JP7273066B2 - Green compact manufacturing method and green compact - Google Patents

Description

The present disclosure relates to a green compact manufacturing method and a green compact.
This application claims priority based on Japanese Patent Application No. 2018-235935 filed in Japan on December 17, 2018, and incorporates all the descriptions described in the Japanese application.

Conventionally, a green compact is produced by filling powder into a mold and compression-molding the powder. Patent Literature 1 describes a hollow hemisphere molding apparatus comprising a fixed mold having a hemispherical recess and a movable mold having a hemispherical projection that is fitted into the fixed mold to form a hemisphere forming part. there is Patent Literature 2 describes a magnetic pole surface spherical bonded magnet in which the magnetic pole surface is formed by a bonded magnet portion and the magnetic pole surface is formed in a substantially spherical shape.

Further, techniques related to rare earth magnets are disclosed in Patent Documents 3 to 5, for example. In Patent Documents 3 to 5, magnet powder obtained by hydrogenating a rare earth-iron alloy is compression-molded into a green compact, and the green compact is dehydrogenated to obtain a rare earth-iron alloy. It is disclosed to produce a rare earth-iron magnet, ie, a dust magnet, which is made of a dust body of .

JP-A-2001-11508 JP-A-2006-41138 JP 2011-236498 A Japanese Unexamined Patent Application Publication No. 2011-137218 JP 2012-241280 A

The method for producing a green compact of the present disclosure includes:
A first step of preparing a mold comprising a die that defines a hollow portion on the inner peripheral surface of a cylindrical body, a lower punch that is inserted into the hollow portion, and an upper punch that is inserted into the hollow portion. ,
The inner peripheral surface of the die is
a spherical first inner peripheral surface;
a cylindrical second inner peripheral surface provided on one end side of the first inner peripheral surface in the axial direction;
a cylindrical third inner peripheral surface provided on the other end side in the axial direction of the first inner peripheral surface,
The first inner peripheral surface has an inner diameter that decreases from one axial end to the other axial end,
The second inner peripheral surface has an inner diameter corresponding to the maximum inner diameter of the first inner peripheral surface,
The third inner peripheral surface has an inner diameter corresponding to the minimum inner diameter of the first inner peripheral surface,
The lower punch has a crown-shaped end surface that forms a hemispherical surface by connecting to the first inner peripheral surface,
The end surface of the lower punch has an outer diameter corresponding to the inner diameter of the third inner peripheral surface,
The upper punch is
a cylindrical first upper punch;
a cylindrical second upper punch inserted through the inside of the first upper punch;
The first upper punch has an annular end surface composed of a flat surface,
The end surface of the first upper punch has an outer diameter corresponding to the inner diameter of the second inner peripheral surface,
The second upper punch has a hemispherical end surface protruding toward the lower punch,
The end face of the second upper punch has an outer diameter corresponding to the inner diameter of the first upper punch,
Furthermore,
The end face of the lower punch is positioned within the region surrounded by the third inner peripheral face, the end face of the first upper punch is positioned at the opening of the second inner peripheral face, and the second upper punch Surrounded by the first inner peripheral surface, the second inner peripheral surface and the third inner peripheral surface of the die in a state where the boundary between the end surface and the cylindrical surface of the die is at the same position as the end surface of the first upper punch a second step in which the raw material powder is filled in the hollow portion;
a third step of lowering the first upper punch and the second upper punch with respect to the die and raising the lower punch to compress the raw material powder from above and below to obtain a hollow hemispherical green compact; , provided.

The green compact of the present disclosure is
has a hollow hemispherical shape,
When a line parallel to the central axis connecting the center and the vertex of the hollow hemisphere and passing through the inner peripheral edge of the open end face of the hollow hemisphere is defined as a parting line, the part located on the central axis side of the parting line The top part and the remaining part located on the opposite side of the central axis from the parting line are the skirt part,
A difference in relative density between the top portion and the bottom portion is 5% or less.

FIG. 1A is a schematic cross-sectional view showing an example of a mold used in a method for manufacturing a green compact according to an embodiment. FIG. 1B is a schematic cross-sectional view of a die that constitutes the mold shown in FIG. 1A. FIG. 2 is a schematic cross-sectional view showing a second step in the method for producing a powder compact according to the embodiment. FIG. 3 is a schematic cross-sectional view for explaining the A step in the second step. FIG. 4 is a schematic cross-sectional view for explaining step B in the second step. FIG. 5 is a schematic cross-sectional view for explaining step C in the second step. FIG. 6 is a schematic cross-sectional view for explaining step D in the second step. FIG. 7 is a schematic cross-sectional view showing the third step in the method for manufacturing a green compact according to the embodiment. FIG. 8 is a schematic perspective view showing an example of the green compact according to the embodiment. FIG. 9 is a schematic cross-sectional view showing an example of the green compact according to the embodiment. FIG. 10 is a schematic perspective view showing another example of the green compact according to the embodiment, showing a form having steps on the outer peripheral surface of the green compact. FIG. 11 is a schematic cross-sectional view showing another example of the green compact according to the embodiment, showing a form having steps on the outer peripheral surface of the green compact. FIG. 12 shows another example of having a step on the outer peripheral surface of the powder compact, and is a schematic cross-sectional view showing a case where the step is provided on the top side. FIG. 13 is a schematic cross-sectional view showing another example of having a step on the outer peripheral surface of the powder compact, and showing a case where the step is provided on the skirt side.

[Problems to be Solved by the Present Disclosure]
When a hollow hemispherical green compact is produced by compression-molding the raw material powder with a mold, portions having different densities may occur. In particular, a density difference is likely to occur between the top portion and the bottom portion. Hereinafter, "hollow hemispherical" may be simply referred to as "hemispherical". If there is a partial difference in density in the green compact, the physical properties will differ depending on the location. For example, when a powder magnet or a powder magnetic core is formed of a hemispherical powder compact using magnet powder or soft magnetic powder as raw material powder, if the density is non-uniform, residual magnetic flux density (Br) and saturation magnetic flux Performance is affected, such as non-uniform magnetic properties such as density (Bs).

Therefore, it is desired to make the density uniform in the hemispherical green compact.

One object of the present disclosure is to provide a method for manufacturing a green compact that can uniformize the density of a hollow hemispherical green compact. Another object of the present disclosure is to provide a hollow hemispherical green compact with a small difference in density between the top portion and the bottom portion.

[Effect of the present disclosure]
The method for producing a green compact according to the present disclosure can uniformize the density of the hollow hemispherical green compact. In addition, the green compact of the present disclosure has a hollow hemispherical shape, and the difference in density between the top portion and the bottom portion is small.

[Description of Embodiments of the Present Disclosure]
First, the embodiments of the present disclosure are listed and described.

(1) A method for manufacturing a green compact according to an embodiment of the present disclosure includes:
A first step of preparing a mold comprising a die that defines a hollow portion on the inner peripheral surface of a cylindrical body, a lower punch that is inserted into the hollow portion, and an upper punch that is inserted into the hollow portion. ,
The inner peripheral surface of the die is
a spherical first inner peripheral surface;
a cylindrical second inner peripheral surface provided on one end side of the first inner peripheral surface in the axial direction;
a cylindrical third inner peripheral surface provided on the other end side in the axial direction of the first inner peripheral surface,
The first inner peripheral surface has an inner diameter that decreases from one axial end to the other axial end,
The second inner peripheral surface has an inner diameter corresponding to the maximum inner diameter of the first inner peripheral surface,
The third inner peripheral surface has an inner diameter corresponding to the minimum inner diameter of the first inner peripheral surface,
The lower punch has a spherical crown-shaped end surface that forms a hemispherical surface by being connected to the first inner peripheral surface,
The end surface of the lower punch has an outer diameter corresponding to the inner diameter of the third inner peripheral surface,
The upper punch is
a cylindrical first upper punch;
a cylindrical second upper punch inserted through the inside of the first upper punch;
The first upper punch has an annular end surface composed of a flat surface,
The end surface of the first upper punch has an outer diameter corresponding to the inner diameter of the second inner peripheral surface,
The second upper punch has a hemispherical end surface protruding toward the lower punch,
The end face of the second upper punch has an outer diameter corresponding to the inner diameter of the first upper punch,
Furthermore,
The end face of the lower punch is positioned within the region surrounded by the third inner peripheral face, the end face of the first upper punch is positioned at the opening of the second inner peripheral face, and the second upper punch Surrounded by the first inner peripheral surface, the second inner peripheral surface and the third inner peripheral surface of the die in a state where the boundary between the end surface and the cylindrical surface of the die is at the same position as the end surface of the first upper punch a second step in which the raw material powder is filled in the hollow portion;
a third step of lowering the first upper punch and the second upper punch with respect to the die and raising the lower punch to compress the raw material powder from above and below to obtain a hollow hemispherical green compact; , provided.

According to the green compact manufacturing method of the present disclosure, the density of the hollow hemispherical green compact can be uniformed by using the specific mold and performing the second step and the third step.

The mold prepared in the first step forms the outer peripheral surface of the hemispherical compact with the first inner peripheral surface of the die and the end surface of the lower punch, and the end surface of the first upper punch and the second upper punch. The opening end face and the inner peripheral face of the green compact are formed at the end face of the green compact. The first inner peripheral surface of the die forms the spherical surface of the hemispherical outer peripheral surface of the green compact, and forms the outside of the hem portion of the green compact. The end face of the lower punch forms the remaining spherical crown surface of the outer peripheral surface of the green compact and forms the outside of the top portion of the green compact.

A spherical zone is a portion of a hemisphere that is sandwiched between the end face of the hemisphere and the plane when the hemisphere is cut by a plane parallel to the end face of the hemisphere, that is, a plane perpendicular to the central axis that connects the center and the vertex of the hemisphere. The crown is the part of the hemisphere on the vertex side of the plane perpendicular to the central axis connecting the center and vertex of the hemisphere. In addition, the top part of the powder compact is parallel to the central axis line connecting the center and the vertex of the hollow hemisphere, and when a line passing through the inner peripheral edge of the open end face of the hollow hemisphere is taken as a dividing line, the center Refers to the part located on the axis side. The bottom part of the powder compact refers to the remaining part located on the side opposite to the central axis from the parting line.

