JP6287684B2 - Rare earth magnet manufacturing method - Google Patents

Description

  The present invention relates to a method for producing a rare earth magnet, in which a sintered body is subjected to hot upsetting to produce a rare earth magnet.

  Rare earth magnets using rare earth elements such as lanthanoids are also called permanent magnets, and their uses are used in motors for driving hard disks and MRI, as well as drive motors for hybrid vehicles and electric vehicles.

  Residual magnetization (residual magnetic flux density) and coercive force can be cited as indicators of the magnet performance of this rare earth magnet. However, in response to increased heat generation due to miniaturization of motors and higher current density, rare earth magnets used also The demand for heat resistance is further increasing, and how to maintain the magnetic properties of the magnet under high temperature use is one of the important research subjects in the technical field.

  As rare earth magnets, in addition to general sintered magnets with a crystal grain (main phase) scale of 3 to 5 μm constituting the structure, nanocrystal magnets with crystal grains refined to a nanoscale of about 50 nm to 300 nm are available. Among them, nanocrystal magnets that can reduce the amount of expensive heavy rare earth elements added or eliminate the addition of heavy rare earth elements while miniaturizing the crystal grains described above are currently attracting attention.

  An outline of an example of a method for producing a rare earth magnet is as follows. For example, a fine powder (magnetic powder) obtained by rapidly solidifying an Nd-Fe-B metal melt is pressed into a sintered body, and this sintered body is formed. In general, a method of producing a rare earth magnet (orientated magnet) by performing hot plastic working to impart magnetic anisotropy to the magnet is applied. In addition, extrusion processing such as backward extrusion processing and forward extrusion processing, upsetting processing (forging processing), and the like are applied to the hot plastic processing.

  In addition, there are free forging, semi-hermetic forging, and hermetic forging. In free forging, a workpiece is placed on a flat surface of the lower die, for example, the upper die is lowered with respect to the lower die, and the workpiece is pressed with a flat pressing surface of the upper die, for example, and then crushed to the side. It is a forging method that does not constrain the spreading work sideways. On the other hand, semi-hermetic forging is a forging method in which a side surface mold is disposed on a part of the side, and a part of the side of the workpiece that is crushed and spread laterally is restrained. Sealing forging is a forging method that includes a side die that completely closes the upsetting space in addition to the upper die and the lower die, and completely restrains the side of the workpiece that is crushed and spread laterally.

  By subjecting the sintered body to hot upsetting and imparting magnetic anisotropy, the processed rare earth magnet is strained throughout the entire crystal and is easily magnetized (hexagonal c-axis direction). As a result, high magnetization (residual magnetic flux density) is obtained. On the other hand, crystal grains grow by applying strain to the crystal, and the grain boundary phase contributing to the magnetic separation between the crystals decreases as the crystal grains grow, resulting in a decrease in coercive force. It will be.

  Incidentally, a rare earth magnet, which is a permanent magnet embedded in a rotor such as an IPM motor, is required to have a coercive force that can resist demagnetization due to an external magnetic field incident from the stator core side. The external magnetic field acting on the rare earth magnet is generally such that when the rotor embedded with the rare earth magnet is viewed in plan, the corner of the rare earth magnet on the stator core side is the largest and the center side of the rotor core is small. .

Therefore, it is not necessary for the entire area of the rare earth magnet to have the same degree of coercive force performance, and it is sufficient if the rare earth magnet has a relatively large coercive force performance at a location where a high coercive force is required.
From such a viewpoint, Patent Document 1 discloses a permanent magnet formed by combining magnets having different required coercive forces for each part.

  For example, by producing a plurality of magnets having different coercive force performance by varying the processing rate by the upsetting process, and by combining a magnet having a coercive force necessary for each part, a permanent magnet can be produced. A permanent magnet having a relatively large coercive force and having a coercive force distribution can be manufactured at the corner.

  However, in this method, when manufacturing one permanent magnet (rare earth magnet), a plurality of magnets having different coercive forces are prepared, and the prepared magnets are magnets specific to each part according to the required coercive force. It can be easily understood that a magnet manufacturing process is required to be assembled in such a manner that a large amount of time and labor are required.

