JP2015090888A - Method of manufacturing rare-earth magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a rare earth magnet capable of manufacturing a rare earth magnet of high residual magnetization under high product yield, by eliminating orientation disturbance of crystalline structure due to shear friction force acting from a plastic working mold, when manufacturing a rare earth magnet, which is an orientation magnet, by applying hot plastic working, i.e., upsetting, to a compact.SOLUTION: In a manufacturing method consisting of a first step for manufacturing a compact S, and a second step for manufacturing an oriented magnet (rare earth magnet) by applying hot plastic working while pressing the compact S by using a plastic working mold, the second step is further constituted of two steps A, B using first and second plastic working molds 10, 20 of different structure. In the step A, the compact S is pressed until a predetermined processing rate is achieved by using the first plastic working mold 10 having a tapered surface. In the step B, an oriented magnet precursor S' is pressed using the second plastic working mold 20, where all surfaces facing the cavity are flat surfaces, thus manufacturing an oriented magnet.

Description

  The present invention relates to a method for producing a rare earth magnet that is an oriented magnet by hot plastic working.

  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.

  An outline of an example of a method for producing a rare earth magnet is as follows. For example, a fine powder obtained by rapid solidification of a Nd-Fe-B metal melt is formed into a compact while being pressed, and the magnetic anisotropy is applied to the compact. In general, a method of producing a rare earth magnet (orientated magnet) by performing hot plastic working to impart the above-mentioned properties is applied.

  In the hot plastic working, a molded body is placed in a cavity constituted by a side face mold and a bottom face mold that constitute a plastic working mold, and an upper surface movable mold (also called a punch or a punch) that is slidable within the side mold, and heated. On the other hand, an upsetting process is generally applied in which the upper surface mold is pressed for a short time of, for example, about 1 second or less and pressed until a predetermined processing rate is reached. While this hot plastic working can give magnetic anisotropy to the molded body, when the molded body tries to deform laterally by pressing with the upper surface mold during upsetting, the molded body is movable on the upper surface. It is known to receive a shear frictional force in the direction opposite to the direction of deformation from the bottom surface mold. This will be described in detail with reference to FIG.

  FIG. 16a shows an analysis model of a molded body sandwiched between an upper surface mold and a lower surface mold before upsetting (the model is a set of a large number of element cells when a finite element analysis is performed by a computer). Fig. 16b shows the state of deformation of the analytical model after upsetting with a processing rate of 50%. Note that the analysis model shown is a model of only the right cross section because the analysis results are the same on the left and right sides of the compact.

  When the molded body is pressed by the upper surface movable mold as shown in FIG. 16a, the free end face of the molded body not subjected to any constraint as shown in FIG. 16b is deformed sideways. During this lateral deformation, the upper surface and the lower surface of the molded body are subjected to a shear friction force in a direction opposite to the lateral deformation direction from the upper surface movable mold and the lower mold. As a result, the central region of the compact becomes a high strain region due to the progress of plastic deformation as compared to the surrounding region, resulting in disorder of the orientation of the crystal structure, which leads to a decrease in residual magnetization and the material. This leads to problems such as an increase in manufacturing cost due to a decrease in yield.

  Here, in Patent Document 1, a forging alloy is inserted into a capsule, and die forging is performed at a high temperature to provide magnetic anisotropy. In the rare earth magnet manufacturing method, hot forging uses two or more dies. Thus, a method of performing in multiple stages is disclosed. By applying this manufacturing method, the problem that the magnet breaks during hot forging can be solved, but the above-described problem, that is, the central region of the molded body is more plastically deformed than the surrounding region. As a result, it becomes a high strain region, resulting in disorder of the orientation of the crystal structure, which leads to a decrease in residual magnetization and a problem that leads to an increase in manufacturing cost due to a deterioration in material yield.

JP-A-4-134804

  The present invention has been made in view of the above-described problems. In producing a rare earth magnet as an oriented magnet by subjecting a molded body to hot plastic processing, which is an upsetting process, the molded body is subjected to lateral deformation. Production of rare earth magnets with high remanence due to the high degree of orientation by eliminating the disorder of orientation of the crystal structure due to the shear frictional force acting from the upper surface movable type and the lower side die constituting the plastic working mold An object of the present invention is to provide a method for producing a rare earth magnet that can be manufactured.

