Manufacturing method of magnet unit and magnet unit

Abstract

To provide a manufacturing method of a magnet unit capable of suppressing deformation of a hold member, and a magnet unit.SOLUTION: Provided is a manufacturing method of a magnet unit comprising a hold member, in which a plurality of slots is provided, and bond magnets disposed inside of the plurality of slots. The manufacturing method includes the steps of: injecting a magnet material from an opening at the side of one end in each of the plurality of slots via a plurality of gates; and cutting the magnet material in the plurality of gates. A cross-sectional area of each of the plurality of gates is set in such a manner that an internal pressure of the magnet material does not exceed a threshold, at which the hold member is plastically deformed, inside of each of the plurality of slots, and the threshold is calculated based on a shape of the hold member.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a magnet unit and a magnet unit.

Background Art

[0002] Patent Document 1 describes an embedded magnet type motor including a magnet embedded in a hole of a rotor core. In the hole of the rotor core, a bonded magnet is formed by injection molding.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When injecting the material of the bonded magnet into the hole of a magnet unit such as a rotor core, there may be a problem that the holding member of the magnet unit is deformed due to the internal pressure generated inside the hole.

[0005] An embodiment according to the present disclosure has been made in view of the above problems, and an object thereof is to provide a method for manufacturing a magnet unit and a magnet unit capable of suppressing deformation of the holding member.

Means for Solving the Problems

[0006] In one aspect of the present disclosure, there is provided a method for manufacturing a magnet unit having a holding member provided with a plurality of slots and bonded magnets disposed inside each of the plurality of slots. The manufacturing method includes a step of injecting a magnet material through each of a plurality of gates from an opening on one end side of each of the plurality of slots, and a step of cutting the magnet material at the plurality of gates. The cross-sectional area of each of the plurality of gates is set such that the internal pressure of the magnet material does not exceed a threshold value at which the holding member plastically deforms inside each of the plurality of slots, and the threshold value is calculated based on the shape of the holding member.

[0007] A magnet unit according to one aspect of the present disclosure has a holding member provided with a plurality of slots and bonded magnets disposed inside each of the plurality of slots. The magnet unit includes a pair of end faces in which a plurality of slots penetrating along a central axis are formed, and the bonded magnet has a gate mark formed when a magnet material is injected into the inside of the slot from one side of the pair of end faces, and the areas of the gate marks having different radial distances from the central axis are different, the magnet unit.

Advantages of the Invention

[0008] According to the embodiment of the present disclosure, it is possible to provide a method for manufacturing a magnet unit and a magnet unit capable of suppressing deformation of a holding member.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Mode for Carrying Out the Invention

[0010] Hereinafter, with reference to the drawings, a magnet unit and a method for manufacturing the magnet unit according to an embodiment of the present disclosure will be described. The following embodiments exemplify a magnet unit and a method for manufacturing the magnet unit for embodying the technical idea of the present embodiment, and are not limited thereto. In addition, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the embodiments are not intended to limit the scope of the present disclosure only thereto without specific description, but are merely illustrative examples. Note that the sizes, positional relationships, etc. of the members shown in each drawing may be exaggerated for clarity of explanation. In the following description, the same names and reference numerals indicate the same or similar members, and detailed descriptions will be omitted as appropriate. In the following description, "area" means "area" in a plan view unless otherwise specified. Also, "shape" is used as a concept including size. For example, when two shapes are similar to each other but different in size, the two shapes are different.

[0011] <1. First Embodiment> (1.1. Magnet Unit 1) The magnet unit 1 according to the first embodiment will be described with reference to FIGS. 1 and 2. The magnet unit 1 is, for example, a rotor core and includes a holding member 10 and a plurality of bonded magnets 40. As shown in FIG. 1, the holding member 10 is formed in a cylindrical shape as an example, and includes an outer surface 13 along the central axis A of the holding member 10 and a pair of end faces, a first end face 11 and a second end face 12, that are perpendicular to the central axis A. The holding member 10 is provided with a plurality of slots 14 as holes penetrating from the first end face 11 to the second end face 12 along the central axis A. Each of the plurality of bonded magnets 40 is disposed inside each of the plurality of slots 14. A gate mark 50 is formed on an exposed surface 41 exposed on the first end face 11 side of the bonded magnet 40.

