JP2003347143A - Rare-earth magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a high degree of orientation at the time of manufacturing a raidally oriented magnet by using multistage filling. <P>SOLUTION: In a rare-earth alloy powder molding method, a powder filling step of packing a rare-earth alloy powder 24 in a cavity formed by inserting the lower punch 14 of a powder molding apparatus into the through hole of a die 10 and an orienting and compressing step of pressurizing the rare-earth alloy powder while an oriented magnetic field is impressed are repeated several times. At the time of performing the (n+1)-th (wherein, n is an integer of ≥1) orienting and compressing step, the upper end face of the molded body 26 formed in the n-th orienting and compressing step is disposed higher in level than the lower end face of the magnetic material portion 10a of the die 10. Consequently, the distortion of a radial magnetic field caused by the presence of the molded body 26 can be suppressed. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a rare earth alloy powder compact, a rare earth magnet, and a powder compacting apparatus, and more particularly, to a rare earth magnet having a form that requires multistage filling and multistage compaction of the rare earth alloy powder. For a powder pressing method.

[0002]

2. Description of the Related Art A powder molding apparatus (press apparatus) for forming magnetic powder.
If you fill in a cavity and simply compress it,
The magnetic moment of the powder particles will be oriented randomly. In contrast, a magnetic field is formed in the cavity,
If the magnetic powder is oriented and compressed in this magnetic field, a molded body in which the powder particles are oriented in an appropriate direction can be produced.
If such a compact is made from a rare earth alloy powder having excellent magnetic properties, a high-performance anisotropic magnet can be produced.

FIG. 1 shows a typical molding apparatus used for orienting a magnetic powder in a radial direction. FIG.
Is a magnetic core 1 having a die 10 having a through hole and an outer peripheral surface facing an inner wall surface of the through hole of the die 10.
2, a cylindrical lower punch 14 inserted into the through hole of the die 10 from below, and a cylindrical upper punch 16 inserted into the through hole of the die 10 from above.
The magnetic core 12 includes an upper core 12a and a lower core 12b, and the upper core 12a and the lower core 12b are respectively
It is inserted into the core holes of the upper punch 16 and the lower punch 14. The upper core 12a and the lower core 12b are formed from a ferromagnetic material, while the upper punch 16 and the lower punch 14 are formed from a non-magnetic material.

A die 10 shown in FIG. 1 has an upper portion (magnetic portion) 10a formed of a ferromagnetic material and a lower portion (nonmagnetic portion) 10 formed of a nonmagnetic material.
b is laminated. Inside the through hole of the die 10, a cylindrical space is formed between the outer peripheral surface of the core 12 and the inner wall surface of the magnetic portion 10a of the die 10. The upper side of this cylindrical space is closed by an upper punch 16, and the lower side is closed by a lower punch 14. As described above, the “cavity” filled with the powder is formed by the outer peripheral surface of the core 12, the inner wall surface of the die 10, and the upper end surface of the lower punch.
The magnetic powder 24 filled in the cavity is
6 and the lower punch 14, and compression molded. The cavity is defined by the upper end surface of the lower punch 14, the outer peripheral surface of the core 12, and the inner wall surface of the magnetic body portion 10a of the die 10. However, the inner surface of the through hole of the die 10 is made of a non-magnetic material so that a step does not occur between the non-magnetic material portion and the ferromagnetic material portion during use and the molded body is not damaged when the molded body is taken out. In some cases, the formed cylindrical sleeve 11 is provided. In that case, the cavity is defined by the upper end surface of the lower punch 14, the outer peripheral surface of the core 12, and the inner wall surface of the sleeve 11.

An upper coil 20 and a lower coil 22 are provided for forming a radial magnetic field in the cavity. The magnetic field formed by the upper coil 20 and the magnetic field formed by the lower coil 22 repel each other near the center of the magnetic core 12, forming a radial magnetic field that spreads radially from the center of the core 12 to the die 10. . The arrows in FIG. 1 schematically show the magnetic flux in the magnetic body.

[0006] In order to improve the degree of orientation of the molded article to be produced, it is necessary to form a strong radial magnetic field in the cavity. To increase the strength of the radial magnetic field, it is desirable to optimize the size and material of the core 12 in addition to increasing the power supplied to the coils 20 and 22. However, the increase in power applied to the coil increases the manufacturing cost and raises the problem of heat generation. Further, the core size (core thickness) is limited by the inner diameter of the molded body to be produced, and there is a limit in improving the core material.

For this reason, when manufacturing a cylindrical magnet elongated in the axial direction, a multi-stage molding process in which the powder filling step and the pressing step are repeated a plurality of times is performed in order to apply a sufficiently strong orientation magnetic field. ing. According to the multi-stage molding method,
Even in the case of producing a long cylindrical molded product, since the powder filling / orientation compression cycle is repeated by dividing in the axial direction, the cavity length per cycle is shortened, thereby increasing the strength of the radial magnetic field formed in the cavity. Because you can.

Hereinafter, a conventional example of the multistage filling method will be described with reference to FIGS. 1, 2A and 2B.

First, as shown in FIG. 1, a magnetic powder 24 filled in a cavity is pressurized in an orientation magnetic field to produce a first-stage molded body 26 (first-stage orientation compression step). Thereafter, as shown in FIG.
The next magnetic powder 24 is filled in the cavity formed above the substrate, and the magnetic powder 24 is pressurized in the orientation magnetic field (the second stage of the orientation compression step). In the second-stage orientation compression step, the cavity is defined by the upper surface of the first-stage formed body 26 formed last time, the outer peripheral surface of the core 12, and the inner wall surface of the magnetic portion 10a of the die 10. . As shown in FIG. 2B, a second-stage compaction process forms a second-stage compact 28 on the first-stage compact 26, integrates the two compacts, and forms one compact 30. .

By repeating the powder filling step and the orientation compressing step a plurality of times in this manner, the magnetic portion 10
It is possible to manufacture an anisotropic ring magnet having a desired axial length without being limited by the axial size L of a (see FIG. 1). A method of manufacturing an anisotropic ring magnet for performing such multi-stage filling and molding is described in, for example, JP-A-9-23.
It is disclosed in Japanese Patent No. 3776.

[0011]

However, in the anisotropic magnet manufactured according to the above-mentioned prior art, the orientation is disturbed at the boundary between the first-stage molded body 26 and the second-stage molded body 28, which causes a problem. Therefore, there is a problem that the degree of magnetization is deteriorated at the boundary portion.

