JP2025098921A - Magnet unit manufacturing method and magnet unit - Google Patents

Abstract

[Problem] To provide a magnet unit and a manufacturing method thereof capable of suppressing deformation of a holding member. [Solution] A manufacturing method of a magnet unit is provided, the magnet unit having a holding member with a plurality of slots and a bonded magnet disposed inside each of the plurality of slots. The manufacturing method includes 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, and cutting the magnetic material at the plurality of gates, the cross-sectional area of each of the plurality of gates being set such that the internal pressure of the magnetic material inside each of the plurality of slots does not exceed a threshold value at which the holding member undergoes plastic deformation, the threshold value being calculated based on the shape of the holding member. [Selected Figure] Figure 3

Description

This disclosure relates to a method for manufacturing a magnet unit and a magnet unit.

Patent document 1 describes an embedded magnet motor that includes magnets embedded in holes in a rotor core. Bonded magnets are formed in the holes in the rotor core by injection molding.

JP 2015-61430 A

When the material of the bonded magnet is injection molded into the hole of the magnet unit such as the rotor core, the internal pressure generated inside the hole can cause the retaining member of the magnet unit to deform.

The embodiments of the present disclosure have been made in consideration of the above-mentioned problems, and aim to provide a magnet unit and a manufacturing method thereof that can suppress deformation of the retaining member.

In one aspect of the present disclosure, a method for manufacturing a magnet unit having a holding member with multiple slots and a bonded magnet disposed inside each of the multiple slots is provided. The method includes the steps of injecting a magnetic material through each of multiple gates from an opening on one end side of each of the multiple slots, and cutting the magnetic material at the multiple gates, and the cross-sectional area of each of the multiple gates is set so that the internal pressure of the magnetic material inside each of the multiple slots does not exceed a threshold value at which the holding member undergoes plastic deformation, and the threshold value is calculated based on the shape of the holding member.

A magnet unit according to one aspect of the present disclosure includes a holding member having a plurality of slots and a bonded magnet disposed inside each of the plurality of slots. The magnet unit includes a pair of end faces having a plurality of slots formed therethrough along a central axis, the bonded magnet having a gate mark formed when a magnetic material is injected into the slot from one side of the pair of end faces, and the gate marks having different radial distances from each other with respect to the central axis have different areas.

Embodiments of the present disclosure provide a magnet unit and a manufacturing method thereof that can suppress deformation of the retaining member.

FIG. 2 is a perspective view of the magnet unit 1 according to the embodiment. FIG. 2 is a plan view of the magnet unit 1. 4 is a flowchart for explaining a manufacturing process of the magnet unit 1. 10A to 10C are schematic diagrams illustrating an intensity simulation in a threshold calculation step (S100). 11 is a graph illustrating the internal pressure threshold value in the threshold value calculation step (S100). FIG. 11 is a cross-sectional view for explaining placement on a mold in the placement step (S300). 2 is a perspective view showing a schematic view of a plurality of flow paths 21 provided in a mold 20. FIG. 2 is a plan view showing a schematic diagram of a plurality of flow passages 21 provided in a mold 20. FIG. FIG. 11 is a cross-sectional view for explaining the injection step (S400). FIG. 13 is a perspective view of a magnet unit 2 according to a modified example. FIG. 13 is a plan view showing a schematic view of a plurality of flow passages 21 provided in a mold 20 in a modified example. FIG.

The magnet unit and the manufacturing method of the magnet unit according to the embodiment of the present disclosure will be described below with reference to the drawings. The embodiments shown below are examples of the magnet unit and the manufacturing method of the magnet unit for realizing the technical idea of the present embodiment, and are not limited to the following. Furthermore, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the embodiments are merely explanatory examples, and are not intended to limit the scope of the present disclosure, unless otherwise specified. The size, positional relationship, etc. of the components shown in each drawing may be exaggerated to clarify the explanation. In the following explanation, the same name and symbol indicate the same or similar components, and detailed explanations will be omitted as appropriate. In the following explanation, "area" means "area" in a planar view unless otherwise specified. Furthermore, "shape" is used as a concept including size. For example, if two shapes are similar to each other but have different sizes, the two shapes are different.

