WO2014080852A1

WO2014080852A1 - Method for manufacturing rare-earth magnet

Info

Publication number: WO2014080852A1
Application number: PCT/JP2013/080974
Authority: WO
Inventors: 大小淵; 伸也西ヶ谷; 祐介横田; 彰加納
Original assignee: トヨタ自動車株式会社
Priority date: 2012-11-20
Filing date: 2013-11-18
Publication date: 2014-05-30
Also published as: JP2014103251A

Abstract

Provided is a method for manufacturing a rare-earth magnet, which is an orientation magnet, by subjecting a compact to hot plastic working, in which cracks do not form in the compact and there is no orientation disruption due to the shear friction force applied by a punch or the like during lateral deformation of the compact. The method comprises: a first step for manufacturing a compact (S); and a second step for manufacturing a rare-earth magnet (C), which is an orientation magnet, by preparing a plastic working mold (10) comprising a die (1) and a punch (2), placing the compact (S) in a cavity (Ca) of the mold (10), and subjecting the compact (S) to hot plastic working. The second step comprises steps (A) and (B). Step (A) comprises: causing a side surface of the compact (S), which is a free end-face, to project laterally due to the pressure from the punch (2); applying pressure to the side surface from a side-surface mold (1c); and continuing the application of pressure up to a prior stage where the working rate required to impart anisotropic properties is reached, to manufacture an orientation magnet precursor (S'). Step (B) comprises returning the side surface of the orientation magnet precursor (S') to the free end-face and continuing the application of pressure until the working rate required to impart anisotropic properties is reached, to manufacture the orientation magnet (C).

Description

Rare earth magnet manufacturing method

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

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

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

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

In the hot plastic working, a compact is disposed between a lower die constituting a plastic working die and a punch (also referred to as a punch), and pressed with the lower die and the punch for a short time of about 1 second or less while being heated. In general, upsetting that presses until a predetermined processing rate is achieved is applied. While this hot plastic working can give magnetic anisotropy to the molded body, the molded body is plastically deformed in the process of being crushed while being plastically deformed by the lower die and the press by the punch during the hot plastic working. There was a problem that cracks (including fine cracks) were likely to occur on the side surfaces of the body.

This is partly because the part in contact with the lower mold and the punch is deformed too much, and the center part of the side surface is excessively swollen to the extent that it is so-called drum-shaped. When this crack occurs, the processing strain formed to increase the degree of orientation is released at the cracked location, and the strain energy cannot be sufficiently directed to the crystal orientation, resulting in a high degree of orientation (this Therefore, it is difficult to obtain an oriented magnet having high magnetization.

In addition, since the outer peripheral portion is cracked in this way, in the oriented magnet formed by hot plastic working, the oriented magnet of a predetermined dimension is cut out from the center portion without cracking, and commercialization is attempted. There was also a problem that the material yield was low.

Therefore, a manufacturing method disclosed in Patent Document 1 can be cited as a prior art that can solve the problem of cracking during such hot plastic working. In this manufacturing method, the whole molded body is encapsulated in a metal capsule, and then hot plastic working is performed while pressing the metal capsule with a lower mold and a punch. It is said that the magnetic anisotropy of the material will be further improved. In addition to this, Patent Documents 2 to 5 disclose other techniques for performing hot plastic working in a state where a molded body is sealed in a metal capsule.

However, if the entire molded body is completely surrounded by the metal capsule, the plastic deformation to the side of the molded body due to pressing from above and below is extremely restricted, and the side surface of the molded body after plastic deformation is cracked. In spite of the fact that no deformation occurs, it is difficult to perform sufficient plastic deformation, resulting in another problem that it is difficult to obtain a high degree of orientation. For example, when taking a cylindrical shaped body having an upper surface, a lower surface and a circumferential side surface as an example, when a side region corresponding to the side surface of the molded body of the metal capsule is about to be plastically deformed laterally, The upper surface region and the lower surface region corresponding to the upper surface and the lower surface of the molded body integrated with the side surface region are constrained by restraining the spread of the side surface region.