FIG. 3 is a graph showing the surface magnetic flux density (Bg) on the outer peripheral surface side of a ring magnet (cylindrical magnet) manufactured by a conventional multistage molding method. Here, a ring magnet having dimensions of 16.4 mm in outer diameter, 10.5 mm in inner diameter, and 20 mm in axial length after surface processing was prepared and evaluated. In the graph, the solid line indicates the surface magnetic flux density (Bg) on the outer peripheral surface side. The measurement was performed by using a Gauss meter and scanning the surface of the magnet with a measurement probe. In the graph of FIG. 3, the area B corresponds to the measured value of the second-stage molded body 28, and the area C corresponds to the measured value of the first-stage molded body 26.

FIG. 4 shows a cylindrical magnet 32 to be measured.
It is a perspective view of. The magnet 32 (formed body 30) shown in FIG.
Corresponds to the upper side (upper side in the pressing direction) of the forming apparatus.

As can be seen from the graph of FIG. 3, a large drop in the surface magnetic flux density (Bg) is observed at the boundary between the first-stage compact 26 and the second-stage compact 28. The surface magnetic flux density (Bg) at the boundary portion is reduced to about 60% or less of the maximum value of the surface magnetic flux density (Bg) at other portions.

The present inventor has proposed such a magnetic flux density (B
It was considered that the local decrease in g) occurred as follows. That is, as shown in FIGS. 2A and 2B,
When the second-stage orientation compression step is performed in a state where the first-stage formed body 26 is disposed on the upper surface of the lower punch 14, magnetic flux leaks into the first-stage formed body 26, which is a magnetic material, and the radial magnetic field decreases. The distribution is distorted. This is the lower core 12
The magnetic flux supplied from b is generated because it is concentrated near the upper end surface of the first-stage formed body 26 in which the magnetic flux is more likely to pass than the rare-earth alloy powder 24 filled in the second time. In this way, the magnetic flux is short-circuited in the upper part of the first-stage formed body 26 having a high magnetic permeability, so that the magnetic part 10
As a result, the distribution of the radial magnetic field is significantly distorted at the boundary between the first-stage molded body 26 and the second-stage molded body 28 and in the vicinity thereof. This means
This means that the radial component of the alignment magnetic field decreases and the axial component increases. When the axial component of the orientation magnetic field increases, the orientation of the magnetic powder 24 is disturbed, and the degree of orientation decreases.

If at least disturbance in the distribution of the radial magnetic field formed in the first-stage orientation compression step occurs, the disturbance occurs in the distribution of the radial magnetic field formed in the second-stage orientation compression step.
Disorder of the orientation occurs not only in the second-stage formed body 28 but also in the first-stage formed body 26. This is because even if the magnetic powder 24 is once oriented and compressed, for example, 0.4 MA / m
This is because the particles are reoriented in the strong magnetic field. If a lubricant is added to the magnetic powder 24, the rotation of the powder particles is likely to occur, so that the orientation disorder in the first-stage compact 26 is further increased. Further, the stronger the orientation magnetic field applied in the second stage of the orientation compression step,
The degree of orientation of the step-formed body 26 is also deteriorated.

It should be noted that, compared to the case of manufacturing a bonded magnet,
It is considered that the degree of orientation is more likely to decrease when a sintered magnet is manufactured. This is because, when the magnet powder is molded for sintering, the compression density of the powder is made relatively small, so that the first-stage compact 26 is easily affected by the disturbed magnetic field.

Further, when a compact produced by a conventional multistage molding method is sintered, there is another problem that the dimensional accuracy of the obtained sintered body is not good. The cause is that the alloy powder for rare earth sintered magnets is extremely poor in fluidity unless granulation (processing of powder shape) is performed, and it is difficult to fill the cavity with uniform density. Can be
In addition, it is difficult to fill a cylindrical cavity with a pre-measured amount of powder. For this reason, a feeder box containing a much larger amount of powder than it should be charged is moved onto the cavity, the powder is allowed to fall freely, and the powder filled in the cavity is rubbed at the bottom edge of the feeder box. Wear. In such a case, the filling amount of the powder fluctuates, for example, because the filling density varies every time the powder is supplied.

In the conventional pressing operation, the operation of the die and the punch is controlled on the assumption that the density of the powder filled in the cavity is uniform, and the positions of the die and the punch during the compression are set in advance each time. Follow the given position. Therefore, when there is a variation in the packing density of the powder, the compact density varies, and as a result, the shrinkage ratio during sintering varies. There has been a problem that the thickness varies in the thickness direction.

The present invention has been made in view of the above points, and a main object of the present invention is to provide a high-quality molded article in which a local decrease in the degree of orientation is suppressed even when performing multi-stage filling and molding. It is an object of the present invention to provide a permanent magnet excellent in magnet properties by using a radially oriented compact produced by a method for producing a rare earth alloy powder that can be produced.

[0021]

A rare earth magnet according to the present invention comprises a powder filling step of filling a rare earth alloy powder in a cavity and an orientation compression step of pressing the rare earth alloy powder while applying an orientation magnetic field a plurality of times. It is a rare earth magnet manufactured by repeating, and the n + 1 th stage (n
Is an integer of 1 or more), and the surface magnetic flux density at the boundary between the upper compact formed by the orientation compression step of the n-th stage and the lower compact formed by the n-th orientation compression step is the other part. 6 for the maximum value of the surface magnetic flux density at
5% or more.

In the method for producing a molded body of a rare earth alloy powder according to the present invention, a die having a non-magnetic material portion and a magnetic material portion laminated thereon and having a through hole and an inner wall surface of the through hole of the die are opposed to each other. A magnetic core having an outer peripheral surface, a lower punch inserted from below into a space formed between an inner peripheral surface of the through hole of the die and an outer peripheral surface of the magnetic core, Using a forming apparatus having an upper punch inserted from above into a space formed between the inner peripheral surface of the through hole and the outer peripheral surface of the magnetic core, the lower punch is inserted into the through hole of the die. A method for producing a molded product of a rare earth alloy powder in which a powder filling step of filling a rare earth alloy powder in a cavity formed by insertion and an orientation compression step of pressing the rare earth alloy powder while applying an orientation magnetic field are repeated a plurality of times And the (n + 1) th stage When performing the orientation compression step (where n is any integer of 1 or more), the upper end face of the molded body formed in the n-th stage orientation compression step is positioned above the lower end face of the magnetic material portion of the die. Deploy.

The method for producing a molded body of rare earth alloy powder according to the present invention is a method of filling a rare earth alloy powder into a cavity formed in an orientation space between a first magnetic member and a second magnetic member. A method for producing a molded body of rare earth alloy powder in which a process and an orientation compression process of pressing the rare earth alloy powder while applying an orientation magnetic field are repeated a plurality of times, wherein an (n + 1) th stage (n is any integer of 1 or more) )), At least a part of the molded body formed in the n-th stage alignment compression step is placed in an alignment space between the first magnetic member and the second magnetic member. To be placed.