1. First embodiment
(1.1. Magnet unit 1)
A 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, for example, formed in a cylindrical shape, and includes an outer side surface 13 along the central axis A of the holding member 10, and a pair of end surfaces, a first end surface 11 and a second end surface 12, which 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 surface 11 to the second end surface 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 surface 11 side of the bonded magnet 40.

The holding member 10 may be a magnetic material, and as an example, the holding member 10 may be a laminated steel plate composed of multiple steel plates stacked in a direction from the second end face 12 to the first end face 11. The laminated steel plate may be, for example, an electromagnetic steel plate.

The bonded magnet 40 includes a resin and a magnetic powder. The resin may be a material described later as a resin constituting the magnet material 30. The magnetic powder may be a material described later as a magnetic powder constituting the magnet material 30. As an example, the bonded magnet 40 may have a resin and a SmFeN magnetic powder. The content of the magnetic powder in the bonded magnet 40 is preferably 50% by volume or more, and more preferably 60% by volume or more. This improves the residual magnetic flux density of the bonded magnet 40. The volumetric ratio of the filling rate of the magnetic powder in the bonded magnet 40 may be calculated from a cross section of a part of the bonded magnet 40. For example, a scanning electron microscope (SEM) image of a cross section of a part 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 volumetric ratio of the filling rate of the magnetic powder in the bonded magnet 40.

The shape, size, number, etc. of the multiple slots 14 provided in the holding member 10 are set according to the target values of the magnetic properties of the magnet unit 1. As an example, the number of multiple slots 14 is 2 or more, may be 8 or more, or may be 30 or more.

Preferably, the magnet unit 1 has rotational symmetry with respect to the central axis A. In this embodiment, as an example, the slots 14 are provided in the holding member 10 so as to have four-fold symmetry with respect to the central axis A. That is, as shown in FIG. 2, the slots 14 are formed so as to have rotational symmetry every 90° with respect to the central axis A in a plan view. The slots 14 have an outer slot 14a that is curved in an arc shape in the opposite direction to the outer surface 13 of the holding member 10 in a plan view, and an inner slot 14b that is arranged closer to the central axis A than the outer slot 14a and curved in an arc shape in the same direction as the outer slot 14a. The inner slot 14b is divided into three and includes one central portion 14b1 and two end portions 14b2.

The shapes of the multiple slots 14 in plan view may all be similar to each other (i.e., when one is enlarged or reduced, the shape roughly matches the other), or some may be similar to each other and other parts may be different shapes. In this case, in an area with rotational symmetry with respect to the central axis A, multiple slots 14 with similar shapes may be mixed with one or more slots 14 of different shapes.

It is preferable that the ratio of the width W to the depth H of the multiple slots 14 satisfies the relationship 1/10≦W/H≦1/50, and it is even more preferable that the relationship 1/20≦W/H≦1/50 is satisfied. In this way, the greater the depth H is relative to the width W, the more difficult it is to fill multiple slots 14 simultaneously, making it easier to obtain the effect of the technical idea of the present disclosure. In addition, when the area of the largest slot 14 in a plan view is Smax and the area of the smallest slot 14 is Smin, it is preferable that the relationship 1/1≦Smin/Smax≦1/10 is satisfied. In this way, the greater the difference in area between the multiple slots 14 in a plan view, the more difficult it is to fill multiple slots 14 simultaneously, making it easier to obtain the effect of the technical idea of the present disclosure.

The gate mark 50 formed on the exposed surface 41 of the bonded magnet 40 is formed when the magnetic material 30 is injected into 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, a circle, an ellipse, or an oval. One or more gate marks 50 are provided on one bonded magnet 40.