[0012] The holding member 10 may be a magnetic material. As an example, the holding member 10 may be a laminated steel plate composed of a plurality of steel plates laminated in a direction from the second end face 12 toward the first end face 11. The laminated steel plate may be, for example, an electromagnetic steel plate.

[0013] The bonded magnet 40 includes a resin and magnetic powder. As the resin constituting the magnet material 30, materials described later can be used. As the magnetic powder constituting the magnet material 30, materials described later can be used. As an example, the bonded magnet 40 can have a resin and SmFeN-based magnetic powder. The content rate of the magnetic powder in the bonded magnet 40 is preferably 50% by volume or more, and more preferably 60% by volume or more. Thereby, the residual magnetic flux density of the bonded magnet 40 can be improved. The volume ratio of the filling rate of the magnetic powder in the bonded magnet 40 may be calculated from a partial cross section of the bonded magnet 40. For example, a scanning electron microscope (SEM) image of a partial cross section of the bonded magnet 40 may be taken, and the ratio of the area of the magnetic powder to the area of the bonded magnet 40 in the SEM image may be regarded as the volume ratio of the filling rate of the magnetic powder in the bonded magnet 40.

[0014] The shape, size, number, etc. of the plurality of slots 14 provided in the holding member 10 are set according to the target value of the magnetic characteristics of the magnet unit 1. As an example, the number of the plurality of slots 14 may be 2 or more, may be 8 or more, and may be 30 or more.

[0015] Preferably, the magnet unit 1 has rotational symmetry with respect to the central axis A. In the present embodiment, as an example, the slots 14 are provided in the holding member 10 so as to be rotationally symmetric four times with respect to the central axis A. That is, as shown in FIG. 2, in a plan view, the slots 14 are formed so as to have rotational symmetry every 90° with respect to the central axis A. The slot 14 includes an outer slot 14a that is arcuately warped in a direction opposite to the outer surface 13 of the holding member 10 in a plan view, and an inner slot 14b that is disposed closer to the central axis A side than the outer slot 14a and is arcuately warped in the same direction as the outer slot 14a. The inner slot 14b is divided into three parts and includes one central part 14b1 and two end parts 14b2.

[0016] Note that the shapes of the plurality of slots 14 in a plan view may all be similar to each other (that is, when one is enlarged or reduced, it substantially coincides with the other), or some may be similar to each other and the other parts may have different shapes. In this case, in a region having rotational symmetry with respect to the central axis A, a plurality of slots 14 having similar shapes and one or a plurality of slots 14 having different shapes may be mixed.

[0017] It is preferable that the ratio of the width W to the depth H in the plurality of slots 14 satisfies the relationship of 1 / 10 ≦ W / H ≦ 1 / 50, and it is more preferable that the relationship of 1 / 20 ≦ W / H ≦ 1 / 50 is satisfied. In this way, the larger the depth H is with respect to the width W, the more difficult it becomes to fill the plurality of slots 14 simultaneously, so that the effects of the technical idea of the present disclosure can be easily obtained. Further, in a plan view, when the area of the largest slot 14 is Smax and the area of the smallest slot 14 is Smin, it is preferable that the relationship of 1 / 1 ≦ Smin / Smax ≦ 1 / 10 is satisfied. In this way, the larger the difference in area between the plurality of slots 14 in a plan view, the more difficult it becomes to fill the plurality of slots 14 simultaneously, so that the effects of the technical idea of the present disclosure can be easily obtained.

[0018] The gate mark 50 formed on the exposed surface 41 of the bonded magnet 40 is formed when the magnet material 30 is injected into the inside of the slot 14 from the first end face 11 side. As an example, the gate mark 50 has, for example, a convex shape on the exposed surface 41. The shape of the gate mark 50 in a plan view is, for example, circular, elliptical or oval. One or more gate marks 50 are provided on one bonded magnet 40.

[0019] The gate mark 50 includes a first gate mark 50a and a second gate mark 50b. The area of the gate mark 50 differs depending on the distance from the central axis A. The first gate mark 50a is located at a position where the distance (hereinafter also simply referred to as the distance) in a plan view is longer than that of the second gate mark 50b with respect to the central axis A, and the area of the first gate mark 50a is larger than the area of the second gate mark 50b. As shown in FIG. 2, the central portion 14b1 of the inner slot 14b is provided with the second gate mark 50b, and the end portion 14b2 of the inner slot 14b and the outer slot 14a are provided with the first gate mark 50a.

