JP7478697B2 - Manufacturing method of a stator for a rotating electric machine - Google Patents

Description

This disclosure relates to a method for manufacturing a stator for a rotating electric machine.

A method for manufacturing a stator is known in which the ends of one coil piece and another coil piece used to form a stator coil for a rotating electric machine are brought into contact with each other, and a laser beam is irradiated onto the welding target area associated with the abutted ends in such a way that the irradiation position moves in a loop (see, for example, Patent Document 1).

JP 2018-20340 A

Conventional techniques such as those described in Patent Document 1 can make the molten pool reach the contact surface between the ends of the coil pieces by gradually expanding the diameter of the loop-shaped scanning trajectory, but require a relatively large heat input to ensure a sufficient joining area.

Therefore, in one aspect, the present disclosure aims to achieve both ensuring the bonding area and reducing the number of spatters that occur.

In one aspect, the method includes: assembling coil pieces of the stator coil to a stator core;
a joining step of joining ends of the coil pieces to each other or joining the ends of the coil pieces to ends of bus bars by laser welding after the assembling step,
The joining step includes:
a setting process in which two ends of the objects to be joined are brought into contact with each other;
and an irradiation step of irradiating the two ends with a laser beam,
The irradiation section of the laser beam in the irradiation step includes a continuous irradiation section in which the irradiation position of the laser beam changes continuously,
A method for manufacturing a stator for a rotating electric machine is provided, wherein the continuous irradiation sections include, in a sequence along the movement direction of the irradiation position of the laser beam from the irradiation start position to the irradiation end position, a first section in which the irradiation position of the laser beam changes at a first speed, a second section in which the irradiation position of the laser beam changes at a second speed lower than the first speed, and a third section in which the irradiation position of the laser beam changes at a third speed higher than the second speed.

In one aspect, this disclosure makes it possible to ensure a sufficient bonding area while reducing the number of spatters that occur.

1 is a cross-sectional view showing a schematic cross-sectional structure of a motor according to an embodiment; FIG. 2 is a plan view of the stator core in a single component state. 3A and 3B are diagrams illustrating a pair of coil pieces to be assembled to a stator core. FIG. 2 is a perspective view of the periphery of a coil end of a stator. FIG. 4 is a perspective view showing a part of a coil piece of the same phase. FIG. 2 is a schematic front view of one coil piece. 1 is a diagram showing the tip portions of the coil pieces joined together and their vicinity; FIG. 8 is a cross-sectional view taken along line AA in FIG. 7 through the area to be welded. FIG. 1 is a diagram showing the relationship between the laser wavelength and the laser absorptance of various solid materials. FIG. 4 is an explanatory diagram of a change in absorption rate during welding. FIG. 13 is an image diagram of a keyhole etc. when a green laser is used. FIG. 13 is an image diagram of a keyhole etc. when an infrared laser is used. 1 is an explanatory diagram of a welding method using a green laser according to an embodiment of the present invention. FIG. FIG. 13 is a diagram showing the relationship between welding speed and welding depth in the case of a green laser. FIG. 13 is a diagram showing the relationship between welding speed and the number of spatters generated in the case of a green laser. FIG. 13 is a diagram showing the relationship between laser output and welding depth in the case of a green laser. FIG. 13 is a diagram showing the relationship between the laser output and the number of spatters generated in the case of a green laser. FIG. 1 is an illustration of a welding speed profile with a relatively low welding speed. FIG. 1 is an illustration of a welding speed profile with a relatively high welding speed. FIG. 10 is an explanatory diagram of the state of welding at each time point when welding is performed with a welding speed profile using a relatively low welding speed. FIG. 10 is an explanatory diagram of the state of welding at each time point when welding is performed with a welding speed profile using a relatively high welding speed. FIG. 4 is an explanatory diagram of a welding speed profile according to the present embodiment. 10 is a schematic diagram showing an example of a manner in which a laser output for one pass changes depending on an irradiation position. FIG. 13 is a schematic diagram showing another example of a manner in which the laser output for one pass changes depending on the irradiation position. FIG. FIG. 13 is a diagram showing a preferred welding speed profile when two passes of a green laser are performed on one welding point. 4 is a flowchart illustrating a manufacturing method of a motor stator. FIG. 4 is a perspective view illustrating a joint between a bus bar and a coil piece.

Each embodiment will be described in detail below with reference to the attached drawings. Note that the dimensional ratios in the drawings are merely examples and are not limiting, and shapes in the drawings may be partially exaggerated for the sake of explanation. In this specification, the word "predetermined" is used to mean "predetermined in advance."

Figure 1 is a cross-sectional view that shows a schematic cross-sectional structure of a motor 1 (an example of a rotating electric machine) according to one embodiment.

Figure 1 shows the rotating shaft 12 of the motor 1. In the following description, the axial direction refers to the direction in which the rotating shaft (center of rotation) 12 of the motor 1 extends, and the radial direction refers to the radial direction centered on the rotating shaft 12. Therefore, the radially outer side refers to the side away from the rotating shaft 12, and the radially inner side refers to the side toward the rotating shaft 12. Additionally, the circumferential direction corresponds to the direction of rotation around the rotating shaft 12.

Motor 1 may be a motor for driving a vehicle, such as that used in a hybrid vehicle or an electric vehicle. However, motor 1 may also be used for any other purpose.

The motor 1 is an inner rotor type, and the stator 21 is arranged to surround the radial outside of the rotor 30. The radial outside of the stator 21 is fixed to the motor housing 10.

The rotor 30 is disposed radially inside the stator 21. The rotor 30 includes a rotor core 32 and a rotor shaft 34. The rotor core 32 is fixed to the radial outside of the rotor shaft 34 and rotates together with the rotor shaft 34. The rotor shaft 34 is rotatably supported by the motor housing 10 via bearings 14a and 14b. The rotor shaft 34 defines the rotating shaft 12 of the motor 1.

The rotor core 32 is formed, for example, from laminated steel plates of a magnetic material having a circular shape. Permanent magnets 321 are inserted inside the rotor core 32. The number and arrangement of the permanent magnets 321 are optional. In a modified example, the rotor core 32 may be formed from a green compact in which magnetic powder is compressed and solidified.