The gate mark 50 includes a first gate mark 50a and a second gate mark 50b. The gate mark 50 has a different area depending on the distance from the central axis A. The first gate mark 50a is located at a longer distance in a plan view (hereinafter also simply referred to as distance) from the central axis A than the second gate mark 50b, 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 center portion 14b1 of the inner slot 14b includes the second gate mark 50b, and the end portion 14b2 of the inner slot 14b and the outer slot 14a include the first gate mark 50a.

(1.2. Manufacturing method of magnet unit 1)
The manufacturing method of the magnet unit 1 according to the present disclosure will be described in detail below with reference to Figures 3 to 9. In this specification, the term "process" includes not only an independent process, but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.

As shown in FIG. 3, the manufacturing process of the magnet unit 1 of the embodiment includes a threshold calculation process S100, a gate area setting process S200, a placement process S300, an injection process S400, and a removal process S500. Each process will be described in detail below.

(1.2.1. Threshold calculation process)
In the threshold calculation step (S100), a threshold of the internal pressure generated when the magnetic material 30 is injected 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 is plastically deformed by performing a strength analysis simulation based on the shape of the holding member 10.

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

As an example, when performing a strength analysis simulation on a retaining member 10 having the shape shown in FIG. 4, the areas where plastic deformation due to internal pressure within the slot 14 is likely to occur include area B1 between the end 14b2 of the inner slot 14b and the outer surface 13, area B2 between the center 14b1 and the end 14b2 of the inner slot 14b, and area B3 between the outer slot 14a and the outer surface 13. When a strength analysis simulation is performed on these areas, for example, the graph shown in FIG. 5 is obtained as the analysis result.

The graph in Figure 5 shows the equivalent stress that can occur in parts B1 to B3 when the internal pressure in the injection process is increased. When the equivalent stress exceeds the yield stress F1 of the holding member 10, plastic deformation occurs. From the analysis results shown in Figure 5, it can be read that when the internal pressure is P1, plastic deformation can occur in part B3. Therefore, the threshold internal pressure when injecting the magnetic material 30 into the slot 14 of the holding member 10 is calculated to be P1.

(1.2.2. Gate area setting process)
In the gate area setting step (S200), a cross-sectional area of the gate 24 (see FIG. 6) is set when the magnetic material 30 is injected into the slot 14 in the subsequent injection step (S400). In this 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.

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

When the flow analysis simulation is performed, it is possible to analyze how the magnetic material 30 is filled in each slot 14 of the holding member 10 having the input shape. For example, if the cross-sectional area of the gate 24 for injecting the magnetic material into each slot 14 of the holding member 10 is set to a constant value, the analysis result is output such that when the filling of the center portion 14b1 of the inner slot 14b is completed, the filling of the other slots 14 (i.e., the end portion 14b2 of the inner slot 14b and the outer slot 14a) is not completed. In this way, if there is a difference in the filling timing for each slot 14, the internal pressure inside the slot 14 that is filled early will rise suddenly, which may cause plastic deformation of the holding member 10. Therefore, in this embodiment, the cross-sectional area of each of the multiple gates 24 is set so that the multiple slots 14 are filled at approximately the same time. In this disclosure, "filled at approximately the same time" means that the multiple slots 14 have a filling rate of 90% to 100% at a certain point in time, and more preferably, the multiple slots 14 have a filling rate of 95% to 100%.

Specifically, for example, the cross-sectional area of the gates 24 is set so that the gate 24 located at a greater distance in plan view from the sprue 22 (see Figures 7 and 8) from which the magnetic material 30 flows out is larger. In other words, by reducing the cross-sectional area of the gate 24 facing the center portion 14b1, it is possible to adjust the timing so that the magnetic material 30 is filled at the same time as the other slots 14 (the end portion 14b2 of the inner slot 14b and the outer slot 14a). Note that 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.

