Manufacturing method of field element

Abstract

To provide a manufacturing method of a field magneton which enables an inter peripheral surface of a bond magnet pressed into a yoke to have a predetermined accuracy regardless of an accuracy of an outer peripheral surface of the yoke.SOLUTION: In a manufacturing method of a field magneton, a field magneton is produced by fixing a cylindrical bond magnet (2) in which magnet particles are bonded with a thermoset resin to a cylindrical yoke (1) made of a magnetic material. Concretely, the method includes a softening step of re-heating and softening the bond magnet after a thermal cure processing, and a press-fit step of press fitting the bond magnet after the softening step from a taper part (114) on one end side of the yoke and bringing an outer peripheral surface (22b) of the bond magnet into pressure-contact with an inner peripheral surface (12a) of the yoke. The press-fit step allows relative attitude variation between the bond magnet and the yoke and sends the bond magnet relatively into the yoke. Thereby, an inner peripheral surface of the bond magnet is formed again into a shape along the inner circumference surface of the yoke and shows the precision similar to that of the inner peripheral surface of the yoke.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a field element consisting of a bonded magnet and a yoke (case, etc.). [Background technology]

[0002] Permanent magnet field type electric motors (including generators, simply referred to as "motors") are widely used as drive sources for various devices. In order to improve the performance, reduce the size, and reduce the cost of such motors, it has been proposed to integrate a cylindrical bonded magnet (permanent magnet for the field) into a cylindrical yoke (for example, the case of a motor). The following patent documents contain relevant descriptions. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-184642 A [Patent Document 2] WO2006 / 1304 publication [Patent Document 3] WO2011 / 126026 publication [Patent Document 4] JP 2005-33844 A [Patent Document 5] WO2006 / 059603 publication Summary of the Invention [Problem to be solved by the invention]

[0004] All of the patent documents propose a method of bonding a bonded magnet to the inner peripheral surface of a yoke without using an adhesive. Specifically, in Patent Document 1, the bonded magnet disposed in the yoke is bonded to the magnet by utilizing the fact that the bonded magnet expands due to oxidation when heated. In Patent Document 2, a molded body (bonded magnet before heat curing) is directly pressed into the yoke from a cavity, and the molded body's springback is utilized to bond the two together. In Patent Document 3, a molded body in a warm state is directly pressed into a case (yoke), and then the molded body is bonded to the magnet by utilizing the amount of expansion of the molded body that occurs during a heat curing process (cure process). Patent Documents 1 to 3 have in common that the molded body is placed or fitted into the yoke (case) before the heat curing process.

[0005] In Patent Documents 4 and 5, the molded body after the thermosetting treatment is reheated to a temperature below its glass transition point, and then pressed into a housing (yoke / case) to press the two together. Although the press-fitting performed at this time is not described in detail in these patent documents, it is performed by constraining the outer periphery of the housing, on the premise that high precision (coaxiality, roundness, cylindricity, etc.) is ensured between the outer periphery and inner periphery of the housing.

[0006] However, the precision of the outer peripheral surface of the housing itself is fundamentally unrelated to the performance of the motor. If high precision is not required for the outer peripheral surface, the manufacturing costs of the housing (case / yoke) can be reduced, which in turn makes it possible to reduce the cost of the motor.

[0007] The present invention has been made in consideration of these circumstances, and has an object to provide a new manufacturing method that, unlike conventional methods, can reduce the cost of a field element consisting of a bonded magnet and a yoke. [Means for solving the problem]

[0008] The inventors conducted extensive research to solve this problem and succeeded in press-fitting a bonded magnet into a yoke (case) without constraining the outer periphery of the yoke. By expanding on this success, they were able to complete the present invention, which is described below.

[0009] <<Method of manufacturing field element>> (1) The present invention is a method for manufacturing a field element in which a cylindrical bonded magnet, formed by bonding magnetic particles with a thermosetting resin, is fixed inside a cylindrical yoke made of a magnetic material, and includes a softening process in which the bonded magnet after thermal hardening is reheated to soften it, and a press-in process in which the bonded magnet after the softening process is fitted into one end of the yoke and the outer peripheral surface of the bonded magnet is pressed against the inner peripheral surface of the yoke, and the press-in process feeds the bonded magnet relatively into the yoke while allowing for relative posture fluctuations between the bonded magnet and the yoke.