End plates 35A and 35B are attached to both axial sides of the rotor core 32. In addition to supporting the rotor core 32, the end plates 35A and 35B may also have a function to adjust imbalance of the rotor 30 (a function to eliminate imbalance by cutting, etc.).

As shown in FIG. 1, the rotor shaft 34 has a hollow portion 34A. The hollow portion 34A extends over the entire axial length of the rotor shaft 34. The hollow portion 34A may function as an oil passage. For example, as shown by the arrow R1 in FIG. 1, oil is supplied to the hollow portion 34A from one axial end side, and the oil flows along the radially inner surface of the rotor shaft 34, thereby cooling the rotor core 32 from the radially inner side. In addition, the oil flowing along the radially inner surface of the rotor shaft 34 may be ejected radially outward through oil holes 341, 342 formed at both ends of the rotor shaft 34 (arrows R5, R6) and used to cool the coil ends 220A, 220B.

Although FIG. 1 shows a motor 1 with a specific structure, the structure of the motor 1 is arbitrary as long as it has a stator coil 24 (described later) joined by welding. Thus, for example, the rotor shaft 34 may not have a hollow portion 34A, or may have a hollow portion with an inner diameter significantly smaller than that of the hollow portion 34A. Furthermore, while FIG. 1 shows a specific cooling method, the cooling method of the motor 1 is arbitrary. Thus, for example, an oil introduction pipe inserted into the hollow portion 34A may be provided, or oil may be dripped from an oil passage in the motor housing 10 from the radial outside toward the coil ends 220A, 220B.

In addition, while FIG. 1 shows an inner rotor type motor 1 in which the rotor 30 is disposed inside the stator 21, the present invention may be applied to other types of motors. For example, the present invention may be applied to an outer rotor type motor in which the rotor 30 is disposed concentrically outside the stator 21, or a dual rotor type motor in which the rotor 30 is disposed both outside and inside the stator 21.

Next, the configuration of the stator 21 will be described in detail with reference to Figure 2 onwards.

Figure 2 is a plan view of the stator core 22 in a single state. Figure 3 is a schematic diagram of a pair of coil pieces 52 to be assembled to the stator core 22. Figure 3 shows the relationship between the pair of coil pieces 52 and the slots 220 with the radially inner side of the stator core 22 unfolded. Also, in Figure 3, the stator core 22 is shown by dotted lines, and part of the slots 220 is not shown. Figure 4 is a perspective view of the periphery of the coil end 220A of the stator 21. Figure 5 is a perspective view showing part of the coil pieces of the same phase.

The stator 21 includes a stator core 22 and a stator coil 24.

The stator core 22 is made of, for example, a circular magnetic laminated steel plate, but in a modified example, the stator core 22 may be formed of a green compact in which magnetic powder is compressed and solidified. The stator core 22 may be formed of a split core that is split in the circumferential direction, or may not be split in the circumferential direction. A plurality of slots 220 around which the stator coil 24 is wound are formed on the radial inner side of the stator core 22. Specifically, as shown in FIG. 2, the stator core 22 includes a circular back yoke 22A and a plurality of teeth 22B extending radially inward from the back yoke 22A, and the slots 220 are formed between the plurality of teeth 22B in the circumferential direction. The number of slots 220 is arbitrary, but in this embodiment, as an example, 48 slots are used.

The stator coil 24 includes a U-phase coil, a V-phase coil, and a W-phase coil (hereinafter, when U, V, and W are not distinguished, they will be referred to as "phase coils"). The base end of each phase coil is connected to an input terminal (not shown), and the end of each phase coil is connected to the end of the other phase coil to form the neutral point of the motor 1. In other words, the stator coil 24 is star-connected. However, the connection mode of the stator coil 24 may be changed as appropriate depending on the required motor characteristics, etc. For example, the stator coil 24 may be delta-connected instead of star-connected.

Each phase coil is formed by joining multiple coil pieces 52. FIG. 6 is a schematic front view of one coil piece 52. The coil pieces 52 are in the form of segment coils in which the phase coil is divided into units that are easy to assemble (for example, units that can be inserted into two slots 220). The coil pieces 52 are formed by coating a linear conductor (rectangular wire) 60 with a rectangular cross section with an insulating coating 62. In this embodiment, the linear conductor 60 is formed of copper, as an example. However, in a modified example, the linear conductor 60 may be formed of another conductive material such as iron.

Before being assembled to the stator core 22, the coil piece 52 may be formed into a generally U-shaped shape having a pair of straight portions 50 and a connecting portion 54 connecting the pair of straight portions 50. When the coil piece 52 is assembled to the stator core 22, the pair of straight portions 50 are inserted into the slots 220 (see FIG. 3). As a result, the connecting portion 54 extends in the circumferential direction so as to straddle a plurality of teeth 22B (and therefore a plurality of slots 220) at the other axial end side of the stator core 22, as shown in FIG. 3. The number of slots 220 that the connecting portion 54 straddles is arbitrary, but is three in FIG. 3. After being inserted into the slot 220, the straight portion 50 is bent in the circumferential direction in the middle, as shown by the two-dot chain line in FIG. 6. As a result, the straight portion 50 becomes a leg portion 56 that extends axially within the slot 220 and a bridge portion 58 that extends circumferentially at one axial end of the stator core 22.

In FIG. 6, the pair of straight portions 50 are bent in a direction away from each other, but this is not limited thereto. For example, the pair of straight portions 50 may be bent in a direction toward each other. The stator coil 24 may also have a neutral point coil piece for connecting the ends of the three phase coils to form a neutral point.

In one slot 220, multiple leg portions 56 of the coil pieces 52 shown in FIG. 6 are inserted side by side in the radial direction. Therefore, multiple circumferentially extending bridge portions 58 are lined up in the radial direction at one axial end side of the stator core 22. As shown in FIG. 3 and FIG. 5, the bridge portion 58 of one coil piece 52 protruding from one slot 220 and extending to a first circumferential side (e.g., clockwise direction) is joined to the bridge portion 58 of another coil piece 52 protruding from another slot 220 and extending to a second circumferential side (e.g., counterclockwise direction).

