Method for producing r-t-b sintered magnet

Abstract

Provided is a method for producing an R-T-B sintered magnet, which does not require the preparation of an inert gas atmosphere. This method for producing an R-T-B sintered magnet comprises: a pulverization step for preparing an alloy powder for an R-T-B sintered magnet; a molding step for preparing a powder molded body using the powder; a cutting step for obtaining a molded body sheet by cutting the powder molded body; and a sintering step for preparing a sintered body by sintering the molded body sheet, in the cutting step, the powder molded body immersed in the liquid is cut by the movement of a metal wire, and the metal wire is a metal stranded wire.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for producing an R-T-B based sintered magnet. BACKGROUND

[0002] An R-T-B based sintered magnet (R is a rare earth element and must contain at least one selected from the group consisting of Nd, Pr, Ce, T is at least one of transition metals and must contain Fe, and B is boron) is composed of a main phase of a compound having an R2Fe 14 B type crystal structure, a grain boundary phase located at a grain boundary portion of the main phase, and a compound phase generated by the influence of trace additive elements and impurities, etc. Since the R-T-B based sintered magnet exhibits high residual magnetic flux density B r (sometimes also simply referred to as "B r " hereinafter) and high coercive force H cJ (sometimes also simply referred to as "H cJ " hereinafter), it has excellent magnetic properties, and is therefore regarded as the highest performance magnet among permanent magnets. Therefore, the R-T-B based sintered magnet is used in various motors such as voice coil motors (VCM) for hard disk drives, motors for electric vehicles (EV, HV, PHV), motors for industrial equipment, and various uses such as home electric appliances.

[0003] Such an R-T-B based sintered magnet is manufactured through, for example, a process of preparing an alloy powder, a process of press-molding the alloy powder to produce a powder molded body, and a process of sintering the powder molded body. The alloy powder is prepared by, for example, the following method.

[0004] First, an alloy is produced from molten metal of various raw material metals by a method such as an ingot casting method or a strip casting method. The obtained alloy is used in a pulverization process to obtain an alloy powder having a prescribed particle size distribution. The pulverization process generally includes a coarse pulverization process and a fine pulverization process, the former of which is performed using, for example, a hydrogen embrittlement phenomenon, and the latter of which is performed using, for example, an air jet type pulverizer (jet mill).

[0005] A sintered body obtained by the process of sintering the powder molded body is then subjected to mechanical processing such as grinding, cutting, etc., to form a single body having a desired shape and size. More specifically, first, an R-Fe-B based rare earth magnet powder is compression-molded using a press device to produce a molded body having a size larger than that of a final magnet product; then, the molded body is sintered by a sintering process to produce a sintered body, and thereafter, the sintered body is subjected to grinding processing using, for example, a super-hard alloy knife saw or a rotary grindstone (abrasive wheel), etc., to have a desired shape. For example, first, a sintered body in the form of a block is produced, and thereafter, the sintered body is sliced by a knife saw, etc., to thereby cut into a plurality of plate-shaped sintered body portions.

[0006] However, the sintered body of a rare earth alloy magnet such as an R-Fe-B sintered magnet is not only very hard and brittle, but also has a large processing load, so high-precision grinding processing will be a difficult job that requires a long processing time. Furthermore, it is inevitable that a portion of the material will be lost due to processing. Therefore, the processing step is a major cause of increased manufacturing costs.

[0007] Patent Document 1 describes a method for reducing processing costs by processing a powder molded body in the state of a molded body (green body) before sintering. In this method, an abrasive wire having abrasive grains attached to the outer peripheral surface is moved parallel to each other. Patent Document 1 describes that by holding the chips between two abrasive wires moving along the moving line, the chips can be efficiently discharged.

[0008] Patent Document 2 describes a molded body processing method that does not require preparation of an inert gas environment with a limited oxygen concentration by immersing a powder molded body in a liquid and cutting it with a moving metal bare wire.

[0009] Prior Art Documents

[0010] Patent Documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2007-276001

[0012] Patent Document 2: Japanese Patent Application Publication No. 2022-054683 SUMMARY

[0013] PROBLEMS TO BE SOLVED BY THE INVENTION

[0014] It is known that according to the method of Patent Document 2, when the cutting speed is excessively increased in order to improve productivity, the abrasive wire cannot operate as planned, the surface roughness of the cutting face deteriorates, and corrugation can occur. In addition, according to the research by the inventor of the present invention, if the abrasive wire having abrasive grains attached to the outer peripheral surface described in Patent Document 1 is used in the method of Patent Document 2, the chips cannot be efficiently discharged into the liquid.

[0015] The present invention provides a method for manufacturing an R-T-B sintered magnet that can solve the above technical problem.

[0016] TECHNICAL SOLUTION FOR SOLVING THE PROBLEM

[0017] The present invention relates to a method for manufacturing an R-T-B sintered magnet described in the following items.

[0018] [Item 1]

[0019] A method for manufacturing an R-T-B sintered magnet, comprising:

[0020] a pulverization process of preparing an alloy powder for an R-T-B sintered magnet (R is a rare earth element and must contain at least one selected from the group consisting of Nd, Pr, and Ce, T is at least one of transition metals and must contain Fe, and B is boron);

[0021] a molding process of preparing a powder molded body using the above powder;

[0022] a cutting process of cutting the above powder molded body to obtain a molded body sheet; and

[0023] a sintering process of sintering the above molded body sheet to prepare a sintered body,

[0024] in the above cutting process, the above powder molded body immersed in a liquid is cut by movement of a metal wire,

[0025] the above metal wire is a metal wire strand.

[0026] [Item 2]

[0027] The production method of the R-T-B sintered magnet according to Item 1, wherein in the above cutting process, the above metal wire is moved at a speed of 100 m / minute or more in one direction for 250 m or more.

[0028] [Item 3]

[0029] The production method of the R-T-B sintered magnet according to Item 1 or 2, wherein in the above cutting process, the moving speed of the above metal wire is 400 m / minute or more.

[0030] [Item 4]

[0031] The production method of the R-T-B sintered magnet according to any one of Items 1 to 3, wherein in the above cutting process, the cutting speed of the above metal wire into a direction perpendicular to the moving direction is 600 mm / minute or more.

[0032] [Item 5]

[0033] The production method of the R-T-B sintered magnet according to any one of Items 1 to 4, wherein the process of preparing the above powder molded body includes a process of molding the above powder by wet pressing.

