JP2015032669A - Method for producing sintered magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a sintered magnet in which material yield of an arc-shaped sintered magnet is improved.SOLUTION: A method for producing a sintered magnet includes: a magnet field molding step in which, by performing press formation of magnetic powder constituting an R-Fe-B sintered magnet containing a rare earth element R having Nd as a main component, the magnetic powder is compressed to form a green compact and magnetic orientation is conducted in the direction parallel to the thickness direction of the green compact; a sintering step in which, under a situation of being heated to the sintering temperature, the green compact is sintered to mold the sintered magnet; and a dimension correction step in which, under the situation of being heated to the temperature not exceeding the sintering temperature, pressing parts 13a, 14a perform pressure molding of the sintered magnet using arc-shaped molds 13, 14, thereby molding the sintered magnet into an arc-shape and correcting dimension of the sintered magnet.

Description

  The present invention relates to a method for producing a sintered magnet used for a high performance motor or the like.

  Nd—Fe—B based sintered magnets are often used for permanent magnets used in motors of hybrid vehicles, etc., and it is considered that demand will increase in the future because of excellent magnetic properties.

  A conventional method for producing a Nd-Fe-B sintered magnet is to dissolve raw materials such as Nd, Fe, and B in a vacuum or an argon gas atmosphere, and roughen the raw materials dissolved using a jaw crusher and a jet mill. Grind and pulverize. Then, the pulverized raw material is formed into a predetermined shape in a magnetic field, sintered and heat-treated, cut and ground using a slicer and a grinding machine, and subjected to surface treatment and inspection, and then magnetized.

Neomag Co., Ltd., “Neodymium Magnet Manufacturing Method Series (6)” [online], November 2009, Internet <URL: http: // www. neomag. jp / mailmagazines / 20091 / letter200911. php>

  Since sintered magnets are brittle and difficult to be plastically deformed, it is common to perform machining such as grinding and cutting after sintering in order to make a product into a desired shape. Currently, it is necessary to provide a lot of machining allowance for grinding or the like. However, in addition to Nd, rare earth metals such as Dy and Tb are used for Nd—Fe—B based sintered magnets, and the prices of rare earth metals such as Dy and Tb have been rising recently. Therefore, improving the material yield of sintered magnets using rare earth metals such as Dy and Tb is an important issue. Further, in addition to a flat magnet having a flat shape when installed, a magnet having an arc shape in cross section may be manufactured. Since arc-shaped magnets have a curved surface shape compared to flat magnets, machining is more difficult than flat shapes, and it is difficult to machine to meet the specified dimensional accuracy with high yield. There is.

  The present invention has been made to solve the above-described problems, and it is an object of the present invention to provide a method for manufacturing a sintered magnet that improves the material yield of an arc-shaped sintered magnet.

  In the method according to the present invention for achieving the above object, the magnet powder is first compressed by press-molding the magnet powder constituting the R—Fe—B based sintered magnet containing the rare earth element R mainly composed of Nd. The formed green compact is molded, and magnetic field orientation is performed in a direction parallel to the thickness direction of the green compact. Next, the green compact is sintered to form a sintered magnet, and the sintered portion is pressure-molded using a die having a circular arc shape under a condition where the sintered magnet is heated to a temperature not exceeding the sintering temperature. Thus, the sintered magnet is formed into an arc shape, and the dimension of the sintered magnet is corrected.

  According to the method for producing a sintered magnet according to the present invention, the magnetic field orientation is set in a direction parallel to the thickness direction of the green compact formed by press-molding the magnet powder constituting the R-Fe-B sintered magnet. Do. Then, the green compact is sintered to form a sintered magnet, and in a state where the sintered magnet is heated to a temperature not exceeding the sintering temperature of the sintered magnet, the pressed portion is circularly shaped using an arc-shaped mold. It is molded into an arc shape and dimension correction is performed. Therefore, by improving the brittleness of sintered magnets and press-molding without destroying sintered magnets, cutting and grinding processes are abolished or reduced, and machining costs necessary for these processes are eliminated or reduced. However, the material yield of the arc-shaped sintered magnet can be improved. In addition, after sintering the green compact oriented in parallel with the magnetic field, the magnetic field orientation parallel to the thickness direction of the green compact (sintered magnet) is changed to a radial magnetic field orientation by plastic deformation into a circular arc shape. To do. That is, the interval between the magnetic field generators for radial orientation can be reduced, and the magnetic field to be applied can be equivalent to a simple rectangular parallelepiped shape, and an arc-shaped sintered magnet with no reduction in orientation can be manufactured.

