc.

[0056] When the welding work for all welding portions 310 on the stator core 2 is not completed (Step S4; NO), the controller 100 rotationally moves the stator core 2 about its central axis such that the position of the wall member 6 matches the phase of one adjacent coil end row 30 on the stator core 2 (Step S5). Thereafter, the controller 100 repeats the processing from Step S2 described above, and terminates the laser welding for the stator core 2 when it is determined in Step S4 that the welding work for all welding portions 310 on the stator core 2 has been completed.

[0057] Next, the molten pool forming step and the weld bead forming step during laser welding in Step S2 described above will be described.

[0058] First, in the molten pool forming step, as shown in FIG. 14, laser beam LB is irradiated from the laser irradiation unit 41 to the welding portion 310 to melt the metal of the two coil ends 31, 31 of the welding portion 310, thereby forming a molten pool 32 made of molten metal at the welding portion 310. In the present embodiment, the laser welding performed by the laser welding apparatus 1 is assumed to be performed in an environment with a temperature of 45°C and a relative humidity of 100%.

[0059] Since the segment coil 3 contains copper(I) oxide, it is unavoidable that the molten pool 32 contains oxygen (oxygen ion [O 2- ) dissociated from copper(I) oxide. This oxygen (oxygen ion [O 2- ) combines with hydrogen (hydrogen ion [H + ) contained in moisture in the atmosphere, thereby generating water (water vapor) that causes hydrogen embrittlement of the weld bead 33. Therefore, in order to suppress hydrogen embrittlement of the weld bead 33, it is important to implement at least one of, and preferably both of: an approach of minimizing dissolution of hydrogen (hydrogen ion [H + ) into the molten pool 32 as much as possible (hereinafter referred to as the IN-side approach), and an approach of discharging hydrogen (hydrogen ion [H + ) dissolved in the molten pool 32 from the molten pool 32 as much as possible (hereinafter referred to as the OUT-side approach).

[0060] The amount of oxygen and hydrogen dissolved in the molten pool 32 is proportional to the temperature of the molten pool 32. The higher the temperature of the molten pool 32, the greater the amount of oxygen and hydrogen dissolved. Therefore, as an IN approach, hydrogen (hydrogen ions [H) is added to the molten pool 32. + To suppress the amount of copper(I) dissolved, it is desirable that the temperature of the weld area 310 when forming the molten pool 32 be low. However, the melting point of copper(I) oxide is 1235°C, and in order to completely melt the copper(I) oxide, it is necessary to heat the weld area 310 to a temperature of 1235°C or higher. However, generally speaking, even though it is copper(I) oxide, the majority of it is copper, so when the temperature exceeds the melting point of copper, 1085°C, the copper(I) oxide begins to melt. In the initial stages of melting, the molten pool 32 consists of solid (unmelted) copper(I) suspended in liquid copper.

[0061] Therefore, as one method of the IN side approach, in the molten pool formation process, the output of the laser beam LB of the laser irradiation device 4 is adjusted so that the temperature of the weld area 310 is higher than the melting point of copper and lower than the melting point of copper(I) oxide. Specifically, the output of the laser beam LB of the laser irradiation device 4 is adjusted so that the amount of heat generated at the weld area 310 is 1100°C or higher, which is higher than the melting point of copper, and 1200°C or lower, which is lower than the melting point of copper(I) oxide. By setting the temperature at which the weld area 310 is melted in this way, hydrogen (hydrogen ions [H]) is introduced into the molten pool 32. + The amount of ]) dissolved is suppressed.

[0062] Furthermore, the amount of oxygen contained in the winding of tough pitch copper is approximately 500 ppm or less, and hydrogen (hydrogen ions [H]) is solid-soluble in the molten bead containing copper(I) oxide. + The hydrogen content (hydrogen ions [H]) is 1.8 ppm. In other words, when copper(I) oxide melts, the hydrogen content (hydrogen ions [H]) is 1.8 ppm or more. +When hydrogen dissolves, water (water vapor) is more easily generated. Therefore, as another method of the IN side approach, in the molten pool formation process, assist gas is injected from the nozzle 511 of the assist gas injection unit 51 into the wall member 6, and the area around the welding location 310 is filled with an atmosphere gas consisting of assist gas. As a result, the amount of moisture around the welding location 310 is reduced and the hydrogen concentration decreases, so that hydrogen (hydrogen ions [H]) dissolves into the molten pool 32 from the surroundings. + ]) is suppressed. Since the welding area 310 is sandwiched between a pair of plate portions 61, 61 of the wall member 6, by continuously spraying assist gas during irradiation with laser beam LB, not only are impurities blown away as described above, but an atmosphere gas-filled area with assist gas can be easily and stably formed around the welding area 310. The laser irradiation device 4 irradiates the welding area 310 with laser beam LB in this atmosphere gas-filled area to form a molten pool 32.