In the second step, the end surface of the lower punch is positioned within a region surrounded by the third inner peripheral surface, the end surface of the first upper punch is positioned at the opening of the second inner peripheral surface, and the second upper punch is positioned in the opening of the second inner peripheral surface. It is assumed that the boundary between the end face of the punch and the cylindrical face is at the same position as the end face of the first upper punch. In this state, the hollow portion surrounded by the first inner peripheral surface, the second inner peripheral surface and the third inner peripheral surface of the die is filled with the raw material powder. As a result, when compressing the raw material powder in the third step described later, the center side of the hollow portion sandwiched between the second upper punch and the lower punch, that is, the upper side of the lower punch, the first upper punch and the first die It is possible to reduce the difference in compressibility of the raw material powder between the outer peripheral side of the hollow portion sandwiched between the inner peripheral surfaces, that is, the first inner peripheral surface side. Since the difference between both compression ratios is small, the density of the green compact can be made uniform.

Since the end surface of the lower punch is positioned within the area surrounded by the third inner peripheral surface, the end surface of the lower punch is positioned below the other end of the first inner peripheral surface. As a result, the raw material powder can be compressed from above and below by the lower punch and the second upper punch in the third step, which will be described later, and the density of the green compact can be easily increased. In addition, if the end face of the lower punch were to protrude into the hollow portion surrounded by the first inner peripheral surface before the raw material powder was compressed, the peripheral edge of the end face of the lower punch would be deformed when the raw material powder was compressed. easily damaged. By positioning the end surface of the lower punch within the region surrounded by the third inner peripheral surface, damage to the peripheral edge of the end surface of the lower punch during compression can be suppressed.

In the third step, the first upper punch and the second upper punch are lowered with respect to the die, and the lower punch is raised to compress the raw material powder from above and below to obtain a hollow hemispherical powder compact. By compressing the raw material powder from the state of the second step to form a hemispherical green compact, the density can be made uniform and the density difference between the top portion and the bottom portion can be reduced.

(2) As one embodiment of the method for producing a compact according to the present disclosure,
The difference between the compression rate of the raw material powder compressed between the first upper punch and the die and the compression rate of the raw material powder compressed between the second upper punch and the lower punch is 50. % or less.

The absolute value of the difference between the compressibility of the raw material powder compressed between the first upper punch and the die and the compressibility of the raw material powder compressed between the second upper punch and the lower punch is within the above range. As a result, the density of the powder compact can be made uniform, and the density difference between the top portion and the bottom portion can be reduced.

Each compressibility can be obtained from the state of the mold before compressing the raw material powder in the second step and the state of the mold after compressing the raw material powder in the third step. Specifically, it can be obtained as follows.

In the state of the die before compression, the maximum distance between the end surface of the first upper punch and the first inner peripheral surface of the die is A1, and the distance between the vertices between the end surface of the second upper punch and the end surface of the lower punch is A2. do. Also, in the state of the die after compression, the maximum distance between the end surface of the first upper punch and the first inner peripheral surface of the die is B1, and the distance between the vertices between the end surface of the second upper punch and the end surface of the lower punch is B2. The maximum distance B1 between the end surface of the first upper punch and the first inner peripheral surface of the die refers to the distance between the end surface of the first upper punch and the other end of the first inner peripheral surface. Then, the ratio of the maximum distance A1 before compression and the maximum distance B1 after compression ([B1/A1] × 100) is calculated as the compression rate C1 of the raw material powder between the first upper punch and the die ( %). Further, the ratio of the vertex distance A2 before compression and the vertex distance B2 after compression ([B2/A2] × 100) is the compression of the raw material powder between the second upper punch and the lower punch. Let the rate be C2 (%).

(3) As one aspect of the method for producing a compact according to the present disclosure,
In the second step, after filling the raw material powder into the hollow portion of the die, the peripheral edge of the end surface of the lower punch is lowered below the other end of the first inner peripheral surface, and the lower punch locating the end face of in the region surrounded by the third inner peripheral face.

The filling of the raw material powder is carried out by inserting a lower punch into the hollow portion of the die, engaging the lower punch with the third inner peripheral surface, and filling the hollow portion with the raw material powder. After filling the raw material powder, the end surface of the lower punch is lowered below the other end of the first inner peripheral surface so that the upper surface of the raw material powder filled on the upper side of the lower punch is pushed into the opening of the second inner peripheral surface. It can be sunk more to provide a concave space. By providing such a concave space, it becomes easier to insert the end surface of the second upper punch into the hollow portion of the die.

(4) As one aspect of the method for producing a compact according to the present disclosure,
In the second step, after filling the raw material powder into the hollow portion of the die, before inserting the end surface of the second upper punch into the hollow portion of the die, the end surface of the first upper punch The step of partially closing the opening of the second inner peripheral surface may be included.

Before inserting the end face of the second upper punch into the hollow part of the die, the end face of the second upper punch is hollowed by partially closing the opening of the second inner peripheral face with the end face of the first upper punch. It is possible to prevent the raw material powder from leaking from the opening of the second inner peripheral surface when the second inner peripheral surface is inserted into the opening. By inserting the end surface of the second upper punch into the hollow portion of the die, the end surface of the second upper punch can be pressed against the raw material powder. By pressing the end surface of the second upper punch against the raw material powder, the raw material powder filled in the upper side of the lower punch is caused to flow toward the first inner peripheral surface of the die. As a result, it is possible to uniformly control the filling amount of the raw material powder on the upper side of the lower punch and the first inner peripheral surface side of the die, and the difference in the filling amount becomes smaller.

(5) As one aspect of the method for producing a compact according to (4) above,
In the second step, after partially closing the opening of the second inner peripheral surface, the second upper punch is lowered to insert the end surface of the second upper punch into the hollow portion, The step of aligning the boundary between the end surface of the second upper punch and the cylindrical surface with the position of the end surface of the first upper punch may be included.

With the end surface of the first upper punch partially closing the opening of the second inner peripheral surface, the second upper punch is lowered to press the end surface of the second upper punch against the raw material powder, thereby forming the upper side of the lower punch. The raw material powder filled in the die can be made to flow to the first inner peripheral surface side of the die. In this state, the raw material powder is not compressed and has a low density. Therefore, it is possible to flow the raw material powder on the upper side of the lower punch to the outer peripheral side. By pressing the end surface of the second upper punch against the raw material powder, it is possible to uniformly control the filling amount of the raw material powder on the upper side of the lower punch and the first inner peripheral surface side of the die, and the difference in filling amount is become smaller.

(6) As one aspect of the method for producing a compact according to (3) above,
In the second step, the first inner peripheral surface and the second inner peripheral surface are protruded into the hollow portion surrounded by the first inner peripheral surface of the die with the peripheral edge of the end surface of the lower punch projecting. and a step of filling the raw material powder into the hollow portion surrounded by .

When the lower punch is positioned so that the first inner peripheral surface of the die and the end surface of the lower punch form a hemispherical surface when filling the raw material powder, the first inner peripheral surface of the die and the end surface of the lower punch constitute the The space becomes hemispherical. The position of the lower punch when the first inner peripheral surface of the die and the end surface of the lower punch form a hemispherical surface is defined as the reference position. When the raw material powder is filled in the hollow portion with the lower punch positioned at the reference position, the filling depth on the center side of the hollow portion, that is, the upper side of the lower punch, is the outer peripheral side of the hollow portion, that is, the first inner periphery. It becomes larger than the filling depth on the face side. On the other hand, when filling the raw material powder, when the peripheral edge of the end face of the lower punch is projected into the hollow portion surrounded by the first inner peripheral surface, the opening of the second inner peripheral surface, that is, the upper surface of the die The distance from the opening of the lower punch to the end face of the lower punch becomes smaller. Therefore, the filling depth above the lower punch can be reduced. Therefore, the difference in filling amount of the raw material powder between the upper side of the lower punch and the first inner peripheral surface side of the die is reduced.

(7) As one form of the method for producing a compact according to (6) above,
When the distance from the opening of the second inner peripheral surface to the peripheral edge of the end surface of the lower punch when the first inner peripheral surface of the die and the end surface of the lower punch form a hemispherical surface is 100,
Said 2nd process WHEREIN: The protrusion amount which makes the peripheral edge of the end surface of said lower punch protrude in said hollow part enclosed by said 1st inner peripheral surface is 10-70.

By setting the amount of protrusion of the lower punch from the reference position to 10 or more and 70 or less, the difference in filling amount of the raw material powder between the upper side of the lower punch and the first inner peripheral surface side of the die can be sufficiently reduced.

(8) As one embodiment of the method for producing a compact according to (3), (6) or (7) above,
Said 2nd process WHEREIN: The lowering amount which makes the peripheral edge of the end surface of said lower punch descend from the other end of said 1st inner peripheral surface is 1 mm or more and 10 mm or less.

By setting the amount of descent of the lower punch to 1 mm or more, it is easy to sufficiently secure the recessed space on the upper surface of the raw material powder filled on the upper side of the lower punch. On the other hand, if the lower punch is lowered too much, when the end surface of the second upper punch is pressed against the raw material powder as described above, it becomes difficult to flow the raw material powder filled above the lower punch toward the first inner peripheral surface of the die. . In addition, if the lower punch is lowered too much, when the raw material powder is compressed in the third step, the difference in the compressibility of the raw material powder between the upper side of the lower punch and the first inner peripheral surface side of the die becomes large. Cracks are likely to occur at the boundary between the top portion and the bottom portion of the green compact. Therefore, it is preferable that the lower punch is lowered by 10 mm or less. As a result, it is easy to uniformize the compressibility during compression while ensuring the fluidity of the raw material powder during pressing.

(9) As one aspect of the method for producing a compact according to the present disclosure,
The ratio of the outer diameter of the lower punch to the outer diameter of the second upper punch is 0.8 or more and 1.2 or less.

Since the ratio of the outer diameter of the lower punch to the outer diameter of the second upper punch is 0.8 or more and 1.2 or less, when the lower punch is lowered in the second step as described above, the upper side of the lower punch It is easy to provide the recessed space having a size corresponding to the outer diameter of the second upper punch on the upper surface of the filled raw material powder.

(10) As one embodiment of the method for producing a compact according to the present disclosure,
In the third step, the molding pressure for compressing the raw material powder may be set to 980 MPa or higher.

By setting the molding pressure to 980 MPa or more, the density of the green compact can be increased. This can improve the physical properties of the green compact.

(11) As one aspect of the method for producing a compact according to the present disclosure,
In the third step, the position of the peripheral edge of the end surface of the lower punch at the end of compression may be within a range of 0.1 mm or less downward from the other end of the first inner peripheral surface.

By locating the peripheral edge of the end surface of the lower punch at the end of compression below the other end of the first inner peripheral surface, damage to the peripheral edge of the end surface of the lower punch can be easily suppressed. In addition, by setting the position of the peripheral edge of the end surface of the lower punch within a range of 0.1 mm or less downward from the other end of the first inner peripheral surface, the step provided on the outer peripheral surface of the hemispherical compact is 0. .1 mm or less. If the step on the outer peripheral surface is 0.1 mm or less, it can be considered that there is no step, and the outer peripheral surface of the green compact can be configured as a smooth hemispherical surface. Since the step on the outer peripheral surface of the green compact is 0.1 mm or less, when a separate hemispherical member is assembled to the outside of the green compact, the outer peripheral surface of the green compact and the inner peripheral surface of the separate member can be It is possible to suppress the provision of a gap therebetween.