It is a flowchart which shows the manufacturing method of the sintered magnet which concerns on Embodiment 1 of this invention. 2 (A) and 2 (B) are conceptual diagrams for explaining the method for producing the sintered magnet. FIGS. 3A and 3B are conceptual diagrams for explaining the method for manufacturing the sintered magnet. It is sectional drawing which shows the dimension correction apparatus used for the manufacturing method of the sintered magnet. It is a side view which shows the same dimension correction apparatus. It is a perspective view which shows the inside of a storage container in the state which cut off the upper part of the storage container of the same dimension correction apparatus. It is a top view which shows the inside of the storage container of the same dimension correction apparatus. It is a front view which shows the mode of the workpiece | work process vicinity inside the storage container of the same dimension correction apparatus. It is a side view which shows the dimension correction apparatus used for the manufacturing method of the sintered magnet which concerns on Embodiment 2 of this invention. It is a top view which shows the inside of the storage container of the same dimension correction apparatus. It is a top view shown about the positioning fixing jig provided in the table which inserts and takes out a sintered magnet in the same dimension correction apparatus. It is explanatory drawing which shows a mode that the sintered magnet clamped by the positioning fixing jig is mounted on a metal mold | die. It is a graph which shows the experimental result of the yield stress and deformation rate accompanying the temperature change by the heating of the sintered magnet test piece which concerns on Experimental example 1 of this invention. It is a graph which shows the experimental result of the curvature amount accompanying the displacement of the horizontal direction from the one end part of the sintered magnet test piece before and behind the dimension correction which concerns on Experimental example 2 in this invention. It is a histogram of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the following description does not limit the technical scope and terms used in the claims. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from actual ratios.

(Embodiment 1)
FIG. 1 is a flowchart showing a method of manufacturing a sintered magnet according to Embodiment 1 of the present invention, and FIGS. 2A, 2B, 3A, and 3B are explanations of the method of manufacturing the sintered magnet. It is a conceptual diagram with which it uses. In this embodiment, the R—Fe—B based sintered magnet is made of a raw material alloy (step S1), coarsely pulverized (step S2), finely pulverized (step S3), molded in a magnetic field (step S4), and sintered. Manufacture is performed through the steps of sizing (step S5), dimensional correction (step S6), aging heat treatment (step S7), surface treatment (step S8), inspection (step S9), and magnetization (step S10).

The raw material alloy is manufactured by a strip casting method or other melting method in a vacuum or an inert gas atmosphere (step S1). The sintered magnet according to the present embodiment has Nd ₂ Fe ₁₄ B as a main phase, and Dy, Tb, Pr, or the like is added to Nd in the sintered magnet using a grain boundary diffusion treatment or the like. By adding the rare earth metal to Nd, the holding power of the sintered magnet can be improved.

  The produced raw material alloy is coarsely pulverized using a jaw crusher, a brown mill, or the like until the particle size becomes about several hundred μm (step S2). The coarsely pulverized alloy is finely pulverized to a particle size of about 3 to 5 μm by a jet mill or the like (step S3). In the pulverization step, it is preferable to make the particle size 3 to 4 μm, since the coercive force can be increased.

  Next, the finely pulverized magnetic material is molded in a magnetic field to obtain a green compact (step S4). The green compact can be formed using various methods such as a parallel magnetic field forming method and an orthogonal magnetic field forming method. In the first embodiment, as shown in FIG. 2B, magnetic field orientation is performed in parallel with the thickness direction of the workpiece W that is a green compact. In the present embodiment, the steps from the production of the raw material alloy to the forming in the magnetic field are collectively referred to as green compact forming.

  The green compact molded in the magnetic field is sintered in an inert gas atmosphere such as vacuum or argon gas to obtain an R—Fe—B based sintered magnet (step S5). The sintering temperature varies depending on the material composition, pulverization method, and particle size of the green compact, but is performed at about 1100 ° C.

  In the dimensional correction process, as shown in FIG. 2A and FIG. 3A, generally, a press device is used to form a workpiece W by an upper mold 13 and a lower mold 14 which are molds having a circular arc shape. Press molding is performed, and dimensional correction of the sintered magnet deformed in the sintering process is performed at, for example, 620 ° C. to 1000 ° C. (step S6). 3B, the magnetic field orientation direction of the workpiece W, which is a sintered magnet, changes in the radial direction as the workpiece W is deformed. Details are given below.

