Method for manufacturing sintered magnet

Abstract

To provide a method for manufacturing a sintered magnet, which can machine the outer peripheral surface of the sintered magnet larger in outer diameter in a ring shape than its thickness with high dimension accuracy.SOLUTION: This method for manufacturing a sintered magnet comprises: a step of preparing a plurality of sintered magnet workpieces having ring shapes; a step of fixing the sintered magnet workpieces to a rotary shaft such that an opening hole of each of the sintered magnet workpieces passes through the rotary shaft of a grinder; and a step of rotating the sintered magnet workpieces integrally with the rotary shaft and grinding the outer peripheral surfaces of the sintered magnet workpieces by a grindstone; a step of disposing a spacer having a hollow cylindrical shape so as to surround the center of the rotating shaft in the long-axis direction and of arranging the sintered magnet workpieces on both sides of the spacer in the long-axis direction; and a step of applying a force to both ends of the sintered magnet workpieces by a pressing member and fixing the sintered magnet workpieces to the rotary shaft.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing a sintered magnet. [Background technology]

[0002] Sintered magnets such as RTB sintered magnets (R is a rare earth element, T is Fe or Fe and Co, and B is boron) and ferrite magnets generally include a step of compressing raw alloy powder with a press to produce a powder compact, a step of sintering the powder compact to produce a sintered body, and a step of mechanically processing the sintered body.

[0003] There are various shapes of sintered magnets. When manufacturing a ring-shaped sintered magnet (a magnet or ring magnet having a hollow cylindrical shape), a step of grinding each of the inner and outer circumferential surfaces of the sintered body with a grindstone is carried out.

[0004] Patent Document 1 discloses a technique for grinding the inner peripheral surface of a hollow cylindrical sintered magnet. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2023-046877 A Summary of the Invention [Problem to be solved by the invention]

[0006] When the outer peripheral surface of a ring-shaped sintered magnet is machined, the roundness of the outer diameter may decrease. An embodiment of the present disclosure provides a manufacturing method for a sintered magnet that can machine the outer peripheral surface of a ring-shaped sintered magnet with high dimensional accuracy (high roundness). [Means for solving the problem]

[0007] In one exemplary embodiment, the method for producing a sintered magnet according to the present disclosure includes the steps of: preparing a plurality of sintered magnet workpieces each having a ring shape defined by a thickness, an inner diameter, and an outer diameter; fixing the sintered magnet workpieces to a rotating shaft of a grinding device so that the openings of each of the sintered magnet workpieces pass through the rotating shaft; and grinding the outer circumferential surface of the sintered magnet workpieces with a grindstone while rotating the sintered magnet workpieces together with the rotating shaft. The step of fixing the sintered magnet workpiece to the rotating shaft includes the steps of arranging a spacer having a hollow cylindrical shape so as to surround the center of the rotating shaft in the longitudinal direction and arranging the sintered magnet workpieces on both sides of the spacer in the longitudinal direction; and applying a force in the longitudinal direction to both ends of the arranged sintered magnet workpiece by a pressing member to fix the sintered magnet workpiece to the rotating shaft. The size of the spacer in the longitudinal direction is at least twice the thickness of the sintered magnet workpiece. Effect of the Invention

[0008] According to an embodiment of the present disclosure, when a ring-shaped sintered magnet workpiece is fixed to a rotating shaft and its outer circumferential surface is ground, a spacer is placed on the rotating shaft and the sintered magnet workpiece is placed on both sides of the spacer. By making the size of the spacer in the major axis direction at least twice the thickness of the sintered magnet workpiece, it becomes possible to process the outer circumferential surface of the sintered magnet with high dimensional accuracy (high roundness). [Brief description of the drawings]