(12) As one aspect of the method for producing a compact according to the present disclosure,
In the third step, the position of the peripheral edge of the end surface of the lower punch at the end of compression is set to be within a range of more than 0.1 mm and 0.3 mm or less downward from the other end of the first inner peripheral surface. be done.

By locating the peripheral edge of the end surface of the lower punch at the end of compression below the other end of the first inner peripheral surface, damage to the peripheral edge of the end surface of the lower punch can be easily suppressed. Further, by setting the position of the peripheral edge of the end surface of the lower punch to within a range of more than 0.1 mm and not more than 0.3 mm downward from the other end of the first inner peripheral surface, the outer peripheral surface of the hemispherical green compact has a thickness of 0.3 mm. A step of more than 1 mm and 0.3 mm or less can be provided. Since there is a step of more than 0.1 mm on the outer peripheral surface of the powder compact, this step can be used for positioning with respect to the other member when assembling a separate hemispherical member to the outside of the compact. In this case, a stepped portion corresponding to the stepped portion is provided on the inner peripheral surface of the separate member. When the position of the peripheral edge of the end face of the lower punch at the end of compression is positioned below the other end of the first inner peripheral surface, the compression ratio on the upper side of the lower punch decreases, but if it is within 0.3 mm , has little impact on compression ratio and is practically no problem.

(13) As one aspect of the method for producing a compact according to the present disclosure,
The raw material powder includes magnetic powder made of hydrogenated powder obtained by hydrogenating a rare earth-iron alloy containing a rare earth element and iron,
After the third step, a step of dehydrogenating the green compact may be provided.

By using magnet powder made of hydrogenated rare earth-iron alloy powder as raw material powder, it is possible to obtain a high-density green compact containing hydrogenated powder. By dehydrogenating the hydrogenated powder green compact, a high-density green compact containing the rare earth-iron alloy powder can be obtained. A rare earth-iron alloy compact can be used as a rare earth-iron magnet.

The reason why the density of the powder compact can be increased by using the hydrogenated rare earth-iron alloy powder is as follows. When a rare earth-iron based alloy is hydrotreated, it undergoes a disproportionation reaction and decomposes into phases of rare earth element hydrides and iron-bearing iron-bearing substances. That is, the hydrotreated alloy has a mixed structure of rare earth hydride phases and iron-bearing iron-bearing phases. Hydrogenated powders of rare earth-iron alloys contain a soft iron-containing phase in the structure, so plastic deformation is easier than unhydrogenated rare earth-iron alloy powders, resulting in poor formability. Excellent. Therefore, when the hydrogenated rare earth-iron alloy powder is used, it is possible to increase the density of the powder compact.

By dehydrogenating the green compact of the hydrogenated powder, hydrogen is released from the hydride of the rare earth element, causing a recombination reaction and returning to the original state of the rare earth-iron alloy. Therefore, a hemispherical rare earth-iron alloy magnet made of the rare earth-iron alloy green compact is obtained.

(14) The green compact according to the embodiment of the present disclosure is
has a hollow hemispherical shape,
When a line parallel to the central axis connecting the center and the vertex of the hollow hemisphere and passing through the inner peripheral edge of the open end face of the hollow hemisphere is defined as a parting line, the part located on the central axis side of the parting line The top part and the remaining part located on the opposite side of the central axis from the parting line are the skirt part,
A difference in relative density between the top portion and the bottom portion is 5% or less.

According to the green compact of the present disclosure, the density difference between the top portion and the bottom portion is small because it has a hollow hemispherical shape and the difference in relative density between the top portion and the bottom portion is 5% or less. Accordingly, the compacts of the present disclosure have uniform densities and uniform physical properties.

(15) As one form of the green compact of the present disclosure,
For example, the relative density of the entire green compact is 80% or more.

A compact having a relative density of 80% or more has a high density and excellent physical properties.

(16) As one form of the green compact of the present disclosure,
A step of 0.1 mm or less is provided on the outer peripheral surface of the powder compact.

When the step provided on the outer peripheral surface of the green compact is 0.1 mm or less, there is substantially no step, and the outer peripheral surface of the green compact can be configured as a smooth hemispherical surface. Since the step on the outer peripheral surface of the green compact is 0.1 mm or less, when a separate hemispherical member is assembled to the outside of the green compact, there is a gap between the outer peripheral surface of the green compact and the inner peripheral surface of the separate member. It is possible to suppress the provision of a gap in the

(17) As one form of the green compact of the present disclosure,
It is mentioned that a step of more than 0.1 mm and less than or equal to 0.3 mm is provided on the outer peripheral surface of the green compact.

Since the step of more than 0.1 mm is provided on the outer peripheral surface of the green compact, the step can be used for positioning with respect to the separate hemispherical member when assembling it to the outside of the green compact. If the step on the outer peripheral surface of the green compact is 0.3 mm or less, the gap provided between the outer peripheral surface of the green compact and the inner peripheral surface of the separate member can be reduced.

(18) As one form of the green compact of the present disclosure,
It is mentioned that the thickness of the powder compact is 1/30 times or more and 1/2 times or less of the outer peripheral radius of the opening end face.

When the thickness of the powder compact is within the above range, it is easy to achieve uniform density and high density.

(19) As one form of the green compact of the present disclosure,
It includes a powder of a rare earth-iron alloy containing a rare earth element and iron.

A hemispherical green compact containing rare earth-iron alloy powder can be used as a rare earth-iron magnet. A hemispherical rare earth-iron alloy magnet made of a rare earth-iron alloy compact can be used, for example, as a magnet that constitutes a spherical motor used in the joints of a robot.

[Details of the embodiment of the present disclosure]
Hereinafter, a method for manufacturing a green compact according to an embodiment of the present disclosure and a specific example of the green compact will be described with reference to the drawings. The same reference numerals in the drawings indicate the same names. The present invention is not limited to these exemplifications, but is indicated by the scope of the claims, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims.

<Embodiment>
[Method for producing green compact]
A method for manufacturing a green compact according to an embodiment will be described with reference to FIGS. 1A, 1B, and 2 to 7. FIG. The method for producing a green compact according to the embodiment comprises compressing the raw material powder 100p with the mold 1 to produce the hollow hemispherical green compact 100 (see FIGS. 8 and 9). The green compact production method according to the embodiment is characterized by the mold 1 to be used and the operation of the mold 1 . First, the configuration of the mold 1 will be described with reference to FIGS. 1A and 1B, and then the operation of the mold 1 will be described mainly with reference to FIGS. 2 to 7. FIG.

(Mold)
As shown in FIG. 1A, the mold 1 includes a die 10 having a hollow portion 10h, a lower punch 20 inserted into the hollow portion 10h, and an upper punch 30 inserted into the hollow portion 10h. The die 10 is a tubular body, and an inner peripheral surface 10i of the tubular body forms a hollow portion 10h (see also FIG. 1B). The inner peripheral surface 10i is composed of a first inner peripheral surface 11, a second inner peripheral surface 12, and a third inner peripheral surface 13, as shown in FIG. 1B. The upper punch 30 has a first upper punch 31 and a second upper punch 32, as shown in FIG. 1A. The mold 1 forms an outer peripheral surface 102 of a hemispherical green compact 100 (see FIGS. 8 and 9) with a first inner peripheral surface 11 of the die 10 and a concave end surface 21 of the lower punch 20, and a first upper The annular end face 31c of the punch 31 and the convex end face 32h of the second upper punch 32 shape the opening end face 103 and the inner peripheral face 101 of the compact 100 . Each element will be described in detail below.

The inner peripheral surface 10i of the die 10 has a first inner peripheral surface 11, a second inner peripheral surface 12, and a third inner peripheral surface 13, as shown in FIG. 1B. The first inner peripheral surface 11 is a spherical belt-like surface whose inner diameter decreases from one axial end 11a to the other axial end 11b. The axial direction refers to the direction of the central axis _C10 of the first inner peripheral surface 11 . This central axis _C10 is indicated by a dashed line in FIG. 1B. The direction of the central axis _C10 is the vertical direction on the paper surface of FIG. 1B. The one end 11a side of the first inner peripheral surface 11 is the upper side of the paper surface of FIG. 1B. The other end 11b side of the first inner peripheral surface 11 is the lower side of the paper surface of FIG. 1B. The second inner peripheral surface 12 is provided on the one end 11a side of the first inner peripheral surface 11 . The second inner peripheral surface 12 is a cylindrical surface having the same inner diameter (d ₁₂ in FIG. 1B) as the maximum inner diameter of the first inner peripheral surface 11 . The third inner peripheral surface 13 is provided on the other end 11b side of the first inner peripheral surface 11 . The third inner peripheral surface 13 is a cylindrical surface having the same inner diameter (d ₁₃ in FIG. 1B) as the minimum inner diameter of the first inner peripheral surface 11 . In the following description, one end 11a side with a large inner diameter of the first inner peripheral surface 11, i.e., the second inner peripheral surface 12 side, is upper, and the other end 11b side with a smaller inner diameter, i.e., the third inner peripheral surface 13 side is lower. .

The first inner peripheral surface 11 of the die 10 forms a spherical surface of the hemispherical outer peripheral surface 102 of the green compact 100 (see FIGS. 8 and 9), and forms the outer periphery of the skirt portion 120 of the green compact 100. shape the surface. The vertical length of the second inner peripheral surface 12 may be, for example, 2 mm or more and 10 mm or less. The vertical length of the third inner peripheral surface 13 may be, for example, 5 mm or more, or 40 mm or more.

The lower punch 20 is a cylindrical member. The lower punch 20 is inserted from the lower side of the hollow portion 10 h of the die 10 and fitted to the third inner peripheral surface 13 . As shown in FIG. 1A, the lower punch 20 has a crown-shaped concave end surface 21 that forms a hemispherical surface by connecting to the first inner peripheral surface 11 . The concave end face 21 of the lower punch 20 is the remaining spherical crown excluding the spherical zone surface formed by the first inner peripheral surface 11 of the die 10 in the outer peripheral surface 102 of the green compact 100 (see FIGS. 8 and 9). The surface is molded, and the outer peripheral surface of the top portion 110 of the green compact 100 is molded. The lower punch 20 has an outer diameter D ₂₀ corresponding to the inner diameter d ₁₃ (see FIG. 1B) of the third inner peripheral surface 13 of the die 10 . The outer diameter D ₂₀ of the lower punch 20 is substantially the same as the inner diameter d ₁₃ of the third inner peripheral surface 13 . The term "substantially identical" means that the error is within -0.3% to -0.02%.