  After dimensional correction, aging heat treatment is performed in a vacuum or an inert gas atmosphere to adjust the coercivity of the sintered magnet (step S7). Aging heat treatment is generally performed in two stages of about 900 ° C and about 500 ° C. Thus, dimension correction of a sintered magnet may be performed at a temperature higher than aging heat treatment. Therefore, it is preferable to carry out dimensional correction of the sintered magnet before the aging heat treatment. This is because the temperature at which the heat treatment is performed may change the structure of the magnet and may affect the magnet characteristics.

  After the aging heat treatment, surface treatment is performed by Ni plating or the like in order to prevent rust and corrosion of the sintered magnet (step S8). When the surface treatment is finished, the magnetic properties, appearance, dimensions, etc. are inspected (step S9), and finally a sintered magnet is manufactured by applying a pulse magnetic field or a static magnetic field and magnetizing (step S10). ).

  Next, a dimensional correction apparatus that embodies the dimensional correction step in the sintered magnet manufacturing method according to the present embodiment will be described in detail. 4 is a cross-sectional view showing a dimension correcting device used in a dimension correcting step according to the method for manufacturing a sintered magnet according to Embodiment 1, FIG. 5 is a side view showing the same dimension correcting device, and FIG. 6 is the same dimension correcting device. FIG. 7 is a perspective view showing the inside of the storage container in a state where the upper part of the inside storage container is cut off, FIG. 7 is a plan view showing the inside of the storage container, and FIG. 8 is a front view showing the dimensional correction device.

  The sintered magnet dimensional correction apparatus includes a press apparatus main body 200 including an upper slide 201 and a bolster 202 that are relatively close to and away from each other, and a die set 100 that can be attached to and detached from the press apparatus main body 200. The die set 100 includes an upper die 11, a lower die 12 disposed to face the upper die 11, an adjustment mechanism 40 for aligning the upper die 11 and the lower die 12, and a workpiece W (target for dimension correction processing). And a storage container 20 that is placed on the lower die 11 and provided with a correction die for correcting the dimensions of the sintered magnet.

  The storage container 20 includes a heating device 21 that heats the sintered magnet, a globe 22 that is used when the sintered magnet is moved, a piping duct 23 that evacuates the interior of the storage container 20, and a post-dimension correction. A cooling plate 24 for cooling the sintered magnet, a cooling pipe 25 for circulating cooling water or the like through the cooling plate 24, and a sensor assembly 26 for detecting the shape of the sintered magnet.

  The press apparatus main body 200 includes an upper slide 201 and a bolster 202 that are relatively close to and away from each other in the vertical direction in FIG. In the illustrated example, the upper slide 201 moves close to and away from the bolster 202 by hydraulic pressure. The upper slide 201 has a connecting pin 17 for detachably fixing the upper die 11 of the die set 100, and the bolster 202 has a connecting pin 17 for detachably fixing the lower die 12 of the die set 100. The bolster 202 is provided with a knockout bar 203 that allows the sintered magnet, whose dimensions have been corrected, to be taken out of the correction mold, so that it can be raised and lowered.

  The straightening mold includes an upper mold 13, a lower mold 14, and an outer peripheral mold 15. The knockout bar 203 and the lower mold 14 constitute a knockout mechanism for taking out the workpiece W. In the figure, reference numeral 204 denotes a hydraulic cylinder that drives the knockout bar 203 up and down.

  The die set 100 is fixed to the press apparatus main body 200 by fixing the upper die 11 to the upper slide 201 by the connecting pin 17 and fixing the lower die 12 to the bolster 202 by the connecting pin 17. The upper die 11 is interlocked with the operation of the upper slide 201 of the press apparatus main body 200.

  The adjustment mechanism 40 includes a guiding rod 41 provided on the lower die 12 and a guiding cylinder 42 that holds the guiding rod 41 provided on the upper die 12 so as to be slidable. When the guiding rod 41 slides in the guiding cylinder, the upper die 11 and the lower die 12 are aligned. In the present embodiment, even when the upper die 11 is farthest from the lower die 12, the guiding rod 41 is not detached from the guiding cylinder 42, thereby ensuring positional accuracy.

  Further, the upper die 11 and the lower die 12 are fixed to the press apparatus main body 200 by the connecting pins 17. Therefore, only by removing the connecting pin 17, the die set 100 can be easily attached to and removed from the press apparatus main body 200 as shown by the broken line in FIG.