[0020] (1.2. Manufacturing method of the magnet unit 1) Hereinafter, with reference to FIGS. 3 to 9, the manufacturing method of the magnet unit 1 in the present disclosure will be described in detail. In this specification, the term "step" includes not only an independent step but also a step that cannot be clearly distinguished from other steps as long as the intended purpose of the step is achieved.

[0021] As shown in FIG. 3, the manufacturing process of the magnet unit 1 of the embodiment includes a threshold calculation step S100, a gate area setting step S200, an arrangement step S300, an injection step S400, and a take-out step S500. Hereinafter, each step will be described in detail.

[0022] (1.2.1. Threshold calculation step) In the threshold calculation step (S100), the threshold of the internal pressure generated when injecting the magnet material 30 into the slot 14 in the subsequent injection step (S400) is calculated. As an example, the threshold can be obtained as the pressure at which the magnet unit 1 undergoes plastic deformation by performing a strength analysis simulation based on the shape of the holding member 10.

[0023] Specifically, for example, a strength analysis simulation is performed using well-known finite element method analysis software. In this simulation, three-dimensional model data showing the shape of the holding member 10 and information on the material of the holding member 10 are used as input parameters for the strength analysis. Examples of the information on the material of the holding member 10 include material, material quality (standard), manufacturer, Young's modulus, Poisson's ratio, yield stress (F1), tensile strength, coefficient of linear expansion, and the like.

[0024] As an example, when performing a strength analysis simulation on the holding member 10 having the shape shown in FIG. 4, as parts where plastic deformation is likely to occur due to the internal pressure in the slot 14, there are parts B1 between the end 14b2 of the inner slot 14b and the outer surface 13, part B2 between the central part 14b1 and the end 14b2 of the inner slot 14b, part B3 between the outer slot 14a and the outer surface 13, and the like. Therefore, when performing a strength analysis simulation on these parts, for example, a graph shown in FIG. 5 can be obtained as the analysis result.

[0025] In the graph shown in FIG. 5, when the internal pressure in the injection process is increased, the equivalent stress that can occur at sites B1 to B3 is shown. When the equivalent stress exceeds the yield stress F1 of the holding member 10, plastic deformation occurs. From the analysis results shown in FIG. 5, it can be read that plastic deformation can occur at site B3 when the internal pressure is P1. Therefore, the threshold value of the internal pressure when injecting the magnet material 30 into the slot 14 of the holding member 10 is calculated as P1.

[0026] (1.2.2. Gate Area Setting Process) In the gate area setting step (S200), the cross-sectional area of the gate 24 (see FIG. 6) is set when injecting the magnet material 30 into the slot 14 in the subsequent injection step (S400). In the present disclosure, the cross-sectional area of the gate 24 means the cross-sectional area of the opening of the gate 24. The cross-sectional area is set by performing a flow analysis simulation.

[0027] Specifically, for example, a flow analysis simulation regarding the filling of the magnet material 30 into the slot 14 is performed using well-known flow analysis software. In the simulation, three-dimensional model data showing the shape of the holding member 10, information regarding the material of the magnet material 30 injected into the slot 14 in the injection process, information regarding the molding conditions when performing the injection process, and information regarding the cross-sectional area of the gate 24 are input into the flow analysis software as input parameters. Examples of the information regarding the material of the magnet material 30 include the material name and the mixing ratio of the materials. Examples of the information regarding the molding conditions include the resin temperature, the mold temperature, and the injection speed (or injection pressure).

[0028] When performing a fluid analysis simulation, it is possible to analyze in what manner the magnet material 30 is filled in each slot 14 of the holding member 10 having the input shape. For example, when the cross-sectional area of the gate 24 for injecting the magnet material into each slot 14 of the holding member 10 is set to be constant, analysis results such as that the filling of the other slots 14 (that is, the end portions 14b2 of the inner slot 14b and the outer slot 14a) is not completed at the timing when the filling of the central portion 14b1 of the inner slot 14b is completed are output. Thus, if there is a deviation in the filling timing for each slot 14, the internal pressure inside the slot 14 with early filling will rapidly increase, which may cause plastic deformation of the holding member 10. Therefore, in the present embodiment, the cross-sectional areas of the plurality of gates 24 are set so that the filling is performed at substantially the same timing in the plurality of slots 14. In the present disclosure, "filled at substantially the same timing" means that at a certain point in time, the filling rates of the plurality of slots 14 are 90% to 100%, and more preferably, the filling rates of the plurality of slots 14 are 95% to 100%.

