JP6677140B2 - Rare earth magnet manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a rare earth magnet.

  The rare earth magnet is a component such as a motor or an actuator. For example, a hard disk drive, a hybrid vehicle, an electric vehicle, a magnetic resonance imaging device (MRI), a smartphone, a digital camera, a thin TV, a scanner, an air conditioner, a heat pump, a refrigerator, and a vacuum cleaner , Washing and drying machines, elevators and wind power generators. The size and shape required for the rare earth magnet are different depending on these various uses. Therefore, in order to efficiently produce various kinds of rare earth magnets, a molding method capable of easily changing the size and shape of the rare earth magnet is desired.

  In the production of a conventional rare earth magnet, a magnetic field is applied to a metal powder while a metal powder containing a rare earth element (for example, an alloy powder) is pressurized at a high pressure (for example, 50 MPa or more and 200 MPa or less). As a result, a compact is formed from the metal powder oriented along the magnetic field. Hereinafter, such a forming method is referred to as a “high-pressure magnetic field pressing method”. According to the high-pressure magnetic field pressing method, it is possible to obtain a molded body in which the metal powder is easily oriented and has high residual magnetic flux density Br and excellent shape retention. A sintered body is obtained by sintering the molded body, and the sintered body is processed into a desired shape, thereby completing a magnet product.

  However, in the high-pressure magnetic field press method, since a high pressure needs to be applied to the metal powder in a magnetic field, a large-scale and complicated molding device is required, and the size and shape of a molding die are limited. Due to this limitation, the shape of a general molded body obtained by the high-pressure magnetic field pressing method is limited to a coarse block. Therefore, when manufacturing various types of magnet products by the conventional method, after sintering the block-shaped molded body to obtain a sintered body, the sintered body is formed according to the dimensions and shape required for the magnet product. Need to be processed. In the processing of the sintered body, since the sintered body is cut or polished, waste containing expensive rare earth elements is generated. As a result, the yield rate of the magnet product is reduced. In the high-pressure magnetic field press method, the mold or the molded body is easily damaged by galling between the molds or galling between the mold and the molded body. For example, a compact obtained by a high-pressure magnetic field pressing method may have cracks.

  For the reasons described above, the manufacturing method using the conventional high-pressure magnetic field pressing method is not suitable for manufacturing a variety or a small amount of magnet products. As a molding method that replaces the high-pressure magnetic field pressing method, Patent Literature 1 below discloses a method of molding an alloy powder at a low pressure (not less than 0.98 MPa and not more than 2.0 MPa). This method of manufacturing a rare earth magnet includes a step of filling an alloy powder into a mold and pressing the alloy powder at a low pressure to form a compact (filling step), and applying a magnetic field to the compact in the mold. A step of orienting the alloy powder in the compact (orienting step) and a step of sintering the compact taken out of the mold (sintering step). And in the manufacturing method of the following patent document 1, a filling process and an orientation process are performed in another place.

WO2016 / 047593

  When the alloy powder is molded at a low pressure as in the molding method described in Patent Document 1, durability against high pressure is not required for a mold, and a large-scale and complicated molding apparatus is not required. Therefore, when molding the alloy powder at a low pressure, the material, dimensions and shape of the mold are not limited, and it is relatively easy to manufacture various kinds of rare earth magnets using molds having various dimensions and shapes. it can. In the high-pressure magnetic field pressing method, it takes a long time to mold and orient the metal powder. However, by molding the alloy powder at a low pressure, the time required for the shaping and orientation is greatly reduced, and the productivity of the rare earth magnet is improved. I do.

  By the way, even when the alloy powder is formed at a low pressure, burrs often occur on the formed body. Since burrs after sintering are hard and difficult to remove, it is desirable to remove burrs from the molded body before sintering. However, in the case of the compact obtained by low-pressure molding, when the burr of the compact before sintering is removed, the non-burr portion is also removed, and the shape of the compact may be damaged.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for manufacturing a rare-earth magnet that can accurately remove burrs before sintering even in a compact obtained by low-pressure molding. .