[0009] [Figure 1A] FIG. 2 is a front view of a ring-shaped sintered magnet workpiece. [Figure 1B] 1B is a cross-sectional view of the sintered magnet workpiece shown in FIG. 1A along line BB. [Diagram 2] FIG. 1 is a top view showing a schematic diagram of a plurality of sintered magnet workpieces fixed to a rotating shaft of a grinding device being ground with a grinding wheel in the prior art. [Diagram 3] FIG. 2 is a diagram showing the rotation axis of a grinding device through which an opening hole of a sintered magnet workpiece passes. [Figure 4]1 is a flowchart showing a method for producing a sintered magnet according to an embodiment of the present disclosure. [Figure 5A] FIG. 2 is a front view of a spacer having a hollow cylindrical shape used in an embodiment of the present disclosure. [Figure 5B] 5B is a cross-sectional view of the spacer taken along line BB in FIG. 5A. [Figure 6] FIG. 2 is a side view showing a state in which several sintered magnet workpieces are loaded on a rotating shaft of a grinding device in an embodiment of the present disclosure. [Figure 7] 1 is a side view showing a state in which a spacer is loaded onto a rotating shaft of a grinding device in an embodiment of the present disclosure; FIG. [Figure 8] FIG. 2 is a side view showing a state in which a plurality of sintered magnet workpieces and spacers are loaded on a rotating shaft of a grinding device in an embodiment of the present disclosure. [Figure 9] FIG. 2 is a side view showing a state in which a plurality of sintered magnet workpieces are fixed to a rotation shaft of a grinding device in an embodiment of the present disclosure. [Figure 10] FIG. 2 is a top view illustrating a state in which a plurality of sintered magnet workpieces fixed to a rotating shaft of a grinding device are ground with a grinding wheel in an embodiment of the present disclosure. [Figure 11] FIG. 13 is a top view showing a schematic diagram of grinding with a grindstone using a spacer fixed to a rotation shaft of a grinding device in an embodiment of the present disclosure. [Figure 12] 13 is a graph showing the relationship between the position and the roundness of a sintered magnet workpiece in a comparative example. [Figure 13] 13 is a graph showing the relationship between the position and the roundness of a sintered magnet workpiece in a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] First, an example of the shape of a ring-shaped sintered magnet workpiece will be described with reference to Figures 1A and 1B. Figure 1A is a front view of a ring-shaped sintered magnet workpiece 10, and Figure 1B is a cross-sectional view taken along line BB.

[0011] Examples of the sintered magnet workpiece 10 include an RTB based sintered magnet (R is a rare earth element, T is Fe or Fe and Co, and B is boron) and a ferrite magnet.

[0012] In the illustrated example, the sintered magnet workpiece 10 has a ring shape (hollow cylindrical shape) with a thickness t0, an inner diameter d0, and an outer diameter d1. The sintered magnet workpiece 10 has an inner peripheral surface 10A that defines the inner diameter d0, an outer peripheral surface 10B that defines the outer diameter d1, and a pair of end faces 10C and 10D. An opening hole is defined by the inner peripheral surface 10A. In this embodiment, the end face 10C and the end face 10D are parallel to each other. Furthermore, the inner peripheral surface 10A and the outer peripheral surface 10B are ideally cylindrical surfaces having a common central axis.

[0013] In this embodiment, the outer diameter d1 of the sintered magnet workpiece 10 is 45 mm or more, for example, 65 mm or more, preferably 80 mm or more, and more preferably 90 mm or more. The thickness t1 of the sintered magnet workpiece 10 is 30 mm or less, for example, 25 mm or less, and preferably 20 mm or less. The lower limit of the thickness t1 is, for example, 5 mm. The outer diameter d1 of the sintered magnet workpiece 10 is, for example, three times or more than the thickness t1. The larger the ratio (d1 / t1) of the outer diameter d1 to the thickness t1, the more likely it is that the sintered magnet workpiece 10 will be distorted or deformed when an external force is applied to the outer peripheral surface 10B of the sintered magnet workpiece 10. In this embodiment, the inner diameter d0 is, for example, 70% or more of the outer diameter d1. When machining the outer peripheral surface of a sintered magnet whose ring-shaped outer diameter is larger than its size (thickness) in the axial direction, the roundness of the outer diameter may decrease.