[0029] Specifically, for example, the cross-sectional areas of the plurality of gates 24 are set such that the gate 24 having a longer distance in a plan view from the sprue 22 (see FIGS. 7 and 8) from which the magnet material 30 flows out is larger. That is, by reducing the cross-sectional area of the gate 24 facing the central portion 14b1, it is possible to adjust so that the magnet material 30 is filled at the same timing as the other slots 14 (the end portions 14b2 of the inner slot 14b and the outer slot 14a). When the cross-sectional shape of the gate 24 is circular, the cross-sectional area of the gate 24 may be set by setting the diameter of the gate 24. Note that the diameter of the gate 24 means the diameter of the opening of the gate 24.

[0030] In the fluid analysis simulation, in accordance with the filling timing of the slot 14, the pressure generated inside the slot 14 is also analyzed. In this way, the cross-sectional area of each of the plurality of gates 24 is set such that the internal pressure generated by the bonded magnet material inside each of the plurality of slots 14 does not exceed the threshold value at which the holding member 10 calculated in the threshold value calculation step (S100) undergoes plastic deformation.

[0031] (1.2.3. Arrangement step) In the arrangement step (S300), the holding member 10 is arranged in the mold 20. As shown in FIG. 6, the mold 20 is composed of a plurality of parts. Since the mold 20 is composed of a plurality of parts, it is easy to fix the holding member 10 by the mold 20, and the holding member 10 can be easily taken out from the mold 20. Inside the mold 20, a plurality of flow paths 21 through which the magnet material 30 flows are provided.

[0032] FIGS. 7 and 8 schematically show a plurality of flow paths 21 provided inside the mold 20. As shown in FIGS. 7 and 8, the plurality of flow paths 21 include a sprue 22 extending in the vertical direction, a plurality of runners 23 extending horizontally from the sprue, and a plurality of gates 24 extending from the plurality of runners 23 toward the holding member 10 side. As an example, the sprue 22 is arranged on the extension line of the central axis A of the holding member 10. The gate 24 is provided at the end of the plurality of runners 23 and is arranged to face the opening of the slot 14 on the first end face 11.

[0033] Inside the mold 20, a pressure sensor 25 is further provided. As an example, as shown in FIG. 6, the pressure sensor 25 is arranged to face the opening on the second end face side of the slot 14. Thereby, the internal pressure of the magnet material 30 filled in the slot 14 can be accurately measured.

[0034] As shown in Fig. 8, in a plan view, the flow path 21 has rotational symmetry every 90° with respect to the central axis A of the holding member 10. The runner 23 includes an extension portion 23a extending radially from the sprue 22 and a branch portion 23b branching from the extension portion 23a. In this way, by arranging the sprue 22 on the extension line of the central axis A of the holding member 10 and providing a plurality of runners 23 extending horizontally from the sprue 22 and a plurality of gates 24 extending from the plurality of runners 23 in rotational symmetry with respect to the central axis A, it becomes easy to uniformly fill the magnet material 30 into each slot 14.

[0035] Also, as described above, the cross-sectional areas of the plurality of gates 24 are set such that the gate 24 with a longer distance from the sprue 22 from which the magnet material 30 flows out is larger. As shown in Fig. 8, the gate 24 includes a first gate 24a and a second gate 24b. The first gate 24a is farther from the sprue 22 than the second gate 24b, and the cross-sectional area of the first gate 24a is larger than the cross-sectional area of the second gate 24b.

[0036] (1.2.4. Injection process) In the injection process (S400), the magnet material 30 is injected into the plurality of slots 14 by injection molding to fill the slots 14 with the magnet material 30. As shown in Fig. 9, the magnet material 30 is injected from the sprue 22 into the mold 20 and reaches the slot 14 via the runner 23 and the gate 24. The injection process can be performed, for example, until the slot 14 is filled with the magnet material 30. The degree of filling at which the injection molding is terminated may be appropriately set according to the magnetic characteristics of the target magnet unit.

[0037] The magnet material 30 has a resin and magnetic powder. The resin may be a thermoplastic resin or a thermosetting resin. The resin may include both a thermosetting resin and a thermoplastic resin. Although the resin is, for example, a thermoplastic resin, it is also possible to preferably implement the technical idea in the present disclosure by using a thermosetting resin.