Actually, there is no mention of the strain rate in each of the above patent documents, and it is assumed that hot plastic working is performed at a strain rate of 0.1 / sec or more and a processing rate of 50% or more (for example, 70% or more). It is not possible to completely prevent cracking. The reason is that if the steel structure is welded with a steel material of a certain thickness or more and processed at a strain rate of 0.1 / sec or more with the entire surface covered, the magnet structure is too shocked or heated when cooled. This is because the molded body that has been hot plastic processed due to the difference in expansion is strongly restrained by the metal capsule as described above.

In order to solve this problem, Patent Document 6 discloses a technique for thinning a metal capsule by forging in multiple stages, but the disclosed embodiment uses an iron plate having a thickness of 7 mm or more. In addition to being unable to completely prevent cracking, the magnet shape after forging cannot be said to be a near net shape, and finishing work is absolutely necessary, resulting in a decrease in material yield and an increase in processing costs. Becomes prominent.

As disclosed in Patent Document 1, etc., when the thickness of the metal capsule that completely covers the entire surface of the molded body is reduced, the metal capsule is destroyed at a strain rate of 1 / sec or more, and the molded body is Since discontinuous irregularities occur and cause disorder of alignment, it is not a preferable method.

From the above, it is possible to obtain a sufficient effect even by applying a method in which the molded body is surrounded and pressed with a metal capsule or the like as a measure to eliminate the occurrence of cracks in the molded body, which is a problem in hot plastic working. Therefore, a method for producing an oriented magnet having a high degree of orientation without causing cracks in the molded body during hot plastic working is eagerly desired.

Here, it is not a method of constraining the side of the molded body with a metal ring or the like, but heat by conventional upsetting that presses the upper and lower surfaces of the molded body with both the lower die and the punch constituting the plastic working die. Returning to the inter-plastic processing, in this method, in addition to the problem that the side surface of the molded body described above is likely to crack, the molded body tends to be deformed to the side by pressing with a punch during upsetting. In this case, there is also a problem that the molded body receives a shear frictional force opposite to the direction of deformation from the punch and the lower mold. This will be described with reference to FIG.

FIG. 11a shows an analysis model of a molded body sandwiched between a punch and a lower mold before upsetting (the model is an assembly of a large number of element cells when performing finite element analysis by a computer. FIG. 11b shows a state of deformation of the analytical model after upsetting with a processing rate of 50%. Note that the analysis model shown is a model of only the right cross section because the analysis results are the same on the left and right sides of the compact.

When the molded body is pressed with a punch as shown in FIG. 11a, the free end face of the molded body not subjected to any constraint as shown in FIG. 11b is deformed laterally. During the lateral deformation, the upper surface and the lower surface of the molded body are subjected to a shear frictional force in a direction opposite to the lateral deformation direction from the punch and the lower die. As a result, the central region of the compact becomes more highly strained due to the progress of plastic deformation compared to the surrounding region, resulting in disorder of the orientation of the crystal structure, which leads to a decrease in residual magnetization and the material. This leads to problems such as an increase in manufacturing cost due to a decrease in yield.

JP-A-2-250920 Japanese Patent Laid-Open No. 2-250922 JP-A-2-250919 JP-A-2-250918 JP-A-4-04301 JP-A-4-134804

The present invention has been made in view of the above-described problems, and in producing a rare earth magnet that is an oriented magnet by performing hot plastic processing that is upsetting processing on a molded body, without causing cracks in the molded body, Moreover, it is an object of the present invention to provide a method for producing a rare earth magnet in which the orientation disorder of the crystal structure does not occur due to the shear frictional force acting from the punch or the lower mold when the compact is laterally deformed.

In order to achieve the above object, a method for producing a rare earth magnet according to the present invention comprises a first step of producing a columnar shaped body by pressure-molding a powder as a rare earth magnet material, and a cavity in which the shaped body is accommodated. A plastic working die comprising a die provided with a punch slidable in the cavity is prepared, and the cavity has a cross section having a larger cross-sectional dimension than a cross section perpendicular to the pressing direction of the molded body by the punch. The molded body is accommodated in the cavity and sandwiched between the lower die of the die and the punch, and hot plastic working is performed to give anisotropy while directly pressing the upper surface and the lower surface of the molded body with the punch and the lower die. The second step of manufacturing a rare earth magnet as an orientation magnet is composed of two steps. In the first step A, the lower die and the punch are pressed. The side of the molded body, which is the free end face that is not pressed by the lower mold and the punch, protrudes to the side and is pressed from the side mold of the die on the side of the molded body, and the processing rate necessary for imparting anisotropy In the next step B, the side face of the oriented magnet precursor is not pressed from the side face mold of the die. The magnet is returned to the free end face and pressed with a lower die and a punch until a processing rate necessary for imparting anisotropy is reached to produce an oriented magnet.