  The storage container 20 is placed on the lower die 12 in order to process a sintered magnet to be processed in a vacuum or a low oxygen atmosphere. The piping duct 23 is connected to a vacuum pump (not shown) in order to form a room in a vacuum or low oxygen atmosphere. A valve (not shown) is provided in the middle of the piping path, and an inert gas such as nitrogen gas can be filled into the storage container by switching the path with the valve after the inside of the storage container is evacuated. The oxygen concentration in the room is preferably 10 ppm or less in the Nd—Fe—B sintered magnet, and is preferably 1 ppm or less when the grain boundary diffusion treatment is performed by adding a metal such as Dy, Tb, or Pr to Nd. This is because Dy, Tb, and Pr are more easily oxidized than Nd.

  In the containment vessel, a correction die attached to the upper die 11 and the lower die 12 in a vacuum state is inserted into the containment vessel from the vertical direction in FIG. From the lower die 12, the lower mold 14 is fixed and installed by a fixing jig 16, and the upper mold 13 is fixed and installed by the fixing jig 16 on the upper die 11 in the same manner as the lower mold 14. . Further, in FIG. 4, an outer peripheral mold 15 surrounding a sintered magnet to be processed is attached to the lower mold 14 by engaging with a bowl shape at the tip of the lower mold 14. In addition, the upper mold 13 and the lower mold 14 are formed in order to form a substantially flat workpiece W so that the cross section has an arc shape as shown in FIGS. 2 (A) and 3 (A). The pressing portions 13a and 14a are formed to have arc portions.

  In addition, the storage container 20 is provided with a magnet insertion / removal mechanism for placing a sintered magnet input from the outside on the lower mold and replacing the workpiece W with the next workpiece W after dimensional correction.

  In this embodiment, the magnet insertion / removal mechanism is configured by providing a glove 22 shaped like a hand from the side surface of the storage container in FIG. 5 to the internal space. The globe 22 is made of, for example, a material such as natural rubber, has excellent stretchability, and enables quick insertion and removal of the sintered magnet. The work by the glove 22 is performed after the press device main body 200 is stopped in advance so that the operator is not injured.

  In addition, as shown in FIG. 5, the storage container 20 is configured such that an operator can easily visually recognize the inside by forming one upper portion of the side wall of the storage container 20 on an inclined surface.

  The heating device 21 is composed of a heater or the like, and is provided in the vicinity of the upper mold 13, the lower mold 14, and the outer mold 15, and is formed in a hollow shape so that the upper mold 13 can slide up and down. . Although the structure of the heating apparatus 21 is not specifically limited, An electric heater, a far-infrared heater, etc. can be mentioned.

  Further, the cooling plate 24 is disposed inside the storage container. A water jacket is formed inside the cooling plate 24, and the water guided from the cooling pipe 25 cools the cooling plate 24, thereby forcibly cooling the workpiece W placed on the cooling plate 24. Conventionally, the heated workpiece is naturally cooled, but by using the cooling plate 24, the cooling time can be shortened and the machining time can be reduced.

  The sensor assembly 26 includes transmission units 27a, 27b, and 27c and reception units 28a, 28b, and 28c. As shown in FIG. 6, the transmission units 27a, 27b, and 27c are attached to the side surface of the storage container 20, and the reception units 28a, 28b, and 28c are opposed to the transmission units 27a, 27b, and 27c with the workpiece W interposed therebetween. It is attached to the side of In FIG. 6, the outer peripheral mold 15 and the heating device 21 are shown. It is omitted to show the arrangement of the transmission units 27a, 27b, and 27c. FIG. 8 is a view of the other side facing from one side in the containment vessel. In order to show the correspondence between the positions of the transmitting units 27a, 27b, 27c and the receiving units 28a, 28b, 28c, The transmission units 27a, 27b, and 27c are illustrated.

  The sensor assembly 26 transmits a medium such as a laser from the transmitting units 27a, 27b, and 27c, and the receiving units 28a, 28b, and 28c detect a change in reception of the laser and the like from the transmitting units 28a, 28b, and 28c. The outline of the sintered magnet is specified and the shape is specified. In the present embodiment, the sensor assembly 26 detects the distortion of the workpiece W, which is a sintered magnet, and determines the placement direction of the workpiece W on the lower mold based on the detection result of the distortion. In the sintering process, shrinkage distortion occurs, and the workpiece W becomes a minute arc shape. On the other hand, by detecting the direction of the arc in which the workpiece W is bent by the sensor assembly 26, the amount of deformation of the workpiece W can be reduced to reduce the phenomenon of cracks and the like, thereby suppressing a decrease in yield. .