In addition, in the flow analysis simulation, the pressure generated inside the slot 14 is also analyzed in conjunction with the timing of filling the slot 14. In this way, the cross-sectional area of each of the multiple gates 24 is set so that the internal pressure generated by the bonded magnet material inside each of the multiple slots 14 does not exceed the threshold value calculated in the threshold calculation process (S100) at which the holding member 10 undergoes plastic deformation.

(1.2.3. Placement process)
In the placement step (S300), the holding member 10 is placed in a 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, the holding member 10 can be easily fixed by the mold 20, and the holding member 10 can be easily removed from the mold 20. A plurality of flow paths 21 through which the magnetic material 30 flows are provided in the mold 20.

7 and 8 show a schematic diagram of a plurality of flow passages 21 provided in a mold 20. As shown in FIG. 7 and FIG. 8, the plurality of flow passages 21 have a sprue 22 extending in the vertical direction, a plurality of runners 23 extending in the horizontal direction from the sprue, and a plurality of gates 24 extending from the plurality of runners 23 toward the holding member 10. As an example, the sprue 22 is disposed on an 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 disposed opposite the opening of the slot 14 in the first end face 11.

A pressure sensor 25 is further provided within the mold 20. As an example, as shown in FIG. 6, the pressure sensor 25 is disposed opposite the opening on the second end face side of the slot 14. This allows the internal pressure of the magnet material 30 filled in the slot 14 to be accurately measured.

As shown in FIG. 8, in a plan view, the flow passage 21 has rotational symmetry at 90° intervals with respect to the central axis A of the holding member 10. The runner 23 has an extension portion 23a extending radially from the sprue 22 and a branch portion 23b branching off from the extension portion 23a. In this way, by arranging the sprue 22 on an extension line of the central axis A of the holding member 10 and providing multiple runners 23 extending horizontally from the sprue 22 and multiple gates 24 extending from the multiple runners 23 with rotational symmetry with respect to the central axis A, it becomes easier to evenly fill each slot 14 with the magnetic material 30.

As described above, the cross-sectional area of the multiple gates 24 is set to be larger for gates 24 located at a greater distance from the sprue 22 through which the magnetic material 30 flows. As shown in FIG. 8, the gates 24 include a first gate 24a and a second gate 24b. The first gate 24a is located at a greater distance from the sprue 22 than the second gate 24b, and the elastic area of the first gate 24a is larger than the cross-sectional area of the second gate 24b.

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

The magnet material 30 includes a resin and a 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. The resin is, for example, a thermoplastic resin, but the technical idea of this disclosure can also be suitably implemented using a thermosetting resin.

Examples of thermoplastic resins include nylon resins (polyamide resins); polyolefins such as polypropylene (PP) and polyethylene (PE); polyesters; polycarbonates (PC); polyphenylene sulfide resins (PPS); polyether ether ketones (PEEK); polyacetals (POM); and liquid crystal polymers (LCP). Examples of nylon resins include polylactams 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; copolymer polyamides such as nylon 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, and nylon 6-nylon/polyether; nylon 6T, nylon 9T, nylon MXD6, aromatic nylon, and amorphous nylon. Examples of the thermoplastic resin that can be used include nylon 12.

The magnetic powder may be, for example, a rare earth magnetic powder such as SmFeN, NdFeB, or SmCo. The magnetic powder may be a SmFeN magnetic powder. In this case, the magnet material 30 has a resin and a SmFeN magnetic powder. The SmFeN magnetic powder may be a nitride consisting of a rare earth metal Sm, iron Fe, and nitrogen N, whose general formula is Sm _x Fe _100-x-y N _y . It is preferable that 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 remainder is mainly Fe. The magnetic powder may be a SmFeN magnetic powder having a crystal structure of Th2Zn17 type. The magnetic powder may be a SmFeN anisotropic magnetic powder. The SmFeN magnetic powder can be produced, for example, by the method disclosed in JP-A-11-189811. The magnetic powder may have an SmFeN core and a coating containing P and O. The magnetic powder may be surface-treated with a silane coupling agent or the like.