[0038] Thermoplastic resins include, for example, nylon resins (polyamide resins); polyolefins such as polypropylene (PP) and polyethylene (PE); polyesters; polycarbonate (PC); polyphenylene sulfide resin (PPS); polyetheretherketone (PEEK); polyacetal (POM); liquid crystal polymer (LCP), etc. Nylon resins include polyamides such as nylon 6, nylon 11, and nylon 12; condensates of dicarboxylic acids and diamines such as nylon 6,6, nylon 6,10, and nylon 6,12; copolyamides such as 6 / 6,6 nylon, 6 / 6,10 nylon, 6 / 12 nylon, 6 / 6,12 nylon, 6 / 6,10 / 6,10 nylon, 6 / 6,6 / 6,12 nylon, and 6-nylon / polyether; nylon 6T, nylon 9T, nylon MXD6, aromatic nylon, amorphous nylon, etc. As the thermoplastic resin, for example, nylon 12 can be used.

[0039] Magnetic powders include, for example, rare earth magnetic powders such as SmFeN-based, NdFeB-based, and SmCo-based. The magnetic powder may be a SmFeN-based magnetic powder. In this case, the magnet material 30 has a resin and a SmFeN-based magnetic powder. Examples of the SmFeN-based magnetic powder include nitrides composed of the rare earth metal Sm, iron Fe, and nitrogen N represented by the general formula x Fe 100-x-y N y Preferably, x is 8.1 atomic % or more and 10 atomic % or less, y is 13.5 atomic % or more and 13.9 atomic % or less, and the balance is mainly Fe. The magnetic powder may be a SmFeN-based magnetic powder having a Th2Zn17-type crystal structure. The magnetic powder may be a SmFeN-based anisotropic magnetic powder. The SmFeN-based magnetic powder can be produced, for example, by the method disclosed in JP-A-11-189811. The magnetic powder may have a SmFeN-based core portion and a coating portion containing P and O. The magnetic powder may be surface-treated with a silane coupling agent or the like.

[0040] The average particle size of the magnetic powder is preferably 10 μm or less. Thereby, the crystal grain size can be reduced, and the coercive force of the magnetic powder can be increased. The smaller the average particle size of the magnetic powder, the more likely the fluidity of the magnet material 30 is to decrease. The average particle size of the magnetic powder is more preferably 6 μm or less, and even more preferably 4 μm or less. Thereby, the coercive force of the magnetic powder can be further increased. The average particle size of the magnetic powder is preferably 1 μm or more. Thereby, the filling rate of the magnetic powder in the magnet material 30 can be increased. The average particle size of the magnetic powder is more preferably 2 μm or more, and even more preferably 2.5 μm or more. The average particle size of the magnetic powder is preferably 1 μm or more and 10 μm or less, more preferably 2 μm or more and 10 μm or less, and even more preferably 2 μm or more and 4 μm or less. The average particle size is measured as the particle size corresponding to 50% volume cumulative from the small particle size side in the particle size distribution, and can be measured, for example, by a laser diffraction particle size distribution measuring device (HELOS&RODOS of Nippon Laser Co., Ltd.).

[0041] Span of the magnetic powder defined as follows: Span = (D90 - D10) / D50 (Here, the particle sizes D90, D10, and D50 are the particle sizes corresponding to 90%, 10%, and 50% of the integrated value of the particle size distribution.) can be 2 or less, and preferably 1.5 or less. If it exceeds 2, the proportion of minute magnetic powder with a small coercive force increases, and thus the coercive force tends to decrease.

[0042] The filling rate of the magnetic powder in the magnet material 30 is preferably 50% by volume or more, and more preferably 60% by volume or more. Thereby, the residual magnetic flux density of the obtained bonded magnet 40 can be improved.

[0043] In order to obtain the bonded magnet 40 with the magnetic powder oriented, in the injection step (S400), a step of applying an orientation magnetic field to the magnet material 30 to magnetize it may be performed. The application of the orientation magnetic field starts at least before the resin is completely solidified. By applying a magnetic field to the magnet material 30, the magnetization easy axes of the magnetic powder contained in the magnet material 30 can be aligned. In order to apply a magnetic field to the magnet material 30, an orientation magnet may be provided in the mold 20. As the orientation magnet, an electromagnet or a permanent magnet can be used. When a permanent magnet is used as the orientation magnet, injection molding and the application of the magnetic field are performed simultaneously. The magnitude of the orientation magnetic field can be, for example, 637 kA / m (8 kOe) or more and 1511 kA / m (19 kOe) or less.