Preferably, the intensity of the alignment magnetic field in the cavity is 0.4 MA / m or more.

A lubricant may be added to the rare earth alloy powder.

In the powder filling step of the (n + 1) th stage (n is any integer of 1 or more), the amount of rare earth alloy powder to be filled in the cavity is larger than that of the rare earth alloy powder in the cavity in the nth stage. It is preferable to increase the amount of the rare earth alloy powder to be filled.

In the (n + 1) -th stage orientation compression step, the level difference between the upper end surface of the molded body formed in the n-th stage orientation compression process and the lower end surface of the magnetic material portion of the die is 3 mm. It is preferable to make the above.

In the (n + 1) th stage of the orientation compression step, it is preferable that the height of a portion included in the orientation space of the molded body formed in the (n) th stage of the orientation compression step is 3 mm or more.

In a preferred embodiment, the rare earth alloy powder is an RT- (M) -B alloy (R is Y, La,
Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, E
A rare earth element containing at least one element of r, Tm and Lu, T is Fe or a mixture of Fe and Co, M is an additional element, and B is boron).

[0030] In a preferred embodiment, the compact has a cylindrical shape, and the orientation magnetic field is a radial magnetic field.

It is preferable that the density of the compact formed in the n-th stage orientation compression step is 3.5 g / cm ³ or more.

In a preferred embodiment, the step of compressing the rare earth alloy powder while applying the alignment magnetic field includes a step of measuring a pressure applied to the rare earth alloy powder filled in the cavity.

In a preferred embodiment, the density of the compact formed in the orientation compression step is adjusted by controlling the pressure applied to the rare earth alloy powder.

In the method for producing a rare earth magnet according to the present invention, the compact produced by any of the above-described methods for producing a compact of a rare earth alloy powder is sintered to obtain a permanent magnet.

A powder molding apparatus according to the present invention includes a die having a non-magnetic part and a magnetic part in a laminated state, and having a through-hole penetrating the non-magnetic part and the magnetic part; A magnetic core having an outer peripheral surface facing the inner wall surface of the through hole, and a space formed between the inner peripheral surface of the through hole of the die and the outer peripheral surface of the magnetic core inserted from below. A lower punch, an upper punch inserted from above into a space formed between the inner peripheral surface of the through hole of the die and the outer peripheral surface of the magnetic core, and the lower punch inserted into the through hole of the die. A powder supply device that fills the magnetic powder in the cavity formed by inserting the magnetic powder, a magnetic field generator that applies an orientation magnetic field to the magnetic powder filled in the cavity, and a relative position between the die and the lower punch. A first controller for controlling the general position; A second controller for controlling the relative position of the upper punch and the lower punch, a powder filling step of filling the cavity with a magnetic powder, and applying the orientation magnetic field. What is claimed is: 1. A powder compacting apparatus which operates so as to repeat an orientation compression step of pressing a magnetic powder a plurality of times, wherein the first controller comprises an (n + 1) th stage (n is an integer of 1 or more) orientation compression. When performing the step, the die and the lower punch between the die and the lower punch, so that the upper end surface of the molded body formed in the n-th stage orientation compression step is disposed above the lower end surface of the magnetic material portion of the die Control relative position.

[0036] In a preferred embodiment, a pressure sensor for measuring a pressure applied to the magnetic powder is provided.

In a preferred embodiment, the pressure sensor includes a strain gauge for detecting a strain of the upper punch or the lower punch.

In a preferred embodiment, the second controller controls a relative position between the upper punch and the lower punch based on a pressure measured by the pressure sensor.

The method for producing a molded body of rare earth alloy powder according to the present invention includes a first cavity forming step of forming a first cavity by a die and a lower punch, and a first step of filling the first cavity with the rare earth alloy powder. A first compression step of compressing the powder filled in the first cavity until the pressure applied to the powder in the first cavity reaches a first predetermined value; A second cavity forming step of forming a second cavity above the compressed powder by relatively moving a die and a lower punch forming the cavity, and filling the second cavity with the powder. And a second pressure for compressing the powder filled in the second cavity until the pressure applied to the powder in the second cavity reaches a second predetermined value. It includes a step.

In a preferred embodiment, a storing step of storing an upper end position of the compact formed by the first compressing step, and a die and a lower punch are relatively moved based on the upper end position, and the second cavity is formed. And forming a second cavity.

[0041] In a preferred embodiment, the first cavity and the second cavity are cylindrical.

[0042]

Embodiments of the present invention will be described below with reference to the drawings.

First, the overall configuration of the powder molding apparatus will be described with reference to FIG. The powder molding apparatus 5 includes a die 10 having a through hole, a cylindrical lower punch 14 inserted into the through hole of the die 10 from below, and an insert into the through hole of the die 10 from above. And a cylindrical upper punch 16. A magnetic core 12a for forming a radial magnetic field is formed in a core hole provided in each of the punches 14 and 16.
And 12b are inserted. The die 10 has a configuration in which an upper portion (magnetic portion) formed of a ferromagnetic material and a lower portion (nonmagnetic portion) formed of a nonmagnetic material are stacked. In this specification, “non-magnetic material” refers to a material having a saturation magnetization of 0.6 T or less. The configuration for forming the above-described press section is the same as that of the apparatus shown in FIG. The same members as those in FIG. 1 are denoted by the same reference numerals.

The die 10 is fixed to a die set 50, and the die set 50 is
2 is connected to a lower plate 56 via a guide rod 54 penetrating therethrough. The lower plate 56 is connected to a lower hydraulic cylinder 58b via a cylinder rod 58a. With this configuration, the die 10 can be moved up and down using the lower hydraulic cylinder 58b. The position of the die 10 is measured by a suitable position sensor 59 configured using a linear scale or the like. If the operation of the lower hydraulic cylinder 58b is controlled based on this measured value, the die 10 can be set at any desired position.

The lower punch 14 is provided with a base plate 52 at a position where it is inserted from below into the through hole of the die 10.
Fixed on top. In the powder molding apparatus 5, since the die 10 provided with the through holes as described above can be moved in the vertical direction (floating die method), it is not necessary to move the lower punch 14 in the vertical direction. .

The upper end of the upper punch 16 is
Attached to The upper plate 60 is connected to an upper hydraulic cylinder 62b via a cylinder rod 62a. In the vicinity of both ends of the upper plate 60, guide rods 64 fixed to the die set 50 penetrate.
The upper plate 60 and the upper punch 16 are provided with guide rods 64.
While being guided by the upper hydraulic cylinder 62b,
It can move up and down. The position of the upper punch 16 is measured by an appropriate position sensor 66 configured using a linear scale or the like. If the operation of the upper hydraulic cylinder 62b is controlled based on this measured value, the upper punch 16 can be set at any desired position.