  In order to achieve the above object, a method for producing a rare earth magnet according to the present invention comprises a first step of producing a columnar shaped body by pressure-molding a powder as a rare earth magnet material, and a cavity in which the shaped body is accommodated. A second step of producing a rare earth magnet which is an oriented magnet by preparing a plastic working die having a structure, housing a compact in the cavity, and performing hot plastic working to provide anisotropy while pressing the compact. The second step is composed of two steps using the first and second plastic working molds of different structures, and in the first step A, the first plasticity used here is The processing mold includes a first side mold formed of at least three side faces, a first lower face mold, a first upper surface movable mold that slides up and down in the first side mold, and a first With the first side mold disposed in the side mold A first vertical mold that forms a cavity in which the molded body is accommodated, and a surface facing the cavity is a tapered surface on at least one side of the first upper surface movable mold and the first side mold. At least the first vertical mold and the remaining side faces of the first side mold are flat surfaces facing the cavities, and the upper surface movable mold is slid to obtain a predetermined first The molded body is pressed until the processing rate is reached, and at least one side surface and the upper surface of the molded body are formed into a tapered surface to produce an oriented magnet precursor. In the next step B, the first step used here is performed. A second side mold, a second lower mold, and a second upper surface movable mold that slides up and down in the second side mold; With the second side mold disposed in the second side mold. The second vertical mold that forms the cavity in which the oriented magnet precursor is accommodated, and the second vertical mold, the second side mold, the second upper surface movable mold, and the second lower mold are all, The surface facing the cavity is a flat surface, and the oriented magnet precursor is pressed until the second upper surface movable mold is slid to a predetermined second processing rate to produce an oriented magnet. .

  The manufacturing method of the rare earth magnet of the present invention, instead of executing hot plastic processing to a desired processing rate by a single pressing by the upper surface movable mold at the time of upsetting, performs a plurality of steps before reaching the desired processing rate. This is a closed forging method in which hot plastic working is performed separately. In the first step (step A), at least one side surface of the molded body is formed using a first plastic working die in which at least a part of the first side surface die and the first upper surface movable die have a tapered surface. Both the upper surface and the upper surface are formed into a tapered surface, and the formed body is pressed until a predetermined first processing rate is reached, thereby producing an oriented magnet precursor. As a result, the shear frictional force acting from the plastic working die can be reduced, and strain is introduced in the direction of easy magnetization by suppressing the lateral deformation of the molded body with the first vertical die. The end of the molded body can be deformed. As a result of the shear friction force being reduced by pressing the molded body with at least one side surface of the first side surface mold and the tapered surface of the first upper surface movable mold, the molded body can easily flow during upsetting. . Then, before the molded body reaches a predetermined processing rate (processing rate necessary for magnetic anisotropy), the first upper surface movable mold and the first upper mold are restrained from the side by the first vertical mold. The orientation of the end of the molded body is corrected by pressing the molded body so as to be sandwiched between the lower surface molds 1.

  In addition, by arranging the first vertical mold in the first side mold, the cavity for accommodating the molded body is automatically formed, and depending on the arrangement position of the first vertical mold. The processing rate in step A can be adjusted.

  Then, in the next step B, a second side mold, a second lower mold, a second upper movable mold, and a second vertical mold that do not have a tapered surface, that is, have only a flat surface. By using the second plastic working mold, the flat surfaces of the second vertical mold and the second movable upper surface are pressed and deformed sequentially from the tapered tip of the tapered surface formed on the oriented magnet precursor. be able to. Therefore, the end portion of the oriented magnet precursor can be intensively oriented, and as a result, a rare earth magnet that is an oriented magnet with little or no orientation disorder can be produced.

  In addition, by disposing the second vertical mold in the second side mold, the cavity for accommodating the oriented magnet precursor is automatically formed, and the second vertical mold is arranged. Depending on the installation position, the processing rate in step B can be adjusted.

  With respect to the first plastic working mold used in step A, at least one side surface of the first side surface mold composed of at least three side surfaces and the first upper surface movable mold are surfaces facing the cavities, and more Specifically, the surface facing the cavity in which the molded body is accommodated is a tapered surface (inclined surface), and the surfaces of other molds, that is, the remaining side surfaces of the first side surface mold and the cavities of the first vertical molds, respectively. The surface opposite to is a flat surface. On the other hand, in the second plastic working die used in Step B, all the side surfaces (at least three side surfaces) of the second side surface mold, the second lower surface mold, the second upper surface movable mold, and the second The surfaces facing the cavities of the vertical types are all flat surfaces.

  Here, among at least three side surfaces constituting the first plastic working mold (from three side surfaces constituting a U-shape in plan view or four side surfaces constituting a rectangular shape in plan view), the first vertical An embodiment in which a pair of two left and right side surfaces that do not face the mold are provided with tapered surfaces may be used.