The first method for manufacturing a sintered magnet according to the present invention is a step of pressing a rare earth alloy powder filled in a die with a punch to obtain a molded body,
Heat-treating the compact,
Removing burr from the molded body after the heat treatment;
Sintering the compact after removing the burr.

  According to the present invention, since the burrs are removed after the heat treatment, the strength of the molded body is increased at the time of the burr removal. Therefore, when removing the burrs, it is suppressed that a portion other than the burrs in the molded body is removed together with the burrs. Further, at the time of removing burrs, handling such as holding / fixing of the molded body becomes easy. Furthermore, since burrs are removed before sintering, there is no possibility that the burrs are too hard to remove.

  In this case, the burr can be removed from the molded body by irradiating the burr with a laser beam. Burrs can be easily removed by laser ablation or melting.

  The laser light can be near infrared light or green light.

  Such a laser beam is preferable because it is well absorbed by a metal material such as iron.

  Further, the burr can be removed from the molded body by bringing a brush into contact with the burr.

  Further, the burr can be removed from the molded body by bringing a magnet close to the burr.

  Further, the burr can be removed from the molded body by bringing a nozzle for sucking a gas or a nozzle for blowing a gas close to the burr.

  Further, the method may further include a step of removing powder attached to the molded body after the step of removing the burr from the molded body and before the step of sintering the molded body. Thereby, a sintered body having higher shape accuracy can be obtained.

  Further, the pressure of the press can be 0.049 to 20 MPa.

  In the heat treatment, the molded body can be heated to 200 to 450C.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a molded object by low pressure molding, the manufacturing method of the rare earth magnet which can remove a burr | flash accurately is provided.

1A to 1C are schematic cross-sectional views sequentially showing a molding process according to an embodiment of the present invention. FIGS. 2A to 2D are schematic cross-sectional views illustrating a process of removing burrs and powder removal by laser light according to the embodiment of the present invention. FIGS. 3A to 3D are perspective views showing a molded body having burrs. FIGS. 4A to 4C are schematic cross-sectional views illustrating a step of removing burrs according to another embodiment of the present invention.

  A preferred embodiment of a method for manufacturing a rare earth magnet will be described with reference to the drawings.

(Preparation process of rare earth alloy powder)
First, a rare earth alloy powder is prepared. A rare earth alloy is an alloy containing a rare earth element.

  Examples of the rare earth element include one or more elements selected from the group consisting of scandium (Sc), yttrium (Y), and lanthanoids belonging to Group 3 of the long period type periodic table. Here, lanthanoids are lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), and dysprosium (Dy). , Holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu).

Specific examples of the rare earth alloy include an Sm-Co alloy, a Nd-Fe-B alloy, and an Sm-Fe-N alloy. Among these, SmCo-based alloy represented by SmCo ₅ and _Sm 2 _{Co 17, or,} Nd-Fe-B type alloy represented by Nd 2 _{Fe 14} B is preferred.

  When the rare earth alloy is an Nd—Fe—B-based alloy, the content of the rare earth element in the alloy is preferably 8 to 40% by mass, and more preferably 15 to 35% by mass. Further, the content ratio of Fe in the Nd-Fe-B-based alloy is preferably 42 to 90% by mass, and more preferably 60 to 80% by mass. The content ratio of B in the Nd-Fe-B-based alloy is preferably 0.5 to 5% by mass. Further, a part of Fe may be replaced with cobalt (Co). Further, a part of B may be replaced with one or more elements selected from the group consisting of carbon (C), phosphorus (P), sulfur (S), and copper (Cu).

  Rare earth alloys include aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), and bismuth (Bi) from the viewpoints of improving coercive force, improving productivity, and reducing costs. , Niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), antimony (Sb), germanium (Ge), tin (Sn), zirconium (Zr), nickel (Ni), silicon (Si) , Gallium (Ga), copper (Cu), and / or hafnium (Hf).