In the mold 1, the first inner peripheral surface 11 of the die 10 and the concave end surface 21 of the lower punch 20 form a hemispherical surface for molding the outer peripheral surface 102 of the compact 100 (see FIG. 7). The radius R11 of the first inner peripheral surface 11 of the die 10 and the radius _R21 of the concave end surface 21 of the lower punch 20 are equal to the radius of the outer peripheral surface 102 of the green compact ₁₀₀ to be molded. The radius _R11 of the first inner peripheral surface 11 and the radius _R21 of the concave end surface 21 are substantially the same. As shown in FIG. 1A, the position of the lower punch 20 when the first inner peripheral surface 11 of the die 10 and the concave end surface 21 of the lower punch 20 form a hemispherical surface is defined as a reference position _P0 .

The first upper punch 31 is a cylindrical member. The first upper punch 31 has an annular end face 31c. The annular end surface 31c is configured as a flat surface. The shape of the annular end surface 31c is annular. The annular end face 31c of the first upper punch 31 forms the annular open end face 103 of the green compact 100 (see FIGS. 8 and 9). The first upper punch 31 has an outer diameter D ₃₁ corresponding to the inner diameter d ₁₂ of the second inner peripheral surface 12 of the die 10 (see FIG. 1B). The outer diameter D ₃₁ of the first upper punch 31 is substantially the same as the inner diameter d ₁₂ of the second inner peripheral surface 12 . "Substantially identical" means that the error is within -2%. The inner diameter _d12 of the second inner peripheral surface 12 is equal to the diameter of the outer peripheral surface 102 of the green compact 100 to be molded and the outer diameter of the opening end face 103 . The thickness of the first upper punch 31 is substantially the same as the thickness of the open end face 103 of the green compact 100, that is, the width in the radial direction. The term "substantially identical" means that the error is within +5%. The thickness of the first upper punch 31 is half the difference between the inner and outer diameters of the first upper punch 31 .

The second upper punch 32 is a cylindrical member. The second upper punch 32 has a hemispherical convex end face 32h protruding toward the lower punch 20 . A convex end surface 32h of the second upper punch 32 forms a hemispherical inner peripheral surface 101 of the green compact 100 (see FIGS. 8 and 9). The second upper punch 32 has an outer diameter D ₃₂ corresponding to the inner diameter d ₃₁ of the first upper punch 31 . The outer diameter D ₃₂ of the second upper punch 32 is substantially the same as the inner diameter d ₃₁ of the first upper punch 31 . “Substantially identical” means that the error is within −0.3% to −0.02%. The outer diameter D ₃₂ of the second upper punch 32 is equal to the diameter of the inner peripheral surface 101 of the green compact 100 and the inner diameter of the open end surface 103 .

The radius of the convex end surface 32h of the second upper punch 32, when the raw material powder is compressed (see FIG. 7), is the one end 11a of the first inner peripheral surface 11, the annular end surface 31c of the first upper punch 31, and the second The center of the hemispherical surface formed by the first inner peripheral surface 11 and the concave end surface 21 of the lower punch 20 when the boundary 32d between the hemispherical surface that is the convex end surface 32h of the upper punch 32 and the cylindrical surface is at the same position. and the center of the hemispherical surface of the convex end surface 32h. In this case, a hollow hemispherical green compact 100 having a uniform thickness can be formed. Here, the thickness is measured at three points at equal intervals on a line along the circumferential direction passing through the vertex of the green compact 100, and if the difference between the minimum value and the maximum value is 0.3 mm or less, the thickness is substantially are assumed to be uniform. Further, when the raw material powder is compressed (see FIG. 7), even if the center of the hemispherical surface formed by the first inner peripheral surface 11 and the concave end surface 21 does not coincide with the center of the hemispherical surface of the convex end surface 32h, Well, the thickness of the green compact 100 does not have to be uniform. That is, the inner peripheral surface 101 and the outer peripheral surface 102 of the powder compact 100 (see FIGS. 8 and 9) do not have to have similar shapes.

The second upper punch 32 is slidably fitted inside the first upper punch 31 . The first upper punch 31 and the second upper punch 32 can move up and down independently.

The second upper punch 32 is provided so as to face the lower punch 20 . The ratio of the outer diameter D20 of the lower punch 20 to the outer diameter _D32 of the second upper punch ₃₂ ( _D20 / _D32 ) is, for example, 0.8 or more and 1.2 or less, and further 0.9 or more and 1.2 or less. It is mentioned that it is. In FIG. 1A, the outer diameter D 32 of the second upper punch ₃₂ and the outer diameter D ₂₀ of the lower punch 20 are substantially the same, and D ₂₀ /D ₃₂ is one.

The green compact production method according to the embodiment includes the first step of preparing the above-described mold 1 (see FIG. 1), the second step shown below, and the third step.
In the second step, the lower punch 20, the first upper punch 31 and the second upper punch 32 are positioned at specific positions with respect to the die 10, and the raw material powder 100p is placed in the hollow portion 10h of the die 10. Let it be filled (see FIG. 2).
The third step is to lower the first upper punch 31 and the second upper punch 32 with respect to the die 10 and raise the lower punch 20 to compress the raw material powder 100p from above and below (see FIG. 7).
The second step and the third step will be described in detail below.

(Second step)
In the second step, as shown in FIG. 2, the concave end surface 21 of the lower punch 20, the annular end surface 31c of the first upper punch 31, and the boundary 32d of the second upper punch 32 are brought into a specific state. The concave end surface 21 of the lower punch 20 is located within the area surrounded by the third inner peripheral surface 13 . The annular end surface 31c of the first upper punch 31 is located in the opening 12o of the second inner peripheral surface 12. As shown in FIG. A boundary 32 d between a hemispherical surface and a cylindrical surface, which is a convex end surface 32 h of the second upper punch 32 , is located at the same position as the annular end surface 31 c of the first upper punch 31 . Specifically, the recessed end surface 21 of the lower punch 20 is positioned such that the peripheral edge of the recessed end surface 21 is located 1 mm or more and 10 mm or less, further 2 mm or more and 8 mm or less below the other end 11b of the first inner peripheral surface 11. . In this state, the hollow portion 10h (see FIG. 1A) surrounded by the first inner peripheral surface 11, the second inner peripheral surface 12 and the third inner peripheral surface 13 of the die 10 is filled with the raw material powder 100p. .

The second step may include any of steps A to D shown below.
In the A process, the raw material is inserted into the hollow portion 10h of the die 10 with the concave end surface 21 of the lower punch 20 protruding into the hollow portion 10h (see FIG. 1A) surrounded by the first inner peripheral surface 11 of the die 10 (see FIG. 1A). Fill with 100 p of powder (see Figure 3).
In step B, the concave end surface 21 of the lower punch 20 is lowered below the other end 11b of the first inner peripheral surface 11 of the die 10 (see FIG. 4).
In step C, the annular end surface 31c of the first upper punch 31 partially closes the opening 12o of the second inner peripheral surface 12 of the die 10 (see FIG. 5).
In step D, the convex end face 32h of the second upper punch 32 is inserted into the hollow portion 10h (see FIG. 1A) of the die 10 (see FIG. 6).
In this example, the case where the second step includes all of the steps A to D will be described.

(A process)
In the A process, as shown in FIG. 3, a lower punch 20 is inserted from the lower side of the hollow portion 10h (see FIG. 1A) of the die 10 and fitted to the third inner peripheral surface 13. A hollow portion 10h surrounded by the first inner peripheral surface 11 and the second inner peripheral surface 12 is filled with the raw material powder 100p. In step A, when the raw material powder 100p is filled, the peripheral edge of the concave end surface 21 of the lower punch 20 protrudes into the hollow portion 10h surrounded by the first inner peripheral surface 11 of the die 10 . That is, the lower punch 20 is positioned above the reference position P ₀ (see FIG. 1A).

As shown in FIG. 1A, when the lower punch 20 is positioned at the reference position _P0 and a hemispherical space is formed by the first inner peripheral surface 11 and the concave end surface 21, the central side of the hollow portion 10h, that is, the lower punch The filling depth of the upper side of 20 becomes larger than the filling depth of the outer peripheral side of the hollow part 10h, ie, the first inner peripheral surface 11 side. On the other hand, as shown in FIG. 3, by protruding the peripheral edge of the concave end surface 21 of the lower punch 20 into the hollow portion 10h (see FIG. 1A) surrounded by the first inner peripheral surface 11, the lower Compared to when the punch 20 is positioned at the reference position _P0 , the distance from the opening 12o of the second inner peripheral surface 12, that is, the opening of the upper surface of the die 10 to the concave end surface 21 of the lower punch 20 becomes smaller. That is, the filling depth on the upper side of the lower punch 20 becomes smaller. Therefore, when the raw material powder 100p is filled, the difference in filling amount of the raw material powder 100p between the upper side of the lower punch 20 and the first inner peripheral surface 11 side of the die 10 becomes small.

Let 100 be the distance L ₀ (see FIG. 1A) from the opening 12o of the second inner peripheral surface 12 to the peripheral edge of the concave end surface 21 of the lower punch 20 when the lower punch 20 is positioned at the reference position P ₀ . At this time, in step A of the second step, the amount of protrusion _P1 projected into the hollow portion 10h (see FIG. 1A) of the concave end face 21 of the lower punch 20 should be 10 or more and 70 or less from the reference position _P0 . is mentioned. As a result, the difference in filling amount of the raw material powder 100p between the upper side of the lower punch 20 and the side of the first inner peripheral surface 11 of the die 10 can be made sufficiently small. The protruding amount _P1 of the concave end surface 21 of the lower punch 20 is preferably 15 or more and 65 or less, more preferably 20 or more and 60 or less.

The outer diameter _D20 of the lower punch 20 may be determined, for example, according to the thickness of the green compact 100 (see FIGS. 8 and 9) to be molded. Specifically, the outer diameter _D20 of the lower punch 20 is reduced when the thickness is increased, and the outer diameter _D20 of the lower punch 20 is increased when the thickness is decreased. Also, the outer diameter D20 of the lower punch ₂₀ and the outer diameter D32 of the second upper punch ₃₂ are preferably matched.