[0044] (1.2.5. Taking-out step) In the taking-out step (S500), the holding member 10 is removed from the mold 20. Thereby, the magnet unit 1 is obtained. When the magnetization step is performed in the injection step (S400), the magnet material 30 injected into the slot 14 becomes the bonded magnet 40 in the taken-out magnet unit 1. The magnet material 30 remaining at the gate 24 is cut at the opening of the gate 24 and separated from the bonded magnet 40 in the slot 14. Thereby, a gate mark 50 is formed on the exposed surface 41 of the bonded magnet 40, and the area of the gate mark 50 is substantially equal to the cross-sectional area of the gate diameter.

[0045] After the taking-out step (S500), a step of performing secondary magnetization on the magnet material 30 may be performed. In this case, a secondary magnetization magnetic field is applied to the holding member 10 that holds the magnet material 30 in the slot 14. Examples of the magnetization method include a pulse magnetic field generation method or a static magnetic field generation method. The magnitude of the magnetization magnetic field in the magnetization step can be, for example, 1990 kA / m (25 kOe) or more and 4777 kA / m (60 kOe) or less. The magnetization magnetic field in the step of performing secondary magnetization can be made larger than the orientation magnetic field in the injection step (S400). Thereby, the magnet unit 1 with the magnetic force of the bonded magnet 40 in the slot 14 maximally extracted is obtained.

[0046] After the extraction step (S500), in S600, it is determined whether there is a defect in the magnet unit 1. Examples of defects include plastic deformation occurring in the magnet unit 1 and the measured value of the pressure sensor 25 installed in the mold 20 exceeding a predetermined threshold value.

[0047] If there is a defect in the magnet unit 1 (Yes in S600), the molding conditions are changed and injection molding is performed again. For example, if the injection speed into the mold 20 is slow, it is likely to be preferentially injected into the slot 14 close to the sprue 22. Also, if the resin temperature is high, the fluidity of the magnet material 30 increases, so it is likely to be injected into the slot 14 with a long distance from the center even at a low injection pressure. If the defect is not eliminated even after changing the molding conditions in this way, the gate area setting step (S200) is performed again. On the other hand, if there is no defect in the magnet unit 1 or if the defect has been eliminated (No in S600), the manufacturing process is terminated.

[0048] (1.3. Parentheses) As described above, the magnet unit 1 in the present disclosure includes a holding member 10 provided with a plurality of slots 14 and bonded magnets 40 arranged inside each of the plurality of slots 14. The manufacturing method of the magnet unit 1 includes a step of injecting the magnet material 30 through each of the plurality of gates 24 from the openings on one end side of each of the plurality of slots 14 and a step of cutting the magnet material 30 at the plurality of gates. The cross-sectional area of each of the plurality of gates 24 is set so that the internal pressure of the magnet material 30 does not exceed the threshold value at which the holding member 10 undergoes plastic deformation inside each of the plurality of slots 14, and the threshold value is calculated based on the shape of the holding member 10.

[0049] With such a configuration, the internal pressure generated in the slot 14 can be suppressed, and deformation of the holding member 10 can be prevented.

[0050] Further, the cross-sectional areas of the plurality of gates 24 may be set so that the plurality of slots 14 are filled at the same timing. By adopting such a configuration, it is possible to prevent the internal pressure in the slot 14 from rising rapidly due to the acceleration of the filling of the magnet material 30 in a part of the plurality of slots 14.

[0051] Further, in the step of injecting the magnet material 30, the magnet material 30 is passed through a sprue 22 disposed on the extension line of the central axis of the holding member 10, a plurality of runners 23 branched in the radial direction of the magnet unit 1 from the sprue 22, and a plurality of gates 24 that are the ends of the plurality of runners 23, and injected into the slot 14. The cross-sectional areas of the plurality of gates 24 may be set such that the gate 24 farther from the sprue 22 has a larger cross-sectional area. By adopting such a configuration, it is possible to increase the flow rate of the magnet material 30 flowing into the gate 24 that is difficult to fill due to the long distance from the sprue 22, and it becomes easy to fill the plurality of gates 24 at substantially the same timing.