[0063] In the molten pool formation process, the atmosphere gas-filled area is shielded by the injection of assist gas. As the assist gas concentration around the welding area 310 becomes relatively higher than that of the atmosphere (air), the oxygen concentration decreases, and hydrogen (hydrogen ions [H]) enters the molten pool 32. + The amount of ]) dissolved can be further suppressed.

[0064] As an OUT approach, hydrogen (hydrogen ions [H]) dissolved in the melting pool 32 +One method is to diffuse and discharge the fumes around the molten pool 32. As one means of the OUT side approach, in the molten pool formation process, the laser welding apparatus 1 drives a scanning means such as a galvanometer mirror in the laser irradiation unit 41 to scan and move the laser beam LB during the formation of the molten pool 32, as shown in Figure 14, thereby changing the irradiation position of the laser beam LB on the molten pool 32 and stirring the molten pool 32. Specifically, in the liquid phase state of the molten pool 32, a keyhole 321 is formed in the irradiated area by the thermal energy of the laser beam LB. The keyhole 321 is a cavity caused by a depression in the metal surface. The keyhole 321 persists while the laser beam LB is irradiated, due to the balance between the metal vapor pressure and the contraction pressure due to the surface tension of the molten area, and moves within the molten pool 32 as the laser beam LB scans and moves. This generates convection in the molten pool 32, and the molten metal in the molten pool 32 is stirred. The scanning movement of the laser beam LB may be a linear, repetitive movement relative to the molten pool 32, or it may be a movement that draws multiple circles relative to the molten pool 32.

[0065] The conditions for forming a keyhole 321 in the molten pool 32 can be determined from the energy required to generate metal vapor pressure in the keyhole 321 (A), the energy required to melt the copper on the wall surface of the keyhole 321 (B), the energy required for heat transfer from the molten part to the solid part (C), and the energy absorption rate of copper (D). For example, if the segment coil 3 is a flat wire made of tough pitch copper measuring 3.0 mm × 1.5 mm square, and the molten pool 32 is irradiated with laser light LB containing near-infrared wavelength (1070 nm) light with a spot diameter of 250 μm and visible light wavelength (450 nm) light with a spot diameter of 900 μm, then (A) is estimated to be 102.0 W, (B) is 49.7 W, (C) is 47.3 W, and (D) is estimated to be 12% for the near-infrared wavelength (1070 nm) and 60% for the visible light wavelength (450 nm). Using these values ​​and the formula [Supply energy density = (A + B + C) / D / Spot area], the energy density of the laser light at near-infrared wavelength (1070 nm) is calculated to be 33.8 kW / cm². 2 The energy density of laser light at a visible light wavelength (450 nm) is 1.41 kW / cm². 2Therefore, from the viewpoint of effectively generating convection by forming a keyhole 321 in the molten pool 32, the energy density is 33.8 kW / cm². 2 The above-mentioned near-infrared wavelengths of light and an energy density of 1.41 kW / cm² 2 It is preferable to irradiate the molten pool 32 with laser light LB that includes the above visible light wavelengths.

[0066] The metal vapor pressure generated in the keyhole 321 acts around the keyhole 321, as indicated by the arrow in Figure 15, and, combined with the stirring of the molten pool 32 due to the movement of the keyhole 321, generates convection in the molten pool 32. The area around the molten pool 32 is an atmosphere gas-filled region with assist gas, and the hydrogen concentration is low, so the convection generated in the molten pool 32 causes the hydrogen (hydrogen ions [H]) dissolved in the molten pool 32 to be stirred up. + The hydrogen (hydrogen ions [H)) dissolved in the melting pool 32 is discharged by the principle of diffusion into the atmosphere gas-filled area where the hydrogen concentration is relatively low. + The emission of ]) is further promoted.

[0067] In the molten pool formation process described above, the hydrogen concentration in the molten pool 32 is reduced by at least one of the IN-side approach and the OUT-side approach, preferably both approaches. After that, the irradiation of the weld pool 32 with laser light LB is completed, and the process moves on to the weld bead formation process.

[0068] In the welding bead formation process, the supply of heat to the molten pool 32 is stopped, and the molten pool 32 changes from a liquid phase to a solid phase, thereby forming a welding bead 33 at the welding location 310. Because the hydrogen concentration in the molten pool 32 is reduced by the molten pool formation process, oxygen (oxygen ions [O]) is reduced during the process of the molten pool 32 changing from a liquid phase to a solid phase. 2- ]) and hydrogen (hydrogen ions [H + The bonding with ]) is also reduced. As a result, a weld bead 33 with high joint strength and suppressed hydrogen embrittlement is formed.