  The rare earth alloy may contain oxygen (O), nitrogen (N), carbon (C), and / or calcium (Ca) as inevitable impurities.

  The rare earth alloy powder can be prepared by the following procedure. First, an alloy containing the constituent elements of the rare earth metal at a desired ratio is cast by a slip casting method or the like to obtain a rare earth alloy flake. Next, the obtained flakes are roughly pulverized using a pulverizer such as a stamp mill to obtain a coarse powder having a particle size of about 10 to 100 μm. At this time, hydrogen may be absorbed in the flakes before the coarse pulverization, and hydrogen may be released from the coarse powder by heat treatment after the coarse pulverization. Subsequently, if necessary, a lubricant is added, and the mixture is further pulverized to a particle size of about 0.5 to 10 μm using a jet mill or the like to obtain a rare earth alloy powder.

  Examples of lubricants are hydrocarbons such as paraffin wax; fatty acids such as stearic acid and stearyl alcohol; oleamide, stearamide, palmitamide, pentadecylamide, myristic amide, lauric amide, capric amide, Aliphatic amides such as pelargonic acid amide, caprylic acid amide, enanthic acid amide, caproic acid amide, valeric acid amide and butyric acid amide; organic substances such as metal soaps such as metal stearate (zinc stearate, calcium stearate). . Lubricants can be powders or liquids. The concentration of the organic substance serving as a lubricant in the rare-earth alloy powder can be 0.01 to 1.0% by mass.

(Process of forming rare earth alloy powder)
Subsequently, the molding step will be described with reference to FIGS. First, as shown in FIG. 1A, a die 10 having a cylindrical portion 10a and a bottom plate portion 10b, and a punch 15 are prepared. The cylindrical portion 10a is placed on the upper surface of the bottom plate portion 10b, and a cavity V is formed in the die 10. Subsequently, the cavity V of the die 10 is filled with the rare earth alloy powder 5 ′. Note that a magnetic field may be applied to the rare earth alloy powder 5 ′ in the die 10 after filling of the powder and before molding.

  Subsequently, as shown in FIG. 1B, the punch 15 is inserted into the cavity V, and the rare earth alloy powder 5 ′ is pressed by the punch 15 at a predetermined pressure to obtain the compact 5.

The pressing pressure can be low, that is, 0.049 to 20 MPa (0.5 to 200 kgf / cm ² ). The pressing pressure is, for example, the pressure exerted on the alloy powder by the tip surface of the punch. Low pressure molding is preferable because the die and punch are less consumed. Therefore, it is possible to use a die or a punch made of resin or the like, and it is possible to reduce the cost.

  After forming by the punch and before taking out from the die 10, application of a magnetic field and demagnetization may be performed on the formed body 5 in the die 10. The application of a magnetic field may be performed during molding. The strength of the magnetic field can be, for example, 796-5173 kA / m (10-65 kOe).

  Thereafter, as shown in FIG. 1C, the molded body 5 is taken out of the cavity of the die 10. For example, as shown in FIG. 1C, the molded body 5 can be taken out from below the tenth, but there is no limitation on the taking-out method.

The density of the molded body before the heat treatment step is, for example, 3.0 to 4.4 g / cm ³ , preferably 3.2 to 4.2 g / cm ³ , and more preferably 3.4 to 4.0 g / cm ³ . It may be adjusted.

(Heat treatment process of molded body)
Subsequently, since the molded body 5 molded at a low pressure has low strength and is difficult to handle, the molded body is heat-treated to increase the strength of the molded body 5.
The temperature of the compact in the heat treatment step can be adjusted to 200 to 450 ° C. In the heat treatment step, the temperature of the molded body may be adjusted to 200 to 400C or 200 to 350C.