[0034] [Item 6]

[0035] The production method of the R-T-B sintered magnet according to Item 5, wherein the wet pressing is performed by mixing a liquid of the same kind as the above liquid in the above cutting process with the above powder.

[0036] [Item 7]

[0037] The method of producing an R-T-B sintered magnet according to any one of items 1 to 6, wherein the tension of the wire in the cutting step is 40 N or more.

[0038] [Item 8]

[0039] The method of producing an R-T-B sintered magnet according to any one of items 1 to 7, further comprising a step of recovering the particles of the powder scraped off from the powder compact by the cutting step from the liquid.

[0040] Effects of the Invention

[0041] According to the present application, cutting with a wire saw can be performed without preparing an inert gas environment with a limited oxygen concentration for the purpose of suppressing oxidation of the powder compact, and batch productivity is excellent. Moreover, according to the present application, even if the cutting speed (feed rate) is increased, the discharge efficiency of the cutting chips can be improved, thereby reducing wire abrasion flexing due to load, suppressing deterioration of the surface roughness of the cutting surface and generation of ripples. Therefore, it is possible to reduce manufacturing costs by shortening the process time.

[0042] Note that, since the method of producing an R-T-B sintered magnet of the present application does not use an abrasive wire having abrasive grains attached to the outer peripheral surface, it is possible to achieve an effect that impurities are not mixed into the cutting chips due to the detachment of the abrasive grains in the cutting step. This also facilitates the reuse of the cutting chips in the production of magnets. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 is a flowchart showing the main steps of the production method of the embodiment of the present application.

[0044] Figure 2A is a cross-sectional view of an example of an abrasive wire (wire) formed of a metal wire.

[0045] Figure 2B is a side view of an abrasive wire (wire) formed of a metal wire.

[0046] Figure 3A is a cross-sectional view of an example of an abrasive wire formed of a metal bare wire.

[0047] Figure 3B is a side view of an example of an abrasive wire formed of a metal bare wire.

[0048] Figure 4 is a perspective view of the structure of a wire saw device used in the embodiment of the present application.

[0049] Figure 5A is a front view for explaining the step of cutting a powder compact immersed in a liquid with an abrasive wire of a metal wire.

[0050] Figure 5B This is a front view illustrating the process of cutting a powder molded body immersed in a liquid using a metal stranded grinding wire.

[0051] Figure 6A This is a side view used to illustrate the process of cutting a powder molded body immersed in a liquid using a metal strand grinding wire.

[0052] Figure 6B This is a side view used to illustrate the process of cutting a powder molded body immersed in a liquid using a metal strand grinding wire.

[0053] Figure 7 It can be made by Figure 4 A three-dimensional schematic diagram of an example of a shaped sheet produced by a wire saw device.

[0054] Figure 8 This is a table showing how the cutting speed affects the shape of the molded sheet in Reference Examples and Examples 1-4.

[0055] Figure 9 This is a schematic diagram showing how the cutting speed affects the shape of the molded sheet in Example 2.

[0056] Figure 10 This is a schematic diagram showing how the cutting speed affects the shape of the molded sheet in the reference example. Detailed Implementation

[0057] Before describing the embodiments of the present invention, the inventors of the present invention will first explain their understanding.

[0058] When cutting a powder-formed body using the wire saw technique described in Patent Document 1, the hard abrasive grains attached to the surface of the bare metal wire constituting the wire come into contact with the powder-formed body, scraping off a portion of the powder-formed body through friction. In contrast, according to the wire saw technique described in Patent Document 2, by moving a bare metal wire without abrasive grains attached to it and bringing it into contact with a powder-formed body immersed in liquid, the powder-formed body can be ground and cut. It is believed that this is because a high-speed liquid flow (jet) is generated in and around the area where the moving bare metal wire contacts the powder-formed body, thereby scraping off the powder particles constituting the powder-formed body. A portion of the powder particles (grinding debris) scraped off the powder-formed body is entrained between the bare metal wire and the powder-formed body by the high-speed flowing liquid, thus exhibiting the same grinding function as free abrasive grains and promoting the cutting of the powder-formed body.

[0059] However, according to the inventors' research, when using bare metal wire, if the cutting speed (cutting speed) is excessively increased, the grinding wire may fail to operate as planned, resulting in an uneven cut surface. One reason for this is that when using bare metal wire, the efficiency of removing scraped powder particles is relatively low, so increasing the cutting speed leads to an increase in the frictional load on the grinding wire.

[0060] The inventors of this invention have discovered that by using stranded metal wire instead of simple single-wire metal grinding wire, even when the cutting speed (cutting speed) is increased, the chip removal efficiency can be improved and the generation of unevenness on the cutting surface can be suppressed.

[0061] The following describes an embodiment of the manufacturing method for the RTB-based sintered magnet of the present invention. The manufacturing method for the RTB-based sintered magnet in this embodiment is as follows: Figure 1 The flowchart shown includes:

[0062] • A pulverizing process (S10) for preparing alloy powder for RTB sintered magnets (R is a rare earth element and must contain at least one selected from Nd, Pr, Ce, T is at least one transition metal and must contain Fe, B is boron).

[0063] • Molding process for preparing powder molded articles using powder (S20);

[0064] • Cutting process (S30) to obtain molded sheet from powder molding; and

[0065] • The sintering process (S40) of sintering the molded sheet to prepare a sintered body.

[0066] The cutting process (S30) includes the step of cutting the powder molded body immersed in the liquid by moving a metal wire. Hereinafter, the "metal wire" in this invention is sometimes referred to as a "grinding wire." This grinding wire is a stranded metal wire. The "stranded metal wire" in this invention is composed of multiple strands of metal wire twisted together.

[0067] Figure 2A This is a cross-sectional view showing an example of a polished wire (metal wire) 40 made of stranded metal wires. Figure 2B This is a side view of the grinding wire 40. In the illustrated example, the surface of the grinding wire 40 has no abrasive particles attached. For comparison, the cross-section and side view of the grinding wire 40X disclosed in Patent Document 2 are shown respectively. Figure 3A and Figure 3B The grinding wire 40X is the same bare metal wire (metal single wire) as described in Patent Document 2. The surface of the grinding wire 40X is also free of abrasive particles.

[0068] Figure 2A andFigure 2B In the example, the grinding wire 40 is made of seven metal single wires 40a, 40b, 40c, 40d, 40e, 40f, and 40g twisted together. These metal single wires 40a to 40g are all made of the same material and have the same diameter. However, the material and / or diameter of the central metal single wire (core wire) 40g need not be the same as the material and / or diameter of the other metal single wires 40a to 40f. Furthermore, each of the 40a to 40g metal single wires can also be made of different materials and have different diameters. The number of metal single wires constituting the metal stranded wire 40 is not limited to seven.