  As another method for imparting a coercive force distribution to a rare earth magnet, a heavy rare earth element such as dysprosium or an alloy thereof is added to the grain boundary phase of a rare earth magnet (orientated magnet) manufactured by hot plastic working. There is also a way to spread. However, this method diffuses heavy rare earth elements, etc. at the grain boundaries, and therefore increases the manufacturing cost of rare earth magnets due to the material cost and the need for the grain boundary diffusion process of the modified alloy. I can't.

JP 2009-27847 A

  The present invention has been made in view of the above problems, and relates to a manufacturing method for manufacturing a rare earth magnet by subjecting a sintered body to a hot upsetting process, without increasing the manufacturing cost, and in a simple method, It is an object of the present invention to provide a method for producing a rare earth magnet capable of producing a rare earth magnet having a coercive force distribution.

  In order to achieve the above object, a method of manufacturing a rare earth magnet according to the present invention is a hot process for producing a sintered body by press-molding a magnetic powder for a rare earth magnet and imparting magnetic anisotropy to the sintered body. In the method of producing a rare earth magnet by performing plastic working to produce a rare earth magnet, the hot plastic working is performed by placing a sintered body inside a molding die composed of a lower die, an upper die and a side die, This is a hot upsetting process in which either one of the lower molds is moved relative to the other for pressurization. During the hot upsetting process, the sintered body has a relatively high holding capacity compared to other parts. The part where the magnetic force is to be applied is formed in advance on a convex part protruding laterally, and when the sintered body is placed on the mold, the convex part comes into contact with the side surface mold, or the convex part is sintered. Hot upsetting is performed in a state of being closer to the side surface mold than other parts of the body.

  The manufacturing method of the rare earth magnet of the present invention applies hot upsetting as hot plastic working, and uses a forming die having a side die in addition to an upper die and a lower die. In addition to this, with respect to the sintered body accommodated in the upsetting space of the mold, a convex portion is formed at a portion where a relatively high coercive force is to be applied, and the convex portion is brought into contact with the side surface mold. When performing hot upsetting at a location where high coercive force is to be applied, by performing hot upsetting in a state, or by performing hot upsetting with the convex portion close to the side surface mold By reducing the deformation amount as much as possible and reducing the introduced strain, the coercive force decrease is suppressed. Accordingly, a magnetic anisotropy is imparted to the sintered body by hot upsetting to provide a high magnetization performance, and a rare earth magnet having a coercive force distribution having a coercive force is provided at a location requiring a high coercive force. Manufactured.

  The side mold may be in a form (sealing forging method) in which the upsetting space is completely sealed, or may be in a form (semi-sealing forging method) in which it is partially closed.

  As a result of verification by the present inventors, the plastic strain introduced is reduced by suppressing deformation during hot upsetting of the part provided with the convex part, and the coercive force of the part is increased. Has been demonstrated.

  According to the manufacturing method of the present invention, hot upsetting is performed using a mold having a side surface mold, and a convex portion is formed in a portion of the sintered body where a relatively high coercive force is to be applied. By doing so, it becomes possible to manufacture a rare earth magnet having a coercive force applied to a portion requiring a predetermined coercive force by a simple and efficient method without increasing the manufacturing cost.

  Here, for example, when it is desired to give a relatively high coercive force to the upper surface corner portion of the sintered body processed into a rectangular parallelepiped, the four convex portions on the upper surface of the sintered body are laterally provided. An overhanging protrusion may be provided. Also, if you want to give relatively high coercive force to the corners on the upper and lower surfaces of the sintered body, you can provide convex parts that protrude laterally from the total of the eight corners on the upper and lower surfaces of the sintered body. That's fine.

  Or the convex part of the rectangular frame shape projected on the side of a sintered compact can also be provided in the upper surface or upper and lower surfaces of a sintered compact. In this case, the cross-sectional shape of the sintered body is T-shaped when a rectangular frame-shaped convex portion is provided only on the upper surface, and H when the rectangular frame-shaped convex portion is provided on the upper and lower surfaces. It becomes the character shape.

  As described above, when the rare earth magnet is incorporated in the rotor, the portion that requires a high coercive force is, for example, four corners on the teeth side when the rare earth magnet is a rectangular parallelepiped. In the sintered body, convex portions projecting sideways are formed at the four corners on the teeth side when the rare earth magnet is manufactured and incorporated in the rotor. By performing hot upsetting with the four convex parts in contact, the coercive force at the four corners on the teeth side when assembled in the rotor is relative to that of other parts. High-rare earth magnets can be manufactured.