In this embodiment, as an example, six coil pieces 52 are assembled in one slot 220. Hereinafter, they are also referred to as the first turn, second turn, and third turn, starting from the radially outermost coil piece 52. In this case, the first turn coil piece 52 and the second turn coil piece 52 have their tip portions 40 joined together by a joining process described below, the third turn coil piece 52 and the fourth turn coil piece 52 have their tip portions 40 joined together by a joining process described below, and the fifth turn coil piece 52 and the sixth turn coil piece 52 have their tip portions 40 joined together by a joining process described below.

As described above, the coil pieces 52 are covered with an insulating coating 62, but the insulating coating 62 is removed only from the tip portion 40. This is to ensure electrical connection with the other coil pieces 52 at the tip portion 40. Also, as shown in Figures 5 and 6, the axially outer end surface 42 of the tip portion 40 of the coil piece 52, i.e., one end surface in the width direction of the coil piece 52 (axially outer end surface 42), is ultimately made into an arc surface that convex outward in the axial direction.

Figure 7 is a diagram showing the tip 40 of the coil pieces 52 joined together and its vicinity. Note that Figure 7 also shows a schematic circumferential range D1 of the welding target area 90. Figure 8 is a cross-sectional view taken along line A-A in Figure 7, which passes through the welding target area 90.

When joining the tip portions 40 of the coil pieces 52, one coil piece 52 and another coil piece 52 are butted together so that the tip portions 40 form a C-shape in the view shown in FIG. 7 (as viewed in a direction perpendicular to the abutting surface 401). At this time, the two tip portions 40 to be joined together may be overlapped in the thickness direction and joined so that the central axes of the respective arcuate surfaces (axially outer end faces 42) coincide. By overlapping with the central axes aligned in this way, even when the bending angle α is relatively large or small, the axially outer lines of the two tip portions 40 to be joined together coincide and they can be appropriately overlapped.

In this case, the area to be welded 90 extends linearly along the contact surface 401 as shown in ranges D1 and D2. That is, the area to be welded 90 extends linearly across range D1 with a width of range D2 when viewed from the side irradiated with the laser beam 110 (see arrow W in Figures 7 and 8).

Here, in this embodiment, welding is used as a joining method when joining the tip portions 40 of the coil pieces 52. In this embodiment, the welding method is not arc welding, as typified by TIG welding, but laser welding using a laser beam source as a heat source. By using laser welding instead of TIG welding, the axial length of the coil ends 220A, 220B can be reduced. That is, in the case of TIG welding, it is necessary to bend the tips of the coil pieces to be abutted each other axially outward and extend them in the axial direction, whereas in the case of laser welding, such bending is not necessary, and as shown in FIG. 7, welding can be achieved in a state in which the tip portions 40 of the coil pieces 52 to be abutted each other extend in the circumferential direction. As a result, the axial length of the coil ends 220A, 220B can be reduced compared to when the tip portions 40 of the coil pieces 52 to be abutted each other are bent axially outward and extend in the axial direction.

In laser welding, as shown in FIG. 5, a welding laser beam 110 is applied to the welding target area 90 of the two abutted tip portions 40. The irradiation direction (propagation direction) of the laser beam 110 is approximately parallel to the axial direction, and is directed from the axial outside to the axially outer end faces 42 of the two abutted tip portions 40. In the case of laser welding, localized heating is possible, so that only the tip portions 40 and their vicinity can be heated, and damage (carbonization) of the insulating coating 62 can be effectively reduced. As a result, multiple coil pieces 52 can be electrically connected while maintaining appropriate insulation performance.

The circumferential range D1 of the welding area 90 is the entire circumferential range D0 of the axially outer end face 42 at the abutting portion of the tip ends 40 of the two coil pieces 52, excluding both ends, as shown in FIG. 7. This is because it is difficult to ensure sufficient welding depth (see dimension L1 in FIG. 7) at both ends due to the convex arc surface of the axially outer end face 42. The circumferential range D1 of the welding area 90 may be adapted so as to ensure the necessary joint area between the coil pieces 52, the necessary welding strength, etc.

The radial range D2 of the welding target area 90 is centered on the abutment surface 401 between the tips 40 of the two coil pieces 52, as shown in FIG. 8. The radial range D2 of the welding target area 90 may correspond to the diameter (beam diameter) of the laser beam 110. That is, the laser beam 110 is irradiated in such a manner that the irradiation position changes linearly along the circumferential direction without substantially changing in the radial direction. In other words, the laser beam 110 is moved so that the irradiation position changes in a straight line parallel to the abutment surface 401. This allows the laser beam 110 to be irradiated to the linear welding target area 90 more efficiently than when the irradiation position is changed in a loop (spiral) or zigzag (meandering) shape, for example.

Figure 9 is a diagram showing the relationship between the laser wavelength and the laser absorptance (hereinafter simply referred to as "absorption rate") for individual materials. In Figure 9, the horizontal axis represents the wavelength λ and the vertical axis represents the absorptance, and the characteristics of individual materials, copper (Cu), aluminum (Al), silver (Ag), nickel (Ni), and iron (Fe), are shown.

Incidentally, the infrared laser (with a wavelength of 1064 nm) commonly used in laser welding has a low absorption rate of about 10% for copper, the material of the linear conductor 60 of the coil piece 52, as shown by the black circle at the intersection with the dotted line of λ2 = 1.06 μm in Figure 9. In other words, in the case of an infrared laser, most of the laser beam 110 is reflected by the coil piece 52 and not absorbed. For this reason, a relatively large amount of heat input is required to obtain the required joint area between the coil pieces 52 to be joined, which can cause significant thermal effects and unstable welding.

In view of this, in this embodiment, a green laser is used instead of an infrared laser. The term "green laser" refers not only to a laser with a wavelength of 532 nm, i.e., an SHG (Second Harmonic Generation) laser, but also to lasers with wavelengths close to 532 nm. In a modified example, a laser with a wavelength of 0.6 μm or less that does not belong to the category of green lasers may be used. The wavelength of a green laser can be obtained by converting the fundamental wavelength produced by, for example, a YAG laser or YVO4 laser through an oxide single crystal (for example, LBO: lithium triborate).

In the case of a green laser, as shown by the black circle at the intersection with the dotted line of λ1 = 0.532 μm in Figure 9, the absorption rate is high at about 50% for copper, which is the material of the linear conductor 60 of the coil piece 52. Therefore, according to this embodiment, it is possible to ensure the necessary joint area between the coil pieces 52 with a smaller amount of heat input compared to when an infrared laser is used.