(B process)
In step B, after filling the raw material powder 100p into the hollow portion 10h (see FIG. 1A) of the die 10, as shown in FIG. The lower punch 20 is lowered below the end 11b so that the concave end surface 21 of the lower punch 20 is positioned within the area surrounded by the third inner peripheral surface 13. As shown in FIG. That is, the lower punch 20 is positioned below the reference position P ₀ (see FIG. 1A). As a result, the upper surface of the raw material powder 100p filled on the upper side of the lower punch 20 is lowered from the opening 12o of the second inner peripheral surface 12 to form the recessed space 15. As shown in FIG. By providing such a concave space 15, it becomes easier to insert the convex end surface 32h of the second upper punch 32 into the hollow portion 10h in the D process (see FIG. 6). Further, by lowering the concave end surface 21 of the lower punch 20 below the other end 11b of the first inner peripheral surface 11, the lower punch 20 and the second upper punch 32 are separated in the third step (see FIG. 7). The raw material powder can be compressed from above and below, and the density of the green compact 100 can be easily increased. Further, when the concave end surface 21 of the lower punch 20 is projected into the hollow portion 10h surrounded by the first inner peripheral surface 11, the peripheral edge of the concave end surface 21 of the lower punch 20 is deformed when the raw material powder 100p is compressed. and easily damaged. By positioning the concave end surface 21 of the lower punch 20 within the area surrounded by the third inner peripheral surface 13, deformation of the peripheral edge of the concave end surface 21 during compression can be suppressed. Therefore, damage to the periphery of the concave end surface 21 can be suppressed.

In step B of the second step, the descent amount _P2 for lowering the peripheral edge of the concave end surface 21 of the lower punch 20 from the other end 11b of the first inner peripheral surface 11 is set to 1 mm or more and 10 mm or less, further 2 mm or more and 8 mm or less. Things are mentioned. By setting the descending amount _P2 of the lower punch 20 to 1 mm or more, it is easy to sufficiently secure the recessed space 15 on the upper surface of the raw material powder 100p filled on the upper side of the lower punch 20 . On the other hand, if the lower punch 20 is lowered too much, when the convex end surface 32h of the second upper punch 32 is pressed against the raw material powder 100p in step D (see FIG. 6), the raw material powder 100p filled above the lower punch 20 becomes difficult to flow toward the first inner peripheral surface 11 of the die 10 . Also, if the lower punch 20 is lowered too much, the raw material powder 100p will be compressed between the upper side of the lower punch 20 and the first inner peripheral surface 11 side of the die 10 when the raw material powder 100p is compressed in the third step (see FIG. 7). The difference in compression rate becomes large. Therefore, cracks are likely to occur at the boundary between the top portion 110 and the bottom portion 120 of the powder compact 100 (see FIGS. 8 and 9). Therefore, the descending amount _P2 of the lower punch 20 is preferably 10 mm or less. This makes it easy to uniformize the compressibility during compression while ensuring fluidity of the raw material powder 100p during pressing.

When the ratio of the outer diameter D20 of the lower punch ₂₀ to the outer diameter _D32 of the second upper punch 32 ( _D20 / _D32 ) is 0.8 or more and 1.2 or less (see FIG. 1A), the lower When the punch 20 is lowered, the recessed space 15 having a size corresponding to the outer diameter _D32 of the second upper punch 32 can be easily provided on the upper surface of the raw material powder 100p filled on the upper side of the lower punch 20.

(C process)
In the C process, the position of the lower punch 20 in the B process (see FIG. 4) is maintained. When positioned on the lower side, as shown in FIG. 5, the annular end surface 31c of the first upper punch 31 partially closes the opening 12o of the second inner peripheral surface 12. As shown in FIG. Specifically, the annular end surface 31c of the first upper punch 31 is lowered to the position of the opening 12o of the second inner peripheral surface 12, and the annular end surface 31c of the first upper punch 31 is brought into contact with the raw material powder 100p. As a result, when the convex end surface 32h of the second upper punch 32 is inserted into the hollow portion 10h (see FIG. 1A) in step D (see FIG. 6), the raw material powder 100p is pushed into the opening of the second inner peripheral surface 12. Leakage from 12o can be suppressed. In FIG. 5, the annular end surface 31c of the first upper punch 31 and the upper surface of the die 10 are flush with each other. Note that the annular end surface 31c of the first upper punch 31 may be located slightly below the opening 12o of the second inner peripheral surface 12 . The annular end surface 31c of the first upper punch 31 may be positioned, for example, about 0.5 mm to 1 mm below the opening 12o of the second inner peripheral surface 12. As shown in FIG. In step C, the convex end surface 32h of the second upper punch 32 is kept from contacting the raw material powder 100p.

(D process)
In the D process, the position of the first upper punch 31 in the C process (see FIG. 5) is maintained, specifically, the annular end surface 31c of the first upper punch 31 is the opening of the second inner peripheral surface 12. 6, the second upper punch 32 is lowered to insert the convex end surface 32h into the hollow portion 10h (see FIG. 1A). A boundary 32 d between a hemispherical surface and a cylindrical surface, which is a convex end surface 32 h of the second upper punch 32 , is aligned with the position of the annular end surface 31 c of the first upper punch 31 . By pressing the convex end surface 32h of the second upper punch 32 against the raw material powder 100p, the raw material powder 100p filled in the upper side of the lower punch 20 is caused to flow toward the first inner peripheral surface 11 of the die 10. For convenience of explanation, FIG. 6 shows the flowing direction of the raw material powder 100p with a black arrow. Note that the direction of the black arrow is an example. In this state, the raw material powder 100p is not compressed and has a low density. Therefore, it is possible to flow the raw material powder 100p on the upper side of the lower punch 20 to the outer peripheral side. By pressing the convex end face 32h of the second upper punch 32 against the raw material powder 100p, it is possible to uniformly control the filling amount of the raw material powder on the upper side of the lower punch 20 and on the side of the first inner peripheral surface 11 of the die 10. , and the difference in filling amount becomes smaller.

When the ratio of the outer diameter D20 of the lower punch ₂₀ to the outer diameter _D32 of the second upper punch 32 ( _D20 / _D32 ) is 0.8 or more and 1.2 or less (see FIG. 1A), the second upper punch By pressing the convex end surface 32h of 32 against the raw material powder 100p, the raw material powder 100p on the upper side of the lower punch 20 is easily made to flow to the outer peripheral side. Therefore, it is easy to adjust the difference in filling amount of the raw material powder between the upper side of the lower punch 20 and the side of the first inner peripheral surface 11 of the die 10 .

The second step (see FIG. 2) described above can be reached by going through the above-mentioned A step to the D step.

(Third step)
In the third step, as shown in FIG. 7, the first upper punch 31 and the second upper punch 32 are lowered with respect to the die 10, and the lower punch 20 is raised to raise and lower the raw material powder 100p (see FIG. 2). to obtain a hollow hemispherical green compact 100 . Specifically, the peripheral edge of the concave end surface 21 of the lower punch 20 is raised to the other end 11b side of the first inner peripheral surface 11 . Also, the annular end surface 31c of the first upper punch 31 is lowered to the one end 11a side of the first inner peripheral surface 11, and the convex end surface 32h of the second upper punch 32 is surrounded by the first inner peripheral surface 11. 10h (see FIG. 1A).

The annular end face 31c of the first upper punch 31 is preferably stopped slightly above the one end 11a of the first inner peripheral face 11 . It is preferable that the annular end surface 31c of the first upper punch 31 is stopped, for example, about 0.5 mm to 1 mm above the one end 11a of the first inner peripheral surface 11. As shown in FIG. This prevents the annular end surface 31c of the first upper punch 31 from interfering with the first inner peripheral surface 11, thereby suppressing both the annular end surface 31c and the first inner peripheral surface 11 from being damaged.

Moreover, the second upper punch 32 is preferably lowered so that the boundary 32d between the hemispherical surface and the cylindrical surface, which is the convex end surface 32h, coincides with the position of the one end 11a of the first inner peripheral surface 11. As shown in FIG. If the second upper punch 32 is lowered too much, a cylindrical surface will be formed on the opening side of the inner peripheral surface 101 (see FIGS. 8 and 9) of the green compact 100 . On the other hand, if the second upper punch 32 is not sufficiently lowered, a gap is formed between the convex end surface 32h of the second upper punch 32 and the inner peripheral surface of the first upper punch 31, and the opening end surface 103 of the green compact 100 is formed. burrs are likely to occur.

In this example, the position of the boundary 32d of the second upper punch 32 and the annular end surface 31c of the first upper punch 31 are aligned, and the convex end surface 32h of the second upper punch 32 protrudes from the first upper punch 31. , the first upper punch 31 and the second upper punch 32 are lowered synchronously.

By forming the hemispherical compact 100 through the second step and the third step, the density of the compact 100 can be made uniform.

When compressing the raw material powder 100p (see FIG. 2), the compression rate of the raw material powder 100p compressed between the first upper punch 31 and the die 10 and the compression ratio between the second upper punch 32 and the lower punch 20 The absolute value of the difference from the compressibility of 100 p of the raw material powder to be compressed is 50% or less. When the difference in compressibility is within the above range, the density of the green compact 100 can be made uniform, and the density difference between the top portion 110 and the bottom portion 120 can be reduced.

Each compressibility is the state of the mold 1 before compressing the raw material powder 100p in the second step (see FIG. 2) and the state of the mold 1 after compression in the third step (see FIG. 7). can be obtained from the state. In the state of the die 1 before compression, the maximum distance between the annular end surface 31c of the first upper punch 31 and the first inner peripheral surface 11 of the die 10 is A1, and the convex end surface 32h of the second upper punch 32 and the lower Let A2 be the distance between the vertices of the punch 20 and the concave end face 21 . In the state of the die 1 after compression, the maximum distance between the annular end surface 31c of the first upper punch 31 and the first inner peripheral surface 11 of the die 10 is B1, and the convex end surface 32h of the second upper punch 32 is and the concave end surface 21 of the lower punch 20 is defined as B2. The maximum distance between the annular end surface 31 c of the first upper punch 31 and the first inner peripheral surface 11 is the distance between the annular end surface 31 c and the other end 11 b of the first inner peripheral surface 11 . Then, the ratio ([B1/A1]×100) between the maximum distance A1 before compression and the maximum distance B1 after compression is calculated as the compression rate C1 of the raw material powder 100p between the first upper punch 31 and the die 10. (%). Further, the ratio ([B2/A2]×100) between the vertex distance A2 before compression and the vertex distance B2 after compression is calculated as Let the compression rate be C2 (%).

If the difference in compressibility (C1-C2) is within the above range, the difference in compressibility of the raw material powder 100p between the upper side of the lower punch 20 and the first inner peripheral surface 11 side of the die 10 can be reduced. Uniformity of the density of the body 100 can be achieved. The difference in compressibility is preferably 40% or less, more preferably 30% or less.