[0014] An embodiment of the present disclosure can provide a method for manufacturing a sintered magnet that can process the outer circumferential surface of a ring-shaped sintered magnet, whose outer diameter is larger than its thickness, with high dimensional accuracy (high roundness).

[0015] FIG. 2 is a top view showing a schematic configuration of a grinding device 100 capable of grinding the outer peripheral surface. In FIG. 2, for reference, an X-axis, a Y-axis, and a Z-axis that are perpendicular to each other are shown. In the example shown in the figure, the Z-axis is parallel to the vertical direction, and a plane (XY plane) including both the X-axis and the Y-axis is parallel to the horizontal plane. FIG. 3 is a side view showing a configuration example of a rotating shaft (shaft or bar for grinding the outer peripheral surface) 20 of the grinding device 100. As shown in FIG. 2, the grinding device 100 includes a driving device 50 such as a motor that rotates the rotating shaft 20, and a grinding wheel 60 that grinds the outer peripheral surfaces of a plurality of sintered magnet workpieces 10 fixed to the rotating shaft 20. In the example of FIG. 2, the center of rotation of the rotating shaft 20 is defined by a pair of centering guides 52. The driving device 50 rotates the rotating shaft 20 by a member 54.

[0016] The rotating shaft 20 has a shape and size that allows a plurality of sintered magnet workpieces 10 to be arranged (loaded) thereon. Specifically, the outer circumferential surface of the rotating shaft 20 is a smooth cylindrical surface that can slide against the inner circumferential surface 10A of the sintered magnet workpieces 10, and it is preferable that the outer diameter of the rotating shaft 20 has a value slightly smaller than the inner diameter d0 of the sintered magnet workpieces 10.

[0017] The rotating shaft 20 has a cylindrical outer shape that passes through the openings of the sintered magnet workpieces 10. The grinding device is equipped with pressing members (30A, 30B) that apply force to both ends of the sintered magnet workpieces 10 arranged on the rotating shaft 20. The pressing members (30A, 30B) shown in FIG. 2 have a fixed part 30A located on one end side of the rotating shaft 20 and a movable part 30B located on the other end side of the rotating shaft 20. The fixed part 30A is fixed to the rotating shaft 20, while the movable part 30B is screwed to a threaded part 20T provided on the rotating shaft 20. The sintered magnet workpieces 10 loaded on the rotating shaft 20 are sandwiched between the fixed part 30A and the movable part 30B. The sintered magnet workpieces 10 are subjected to pressure from both sides by the fixed part 30A and the movable part 30B, and are placed in a state where they do not slide relative to the fixed part 30A and the movable part 30B due to a strong frictional force.

[0018] 2, the grinding device 100 can move the position of the grinding wheel 60 along the longitudinal direction of the rotating shaft 20 while pressing the grinding wheel 60 against the outer peripheral surface of a plurality of sintered magnet workpieces 10 that rotate together with the rotating shaft 20 rotated by the driving device 50. During the grinding process, when the surface (grinding wheel surface) of the grinding wheel 60 is in contact with the outer peripheral surface of the rotating sintered magnet workpiece 10, the distance from the central axis of the rotating shaft 20 to the surface (grinding wheel surface) of the grinding wheel 60 is shortened (cutting is performed) to grind the outer peripheral surface of the sintered magnet workpiece 10, thereby reducing the outer diameter d1 of the sintered magnet workpiece 10. Grinding is performed until the outer diameter d1 of the sintered magnet workpiece 10 reaches a target value (design dimension).

[0019] According to the inventor's study, when the outer peripheral surfaces of multiple sintered magnet workpieces 10 loaded on a rotating shaft 20 as shown in Fig. 2 are ground, the roundness of the outer peripheral surface of the sintered magnet workpieces 10 after grinding varies greatly depending on the loading position, resulting in a decrease in overall roundness, as shown in the examples described below. After extensive study, the inventor found that this is due to the force applied to the sintered magnet workpieces 10 during grinding inducing bending deformation as a whole in the multiple sintered magnet workpieces 10 aligned in the axial direction. In the present disclosure, such deformation is suppressed, thereby making it possible to increase the roundness of the sintered magnet workpieces 10 after grinding.