[0069] like Figure 2A and Figure 2B As shown, on the surface of the polished wire 40, which is composed of stranded metal wires, concave and convex portions are formed in a generally spiral shape. In other words, the surface of the polished wire 40 has grooves and ridges extending in a spiral shape. The concave portions (grooves) are formed between adjacent metal wires, and the convex portions (ridges) are the exposed surfaces of each metal wire. On the other hand, in conventional non-stranded bare metal wires or metal wires, such as Figure 3A and Figure 3B As shown, the surface of grinding line 40X has no spirally extending concave or convex parts.

[0070] According to the inventors' research, the high-speed liquid flow (jet) generated by the movement of the grinding wire 40, which is made of metal strands, in the liquid will form a spiral fluid flow that advances along the axis of rotation while simultaneously swirling vortices. Therefore, if the moving speed of the grinding wire 40 increases, the powder particles constituting the powder molded body will be scraped off by the high-speed liquid flow (jet), and the scraped powder particles can be efficiently discharged to the outside of the cutting area by the spiraling fluid flow.

[0071] The metal single wires that can be used for metal stranding are, for example, piano strings, high-tensile steel wire, etc. Plating can be applied to the surface of each metal single wire or the surface of the metal stranding. The diameter D of the grinding wire 40 is preferably in the range of, for example, 100 μm to 350 μm, more preferably in the range of 200 μm to 300 μm. When the diameter D of the grinding wire 40 is less than 100 μm, insufficient strength may cause the grinding wire 40 to elongate during the cutting process. Although a larger diameter D of the grinding wire 40 results in better chip (powder) removal, the increased chip quantity reduces the number of finished product pieces; therefore, this diameter is preferably 350 μm or less.

[0072] The turn spacing P of a single metal wire (e.g., metal wire 40a) rotating one turn around the axis of the grinding wire 40 in the metal stranded wire is preferably in the range of 5 to 15 times (e.g., 10 times) the diameter D of the grinding wire 40. For example, when the diameter D is about 300 μm, the turn spacing P is, for example, about 3 mm. If the turn spacing P deviates from the above range relative to the diameter D, the efficiency of the vortex formed by the spiral concave and convex portions on the surface of the metal stranded wire to discharge chips (powder) outward may be reduced. It should be noted that the above mechanism of cutting powder molded bodies by metal stranded wire is not realized in a gas, but for the first time can be realized in a liquid. Examples of liquids that can be used in embodiments of the present invention are oils such as mineral oil or synthetic oil. As will be described later, when preparing powder molded bodies by wet pressing, it is preferable to perform wire saw cutting in a liquid of the same or the same type as the liquid (e.g., oil) mixed with the powder. This is because the oils and other liquids used in wet pressing are confirmed to have components and properties that will volatilize during the sintering process without adversely affecting the performance of the final sintered magnet.

[0073] The metal strands constituting the grinding wire 40 applicable to embodiments of the present invention are made by stranding N (N is an integer of 2 or more) metal single wires, wherein N is preferably 3 or more and 20 or less (e.g., N = 5 to 8). Even when N is 2, it is still possible to cut the powder molded body, but the ability to remove scraped powder particles is relatively small. When N increases to more than 20, due to the stranding of a large number of metal single wires, the depth of the spiral concave portion and the height of the convex portion formed on the surface decreases relative to the diameter D of the grinding wire, which may reduce the ability to remove scraped powder particles.

[0074] It should be noted that the surface of the grinding line 40 can also be treated in some way (surface treatment).

[0075] Thus, according to the manufacturing method of the RTB-based sintered magnet of the present invention, since the powder molded body is cut with a wire saw while immersed in liquid, there is no need to prepare an inert gas environment with limited oxygen concentration to suppress oxidation. Furthermore, since the surface of the metal stranded wire has spirally extending concave and convex portions, it is rapidly discharged into the liquid after being scraped from the powder molded body. Therefore, even if the wire movement speed is increased, wire deflection is less likely to occur, and the reduction in processing accuracy and dimensional accuracy can be suppressed.

[0076] In the cutting process, the flow rate sufficient for cutting the powder molded body is preferably, for example, the moving speed of the grinding wire 40 is 100 m / min or more. As the moving speed of the grinding wire increases, the jet velocity generated in the liquid also increases, thus improving the discharge efficiency of the scraped powder particles. That is, blockage caused by so-called chips in the cutting process is less likely to occur. Therefore, the moving speed of the grinding wire 40 is more preferably 400 m / min or more, and even more preferably 800 m / min or more (e.g., 900 m / min). It should be noted that the moving direction of the grinding wire 40 will be maintained in one direction for a period of 250 m or more. For example, when the grinding wire moves 250 m at a moving speed of 100 m / min, it is possible to move the grinding wire in one direction for more than 15 seconds. Switching the moving direction of the grinding wire 40 within a short time (e.g., less than 15 seconds) will cause the moving speed to be zero at the time of switching, thus temporarily stopping the cutting and reducing work efficiency. Therefore, the distance the grinding wire 40 moves in one direction is preferably 250 m or more. When the metal wire 40 is used in a liquid, even if it continues to move a long distance in a certain direction, chip clogging is unlikely to occur for the reasons mentioned above. Alternatively, after moving a distance of 250m or more, the metal wire can be moved a distance of 250m or more in the opposite direction.

[0077] Furthermore, in the cutting process, the cutting speed (cutting speed or workpiece feed speed) perpendicular to the direction of the grinding wire movement is preferably 300 mm / min or more. This is because if the cutting speed is less than 300 mm / min, the time required for the cutting process will be prolonged, and production efficiency will decrease. A cutting speed of 600 mm / min or more is more preferred, and 900 mm / min or more is even more preferred. According to an embodiment of the present invention, since efficient removal of scraped powder particles can be achieved by increasing the moving speed of the grinding wire, even with an increased cutting speed, the deflection of the grinding wire due to load can be suppressed. As a result, the cut surface can maintain the desired shape, achieving high dimensional accuracy. Therefore, compared with the use of existing bare metal wires in liquids (… Figure 3A , Figure 3B Compared to the previous method, it can achieve a cutting speed of, for example, more than 1.5 times. Specifically, when the grinding wire movement speed is, for example, 1000m / min, the cutting speed can reach more than 900mm / min.