  As can be understood from the above description, according to the method of manufacturing a rare earth magnet of the present invention, hot upsetting is applied as hot plastic processing, and in this processing, a side die is used in addition to an upper die and a lower die. Concerning the sintered body accommodated in the upsetting space of the mold, a convex part is formed at a part where a relatively high coercive force is to be applied, and the convex part is applied to the side mold. The hot upsetting process is performed in a contact state, or the hot upsetting process is performed in a state where the convex portion is close to the side surface mold. As a result, the amount of deformation at the time of hot upsetting at a site where a high coercive force is to be imparted can be reduced as much as possible, and the reduction of the coercive force can be suppressed by reducing the strain introduced. It is possible to easily and efficiently manufacture rare earth magnets that have high magnetization performance by interposition processing and have a coercive force distribution in parts that require high coercive force without increasing the manufacturing cost. it can.

It is the schematic diagram explaining the manufacturing method of the magnetic powder for rare earth magnets used with the manufacturing method of the rare earth magnet of this invention. It is the schematic diagram explaining the manufacturing method of a sintered compact in the manufacturing method of the rare earth magnet of this invention. (A) is the perspective view which showed Embodiment 1 of the sintered compact manufactured with the manufacturing method of FIG. 2, (b) is the perspective view which showed Embodiment 2 of the sintered compact. (C) is the perspective view which showed Embodiment 3 of the sintered compact. It is the schematic diagram explaining the condition which is implementing the hot plastic working (hot upsetting process) using Embodiment 1 of a sintered compact. It is the perspective view which showed the manufactured rare earth magnet with coercive force distribution. (A) is the figure explaining the microstructure of the sintered compact shown in FIG. 3a, (b) is the figure explaining the microstructure of the rare earth magnet shown in FIG. It is the figure explaining the hot upsetting process of an Example and a comparative example, and the figure which showed each process direction strain distribution. (A) is the figure which showed the measurement result of the process direction distortion | strain in the measurement position of an Example and a comparative example, (b) is the figure which showed the measurement result of the coercive force in the measurement position of an Example and a comparative example. .

  Embodiments of a method for producing a rare earth magnet according to the present invention will be described below with reference to the drawings.

(Embodiment of manufacturing method of rare earth magnet)
FIG. 1 is a schematic diagram for explaining a method for producing a magnetic powder for a rare earth magnet used in the method for producing a rare earth magnet of the present invention, and FIG. 2 is a method for producing a sintered body in the method for producing a rare earth magnet of the present invention. It is the schematic diagram explaining the method. FIG. 3 is a view showing an embodiment of the manufactured sintered body. Further, FIG. 4 is a schematic diagram illustrating a situation where hot plastic working (hot upsetting) is performed using the first embodiment of the sintered body, and FIG. 5 is a manufactured coercive force. It is the perspective view which showed the rare earth magnet with distribution.

  In the manufacturing method of the present invention, a sintered body is manufactured by pressure-molding magnetic powder for a rare earth magnet, and a rare earth magnet is manufactured by performing hot plastic working to impart magnetic anisotropy to the sintered body. Is the method. First, a method for producing magnetic powder will be outlined.

  For example, in a furnace (not shown) whose pressure is reduced to 50 kPa or less, the alloy ingot is melted at a high frequency by a melt spinning method using a single roll, and as shown in FIG. Quenching ribbon B (quenching ribbon) is manufactured.

  The produced rapidly cooled ribbon B is roughly pulverized to produce a magnetic powder J. Here, the particle size range of the magnetic powder J is preferably adjusted to be in the range of 75 to 300 μm.

Next, a method for producing a sintered body by pressing the produced magnetic powder will be described.
As shown in FIG. 2, a molding die M1 including an upper die K1, a lower die K2, and a side die K3 having a groove in the center is used. The side surface mold K3 is a cylindrical body having a hollow with a rectangular cross section at the center.

  As shown in the figure, the magnetic powder J is filled in the molding die M1, and the upper die K1 is lowered (X1 direction) to perform pressure molding.

  As shown in FIG. 3 a, a sintered body S <b> 1 having a convex portion S <b> 1 a projecting laterally below the rectangular parallelepiped is manufactured by the pressure molding shown in FIG. 2.