[0010] (2) According to the manufacturing method of the present invention, regardless of the precision of the outer peripheral surface (outer cylinder portion) of the yoke (case, etc.), the inner peripheral surface of the bonded magnet after press-fitting can be given approximately the same level of precision (coaxiality, roundness, etc.) as the inner peripheral surface (inner cylinder portion) of the yoke. Therefore, by preparing a yoke that ensures the desired precision at least on its inner peripheral surface, a field element can be obtained that ensures a desired constant gap between the inner peripheral surface of the bonded magnet and the outer peripheral surface of the rotor (armature). As a result, the cost of the yoke (case, etc.) can be reduced, which in turn enables the cost of the field element and the motor to be reduced.

[0011] The reason why such a field element can be obtained by the manufacturing method of the present invention is believed to be as follows: First, the bonded magnet (simply called a "green body") before the thermosetting treatment (cure treatment) is formed by molding a mixture of magnetic particles and resin that has been softened or melted by heating into the desired shape (cylindrical) within the cavity of a molding die.

[0012] The molded body, which is removed from the cavity and has not yet completely cooled and solidified, is plastic and lacks strength and rigidity, and may therefore be slightly deformed (distorted) during removal from the cavity and subsequent handling during transportation.

[0013] Bonded magnets are usually manufactured by completely cooling (solidifying) the molded body without repairing the distortion that has occurred in the molded body, and then undergoing a heat-hardening process such as batch processing. As a result, the distortion that occurred in the molded body is also inherited by the heat-hardened bonded magnet. Since the bonded magnet after heat-hardening has sufficiently high strength or rigidity, if it is pressed into a yoke as is, the distortion will affect the precision of the inner peripheral surface of the bonded magnet inside the yoke.

[0014] In the manufacturing method of the present invention, the bonded magnet is first reheated after heat hardening to soften it. The softened bonded magnet has the strength and rigidity required for press-fitting, but also has plasticity. When this bonded magnet is fed along the inner surface of the yoke while allowing for some variation in its position relative to the yoke, the bonded magnet takes on a shape that conforms to the inner surface of the yoke with guaranteed precision. In other words, the bonded magnet is not distorted by excessive external forces during pressure feeding, and any deformation that existed before reheating is repaired. It is believed that the inner surface of the bonded magnet now has the same degree of precision as the inner surface of the yoke.

[0015] "others" (1) For convenience, in this specification, the bonded magnet side will be referred to as one end and the yoke side as the other end. In terms of the yoke, the side where the bonded magnet is introduced will be one end, and the opposite side will be the other end. In terms of the bonded magnet, the tip side that is fitted (sent) into the yoke will be the other end, and the rear end (opposite side) will be the one end. If a yoke is placed above the bonded magnet and pressed in, the lower will be one end and the upper will be the other end.

[0016] (2) Unless otherwise specified, "x to y" in this specification includes a lower limit value x and an upper limit value y. Any numerical value included in the various numerical values ​​or numerical ranges described in this specification may be used as a new lower limit value or upper limit value to create a new range such as "a to b". In addition, "x to y μm" in this specification means x μm to y μm. The same applies to other units. [Brief description of the drawings]

[0017] [Figure 1A]4 is a cross-sectional view showing a schematic diagram of a case, a ring magnet, and an assembly jig therefor. FIG. [Figure 1B] FIG. 4 is a plan view of the other end side of the case. [Figure 2A] FIG. 4 is a cross-sectional view showing a schematic diagram of an initial stage of assembly of a case and a ring magnet. [Figure 2B] FIG. 11 is a cross-sectional view showing a schematic diagram of an intermediate stage of assembly of the case and the ring magnet. [Figure 2C] FIG. 11 is a cross-sectional view showing a schematic diagram of a later stage of assembly of the case and the ring magnet. [Diagram 3] FIG. 11 is a cross-sectional view showing a modified example of the case. [Figure 4] FIG. 11 is a cross-sectional view showing a schematic diagram of another example of assembling a ring magnet to a case. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] One or more configurations selected arbitrarily from the items described in this specification may be added to the above-mentioned configuration of the present invention. Which embodiment is best depends on the target, required performance, etc. The configuration related to the manufacturing method may be a configuration related to the product.