  In the heat treatment step, when the temperature of the molded body 5 becomes 200 ° C. or higher, the molded body 5 starts to solidify, and the shape retention of the molded body 5, in other words, the mechanical strength of the molded body 5 is improved. Since the shape retention of the molded body 5 is improved, the molded body 5 is not easily damaged during the transportation of the molded body 5 or the handling of the molded body% in a subsequent step. For example, when the molded body 5 is gripped by a transport chuck or the like and arranged on a firing tray, the molded body 5 is not easily collapsed. As a result, defects of the finally obtained rare earth magnet are suppressed.

  If the temperature of the compact 5 exceeds 450 ° C. in the heat treatment step, cracks are likely to be formed in the compact 5 in the firing step performed after the heat treatment step. The cause of the crack formation is unknown. For example, a crack may be formed in the molded body 5 by causing hydrogen remaining in the molded body 5 to be blown out of the molded body 5 as a gas due to a rapid temperature rise of the molded body 5 in the heat treatment step. However, by adjusting the temperature of the compact 5 to 450 ° C. or less in the heat treatment step, cracks in the compact 5 in the firing step are suppressed. As a result, cracks in the finally obtained rare earth magnet are also easily suppressed. In addition, since the temperature of the compact 5 is adjusted to 450 ° C. or lower in the heat treatment step, the time required for raising or cooling the compact 5 is suppressed, and the productivity of the rare earth magnet is improved. Further, since the temperature of the compact 5 in the heat treatment step is 450 ° C. or lower and lower than a general firing temperature, even if the compact 5 is heated together with a part of the die 10 (for example, the bottom plate portion 10 b), Deterioration or a chemical reaction between the molded body 5 and the die 10 hardly occurs. Therefore, a die composed of a composition (for example, resin) that does not always have high heat resistance can be used.

  The mechanism by which the temperature of the molded body 5 is adjusted to 200 ° C. or more and 450 ° C. or less to improve the shape retention of the molded body 5 is not clear. For example, an organic substance (for example, a lubricant) added to the alloy powder becomes carbon in the heat treatment step, and the alloy powder may be bound to each other via carbon. As a result, the shape retention of the molded body 5 may be improved. If the temperature of the compact 5 exceeds 450 ° C. in the heat treatment step, there is a possibility that carbide of a metal constituting the alloy powder is generated or the alloy powders are directly sintered. On the other hand, when the temperature of the compact 5 is adjusted to 200 ° C. or more and 450 ° C. or less, metal carbide is not necessarily generated, and alloy particles do not necessarily directly sinter.

  The time for which the temperature of the compact 5 is maintained at 200 ° C. or more and 450 ° C. or less in the heat treatment step is not particularly limited, and may be appropriately adjusted according to the size and shape of the compact 5.

  In the heat treatment step, the molded body 5 may be heated by irradiating the molded body 5 with infrared rays. By directly heating the molded body 5 by irradiation of infrared rays (that is, radiant heat), the time required for raising the temperature of the molded body 5 is shortened as compared with the case of heating by conduction or convection, and production efficiency and energy efficiency are increased. However, in the heat treatment step, the compact 5 may be heated by heat conduction or convection in the heating furnace. The wavelength of the infrared ray may be, for example, 0.75 μm or more and 1000 μm or less, preferably 0.75 μm or more and 30 μm or less. The infrared light may be at least one selected from the group consisting of near infrared light, short wavelength infrared light, middle wavelength infrared light, long wavelength infrared light (thermal infrared light), and far infrared light. Near infrared rays among the above infrared rays are relatively easily absorbed by metal. Therefore, when irradiating the molded body with near-infrared rays, it is easy to raise the temperature of the metal (alloy powder) in a short time. On the other hand, far infrared rays among the above infrared rays are relatively easily absorbed by an organic substance and are easily reflected by a metal (alloy powder). Therefore, when irradiating the molded body with far-infrared rays, the above-mentioned organic substance (for example, a lubricant) is easily heated selectively, and the molded body is easily cured by the above-described mechanism caused by the organic substance. When the molded body is irradiated with infrared rays, for example, an infrared heater (such as a ceramic heater) or an infrared lamp may be used.