The average particle size of the magnetic powder is preferably 10 μm or less. This allows the crystal grain size to be reduced, and the coercive force of the magnetic powder to be increased. The smaller the average particle size of the magnetic powder, the lower the fluidity of the magnetic material 30 tends to be. The average particle size of the magnetic powder is more preferably 6 μm or less, and even more preferably 4 μm or less. This allows the coercive force of the magnetic powder to be further increased. The average particle size of the magnetic powder is preferably 1 μm or more. This allows the filling rate of the magnetic powder in the magnetic material 30 to 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 equivalent to 50% of the volume cumulative from the small particle size side in the particle size distribution, and can be measured, for example, by a laser diffraction type particle size distribution measuring device (HELOS & RODOS by Nippon Laser Co., Ltd.).

The span of the magnetic powder is defined as:
Span = (D90 - D10) / D50
(Here, particle sizes D90, D10, and D50 are 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 fine magnetic powder with low coercivity increases, so the coercivity tends to decrease.

The filling rate of the magnetic powder in the magnetic material 30 is preferably 50% by volume or more, and more preferably 60% by volume or more. This improves the residual magnetic flux density of the resulting bonded magnet 40.

In order to obtain a bonded magnet 40 in which the magnetic powder is oriented, a process of magnetizing the magnetic material 30 by applying an orientation magnetic field may be performed in the injection process (S400). The application of the orientation magnetic field is started at least before the resin is completely solidified. By applying a magnetic field to the magnetic material 30, the easy magnetization axis of the magnetic powder contained in the magnetic material 30 can be aligned. In order to apply a magnetic field to the magnetic material 30, an orientation magnet may be provided in the mold 20. An electromagnet or a permanent magnet can be used as the orientation magnet. When a permanent magnet is used as the orientation magnet, the 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.

(1.2.5. Removal process)
In the removal step (S500), the holding member 10 is removed from the mold 20. This results in the magnet unit 1. When the magnetization step is performed in the injection step (S400), the magnetic material 30 injected into the slot 14 becomes a bonded magnet 40 in the extracted magnet unit 1. The magnetic material 30 remaining in the gate 24 is cut at the opening of the gate 24 and separated from the bonded magnet 40 in the slot 14. This forms a gate mark 50 on the exposed surface 41 of the bonded magnet 40, and the area of the gate mark 50 is approximately equal to the cross-sectional area of the gate diameter.

After the removal step (S500), a step of secondary magnetization of the magnetic material 30 may be performed. In this case, a magnetic field for secondary magnetization is applied to the holding member 10 that holds the magnetic material 30 in the slot 14. Examples of magnetization methods include a pulse magnetic field generation method and a static magnetic field generation method. The magnitude of the magnetic field for magnetization in the magnetization step can be, for example, 1990 kA/m (25 kOe) or more, and may be 4777 kA/m (60 kOe) or less. The magnetic field for magnetization in the secondary magnetization step can be larger than the magnetic field for orientation in the injection step (S400). This results in a magnet unit 1 that maximizes the magnetic force of the bond magnet 40 in the slot 14.

After the removal process (S500), in S600, it is determined whether or not there is a defect in the magnet unit 1. Examples of defects include plastic deformation of the magnet unit 1, or the measurement value of the pressure sensor 25 installed in the mold 20 exceeding a predetermined threshold value.

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, the slots 14 closest to the sprue 22 are more likely to be injected preferentially. Also, if the resin temperature is high, the fluidity of the magnetic material 30 increases, so that even with low injection pressure, it is more likely to be injected into slots 14 that are farther from the center. If the defect is not resolved by changing the molding conditions in this way, the gate area setting process (S200) is performed again. On the other hand, if there is no defect in the magnet unit 1 or if the defect has been resolved (No in S600), the manufacturing process is terminated.