  In the present embodiment, laser is transmitted from the transmission units 27a, 27b, and 27c of the sensor assembly 26, and the shape of the workpiece W is detected by the reception units 28a, 28b, and 28c. As described above, by using the laser for detecting the shape of the workpiece W, even a minute distortion can be detected accurately and quickly. As the detection method of the sensor assembly 26, various types such as a transmission type, a diffuse reflection type, a regression reflection type, a distance setting type, and a limited reflection type can be adopted.

  Next, the dimension correction process of the manufacturing method of the sintered magnet which concerns on this embodiment is demonstrated. In the sintered magnet according to the present embodiment, the magnetic field orientation is performed in parallel with the thickness direction of the substantially rectangular parallelepiped sintered magnet as shown in FIG.

  In the dimension correction process, first, the work W is placed on the mold 14 in the storage container, and at the same time, the magnet is housed in the storage container in addition to the work W placed on the mold 14. The outer peripheral mold 15 does not pressurize the sintered magnet in consideration of deformation of the sintered magnet, but may be configured to pressurize when correcting the dimension of the side surface.

  Then, the laser from the transmitting units 27a, 27b, and 27c is detected by the receiving units 28a, 28b, and 28c in a state where the workpiece W is placed, and the direction of strain when the workpiece W is sintered is measured. From the detection result of the sensor assembly 26, when the workpiece W is set to be upwardly convex with respect to the lower mold 14, for example, the workpiece W is set to downwardly convex using the globe 22. To do.

  After the work W is set, the containment vessel 20 is sealed, the containment vessel 20 is evacuated or filled with an inert gas, and the molds 13, 14, 15 and the work W are attached using the heating device 21. Heat to about 620 ° C to 1000 ° C. When the temperature of the workpiece W reaches the set temperature, when the upper slide 201 is lowered while maintaining the temperature, the upper die 13 is lowered accordingly, and the workpiece W is pressure-molded in the space in the correction die. The The set temperature may be maintained by circulating the gas in the storage container when the storage container is filled with an inert gas. The pressure applied in the press working is pressurized at a pressure that does not reach the yield stress while considering that the yield stress of the magnet is reduced by heating the sintered magnet.

  Moreover, heating temperature is 620 degreeC or more, for example, and it carries out in 1000 degrees C or less which is the sintering temperature which the structure | tissue in a sintered magnet changes. In addition, even if it is in the range of 620 degreeC-1000 degreeC, it is more preferable to implement at 800 degrees C or less in consideration of preventing the thermal deformation and oxidation of a sintered magnet itself.

  When the press work is completed, the workpiece W is taken out by the knockout mechanism, and after the press device 200 is stopped, the hand is inserted into the glove 22 provided. In this state, the processed workpiece W is placed on the cooling plate 24 using the globe 22 and cooled, and the unprocessed workpiece W is newly set in the mold 14. When the movement of the workpiece W by the globe 22 is completed, the hand is removed from the globe 22 and the press device main body 200 is started again.

  Thereafter, heating, pressing, taking out of the processed workpiece W, attaching and cooling of the unprocessed workpiece W are repeated, and when all the workpieces W have been processed, the storage container 20 is heated. Is opened and the processed workpiece W is taken out.

  Next, the effect of this embodiment is demonstrated. The sintered magnet put into the dimensional correction apparatus is in a state of being thermally deformed by being heated to several hundred degrees or thousand degrees in the sintering process which is the previous process of this process. In order to satisfy the predetermined dimensional accuracy such as flatness with respect to the distortion generated in the sintered magnet due to thermal deformation in this manner, conventionally, a large machining allowance is provided for the sintered magnet. However, in this case, a large amount of so-called rare earth metals such as Dy and Tb contained in the sintered magnet are ground, resulting in poor material yield. Further, it is more difficult to form an arc-shaped sintered magnet by cutting, and the yield is deteriorated than it is to form on a flat surface, and it is difficult to form with high accuracy.

  On the other hand, in this embodiment, the inside of the storage container is heated using the heating device 21, and the pressing portions 13a and 14a are heated to a temperature not exceeding the sintering temperature so that the structure of the sintered magnet does not change. Is press-molded into the sintered magnet using arc-shaped molds 13 and 14. Sintered magnets are brittle in temperature conditions such as room temperature, and it is difficult to withstand press working. Press forming.