  When the molded body 5 taken out of the cavity of the die 10 is heated in the heat treatment step, deterioration (for example, deformation, hardening or abrasion) of the die 10 due to heating is easily suppressed, and burn-in between the molded body 5 and the die 10 is also suppressed. Easy to do. When heating the molded body 5 taken out from the cavity of the die 10, the molded body 5 is easily heated because there is no heat insulation by the die. As a result, the shape retention of the molded body 5 is improved. When the molded body 5 taken out of the cavity V is heated, the possibility that the die 10 chemically reacts with the molded body 5 is low. Therefore, the heat resistance of the die 10 is not always required, and the material of the die 10 is hardly limited. Therefore, as the material of the die 10, it is easy to process into a desired size and shape, and it is easy to select an inexpensive material. If the compact 5 held in the cavity is heated together with the die 10 in the heat treatment step, stress is applied to the compact 5 due to the difference in the coefficient of thermal expansion between the compact 5 and the die 10. It easily acts, and the molded body 5 is deformed or damaged. In addition, since the volume and heat capacity of the entire heating object are large, the number of compacts 5 is limited, the time required for the heat treatment step is lengthened, energy is wasted, and the productivity of the rare earth magnet decreases.

  In the heat treatment step, for example, the molded body 5 placed on the bottom plate 10b may be heated. In the heat treatment step, the compact 5 placed on the tray for the heat treatment step may be heated. In the heat treatment step, the molded body 5 may be heated in an inert gas or vacuum to suppress oxidation of the molded body 5. The inert gas may be a rare gas such as argon.

  In the heat treatment step, after adjusting the temperature of the molded body 5 to 200 ° C. or more and 450 ° C. or less, the molded body 5 may be cooled to 100 ° C. or less. When the surface of the chuck used for transporting the molded body 5 after the heat treatment step is made of resin, the cooling of the molded body 5 suppresses a chemical reaction between the surface of the chuck and the molded body 5, thereby deteriorating the chuck, and Contamination on the surface of the molded body 5 is suppressed. The cooling method may be, for example, natural cooling.

When the strength of the molded body 5 increases after the heat treatment step, the molded body 5 molded at a low pressure can be easily grasped by a robot hand or the like, and the handling property in the subsequent step is improved.
The density of the compact before sintering is also adjusted to 3.0 to 4.4 g / cm ³ , preferably 3.2 to 4.2 g / cm ³ , and more preferably 3.4 to 4.0 g / cm ^3. May be.

(Deburring process of molded body)
Subsequently, burrs are removed from the molded body 5 after the heat treatment. In the above-mentioned molding, burrs often occur on the molded body 5 due to the rare earth alloy powder entering the gap between the die and the punch.
Specifically, when the punch is pushed in, the gas in the die escapes from the gap between the die and the punch, and at this time, burrs are often formed by involving the rare earth alloy powder.

For example, as shown in FIG. 2A, in the case of the columnar molded body 5, a burr 5BR extending in the axial direction of the press is formed at an edge of an end surface (for example, an upper surface) on which the punch 15 hits. Sometimes.
The burr 5BR is a projection extending from the end of the molded body 5. For example, as shown in FIG. 3A, when the contour of the upper surface 5U of the molded body 5 has three straight lines and one curve, the burrs 5BR may extend upward from each straight line and the curve. When the contour of the upper surface of the molded body 5 has four straight lines as shown in FIG. 3B, the burrs 5BR may extend upward from each straight line. The height of each of these burrs 5BR is not always constant, and often becomes non-uniform as shown in FIGS. 3 (a) and 3 (b). The burrs 5BR may be bent along the upper surface 5U of the molded body 5 as shown in FIGS. 3 (c) and 3 (d). The burr 5BR may be bent along the side surface.