[0052] Further, the cross-sectional area of the gate may be set by setting the diameter of the gate with a circular cross-sectional shape. By adopting such a configuration, it becomes easy to set the cross-sectional area of the gate 24 provided in the mold 20 to an optimal value.

[0053] (1.4. Modification example) With reference to FIGS. 10 to 12, the magnet unit 2 according to the modification example of the present embodiment will be described centering on the differences from the above-described embodiment. Note that the same reference numerals are given to the same configurations as those in the above-described embodiment, and the description will not be repeated.

[0054] As shown in FIGS. 10 and 11, the magnet unit 2 according to the modification example is different from the magnet unit 1 described above in the shape and number of the slots 14. Specifically, the inner slot 14b in the magnet unit 2 is not divided into three and is continuously connected in an arc shape opposite to the outer surface 13 of the holding member 10. Further, the area of the first gate mark 50a provided in the outer slot 14a is smaller than the area of the second gate mark 50b provided in the inner slot 14b.

[0055] Note that the size relationship between the cross-sectional area of the gate 24a facing the outer slot 14a and the cross-sectional area of the gate 24b facing the inner slot 14b may be appropriately changed according to the volume of the slot 14 and the molding conditions. As an example, when the diameter of the gate 24a is B, the volume of the outer slot 14a is D, the diameter of the gate 24b is A, and the volume of the inner slot 14b is C, when C / D ≤ 0.4, it is preferable that A ≤ B, and when 2.5 ≤ C / D, it is preferable that B ≤ A.

[0056] As shown in FIG. 12, in the flow path 21 in the mold 20 used when manufacturing the magnet unit 2, the runner 23 includes only the extending portion 23a extending radially from the sprue 22. Also, the first gate 24a is farther from the sprue 22 than the second gate 24b, and the cross-sectional area of the first gate 24a is smaller than the cross-sectional area of the second gate 24b. Thus, in this modified example, since the inner slots 14b are connected and the volume is large, the cross-sectional area of the second gate 24b facing the inner slot 14b is set to be larger than the cross-sectional area of the first gate 24a facing the outer slot 14a so that more magnet material 30 flows. Even in such a magnet unit 2, by applying the technical idea of the present disclosure, it is possible to obtain the same effects as those in the above-described embodiment.

[0057] <2. Other Embodiments> As described above, the embodiments of the present disclosure have been described, but the present disclosure is not limited to the above. For example, in the above embodiment, the holding member 10 is formed in a cylindrical shape, but other shapes may be used. Also, in the above embodiment, the slot 14 includes an outer slot 14a and an inner slot 14b and has rotational symmetry that is symmetric four times in a plan view, but the present disclosure is not limited to this example. That is, the outer slot 14a and the inner slot 14b may be connected, or may have n-fold rotational symmetry different from four-fold symmetry. Specifically, it may have even-fold rotational symmetry such as n = 2, 6, 8, etc., or odd-fold rotational symmetry such as n = 3, 5, 7, etc. Or, it may not have rotational symmetry.

[0058] Also, in the above embodiment, the presence or absence of defects is confirmed after the extraction step (S500) (S600). However, once the cross-sectional area of the appropriate gate 24 and the molding conditions are determined, the magnet unit 1 may be manufactured by performing the steps from the threshold calculation step (S100) to the extraction step (S500) without confirming the presence or absence of such defects.

[0059] Also, in the above embodiment, a rotor core is disclosed as an example of the magnet unit, but the present invention is not limited to this aspect. That is, the technical idea of the present disclosure can also be applied to magnet units other than the rotor core including the holding member and the bonded magnet, and the same effects as those of the above embodiment can be obtained.