[0019] 《Softening process》 In the softening process, the bonded magnet that has been heat-hardened is reheated to soften it. It is preferable that the magnet is softened to such an extent that it has mechanical properties (rigidity, strength, etc.) that allow it to be pressed into the yoke, and plasticity that allows it to become cylindrical along the inner circumferential surface of the yoke.

[0020] The heating temperature of the bonded magnet is adjusted appropriately depending on the type of thermosetting resin, its mass ratio, thermal history, etc. Usually, the bonded magnet is heated at a temperature lower than its thermosetting treatment temperature (T0) + 100 degrees. For example, the temperature may be T0 + 70 degrees Celsius or lower, T0 + 40 degrees Celsius or lower, T0 + 10 degrees Celsius or lower, T0 or lower, or T0 - 20 degrees Celsius or lower. The temperature may be 40 degrees Celsius or higher, or even 50 degrees Celsius or higher. As an example, if the thermosetting resin is a phenol novolac type epoxy resin, the temperature may be, for example, 270 to 40 degrees Celsius, 240 to 40 degrees Celsius, 210 to 50 degrees Celsius, 180 to 60 degrees Celsius, 150 to 90 degrees Celsius, 140 to 100 degrees Celsius, or even 130 to 110 degrees Celsius. As another example, if the thermosetting resin is a bisphenol A type epoxy resin, the temperature may be, for example, 150 to 40°C, 120 to 40°C, 90 to 40°C, 80 to 50°C, or even 70 to 55°C.

[0021] If the reheating temperature is too high, the rigidity of the bonded magnet will decrease, making it difficult to press in. If the temperature is too low, the plasticity of the bonded magnet will decrease, causing cracks in the bonded magnet and making it difficult to conform to the shape of the inner circumferential surface of the yoke. Note that the heating temperature of the bonded magnet referred to in this specification is the atmospheric temperature of a heating furnace, etc. When the heat-hardening treatment temperature changes or when the heat-hardening treatment is performed in multiple stages, it is recommended that the highest temperature during the heat-hardening treatment be used as the reference reheating temperature (T0).

[0022] The heating time for the bonded magnet can be adjusted appropriately depending on its size (wall thickness), the type and mass ratio of the thermosetting resin, etc. For example, it is recommended to reheat for about 10 seconds to 1 hour, or even 20 seconds to 30 minutes.

[0023] <Press-fitting process> In the press-fitting process, the bond magnet is relatively fed into the yoke while allowing relative positional changes. If at least one of the bond magnet and the yoke is in an unconstrained state (unfixed state), relative positional changes between the two are possible. To the extent that positional changes are possible, at least a part of the bond magnet or the yoke may be supported by a guide. In other words, the press-fitting process may be performed, for example, with the outer periphery side of the yoke in a completely unconstrained state (free state), or with a part of the outer periphery side or end side of the yoke partially restricted by a guide or the like (for example, with reference to FIG. 1A described later, with the flat portion 131 of the case 1 in advance abutting against the inner bottom surface 33a of the receiving jig 3). Similarly, the press-fitting process may be performed, for example, with the inner periphery side (for example, the inner periphery surface 22a shown in FIG. 1A) or the outer periphery side (for example, the outer periphery surface 22b shown in FIG. 1A) of the bond magnet in a completely unconstrained state (free state).

[0024] The posture change may be translational motion only, rotational motion only, or a combination of both. The rotational motion may be rotation around a certain starting point (such as the contact point with the jig) or may be rotation around another instantaneous center. The posture change may be, for example, movement in a lateral direction relative to the feed direction (approximately the central axis direction), so-called swinging. In short, it is preferable that no unnecessary force is applied to the bond magnet during press-fitting, and that the bond magnet is smoothly fitted along the inner peripheral surface of the yoke. The posture change may be achieved by the motion of either the yoke or the bond magnet, or by the motion of both of them (linked).

[0025] During press-fitting, the inner circumferential surface of the yoke, where the tip (other end) of the bonded magnet abuts, preferably has a tapered introduction section (simply called a "tapered section") that widens in diameter toward one end. This allows the bonded magnet to be smoothly pressure-fed into the yoke. The inclination angle of the tapered section may be, for example, 5 to 12 degrees, or even 6 to 10 degrees, relative to the central axis.

[0026] In addition to or in addition to the tapered portion, a chamfered or other tapered portion may be provided on the outer periphery of the tip of the bonded magnet. Even if the case does not have a tapered portion, a separate tapered portion may be provided on one end side.