The characteristic that the absorption rate is higher with a green laser than with an infrared laser is particularly evident in the case of copper, as shown in FIG. 9, but this can also be seen in many other metal materials, not just copper. Therefore, welding with a green laser may be achieved even if the material of the linear conductor 60 of the coil piece 52 is something other than copper.

Figure 10 is an explanatory diagram of the change in absorption rate during welding. In Figure 10, the horizontal axis represents the laser power density, the vertical axis represents the laser absorption rate of copper, and the characteristics 100G for a green laser and 100R for an infrared laser are shown.

Figure 10 shows points P1 and P2 where melting of copper starts for the green laser and the infrared laser, as well as point P3 where a keyhole is formed. As shown by points P1 and P2 in Figure 10, it can be seen that the green laser can start melting copper at a lower laser power density than the infrared laser. Also, due to the difference in absorptivity described above, it can be seen that the difference between the absorptivity at point P3 where the keyhole is formed and the absorptivity at the start of irradiation (i.e., the absorptivity when the laser power density is 0) is smaller for the green laser than for the infrared laser. Specifically, in the case of the infrared laser, the change in absorptivity during welding is about 80%, while in the case of the green laser, the change in absorptivity during welding is about 40%, which is about half.

In this way, with infrared lasers, the change (drop) in absorption rate during welding is relatively large at about 80%, making the keyhole unstable and prone to variations in welding depth and width, and disturbance of the molten pool (e.g., spatter, etc.). In contrast, with green lasers, the change (drop) in absorption rate during welding is relatively small at about 40%, making the keyhole less likely to become unstable, and less likely to cause variations in welding depth and width, and disturbance of the molten pool (e.g., spatter, etc.). Spatter refers to metal particles that fly off when irradiated with a laser, etc.

In the case of infrared lasers, the absorption rate is low as described above, so it is common to make the beam diameter relatively small (for example, φ0.075 mm) to compensate for the low absorption rate. This also causes the keyhole to become unstable. FIG. 11B is an image of a keyhole when an infrared laser is used, where 1100 indicates a weld bead, 1102 indicates a molten pool, and 1104 indicates a keyhole. The arrow R1116 also shows a typical state of gas escape. The arrow R110 also shows a typical state in which the irradiation position of the infrared laser is moved due to the small beam diameter. In this way, in the case of infrared lasers, due to the low absorption rate as described above and the difficulty of making the beam diameter relatively large, a relatively long movement trajectory of the irradiation position including meandering (continuous irradiation time) tends to be required to obtain the required fusion width.

On the other hand, in the case of a green laser, since the absorption rate is relatively high as described above, it is possible to make the beam diameter relatively large (for example, φ0.1 mm or more), and the keyhole can be enlarged and stabilized. This improves gas escape and effectively reduces the occurrence of spatters, etc. FIG. 11A is an image of a keyhole when a green laser is used, and the meaning of the symbols is as described above with reference to FIG. 11B. In the case of a green laser, from FIG. 11A, it is easy to understand the image of how the keyhole is stabilized and gas escape is improved due to the expansion of the beam diameter. In addition, in the case of a green laser, in contrast to the case of an infrared laser, since the absorption rate is relatively high and the beam diameter can be relatively large as described above, the movement trajectory (irradiation time) of the irradiation position required to obtain the required fusion width (see the radial range D2 of the welding target part 90 shown in FIG. 8) can be made relatively short (small).

Figure 12 is an explanatory diagram of the green laser welding method according to this embodiment. In Figure 12, the horizontal axis represents time and the vertical axis represents laser output, and the time series waveform of the laser output during welding is shown diagrammatically.

In this embodiment, as shown in FIG. 12, welding is achieved by pulse irradiation of a green laser with a laser output of 3.8 kW. In FIG. 12, the laser oscillator is pulsed to achieve a laser output of 3.8 kW for 10 msec, and after an interval of 100 msec, the laser oscillator is pulsed again to achieve a laser output of 3.8 kW for 10 msec. Hereinafter, one pulse irradiation (10 msec pulse irradiation) possible by one pulse oscillation in this way is also referred to as "one pass." In FIG. 12, the first pass (N=1) to the third pass (N=3) are shown by pulse waveform 130G, and N represents the Nth pass (similarly in FIG. 18 below). In addition, FIG. 12 also shows a pulse waveform 130R related to pulse irradiation in the case of an infrared laser for comparison.

Here, in the case of green lasers, the output of the laser oscillator is low (for example, a maximum of 400 W during continuous irradiation), making it difficult to obtain the high output (for example, a high laser output of 3.0 kW or more) required to ensure deep penetration. That is, as described above, green lasers are generated through wavelength conversion crystals such as oxide single crystals, and the output decreases when passing through the wavelength conversion crystal. For this reason, if you try to irradiate the laser beam of a green laser continuously, you cannot obtain the high output required to ensure deep penetration.

In this respect, in this embodiment, as described above, the high output (e.g., high output of laser output 3.0 kW or more) required to ensure deep penetration is ensured by pulse irradiation of the green laser. This is because, even if continuous irradiation can only output a maximum of 400 W, for example, pulse irradiation can achieve a high output of, for example, 3.0 kW or more. In this way, pulse irradiation is realized by accumulating continuous energy to increase the peak power and pulsating it. When the circumferential range D1 of one welding target location 90 is relatively wide, multiple pulse oscillations may be realized for the one welding target location. In other words, two or more passes of irradiation with a relatively high laser output (e.g., laser output 3.0 kW or more) may be performed for the one welding target location. As a result, even if the circumferential range D1 of the above-mentioned welding target location 90 is relatively wide, it becomes easier to ensure deep penetration throughout the entire welding target location 90, and high-quality welding can be achieved.

In FIG. 12, the interval is a specific value of 100 msec, but the interval is arbitrary and may be minimized within a range in which the required high output is ensured. Also, in FIG. 12, the laser output is a specific value of 3.8 kW, but the laser output may be changed as appropriate within a range in which the required welding depth is ensured as long as it is 3.0 kW or more.