Further, an upper coil 20 and a lower coil 22 are provided on the upper and lower sides of the cavity, respectively, in order to apply an orientation magnetic field to the powder filled in the cavity. The upper coil 20 is provided on the lower surface of the upper plate 60, for example, and the lower coil 22
Is provided on the lower surface of the die set 50, for example. Due to the repulsive magnetic field formed by the upper coil 20 and the lower coil 22, the powder in the cavity
A radial magnetic field that spreads radially from the center of the core 12 to the die 10 can be applied.

In this embodiment, the upper hydraulic cylinder 6
2b includes a pressure sensor A for measuring the magnitude of the hydraulic pressure.
Is attached. Using the pressure sensor A, the pressure applied to the magnetic powder filled in the cavity can be measured. This method is disclosed in, for example,
No. 52702.

The use of such a pressure sensor A makes it possible to perform the pressing step with a more constant molding density as compared with the case where only the position sensor 66 for measuring the vertical position of the upper punch 16 is used. it can. In particular, when producing a ring-shaped magnet as in the present embodiment, the cavity has a shape in which the powder is difficult to be uniformly filled, so that the powder supplied into the cavity for each filling step is used. Is apt to vary. The RTB-based (R is a rare earth element containing Y, T is Fe or a mixture of Fe and Co, B is boron) alloy powder appropriately used in the present embodiment has a square shape. Many, difficult to fill uniformly. In particular, alloy powder produced by a quenching method (cooling rate of 10 ² to 10 ⁴ ° C./sec) such as a strip casting method (for example, described in US Pat. No. 5,383,987) has a narrow particle size distribution, Since the properties are further reduced, uniform filling becomes difficult.

In the case where the amount of powder to be filled in the cavity varies as described above, it is necessary to set the position of the upper punch 16 (relative position with respect to the lower punch 14) to a predetermined position during powder pressing. Density variation occurs for each compact. On the other hand, when the pressure sensor A is used as in the present embodiment, the pressure applied to the powder (or the compact) in the cavity is measured, and the position of the upper punch relative to the lower punch is changed based on this pressure. Therefore, a predetermined pressure can always be applied to the molded body, and thereby, the density of the molded body can be controlled to be substantially constant.

In the case where a molded body is produced by the multi-stage molding method as in the present embodiment, the use of the pressure sensor A enables the orientation compression step performed a plurality of times to produce the molded body with high accuracy. A desired molding density can be obtained.

For example, in the initial orientation compression step, a compact is prepared in a state of relatively low density (soft),
If a higher pressure is applied and compacted in the final orientation compression step, a compact having a uniform density over the whole can be produced. The molded body produced in this manner does not locally shrink at a different shrinkage rate in the sintering step. Thereby, a sintered magnet having a desired shape and magnetic properties can be obtained.

Further, by using the pressure sensor A, it is possible to control the pressing operation so that a sufficient pressure equal to or higher than a predetermined level is applied to the powder in the cavity in each orientation compression step. Thereby, in each of the orientation compression steps, it is possible to produce a molded body having a density equal to or higher than a predetermined level, and the molding produced in the previous stage is performed by the orientation magnetic field formed in the next stage of the orientation compression process. The body can be prevented from reorienting.

As described later, a strain gauge (not shown) is fixed to the upper punch 16 and the pressure applied to the magnetic powder (or the compact) in the cavity is measured using the strain gauge. Good. Using a strain gauge, compared to measuring the magnitude of the hydraulic pressure of the upper hydraulic cylinder 62b,
The pressure applied to the magnetic powder can be measured more accurately. Therefore, it is possible to reliably produce a ring-shaped molded body having a substantially uniform density.

The feeder box 4 is placed on the die set 50.
0 is placed. The rare earth alloy powder 24 is stored in the feeder box 40. The feeder box 40 is connected to a hydraulic cylinder 42 via a cylinder rod, and is capable of moving forward and backward with respect to a through hole formed in the die 10.

[0056] Incidentally, a cylindrical upper punch 16 and lower punch 14, for example, hardness H _R A (Rockwell hardness)
And the composition is Mo: 1.6 wt.
%, Ni: 20 wt%, and the balance WC is formed of a WC-Ni-based cemented carbide or the like. Here, carbide powder containing at least one of nine elements belonging to Group IVa, Va, or VIa in the periodic table may be used for the cemented carbide, such as Fe, Co, Ni, Mo, An alloy formed by sintering and bonding using an iron group metal such as Sn or an alloy thereof is included. As the cemented carbide, a WC-TaC-Co-based alloy, a WC-TiC-Co-based alloy, or a WC-TiC-TaC-Co-based alloy can also be used.

The upper punch 16 and the lower punch 14
May be formed from an alloy steel. Here, alloy steel includes high-speed steel mainly composed of Fe-C, high-manganese steel,
The upper punch 16 and the lower punch 1
As 4, an alloy steel having a predetermined hardness is used.

[0058] Thus, by forming the upper punch 16 and lower punch 14 and the like H _R A cemented carbide or a steel alloy having 70 or more 93 or less of hardness, the desired toughness to the upper punch 16 and lower punch 14 And can provide elasticity. Thereby, the upper punch 16 and the lower punch 14
Can be hardly damaged even when it is processed into a sharp shape.

Hereinafter, a method for forming a rare earth alloy powder (a method for manufacturing a compact) according to the present embodiment will be described with reference to FIGS. 6 (a) to 6 (f). The present invention can be applied to a case where three or more stages of powder filling / orientation compression cycles are performed. However, in this embodiment, a case where two stages of powder filling / orientation compression cycles are performed will be described for convenience.

First, reference is made to FIG. This figure is
It shows a state immediately after the molded body produced in the immediately preceding orientation compression step is taken out of the molding apparatus. Here, the upper core 12a and the upper punch 16 are raised and separated from the die 10 while the upper end surface of the lower punch 14 is flush with the upper end surface of the die 10.

Thereafter, as shown in FIG.
By raising 0 and the lower core 12b, the relative position of the lower punch with respect to the die 10 and the lower core 12b is lowered, and a cylindrical space (cavity) is formed in the through hole of the die 10. The lower part of this space is defined by the upper end surface of the lower punch 14, but the upper part is opened to form an annular concave portion to be filled with the rare earth alloy magnetic powder.
Next, the feeder box (feeding box) 40 for supplying the rare-earth alloy powder is slid to a position above the cavity, and the powder 24 stored in the feeder box 40 is filled in the cavity (first). Powder filling step). In the first powder filling step, the position of the lower surface of the cavity, that is, the position of the upper end surface of the lower punch 14 is set to a position equal to or slightly higher than the position of the lower end surface of the magnetic portion 10a of the die 10. Is done. For convenience of explanation, considering the case where three or more stages of powder filling are performed,
The space (cavity) filled with the powder in the powder filling step at the stage (n is any integer of 1 or more) may be referred to as “n-th cavity”.