[0020] An embodiment of the method for producing a sintered magnet according to the present disclosure will now be described. In this embodiment, the sintered magnet workpiece 10 and grinding device 100 described with reference to Figures 1 to 3 are also used. Therefore, the description of the sintered magnet workpiece 10 and grinding device 100 will not be repeated.

[0021] The manufacturing method of a sintered magnet in this embodiment includes the steps of: preparing a plurality of (typically four or more) sintered magnet workpieces 10, each having a ring shape defined by a thickness t0, an inner diameter d0 and an outer diameter d1, as shown in FIG. 4 (S10); fixing the plurality of (four or more) sintered magnet workpieces 10 to a rotating shaft 20 of a grinding device 100 so that the opening holes of each of the sintered magnet workpieces 10 pass through the rotating shaft 20 (S20); and grinding the outer peripheral surface 10B of the sintered magnet workpiece 10 with a grinding wheel while rotating the sintered magnet workpiece 10 together with the rotating shaft 20 (S30).

[0022] A characteristic feature of this embodiment is that in the step (S20) of fixing the sintered magnet workpiece 10 to the rotating shaft 20, a spacer 40 having a hollow cylindrical shape is used.

[0023] FIG. 5A is a front view of a spacer 40 having a hollow cylindrical shape used in an embodiment of the present disclosure, and FIG. 5B is a cross-sectional view of the spacer 40 taken along line BB. The illustrated spacer 40 has a hollow cylindrical shape with a thickness t1, an inner diameter d2, and an outer diameter d2. The spacer 40 has an inner peripheral surface 40A that defines the inner diameter d2, an outer peripheral surface 40B that defines the outer diameter d3, and a pair of end faces 40C and 40D. An opening hole is defined by the inner peripheral surface 40A. In this embodiment, the end face 40C and the end face 40D are parallel to each other. In addition, the inner peripheral surface 40A and the outer peripheral surface 40B may be cylindrical surfaces having a common central axis, for example. However, the shape of the outer peripheral surface 40B does not need to be a smooth cylindrical surface, and may have irregularities. In addition, a member for grinding the grindstone may be provided as described later.

[0024] The spacer 40 may be made of a highly rigid material, such as metal or ceramic, that is unlikely to undergo dimensional changes (deformation) due to bending or twisting forces. In this embodiment, the spacer 40 is made of carbon steel for mechanical construction (S45C). The size (thickness t1) of the spacer 40 in the longitudinal direction is at least twice the thickness t0 of the sintered magnet workpiece 10. The size (t1) of the spacer 40 in the longitudinal direction is at least 20% of the distance between the fixed part 30A and the movable part 30B when the spacer 40 and the sintered magnet workpiece 10 are fixed to the rotating shaft 20.

[0025] In this embodiment, the inner diameter d2 of the spacer 40 may be equal to the inner diameter d0 of the sintered magnet workpiece 10, but the outer diameter d3 of the spacer 40 is preferably smaller than the outer diameter d1 of the sintered magnet workpiece 10.

[0026] Next, an example of the step (S20) of fixing the sintered magnet workpiece to a rotating shaft using such a spacer 40 will be described.

[0027] Step (S20) includes a step (S22) of arranging the above-mentioned spacer 40 so as to surround the center of the rotating shaft 20 in the longitudinal direction, and arranging sintered magnet workpieces 10 (typically at least two) on both sides of the spacer 40 in the longitudinal direction, and a step (S24) of applying force in the longitudinal direction to both ends of the arranged sintered magnet workpiece 10 using pressing members (30A, 30B) to fix the sintered magnet workpiece 10 to the rotating shaft 20.