  Further, an embodiment in which a surface of the first lower surface mold facing the cavity is a tapered surface may be used.

  The first lower surface mold is slidable in the vertical direction within the first side surface mold. In Step A, the first upper surface movable mold slides downward, and the first lower surface mold moves upward. The second lower surface mold is slidable in the vertical direction in the second side surface mold, and in step B, the second upper surface movable mold slides downward. In another embodiment, the second lower surface mold slides upward to press the oriented magnet precursor.

  In Step A, an upsetting process is performed until a predetermined first processing rate (for example, about 40%) is reached, and an oriented magnet precursor is manufactured. In Step B, an end of the oriented magnet precursor in which it is difficult to introduce strain. The orientation magnet is manufactured by performing upsetting until a predetermined second processing rate (for example, about 60%) is obtained.

  According to the present inventors, when the angle of the tapered surface of the first side surface mold and the angle of the tapered surface of the first upper surface movable mold in the first plastic working die are both in the range of 12 degrees or more. It has been identified that high product yields can be achieved. Therefore, it is preferable to set both the angles of the tapered surfaces of the first side surface mold and the first upper surface movable mold in the first plastic working mold to about 12 to 20 degrees. In addition, when the first lower surface mold also has a tapered surface, the angle of the tapered surface is preferably set to about 12 to 20 degrees.

  Here, the rare earth magnets to be produced by the production method of the present invention include not only nanocrystalline magnets having a grain size of the main phase (crystal) constituting the structure of about 200 nm or less, but also those having a grain size of 300 nm or more. Furthermore, a sintered magnet having a grain size of 1 μm or more, a bonded magnet in which crystal grains are bonded with a resin binder, and the like are included.

  In the first step, a rapidly cooled ribbon (quenched ribbon), which is a fine crystal grain, is manufactured by liquid quenching, and this is coarsely pulverized to produce magnetic powder for a rare earth magnet. An isotropic molded body can be obtained by filling and sintering while pressing with a punch to achieve bulking.

  This molded body is, for example, a RE-Fe-B main phase with a nanocrystalline structure (RE: at least one of Nd and Pr, more specifically one or more of Nd, Pr and Nd-Pr. ) And a grain boundary phase of the RE-X alloy (X: metal element) around the main phase.

  As can be understood from the above description, according to the method of manufacturing a rare earth magnet of the present invention, when the molded body is accommodated in the plastic working mold and the hot plastic working is performed, the hot plastic working is performed in the first structure of the different structure. In the first step A, the molded body is plastically processed using the first plastic working die having a tapered surface, and the oriented magnet precursor is obtained. In the next step B, an oriented magnet is produced by plastic working the oriented magnet precursor using a second plastic working die whose surface facing the cavity is only a flat surface. . With this manufacturing method, the shear frictional force received from the first plastic working die during the lateral deformation of the molded body can be reduced, and the disorder of the orientation of the crystal structure caused by this can be eliminated. In the mold, a rare earth magnet that is an oriented magnet can be manufactured while the ends of the oriented magnet precursor are intensively oriented. As a result, it is possible to manufacture a rare earth magnet having a high remanence due to a high degree of orientation at a high product yield.