The manufacturing method of the rare earth magnet of the present invention is divided into two or more stages before reaching the desired processing rate instead of performing hot plastic processing to the desired processing rate by pressing once with a punch during upsetting. This is a method of performing hot plastic working. Then, in the first step (Step A), the side of the molded body is in a free state (free end surface) before the hot plastic working, and the molded body is moved to the stage before the desired processing rate is reached. When pressed, the side surface is pressed by a side surface mold of a die.

That is, the molded body undergoes compositional deformation and its side surface deforms to the side. In the course of this deformation, the side surface of the die contacts the die, and the side surface of the molded body is pressed from the side surface die of the die by further pressing. Will be. By pressurizing the side surface of the molded body, a correction force is applied to the sheared friction force that counteracts the shear frictional force that the molded body receives from the punch and the lower mold in the direction opposite to the lateral deformation direction. The resulting disorder in the orientation of the crystal structure can be eliminated.

On the other hand, the molded body pressed by the punch is constrained from the side surface mold of the die after being deformed to the side freely in Step A in which the plastic deformation is performed to the previous stage where the desired processing rate is obtained. In addition, the problem of occurrence of cracks in the case of the conventional manufacturing method in which a desired processing rate can be obtained by one hot plastic working and the side surface of the molded body is always free is effectively solved.

In addition, regarding the 2nd step which manufactures an oriented magnet by performing hot plastic working, after performing Step A which comprises this step once, it transfers to Step B and an oriented magnet (rare earth magnet) is manufactured. In addition to the form, there is also a form in which the oriented magnet is manufactured by moving to step B after executing step A twice or more.

Further, as one embodiment of the plastic working die used in the second step, the side surface die of the die which is a constituent element thereof is configured to be separable or movable, and step A of the second step is completed. In this stage, the side surface mold can be separated or moved so as to be separated from the side surface of the oriented magnet precursor and form a space on the side of the side surface.

For example, when step A is repeated 5 times and then the process proceeds to step B to produce an oriented magnet, the side surface mold of the die is gradually slid to the side and fixed after each step A is completed. Step A may be executed.

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

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

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

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

As can be understood from the above description, according to the method for producing a rare earth magnet of the present invention, when the molded body is accommodated in the plastic working mold and the hot plastic working is performed, the hot plastic working is performed from at least two steps. In the first step A, the side surface of the molded body, which is a free end surface that is not pressed by the lower die and the punch, is pressed from the side surface die of the die by pressing with the lower die and the punch, and processing necessary for imparting anisotropy The oriented magnet precursor is manufactured by performing pressing with the punch and the lower die until the stage before reaching the rate, and in the next step B, the side surface of the oriented magnet precursor is changed to a free end surface without pressure from the side surface die of the die. The oriented magnet is manufactured by performing pressing with the lower die and the punch until the processing rate necessary for imparting anisotropy is reached. With this manufacturing method, it is possible to apply a correction force to the molded body that counteracts the shear frictional force that the molded body receives from the punch and the lower mold in the direction opposite to the lateral deformation direction. It is possible to eliminate the disorder of the orientation of the crystal structure caused by the deformation and to suppress the occurrence of cracks during hot plastic working, and to produce rare earth magnets with high remanence due to high degree of orientation at a high material yield. be able to.