[0060] The present disclosure includes the following aspects. (Appendix 1) A method for manufacturing a magnet unit having a holding member provided with a plurality of slots and bonded magnets disposed inside each of the plurality of slots, the method including: injecting a magnet material through each of a plurality of gates from an opening on one end side of each of the plurality of slots; and cutting the magnet material at the plurality of gates, wherein the cross-sectional area of each of the plurality of gates is set such that the internal pressure of the magnet material does not exceed a threshold value at which the holding member plastically deforms inside each of the plurality of slots, and the threshold value is calculated based on the shape of the holding member. (Appendix 2) The method for manufacturing a magnet unit according to Appendix 1, wherein the cross-sectional area of each of the plurality of gates is set so that the plurality of slots are filled at substantially the same timing. (Appendix 3) In the step of injection, the magnet material is passed through a sprue arranged in a direction along the central axis of the holding member, a plurality of runners branched in the radial direction of the magnet unit from the sprue, and a plurality of gates that are the ends of the plurality of runners, and injected into the slot. The cross-sectional area of the plurality of gates is set so that the gate farther from the sprue in plan view is larger. The method for manufacturing a magnet unit according to Supplementary Note 1. (Supplementary Note 4) The sprue is arranged on the extension line of the central axis. The method for manufacturing a magnet unit according to Supplementary Note 3. (Supplementary Note 5) The cross-sectional shape of the gate is circular. The method for manufacturing a magnet unit according to Supplementary Note 3. (Supplementary Note 6) A pressure sensor is installed so as to face the opening on the side opposite to the gate of the slot, and a step of measuring the internal pressure generated in the slot is provided. The method for manufacturing a magnet unit according to Supplementary Note 1. (Supplementary Note 7) A magnet unit having a holding member provided with a plurality of slots and bonded magnets arranged inside each of the plurality of slots, wherein the bonded magnet has a gate mark on one end face side, and the areas of the gate marks having different radial distances are different with reference to the central axis of the holding member. Magnet unit. (Supplementary Note 8) The gate mark at a position farther from the central axis in plan view has a larger area. The magnet unit according to Supplementary Note 7.

[0061] As described above, the embodiments according to the present disclosure have been described with reference to specific examples. However, the present disclosure is not limited to these specific examples. Based on the above-described embodiments of the present disclosure, all forms that can be appropriately designed and implemented by those skilled in the art also belong to the scope of the present disclosure as long as they include the gist of the present disclosure. In addition, within the scope of the idea of the present disclosure, those skilled in the art can conceive various modification examples and correction examples, and those modification examples and correction examples also belong to the scope of the present disclosure.

Explanation of Reference Numerals

[0062] 1, 2: Magnet unit, 10: Holding member, 11: First end face, 12: Second end face, 13: Outer surface, 14: Slot, 14a: Outer slot, 14b: Inner slot, 14b1: Central part, 14b2: End part, 20: Mold, 21: Flow path, 22: Sprue, 23: Runner, 24: Gate, 25: Pressure sensor, 30: Magnet material, 40: Bonded magnet, 41: Exposed surface, 50: Gate mark, 50a: First gate mark, 50b: Second gate mark.

Claims

1. A manufacturing method of a magnet unit having a holding member having a plurality of slots and a bonded magnet disposed inside each of the plurality of slots, comprising the steps of: injecting a magnetic material through a plurality of gates from an opening on one end side of each of the plurality of slots; cutting the magnetic material at the plurality of gates; Equipped with a cross-sectional area of ​​each of the gates is set such that an internal pressure of the magnetic material within each of the slots does not exceed a threshold at which the retaining member undergoes plastic deformation; A method for manufacturing a magnet unit, wherein the threshold value is calculated based on the shape of the holding member.

2. The method for manufacturing a magnet unit according to claim 1 , wherein a cross-sectional area of ​​each of the plurality of gates is set so that the plurality of slots are filled at approximately the same timing.

3. In the step of injecting, the magnetic material is a sprue disposed in a direction along a central axis of the holding member, a plurality of runners disposed branching out from the sprue in a radial direction of the magnet unit, and a plurality of gates which are terminal ends of the plurality of runners; into the slot, The method for manufacturing a magnet unit according to claim 1 , wherein the cross-sectional areas of the gates are set so that the cross-sectional areas of the gates increase as the gate is positioned farther away from the sprue in a plan view.

4. The method for manufacturing a magnet unit according to claim 3 , wherein the sprue is disposed on an extension of the central axis.

5. The method for manufacturing a magnet unit according to claim 4 , wherein the cross-sectional shape of the gate is circular.

6. The method for manufacturing a magnet unit according to claim 1 , further comprising the step of: installing a pressure sensor to face an opening of the slot on the opposite side to the gate; and measuring an internal pressure generated within the slot.

7. A magnet unit having a holding member having a plurality of slots and a bonded magnet disposed inside each of the plurality of slots, the bonded magnet having a gate mark on one end face side, A magnet unit, wherein the gate marks that are different in radial distance from each other with respect to the central axis of the holding member have different areas.

8. The magnet unit according to claim 7 , wherein the area of ​​the gate marks increases as the gate marks are positioned at a greater distance from the central axis in a plan view.

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