Next, as shown in FIG. 6C, after the feeder box 40 is retracted from above the cavity, both the upper core 12a and the upper punch 16 are lowered, and
The lower end surface of 2a is brought into contact with the upper end surface of lower core 12b. Subsequently, the lower end of the upper punch 16 is inserted into the through hole of the die 10 and further lowered. At this time, when the lower end surface of the upper punch 16 closes the cavity, a repulsive magnetic field is formed in the core 12 and a radial magnetic field is formed in the cavity. In the present embodiment, in order to obtain sufficient magnetic characteristics, the intensity of the alignment magnetic field in the cavity is set to 0.4 MA / m or more. The powder filled in the cavity is
6 and the lower punch 14, and are compression-molded under a radial magnetic field (first-stage orientation compression step). Thus, the first-stage radially-oriented molded body 26 is formed. The state of the orientation magnetic field in the step of FIG. 6C is not different from that shown in FIG. After the completion of the first-stage orientation compression step, a magnetic field having a direction opposite to that of the previously applied orientation magnetic field is applied using the coils 20 and 22 to demagnetize the first-stage formed body 26. I do.

The density of the first-stage compact was 3.5 g / c.
It is preferably at least m ³ . More preferably, 3.
It is set to ^{9g / cm 3 ~4.5g / cm 3} . The reason is that if the compact density is below the above level due to insufficient compression, the first-stage compact 26 may be reoriented.

In the first stage of the orientation compression step, a control method is adopted in which the pressure applied to the filling powder is detected, the compression operation is stopped after the pressure reaches a predetermined value, and the process proceeds to the next step. be able to. Here, pressure detection can be performed using the pressure sensor A shown in FIG. When such a control method is adopted, a molded body can always be produced with a molding density of 3.5 g / cm ³ or more even if the amount of powder to be filled into the cavity varies. Therefore, it is possible to prevent the already molded first-stage molded body from being reoriented by applying a magnetic field when producing the second-stage molded body.

This pressure detection may be performed using a strain gauge (strain sensor) provided on the upper punch 16. As the strain gauge, for example, a strain gauge (F
CA-3-11-1L) can be used. The greater the number of strain gauges, the more effective it is to obtain accurate pressure. In the present embodiment, a four gauge method is employed, and four strain gauges are attached to the side surfaces of the punch. The strain gauges may be provided on the side surfaces of the upper punch 16 and / or the lower punch 14.

The use of such a strain gauge makes it possible to measure the degree of strain at the tip of the upper punch during pressing, and thereby to detect the pressure applied to the compact in real time and with high accuracy. be able to.

Hereinafter, a specific example of a method for producing a molded article using such a strain gauge will be described. First, with the cavity filled with powder, the upper punch 16 is
Lower to 4. This gradually increases the pressure applied to the powder. At this time, the pressure applied to the powder is
By the strain gauge fixed to the side surface of the upper punch 16, it is accurately observed in real time. In this pressurizing process, the die 10 may be lowered together with the upper punch 16 at a lower speed. By doing so, the same pressure effect as when the lower punch 14 is raised while lowering the upper punch 16 can be exerted on the powder in the cavity, and in order to reduce the density variation in the compact. It is valid.

Next, when the strain gauge detects that the pressure applied to the powder (or the compact) has reached a predetermined level, the lowering of the upper punch 16 is stopped, and a compact is formed. . If the compact is manufactured while measuring the pressure using the strain gauge, the compact density of the compact can be set to a predetermined level (for example, 3.5 g / cm ³ ) or more.

Next, reference is made to FIGS. 6C and 6D. From the state shown in FIG. 6C, the die 10 is raised while the molded body is pressed with a predetermined pressure by the upper punch 16 and the lower punch 14, and the lower core 12b, the upper core 12a When these cores 12a, 12a
b is raised. In this way, the die 10 and the core 1
It is possible to prevent the molded body from being damaged by friction generated when the 2a and 12b rise. Thereafter, by raising the upper punch 16, a cavity ("second cavity") is formed again above the upper surface of the molded body. The lower part of the second cavity is defined not by the lower punch 14 but by the upper end surface of the first-stage molded body 26.

In the case of the conventional multi-stage molding method, the upper end surface of the first-stage molded body 26 is arranged at the same level as the lower end surface of the magnetic body portion 10a of the die 10.
The relative positional relationship between the lower punch 14 and the die 10 is controlled such that the upper end surface of the step compact 26 is located above the lower end surface of the magnetic body portion 10a of the die 10. Thereafter, the feeder box 40 is moved above the cavity, and the second cavity is filled with the rare-earth alloy powder (the second-stage powder filling step).

Next, as shown in FIG. 6E, after the feeder box 40 is retracted from above the cavity, the upper core 12a and the upper punch 16 are lowered, and the upper core 12a is lowered.
Is brought into contact with the upper end surface of the upper core 12b. Subsequently, the lower end of the upper punch 16 is inserted into the through hole of the die 10 and further lowered. At this time, when the lower end surface of the upper punch 16 closes the cavity, a repulsive magnetic field is formed in the core 12 and a radial magnetic field is formed in the second cavity. The powder filling the second cavity is compressed in a radial magnetic field (second stage orientation compression step). Thus, the second-stage molded body 28 is formed on the first-stage molded body 26, and the two are integrated to form one molded body 30.
Is formed. In the present embodiment, the axial length of the first-stage formed body 26 is, for example, about 13.5 mm, and the second-stage formed body 2
8 has an axial length of about 10.5 mm.

FIG. 7 is a cross-sectional view showing an orientation magnetic field in the step shown in FIG. When the filling powder is molded in the second-stage orientation compression step, the position of the second cavity is higher than the position of the lower end surface of the magnetic portion 10a of the die 10 in the through hole of the die 10. In other words, the relative position of the first-stage formed body 26 with respect to the magnetic body portion 10a has moved upward as compared with the conventional example. For this reason, in a region where the magnetic flux formed in the lower core 12b spreads radially toward the magnetic material portion 10a of the die 10, the axial component of the magnetic field (or magnetic flux) decreases, and the radial magnetic field shown in FIG. A magnetic field in a close state can be formed.

In the present embodiment, the upper end surface of the first-stage molded body 26 is 3 mm larger than the lower end surface of the magnetic portion 10 a of the die 10.
Or higher. This value of 3 mm is
The size exceeds 10% of the axial length (L = about 24 mm) of the magnetic portion 10a of the die 10 used in the present embodiment. Further, as described above, since the axial length of the first-stage formed body 26 created in the present embodiment is about 13.5 mm, the value of 3 mm is 20 times the axial length of the first-stage formed body 26. %.