[0028] Specifically, first, some of the sintered magnet workpieces 10 are loaded onto the rotating shaft 20 of the grinding device 100 as shown in Fig. 6. Next, a spacer 40 is loaded onto the rotating shaft 20 as shown in Fig. 7. After a plurality of sintered magnet workpieces 10 are loaded onto both sides of the spacer 40 as shown in Fig. 8, the plurality of sintered magnet workpieces are fixed to the rotating shaft 20 by the movable part 30B as shown in Fig. 9.

[0029] FIG. 10 is a top view that typically shows how a plurality of sintered magnet workpieces fixed to a rotating shaft of a grinding device are ground with a grindstone in this embodiment.

[0030] 11 is a top view that typically illustrates how the grindstone 60 is ground by the outer circumferential surface region 40X of the spacer 40 that is fixed to the rotating shaft 20 of the grinding device 100 in an embodiment of the present disclosure. In this manner, when the spacer 40 has the outer circumferential surface region (dress region) 40X for grinding the grindstone 60, the outer diameter d3 of the spacer 40 can be equal to or greater than the outer diameter d1 of the sintered magnet workpiece 10.

[0031] The thicknesses t0 of the multiple sintered magnet workpieces 10 to be loaded do not need to have a common value. If they have different values, the thickness t1 of the spacer 40 is set to be at least twice the thickness of the thickest sintered magnet workpiece 10. EXAMPLES

[0032] Below, examples and comparative examples carried out on ring-shaped RTB based sintered magnet workpieces will be described.

[0033] An RTB sintered magnet workpiece was prepared. The size of the workpiece was an outer diameter of 90 mm, an inner diameter of 84 mm, and a thickness of 15 mm. The size of the spacer was an outer diameter of 88 mm, an inner diameter of 84 mm, and a thickness of 15 mm. The spacer was made of carbon steel for mechanical construction (S45C).

[0034] In the comparative example, 13 RTB based sintered magnet workpieces were loaded onto the rotating shaft of a grinding machine and their outer peripheral surfaces were ground. The roundness measured for each RTB based sintered magnet workpiece after grinding is shown in Fig. 12. The roundness is the difference between the maximum and minimum diameters of the outer peripheral surface divided by 2, and is expressed in mm. In the example, four RTB based sintered magnet workpieces were loaded on the left side of the spacer and five on the right side of the spacer and their outer peripheral surfaces were ground. The roundness after grinding is shown in Fig. 13. The roundness of the workpiece in the 12th position was 0.00 mm.

[0035] As can be seen from Figs. 12 and 13, by inserting a spacer at a position including the center of the rotating shaft, including the cover, the number of workpieces to be ground is reduced, but the deterioration of roundness can be suppressed.

[0036] As can be seen from the above embodiments, the numbers of sintered magnet workpieces loaded on both sides of the spacer may be different from each other.