It is the schematic diagram explaining the 1st step of the manufacturing method of the rare earth magnet of this invention in order of (a) and (b). It is a figure explaining the microstructure of the molded object manufactured at the 1st step. It is the schematic diagram explaining the plastic working type | mold used at the 2nd step of a manufacturing method. It is the flowchart explaining step A of the 2nd step in order of (a) and (b). It is the flowchart explaining step B of the 2nd step in order of (a) and (b). It is a figure explaining the microstructure of the manufactured oriented magnet (rare earth magnet) of this invention. It is the figure which showed the analysis result which specified the distortion distribution of the oriented magnet. FIG. 8 is a flow diagram simulating the change of the metal structure from before the hot plastic working to the end of the hot plastic working in the portion VIII in Example 1 of FIG. 7. It is the figure which showed the analysis result regarding the relationship between a friction coefficient and material yield. It is the figure which showed the analysis result regarding the relationship between the processing rate in step A of a 2nd step, and material yield. (A) is the figure which showed the analysis model of the molded object pinched | interposed with the punch and lower mold | die before a process in the hot plastic forming method by the conventional upsetting process, (b) is an installation model with a processing rate of 50%. It is the figure which showed the deformation | transformation state and distortion distribution (analysis result) of the analysis model after a cutting process.

Hereinafter, an embodiment of a method for producing a rare earth magnet of the present invention will be described with reference to the drawings. In the second step, the manufacturing method shown in the figure is one in which step A is followed by step B to manufacture an oriented magnet, but step A is executed twice or more and then step B is executed. Then, a method of manufacturing an oriented magnet may be used. In addition, although the illustrated oriented magnet is a nanocrystalline magnet (particle size is about 300 nm or less), the oriented magnet targeted by the manufacturing method of the present invention is limited to a nanocrystalline magnet. These include, but not limited to, those having a particle size of 300 nm or more, sintered magnets of 1 μm or more, and bonded magnets in which crystal grains are bound with a resin binder.

(Embodiment of manufacturing method of rare earth magnet)
FIGS. 1a and 1b are schematic views illustrating the first step of the method of manufacturing a rare earth magnet of the present invention in that order, and FIG. 2 is a view illustrating the microstructure of the molded body manufactured in the first step. is there. FIG. 3 is a schematic diagram illustrating a plastic working die used in the second step of the manufacturing method of the present invention. FIG. 4 illustrates step A of the second step in the order of FIGS. 4a and 4b. FIG. 5 is a flowchart illustrating step B of the second step in the order of FIGS. 5a and 5b. Further, FIG. 6 is a diagram illustrating the microstructure of the manufactured oriented magnet (rare earth magnet) of the present invention.

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

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

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

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

When the columnar shaped body S is manufactured in the first step, the shaped body S is transferred to the cavity Ca of the plastic working die 10 shown in FIG. 3, and hot plastic working which is upsetting is performed here.

The plastic working die 10 includes a die 2 and a punch 2 that directly presses the formed body S. The die 1 has a box shape, and includes a lower die 1a, side dies 1b, and 1d. A side surface mold 1c (partition mold) that divides the cavity Ca defined by the

molds

1b and 1d into two is housed.

In the cavity Ca, the side surface mold 1c is slidable laterally, is slid to a desired position, is positioned, and is temporarily fixed.

A second step of the manufacturing method to which the illustrated plastic working die 10 is applied will be described with reference to FIGS. More specifically, FIG. 4 is a diagram illustrating step A of the second step, and FIG. 5 is a diagram illustrating step B of the second step after FIG.

In step A of the second step shown in FIG. 4, upsetting (thermal) is performed up to a processing rate (for example, 40%) of the previous stage out of a desired processing rate (for example, 80%) necessary for imparting anisotropy. In the next step B, the hot plastic working is executed until a desired working rate is obtained. First, as shown in FIG. 4a, the molded body S molded in the first step is accommodated in the cavity Ca defined by the

side molds

1b and 1c and the lower mold 1a constituting the die 1 (molded body S). And the punch P is placed on the upper surface Sa.

In the accommodated posture of the molded body S in the cavity Ca, a space G is formed between one side surface Sc of the molded body S and the side surface mold 1c, and thus the side surface Sc of the molded body S is a free end surface. Yes. The air existing in the space G can be deaerated through an air vent hole (not shown).

Next, the formed body S is pressed in the vertical direction by the punch 2 with the pressing force P1.

When the shaped body S is pressed in the vertical direction by the punch 2, the shaped body S is deformed to the side as shown in FIG. 4b to become the oriented magnet precursor S ', and the space G that was on the side of the side surface Sc becomes the oriented magnet. The state is filled with the precursor S ′.