In the third step, the molding pressure for compressing the raw material powder 100p may be 980 MPa or higher, and more preferably 1176 MPa or higher. Thereby, the density of the green compact 100 can be increased, and the physical properties of the green compact 100 can be improved.

In the third step, the position of the peripheral edge of the concave end surface 21 of the lower punch 20 at the end of compression is within a range of 0.1 mm or less, or more than 0.1 mm downward from the other end 11b of the first inner peripheral surface 11. For example, it should be within the range of 0.3 mm or less. By positioning the peripheral edge of the concave end surface 21 of the lower punch 20 below the other end 11b of the first inner peripheral surface 11 at the end of compression, damage to the peripheral edge of the concave end surface 21 of the lower punch 20 during compression is prevented. easy to suppress.

When the position of the peripheral edge of the concave end surface 21 of the lower punch 20 is within 0.1 mm downward from the other end 11b of the first inner peripheral surface 11, the outer peripheral surface 102 of the green compact 100 (see FIGS. 8 and 9) can be 0.1 mm or less. 0 is included within 0.1 mm. If the step provided on the outer peripheral surface 102 is 0.1 mm or less, it can be considered that there is no step, and the outer peripheral surface 102 of the powder compact 100 can be configured as a smooth hemispherical surface.

On the other hand, when the position of the peripheral edge of the concave end surface 21 of the lower punch 20 is set within a range of more than 0.1 mm and 0.3 mm or less downward from the other end 11b of the first inner peripheral surface 11, the green compact 100 (Fig. 10 , FIG. 11) can be provided with a step 130 of more than 0.1 mm and 0.3 mm or less. This step 130 can be used for positioning with respect to another member, for example, when a hemispherical member is attached to the outside of the green compact 100 . If the position of the peripheral edge of the concave end surface 21 of the lower punch 20 is within 0.3 mm downward from the other end 11b of the first inner peripheral surface 11, the position between the second upper punch 32 and the lower punch 20, that is, the lower punch There is also little effect on compression ratio above 20.

Here, when the step 130 is provided on the outer peripheral surface 102 of the powder compact 100, the position of the step 130 changes depending on the outer diameter _D20 of the lower punch 20 (see FIG. 1A). In this example, the outer diameter D32 of the second upper punch ₃₂ and the outer diameter _D20 of the lower punch 20 are substantially the same, and _D20 / _D32 is one. In this case, as shown in FIGS. 10 and 11 , a step 130 is provided between the top portion 110 and the bottom portion 120 of the outer peripheral surface 102 of the green compact 100 . The outer diameter D32 of the second upper punch ₃₂ and the outer diameter _D20 of the lower punch 20 can also be different. When the outer diameter D ₂₀ of the lower punch 20 is smaller than the outer diameter D ₃₂ of the second upper punch 32 and D ₂₀ <D ₃₂ , a step 130 is provided on the top portion 110 side (see FIG. 12). On the other hand, when the outer diameter D ₂₀ of the lower punch 20 is larger than the outer diameter D ₃₂ of the second upper punch 32 and D ₂₀ >D ₃₂ , a step 130 is provided on the skirt portion 120 side (see FIG. 13). .

(Raw material powder)
The raw material powder 100p (see FIG. 2) can be appropriately selected according to the intended use of the green compact 100 (see FIGS. 8 and 9) to be produced. For example, when forming a powder magnet from the powder compact 100, magnetic powder may be used as the raw material powder 100p. Further, when forming a powder magnetic core from the powder compact 100, soft magnetic powder may be used as the raw material powder 100p.

<Magnet powder>
Examples of magnet powders include powders of rare earth-iron magnets, such as powders of rare earth-iron alloys containing a rare earth element and iron. Typical rare earth-iron alloys include Nd ₂ Fe ₁₄ B and Sm ₂ Fe ₁₇ N ₃ . Magnetic powder includes hydrogenated powder obtained by hydrogenating rare earth-iron alloys such as Nd ₂ Fe ₁₄ B and Sm ₂ Fe ₁₇ , which are raw materials for rare earth-iron magnets. When manufacturing a rare earth-iron alloy magnet made of the rare earth-iron alloy compact 100, it is desirable to use magnetic powder made of hydrogenated rare earth-iron alloy powder as the raw material powder 100p. This is because the green compact 100 with high density can be obtained when the hydrogenated rare earth-iron alloy powder is used.

<Hydrogenated powder>
The hydrogenated rare earth-iron alloy powder can be produced by hydrogenating a pulverized rare earth-iron alloy powder, or by pulverizing a rare earth-iron alloy after hydrogenating it. Rare earth-iron alloys can be produced, for example, by rapid solidification. Examples of rapid solidification methods include strip casting and melt spun methods. Examples of rare earth elements contained in rare earth-iron alloys include neodymium (Nd) and samarium (Sm). The content of the rare earth element in the rare earth-iron alloy is 10% by mass or more and less than 40% by mass. For example, when the rare earth element is Nd, the Nd content is preferably 25% by mass or more and 35% by mass or less, more preferably 28% by mass or more and 35% by mass or less. On the other hand, in the case of Sm, the content of Sm is preferably 25% by mass or more and 26.5% by mass or less. When the content of Nd or Sm is within the above range, a rare earth-iron alloy with a stoichiometric composition of Nd ₂ Fe ₁₄ B or Sm ₂ Fe ₁₇ can be obtained.

In rare earth-iron alloys, elements other than rare earth elements and iron (Fe) include boron (B), especially in the case of a composition containing Nd. In addition, part of Fe is cobalt (Co), nickel (Ni), gallium (Ga), copper (Cu), aluminum (Al), silicon (Si), titanium (Ti), manganese (Mn) and Nb) may be substituted with one or more elements selected from.

By hydrotreating a rare earth-iron alloy, a phase-decomposed structure is formed into a rare earth element hydride phase and an iron-containing phase containing iron. Examples of hydrides of rare earth elements include _NdH2 and _SmH2 . Examples of iron-containing substances include iron compounds such as Fe and Fe ₂ B. The hydrogenation treatment includes heat treatment in a hydrogen-containing atmosphere, for example, at 400° C. or higher and 900° C. or lower, preferably 500° C. or higher and 850° C. or lower. Examples of the hydrogen-containing atmosphere include an H ₂ gas atmosphere and a mixed gas atmosphere. The mixed gas includes a mixture of _H2 gas and inert gas. Inert gases include Ar and _N2 . The atmospheric pressure of the hydrogen-containing atmosphere, that is, the hydrogen partial pressure is, for example, 20.2 kPa (0.2 atmosphere) or more and 1013 kPa (10 atmosphere) or less, and further 50.5 kPa (0.5 atmosphere) or more and 111.1 kPa (1.1 atmosphere). atmospheric pressure). The time for the hydrogenation treatment may be set as appropriate, and may be, for example, 30 minutes or more and 180 minutes or less.

For pulverization, for example, known pulverizers such as jet mills, ball mills, Braun mills, pin mills, disc mills, and jaw crushers can be used. Pulverization is preferably carried out in an atmosphere of an inert gas such as Ar in order to suppress oxidation of the magnet powder.

Hydrogenated powders of rare earth-iron alloys contain a soft iron-containing phase in the structure, so plastic deformation is easier than unhydrogenated rare earth-iron alloy powders, resulting in poor formability. Excellent. Therefore, when the hydrogenated powder of the rare earth-iron alloy is used, the density of the green compact 100 can be increased, and the high-density green compact 100 containing the hydrogenated powder can be obtained.

When the green compact 100 is molded using magnet powder made of hydrogenated rare earth-iron alloy powder as the raw material powder 100p, a step of dehydrogenating the green compact 100 is provided after the third step. When the green compact 100 of the hydrogenated powder is dehydrogenated, hydrogen is released from the hydride of the rare earth element, causing a recombination reaction and returning to the original state of the rare earth-iron alloy. Therefore, by dehydrogenating the green compact 100 of the hydrogenated powder, it is possible to obtain the high-density green compact 100 containing the rare earth-iron alloy powder. Therefore, a hollow hemispherical rare earth-iron alloy magnet made of the compact 100 of rare earth-iron alloy is obtained.

The dehydrogenation treatment includes heat treatment in an inert atmosphere or a reduced pressure atmosphere, for example, at 600° C. or higher and 1000° C. or lower, preferably 650° C. or higher and 800° C. or lower. As an inert atmosphere, for example, an atmosphere of an inert gas such as Ar or _N2 may be used. As the reduced-pressure atmosphere, for example, a vacuum atmosphere with a degree of vacuum of 10 Pa or less can be used. The degree of vacuum of the vacuum atmosphere is more preferably 1 Pa or less, more preferably 0.1 Pa or less. The dehydrogenation treatment time may be set as appropriate, and may be, for example, 30 minutes or more and 180 minutes or less.

As the hydrogenated rare earth-iron alloy powder, when the green compact 100 is molded using the hydrogenated powder of Sm ₂ Fe ₁₇ alloy, a step of nitriding the green compact 100 after dehydrogenation is performed. Be prepared. Specifically, the green compact 100 containing the Sm ₂ Fe ₁₇ alloy powder after the dehydrogenation treatment is nitrided to convert Sm ₂ Fe ₁₇ into Sm ₂ Fe ₁₇ N ₃ . The nitriding treatment includes heat treatment at, for example, 200° C. or higher and 550° C. or lower, preferably 300° C. or higher and 550° C. or lower, in a nitrogen-containing atmosphere. The nitrogen-containing atmosphere includes, for example, an _NH3 gas atmosphere, an _N2 gas atmosphere, or a mixed gas atmosphere. Mixed gases include, for example, a mixture of NH ₃ gas and H ₂ gas, or a mixture of N ₂ gas and H ₂ gas.

A hollow hemispherical rare earth-iron alloy magnet is manufactured by providing a step of magnetizing the green compact 100 of the rare earth-iron alloy after dehydrogenation, optionally after dehydrogenation and nitriding. can.

A binder may be added when a magnet powder made of a rare earth-iron alloy that has not been hydrotreated is used as the raw material powder 100p. Examples of rare earth-iron alloys include Nd ₂ Fe ₁₄ B and Sm ₂ Fe ₁₇ N ₃ . Examples of binders include resins such as epoxy resins.

Examples of soft magnetic powder include pure iron, Fe (iron)-Si (silicon) alloy, Fe (iron)-Al (aluminum) alloy, Fe (iron)-Cr (chromium)-Al (aluminum )-based alloys and Fe (iron)--Cr (chromium)--Si (silicon)-based alloys. Pure iron means a purity of 99% by mass or more. An insulating coating may be applied to the surface of the particles constituting the soft magnetic powder. Examples of insulating coatings include phosphate coatings and silica coatings.