[0078] It should be noted that by cutting the powder molded body in a liquid, the temperature rise caused by frictional heat at the contact point between the powder molded body and the wire saw can be suppressed, and the generated heat is easily dissipated in the liquid. In the atmosphere, the powder molded body, which becomes hot due to the generated frictional heat, will react with oxygen or water vapor in the atmosphere, leading to an increase in the oxygen concentration in the final sintered magnet and a deterioration in the magnet's performance. However, according to the embodiments of the present invention, these problems can also be avoided.

[0079] Another advantage of cutting powder molded bodies in a liquid is that the powder particles scraped off the powder molded body using a wire saw will settle in the liquid and become easy to recover. In a preferred embodiment, the process of preparing the powder molded body includes a process of shaping the powder by wet pressing. In this case, it is preferable to add the same liquid as the liquid used in the cutting process to the powder for wet pressing. This is because the powder particles scraped off the powder molded body by the cutting process are easily recovered from the liquid and thus easily reused.

[0080] Furthermore, even if the cutting of the grinding wire 40 formed from stranded metal is performed in a horizontal direction, the powder molded body can be easily cut as long as it is in a liquid. At least a portion of the surface of the powder molded body (e.g., the upper surface) will have unevenness due to the powder pressing process, thus requiring cutting or grinding after the sintering process. Since such cutting or grinding processes can be eliminated according to the embodiments of the present invention, manufacturing costs can be reduced while maintaining high-performance magnet performance.

[0081] The following is for reference Figure 4 An example of the configuration of a wire saw apparatus that can be used in the above manufacturing method will be described. Figure 4 This is a perspective view of an embodiment of the wire saw apparatus 100 according to the present invention. The X-axis, Y-axis, and Z-axis are shown as perpendicular to each other for reference. In this example, the XY plane is horizontal, and the Z-axis points vertically.

[0082] Figure 4 The wire saw device 100 has rotating rollers 30a, 30b, and 30c arranged parallel to each other on their central axes of rotation, and a continuous grinding wire 40. The grinding wire 40 is the aforementioned stranded metal wire, with no abrasive grains attached to its surface.

[0083] Each of the rotating rollers 30a to 30c is supported by the support device 50 and can rotate. The rotation axis of the rotating rollers 30a to 30c is parallel to the Y-axis. Due to the rotation of the rotating rollers 30a to 30c, the grinding wire 40 moves under tension. The grinding wire 40 is wound on a spool (not shown). It should be noted that the wire saw device 100 may also include other rotating rollers for adjusting tension, etc. The tension of the grinding wire 40 can be set to, for example, 40N or more.

[0084] During cutting, the rotating rollers 30a, 30b, and 30c and the take-up spool rotate. The rotation direction of the rotating rollers 30a, 30b, and 30c depends on their configuration and the way the grinding wire 40 is attached. In the illustrated wire saw apparatus 100, the rotating rollers 30a, 30b, and 30c rotate in the same direction. After a predetermined length of grinding wire 40, for example, more than 250m, is wound onto the take-up spool on one side, the take-up spool and the rotating rollers 30a, 30b, and 30c rotate in opposite directions. Thus, the grinding wire 40 moves in the opposite direction, and by repeatedly performing this process, the reciprocating motion (movement) of the grinding wire 40 can be achieved.

[0085] The specific steps for preparing the powder molded body 10 are described below. It is important to note that the powder molded body 10 is not a sintered body, but rather a molded body (green body) of powder before sintering. The powder molded body is obtained by molding RTB-based sintered magnets using alloy powder (R is a rare earth element and must contain at least one selected from Nd, Pr, and Ce; T is at least one transition metal and must contain Fe; B is boron) in an orientation magnetic field via wet pressing or dry pressing.

[0086] exist Figure 4 In this example, the portion of the grinding wire 40 located between the rotating rollers 30a and 30b contacts the powder molded body 10. The support device 50 has a shape that allows it to move along the Y-axis without interfering with the powder molded body 10 when the powder molded body 10 is cut using the grinding wire 40 that moves between the rotating rollers 30a and 30b. Figure 4 In the example, the support device 50 has an opening 51 that allows the powder molded body 10 to move along the Y-axis. Specifically, rollers 30a and 30b sandwich the opening 51 of the support device 50, located on both sides of the opening 51. The support device 50 of FIG2 has a shape that defines the opening 51 as substantially "U" or "C". The dimension (width) of the opening 51 in the X-axis direction is larger than the dimension (width) of the powder molded body 10 in the X-axis direction. It should be noted that the grinding wire 40 of the metal strand of the present invention can also be used to have the same... Figure 4 The illustrated wire saw device 100 has a different structure than other wire saw devices. For example, when cutting is performed when the powder molded body 10 is not moving along the Y-axis direction, the support device 50 does not need to have an opening 51.

[0087] The powder molded body 10 produced in the molding process (S20) is fixed to the fixing base 20 by a clamp (not shown) and disposed inside the tank 62 storing the liquid 60. In FIG2, the tank 62 is indicated by a dashed line, and the height of the surface of the liquid 60 is indicated by a dotted line. In the example of FIG2, the powder molded body 10 is completely immersed in the liquid 60.

[0088] When the grinding line 40 comes into contact with the powder molded body 10, the direction of movement of the grinding line 40 (hereinafter sometimes simply referred to as the "grind line movement direction") is parallel to the X-axis.

[0089] The wire saw device 100 in this embodiment includes a drive device 70 that moves the relative position of the powder molded body 10 with respect to the grinding wire 40 along the vertical longitudinal direction (Z-axis direction) and the horizontal transverse direction (Y-axis direction). Figure 4 In this example, the drive unit 70 includes a support platform 72 that carries the powder molded body 10, a Z-axis drive unit 74 configured to reciprocate the support platform 72 along the Z-axis direction, and a Y-axis drive unit 76 configured to reciprocate the support platform 72 along the Y-axis direction. The Z-axis drive unit 74 and the Y-axis drive unit 76 each have actuators such as motors. These actuators are capable of moving the support platform 72 and the powder molded body 10 fixed on the support platform 72 in response to drive signals from a control device. In a plan view of the powder molded body 10 viewed from a direction parallel to the grinding line movement direction (X-axis direction), the position of the powder molded body 10 can be defined by coordinates in the YZ coordinate system.