  Therefore, press molding without destroying the sintered magnet eliminates machining and corrects the size of the arc-shaped sintered magnet, which is more difficult to form than the flat surface. Can be manufactured. Further, a rectangular parallelepiped magnet that is magnetically oriented in parallel in the forming step in the magnetic field is pressure-molded by the molds 13 and 14 having the arcuate cross sections of the pressing portions 13a and 14a so that the outline of the cross section becomes an arc shape. Thus, the orientation of the magnet can be made radial. In other words, the interval between the magnetic field generators for radial orientation can be reduced, and an arc-shaped sintered magnet in which the applied magnetic field does not have a degree of orientation reduction equivalent to a simple rectangular parallelepiped shape can be manufactured.

  Moreover, in the dimension correction process, the distortion of the sintered magnet after the sintering process is detected, and the direction of pressurization by the molds 13 and 14 is determined based on the detection result. In the sintering process, the workpiece W, which is a sintered magnet, may be contracted and deformed into an arc shape. In such a case, by detecting the shape of the sintered magnet and determining the direction of pressurization by the molds 13 and 14, the deformation amount of the workpiece W is reduced during the dimensional correction process, so that cracks and the like are less likely to occur. Further, it is possible to further suppress the yield reduction.

  Further, by detecting the shape of the sintered magnet with a laser sensor, it is possible to accurately and quickly detect even a small distortion.

  Moreover, since the inside of the storage container is filled with vacuum or an inert gas by a vacuum pump, it is possible to prevent the magnet characteristics of the sintered magnet from deteriorating. In addition, you may perform addition of Dy, Pr, etc. by grain boundary diffusion processing after implementation of dimension correction. In addition, after the aging heat treatment in FIG. 1, conventional grinding or machining may be performed according to the shape of the magnet to be formed. Even in that case, the material yield can be improved by performing the dimensional correction according to the present embodiment.

  In addition, a device that performs warm press work such as a conventional hot press is not provided with a mechanism for adjusting the alignment between the upper slide and the bolster. Therefore, when correcting the dimensions, it is necessary to perform molding in a state where the upper and lower molds are fitted to the outer peripheral mold, and so-called setup work for installing the mold is required.

  On the other hand, the sintered magnet dimensional correction apparatus according to this embodiment can improve the sliding accuracy between the upper die 11 and the lower die 12 by the adjusting mechanism 40 having the guiding rod 41 and the guiding cylinder 42. . Therefore, it is not necessary to perform a setup operation for installing a mold as in the conventional hot press apparatus, and continuous press working can be performed only by exchanging the work, thereby shortening the working time and improving workability.

  Further, the die set 100 can be easily detached from the press apparatus main body 200 as shown by a broken line in FIG. Therefore, the maintenance of the storage container 20 positioned inside the die set 100 can be performed outside the press apparatus main body 200, and the press apparatus main body 200 can be used for other purposes.

  Further, by configuring the lower mold 14 to move and extract the workpiece W, the workpiece W can be extracted without extracting the entire mold from the storage container 20. Further, by pulling out while sandwiching between the upper mold 13 and the lower mold 14, it is possible to prevent chipping and breakage of the work corner.

  Further, since the storage container 20 is provided with a glove 22 so that the workpiece W can be loaded and unloaded via the globe 22, the workpiece W can be loaded into the molds 13, 14, and 15 without opening the storage container 20. Removal can be performed.

  Further, since the cooling plate 24 is arranged in the storage container 20 so as to forcibly cool the pressed sintered magnet, the workpiece W can be taken out of the storage container 20 earlier than natural cooling. . Further, since only the workpiece W is cooled and the dies 13, 14, and 15 are not cooled, the time for raising the dies 13, 14, and 15 to the temperature required for press working can be shortened, and the next workpiece can be shortened in a shorter time. W can be processed.

(Second Embodiment)
FIG. 9 is a side view showing the dimension correcting device according to the second embodiment, FIG. 10 is a plan view showing the inside of the storage container in the dimension correcting device, and FIG. 11 is a diagram of placing a sintered magnet as a work on a mold. FIG. 12 is an explanatory view for explaining a state in which the sintered magnet is positioned in the lower mold. In addition, the code | symbol uses the same code | symbol as the structure which is common in Embodiment 1, and since the dimension correction apparatus which concerns on Embodiment 2 is the same as that of Embodiment 1, description is abbreviate | omitted.