It is the schematic diagram explaining the 1st step of the manufacturing method of the rare earth magnet of this invention in order of (a) and (b). It is a figure explaining the microstructure of the molded object manufactured at the 1st step. It is the schematic diagram explaining Embodiment 1 of the 1st plastic working type | mold used by step A of the 2nd step of a manufacturing method. It is the schematic diagram explaining Embodiment 1 of the 2nd plastic working type | mold used by step B of the 2nd step of a manufacturing method. It is the schematic diagram explaining Embodiment 2 of the 1st plastic working type | mold used by step A of the 2nd step of a manufacturing method. It is the schematic diagram explaining Embodiment 2 of the 2nd plastic working type | mold used by step B of the 2nd step of a manufacturing method. In step A of a 2nd step, it is the figure which showed the plastic working type | mold and molded object before a process, (a) is a cross-sectional view, (b) is a longitudinal cross-sectional view. In step A of a 2nd step, it is the figure which showed the plastic working type | mold and oriented magnet precursor after a process, (a) is a cross-sectional view, (b) is a longitudinal cross-sectional view. In step B of the second step, it is a diagram showing a plastic working mold and an oriented magnet precursor before processing, where (a) is a transverse sectional view and (b) is a longitudinal sectional view. In step B of the second step, it is a diagram showing a plastic working mold and an oriented magnet after processing, where (a) is a transverse sectional view and (b) is a longitudinal sectional view. It is a figure explaining the microstructure of the manufactured oriented magnet (rare earth magnet) of this invention. It is the figure which showed the experimental result regarding the taper angle and product yield of a side surface of a side surface type, an upper surface movable type | mold, and a lower surface type | mold. As a comparative example, the strain distribution (analysis result) after each upsetting when a plastic working mold without a taper was used and upsetting was performed in the order of 40% processing rate and 60% processing rate was performed. As an example, using a plastic working mold with one side of the side mold and a top movable mold with a tapered surface of 15 degrees, upsetting is performed at a processing rate of 40% in step A and a processing rate of 60% in step B. It is the figure which showed the distortion distribution (analysis result) after each process at the time of performing. It is the photograph which observed the state of the magnetic powder in a comparative example, and the figure which simulated the state of the crystal grain. It is the figure which simulated the state of the crystal grain in Step A and Step B of an example. (A) is the figure which showed the analysis model of the molded object pinched | interposed with the punch and lower mold | die before a process in the hot plastic forming method by the conventional upsetting process, (b) is an installation model with a processing rate of 50%. It is the figure which showed the deformation | transformation state and distortion distribution (analysis result) of the analysis model after a cutting process.

  Embodiments of a method for producing a rare earth magnet according to the present invention will be described below with reference to the drawings. Note that the oriented magnet targeted by the manufacturing method shown in the figure is a nanocrystalline magnet (particle size is about 300 nm or less), but the oriented magnet targeted by the manufacturing method of the present invention is The present invention is not limited to nanocrystalline magnets, and includes those having a particle size of 300 nm or more, sintered magnets of 1 μm or more, and bonded magnets in which crystal grains are bound with a resin binder. Moreover, although the illustrated first and second plastic working dies each have four side surfaces, they may have a U-shape in plan view having both three side surfaces.

(Embodiment of manufacturing method of rare earth magnet)
FIGS. 1a and 1b are schematic views illustrating the first step of the method of manufacturing a rare earth magnet of the present invention in that order, and FIG. 2 is a view illustrating the microstructure of the molded body manufactured in the first step. is there. FIGS. 3 and 5 are schematic diagrams for explaining Embodiments 1 and 2 of the first plastic working mold used in Step A of the second step. FIGS. It is the schematic diagram explaining Embodiment 1 and Embodiment 2 of the 2nd plastic working type | mold used by step B of a 2nd step. 7 is a view showing a plastic working mold and a molded body before processing in Step A of the second step, FIG. 7a is a transverse sectional view, FIG. 7b is a longitudinal sectional view, and FIG. FIG. 8A is a cross-sectional view and FIG. 8B is a vertical cross-sectional view showing a plastic working mold and an oriented magnet precursor after processing in Step A of the second step. Further, FIG. 9 is a view showing a plastic working die and an oriented magnet precursor before processing in Step B of the second step, FIG. 9a is a transverse sectional view, and FIG. 9b is a longitudinal sectional view. 10 is a view showing the plastic working mold and the oriented magnet after processing in Step B of the second step. FIG. 10a is a transverse sectional view, and FIG. 10b is a longitudinal sectional view.

  As shown in FIG. 1a, for example, an alloy ingot is melted at a high frequency by a melt spinning method using a single roll in a furnace (not shown) in an Ar gas atmosphere whose pressure is reduced to 50 kPa or less. To produce a quenched ribbon B (quenched ribbon), which is coarsely pulverized.

  Among the coarsely pulverized quenched ribbons, a quenched ribbon B having a maximum dimension of about 200 nm or less is selected, and this is shown in FIG. Fill the cavity defined by the hard punch P. Then, while applying pressure with the carbide punch P (X direction), current is passed in the pressing direction to conduct current and heat, so that the Nd-Fe-B main phase of the nanocrystal structure (crystal grain size of about 50 nm to 200 nm) And a columnar shaped body S composed of a grain boundary phase of an Nd—X alloy (X: metal element) around the main phase (first step).

  Here, the Nd—X alloy constituting the grain boundary phase is made of Nd and at least one alloy of Co, Fe, Ga, etc., for example, Nd—Co, Nd—Fe, Nd—Ga, One of Nd-Co-Fe and Nd-Co-Fe-Ga, or a mixture of two or more of these, is in an Nd-rich state.

  As shown in FIG. 2, the compact S exhibits an isotropic crystal structure in which the grain boundary phase BP is filled between the nanocrystal grains MP (main phase).