  In addition, by changing the shaping | molding die to be used or performing appropriate post-processing, for example, as shown in FIG. 3b, as shown in FIG. 3b, the sintered body S2 having the convex portions S2a on the upper and lower surfaces of the rectangular parallelepiped, A sintered body S3 having convex portions S3a at four corners on one side surface of the rectangular parallelepiped can also be manufactured. Here, the sintered body S3 shown in FIG. 3c corresponds to the four corner portions having the convex portions S3a when the rare earth magnet formed by hot upsetting is accommodated in the slot of the rotor. The corners of the rare earth magnet are opposed to the teeth TS disposed around the rotor. As described above, among the rare-earth magnets arranged in the rotor, the demagnetization of the corner portion on the side facing the teeth is severe, so that a higher coercive force is required as compared with other parts. Because.

  Here, the sintered body S1 includes a Nd-Fe-B main phase (having an average grain size of 300 nm or less, for example, a crystal grain size of about 50 nm to 200 nm) and a Nd around the main phase. -X alloy (X: metal element) grain boundary phase. The Nd—X alloy constituting the grain boundary phase of the sintered body S1 is made of Nd and at least one alloy of Co, Fe, Ga, and the like. For example, Nd—Co, Nd—Fe, Nd One of -Ga, Nd-Co-Fe, and Nd-Co-Fe-Ga, or a mixture of two or more of these, is in an Nd-rich state.

  Next, a method for producing a rare earth magnet by hot plastic working (hot upsetting) of the sintered body S1 will be described.

  As shown in FIG. 4, a cylindrical side mold K6 having a hollow section with a rectangular cross section is disposed on the lower mold K5, and a molding mold M2 having an upper mold K4 that is slidable in the upsetting space G. Is applied, and the sintered body S1 is placed in the upright space G so that the convex portion S1a comes to the lower mold K5 side, and the convex portion S1a is in contact with the side surface mold K6. That is, the hot upsetting process in the illustrated example is a closed forging process.

  A rectangular parallelepiped rare earth magnet C is manufactured as shown in FIG. 5 by sliding the upper mold K4 downward (in the X2 direction) and upsetting the sintered body S1.

  Here, in the sintered body S1, the portion provided with the convex portion S1a is in contact with the side surface mold K6 at the stage before performing the hot upsetting process, and thus the convex portion S1a during the hot upsetting process. The deformation of is suppressed as compared with other parts. Therefore, in the rare earth magnet C, the plastic strain introduced in the portion corresponding to the convex portion S1a is reduced, and the high coercive force region is formed by increasing the coercive force of the portion, while the convex portion S1a is Other portions corresponding to the portions not provided are relatively low coercive force regions.

  As described above, according to the method of manufacturing a rare earth magnet shown in the drawing, a portion in the sintered body S1 to which a relatively high coercive force is to be applied as compared with other portions is preliminarily laterally. The rare earth magnet C having a coercive force distribution is formed by contacting the convex portion S1a with the side surface mold K6 when the sintered body S1 is placed on the molding die M2. Can be efficiently manufactured. Note that the hot upsetting process may be performed in a state where the convex portion S1a is not brought into contact with the side surface mold K6 and is relatively close to the side surface mold K6 as compared with other portions.

  Note that the strain rate during the hot plastic working is preferably adjusted to 0.1 / sec or more. In addition, when the degree of processing (compression rate) by hot plastic working is large, for example, hot plastic working when the compressibility is about 10% or more can be called strong processing, but the processing rate is about 60-80% It is better to perform hot plastic working in the range.

  6a is a diagram for explaining the microstructure of the sintered body shown in FIG. 3a, and FIG. 6b is a diagram for explaining the microstructure of the rare earth magnet shown in FIG. As shown in FIG. 6a, the sintered body S1 produced by pressure-molding magnetic powder exhibits an isotropic crystal structure in which the grain boundary phase BP is filled between the nanocrystal grains MP (main phase). Yes. In contrast, as shown in FIG. 6b, the rare earth magnet C manufactured by hot plastic working exhibits a magnetic anisotropic crystal structure.

  Thus, according to the method of manufacturing a rare earth magnet of the present invention, in the hot upsetting process, which is a hot plastic process, the mold M2 having the side mold K6 in addition to the upper mold K4 and the lower mold K5 is used. In addition, with respect to the sintered body S1 accommodated in the upsetting space G of the mold M2, a convex portion S1a is formed at a portion where a relatively high coercive force is to be applied, and the convex portion S1a is applied to the side surface mold K6. The hot upsetting process is performed in a contact state, or the hot upsetting process is performed in a state where the convex portion S1a is brought close to the side surface mold K6. As a result, the amount of deformation at the time of hot upsetting at a site where a high coercive force is to be imparted can be reduced as much as possible, and the reduction of the coercive force can be suppressed by reducing the strain introduced. A simple and efficient production of rare earth magnets C with high coercive force and high coercive force distribution with coercive force distribution without increasing production costs. Is possible.