When the molded body S is further pressed in this state, the upper surface S′a and the lower surface S′b of the oriented magnet precursor S ′ that is plastically deformed are pressed by the punch 2 and the lower mold 1a, and the side surface S′c. Is pushed by receiving pressure P2 from the side mold 1c, and therefore the side S′c is no longer a free end face.

In this way, the pressing is finished up to the processing rate of the previous stage of the desired processing rate, and the side surface Sc that is the free end surface of the molded body S that is plastically deformed at this stage is restrained, and further, a pressing force is applied, A forcing force is applied to the molded body in a direction that cancels the shear frictional force acting on the molded body from the punch or lower mold described in FIG. 11, and orientation disorder occurs in the crystalline structure of the molded body during upsetting. The problem of the occurrence of the problem is solved. In addition, since the side surface is restrained appropriately during plastic deformation of the molded body, the problem of cracks occurring in the molded body during hot plastic working is effectively eliminated. Details of the elimination of the shear frictional force will be described later.

When the oriented magnet precursor S ′ is manufactured by pressing the compact S to a pre-processing rate of a desired processing rate, the process proceeds to Step B of the second step. First, as shown in FIG. 5a, the side surface mold 1c existing in the cavity Ca is removed, and the punch to be used is replaced with a punch 2A having the same area and the same shape as the lower mold 1a of the die 1. At 2A, the oriented magnet precursor S ′ is pressed in the vertical direction with the pressing force P3.

When the oriented magnet precursor S ′ is pressed in the vertical direction by the punch 2A, the oriented magnet precursor S ′ is deformed laterally as shown in FIG. 5B, and is oriented by pressing with the punch 2A until a desired processing rate is obtained. The space G that was on the side of the magnet precursor S ′ is filled with the orientation magnet C, and the orientation magnet C is manufactured.

As shown in FIG. 6, the oriented magnet C manufactured by the two-step hot plastic working of steps A and B has a flat nanocrystal grain MP, and the interface substantially parallel to the anisotropic axis is curved or bent. Thus, the oriented magnet C is excellent in magnetic anisotropy.

Then, in the previous stage where the desired processing rate is achieved, the hot plastic working is finished once to produce an oriented magnet precursor, and the side face is restrained from the middle of plastic deformation in the production of this oriented magnet precursor. By applying pressure, a rare earth magnet having a high degree of orientation and high remanence can be produced without causing cracks.

[Analysis and results of strain distribution of oriented magnet]
The inventors of the present invention have disclosed a strain distribution in an oriented magnet (Comparative Example 1) when hot plastic working is performed up to a predetermined working rate in one hot plastic working without constraining the side surface of the molded body, The strain distribution in the oriented magnet (Example 1) produced by the manufacturing method was identified by analysis. In this analysis, the model of Comparative Example 1 is hot plastic processed at a processing rate of 80%, and the model of Example 1 is hot plastic processed in two stages: a processing rate of 40% and then 80%. The result of the analysis is shown in FIG.

From the same figure, in Comparative Example 1, since the side of the plastically deformed model remains the free end surface, the upper and lower surfaces of the plastically deformed molded body are subjected to shear friction force from the punch and the lower mold.

On the other hand, in Example 1, the upper and lower surfaces of the molded body that was plastically deformed as in Comparative Example 1 were subjected to shear frictional force from the punch and the lower mold, but the side surface of the molded body was pressurized from the side mold, A correction force that cancels the shear friction force is applied by the pressure.

In Example 1, the part VIII is taken as a region where the influence of the shear friction force is large, and the deformation, movement and orientation change of the main phase during the hot plastic working in the part VIII are shown as a flow diagram in FIG.

Although the main phase is deformed laterally during the hot plastic working and becomes flat, the main phase is rotated by the shear friction force acting from the punch, and the orientation of the main phase is also dragged in the direction of this shear friction force. By applying pressure from the side mold, a correction force is applied to cancel the shear frictional force, and the orientation is returned to the vertical direction while the main phase rotates. Finally, when hot plastic working is performed to a desired working rate, distortion is corrected in the direction of easy magnetization, and the oriented magnet has an orientation degree substantially aligned in the vertical direction.