In FIG. 12, the pulse waveform 130R is also shown for the case of an infrared laser, when it is continuously irradiated for a relatively long time of 130 msec with a laser output of 2.3 kW. Unlike the green laser, the infrared laser allows for continuous irradiation at a relatively high laser output (2.3 kW). However, as described above, in the case of an infrared laser, a relatively long movement trajectory of the irradiation position (continuous irradiation time) including meandering is required to obtain the required melt width, and in this case, the heat input is approximately 312 J, which is significantly larger than the heat input of approximately 80 J (in the case of two passes) in the case of the green laser shown in FIG. 12.

In this way, according to this embodiment, by using a green laser, welding with a laser beam having a higher absorption rate for the material of the linear conductor 60 of the coil piece 52 (copper in this example) is possible compared to the case of using an infrared laser. This makes it possible to make the movement trajectory (time) of the irradiation position required to obtain the required fusion width (see the radial range D2 of the welding target portion 90 shown in FIG. 8) relatively short (small). In other words, due to the increased keyhole per pulse oscillation caused by the relatively large beam diameter, the number of pulse oscillations required to obtain the required fusion width can be relatively small. As a result, it is possible to secure the required joint area between the coil pieces 52 with a relatively small amount of heat input.

In addition, according to this embodiment, it is possible to perform two or more passes of green laser irradiation on one welding area. In this case, even if the circumferential range D1 of the welding area 90 is relatively wide, it is easier to ensure deep penetration throughout the welding area 90, and high-quality welding can be achieved.

Next, the relationship between the welding speed and various parameters will be described with reference to Figures 13A to 13D. Note that Figures 13A to 13D show the relationship in the case of a green laser, but the same tendency basically occurs in the case of an infrared laser. Therefore, the welding speed profile according to this embodiment described below can also be applied to infrared lasers, etc.

Figure 13A shows the relationship between welding speed and welding depth, with the horizontal axis representing the welding speed (unit: mm/s) and the vertical axis representing the welding depth (unit: mm). In Figure 13A, plots of test data and dotted lines representing approximation lines to these plots are shown (similar to Figure 13C below). Here, a constant laser power is used.

From FIG. 13A, it can be seen that when the laser output is the same, the lower the welding speed, the greater the weld depth (penetration depth). Note that the welding speed is the movement distance of the irradiation position of the laser beam 110 per unit time, and is a value obtained by, for example, dividing the movement distance of the irradiation position of the laser beam 110 over a certain time by the same time.

Figure 13B shows the relationship between welding speed and the number of spatters generated, with the horizontal axis representing the welding speed (unit: mm/s) and the vertical axis representing the number of spatters generated (unit: pieces). Figure 13B shows plots of the test data and a corresponding approximate curve with a dotted line (the same applies to Figure 13D described below).

Figure 13B shows that when the laser output is the same, the lower the welding speed, the more spatter occurs. In other words, it is possible to reduce the occurrence of spatter by increasing the welding speed.

Figure 13C shows the relationship between laser output (unit: [W]) and welding depth, and Figure 13D shows the relationship between laser output and the number of spatters generated. From Figure 13C, it can be seen that when the welding speed is the same, the welding depth (penetration depth) increases as the laser output is lower. Also, from Figure 13D, it can be seen that when the welding speed is the same, the number of spatters generated increases as the laser output is higher.

Next, with reference to Figures 14A to 15B, we will explain the issues involved when a single pass is achieved while maintaining a relatively low welding speed, and when a single pass is achieved while maintaining a relatively high welding speed.

Figure 14A is an explanatory diagram of a case where welding with a green laser is performed in one pass while maintaining a relatively low welding speed, and shows the relationship between the irradiation position and the welding speed (hereinafter also referred to as the "welding speed profile"). Figure 14B is an explanatory diagram of a case where welding with a green laser is performed in one pass while maintaining a relatively high welding speed, and shows the welding speed profile. In Figures 14A and 14B, the horizontal axis is the position and the vertical axis is the welding speed, and the welding speed profile for one pass is shown. Note that the arrow on the line showing the welding speed profile indicates the direction in which time progresses (the direction from the irradiation start position to the irradiation end position in one pass), and this is also the case in similar figures below (Figure 15, etc.).

In the examples shown in Figures 14A and 14B, in the case of one pass in which a relatively high welding speed is maintained, the movement amount of the irradiation position per pass (e.g., per 10 msec) is larger than in the case of one pass in which a relatively low welding speed is maintained, since the welding speed is higher, but the movement amount of the irradiation position may be adjusted appropriately along with the continuous irradiation time.

Figure 15A is a diagram showing a schematic diagram of an early welding state 150A, a middle welding state 150B, and a late welding state 150C when welding is performed with the welding speed profile shown in Figure 14A. Figure 15B is a diagram showing a schematic diagram of an early welding state 150D, a middle welding state 150E, and a late welding state 150F when welding is performed with the welding speed profile shown in Figure 14B. In Figures 15A and 15B, the movement direction of the irradiation position of the laser beam 110 (i.e., the welding direction) is shown typically by the arrow V.

As shown in FIG. 15A, when welding is performed with a welding speed profile with a relatively low welding speed, in the early stages of welding, as shown diagrammatically in state 150A, the weld depth is insufficient and the amount of spatter generated is small. In the middle stages of welding, as shown diagrammatically in state 150B, the necessary weld depth is secured and the keyhole is surrounded by the molten pool. At this time, the amount of spatter generated is small. Then, in the later stages of welding, as shown diagrammatically in state 150C, the weld depth increases further and the molten pool surrounding the keyhole (the part that rises on the surface) becomes larger. In such a molten pool around the keyhole, the part that rises on the surface is easily disturbed, and therefore the amount of spatter generated is large.

In this way, welding at a relatively low welding speed is advantageous in terms of weld depth as can be seen from Figure 13A, but is disadvantageous in that it generates a large amount of spatter.

On the other hand, as shown in FIG. 15B, when welding is performed with a welding speed profile with a relatively high welding speed, in the early stage of welding, as shown diagrammatically in state 150D, the weld depth is insufficient. In the middle stage of welding, as shown diagrammatically in state 150E, the weld depth increases but is still insufficient. At this time, the keyhole moves forward as the irradiation position moves significantly forward. Then, in the later stage of welding, as shown diagrammatically in state 150F, the molten pool (the raised part on the surface) flows backward relative to the keyhole as the irradiation position moves further significantly forward.