[0069] The conductor joining method according to this embodiment provides the following effects. Specifically, it is a conductor joining method comprising: a molten pool formation step of irradiating a welding location 310 between coil ends 31, 31, which are conductors containing copper oxide, with laser light LB to form a molten pool 32 in which the welding location 310 is molten; and a welding bead formation step of solidifying the molten pool 32 to form a welding bead 33. In the molten pool formation step, the laser light LB is irradiated to form the molten pool 32 so that the temperature of the welding location 310 is higher than the melting point of copper and lower than the melting point of copper oxide, and the molten pool 32 is stirred by changing the irradiation position of the laser light LB to the molten pool 32. As a result, coil ends 31, 31, which are conductors containing copper oxide, can be joined together by forming a welding bead 33 in which the generation of voids is suppressed, using a simple method that only requires changing the irradiation position of the laser light LB to the molten pool 32.

[0070] In this embodiment, during the molten pool formation process, the welding area 310 is irradiated with laser light LB in the atmospheric gas-filled area. This makes it possible to suppress the amount of hydrogen that dissolves into the molten pool 32 from around the welding area 310.

[0071] In this embodiment, the copper oxide is tough pitch copper equivalent to JIS C1100. This provides excellent conductivity for the conductor, and the low oxygen content in the tough pitch copper further suppresses the generation of voids in the weld bead 33.

[0072] In this embodiment, the laser beam LB has an energy density of 33.8 kW / cm². 2 The above-mentioned near-infrared wavelengths of light and an energy density of 1.41 kW / cm² 2 This includes light of the above visible light wavelengths. According to this, the keyhole 321 formed in the molten pool 32 by irradiation with laser light LB can effectively generate convection in the molten pool 32. This promotes the discharge of hydrogen dissolved in the molten pool 32 and further suppresses the generation of voids in the weld bead 33.

[0073] In this embodiment, the coil end 31, which is a conductor, is a segment coil 3 that protrudes from the slot 22 of the stator core 2 in the rotating electric machine. This makes it possible to manufacture a rotating electric machine equipped with a stator in which a conductor joint with high bonding strength is formed in a simple manner.

[0074] The laser welding apparatus 1 according to this embodiment has one laser irradiation unit 41, one assist gas injection unit 51, and one wall member 6, but is not limited thereto. The laser welding apparatus 1 may have two or more sets of laser irradiation unit 41, assist gas injection unit 51, and wall member 6, and these may be arranged at predetermined intervals in the circumferential direction X of the stator core 2 to perform laser welding on multiple coil end rows 30 simultaneously.

[0075] In the laser welding apparatus 1 according to this embodiment, the wall member 6 is configured to sandwich the space S above one coil end row 30 from both sides in the circumferential direction X with a pair of plate portions 61, 61, but is not limited to this. The wall member 6 may be configured to sandwich the space S above two or more adjacent coil end rows 30 from both sides in the circumferential direction X with a pair of plate portions 61, 61, and may be configured to perform laser welding on those two or more coil end rows 30 at once.

[0076] In the laser welding apparatus 1 according to this embodiment, the fixing jig 8 is rotated to rotate the stator core 2 when aligning the phases of the wall member 6 and the coil end row 30, but the apparatus is not limited to this. The laser welding apparatus 1 may be configured such that the laser irradiation unit 41, the assist gas injection unit 51 and the wall member 6 move along the circumferential direction X of the stator core 2 with respect to the stator core 2 which is in a fixed position, or the stator core 2 and both the laser irradiation unit 41, the assist gas injection unit 51 and the wall member 6 may be configured to move in opposite directions. [Explanation of symbols]

[0077] 2 Stator Cores 22 slots 3-segment coil 31 Coil ends (conductors) 32 Melting pools 33 Weld bead 310 welding points LB laser light

Claims

1. A process of forming a molten pool by irradiating the welded area between conductors containing copper oxide with laser light to form a molten pool at the welded area, A welding bead forming step, in which the molten pool is solidified to form a welding bead, A conductor joining method having, A conductor joining method comprising the following steps: in the molten pool formation step, irradiating the welding area with laser light to form the molten pool so that the temperature of the welding area is higher than the melting point of copper and lower than the melting point of copper oxide, and stirring the molten pool by changing the irradiation position of the laser light on the molten pool.

2. The conductor joining method according to claim 1, wherein, in the molten pool formation step, laser light is irradiated onto the welding area in the atmosphere gas-filled area.

3. The conductor joining method according to claim 1 or 2, wherein the copper oxide is tough pitch copper equivalent to JIS C1100.

4. The aforementioned laser light has an energy density of 33.8 kW / cm². ２ The above-mentioned near-infrared wavelengths of light and an energy density of 1.41 kW / cm² ２ A conductor joining method according to claim 1 or 2, comprising light of the above visible light wavelengths.

5. The conductor joining method according to claim 1 or 2, wherein the conductor is a coil protruding from a slot of a stator core in a rotating electric machine.

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