  After the columnar shaped body S is manufactured in the first step, in the second step, hot plastic working that provides anisotropy is performed while pressing the formed body S to manufacture a rare earth magnet that is an oriented magnet. Here, the hot plastic working performed in the second step is performed in two stages of upsetting. Hereinafter, first, the first plastic working die 10 (Embodiment 1) used in the first upsetting process (step A) will be described with reference to FIG. 3, and then with reference to FIG. The second plastic working die 20 (Embodiment 1) used in the machining (step B) will be described. 5 and 6, the first plastic working mold 10A and the second plastic working mold 20A of another embodiment will be described. Then, the specific contents of plastic working in steps A and B using the first plastic working mold 10 and the second plastic working mold 20 according to the first embodiment will be described.

  First, the configuration of the first plastic working die 10 used in Step A of the second step will be described with reference to FIG. The illustrated plastic working mold 10 is composed of four side surfaces, and one of the side surfaces 1 ′ is fixed to the first side surface mold 1 and the first side surface mold 1, which are side surfaces having a tapered surface 1 a. The first lower surface mold 2, the first upper surface movable mold 3 that slides in the first side surface mold 1 in the vertical direction (Y direction), and the molded body S disposed in the first side surface mold 1. And a first vertical mold 4 that forms a cavity Ca in which is accommodated. In the illustrated example, illustration of an actuator such as a motor and a piston mechanism that slides on the first movable upper surface mold 3 is omitted.

  In each of the first upper surface movable mold 3 and one side surface 1 ′ of the first side surface mold 1, the surfaces facing the cavity Ca are tapered surfaces 3a and 1a, and the first vertical mold 4 and the first side surface mold 1 The remaining three side surfaces of the one side surface mold 1 and the first lower surface mold 2 all have a flat surface facing the cavity Ca.

  The angle θ1 of the taper surface 3a of the first upper surface movable mold 3 and the angle θ2 of the taper surface 1a of one side surface 1 ′ of the first side surface mold 1 have a range of 12 degrees or more from the verification results described later. It has been specified that it is preferable from the viewpoint of realizing product yield.

  By adjusting the arrangement position of the first vertical mold 4 in the first side mold 1, the processing rate when the first upper movable mold 3 is slid in step A to pressurize the molded body is set. Can be adjusted. The “machining rate” can be expressed by (1−h2 / h1) × 100 (%) when a workpiece having a height h2 is formed by crushing a workpiece having a height h1 in the height direction.

  Next, the configuration of the second plastic working die 20 used in Step B of the second step will be described with reference to FIG. The illustrated plastic working mold 20 includes a second side face mold 1A composed of four side faces, a second bottom face mold 2A fixed to the second side face mold 1A, and an inside of the second side face mold 1A. A second upper surface movable mold 3A that slides in the direction, and a second vertical mold 4A that is disposed in the second side surface mold 1A and forms a cavity Ca that accommodates the oriented magnet precursor. Yes. In the illustrated second plastic working die 20 as well, the actuator that slides on the second upper surface movable die 3A is not shown.

  The second vertical mold 4A, the second side mold 1A, the second upper surface movable mold 3A, and the second lower mold 2A all have a flat surface facing the cavity Ca.

  Next, the configuration of the first plastic working mold 10A of another embodiment used in Step A of the second step will be described with reference to FIG. The illustrated plastic working mold 10A includes a first side surface mold 1B in which two left and right side surfaces 1 ′ that are not opposed to the first vertical mold 4B among the four side surfaces are side surfaces provided with a tapered surface 1a, and a first side surface mold 1B. While sliding in the side mold 1B in the vertical direction (Y direction), the first upper surface movable mold 3B having a tapered surface 3a facing the cavity Ca and the first side mold 1B are slid in the vertical direction. The first lower mold surface 2B that moves (Y direction) and faces the cavity Ca is a tapered surface 2a, and the cavity Ca that is disposed in the first side mold 1B and accommodates the molded body S. The first vertical mold 4B that forms Here, the angle θ1 of the tapered surface 2a of the first lower mold surface 2B is preferably in the range of 12 degrees or more. In the illustrated example, illustration of actuators such as a motor and a piston mechanism that slide on the first upper surface movable mold 3B and the first lower surface mold 2B is omitted.

  When using the first plastic working die 10A, the first upper surface movable die 3B is slid downward and the first lower surface die 2B is slid upward, and the pressing of the formed body is executed from above and below.