In this way, welding at a relatively high welding speed is advantageous in that less spatter is generated, but is disadvantageous in that the weld depth is insufficient (and therefore the joint area is insufficient), as can be seen from Figure 13A.

Therefore, in this embodiment, as described in detail below, a relatively low welding speed and a relatively high welding speed are appropriately used in one pass to ensure both the bonding area and the reduction in the number of spatters generated.

Figure 16 is an explanatory diagram of the welding speed profile according to this embodiment. In Figure 16, similar to Figures 14A and 14B described above, the horizontal axis represents position and the vertical axis represents welding speed, and the welding speed profile for one pass is shown.

As shown in FIG. 16, the welding speed profile in this embodiment includes, in the direction from the irradiation start position to the irradiation end position (see arrow), a first section 15D of a relatively high first speed V1, a second section 15B of a relatively low second speed V2, and a third section 15F of a relatively high third speed V3.

The first section 15D is a section from the irradiation start position, and is realized, for example, during the initial period of continuous irradiation time (e.g., 10 msec) for one pass. The first section 15D has the function of generating and stabilizing a molten pool by a relatively high first speed V1. In the first section 15D, the number of spatters generated is small because the first speed V1 is relatively high (see state 150D in FIG. 15B).

The second section 15B is a section that continues from the first section 15D, and is realized, for example, in an intermediate period of the continuous irradiation time (for example, 10 msec) for one pass. The second section 15B has the function of ensuring the welding depth by the relatively low second speed V2. In the second section 15B, a state similar to the state 150B shown in FIG. 15A is realized, and since the second speed V2 is relatively low, the necessary welding depth can be ensured. In addition, by not maintaining the second section 15B excessively long, the possibility of reaching the state 150C shown in FIG. 15A can be prevented, and the number of spatters generated can be suppressed. In other words, the second section 15B is terminated before reaching the state 150C shown in FIG. 15A.

The third section 15F is a section that continues from the second section 15B, and is realized, for example, in the final period of the continuous irradiation time (for example, 10 msec) for one pass. The third section 15F has a function of reducing the number of spatters generated by the relatively high third speed V3. In the third section 15F, a state similar to the state 150F shown in FIG. 15B is realized. However, in the third section 15F, since the second section 15B is passed through, the necessary welding depth secured in the second section 15B is still likely to be maintained. In other words, the keyhole formed in the second section 15B is likely to be maintained. On the other hand, in the third section 15F, as described above, the molten pool is likely to flow backward with respect to the keyhole (see state 150F shown in FIG. 15B), and the number of spatters generated is also small.

In this way, according to this embodiment, the first section 15D from the irradiation start position generates and stabilizes a molten pool, the second section 15B ensures the required welding depth, and the third section 15F maintains the required welding depth while reducing spatter that may occur if the second section 15B is continued. In this way, according to this embodiment, the joining area can be ensured by ensuring the required welding depth, and the number of spatters generated can be reduced by the third section 15F.

In this embodiment, the first speed V1 and the third speed V3 are preferably significantly greater than 200 mm/s, and more preferably significantly greater than 230 mm/s. The first speed V1 and the third speed V3 may be the same, or as shown in FIG. 16, the first speed V1 may be significantly greater than the third speed V3, or the first speed V1 may be significantly smaller than the third speed V3. In FIG. 16, the first speed V1=350 mm/s, and the third speed V3=250 mm/s.

The second speed V2 is preferably in the range of 100 mm/s to 200 mm/s, more preferably in the range of 120 mm/s to 180 mm/s, and most preferably in the range of 140 mm/s to 160 mm/s. In FIG. 16, the second speed V2 is 150 mm/s.

In the example shown in FIG. 16, the first speed V1 is constant throughout the first section 15D, but may vary. The same is true for the second speed V2 and/or the third speed V3. For example, when transitioning from the first section 15D to the second section 15B, the first speed V1 may be gradually reduced toward the second speed V2.

Here, during one pass according to the welding speed profile of this embodiment, the laser output is preferably constant, as shown in FIG. 17A. FIG. 17A is a schematic diagram showing an example of how the laser output (and welding heat input) for one pass changes depending on the irradiation position, and shows a schematic of the change characteristic 150P of the laser output depending on the irradiation position, and the change characteristic 150L of the welding heat input depending on the irradiation position. In FIG. 17A, as an example, the heat input for the entire one pass is represented by the area Q14.

In the example shown in FIG. 17A, one pass starts from position P10, which is the irradiation start position. That is, one pulse oscillation starts from position P10. In this case, the laser output rises to a predetermined value (3.8 kW in this example, as an example) at position P10 (see arrow R140). Then, the irradiation position is changed linearly from position P10 to position P12. During this time, the laser output is maintained at a predetermined value (3.8 kW in this example, as an example) (see arrow R141). When the irradiation position reaches position P12, which is the irradiation end position, the laser output is lowered from the predetermined value (3.8 kW in this example, as an example) to 0 (see arrow R142). That is, one pulse oscillation is ended. Note that even if the irradiation position reaches position P12, the irradiation position may be changed until it moves to position P13, which is a short distance away from position P12. During this time, a small amount of welding heat input occurs due to the remaining laser output (see Q14 in FIG. 17A). However, in a modified example, the change in the irradiation position may be terminated when the irradiation position reaches position P12 or a position immediately before it (not shown).

According to this irradiation mode, the laser output rises to a predetermined value (3.8 kW in this example) at position P10, but the welding heat input does not increase all at once to its maximum value until the actual laser output reaches the predetermined value. For this reason, as shown by the change characteristic 150L in FIG. 17A, the welding heat input gradually increases from position P10 to position P11. Then, at position P12, the laser output instantaneously falls to 0, but the welding heat input is maintained at its maximum value until immediately before this.

In this case, the welding speed profile according to this embodiment may be applied to the section from position P10 to position P13, or the section from position P11 to position P12, etc. For example, the first section 15D (see FIG. 16) related to the welding speed profile according to this embodiment may be included in the section from position P10 to position P11, or the section from position P11 to position P12. The second section 15B (see FIG. 16) may be included in the section from position P11 to position P12. The third section 15F (see FIG. 16) may be included in the section from position P11 to position P12, or the section from position P11 to position P13.