[0027] The interference is adjusted as appropriate depending on the thickness of the bonded magnet and yoke, the rigidity of the bonded magnet, the application of the motor, etc. The interference should be at least to the extent that the bonded magnet does not fall off the yoke after the press-fitting process.

[0028] "yoke" The yoke is made of a magnetic material. As long as the inner peripheral surface of the yoke is cylindrical, the outer peripheral surface may or may not be cylindrical. It is sufficient that at least the inner peripheral surface of the yoke has a desired accuracy (for example, roundness).

[0029] The yoke may have a flat surface perpendicular to the central axis of the inner circumferential surface. The flat surface serves as a reference for, for example, the assembly precision (e.g., coaxiality) of bonded magnets, armatures, etc. The flat surface may be located, for example, on the other end side of the yoke (opposite the lead-in portion). If the motor case doubles as the yoke, the motor can be made smaller and less expensive.

[0030] Bonded Magnets A bonded magnet is made by subjecting a cylindrical molded body made of magnet particles and a thermosetting resin to a thermosetting treatment.

[0031] (1) At least a portion of the magnet particles may be rare earth magnet particles. This allows the bonded magnet and, in turn, the motor to have higher performance and be more compact. The magnet particles may be isotropic or anisotropic. A bonded magnet made of at least isotropic magnet particles may be magnetized after being pressed into a yoke. A bonded magnet made of anisotropic magnet particles may be a compact formed in a magnetic field orientation. In this case, magnetization may be further performed.

[0032] The rare earth magnet particles are, for example, Nd-Fe-B magnet particles, Sm-Fe-N magnet particles, Sm-Co magnet particles, etc. The magnet particles may be of one type or a mixture of multiple types. The multiple types of magnet particles may have different component compositions, different particle size distributions, or both.

[0033] (2) Thermosetting resins that are binder resins include, for example, epoxy resins, phenolic resins, unsaturated polyester resins, amino resins, polyamide resins, polyimide resins, polyamideimide resins, urea resins, melamine resins, urea resins, diallyl phthalate resins, polyurethanes, etc. In this specification, when a curing agent, a curing assistant, etc. are necessary for thermal curing, these are also referred to as thermosetting resins.

[0034] The bonded magnet may contain small amounts of various additives to improve the wettability and adhesion between the softened or molten thermosetting resin and the magnet powder, etc. Examples of such additives include alcohol-based lubricants, titanate-based or silane-based coupling agents, etc.

[0035] (3) The conditions for the thermosetting treatment are adjusted as appropriate depending on the type of thermosetting resin, the size of the bonded magnet, etc. If the thermosetting resin is an epoxy resin, the conditions may be adjusted, for example, to a heating temperature of 80 to 200°C and a heating time of 10 to 60 minutes, depending on the type. The heating atmosphere may be air, but a non-oxidizing atmosphere (Ar, N2, vacuum, etc.) can prevent the bonded magnet (magnetic particles) from deteriorating due to oxidation.

[0036] 《Field Magnet》 The field element obtained by the manufacturing method of the present invention may be used in a direct current (DC) motor or an alternating current (AC) motor. A typical application of the field element is a small DC motor in which the stator is the stator and the armature is the rotor. Note that the motor in this specification also includes a generator. EXAMPLES

[0037] The present invention will be described more specifically by taking as an example the case where a ring magnet (bonded magnet) is assembled to a motor case (yoke).

[0038] "composition" The case 1 and ring magnet 2 that make up the field element, as well as the receiving jig 3 and feeding jig 4 used for assembling them, are shown in Fig. 1A. For ease of explanation, the up-down direction, left-right direction, feed direction, and lateral direction are taken to be the directions shown in Fig. 1A. In this specification, one end side is the lower side, and the other end side is the upper side.

[0039] Case 1 is formed by forming a soft steel plate (magnetic material) into a generally cylindrical shape with a bottom. Case 1 has, in order from one end, an opening 11, a cylindrical portion 12, and a bottom portion 13. Opening 11 has a tapered portion 114 (introduction portion) on the inside of the other end that smoothly connects from the enlarged one end (opening side) to the cylindrical portion 12 while reducing in diameter. The inner peripheral surface 12a of cylindrical portion 12 has the desired precision (at least roundness), but the precision of its outer peripheral surface 12b is not guaranteed.