  Next, the configuration of the second plastic working die 20A of another embodiment used in Step B of the second step will be described with reference to FIG. The illustrated plastic working mold 20A includes a second side face mold 1A composed of four side faces, a second bottom face mold 2C that slides in the vertical direction (Y direction) in the second side face mold 1A, A second upper surface movable mold 3A that slides up and down in the second side mold 1A and a second cavity Ca that is disposed in the second side mold 1A and accommodates the oriented magnet precursor. It consists of a vertical type 4A. Also in the illustrated second plastic working mold 20A, illustration of actuators that slide on the second upper surface movable mold 3A and the second lower surface mold 2C is omitted.

  When the second plastic working die 20A is used, the second upper surface movable die 3A is slid downward and the second lower surface die 2C is slid upward, and the pressing of the oriented magnet precursor is executed from above and below.

  Next, with reference to FIGS. 7-10, the manufacturing content until it shape | molds an oriented magnet from the molded object by the step A in the 2nd step and the step B is demonstrated. Here, the first plastic working die 10 and the second plastic working die 20 shown in FIGS. 3 and 4 are used.

  As shown in FIGS. 7 a and 7 b, in step A, the molded body S is first accommodated in the cavity Ca of the first plastic working mold 10. In this initial stage, the molded body S is in an unconstrained state that does not receive any restraint from other flat surfaces including the two tapered surfaces 1a and 3a.

  Next, as shown in FIGS. 8a and 8b, the first vertical movable die 3 is slid downward (Y1 direction) in a state where the position of the first vertical die 4 is fixed. The oriented magnet precursor S ′ having a taper surface on the upper surface and one side surface is formed by being pressurized while being deformed by plastic flow and being suppressed in the lateral deformation by the first vertical mold 4. Is done.

  In this step A, a part of the first side surface mold 1 and the first upper surface movable mold 3 use the first plastic working mold 10 provided with the tapered surfaces 1a, 3a, so that one of the molded bodies S is obtained. Tapered surfaces are formed on the side surfaces and the top surface, and pressed until a predetermined first processing rate (for example, about 60%) is reached, whereby the oriented magnet precursor S ′ is manufactured. As a result, the shear friction force acting from the plastic working die 10 can be reduced, and the first vertical die 4 suppresses lateral deformation of the molded body S, thereby introducing strain in the easy magnetization direction. As described above, the end of the molded body S can be deformed. By pressing the molded body with one side surface 1 ′ of the first side surface mold 1 and the tapered surfaces 1a and 3a provided to the first upper surface movable mold 3, the shear frictional force is reduced. As a result, upsetting At this time, the molded body S easily flows. Then, the first upper surface movable mold in a state where the molded body is constrained from the side by the first vertical mold 4 before the molded body S reaches a predetermined processing rate (processing rate necessary for magnetic anisotropy). By pressing the molded body S so as to be sandwiched between 3 and the first lower surface mold 2, the orientation of the end of the molded body is corrected and the oriented magnet precursor S 'is manufactured.

  Next, as shown in FIGS. 9 a and 9 b, in step B, the oriented magnet precursor S ′ is accommodated in the cavity Ca of the second plastic working mold 20. Even in this initial stage, the oriented magnet precursor S 'is in an unconstrained state that is not subject to any restraint from any type of flat surface.

  Next, as shown in FIGS. 10a and 10b, the second upper surface movable mold 3A is slid downward (Y1 direction) while the position of the second vertical mold 4A is fixed, so that the oriented magnet precursor S ′ is plastically flowed and deformed, but is pressed in a state in which lateral deformation is suppressed by the second vertical die 4A, and a cube-shaped oriented magnet C having a flat surface on all surfaces is formed. Is done.

  In this step B, by using the second plastic working die 20 whose surface facing the cavity Ca has only a flat surface, orientation is performed on the flat surfaces of the second vertical die 4A and the second upper surface movable die 3A. The taper surface of the tapered surface formed on the magnet precursor S ′ can be sequentially pressed and deformed. As a result, the end portion of the oriented magnet precursor S ′ can be intensively oriented, and a rare earth magnet that is an oriented magnet C with little or no orientation disorder can be produced.

  As shown in FIG. 11, the oriented magnet C manufactured by hot plastic working in two stages of steps A and B has a flat nanocrystal grain MP, and the interface substantially parallel to the anisotropic axis is curved or bent. Thus, the oriented magnet C is excellent in magnetic anisotropy.