However, during one pass using the welding speed profile according to this embodiment, the laser output does not have to be constant, as shown in FIG. 17B. FIG. 17B is a schematic diagram showing another example of the manner in which the welding heat input for one pass changes depending on the irradiation position, and similarly to FIG. 17A, it shows a schematic diagram of the change characteristic 150P of the laser output depending on the irradiation position and the change characteristic 150L of the welding heat input depending on the irradiation position.

In the example shown in FIG. 17B, one pass starts from position P10, which is the irradiation start position. That is, one pulse oscillation starts from position P10. In this case, the laser output rises to a predetermined value (3.8 kW in this example, as an example) at position P10 (see arrow R140). Then, the irradiation position is changed linearly from position P10 to position P12. While the irradiation position is from position P10 to position P14, the laser output is maintained at a predetermined value (3.8 kW in this example, as an example) (see arrow R141). When the irradiation position reaches position P14, the laser output is stepped down from a predetermined value (3.8 kW in this example, as an example) to 0 (see arrow R143). Specifically, when the irradiation position reaches position P14, the laser output is stepped down by one step, when the irradiation position reaches position P12, the laser output is further stepped down by one step, and when the irradiation position reaches position P15, which is the irradiation end position, the laser output is stepped down to 0. Even if the irradiation position reaches position P15, the irradiation position may be changed until it moves to position P16, which is a small distance away from position P15. During this time, a small amount of welding heat input occurs due to the remaining laser output (see Q14 in FIG. 17A). However, in a modified example, the change in the irradiation position may be terminated when the irradiation position reaches position P15.

In this case, the welding speed profile according to this embodiment may be applied to the section from position P10 to position P15, the section from position P11 to position P12, etc. For example, the first section 15D (see FIG. 16) related to the welding speed profile according to this embodiment may be included in the section from position P10 to position P11, or the section from position P10 to position P14. The second section 15B (see FIG. 16) may be included in the section from position P11 to position P14, or the section from position P11 to position P12. The third section 15F (see FIG. 16) may be included in the section from position P11 to position P14, the section from position P11 to position P12, the section from position P14 to position P12, or the section from position P14 to position P16.

In the above, a case where one pass of the green laser is applied to one welding location 90 has been described, but two or more passes of the green laser may be applied to one welding location 90 depending on the range (length) of the welding location 90.

Figure 18 is a diagram showing a preferred welding speed profile when two passes of a green laser are performed on one welding target area 90. In Figure 18, similar to Figure 16 above, the horizontal axis represents position and the vertical axis represents welding speed, and the welding speed profiles for two passes are shown. Note that in Figure 18, the welding speed profile for the second pass is shown by a dotted line.

In the example shown in FIG. 18, the first pass is achieved by one pulse oscillation for the first irradiation section D11 according to the welding speed profile of this embodiment, and the second pass is achieved by the next pulse oscillation for the second irradiation section D12 according to the welding speed profile of this embodiment. The welding by the first pass and the welding by the second pass cooperate to cover the entire circumferential range D1 (see FIG. 7) of the welding target area 90.

In this embodiment, the first irradiation section D11 of the first pass and the second irradiation section D12 of the second pass preferably overlap each other in such a manner that the first section 15D of one overlaps the second section 15B or the third section 15F of the other. That is, the first section 15D of the first pass overlaps the second section 15B or the third section 15F of the second pass, and the first section 15D of the second pass overlaps the second section 15B or the third section 15F of the first pass. This makes it possible to ensure the necessary welding depth (and the associated joint area) by the second section 15B or the third section 15F of the other pass in the first section 15D of both the first and second passes.

In the example shown in FIG. 18, the first section 15D of the first pass overlaps with the third section 15F of the second pass, and the first section 15D of the second pass overlaps with the third section 15F of the first pass. Also, the second section 15B of the first pass completely overlaps with the second section 15B of the second pass. However, in a modified example, the second section 15B of the first pass may partially overlap or be offset from the second section 15B of the second pass.

In this way, even if the circumferential range D1 of the area to be welded 90 is relatively wide, applying two or more passes of green laser irradiation with the welding speed profile according to this embodiment can ensure the required welding depth (and therefore the required joint area) and reduce the amount of spatter generated.

The example shown in FIG. 18 relates to a case where the welding direction (direction of change in irradiation position) is opposite in the first pass and the second pass, but the welding speed profile according to this embodiment is also applicable when welding is realized by two passes with the same welding direction (direction of change in irradiation position). In this case, the first section 15D of the second pass may be set to overlap the third section 15F (or the second irradiation section D12) of the first pass. This makes it possible to ensure the necessary welding depth (and the associated joint area) by the third section 15F (or the second irradiation section D12) of the first pass in the first section 15D of the second irradiation section D12 of the second pass. That is, it is possible to prevent the inconvenience of a portion in which the welding depth (and the associated joint area) is insufficient due to the first section 15D of the second pass in the circumferential range D1 of the welding target portion 90. In addition, the first section 15D of the first pass may be set outside the circumferential range D1 of the welding target portion 90. In this way, even when welding is achieved using two passes with the same welding direction (direction of change in irradiation position), the welding speed profile according to this embodiment ensures the necessary welding depth (and therefore the necessary joint area) in the circumferential range D1 of the welding target area 90, while reducing the amount of spatter generated.

Figure 19 is a flow chart that shows the outline of the manufacturing method for the stator 21 of the motor 1.

First, this manufacturing method includes an assembly process (step S150) in which the coil pieces 52 are assembled to the stator core 22. In addition, this manufacturing method includes a joining process (step S152) in which the tip ends 40 of the coil pieces 52 are joined together by laser welding after the assembly process. The method for joining the tip ends 40 of the coil pieces 52 together by laser welding is as described above.

In this case, the joining process includes a setting process (step S1521) in which the tip portions 40 of each pair of coil pieces 52 are set so as to abut against each other in the radial direction, as described above. In the setting process, a jig or the like may be used to maintain the state in which the tip portions 40 of each pair of coil pieces 52 are abutted against each other in the radial direction.