[0040] Bottom portion 13 has a shaft hole 132 in the center for supporting one end of a rotor (armature) shaft. Also, as shown in Fig. 1B, three flat portions 131a to 131c (collectively referred to as "flat portion 131") are formed around shaft hole 132 on the outer surface at the other end of bottom portion 13. Flat portion 131 has a predetermined flatness and a predetermined perpendicularity with respect to the central axis of cylindrical inner circumferential surface 12a, and serves as an assembly reference or measurement reference for a field element or a motor.

[0041] The ring magnet 2 is a bonded magnet made by compressing a compound made of rare earth magnet particles and thermosetting resin into a cylindrical shape and then thermosetting the compact. The ring magnet 2 has a cylindrical portion 22, an annular end face 21 at one end, and an annular end face 23 at the other end.

[0042] The roundness and the like are not guaranteed for either the inner peripheral surface 22a or the outer peripheral surface 22b of the cylindrical portion 22. However, the inner peripheral length or wall thickness (horizontal / radial directions) of the cylindrical portion 22 is within a predetermined range.

[0043] The receiving jig 3 is a bottomed cylinder made of tool steel. The receiving jig 3 has an opening 31 on one end side, a cylindrical portion 32, and a bottom portion 33. The inner diameter of the cylindrical portion 32 is larger than the outer diameter of the cylindrical portion 12 of the case 1. Therefore, there is a gap between the inner peripheral surface 32a of the receiving jig 3 and the outer peripheral surface 12b of the case 1, and the position of the case 1 can change within the range of this gap.

[0044] The inner bottom surface 33a of the bottom portion 33 is a smooth plane having a predetermined flatness. The receiving jig 3 is disposed (fixed) so that the inner bottom surface 33a is perpendicular to the vertical direction (feed-in direction).

[0045] The feed jig 4 is a stepped cylindrical body made of tool steel. The feed jig 4 includes a cylindrical base 41 and a cylindrical insert portion 42 extending upward (to the other side) from the base 41. The outer diameter of the base 41 is slightly smaller than the outer diameter of the ring magnet 2 (outer peripheral surface 22b). The outer diameter of the insert portion 42 is smaller than the outer diameter of the base 41 and is smaller than the inner diameter of the ring magnet 2 (inner peripheral surface 22a). The ring magnet 2 is placed with the end face 21 in contact with the annular lower surface 411 formed between the base 41 and the insert portion 42. There is also a gap between the outer peripheral surface 42b of the insert portion 42 and the inner peripheral surface 22a of the ring magnet 2, and the position of the ring magnet 2 can change within the range of the gap.

[0046] The inserted portion 42 is shorter in the vertical direction than the ring magnet 2, and the top surface 421 of the inserted portion 42 does not protrude from the end surface 23 of the ring magnet 2 placed on the feeding jig 4. Therefore, the end surface 23 of the ring magnet 2 can be fed to a position where it abuts against the inner bottom surface 13a of the case 1 or close to that position. At that time, because the top surface 421 of the inserted portion 42 does not abut against the inner bottom surface 13a of the case 1, the precision of the bottom portion 13 (flatness of the flat portion 131, etc.) is also maintained.

[0047] A hydraulic cylinder (not shown) is provided on one end side of the feeding jig 4, and the feeding jig 4 moves up and down at a desired speed by controlling the hydraulic pressure supplied to the hydraulic cylinder.

[0048] Incidentally, at least one of the receiving jig 3 and the feeding jig 4 may also be allowed to change its position in the press-fitting direction. For example, at least one of the jigs may be moved up and down via a universal joint extending in the press-fitting direction. The position change of the receiving jig 3 and / or the feeding jig 4 may be performed together with or instead of the position change between the case 1 and the ring magnet 2.

[0049] 《Assembly》 (1) Softening process First, the ring magnet 2 is preliminarily heated in a heating furnace (in the air) at a temperature lower than the thermal hardening temperature. This allows the ring magnet 2 to exhibit plasticity while retaining the strength and rigidity required for press-fitting.

[0050] (2) Setting process Next, as shown in Fig. 1A, the softened ring magnet 2 is inserted from above into the insertion portion 42 and set in the feeding jig 4. As described above, there is a gap between the inner peripheral surface 22a of the ring magnet 2 and the insertion portion 42 of the feeding jig 4, so the ring magnet 2 can move laterally within the range of that gap.