[0090] While the grinding wire 40 is moving, by using the Z-axis drive unit 74 and the Y-axis drive unit 76 to move the powder molding body 10, the grinding wire 40 can be moved relative to the powder molding body 10 along any cutting direction perpendicular to the moving direction. In particular, by adjusting the moving speed in the Z-axis direction driven by the Z-axis drive unit 74 and the moving speed in the Y-axis direction driven by the Y-axis drive unit 76, the cutting direction of the grinding wire 40 can be freely changed.

[0091] In the above example, the position of the grinding line 40 relative to the YZ coordinate system is fixed, and the powder molding body 10 is in a movable state. However, it is also possible to fix the position of the powder molding body 10 and make the position of the grinding line 40 relative to the YZ coordinate system movable. In this case, the drive support device 50 moves along the Y-axis and Z-axis directions. Alternatively, for example, the support device 50 can move along the Y-axis direction and the powder molding body 10 can move along the Z-axis direction. With the above configuration, in a plan view of the powder molding body 10 viewed from a direction parallel to the grinding line movement direction (X-axis direction), the position of the grinding line 40 relative to the powder molding body 10 (coordinates in the YZ coordinate system) can move in any direction.

[0092] In the following text, for the sake of understanding, details of the cutting process will be described for an embodiment in which the relative position of the grinding line 40 with respect to the fixed powder molded body 10 changes.

[0093] First, refer to Figure 5A and Figure 5B In the following description, the cutting of the powder molded body 10 is performed by the wire saw device 100 shown in the schematic diagram.Figure 5A and Figure 5B These are front views illustrating the process of cutting a powder molded body 10 immersed in liquid 60 using a grinding wire 40. Figure 5A This indicates the state before the cutting process begins. Figure 5B This indicates the status of the cutting process in progress. Figure 5B The dashed lines within the powder molded body 10 schematically indicate the positions of the grinding lines 40 during the cutting of the powder molded body 10.

[0094] In the illustrated example, the grinding line 40 moves at a specified speed along the X-axis, and then moves in a direction perpendicular to the direction of movement of the grinding line 40 (any direction within the YZ plane). This direction perpendicular to the direction of movement of the grinding line 40 is the cutting direction, and its speed (cutting speed) is set to, for example, 300 mm / min or higher. Figure 5B In the example shown, the moving grinding wire 40 moves relative to the stationary powder forming body 10 in a negative direction along, for example, the Z-axis. However, as described above, the powder forming body 10 can also be raised together with the fixing base 20 in the positive direction along the Z-axis. According to the embodiment of the present invention, since the grinding wire 40 is made of the aforementioned stranded metal wire, by increasing the grinding wire moving speed, it is possible to achieve rapid discharge of scraped powder particles and an increase in cutting speed. Figure 5B In the middle, the grinding line 40, represented by the dashed line, extends in a straight line along the horizontal direction. However, even if the cutting speed is increased, the deflection caused by the load is suppressed, so it is not easy to form unevenness on the cutting surface.

[0095] Figure 6A and Figure 6B These are side views illustrating the process of cutting a powder molded body 10 immersed in liquid 60 using a grinding wire 40. Figure 6A This indicates the state before the cutting process begins. Figure 6B This indicates the status of the cutting process in progress.

[0096] Figure 6A and Figure 6B This is a side view illustrating the process of cutting a powder molded body 10 immersed in liquid 60 in a horizontal direction using a grinding wire 40. In the example shown, during the cutting process, rollers 30a, 30b, and 30c move relative to the powder molded body 10 in a horizontal direction (the direction of the rotation axis of each roller).

[0097] In this embodiment, the process of cutting the powder molded body 10 with the grinding wire 40 is performed while the powder molded body 10 is immersed in the liquid 60. When the powder molded body 10 is a powder molded body formed by wet pressing, a preferred example of the liquid 60 is an oil of the same type as the dispersing medium such as the oil used in wet pressing (mineral oil or synthetic oil).

[0098] When processing the powder compact 10 by such a wire saw device 100, the powder particles constituting the powder compact 10 form debris and fall off from the portion cut by the abrasive wire 40. These debris are the exfoliates in which the powder particles constituting the powder compact 10 fall off from the powder compact 10, and each particle does not have a rough fracture surface like metallic debris (cutting debris). The shape and size of the particles constituting the chips scraped off from the powder compact before sintering by the abrasive wire are the same as those of the powder particles used in the preparation of the powder compact 10. The inventors of the present invention have also studied the reuse of these chips. When the hard sintered body obtained by sintering the powder compact is cut, the chips are particles or particle aggregates in which the particle growth has occurred due to sintering or the composition has changed due to a chemical reaction. Therefore, even if it is mixed with the rare earth magnet powder and reused, the magnet performance is likely to deteriorate. In contrast, if the chips are obtained from the powder compact before sintering, since the composition and size are the same as those of other particles contained in the powder compact, it is convenient for reuse.

[0099] In addition, in the case where the powder compact 10 is prepared by wet pressing, if wire sawing is performed in an oil agent of the same type as the dispersant, the recovered powder (chips) can be directly used for wet pressing, thereby improving the production efficiency.

[0100] The manufacturing method of the R-T-B sintered magnet according to the present embodiment will be described in detail below.

[0101] S10: Crushing process

[0102] In the crushing process (S10), an alloy powder for an R-T-B sintered magnet is prepared. The composition of the alloy for the R-T-B sintered magnet, the manufacturing process of the alloy, and the preparation process of the alloy powder will be described in sequence below.

[0103] <Composition of the alloy for the R-T-B sintered magnet>

[0104] R is a rare earth element and must contain at least one selected from Nd, Pr, and Ce. It is preferably a combination of rare earth elements represented by Nd-Dy, Nd-Tb, Nd-Dy-Tb, Nd-Pr-Dy, Nd-Pr-Tb, Nd-Pr-Dy-Tb, Nd-Ce-Dy, Nd-Ce-Tb, Nd-Ce-Dy-Tb, Nd-Pr-Ce-Dy, Nd-Pr-Ce-Tb, Nd-Pr-Ce-Dy-Tb.

[0105] In R, Dy and Tb are in H cJIt is particularly effective in terms of improvement. In addition to the above elements, other rare earth elements such as La may also be contained, and rare earth metal mixtures or neodymium praseodymium mixtures, etc. may also be used. In addition, R may not be a pure element, but a product containing inevitable impurities in the industrially available range. Its content is, for example, 27% by mass or more and 35% by mass or less. Preferably, the R content of the R-T-B system sintered magnet is 31% by mass or less (27% by mass or more and 31% by mass or less, preferably 29% by mass or more and 31% by mass or less). By making the R content of the R-T-B system sintered magnet 31% by mass or less and the oxygen content 500 ppm or more and 3500 ppm or less (preferably 500 ppm or more and 3200 ppm or less, more preferably 500 ppm or more and 2500 ppm or less), higher magnetic properties can be obtained.