  The oriented magnet manufactured in the second step diffuses modified alloys such as Nd-Cu alloy, Nd-Al alloy, Pr-Cu alloy, Pr-Al alloy, etc. at the grain boundary to further increase the coercive force. It may be an enhanced rare earth magnet. The eutectic point of Nd-Cu alloy is about 520 ° C, the eutectic point of Pr-Cu alloy is about 480 ° C, the eutectic point of Nd-Al alloy is about 640 ° C, and the eutectic point of Pr-Al alloy is 650 ° C. These are particularly suitable when the rare earth magnet is a nanocrystalline magnet, since both are greatly below 700 ° C. to 1000 ° C., which promotes the coarsening of the crystal grains constituting the nanocrystalline magnet.

[Experiments and Results on Tapered Angle and Product Yield of One Side and Side Movable Type]
The inventors conducted experiments on one side surface of the side surface type, the taper angle of the upper surface movable type, and the product yield. In this experiment, the processing rate of step A in the second step was 40%, the processing rate of step B was 80%, the processing rate of step A was 60%, and the processing rate of step B was 80%. In two cases, the product yield when the angles θ1 and θ2 of the respective taper surfaces are changed by 3 degrees, 6 degrees, 9 degrees, 12 degrees, 15 degrees, and 20 degrees is verified. Note that the product yield indicates how much work strain of 75% or more is included in the finally obtained oriented magnet. The experimental results are shown in FIG.

  From the figure, it can be seen that in both cases, the angle of the taper surface reaches an inflection point at 12 degrees, and saturates at a high yield of 93% to 95% beyond that. As a result of this experiment, the taper angle between the side surface of the side surface type and the upper surface movable type is determined to be in a range of 12 degrees or more. The above analysis results are the same even if the top / bottom / left / right / front / back are symmetric.

[Analysis and results of strain distribution after upsetting]
The inventors of the present invention used two types of plastic working molds that do not have a tapered surface (comparative example) to produce an oriented magnet with a processing rate of 80% in a two-stage upsetting process (comparative example). In the case of using a plastic working die having a tapered surface in the first step A described with reference to FIGS. 3 to 8 (Example), in step A having a working rate of 40% and step B having a subsequent working rate of 60%. The strain distribution was verified. FIG. 13 shows the strain distribution when the upper stage is Step A and Step B of the comparative example, and the lower stage shows the strain distribution when Step A and Step B of the embodiment (taper surface angle is 15 degrees). ing. 14 is a photograph observing the state of magnetic powder in the comparative example and a diagram simulating the state of crystal grains, and FIG. 15 is a diagram simulating the state of crystal grains in step A and step B of the example. .

  From FIG. 13, in the comparative example, the direction of the material flow during plastic processing changes due to the shear frictional force received from the plastic working die, and distortion in the easy magnetization direction does not enter the end of the molded body, resulting in a decrease in product yield. To do.

  On the other hand, in the embodiment, since the molded body is processed by the side surface mold having the tapered surface and the upper surface movable mold in Step A, the material easily flows. Further, the tapered surface is formed on the oriented magnet precursor formed in step A, so that the end of the oriented magnet precursor, which is difficult to be distorted, is sequentially processed from the tip of the taper at the time of processing in the next step B. Thus, strain can be introduced in the direction of easy magnetization while reducing the influence of shear friction as much as possible. Therefore, the product yield of the manufactured oriented magnet can be improved.

  On the other hand, FIG. 14 shows a photograph of an image of the state of the crystal grains at the end of the oriented magnet of the comparative example and the magnetic powder at the end of the oriented magnet of the comparative example actually manufactured by this method. From the figure, it can be seen that the direction of the magnetic powder at the end of the oriented magnet is greatly affected by the shear frictional force, and the degree of orientation is low.

  On the other hand, FIG. 15 shows the state of the crystal grains of the oriented magnet precursor and oriented magnet produced in steps A and B of the embodiment.

  As shown in the figure, in step A, the shear frictional force acting on the molded body is reduced by the tapered surface, and as a result, the orientation disorder of the end portion of the manufactured oriented magnet precursor is alleviated. In addition to this, in the next step B, since the upper surface movable type flat surface is gradually pressurized from the top of the tapered surface of the oriented magnet precursor, the contact area between the upper surface movable type and the oriented magnet precursor is reduced. This also reduces the shear frictional force. As a result, the shear frictional force that the molded body and the oriented magnet precursor receive from the plastic working die through Step A and Step B are greatly reduced, and an oriented magnet having a high degree of orientation at the ends as shown in the drawing is produced.