[0051] Furthermore, the opening 11 of the case 1 is inserted from above into the ring magnet 2. At this time, the case 1 is held in a state where the inner peripheral surface of the tapered portion 114 abuts against the outer peripheral edge of the end face 23 of the ring magnet 2.

[0052] (3) Press-in process With the case 1 still placed on the ring magnet 2, the hydraulic cylinder is operated to move the feeding jig 4 upward. This causes the bottom 13 and cylindrical portion 12 of the case 1 to enter inside the cylindrical portion 32 of the receiving jig 3. As described above, there is a gap between the outer circumferential surface 12b of the case 1 and the cylindrical portion 32 of the receiving jig 3, so the case 1 can also move laterally within the range of that gap.

[0053] As the feed jig 4 rises further, the outer edge of the upper surface of the bottom 13 of the case 1 begins to come into partial contact with the inner bottom surface 33a of the receiving jig 3, as shown in FIG. 2A.

[0054] When the feed jig 4 further moves upward, the case 1 and the ring magnet 2 change position or move laterally, while the outer edge of the upper surface of the bottom 13 of the case 1 slides on the inner bottom surface 33a of the receiving jig 3. Then, as shown in FIG. 2B, the flat surface 131 of the case 1 comes into contact with the inner bottom surface 33a of the receiving jig 3. In this way, the case 1 and the ring magnet 2 are automatically aligned. In other words, their central axes are approximately aligned along a direction (vertical direction) perpendicular to the flat surface 131 and the inner bottom surface 33a.

[0055] After the case 1 and the ring magnet 2 are aligned, the ring magnet 2 is fed into the case 1 as the feed jig 4 further rises, as shown in FIG. 2C. Here, the ring magnet 2 has sufficient strength and rigidity not to buckle, and also has the plasticity to be deformed into a shape that conforms to the inner circumferential surface 12a of the case 1. Therefore, as the ring magnet 2 is fed into the case 1, it is reshaped along the inner circumferential surface 12a of the case 1, whose roundness is ensured. As a result, the inner circumferential surface 22a of the ring magnet 2 is given approximately the same precision (roundness) as the inner circumferential surface 12a of the case 1.

[0056] Ring magnet 2 may be inserted into case 1 until end face 23 abuts against inner bottom face 13a, or may be stopped at a predetermined position before the abutment.

[0057] In this way, a field element is obtained in which the ring magnet 2 is press-fitted into the case 1. The inner circumferential surface 22a of this field element has a predetermined precision (roundness, etc.) around the central axis perpendicular to the flat surface portion 131 of the case 1. As is clear from the above-mentioned process, the precision of the inner circumferential surface 22a is ensured without depending on the precision of the outer circumferential surface 12b of the case 1, etc.

[0058] <<Variation>> (1) Instead of the case 1, a case 5 having an open end can be used as shown in Fig. 3. Note that the same reference numerals as those already described are used for the parts already described, and the description thereof will be omitted (hereinafter the same).

[0059] In the case of case 5, the ring magnet 2 is fed into case 5 after the annular end face 53 (or its outer edge) slides against and abuts against the inner bottom surface 33a of the receiving jig 3. If the end face 53 has the same precision as the flat portion 131, the precision (coaxiality, etc.) of the inner peripheral surface 22a of the ring magnet 2 can be ensured even when case 5 is used.

[0060] (2) Instead of case 1, case 6 having bottom 63 may be used as shown in Fig. 4. Bottom 63 has three recesses around shaft hole 632 (corresponding to shaft hole 132), and flat surfaces 631a to 631c (collectively referred to as "flat surface 631") are formed on the upper surface of each recess (flat surface 631c is omitted). Like flat surface 131, flat surface 631 is ensured to have the desired accuracy (perpendicularity) with respect to the central axis.

[0061] The receiving jig 3 is changed to a jig having protrusions 71a-71c (collectively referred to as "protrusions 71") that come into contact with each flat surface 631 (protrusion 71c is omitted). If the ring magnet 2 is fed into the case 6 by the feeding jig 4 while the flat surface 631 of the case 6 is supported by the protrusions 71, the precision of the inner peripheral surface 22a of the ring magnet 2 is ensured, as in the case described above.

[0062] Evaluation example: (1) Case and ring magnet Using an actual manufactured case 1 and ring magnet 2, the effects of the softening process and press-fitting process described above were confirmed.