[0106] T includes iron (including the case where T consists essentially of iron), and 50% or less of it can be replaced by cobalt (Co) in terms of mass ratio (including the case where T consists essentially of iron and cobalt). Co can effectively improve the temperature performance and corrosion resistance, and the alloy powder can contain 10% by mass or less of Co. The content of T can account for the remaining part other than R, B, or R, B, and M described later.

[0107] The content of B can be a known content. For example, the range of 0.9% by mass to 1.2% by mass is a preferred range. When it is less than 0.9% by mass, it may sometimes be impossible to achieve high H cJ while when it is more than 1.2% by mass, B r may be reduced. It should be noted that part of B can also be replaced by C (carbon).

[0108] In addition to the above elements, M elements can also be added to improve H cJ . The M element is one or more selected from Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, In, Sn, Hf, Ta, and W. The addition amount of the M element is preferably 5.0% by mass or less. This is because if it exceeds 5.0% by mass, then B r may be reduced. In addition, the presence of inevitable impurities is also allowed. <l

[0109] The N (nitrogen) content in the R-T-B system sintered magnet is preferably 50 ppm or more and 600 ppm or less. In addition, the C (carbon) content in the R-T-B system sintered magnet is preferably 50 ppm or more and 1000 ppm or less.

[0110] <Manufacturing process of alloy for R-T-B system sintered magnet>

[0111] The manufacturing process of the alloy for the R-T-B system sintered magnet will be described by way of example. An alloy ingot can be obtained by the ingot casting method in which a metal or alloy previously adjusted to the above composition is melted and poured into a mold. In addition, an alloy sheet can also be manufactured by a quenching method typified by a strip casting method or a centrifugal casting method in which molten metal is brought into contact with a single roll, a double roll, a rotating disk, or a rotating cylindrical mold to perform quenching to prepare a solidified alloy strip thinner than the alloy made by the ingot casting method.

[0112] In an embodiment of the present invention, materials manufactured by either the ingot casting method or the quenching method can be used, but it is preferably manufactured by a quenching method such as the strip casting method. The thickness of the quenched alloy prepared by the quenching method is usually in the range of 0.03 mm to 1 mm and is in the form of a sheet. The alloy melt starts to solidify from the surface in contact with the cooling roll (roll contact surface), and the crystals grow columnarly along the thickness direction from the roll contact surface. Compared with the alloy (ingot alloy) made by the conventional ingot casting method (die casting method), the quenched alloy can be cooled in a short time, so the structure is refined, the crystal grain size is smaller, and the grain boundary area is wide. Since the R-rich phase with more R than the target composition and easy to form hydrogen bonds diffuses significantly within the grain boundaries, the R-rich phase dispersibility of the quenching method is excellent. Therefore, it is easy to generate fractures at the grain boundaries by the hydrogen crushing method. By subjecting the quenched alloy to hydrogen crushing treatment, the size of the hydrogen crushed powder (coarse crushed powder) can reach, for example, 1.0 mm or less. The coarse crushed powder thus obtained is finely pulverized by, for example, a jet mill.

[0113] <Preparation process of alloy powder for R-T-B system sintered magnet>

[0114] The rare earth alloy powder for the R-T-B system sintered magnet is chemically active and easy to oxidize. Therefore, as the gas used in the jet mill, in order to avoid the risks of heat release and ignition, reduce the content of oxygen as an impurity, and achieve high performance of the magnet, inert gases such as nitrogen, argon, and helium can be used.

[0115] For example, after the material to be pulverized (coarse crushed powder) fed into the jet mill is pulverized into fine powder having a particle size distribution with an average particle size (median particle size: d50) of 2.0 μm or more and 4.5 μm or less, it is moved to a cyclone separator trapping device. The cyclone separator trapping device is used to separate the powder from the gas stream carrying the powder. Specifically, the coarse crushed powder of the alloy for the R-T-B system sintered magnet is pulverized by the jet mill in the previous stage, and the fine powder generated by the pulverization and the gas used for the pulverization are supplied to the cyclone separator trapping device together. A mixture of the inert gas (pulverizing gas) and the pulverized fine powder forms a high-speed gas stream and is transported to the cyclone separator trapping device. The cyclone separator trapping device is used to separate these pulverizing gases and fine powder. The fine powder separated from the pulverizing gas is recovered by a powder trap.

[0116] S20: Molding process

[0117] In the molding process (S20), powder molded body is prepared using the powder obtained in the pulverizing process (S10).

[0118] In this embodiment, a powder molded body is prepared from the above-mentioned powder by a pressing process in a magnetic field. From the perspective of oxidation suppression, the pressing process in a magnetic field preferably forms the powder molded body by pressing or wet pressing in an inert gas environment. In particular, in wet pressing, the surface of the particles constituting the powder molded body is coated with a dispersant such as an oil, which suppresses contact with oxygen and water vapor in the atmosphere. Therefore, it is possible to prevent or suppress the oxidation of the particles by the atmosphere before, during, or after the pressing process.

[0119] In a magnetic field-based wet pressing process, a slurry containing a dispersion medium mixed with fine powder is prepared, fed into the cavity of a mold in a wet pressing apparatus, and pressed into shape under a magnetic field. The resulting powder molded body has, for example, a density of 4 g / cm³. 3 Above, 5g / cm 3 The following densities.

[0120] • Dispersion medium

[0121] A dispersion medium is a liquid in which alloy powders can be dispersed to form a slurry.

[0122] Mineral oil or synthetic oil can be cited as a preferred dispersion medium for this invention. The type of mineral oil or synthetic oil is not specific, but when the kinematic viscosity at room temperature exceeds 10 cSt, the bonding force between the alloy powders increases with the increase in viscosity, which adversely affects the orientation of the alloy powders during the wet forming process in a magnetic field. Therefore, the kinematic viscosity of mineral oil and synthetic oil at room temperature is preferably below 10 cSt. Furthermore, when the fractionation temperature of mineral oil and synthetic oil exceeds 400°C, it may make it difficult to remove the oil after obtaining the molded body, resulting in increased residual carbon content in the sintered body and weakened magnetism. Therefore, the fractionation temperature of mineral oil and synthetic oil is preferably below 400°C. In addition, vegetable oil can also be used as a dispersion medium. Vegetable oil refers to oil extracted from plants, and the types of plants are not limited to specific plants.