The average particle size of the raw material powder 100p is, for example, 20 μm or more and 200 μm or less, preferably 50 μm or more and 150 μm or less. By setting the average particle size of the raw material powder 100p within the above range, it is easy to handle and easy to pressure-mold. Furthermore, by setting the average particle size of the raw material powder 100p to 20 μm or more, it is easy to ensure the fluidity of the raw material powder 100p. By setting the average particle size of the raw material powder 100p to 200 μm or less, it is easy to increase the density of the green compact 100 . The average particle size of the raw material powder 100p is the average particle size of the particles constituting the raw material powder 100p. ).

[Green compact]
A green compact 100 according to the embodiment will be described with reference to FIGS. 8 to 13 . The green compact 100 according to the embodiment can be manufactured by the green compact manufacturing method according to the embodiment described above. One of the characteristics of the powder compact 100 is that it has a hollow hemispherical shape and the absolute value of the difference in relative density between the top portion 110 and the bottom portion 120 is 5% or less. A dashed line in FIGS. 9, 11, 12, and 13 indicates a central axis line C100 connecting the center and the vertex of the hollow hemispherical green compact _100. As shown in FIG. The center is indicated by point O in the figure. A vertex is indicated by a point P in the figure. 9, 11, 12, and 13 indicate the dividing line _D100 , which is the boundary between the top portion 110 and the skirt portion 120. As shown in FIG. The green compact 100 shown in FIGS. 8 and 9 exemplifies a form in which the outer peripheral surface 102 of the green compact 100 has substantially no steps. "Substantially free of steps" includes steps of 0.1 mm or less. The green compact 100 shown in FIGS. 10, 11, 12, and 13 exemplifies a form having a step 130 on the outer peripheral surface 102 of the green compact 100. FIG.

(difference in relative density between top and bottom)
In the compact 100, the density difference between the top portion 110 and the bottom portion 120 is small because the difference in relative density between the top portion 110 and the bottom portion 120 is 5% or less. Therefore, the green compact 100 has uniform density and uniform physical properties. The difference in relative density between the top portion 110 and the bottom portion 120 is preferably 2% or less, particularly 1% or less.

Here, the top portion 110 and the bottom portion 120 of the hollow hemispherical green compact 100 are defined as follows. When a line parallel to the central axis C ₁₀₀ connecting the center O of the hollow hemisphere and the vertex P and passing through the inner peripheral edge of the open end face 103 of the hollow hemisphere is defined as a dividing line D ₁₀₀ , the central axis C is located closer to the dividing line D ₁₀₀ The portion located on _{the 100} side is a top portion 110, and the remaining portion located on the side opposite to the central axis _C100 with respect to the dividing line _D100 is a skirt portion 120.

(relative density)
The relative density of the entire green compact 100 is 80% or more. The green compact 100 having a relative density of 80% or more has high density and excellent physical properties. Further, the relative density of the green compact 100 is preferably 85% or more.

(Step)
Steps may be provided on the outer peripheral surface 102 of the powder compact 100 . The compact 100 shown in FIGS. 8 and 9 has an outer peripheral surface 102 with a distance of 0.1 mm or less between the spherical crown surface that is the outer peripheral surface of the top portion 110 and the spherical zone surface that is the outer peripheral surface of the skirt portion 120. There is a step. 0 is included in 0.1 mm or less. Since the step provided on the outer peripheral surface 102 of the green compact 100 is 0.1 mm or less, there is substantially no step, and the outer peripheral surface 102 of the green compact 100 can be configured as a smooth hemispherical surface. Since the step of the outer peripheral surface 102 of the green compact 100 is 0.1 mm or less, when a separate hemispherical member is assembled to the outside of the green compact 100, the outer peripheral surface of the green compact 100 and the inside of the separate member It is possible to suppress the formation of a gap with respect to the peripheral surface. Illustration of separate members is omitted.

10 and 11, the green compact 100 shown in FIGS. A step 130 of 3 mm or less is provided. Since the step 130 of more than 0.1 mm is provided on the outer peripheral surface 102 of the green compact 100, when a separate hemispherical member is assembled to the outside of the green compact 100, this step can be used for positioning with respect to the separate member. can. In this case, a step portion corresponding to the step 130 is provided on the inner peripheral surface of the separate member. Illustration of separate members is omitted as described above.

The position of step 130 is not limited to between top portion 110 and skirt portion 120 . For example, as shown in FIG. 12 , a step 130 may be provided on the outer peripheral surface 102 of the green compact 100 on the top portion 110 side of the dividing line D ₁₀₀ that is the boundary between the top portion 110 and the bottom portion 120. . Alternatively, as shown in FIG. 13, even if a step 130 is provided on the outer peripheral surface 102 of the green compact 100 on the side of the skirt portion 120 from the dividing line D ₁₀₀ that is the boundary between the top portion 110 and the skirt portion 120. good. The position of the step 130 is set at a position in the green compact 100 that is 0.8 to 1.2 times the inner circumference radius r ₁₀₃ of the opening end face 103 in the radial direction from the central axis C ₁₀₀ . mentioned. That is, the step 130 is provided at a position within ±20% of the inner radius r ₁₀₃ from the dividing line D ₁₀₀ that is the boundary between the top portion 110 and the bottom portion 120 .

(thickness)
The thickness of the powder compact 100 is, for example, 1/30 times or more, more preferably 1/25 times or more, and 1/2 times or less of the outer circumference radius R ₁₀₃ of the opening end face 103 . The thickness of the green compact 100 means the length of the green compact 100 in the radial direction, that is, 1/2 of the difference between the inner and outer diameters. When the thickness of the powder compact 100 is within the above range, uniform density and high density can be easily achieved.

(material)
Examples of the constituent material of the powder compact 100 include magnet powder and soft magnetic powder. Magnetic powders include, for example, powders of rare earth-iron alloys containing rare earth elements and iron. Examples of rare earth-iron alloys include Nd ₂ Fe ₁₄ B and Sm ₂ Fe ₁₇ N ₃ . The green compact 100 containing rare earth-iron alloy powder can be used as a rare earth-iron magnet. A green compact 100 containing soft magnetic powder can be used as a powder magnetic core.

(Application)
A hemispherical rare earth-iron alloy magnet made of the rare earth-iron alloy compact 100 can be used, for example, as a magnet that constitutes a spherical motor used in the joints of a robot. When a magnetic circuit is configured using a hemispherical magnet made of a rare earth-iron alloy compact 100, the compact 100 may be covered with a hemispherical yoke. Illustration of the yoke is omitted. For example, as in the green compact 100 shown in FIGS. 8 and 9, when the outer peripheral surface 102 has no step, the gap provided between the outer peripheral surface 102 of the green compact 100 and the inner peripheral surface of the yoke can be made small. , the magnetic resistance can be reduced. On the other hand, for example, in a form having a step 130 on the outer peripheral surface 102 like the green compact 100 shown in FIGS. 10 and 11, the step 130 can be used for positioning with respect to the yoke. Magnetization of the rare earth-iron alloy compact 100 includes, for example, magnetization in the radial direction from the center of the compact 100 .

A hemispherical dust core made of the green compact 100 of soft magnetic powder can be used, for example, as a yoke that constitutes the magnetic circuit described above.

{Effect of embodiment}
The green compact manufacturing method and the green compact 100 according to the above-described embodiments have the following effects.

In the green compact production method of the embodiment, the mold 1 is used, and the operation of the mold 1 is controlled according to the second step and the third step to produce a hollow hemispherical green compact 100. can homogenize the density of In particular, in the second step, the green compact 100 having a uniform density can be easily manufactured by performing the steps A to D above.

The green compact 100 of the embodiment has a hollow hemispherical shape, and the difference in relative density between the top portion 110 and the bottom portion 120 is 5% or less.

[Test Example 1]
A hollow hemispherical compact was produced by the method for producing a compact according to the embodiment described above.

A hydrogenated powder of Nd ₂ Fe ₁₄ B alloy was used as the raw material powder. This hydrogenated powder was obtained by hydrogenating a Nd ₂ Fe ₁₄ B alloy powder. As a hydrogenation treatment, heat treatment was performed at 850° C. for 150 minutes in an atmosphere of H ₂ gas at atmospheric pressure. The average particle size (D50) of the hydrogenated powder is 130 μm.

The dimensions of each element of the mold are as follows.
Inner diameter of the second inner peripheral surface of the die: 30 mm
Length of the second inner peripheral surface of the die: 5 mm
Inner diameter of the third inner peripheral surface of the die: 20 mm
Radius of first inner peripheral surface of die (R ₁₁ ): 15 mm
Outer diameter of first upper punch ( _D31 ): 30 mm
Inner diameter of first upper punch (d ₃₁ ): 20 mm
Outer diameter of second upper punch (D ₃₂ ): 20 mm
Outer diameter of lower punch ( _D20 ): 20mm
Radius of end face of lower punch (R ₂₁ ): 15 mm
Outer diameter of the hemispherical surface composed of the first inner peripheral surface of the die and the end surface of the lower punch: 30 mm
Outer diameter of the hemispherical end surface of the second upper punch: 20 mm
Distance (L ₀ ) from the opening of the second inner peripheral surface to the peripheral edge of the end face of the lower punch when the lower punch is positioned at the reference position (P ₀ ): 16.18 mm

Using the above-described mold, a hemispherical compact having an outer diameter of φ30 mm, an inner diameter of φ20 mm, and a thickness of 5 mm was molded according to the above-described second step A to D and the third step. . That is, the compact has an outer radius (R ₁₀₃ ) of 15 mm and an inner radius (r ₁₀₃ ) of 10 mm. The molding pressure was 1960 MPa.

Here, in the second step, the protrusion amount (P ₁ ) of the end surface of the lower punch in the A step was set to 9.5 mm (P ₁ /L ₀ : 0.587). Further, in the second step, the lowering amount (P ₂ ) of the end face of the lower punch in the B step was set to 2 mm. In the third step, the position of the peripheral edge of the end face of the lower punch at the end of compression is within 0.1 mm downward from the other end of the first inner peripheral surface, or within a range of more than 0.1 mm and 0.3 mm or less set.

Sample No. 1 is a powder compact in which the position of the concave end surface 21 of the lower punch 20 at the end of compression is set to "within 0.1 mm". 1A. Sample No. 1 is a green compact in which the position of the concave end face 21 of the lower punch 20 at the end of compression is set to "within the range of more than 0.1 mm and 0.3 mm or less". 1B. The difference in compressibility (C1-C2) mentioned above ranged from about 25% to about 27%.