(Experiment and results of measuring strain and coercivity of rare earth magnets manufactured by the conventional manufacturing method and the manufacturing method of the present invention)
The present inventors conducted experiments to measure strain and coercivity of rare earth magnets manufactured by the conventional manufacturing method and the manufacturing method of the present invention.

  Here, FIG. 7 is a diagram illustrating hot upsetting of Examples 1 and 2 and a comparative example, and a diagram showing strain distribution in each processing direction. The experimental model diagram shown on the left side of FIG. 7 shows only the right side of the center line CL because the sintered body and the mold are symmetrical, and the strain distribution diagram shown on the right side of FIG. is there.

  Example 1 is a case in which the sintered body S1 shown in FIG. 3a is hot upset processed, and Example 2 is a case in which the sintered body S2 shown in FIG. 3b is hot upset processed. The comparative example is a case where a conventional general rectangular parallelepiped sintered body S 'is hot upset processed.

  From the strain distribution diagram of FIG. 7, the distortion of the corner portion of the rare earth magnet of the comparative example is large, while the distortion of the corner portion (region A1, A2) of the rare earth magnet of Examples 1 and 2 is extremely small. ing.

  Moreover, the measurement result regarding the process direction distortion | strain in each measurement point P1, P2, P3 in the strain distribution map of FIG. 7 and the measurement result regarding a coercive force are each shown to FIG.

  From FIG. 8a, it can be seen that the strains of Examples 1 and 2 are almost close to zero with respect to the strain -0.5 of the comparative example.

  8b shows that the coercive force of the comparative example is about 17 kOe, while the coercive force of Examples 1 and 2 is about 22 kOe, which is 5 kOe higher than that of the comparative example. Has been.

  In this way, a convex portion is provided in a sintered body portion to which a high coercive force is to be imparted, and the deformation of the convex portion is suppressed during hot upsetting to diffuse expensive heavy rare earth elements and the like at grain boundaries. Therefore, it becomes possible to produce a rare earth magnet excellent in coercive force performance.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

  M1, M2 ... Mold, K1, K4 ... Upper mold, K2, K5 ... Lower mold, K3, K6 ... Side face mold, G ... Installation space, R ... Copper roll, B ... Quenching ribbon (quenching ribbon), J ... Magnetic powder, S1, S2, S3 ... Sintered body, S1a, S2a, S3a ... Convex part, C ... Rare earth magnet (orientation magnet), MP ... Main phase (crystal grains, crystals), BP ... Grain boundary phase

Claims (3)

In a method for producing a rare earth magnet, a magnetic powder for a rare earth magnet is pressure-molded to produce a sintered body, and the sintered body is subjected to hot plastic processing for imparting magnetic anisotropy to produce a rare earth magnet.
In the hot plastic working, a sintered body is placed inside a molding die composed of a lower die, an upper die, and a side die, and either the upper die or the lower die is moved relative to the other and pressed. Hot upsetting,
At the time of hot upsetting, a portion of the sintered body to which a relatively high coercive force is to be imparted compared to other parts is formed in a convex portion protruding in the side in advance, and the sintered body is molded. When placed on the mold, the convex part comes into contact with the side surface mold, or the convex part is in a state closer to the side surface mold than the other parts of the sintered body, and hot upsetting is performed. A method for producing a rare earth magnet. In the sintered body, the location where a relatively high coercive force is desired compared to other parts is the end of the upper surface or the lower surface of the sintered body,
The method for producing a rare earth magnet according to claim 1, wherein a portion of the side surface of the sintered body corresponding to the end portion of the upper surface or the lower surface is protruded laterally to form the convex portion. The places where you want to give a relatively high coercive force compared to other parts in the sintered body are the upper and lower ends of the sintered body,
The method for producing a rare earth magnet according to claim 1, wherein, among the side surfaces of the sintered body, portions corresponding to the end portions of the upper surface and the lower surface are projected sideways to form the convex portions.

Images