[0037] The present disclosure includes the inventions described in the following items. [Item 1] preparing a plurality of sintered magnet workpieces, each having a ring shape defined by a thickness, an inner diameter, and an outer diameter; a step of fixing the sintered magnet workpieces to a rotation shaft of a grinding device so that each of the opening holes of the sintered magnet workpieces passes through the rotation shaft; grinding an outer peripheral surface of the sintered magnet workpiece with a grindstone while rotating the sintered magnet workpiece together with the rotating shaft; Including, The step of fixing the sintered magnet workpiece to the rotating shaft includes: a step of disposing a spacer having a hollow cylindrical shape so as to surround a center in a longitudinal direction of the rotating shaft, and disposing the sintered magnet workpiece on both sides of the spacer in the longitudinal direction; applying a force in the longitudinal direction to both ends of the sintered magnet workpiece by a pressing member to fix the sintered magnet workpiece to the rotating shaft; Including, A method for producing a sintered magnet, wherein the size of the spacer in the major axis direction is at least twice the thickness of the sintered magnet workpiece. [Item 2] 2. The method for producing a sintered magnet according to claim 1, wherein the pressing member includes a fixed part fixed to the rotating shaft and a movable part screwed to the rotating shaft, and the spacer and the sintered magnet workpiece are sandwiched between the fixed part and the movable part. [Item 3] 3. The method for producing a sintered magnet according to item 1 or 2, wherein the size of the spacer in the longitudinal direction is 20% or more of the distance between the fixed part and the movable part when the spacer and the sintered magnet are fixed to the rotating shaft. [Item 4] 4. The method for producing a sintered magnet according to any one of items 1 to 3, wherein the sintered magnet workpiece has an outer diameter of 45 mm or more and a thickness of 30 mm or less. [Item 5] 5. The method for producing a sintered magnet according to any one of items 1 to 4, wherein an outer diameter of the sintered magnet workpiece is three times or more a thickness of the sintered magnet workpiece. [Item 6] 6. The method for producing a sintered magnet according to any one of claims 1 to 5, wherein an outer diameter of the spacer is smaller than an outer diameter of the sintered magnet workpiece. [Item 7] 7. The method for producing a sintered magnet according to any one of claims 1 to 6, wherein the spacer is made of a metal material. [Item 8] 8. The method for producing a sintered magnet according to any one of items 1 to 7, wherein the spacer has an outer peripheral surface region (dress region) for grinding the grindstone. [Industrial Applicability]

[0038] The embodiments of the present invention can be widely used in the manufacture of sintered magnets, such as RTB-based sintered magnets and ferrite magnets, having a ring shape. [Explanation of symbols]

[0039] 10. Sintered magnet workpiece 20 Rotation axis 30A: Pressing member fixing part 30B: Movable part of pressing member 40 Spacer 50 Drive unit 60... Grindstone 100 Grinding equipment

Claims

1. preparing a plurality of sintered magnet workpieces, each having a ring shape defined by a thickness, an inner diameter, and an outer diameter; a step of fixing the sintered magnet workpieces to a rotation shaft of a grinding device so that each of the opening holes of the sintered magnet workpieces passes through the rotation shaft; grinding an outer peripheral surface of the sintered magnet workpiece with a grindstone while rotating the sintered magnet workpiece together with the rotating shaft; Including, The step of fixing the sintered magnet workpiece to the rotating shaft includes: a step of disposing a spacer having a hollow cylindrical shape so as to surround a center in a longitudinal direction of the rotating shaft, and disposing the sintered magnet workpiece on both sides of the spacer in the longitudinal direction; applying a force in the longitudinal direction to both ends of the sintered magnet workpiece by a pressing member to fix the sintered magnet workpiece to the rotating shaft; Including, a size of the spacer in the long axis direction is at least twice the thickness of the sintered magnet workpiece,

2. 2. The method for producing a sintered magnet according to claim 1, wherein the pressing member includes a fixed part fixed to the rotating shaft and a movable part screwed to the rotating shaft, and the spacer and the sintered magnet workpiece are sandwiched between the fixed part and the movable part.

3. 2. The method for producing a sintered magnet as described in claim 1, wherein the size of the spacer in the longitudinal direction is at least 20% of the distance between the fixed portion and the movable portion when the spacer and the sintered magnet are fixed to the rotating shaft.

4. The method for producing a sintered magnet according to claim 1 , wherein the outer diameter of the sintered magnet workpiece is 45 mm or more, and the thickness of the sintered magnet workpiece is 30 mm or less.

5. The method for producing a sintered magnet according to claim 4, wherein an outer diameter of the sintered magnet workpiece is three times or more as large as a thickness of the sintered magnet workpiece.

6. The method for producing a sintered magnet according to claim 1 , wherein an outer diameter of the spacer is smaller than an outer diameter of the sintered magnet workpiece.

7. The method for producing a sintered magnet according to claim 1 , wherein the spacer is made of a metallic material.

8. The method for producing a sintered magnet according to claim 1 , wherein the spacer has an outer peripheral surface area for sharpening the grindstone.

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