[Analysis and results on the relationship between friction coefficient and material yield]
The present inventors further provide an oriented magnet (Comparative Example 2) when the hot plastic working is performed up to a predetermined working rate in one hot plastic working without constraining the side surface of the molded body, the second step. Is an oriented magnet according to the manufacturing method of the present invention consisting of two-step molding of steps A and B (Example 2), and the second step is a six-step molding of step A and the next step B of seven steps For each oriented magnet of the oriented magnet according to the method (Example 3), CAE analysis was performed to identify the material yield when changing the coefficient of friction between the compact, the punch and the lower die.

In this analysis, the friction coefficient was implemented in three cases of 0.1, 0.2, and 0.3. Note that BN lubricant is used in the case with a friction coefficient of 0.2. The analysis results are shown in FIG.

From the same figure, it is the same in Comparative Example 2 and Examples 2 and 3 that the material yield tends to decrease as the friction coefficient increases. It is specified that the material yield is improved by 5%, and the material yield of Example 3 of the seven-step molding is improved by 10% as compared with Comparative Example 2.

[Analysis and result of relation between processing rate and material yield in step A of the second step in the manufacturing method of the present invention]
The present inventors further relate to an oriented magnet according to the manufacturing method of the present invention when the second step comprises two-step molding of steps A and B, and the friction coefficient between the molded body, the punch and the lower mold is changed. Then, CAE analysis was performed to identify the material yield when changing the processing rate in Step A.

In this analysis, the friction coefficient was 0.1, 0.2, and 0.3. Note that BN lubricant is used in the case with a friction coefficient of 0.2. The analysis result is shown in FIG.

From the figure, it is specified that the optimum material yield is obtained at a processing rate of 30% when the friction coefficient is 0.2 and 0.3, and the optimum material yield is obtained at a processing rate of 40% when the friction coefficient is 0.4. Has been. From this result, it was found that production with a high material yield can be realized by appropriately changing the processing rate in Step A according to the friction coefficient.

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

DESCRIPTION OF SYMBOLS 1 ... Dies, 1a ... Lower type | mold, 1b, 1d ... Side surface type | mold, 1c ... Side surface type | mold (partition type | mold), 2,2A ... Punch, 10 ... Plastic working type | mold, R ... Copper roll, B ... Quenching ribbon (quenching ribbon) ), D ... carbide die, P ... carbide punch, Ca ... cavity, G ... space, S ... shaped body, S '... oriented magnet precursor, C ... oriented magnet (rare earth magnet), MP ... main phase (nano Crystal grain, crystal grain, crystal), BP ... grain boundary phase

Claims

A first step of producing a columnar shaped body by pressure-molding a powder to be a rare earth magnet material;
A plastic working die comprising a die having a cavity in which the molded body is accommodated and a punch slidable in the cavity is prepared, and the cavity has a cross section perpendicular to the pressing direction of the molded body by the punch. Also has a large cross-sectional dimension,
The molded body is accommodated in the cavity and sandwiched between a lower die and a punch of the die, and subjected to hot plastic processing that gives anisotropy while directly pressing the upper surface and the lower surface of the molded body with the punch and the lower die, and using an oriented magnet. A second step of producing a rare earth magnet,
The second step further comprises two steps,
In the first step A, the side surface of the molded body, which is a free end surface not pressed by the lower mold and the punch, protrudes to the side by pressing with the lower mold and the punch, and is added from the side surface mold of the die on the side of the molded body. Pressed and punched to the stage before reaching the processing rate necessary for imparting anisotropy to produce an oriented magnet precursor by pressing with a punch and a lower die,
In the next step B, the side surface of the oriented magnet precursor is returned to the free end surface without pressure from the side surface mold of the die, and pressing with the lower mold and punch is performed until the processing rate necessary for imparting anisotropy is reached. A method for producing a rare earth magnet that produces an oriented magnet.
The method for producing a rare earth magnet according to claim 1, wherein the step A is repeated twice or more, and then the process proceeds to step B to produce an oriented magnet.
The side surface mold of the die is configured to be separable or movable, and when the step A of the second step is completed, the side surface mold is separated or moved to move away from the side surface of the oriented magnet precursor. The method for producing a rare earth magnet according to claim 1, wherein a space is formed on the side.