  In the first embodiment, the shape of the globe 22 is provided on one of the side walls of the storage container 20, and the embodiment in which the workpiece W is manually attached to and detached from the molds 13, 14, and 15 has been described. However, the embodiment is not limited thereto. . The sintered magnets 13, 14 and 15 may be automatically installed by using a rotary table 29 as shown in FIG.

  In this embodiment, the rotary table 29 is rotatably installed on an installation table (not shown) on which the rotary table 29 is installed, and the installation table is supported by a bar (not shown) extending from the side surface of the storage container 20. . The rotary table 29 is provided with seven positioning fixing jigs 29 </ b> A to 29 </ b> G that sandwich and place the workpiece W at the installation position of the lower mold 14. The positioning and fixing jigs 29 </ b> A to 29 </ b> G constitute a space for moving the pressing pin 31 and the pressing pin 31 for holding and releasing the workpiece W in order to place the workpiece W on the lower mold 14 from the state in which the workpiece W is held. A drive cylinder 32 is provided. The workpiece W placed on any one of the fixing jigs 27A to 27G is installed on the lower mold 14 by moving the pressing pin 29 away from the workpiece W by the drive cylinder 31. In addition, the workpiece W after the pressure molding is pushed upward by the knockout mechanism and the lower die 14, and the workpiece W is pushed onto the rotary table by operating the drive cylinder 31 and pressing the workpiece W with the pressing pin 29. Retained.

  The dimension correction of the sintered magnet according to the second embodiment is performed as follows. First, a predetermined number, for example, seven workpieces W are set on the positioning and fixing jigs 27 </ b> A to 27 </ b> G of the rotary table 27. Next, the storage container 20 is sealed, evacuated or filled with an inert gas, the holding of the work W by the pressing pin 31 is released, and the work W is placed on the mold 14.

  Thereafter, as in the first embodiment, the dies 13, 14, 15 and the workpiece W are heated to raise the temperature to a predetermined temperature, and press working is performed in a state where the temperature is maintained. After the processing, the workpiece W is taken out by the knockout bar 203 and the mold 14, and the processed workpiece W is cooled by spraying a cooling gas with a positioning fixing jig 27 </ b> G in which the cooling nozzle 25 of the rotary table 29 is set. Is done. Then, in a state where the workpiece is held by the pressing pins 31 of the positioning fixing jigs 29 </ b> A to 29 </ b> G of the rotary table 29, the rotary table 27 is rotated to release the next workpiece W and set in the mold 14.

  Thereafter, heating, pressing, removing, setting and cooling of the next workpiece W are repeated, and when all the workpieces W have been processed, the storage container 20 is opened and the processed workpiece W is taken out.

  As described above, according to the method for manufacturing a sintered magnet according to the second embodiment, the rotary table 29 is used to automatically insert and remove the workpiece W from the mold. Therefore, similarly to the first embodiment, the work W can be inserted and removed from the dies 13, 14, and 15 without opening the storage container 20, and workability can be improved. With this configuration, it is possible to remove and replace the sintered magnet that has been automatically input without requiring an operator in the containment vessel.

  The present invention is not limited to the above-described embodiments, and various modifications can be made according to the scope of the claims.

  Although the embodiment has been described above in which R-Fe-B based sintered magnets are subjected to pressure forming to perform dimensional correction, the present invention is not limited to this. In addition to the above, the R—Fe—B sintered magnet may be subjected to grain boundary diffusion treatment with rare earth such as Dy or Tb to correct the dimensions. In addition, since the surface of the grain boundary diffusion treatment is very easily oxidized, the oxygen concentration in the dimensional correction process is desirably 1 ppm or less. Further, the grain boundary diffusion treatment may be performed under the condition where the workpiece is heated in the storage container after the dimension correction process.

  Further, in the forming process in the magnetic field, the shape of the magnet set in the forming process in the magnetic field may be detected by the sensor assembly in the same manner as in the dimension correction process, and the shape of the workpiece W that is a magnet may be associated with the orientation of the magnetic field orientation. Based on this result, by setting the magnet in the dimensional correction process, the direction of orientation and the direction of pressure deformation can be more accurately related, and the completed arc-shaped magnet can be oriented more accurately in the radial direction. Can do.

(Experimental example 1)
Next, in the method for manufacturing a sintered magnet according to this embodiment. An experiment related to the molding temperature of the press working performed during the dimension correction process will be described.