[0063] For the case 1, a bottomed cylinder made of cold-rolled steel plate (outer diameter: φ34.0 mm, inner diameter: φ30.0 mm, length: 70.0 mm) was prepared. The tapered portion 114 (introduction portion) provided on the inner peripheral surface side had an inclination angle of 8° with respect to the central axis. The roundness of the inner peripheral surface 12a of the case 1 was 0.10 mm. The roundness was measured according to JIS B0021 (same below).

[0064] The ring magnet 2 was manufactured as follows. The raw material was a compound consisting of NdFeB rare earth anisotropic magnet particles (Aichi Steel Corporation Magfine Magnet Powder MF15P) and epoxy resin. The amount of epoxy resin in the entire compound was 3 mass%. The epoxy resin was a phenol novolac type, and its heat curing temperature was 150°C.

[0065] The compound was heated and compressed in the cavity of the mold (150°C x 130 MPa x 6 seconds) to obtain a cylindrical compact (outer diameter: 30.2 mm x inner diameter: 28.1 mm x length: 30 mm). This compact was heated in an air-conditioned heating furnace for thermal curing (150°C x 40 minutes). In this way, a ring magnet 2 made of a bonded magnet was prepared.

[0066] (2) Assembly First, the ring magnet 2 after the softening process was assembled into the case 1 using the receiving jig 3 and the feeding jig 4 shown in Fig. 1A (press-fit process). In the softening process, the ring magnet 2 was heated in a heating furnace in an air atmosphere (150°C x 30 seconds). The press-fit process was performed with a load of 985N and a movement speed of 30mm / sec.

[0067] The inner peripheral surface 22a of the ring magnet 2 thus assembled into the case 1 had a circularity of 0.12 mm.

[0068] (3) Comparative Example When the above-mentioned press-fit process is performed on a ring magnet 2 that has not been subjected to a softening process, cracks may occur on the inner peripheral surface 22a of the ring magnet 2. Furthermore, if the ring magnet 2 after the above-mentioned softening process is sent into the case 1 without allowing any change in the posture of the case 1 and the ring magnet 2, an abnormal load occurs and the ring magnet cannot be pressed in.

[0069] (4) Evaluation From the respective measurement results (roundness), it was confirmed that the inner peripheral surface 22a of the ring magnet 2 can be made to the desired precision by pressing the softened ring magnet 2 into the case 1 while allowing for posture fluctuation. Conversely, it was also found that it is difficult to properly press the ring magnet 2 into the case 1 if the softening process is omitted or if the press-fitting process is performed without allowing for posture fluctuation. [Explanation of symbols]

[0070] 1 Case (York) 2 Ring magnets (bonded magnets) 3 Receiving jig 4 Feeding jig

Claims

1. A method for manufacturing a field element in which a cylindrical bonded magnet, which is made by bonding magnet particles with a thermosetting resin, is fixed to the inner peripheral surface side of a cylindrical yoke made of a magnetic material, comprising: a softening step of reheating the bonded magnet after the heat-hardening treatment to soften it; a press-fitting step of fitting the bonded magnet after the softening step into one end side of the yoke and pressing the outer circumferential surface of the bonded magnet into the cylindrical inner circumferential surface of the yoke, The press-fitting process uses a receiving jig that is positioned on the other end side of the yoke and has an inner surface that leaves a gap with the outer circumferential surface of the yoke, and a feeding jig that is positioned on one end side of the bonded magnet and has an insertion portion that leaves a gap with the inner circumferential surface of the bonded magnet, to relatively feed the bonded magnet into the yoke without restraining the outer circumferential side of the yoke, while allowing relative positional fluctuations between the bonded magnet and the yoke.

2. The softening step is performed at a thermosetting temperature (T ０ ) at a temperature 100° C. higher (T ０ 2. The method for manufacturing a field element according to claim 1, wherein the bonded magnet is heated to a temperature lower than a temperature of 100° C. or lower.

3. 3. The method for manufacturing a field element according to claim 1, wherein an inner peripheral surface of the yoke is formed with a tapered introduction portion that expands in diameter toward one end.

4. The method for manufacturing a field element according to any one of claims 1 to 3, wherein the yoke has a flat portion on the other end thereof that is perpendicular to the central axis of the inner circumferential surface.

5. The method for manufacturing a field element according to any one of claims 1 to 4, wherein the yoke is a case of a motor.

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