(1.3. Summary)
As described above, the magnet unit 1 in the present disclosure has a holding member 10 provided with a plurality of slots 14, and a bonded magnet 40 disposed inside each of the plurality of slots 14. The manufacturing method of the magnet unit 1 includes a step of injecting the magnetic material 30 through each of the plurality of gates 24 from an opening on one end side of each of the plurality of slots 14, and a step of cutting the magnetic 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 magnetic material 30 inside each of the plurality of slots 14 does not exceed a threshold value at which the holding member 10 undergoes plastic deformation, and the threshold value is calculated based on the shape of the holding member 10.

This configuration makes it possible to suppress the internal pressure generated within the slot 14, thereby preventing deformation of the retaining member 10.

The cross-sectional area of each of the multiple gates 24 may be set so that multiple slots 14 are filled at the same time. This configuration can prevent the internal pressure in some of the multiple slots 14 from increasing suddenly due to the magnetic material 30 being filled earlier than expected.

In addition, in the process of injecting the magnetic material 30, the magnetic material 30 is injected into the slot 14 by passing through the sprue 22 arranged on an extension of the central axis of the holding member 10, the multiple runners 23 arranged branching off from the sprue 22 in the radial direction of the magnet unit 1, and the multiple gates 24 at the ends of the multiple runners 23, and the cross-sectional areas of the multiple gates 24 may be set to be larger for gates 24 that are farther away from the sprue 22. With this configuration, the flow rate of the magnetic material 30 flowing into the gates 24 that are difficult to fill due to their long distance from the sprue 22 can be increased, making it easier to fill the multiple gates 24 at approximately the same time.

Alternatively, the cross-sectional area of the gate may be set by setting the gate diameter with the cross-sectional shape of the gate being circular. This configuration makes it easy to set the cross-sectional area of the gate 24 provided in the mold 20 to an optimal value.

(1.4. Modifications)
10 to 12, a magnet unit 2 according to a modification of this embodiment will be described, focusing on the differences from the above embodiment. Note that the same components as those in the above embodiment will be denoted by the same reference numerals, and description thereof will not be repeated.

As shown in Figures 10 and 11, the magnet unit 2 according to the modified example differs from the magnet unit 1 described above in the shape and number of slots 14. Specifically, the inner slot 14b in the magnet unit 2 is not divided into three, but is connected in an arc shape in the opposite direction to the outer surface 13 of the holding member 10. In addition, the area of the first gate mark 50a of the outer slot 14a is smaller than the area of the second gate mark 50b of the inner slot 14b.

The 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 changed as appropriate depending on the volume of the slot 14 and the molding conditions. As an example, if 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, then if C/D≦0.4, it is preferable to set A≦B, and if 2.5≦C/D, it is preferable to set B≦A.

As shown in FIG. 12, in the flow passage 21 in the mold 20 used to manufacture the magnet unit 2, the runner 23 only has an extension 23a extending radially from the sprue 22. The first gate 24a is longer than the second gate 24b with respect to the sprue 22, and the elastic area of the first gate 24a is smaller than the cross-sectional area of the second gate 24b. In this manner, in the modified example, the inner slots 14b are connected together to increase the volume, so that the cross-sectional area of the second gate 24b facing the inner slots 14b is made larger than the cross-sectional area of the first gate 24a facing the outer slots 14a, so that more magnet material 30 flows. Even in such a magnet unit 2, the technical idea of the present disclosure can be applied to obtain the same effect as the above embodiment.

2. Other embodiments
Although the embodiment of the present disclosure has been described above, 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 may have other shapes. In addition, in the above embodiment, the slot 14 includes the outer slot 14a and the inner slot 14b, and has four-fold rotational symmetry 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 symmetry different from four-fold symmetry. Specifically, the rotational symmetry may be an even number such as n=2, 6, 8, or an odd number such as n=3, 5, 7. Alternatively, the rotational symmetry may not be provided.