  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. For example, in FIG. 3, the lower surface mold does not have a tapered surface, but by making FIG. 3 vertically symmetric, the lower surface mold may have a tapered surface as shown in FIG. Similarly, although not shown, the first vertical type may be left and right with FIG. Furthermore, the form of FIGS. 3 and 4 may be symmetrical on the front and back of the drawing. That is, the configuration shown in FIGS. 3 and 4 may be used alone, or if this is made up-down, left-right, or front-rear symmetrical, the configuration shown in FIGS. Further, if a plurality of symmetry planes are combined, the forms of FIGS. 3 and 4 are positioned as a 1/4 symmetry model and a 1/8 symmetry model.

  DESCRIPTION OF SYMBOLS 1, 1B ... 1st side surface type | mold, 1a ... Tapered surface, 1A ... 2nd side surface type | mold, 2, 2B ... 1st lower surface type | mold, 2a ... Tapered surface, 2A, 2C ... 2nd lower surface type | mold, 3, 3B: First movable upper surface type, 3a: Tapered surface, 3A: Second upper surface movable type, 4: First vertical type, 4A: Second vertical type, 10, 10A: First plastic working die ( 20, 20A ... second plastic working die (plastic working die), R ... copper roll, B ... quenching ribbon (quenching ribbon), D ... super hard die, P ... super hard punch, Ca ... Cavity, S ... molded body, S '... oriented magnet precursor, C ... oriented magnet (rare earth magnet), MP ... main phase (nanocrystal grains, crystal grains, crystals), BP ... grain boundary phase

Claims (7)

A first step of producing a columnar shaped body by pressure-molding a powder to be a rare earth magnet material;
A rare earth metal which is an oriented magnet by preparing a plastic working die having a cavity in which the compact is accommodated, accommodating the compact in the cavity, and applying hot plastic working to give anisotropy while pressing the compact. Consisting of a second step of manufacturing a magnet,
The second step is further composed of two steps using first and second plastic working molds of different structures,
In the first step A, the first plastic working die used here is a first side die composed of at least three side surfaces, a first lower surface die, and the inside of the first side die in the vertical direction. A first upper surface movable mold that slides into the first side mold, and a first vertical mold that is disposed in the first side mold and forms a cavity in which the molded body is accommodated together with the first side mold, In at least one side of the first upper surface movable mold and the first side mold, the surface facing the cavity is a tapered surface, and at least the remaining side surfaces of the first vertical mold and the first side mold Both have a flat surface facing the cavity,
The oriented magnet precursor is manufactured by sliding the upper surface movable mold and pressing the molded body until a predetermined first processing rate is achieved, and molding at least one side surface and the upper surface of the molded body into a tapered surface. ,
In the next step B, the second plastic working die used here is a second side die composed of at least three side surfaces, a second lower surface die, and the second side die in the vertical direction. And a second vertical mold which is disposed in the second side mold and forms a cavity for accommodating the oriented magnet precursor together with the second side mold. The second vertical mold, the second side mold, the second upper surface movable mold, and the second lower mold have a flat surface facing the cavity,
A method for producing a rare earth magnet, wherein an oriented magnet is produced by pressing an oriented magnet precursor until the second upper surface movable mold is slid to a predetermined second processing rate.   2. The method for producing a rare earth magnet according to claim 1, wherein, of at least three side surfaces constituting the first plastic working die, a pair of two left and right side surfaces not opposed to the first vertical die are provided with tapered surfaces. .   The method for producing a rare earth magnet according to claim 1 or 2, wherein a surface of the first lower surface mold facing the cavity is a tapered surface.   First plastic working in which two or more first plastic working molds are combined with at least one side face of the first side face mold and / or the first lower face mold as opposed to the first vertical mold. The method for producing a rare earth magnet according to any one of claims 1 to 3, wherein a processing die having a unit structure of a die is used. The first lower surface mold is slidable in the vertical direction in the first side surface mold. In Step A, the first upper surface movable mold slides downward, and the first lower surface mold slides upward. Move to press the compact,
The second lower surface mold is slidable in the vertical direction within the second side surface mold. In Step B, the second upper surface movable mold slides downward, and the second lower surface mold slides upward. The method for producing a rare earth magnet according to any one of claims 1 to 4, wherein the magnet is moved to press the oriented magnet precursor.   The method for producing a rare earth magnet according to claim 1 or 2, wherein the angle of the tapered surface of the first side surface type and the angle of the tapered surface of the first movable upper surface type are both in the range of 12 degrees or more.   6. The method for producing a rare earth magnet according to claim 3, wherein the angle of the tapered surface of the first lower surface mold is in a range of 12 degrees or more.

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