  In this experiment, a sintered magnet test piece (with a thickness of 3.8 mm and a cross-sectional length of 6 mm × 6 mm), which is almost the same as the actual product, was used using an upper slide, a bolster, and an outer mold as in FIG. The magnet test piece was fixed, the temperature was raised from room temperature while applying pressure, and the amount of deformation of the test piece was measured. The sintered magnet metal according to Experimental Example 1 is composed of Fe 70%, Nd 22%, B 0.4%, Dy 2.5%, and Pr 2.5%. Table 1 is a table of molding temperature and deformation rate (%) when the sintered magnet test piece according to Experimental Example 1 is heated and pressurized, and FIG. 13 is a graph of Table 1.

  From Table 1 and FIG. 13, it was found that the R—Fe—B based sintered magnet according to Experimental Example 1 undergoes plastic deformation from 620 degrees. As mentioned above, if it is 620 degreeC or more, the dimension correction of a sintered magnet can be performed by press work, However, The sintering temperature of the said R-Fe-B type sintered magnet is 1000 degreeC. Even if the temperature is 620 ° C. or higher, if the molding temperature exceeds the sintering temperature, the structure and magnetic properties of the sintered magnet change, and therefore the dimension correction process according to the above embodiment does not exceed the sintering temperature from 620 ° C. 1000 It has been found preferable to carry out in the range of ° C. In this case, it was found from Table 1 that the yield stress at which the magnet was plastically deformed by pressing the magnet was 36 to 262 MPa.

(Experimental example 2)
Next, regarding the dimensional accuracy of the sintered magnet manufactured by the method for manufacturing a sintered magnet, the amount of warpage of the sintered magnet has been confirmed and will be described.

  In this experiment, a sintered magnet test piece (thickness 4 mm, cross-sectional length 8 mm × 28 mm) substantially equal to that of an actual product was heated to 720 ° C. to perform warm press forming, and according to the above embodiment. The amount of warpage of the Nd sintered magnet test piece before and after carrying out the method was confirmed. Since the temperature of the test piece cannot be measured directly, the result was calculated by converting from the temperature of the mold surface. FIG. 14 shows the experimental results of the amount of warp of the sintered magnet when it is spaced apart from one end of the test piece in the horizontal direction, and FIG. 15 shows the warp of the sintered magnet before and after the execution of the method according to the above embodiment. The amount is shown as a histogram.

  As can be seen from FIG. 14, the width of the amount of warpage of the sintered magnet test piece before and after the execution of the method according to the above embodiment was able to be suppressed from 0.093 mm to 0.027 mm to about 30% before the execution. all right. Further, as can be seen from FIG. 15, it was found that the amount of warping of the test piece after the method according to the above embodiment is less than the upper limit standard, so that it is not necessary to separately perform grinding or the like.

  Thus, it was confirmed that the machining cost required for the sintered magnet can be reduced and the material yield of rare earth metals such as Dy and Tb can be improved by carrying out the method for manufacturing the sintered magnet according to the above embodiment.

11 Upper die,
12 Lower die,
13 Upper mold,
14 Lower mold,
15 peripheral mold,
16 Fixing jig,
17 Connecting pin,
100 die sets,
20 containment vessel,
200 Press machine body,
201 slide up,
202 Bolster,
203 Knockout Bar,
204 hydraulic cylinder,
21 heating device,
22 Globe,
23 Piping duct 24 Cooling plate,
25 Cooling pipe,
26 sensor assembly,
27a, 27b, 27c transmission unit,
28a, 28b, 28c receiving unit,
29 Rotary table,
29A-29G Positioning fixture
31 holding pin,
32 drive cylinder,
40 adjustment mechanism,
41 Guiding rod,
42 guiding cylinder,
W Work.

Claims (3)

The magnet powder is compressed into a green compact by press-molding a magnet powder constituting an R—Fe—B based sintered magnet containing a rare earth element R containing Nd as a main component. The thickness of the green compact A magnetic field forming step of performing magnetic field orientation in a direction parallel to the direction;
A sintering step in which the green compact is sintered under the condition of being heated to a sintering temperature to form a sintered magnet;
The sintered magnet is formed into an arc shape by pressure-molding the sintered magnet using a die having an arc-shaped pressing portion under a condition where the sintering magnet is heated to a temperature not exceeding the sintering temperature. A method for producing a sintered magnet comprising: a dimension correcting step for correcting a dimension of a magnet.   The method for producing a sintered magnet according to claim 1, wherein in the dimension correction step, distortion of the sintered magnet is detected, and the sintered magnet is pressure-formed based on the detected distortion.   The method for manufacturing a sintered magnet according to claim 2, wherein the strain is detected by a laser sensor.