In addition, in the above embodiment, the presence or absence of defects is checked (S600) after the removal process (S500), but once the appropriate cross-sectional area and molding conditions of the gate 24 are determined, the magnet unit 1 may be manufactured by performing the threshold calculation process (S100) through the removal process (S500) without checking for the presence or absence of the defects.

In addition, in the above embodiment, a rotor core is disclosed as an example of a magnet unit, but the present invention is not limited to this aspect. In other words, the technical idea of the present disclosure can be applied to magnet units other than a rotor core that includes a retaining member and a bonded magnet, and the same effects as those of the above embodiment can be obtained.

The present disclosure includes the following aspects.
(Appendix 1)
A method for manufacturing a magnet unit having a holding member having a plurality of slots and a bonded magnet arranged inside each of the plurality of slots, the method comprising the steps of: injecting a magnetic 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 magnetic 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 magnetic material inside each of the plurality of slots does not exceed a threshold value at which the holding member undergoes plastic deformation, and the threshold value is calculated based on the shape of the holding member.
(Appendix 2)
The method for manufacturing a magnet unit described in Appendix 1, further comprising setting a cross-sectional area of each of the gates so that the slots are filled at approximately the same time.
(Appendix 3)
A method for manufacturing a magnet unit as described in Appendix 1, in which, in the injection process, the magnet material is injected into the slot by passing it through a sprue arranged in a direction along the central axis of the holding member, a plurality of runners arranged branching off from the sprue in the radial direction of the magnet unit, and a plurality of gates which are the ends of the plurality of runners, and the cross-sectional areas of the plurality of gates are set so that the larger the gate is located at a longer distance from the sprue in a planar view.
(Appendix 4)
The method for manufacturing a magnet unit according to claim 3, wherein the sprue is arranged on an extension of the central axis.
(Appendix 5)
The method for manufacturing a magnet unit described in Appendix 3, wherein the cross-sectional shape of the gate is circular.
(Appendix 6)
A method for manufacturing a magnet unit as described in Appendix 1, comprising a step of installing a pressure sensor facing an opening of the slot on the opposite side to the gate, and measuring the internal pressure generated within the slot.
(Appendix 7)
A magnet unit having a holding member having a plurality of slots and a bonded magnet 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 that are different in radial distance from each other based on the central axis of the holding member are different.
(Appendix 8)
The magnet unit according to claim 7, wherein the gate marks have a larger area as they are positioned at a greater distance from the central axis in a planar view.

Above, the embodiments of the present disclosure have been described with reference to specific examples. However, the present disclosure is not limited to these specific examples. All forms that a person skilled in the art can implement by appropriately modifying the design based on the above-described embodiments of the present disclosure also fall within the scope of the present disclosure as long as they include the gist of the present disclosure. In addition, within the scope of the concept of the present disclosure, a person skilled in the art can come up with various modifications and amendments, and these modifications and amendments also fall within the scope of the present disclosure.

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: center, 14b2: end, 20: mold, 21: flow passage, 22: sprue, 23: runner, 24: gate, 25: pressure sensor, 30: magnetic material, 40: bonded magnet, 41: exposed surface, 50: gate mark, 50a: first gate mark, 50b: second gate mark.

Claims (8)

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. The method for manufacturing a magnet unit according to claim 1, wherein the cross-sectional area of each of the gates is set so that the slots are filled at approximately the same time. 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 plurality of 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. The method for manufacturing a magnet unit according to claim 3, wherein the sprue is positioned on an extension of the central axis. The method for manufacturing a magnet unit according to claim 4, wherein the cross-sectional shape of the gate is circular. The method for manufacturing the magnet unit according to claim 1 further comprises a step of installing a pressure sensor facing the opening of the slot on the opposite side to the gate, and measuring the internal pressure generated within the slot. 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. The magnet unit of claim 7, in which the area of the gate marks increases as the distance from the central axis increases in plan view.

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