After the completion of the second-stage orientation compression step, a magnetic field having a direction opposite to the direction of the orientation magnetic field applied before is applied by using the coils 20 and 22 to demagnetize the compact 30. I do. Thereafter, as shown in FIG. 6F, the upper punch 16 and the upper core 12a are raised, and
The molded body 30 is taken out by lowering the zero position.

After sintering the compact 30 thus produced, it is subjected to a surface treatment and magnetized to produce a radially oriented anisotropic ring magnet.

In the step of extracting the compact 30, the operations of the upper punch 16 and the die 10 may be controlled based on the compact pressure measured using the above-described strain gauge. Hereinafter, an example of the removal process of the molded body 30 will be described with reference to FIG.

FIG. 8 is a graph showing a change in the pressure P of the compact. As shown in the graph, after a molded body 30 at a predetermined molded body pressure P ₁ in the compressed orientation step S1, rise at a rate slow the upper punch 16 (or decrease the applied pressure) is, thereby, forming The body pressure P is gradually reduced. Since the formed compact tends to extend in a direction opposite to the pressing direction by a so-called springback phenomenon, the compact pressure P gradually increases while the upper punch 16 and the compact remain in contact with each other. descend. The change in the compact pressure at this time is detected by a strain gauge.

In this process, when the compact pressure P has decreased to a predetermined value P ₂ , the die 10 starts to lower.
Thereby, the molded body 30 starts to be exposed outside the cavity. The upper punch 16 is still raised at a slow speed, and the compact pressure P further decreases.

[0079] Then, drop die 10 proceeds, the molded body is at a time before the withdrawn completely from the cavity, the rise of the upper punch is stopped, the holding pressure P ₃ to maintain the compact pressure. The use of strain gauges, it is possible to set the holding pressure P ₃ to a relatively small value. Moldings, in a state in which the holding pressure P ₃ is applied, is completely withdrawn from the cavity. After that, the molded body 30 is
The upper punch 16 is raised again in a state where the upper punch 16 is exposed,
The step of extracting the compact is completed.

As described above, the reason why the operations of the upper punch 16 and the die 10 are controlled based on the pressure of the compact measured using the strain gauge is to reduce cracking and crushing of the compact in the step of extracting from the cavity. That's why.

When removing the molded body 30 from the cavity,
The friction between the die 10 and the molding 30 causes the molding 30
Is applied to the molded body 30, which may cause cracks in the molded body 30. At this time, if a predetermined compact pressure is applied to the compact by the upper punch 16, cracks can be prevented. For this reason, pressure is applied to the compact until the removal of the compact is completed.

However, if the value of the pressure applied to the compact is too large, the compact 30 extracted from the cavity will be crushed. Particularly, the molded body 30 is very easily crushed immediately before being completely removed from the cavity. Therefore, to set the holding pressure P ₃ to a small value, thereby preventing the collapse.

As described above, when the strain gauge is used, the pressure of the compact can be accurately detected in real time, so that both cracking and crushing of the compact are prevented.
The operation of the upper punch 16 and the die 10 can be controlled to perform an appropriate extraction process.

Further, in the embodiment using the strain gauge as described above, it is possible to adjust the size of the compact as well as the density of the compact. Hereinafter, FIGS. 5, 9 and 10
This embodiment will be described with reference to FIG.

FIG. 9 is a block diagram showing a control mechanism associated with the powder molding apparatus shown in FIG. Central control circuit 9 provided for controlling the operation of powder molding apparatus 5
Reference numeral 0 includes a CPU for executing calculations, a RAM for storing information from a strain gauge, a position sensor, and the like, and a ROM for storing a control program. The central control circuit 90 includes an operation panel (OP PANEL)
Is connected, and the operator can arbitrarily input control information as needed.

The strain gauge driving circuit applies a predetermined voltage to the strain gauge attached to the upper punch or the like, and based on the output from the strain gauge at this time, the magnitude of the strain (that is, the pressure of the pressure applied to the filling powder). Size) is detected. The magnitude of the strain is expressed as a change in the electric resistance of the strain gauge. In this way, the strain gauge drive circuit transmits information on the pressure applied to the powder to the central control circuit 90 as a digital signal using an A / D converter (not shown).

The hydraulic cylinder drive circuit includes a central control circuit 9
The upper hydraulic cylinder 62b and the lower hydraulic cylinder 58b are driven based on a command from 0. The upper punch 16 and the die 10 can be moved to predetermined positions by using the hydraulic cylinder drive circuit.

The position sensors 66 and 59 provided in association with the upper punch 16 and the die 10 detect the positions of the upper punch 16 and the die 10 and transmit the position information to the central control circuit 90.

The feeder box drive circuit controls the movement and retreat of the feeder box 40 onto the cavity. When a powder filling auxiliary device such as a shaker (or a stirrer) is provided in the feeder box 40, the operation of these devices is also controlled. The coil driving circuit drives the magnetic field generating coils 20 and 22 for applying an orientation magnetic field to the powder in the cavity. The central control circuit 90 controls these drive circuits.

Next, with reference to FIGS. 10A and 10B, a process for producing a molded body using the above-described control mechanism will be described.

When the start button on the operation panel is pressed, the central control circuit 90 instructs each drive circuit to perform an initial operation. When all the drive circuits return the READY signal, the central control circuit 90 starts the press operation (S1). And S2). First, the die is raised by driving the lower hydraulic cylinder to form a first cavity (S3). The central control circuit 90 gives an instruction to the feeder box drive circuit to fill the first cavity with the powder (S4). When the feeder box drive circuit notifies that the filling of the powder has been completed, the central control circuit 90 drives the upper hydraulic cylinder to lower the upper punch (S5). Further, the magnetic field generating coil is driven while the cavity is covered by the upper punch, and the powder in the cavity is oriented (S6).

In this orientation compression step, the output of the strain gauge drive circuit is monitored from the time when the upper punch starts compressing the powder, and the pressure applied to the powder in the cavity is measured. With the lowering of the upper punch, the magnitude of the pressure applied to the powder increases. In this process, when it is detected that a predetermined pressure is applied to the powder (S7), the lowering of the upper punch is stopped. At the same time, the application of the alignment magnetic field is stopped (S8).

At this time, the position of the upper punch in the compressed state is detected by the position sensor. The position information from the position sensor is stored (stored) in the RAM in the central control circuit 90 (S9).