[0123] • Preparation of slurry

[0124] By mixing the obtained alloy powder with a dispersion medium, a slurry can be obtained.

[0125] There are no particular limitations on the mixing ratio of alloy powder and dispersion medium, but the concentration of alloy powder in the slurry, by mass ratio, is preferably 70% or more (i.e., 70% by mass or more). This is because in the range of 20–600 cm⁻¹… 3At a flow rate of / sec, not only can alloy powder be efficiently supplied into the cavity, but excellent magnetic properties can also be achieved. The concentration of alloy powder in the slurry, by mass ratio, is preferably 90% or less. There are no particular restrictions on the mixing method of the alloy powder and the dispersion medium. The alloy powder and the dispersion medium can be prepared separately, weighed in a specified amount, and mixed to produce the slurry. Alternatively, when obtaining alloy powder by dry grinding of coarse powder using a jet mill or the like, a container containing the dispersion medium can be placed at the alloy powder discharge port of the jet mill or similar grinding device, so that the pulverized alloy powder is directly recovered by the dispersion medium in the container to obtain a slurry. In this case, the interior of the container is preferably set to a nitrogen and / or argon atmosphere, so that the obtained alloy powder is directly recovered by the dispersion medium to form a slurry without contacting the atmosphere. Furthermore, while the coarse powder is held in the dispersion medium, a slurry containing alloy powder and dispersion medium can be obtained by wet grinding using a vibratory mill, ball mill, or stirred mill.

[0126] By molding the slurry thus obtained using a known wet pressing device, a powder molded body with a set size and shape can be obtained. Conventionally, this powder molded body is usually sintered to obtain a sintered body, but in this embodiment, as described below, the powder molded body is segmented by a wire saw before sintering.

[0127] S30: Cutting process

[0128] In the cutting process (S30), the powder molded body is cut to obtain a molded body sheet. In this process, one molded body sheet or multiple molded body sheets can be obtained from one powder molded body.

[0129] In this process, the following can be used Figure 2A and Figure 2B The grinding line 40 of the structure shown is, for example, through Figure 4 The wire saw device 100 cuts the powder molded body.

[0130] In addition to producing the usual rectangular shaped pieces from block powder molding, the cutting process can also produce, for example, [structures with specific shapes]. Figure 7 The molded sheet shown in the figure. Figure 7 This is a perspective view of an example of a molded sheet 10P that can be manufactured according to an embodiment of the present invention. Figure 7 The molded sheet 10P1 on the left side shown has an "arch" shape, and the molded sheet 10P2 on the right side has a "fish cake" shape. According to an embodiment of the invention, it can be made from, for example, a powder molded body 10 having a cuboid shape. Figure 7The diagram shows multiple molded body pieces 10P. It should be noted that the shapes of the molded body pieces that can be produced are not limited to the examples shown in the attached diagram. Alternatively, multiple molded body pieces can be obtained simultaneously using, for example, a multi-wire saw with multiple grinding lines arranged in parallel.

[0131] S40: Sintering process

[0132] In the sintering process (S40), a sintered body is prepared by sintering the molded body sheets. That is, each molded body sheet cut in the above-mentioned cutting process is sintered to obtain an RTB-based sintered magnet (sintered body). The sintering process can sinter multiple molded body sheets simultaneously. When the sintering of multiple molded body sheets is carried out in the same sintering process, each molded body sheet can be either a molded body sheet divided from a single powder molded body, or a collection of molded body sheets obtained from different powder molded bodies. It should be noted that a portion of the multiple molded body sheets may also include molded body sheets obtained by cutting powder molded bodies using a device different from the wire saw device in the above-mentioned cutting process.

[0133] The sintering process can be carried out at, for example, 0.13 Pa (10 ﹣3 Torr) or less, preferably 0.07 Pa (5.0 × 10⁻⁶ Pa). ﹣4 The process is carried out under pressures below Torr and at temperatures ranging from, for example, 1000°C to 1150°C. To prevent oxidation caused by sintering, residual gases in the environment can be replaced with inert gases such as helium or argon. It is preferable to subject the resulting sintered body to additional heat treatment, such as aging. This type of heat treatment improves the magnetic properties. Known conditions can be used for heat treatment, including temperature and time. The resulting RTB-based sintered magnet is then subjected to grinding / polishing, surface treatment, and magnetization processes as needed to finally complete the RTB-based sintered magnet.

[0134] In a preferred embodiment, the method for manufacturing the RTB-based sintered magnet of the present invention further includes a diffusion step in which a heavy rare earth element RH (RH is at least one of Tb, Dy, and Ho) diffuses from the surface of the sintered body into its interior. If the heavy rare earth element RH diffuses from the surface of the sintered body into its interior, the coercivity can be effectively improved. The method of the diffusion step is not specific; known methods can be used.

[0135] (Example)

[0136] The raw materials, with a composition of Nd: 22.6%, Pr: 7.8%, B: 0.9%, Co: 0.5%, Al: 0.1%, Cu: 0.2%, Ga: 0.4% (all by mass%), and the remainder being Fe, were weighed and an alloy was produced by strip casting. The resulting alloy was then subjected to hydrogen pulverization to obtain coarse powder.

[0137] Next, zinc stearate, mixed as a lubricant, was added to the obtained coarsely ground powder at a ratio of 0.04% by mass relative to 100% by mass of the coarsely ground powder, and then dry-milled in a nitrogen stream using a jet mill to obtain a particle size D. 50 The powder is a 4μm micro-pulverized powder (alloy powder). The micro-pulverized powder is immersed in mineral oil with a fractionation temperature of 250℃ and a kinematic viscosity of 2cSt at room temperature under a nitrogen atmosphere to prepare a slurry. The slurry concentration is 85% by mass. The resulting slurry is then molded in a magnetic field (wet molding) to produce a powder molded body. The dimensions of the powder molded body are 80mm × 45mm × 60mm.

[0138] The powder molded body described above was divided into eight molded body pieces using the grinding lines of this embodiment (Examples 1 to 4) and the reference example.

[0139] Details of the grinding threads used in Examples 1-4 and the Reference Example are described below.

[0140] • Grinding wire of Example 1: a metal stranded wire made of 7 SUS304 (metal material name) single wires with a diameter of 110μm each (diameter: 330μm, Z-axis winding, turn spacing: 3.4mm).