  In this step, such burrs 5BR are removed from the molded body 5. Specifically, as shown in FIG. 2B, a laser beam LB from a laser light source LS is applied to a burr 5BR (for example, a root) of the molded body 5, and the molded body 5 is ablated or melted. The burrs 5BR are cut, whereby the burrs 5BR can be removed from the molded body 5.

The laser beam LB is preferably near-infrared (750 to 2500 nm) or green light (495 to 570 nm) from the viewpoint of a high absorption rate for metal. Specifically, it is preferable to use an Nd: YAG laser (basic wavelength 1064 nm, second harmonic 532 nm (green laser)) or an Nd: YVO ₄ laser (1064 nm). Further, Yb: a fiber laser (1090 nm), a semiconductor laser (375 to 2000 nm), or the like may be used. On the other hand, a CO ₂ laser of 10.6 μm has a low absorptivity for metal and is not very suitable.

The laser beam LB may be irradiated in parallel to the upper surface 5U (along the upper surface) as shown in FIG. 2B, but at an angle of, for example, 30 to 60 ° with respect to the upper surface 5U. Irradiation may be performed only on the corners of the molded body 5.
As a result, as shown in FIG. 2C, a molded body 5 from which burrs have been removed is obtained.

(Process of removing fine powder from molded body)
Fine powder may adhere to the surface of the molded body 5 by the deburring described above. Therefore, the fine powder P generated by deburring is removed from the molded body 5 as needed. For example, as shown in FIG. 2D, fine powder can be removed by the suction device VA. The suction device VA includes a suction pump 56, a nozzle 52, and a line 54 connecting the suction pump 56 and the nozzle 52. By bringing the gas suction nozzle 52 close to the surface of the molded body 5, the fine powder P adhered to the surface of the molded body 5 can be removed by suction together with the surrounding gas. Note that the suction pump 56 of the suction device VA may blow gas from the nozzle 52 instead of the blower. In this case, by bringing the nozzle 52 for ejecting gas close to the surface of the molded body 5, the fine powder P attached to the molded body 5 can be blown off and removed.

(Sintering process of molded body)
Next, the compact 5 from which burrs have been removed is sintered to obtain a sintered body. A conventionally known method can be applied to sintering. The sintering temperature and the sintering time can be appropriately set according to the rare earth alloy. The sintering temperature can be, for example, 900 ° C. or more and 1200 ° C. or less. The sintering time can be, for example, 0.1 hours or more and 100 hours or less. The sintering step may be repeated. In the sintering step, the compact may be heated in an inert gas or vacuum. The inert gas may be a rare gas such as argon. The sintered body after sintering can be subjected to post-processing steps such as cutting and grinding, a surface treatment step, and a magnetization step as needed.

(Action)
According to the method for manufacturing a rare earth magnet according to the present embodiment, since the burr is removed after the heat treatment, the strength of the molded body is increased at the time of burr removal. Therefore, even in the case of low-pressure molding, it is possible to prevent a portion other than the burrs in the molded body from being removed together with the burrs when removing the burrs. In addition, handling such as holding / fixing of the molded body during deburring becomes easy. Furthermore, since burrs are removed before sintering, there is no possibility that the burrs are too hard to remove. As a result, a sintered body having high shape accuracy can be easily obtained.

  Furthermore, since laser light is used, deburring can be performed quickly. In particular, near-infrared laser and green laser light are suitable because of their high absorptivity to metals such as iron.

  Further, since fine powder is removed by gas suction or gas blowing, the shape accuracy of the sintered body can be further improved.

  The present invention is not limited to the above embodiment, and various modified embodiments are possible.