As described above, when the compression step is performed based on the pressure applied to the powder, if the amount of the powder filled in the cavity is different, the position of the upper punch at the time of compression is different, and the first alignment is performed. The size (height) of the compact produced in the compression step may vary. On the other hand, in this embodiment, based on the position of the upper punch,
The depth of the cavity (second cavity) to be formed in the second orientation compression step is calculated (S10). Specifically, the height of the first compact (first-stage compact) determined from the position of the upper punch from the height of the entire compact to be formed after the next stage (second) of the orientation compression step By subtracting the depth, the depth of the cavity to be formed in the next step is determined. In this way, a molded body with high dimensional accuracy can be manufactured even if the powder filling amount varies. If the height of the first-stage molded product is too high or too low and is out of the predetermined range, the first-stage molded product is removed from the cavity before performing the second orientation compression step, and newly formed. The first-stage molded body may be manufactured.

When the depth of the cavity in the next stage is determined in this way, the die and the core are removed based on the calculated cavity depth while the compact is sandwiched between the upper punch and the lower punch. Raise to a predetermined position, and then
By raising the upper punch, a second cavity is formed (S11 and S12).

Thereafter, in the same manner as in the first orientation compression step, the powder filling step (S13) and the orientation compression step (S14 to S14) are performed.
S16) is performed to produce a molded body. During the second press operation, a predetermined pressure is applied to the powder using the strain gauge. This makes it possible to produce a molded body having a uniform density and high dimensional accuracy.

The molded body manufactured by using the multi-stage molding method in this manner is taken out of the cavity while preventing damage by the method described with reference to FIG. 8, for example (S17). The body manufacturing process is completed (S1
8).

FIG. 11 is a graph showing the surface magnetic flux density (Bg) of the magnet according to the present embodiment, and corresponds to the graph of FIG. Here, the surface is processed after sintering,
Outer diameter 16.4mm, inner diameter 10.5mm, axial length 20
mm ring magnets were prepared and evaluated. For easy evaluation, the magnetization was performed using a magnetic field perpendicular to the axial direction.

As can be seen from the graph of FIG. 11, the drop of the surface magnetic flux density (Bg) at the boundary between the first-stage molded body 26 and the second-stage molded body 28 is smaller than that of the conventional example (FIG. 3). Significantly reduced. In the example of FIG. 11, the surface Bg at the boundary portion has a value of 70% or more of the maximum value of the surface magnetic flux density (Bg) at another portion. According to the present invention, the surface magnetic flux density (B
g) can be set to 65% or more of the maximum value of the surface magnetic flux density (Bg) in other portions even when it is low.
% Or 80% or more.

When a magnet having high magnetic properties as a whole is used for a motor, energy efficiency is improved.
The magnet manufactured according to the present embodiment is particularly suitably used for a motor for a robot that realizes factory automation (FA).

According to the present embodiment, it is possible to suppress a decrease in the surface magnetic flux density (Bg) at the boundary of the multi-stage molding. The reason is that when the second orientation compression step is performed, the relative position of the first-stage molded body 26 is raised as compared with the conventional example, and at least a part of the first-stage molded body 26 is arranged in the orientation space. This is because the axial component of the orientation magnetic field due to the presence of the first-stage formed body 26 is reduced, and the degree of orientation is greatly improved. As described above, when a part of the molded body that has been subjected to the orientation treatment is positioned in the orientation space, the dimension of the molded body to be formed in the next stage is reduced. Therefore, according to the conventional concept, the molded body that has been subjected to the orientation treatment, that is, here, the first-stage molded body 26 is
It is inefficient to dispose it in the space (orientation space) between the magnetic body portion 10a and the core 10. However, in the present invention, such a thing is dared to be performed, and thereby, it has succeeded in remarkably suppressing a decrease in the degree of orientation due to the multi-stage molding.

As the magnetic powder, a powder produced by a strip casting method is preferably used. A procedure for producing a magnetic powder by a strip casting method is, for example, as follows.

First, 31Nd-1B-68Fe as disclosed in US Pat. No. 5,383,978.
An alloy having a composition of (% by mass) is melted in an argon atmosphere by a high-frequency melting method to produce a molten alloy. Of the above alloys, those having a composition in which a part of Fe is replaced by Co may be used. No. 4,770,72.
An alloy having the composition disclosed in the specification of Japanese Patent No. 3 may be used.

While maintaining the temperature of the molten alloy at 1350 ° C., the molten alloy is brought into contact with the surface of the rotating single roll, thereby rapidly cooling the molten alloy to obtain a rapidly solidified alloy having a desired composition. When the cooling conditions at this time are, for example, a roll peripheral speed of about 1 m / sec, a cooling speed of 500 ° C./sec, and a degree of subcooling of 200 ° C., a flake-like alloy having an average thickness of 0.3 mm is obtained.

After the alloy thus obtained is embrittled by absorbing hydrogen, it is roughly pulverized by a feather mill to a size of about 5 mm. Next, the coarsely pulverized alloy is finely pulverized by a jet mill until a powder having an average particle diameter of 3.5 μm is obtained. Thereafter, the fatty acid ester diluted with a petroleum solvent is added as a lubricant and mixed. The amount of lubricant added is
What is necessary is just to make it 0.3 mass% with respect to alloy powder, for example. In addition, a solid lubricant such as zinc stearate can be used as the lubricant.

As described above, the rare-earth alloy powder produced by the strip casting method has a sharper particle size distribution than the powder produced by another method (ingot method). Therefore, when a compact is produced using such a rare earth alloy powder and sintered, a sintered compact having a uniform particle size can be produced, and excellent magnetic properties can be obtained. On the other hand, since the particle size distribution is sharp, there is a problem that the fluidity of the powder is poor and the filling tends to be uneven.
In contrast, by controlling the pressure applied to the molded body using the pressure sensor as described above, the molded density can be made uniform and a highly oriented molded body having a density equal to or higher than a predetermined level can be produced. .

The rare earth alloy preferably used in the powder compacting method of the present invention is generally an RT- (M) -B alloy powder (R is a rare earth element containing Y, T is Fe or Fe and Co
, M is an additive element, and B is boron). As the rare earth element R, Y, La, Ce, Pr, N
d, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu
A raw material containing at least one kind of element can be used. However, in order to obtain sufficient magnetization, it is preferable that 50 at% or more of the rare earth element R is occupied by one or both of Pr and Nd.

When the rare earth element R is 10 at% or less, α-
The coercive force decreases due to the precipitation of the Fe phase. If the rare earth element R exceeds 20 at%, the target tetragonal Nd
_{In addition to the 2} Fe ₁₄ B-type compound, a large amount of the R-rich second phase precipitates, and the magnetization decreases. For this reason, the rare earth element R is preferably in the range of 10 to 20 at% of the whole.

T is an iron group element and includes Fe and Co. When T is less than 67 at%, the second phase having low coercive force and low magnetization is precipitated, so that the magnetic properties deteriorate. T
Exceeds 85 at%, the coercive force decreases due to the precipitation of the α-Fe phase, and the squareness of the demagnetization curve also decreases. Therefore, the content of T is preferably in the range of 67 to 85 at%.