[0141] • Grinding wire of Example 2: a metal stranded wire made of 7 SUS304 metal single wires with a diameter of 90μm (diameter: 270μm, turn spacing: 2.7mm).

[0142] • Grinding wire of Example 3: a metal stranded wire (diameter: 240μm, Z-axis winding, turn spacing: 2.52mm) made of 7 SWP-EX (metal material name) single metal wires with a diameter of 80μm each.

[0143] • Grinding wire of Example 4: a metal stranded wire made of 7 SWP-EX metal single wires with a diameter of 85μm (diameter: 255μm, Z-axis winding, turn spacing: 2.72mm).

[0144] • Reference grinding wire: SWP-B (metal material name) single metal wire (diameter: 250μm)

[0145] As described above, cutting was performed with the powder-molded body immersed in a liquid (the same liquid used during molding as the aforementioned mineral oil). Regarding the tension applied to the grinding wire before cutting, the tension was 80 N for Example 1, 50 N for Example 2, 80 N for Example 3, 80 N for Example 4, and 80 N for the reference example. Furthermore, the grinding wire movement speed during cutting was 800 m / min.

[0146] Figure 8This is a schematic table illustrating how the cutting speed [mm / min] affects the shape of the molded body in Reference Examples and Examples 1-4. The examples use... Figure 2A and Figure 2B The image shows the result of wire sawing a single metal wire (bare metal wire). A reference example is obtained using... Figure 3A and Figure 3B The image shows the result after the metal wire (bare metal wire) was cut by a wire saw.

[0147] Figure 8 The “×” in the diagram means that the cut surface of the molded body after being divided by wire sawing has relatively large unevenness, “△” means that relatively small unevenness is produced, and “○” means that no unevenness is produced and it can be cut into well-shaped molded pieces.

[0148] like Figure 8 As shown, in Example 1, a good cut surface shape was obtained within a cutting speed range of 600 mm / min to 900 mm / min. It should be noted that even at a cutting speed of 1000 mm / min, only slight unevenness was formed, which is sufficient for practical use. Furthermore, in Examples 2-4, when the grinding wire diameter was 270 μm or less, a good cut surface shape was obtained within a cutting speed range of 600 mm / min to 1400 mm / min.

[0149] Figure 9 This is a graph showing how the cutting speed affects the shape of the molded piece in Example 2. Specifically, using a laser displacement meter, the displacement near the center of the cut surface of the molded piece is measured as the height while the support platform carrying the molded piece moves along the cutting direction. Figure 9 (a) shows an example with a cutting speed of 600 mm / min. Figure 9 (b) shows an example with a cutting speed of 800 mm / min. Figure 9 (c) shows the relevant measurement results for an example with a cutting speed of 1400 mm / min. In each graph, the vertical axis represents the measured value of the actual cutting surface height with the target cutting surface height as a reference (height 0 mm), and the horizontal axis represents the position in the cutting direction. Figure 9 The graph shows that the surface roughness of the cut surface and the width of the height fluctuation caused by the ripples exhibit small values ​​below 0.1 mm within a 45 mm range in the cutting direction. It should be noted that even at cutting speeds of 1000 mm / min and 1200 mm / min, similar results can be obtained. Figure 9 The same results are shown in graph (b). That is, in Example 2, a good cut surface shape was obtained in the range of cutting speeds above 600 mm / min and below 1400 mm / min. Furthermore, similar results were obtained in Examples 3 and 4.Figure 9 The results shown are the same.

[0150] In contrast, when the same cut was performed using the 40X grinding line shown in Figure 3, such as Figure 10 As shown in the curve, the cut surface exhibits significant fluctuations, with the height of the cut surface fluctuating by more than 0.1 mm within a 45 mm range along the cutting direction.

[0151] Thus, according to this embodiment, even with increased cutting speed, chip removal efficiency can be improved, grinding wire deflection caused by load can be reduced, and the deterioration of surface roughness and the generation of ripples on the cut surface can be suppressed. This achieves improved cutting accuracy and reduced processing time, thereby reducing manufacturing costs. Furthermore, the improved dimensional accuracy of the molded body reduces the amount of post-sintering processing, thus increasing the yield of raw materials.

[0152] Industrial applicability

[0153] The RTB-based sintered magnet of the present invention can be used as a permanent magnet in a wide variety of applications, such as voice coil motors (VCMs) for hard disk drives, motors for electric vehicles (EVs, HVs, PHVs), motors for industrial equipment, and motors for household appliances.

[0154] Symbol Explanation

[0155] 10: Powder molding body; 20: Base for fixing; 30a, 30b, 30c: Rotary rollers; 40: Grinding line;

[0156] 50: Support device; 60: Liquid; 70: Drive device; 100: Wire saw device.

Claims

1. A method for manufacturing an RTB-based sintered magnet, characterized in that, include: The process of pulverizing alloy powder for RTB sintered magnets, wherein R is a rare earth element and must contain at least one selected from Nd, Pr, Ce, T is at least one transition metal and must contain Fe, and B is boron. The molding process of preparing powder molded articles using the powder; A cutting process for cutting the powder molded body to obtain a molded body sheet; and The sintering process of sintering the molded sheet to prepare a sintered body. In the cutting process, the powder-molded body immersed in the liquid is cut by the movement of a metal wire. The metal wire is a stranded metal wire.

2. The method for manufacturing an RTB-based sintered magnet as described in claim 1, characterized in that, In the cutting process, the metal wire moves at a speed of 100 m / min or more in one direction for more than 250 m.

3. The method for manufacturing an RTB-based sintered magnet as described in claim 2, characterized in that, During the cutting process, the metal wire moves at a speed of 400 m / min or more.

4. The method for manufacturing an RTB-based sintered magnet as described in claim 1, characterized in that, In the cutting process, the metal wire is cut at a speed of 600 mm / min or higher in a direction perpendicular to the direction of movement.

5. The method for manufacturing an RTB-based sintered magnet as described in claim 1, characterized in that, The process of preparing the powder molded body includes the process of molding the powder by wet pressing.

6. The method for manufacturing an RTB-based sintered magnet as described in claim 5, characterized in that, The wet pressing is performed by mixing the powder with a liquid of the same type as the liquid used in the cutting process.

7. The method for manufacturing an RTB-based sintered magnet as described in claim 1, characterized in that, Also includes: The process of recovering the powder particles scraped off from the powder molded body by the cutting process from the liquid.

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