  For example, as shown in FIG. 4A, the bristles 42 of the brush BRS are brought into contact with the burr 5BR, for example, by rubbing the surface of the formed body 5 with the brush BRS, and the burr 5BR is broken to separate the burr 5BR from the formed body 5. It can also be removed. Specifically, the surface having the burr 5BR (for example, the upper surface) is swept from the center toward the edge by the brush BRS, or swept from the edge toward the center, or at the edge of the surface having the burr 5BR. The brush BRS can sweep along the circumference. The brush BRS has bristles 42 and a holding unit 40 that holds the bristles 42. Specific examples of the brush BRS include a linear brush in which the bristle 42 is linearly provided on the holding unit 40 and a roll brush in which bristle is radially provided on the outer peripheral surface of the cylindrical holding unit. Examples of the hair 42 are horse hair and nylon hair, and the hair diameter is, for example, 0.01 to 0.05 mm.

  Also, as shown in FIG. 4B, a strong magnet Mg may be brought close to the burr 5BR, and the burr 5BR may be attracted to the magnet Mg to remove the burr 5BR from the molded body 5. Suitable magnets are permanent magnets, electromagnets (coils). A direct current or an alternating current can be applied to the electromagnet to form a direct magnetic field or an alternating magnetic field. The strength of the magnetic field (magnetic flux density) can be 500-1000G.

  Further, as shown in FIG. 4C, the tip of the nozzle 52 connected to the suction pump 56 is brought close to the burr 5BR by using the above-described suction device VA, so that the burr 5BR is sucked into the nozzle 52. Burrs 5BR can be removed from the molded body 5. When suctioning burrs with the nozzle 52, it is also possible to suction unnecessary raw material powder attached to the surface of the molded body, such as powder generated when removing the burrs 5BR. Alternatively, the suction pump 56 may be replaced with a blower, and the gas coming out of the nozzle 52 may blow off burrs.

  Further, in the above embodiment, the pressing pressure is in the range of the above low pressure, but the embodiment can be carried out by molding at a higher pressing pressure.

  Further, the shapes and structures of the die 10 and the punch 15 and the shape of the cavity V are not limited to the above-described embodiment, but may take various shapes according to the desired shape of the magnet. For example, in the above embodiment, the die can be divided into two upper and lower dies. However, the die may be divided into three or more, or may not be divided.

  The size and shape of the rare earth magnet vary depending on the use of the rare earth magnet, and are not particularly limited. The shape of the rare earth magnet may be, for example, a rectangular parallelepiped, a cube, a polygonal column, a segment, a fan, a rectangle, a plate, a sphere, a disk, a column, a ring, or a capsule. The cross-sectional shape of the rare earth magnet may be, for example, polygonal, chordal, arcuate, or circular.

  Reference Signs List 10: die, 15: punch, 5 ': rare earth alloy powder, 5: molded body, 5BR: burr, LB: laser beam, BRS: brush, Mg: magnet, 52: nozzle, P: fine powder.

Claims (9)

A step of pressing a rare earth alloy powder filled in a die with a punch to obtain a compact,
Heat-treating the compact,
Removing burr from the molded body after the heat treatment;
Sintering the compact after removing the burrs.   The method according to claim 1, wherein the burr is irradiated with a laser beam to remove the burr from the molded body.   3. The method according to claim 2, wherein the laser light is near infrared light or green light.   The method according to claim 1, wherein the burr is removed from the compact by contacting a brush with the burr.   The method according to claim 1, wherein the burr is removed from the compact by bringing a magnet close to the burr.   The method according to claim 1, wherein a nozzle for sucking gas or a nozzle for blowing gas is brought close to the burr to remove the burr from the molded body.   The method according to any one of claims 1 to 6, further comprising, after the step of removing the burr from the molded body, and before the step of sintering the molded body, removing a powder attached to the molded body. The method described in.   The method according to any one of claims 1 to 7, wherein the pressure of the press is 0.049 to 20 MPa.   The method according to claim 1, wherein in the heat treatment, the molded body is heated to 200 to 450 ° C. 9.

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