The joining process includes an irradiation process (step S1522) in which the laser beam 110 is irradiated onto the welding target points 90 as described above after the setting process. The setting process and the irradiation process may be performed as a set for one or more predetermined number of welding target points 90, or may be performed collectively for all welding target points 90 related to one stator 21. The present manufacturing method may end by completing the stator 21 by appropriately performing various necessary processes after the joining process.

Although each embodiment has been described in detail above, it is not limited to a specific embodiment, and various modifications and changes are possible within the scope of the claims. It is also possible to combine all or a combination of multiple components of the embodiments described above. Furthermore, among the effects of each embodiment, the effects related to the dependent claims are additional effects that are distinguished from the superordinate concept (independent claim).

For example, in the above-described embodiment, the welding target area 90 extends linearly along the contact surface 401 as shown in ranges D1 and D2 in FIG. 7 and FIG. 8, but is not limited to this. The welding target area 90 may be set in a curved manner when viewed from the side irradiated with the laser beam 110. In this case, the irradiation section by the laser beam 110 may include a section where the irradiation position changes linearly and a section where the irradiation position changes curvedly. The welding speed profile according to the above-described embodiment may be applied to the section where the irradiation position changes curvedly.

In the above embodiment, since the continuous irradiation time that can secure the necessary laser output is relatively short in the case of a green laser as described above, the welding speed profile according to this embodiment consists of the first section 15D, the second section 15B, and the third section 15F, but is not limited to this. If the continuous irradiation time that can secure the necessary laser output can be lengthened with future technological developments, the welding speed profile according to this embodiment may include the first section 15D, the second section 15B, the third section 15F, the second section 15B, and the third section 15F, and so on, in which the second section 15B and the third section 15F are alternately repeated after the first section 15D. In this case, the number of sets of the second section 15B and the third section 15F is any number equal to or greater than 2. In this case, the welding speed profile may end at the third section 15F or may end at the second section 15B. This welding speed profile, which alternates between the second section 15B and the third section 15F, is also suitable for infrared lasers, which are capable of relatively long, continuous irradiation.

The above-described embodiment relates to joining the tip ends 40 of the coil pieces 52 together, but it can also be applied to joining the tip end 40 of the coil piece 52 to the end of a bus bar (not shown). In this case, the tip end 40 of the coil piece 52 joined to the end of the bus bar may be the tip end of a transition part that forms a power line or a neutral point.

For example, in FIG. 20, the ends 80 and 81 of the busbar held by the terminal block 70 and the tip 40A of the coil piece 52A are joined together. In this case, the busbar held by the terminal block 70 is electrically connected to a three-phase external terminal 71 within the terminal block 70. Laser welding using the welding speed profile according to this embodiment may also be applied to the joint between the ends 80 and 81 of the busbar and the tip 40A of the coil piece 52A. In this case, the welding target points may be set to the abutment surfaces appearing on the tip surfaces of the ends 80 and 81 of the busbar and the tip 40A of the coil piece 52A. In FIG. 20, the L direction corresponds to the axial direction, the R direction corresponds to the radial direction, the R1 side corresponds to the radial inner side, and the R2 side corresponds to the radial outer side. In FIG. 20, the ends 80 and 81 of the busbar and the tip 40A of the coil piece 52A are in contact with each other in a manner that completely overlaps when viewed in the radial or axial direction, but they may also be in contact in a specific direction, such as an X-shaped crossing or a C- or L-shaped crossing when viewed in a specific direction (for example, the circumferential direction). In this case, the welding target area 90 may be set in a straight line along the axially outer edge of the contact surface.

In the above-mentioned embodiment, the coil pieces 52 having the tip portions 40 whose axially outer end faces 42 are machined into convex arc surfaces as shown in FIG. 6 are brought into radial contact with each other as shown in FIG. 7 to form the welding target portion 90, but this is not limited thereto. For example, the coil pieces having such unmachined tip portions (i.e., a configuration in which the axially outer end faces 42 extend linearly and connect to the tip faces as viewed in the radial direction) may be brought into radial contact with each other to form the welding target portion 90. In this case, the coil pieces may be brought into radial contact with each other such that the tip portions 40 (unmachined tip portions 40) cross each other in an X-shape as viewed in the radial direction, or in a C-shape or L-shape as viewed in the radial direction.

1: motor (rotating electric machine), 24: stator coil, 52: coil piece, 40: tip (end), 22: stator core, 80, 81: end of bus bar, 110: laser beam

Claims (5)

an assembly process of assembling coil pieces of the stator coil onto a stator core;
a joining step of joining ends of the coil pieces to each other or joining the ends of the coil pieces to ends of bus bars by laser welding after the assembling step,
The joining step includes:
a setting process in which two ends of the objects to be joined are brought into contact with each other;
and an irradiation step of irradiating the two ends with a laser beam,
The irradiation section of the laser beam in the irradiation step includes a continuous irradiation section in which the irradiation position of the laser beam changes continuously,
the continuous irradiation section includes, in a sequence along a moving direction of the irradiation position of the laser beam from an irradiation start position to an irradiation end position, a first section in which the irradiation position of the laser beam changes at a first speed, a second section in which the irradiation position of the laser beam changes at a second speed lower than the first speed, and a third section in which the irradiation position of the laser beam changes at a third speed higher than the second speed ;
In the continuous irradiation section, the irradiation position of the laser beam moves on a straight line connecting the irradiation start position and the irradiation end position . The method for manufacturing a stator for a rotating electric machine according to claim 1, wherein the continuous irradiation section is such that the irradiation position of the laser beam changes linearly, the first section starts from an irradiation start position, the second section continues from the first section, and the third section continues from the second section. The irradiation step includes generating a laser beam having a wavelength of 0.6 μm or less for each pulse oscillation of a laser oscillator,
3. The method for manufacturing a stator for a rotating electric machine according to claim 1, wherein one of the continuous irradiation sections is realized by one pulse oscillation. The method for manufacturing a stator for a rotating electric machine according to claim 3, wherein the irradiation process joins the two ends by two or more pulse oscillations in such a manner that one continuous irradiation section is realized for each pulse oscillation. The method for manufacturing a stator for a rotating electric machine according to claim 4, wherein one of the continuous irradiation sections and another of the continuous irradiation sections overlap each other in such a manner that one of the first sections overlaps with one of the second section or the third section.