T may be composed only of Fe, but the addition of Co increases the Curie temperature and improves heat resistance. Preferably, at least 50 at% of T is occupied by Fe. This is because the saturation magnetization itself of the Nd ₂ Fe ₁₄ B type compound decreases when the proportion of Fe is less than 50 at%.

B is essential for stably depositing a tetragonal Nd ₂ Fe ₁₄ B type crystal structure. The amount of B added is 4a
If the amount is less than t%, the coercive force decreases due to precipitation of the R ₂ T ₁₇ phase, and the squareness of the demagnetization curve is significantly impaired. On the other hand, if the addition amount of B exceeds 10 at%, a second phase having a small magnetization is precipitated. Therefore, the content of B is 4 to 10 at%.
Is preferably within the range. Note that part or all of B can be replaced with C.

An additional element M may be added for the purpose of improving the magnetic properties and corrosion resistance of the powder. Additional element M
Are Al, Ti, Cu, V, Cr, Ni, Ga,
At least one element selected from the group consisting of Zr, Nb, Mo, In, Sn, Hf, Ta, and W is preferably used. Such an additive element M may not be added at all, but when it is added, the amount added is 10 at%.
It is preferable to set the following. If the addition amount exceeds 10 at%, a second phase that is not ferromagnetic is precipitated and the magnetization is reduced.

It is preferable to select a material having a high magnetic permeability and a high saturation magnetic flux density and excellent abrasion resistance as the material of the magnetic portion and the core of the die. Examples of such a material include carbon tool steel (SK), alloy tool steel (SKS, SKD), high-speed tool steel (SKH), and permendur. When importance is placed on wear resistance, a coating layer of a cemented carbide may be provided on a substrate having a high magnetic permeability and a high saturation magnetic flux density, for example, a permendur material, a permalloy material, a sendust material, or the like.

The application of the present invention is not limited to the production of a sintered magnet, but also broadly includes the production of a bonded magnet. When the present invention is applied to the formation of a bonded magnet, a magnetic powder to which a binder has been added is filled in a cavity of a molding apparatus. As the binder, a thermosetting resin such as an epoxy resin or a phenol resin can be used. In order to complete the bonded magnet, a curing process at about 120 ° C. is performed after the molding.

Further, the present invention can be applied to the case of manufacturing magnets other than cylindrical magnets. For example, JP-A-4-35
The present invention can also be applied to a case where an arc-shaped magnet as disclosed in Japanese Patent Publication No. 2402 is manufactured by a multi-stage filling method.

The powder molding apparatus used in the present invention is not limited to the one described in the above embodiment. The raising and lowering operations of the upper and lower punches and dies are merely relative, and it is needless to say that various modifications are possible.

When one magnet is manufactured from three or more molded bodies, the upper end surface of the molded body produced in the immediately preceding orientation compression step in the second and subsequent orientation compression steps is always used as the magnetic material portion of the die. It is not necessary to arrange above the position of the lower end face. When producing a long cylindrical magnet from many steps, depending on the application, it may be sufficient to increase only the degree of orientation of a necessary portion. In the case where a molding boundary is included in a portion where the degree of orientation is to be increased, the present invention may be applied so that at least the degree of orientation of the boundary is increased.

In the above embodiment, the dry compaction method (dry press) in which the rare earth alloy powder is compacted in a powder state has been described as an example. However, the present invention relates to mixing the rare earth alloy powder with mineral oil or the like. It can also be applied to a wet molding method in which the slurry obtained by the above is oriented and compressed in a cavity.

[0119]

According to the present invention, it is possible to provide a high-performance radially oriented anisotropic magnet because a high degree of orientation can be realized when radial orientation is performed using multi-stage filling and molding. is there. In particular, when a rare earth alloy powder having excellent magnetic properties is used, the molding density is kept low and a strong orientation magnetic field is often applied, so that the degree of orientation tends to decrease. Even in such a case, since a local decrease in the degree of orientation due to the multi-stage filling can be suppressed, a remarkable effect can be exhibited.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a typical powder molding (press) apparatus used for orienting a magnetic powder in a radial direction.

FIG. 2A is a cross-sectional view schematically showing a state of an orientation magnetic field in a second-stage orientation compression step in a case where a magnetic powder is oriented in a radial direction by multistage filling.

FIG. 2B is a cross-sectional view schematically showing a state of an orientation magnetic field in a second-stage orientation compression step in a case where a magnetic powder is oriented in a radial direction by multi-stage filling.

FIG. 3 is a graph showing an outer peripheral surface magnetic flux density (Bg) of a cylindrical magnet manufactured by a conventional multistage molding method.

FIG. 4 is a perspective view of a cylindrical magnet as a measurement target of the graph of FIG. 3;

FIG. 5 is a side view showing the entire configuration of the powder molding apparatus according to the present embodiment.

FIGS. 6A to 6F are process cross-sectional views illustrating a method for forming a rare earth alloy powder in the present embodiment.

FIG. 7 is a cross-sectional view schematically showing the state of the alignment magnetic field in the step shown in FIG.

FIG. 8 is a graph showing a change in a pressure (molding body pressure) P applied to a molded body.

FIG. 9 is a block diagram showing a control mechanism associated with the powder molding apparatus shown in FIG.

FIG. 10 is a flowchart in the case of producing a molded body using the control mechanism shown in FIG.

FIG. 11 is a graph showing an outer peripheral surface magnetic flux density (Bg) of the magnet according to the embodiment of the present invention.

[Explanation of symbols]

10 dies 10a Magnetic part of die 10b Non-magnetic part of die 12 Magnetic core 12a Upper core 12b lower core 14 Lower punch 16 Upper punch 20 Upper coil 22 Lower coil 24 Magnetic powder 26 First-stage molded body 28 Second-stage compact 30 molded body 32 ring magnet

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Atsuo Tanaka             1062 Oyabu, Yabu-cho, Yabu-gun, Hyogo             Tokuden Co., Ltd. F term (reference) 4K018 AA27 AB10 AC01 BA04 BA18                       BA20 BB04 BC08 BD01 CA02                       CA14 FA21 JA03 KA45                 5E040 AA04 CA01 HB05                 5E062 CC02 CD04 CD05 CE04

Claims (1)

[Claims] 1. A rare earth magnet manufactured by repeating a powder filling step of filling a rare earth alloy powder in a cavity and an orientation compression step of pressing the rare earth alloy powder while applying an orientation magnetic field a plurality of times. Surface at the boundary between the upper molded body formed by the (n + 1) th stage (n is an integer of 1 or more) orientation compression step and the lower molded body formed by the nth stage orientation compression step A rare earth magnet having a magnetic flux density of 65% or more of the maximum value of the surface magnetic flux density in other parts.