The green compact thus obtained is composed only of the hydrogenated powder of the Nd ₂ Fe ₁₄ B alloy. Sample no. The overall relative density was determined for the compacts of 1A and 1B. The relative density was obtained as a percentage of [measured density/true density] by obtaining the measured density from the volume and mass. The actual density was measured by the Archimedes method. The true density was taken as the density of the starting raw material Nd ₂ Fe ₁₄ B alloy. This density was set to 7.6 g/cm ³ in this example. Table 1 shows the results. Also, the relative densities of the top portion and the bottom portion of the powder compact were obtained, and the absolute value of the difference in relative density between the top portion and the bottom portion was calculated. The results are also shown in Table 1.

The relative densities of the top and tail were determined as follows. A method for measuring the relative density in this test example will be described with reference to FIG. With the opening end face 103 of the green compact 100 placed horizontally, a cutting line passing through the vertex P and dividing the green compact 100 into four equal parts is drawn on the outer peripheral surface 102 . A contour line overlapping the inner peripheral edge of the opening end face 103 is drawn on the outer peripheral surface 102 when the powder compact 100 is viewed from the vertex P side in the direction of the central axis C ₁₀₀ passing through the vertex P and the center O. This contour line is a circle that passes through the dividing line D ₁₀₀ that is the boundary between the top portion 110 and the bottom portion 120 on the outer peripheral surface 102 of the green compact 100 . On the outer peripheral surface 102 of the powder compact 100, the points of intersection between the contour line and each cutting line are taken, and arc lines connecting the points of intersection adjacent in the circumferential direction are drawn. This circular arc line is centered on the center O of the green compact 100 . The center O of the green compact 100 is the center of the open end face 103 . After cutting the green compact 100 along each cutting line into four split pieces, each split piece is cut into two along the arc line. The cutting along the arc line is performed by cutting along a plane including the center O of the green compact 100 and the intersection point on the outer peripheral surface 102 in each split piece. That is, when cutting each split piece along an arc line, the cut is made so as to pass through the center O of the green compact 100 and the intersection point on the outer peripheral surface 102, as indicated by the dotted line in FIG. Of the obtained cut pieces, the portion on the vertex P side is used as the top piece, and the remaining portion on the outer peripheral side is used as the bottom piece. For each top piece, the actual density was measured and the relative density was calculated and obtained, and the average value of the relative densities was taken as the relative density of the top. In addition, the measured density of each skirt piece was measured, the relative density was calculated, and the average value of the relative densities was taken as the relative density of the skirt.

In the case of the relative density measurement method described above, the skirt piece will strictly include a portion of the top portion 110, as shown in FIG. However, since the volume ratio of the top portion 110 included in the bottom piece is very small compared to the volume ratio of the bottom portion 120, the influence of part of the top portion 110 on the density of the bottom portion piece is small. Therefore, even if a part of the top portion 110 is included in the bottom piece, its influence is within the range of error, and there is no problem even if the relative density of the bottom piece is regarded as the relative density of the bottom portion.

As shown in Table 1, sample no. The green compacts of 1A and 1B have a difference in relative density of 2% or less between the top portion and the bottom portion, and the density difference is small.

Moreover, sample no. When the step provided on the outer peripheral surface of each of the powder compacts 1A and 1B was measured, a step having a size corresponding to the set value of the position of the end surface of the lower punch at the end of compression was provided. Furthermore, sample no. After 100 green compacts of 1A and 1B were produced, the peripheral edge of the end face of the lower punch was checked, and no deformation or damage was found on the peripheral edge of the end face.

Reference Signs List 1 mold 10 die 10i inner peripheral surface 10h hollow portion 11 first inner peripheral surface 11a one end 11b other end 12 second inner peripheral surface 12o opening 13 third inner peripheral surface 15 space 20 lower punch 21 concave end surface 30 upper punch 31 First upper punch 31c Annular end surface 32 Second upper punch 32h Convex end surface 32d Boundary 100 Green compact 101 Inner peripheral surface 102 Outer peripheral surface 103 Opening end surface 110 Top 120 Bottom 130 Step 100p Raw material powder _d12 , _d13 inner diameter R ₁₁ , R ₂₁ Radius _{D 20} Outer diameter D ₃₁ , D ₃₂ Outer diameter d ₃₁ Inner diameter L ₀ Distance P 0 Reference position P ₁ Projection amount P ₂ Lowering amount A1 Maximum distance A2 Distance between vertices B1 Maximum distance B2 Distance between vertices R ₁₀₃ Outer radius r ₁₀₃ Inner radius O Center P Vertex C ₁₀ , C ₁₀₀ central axis D ₁₀₀ dividing line

Claims (17)

A first step of preparing a mold comprising a die having a hollow portion constituted by the inner peripheral surface of a cylindrical body, a lower punch inserted into the hollow portion, and an upper punch inserted into the hollow portion. with
The inner peripheral surface of the die is
a spherical first inner peripheral surface;
a cylindrical second inner peripheral surface provided on one end side of the first inner peripheral surface in the axial direction;
a cylindrical third inner peripheral surface provided on the other end side in the axial direction of the first inner peripheral surface,
The first inner peripheral surface has an inner diameter that decreases from one axial end to the other axial end,
The second inner peripheral surface has an inner diameter corresponding to the maximum inner diameter of the first inner peripheral surface,
The third inner peripheral surface has an inner diameter corresponding to the minimum inner diameter of the first inner peripheral surface,
The lower punch has a crown-shaped end surface that forms a hemispherical surface by connecting to the first inner peripheral surface,
The end surface of the lower punch has an outer diameter corresponding to the inner diameter of the third inner peripheral surface,
The upper punch is
a cylindrical first upper punch;
and a cylindrical second upper punch that is inserted inside the first upper punch,
The first upper punch has an annular end surface composed of a flat surface,
The end surface of the first upper punch has an outer diameter corresponding to the inner diameter of the second inner peripheral surface,
The second upper punch has a hemispherical end surface protruding toward the lower punch,
The end face of the second upper punch has an outer diameter corresponding to the inner diameter of the first upper punch,
Furthermore,
In the hollow portion surrounded by the first inner peripheral surface, the second inner peripheral surface and the third inner peripheral surface of the die, the end surface of the lower punch is located within the region surrounded by the third inner peripheral surface. and the end surface of the first upper punch is positioned at the opening of the second inner peripheral surface, and the boundary between the end surface of the second upper punch and the cylindrical surface is at the same position as the end surface of the first upper punch. a second step of filling the raw material powder in the hollow portion in the state of
a third step of lowering the first upper punch and the second upper punch with respect to the die and raising the lower punch to compress the raw material powder from above and below to obtain a hollow hemispherical green compact; , and
The second step is
a step of filling the raw material powder into the hollow portion with the peripheral edge of the end surface of the lower punch protruding into the region surrounded by the first inner peripheral surface;
After filling the hollow portion with the raw material powder, the peripheral edge of the end surface of the lower punch is lowered below the other end of the first inner peripheral surface, and the end surface of the lower punch is moved to the third inner peripheral surface. positioning within the enclosed area;
After filling the raw material powder into the hollow portion, the end surface of the first upper punch is lowered to the position of the opening of the second inner peripheral surface, and the second upper punch is lowered to remove the second upper punch. inserting the end face of the second upper punch into the hollow portion, and aligning the boundary between the end face of the second upper punch and the cylindrical face with the position of the end face of the first upper punch;
A method for producing a green compact. The difference between the compression rate of the raw material powder compressed between the first upper punch and the die and the compression rate of the raw material powder compressed between the second upper punch and the lower punch is 50. % or less. In the second step, after filling the raw material powder into the hollow portion of the die, before inserting the end surface of the second upper punch into the hollow portion of the die, the end surface of the first upper punch 3. The method of manufacturing a green compact according to claim 1, further comprising a step of partially blocking the opening of the second inner peripheral surface. In the second step, after partially closing the opening of the second inner peripheral surface, the second upper punch is lowered to insert the end surface of the second upper punch into the hollow portion, 4. The method of manufacturing a green compact according to claim 3 , further comprising the step of aligning a boundary between the end surface of the second upper punch and the cylindrical surface with the position of the end surface of the first upper punch. When the distance from the opening of the second inner peripheral surface to the peripheral edge of the end surface of the lower punch when the first inner peripheral surface of the die and the end surface of the lower punch form a hemispherical surface is 100,
2. From claim 1, wherein in said second step, when said raw material powder is filled, said lower punch has a peripheral edge of said lower punch that protrudes into a region surrounded by said first inner peripheral surface by an amount of 10 or more and 70 or less. The method for producing a green compact according to claim 4 . In the second step, after the raw material powder is filled, the peripheral edge of the end surface of the lower punch is lowered from the other end of the first inner peripheral surface by a lowering amount of 1 mm or more and 10 mm or less . 6. The method for producing a green compact according to any one of 5 . 7. The method of manufacturing a green compact according to any one of claims 1 to 6 , wherein the ratio of the outer diameter of the lower punch to the outer diameter of the second upper punch is 0.8 or more and 1.2 or less. 8. The method for producing a green compact according to any one of claims 1 to 7 , wherein in said third step, a molding pressure for compressing said raw material powder is set at 980 MPa or higher. 9. In the third step, the position of the peripheral edge of the end face of the lower punch at the end of compression is set within a range of 0.1 mm or less downward from the other end of the first inner peripheral surface. A method for producing a green compact according to any one of the above. 2. In the third step, the position of the peripheral edge of the end surface of the lower punch at the end of compression is set to be within a range of more than 0.1 mm and less than or equal to 0.3 mm downward from the other end of the first inner peripheral surface. The method for producing a green compact according to any one of claims 9 to 10. The raw material powder includes magnetic powder made of hydrogenated powder obtained by hydrogenating a rare earth-iron alloy containing a rare earth element and iron,
11. The method for producing a green compact according to any one of claims 1 to 10 , further comprising a step of dehydrogenating the green compact after the third step. has a hollow hemispherical shape,
When a plane parallel to the central axis connecting the center and the vertex of the hollow hemisphere and along a line passing through the inner peripheral edge of the open end face of the hollow hemisphere is defined as a dividing plane, it is closer to the central axis than the dividing plane . The portion located is the top portion , and the remaining portion located on the opposite side of the dividing surface to the central axis is the bottom portion,
The difference in relative density between the top portion and the bottom portion is 5% or less.
Green compact. 13. The compact according to claim 12 , wherein the overall relative density of the compact is 80% or more. 14. The green compact according to claim 12 , wherein a step of 0.1 mm or less is provided on the outer peripheral surface of the green compact. The green compact according to claim 12 or 13, wherein a step of more than 0.1 mm and not more than 0.3 mm is provided on the outer peripheral surface of the green compact. 16. The green compact according to any one of claims 12 to 15 , wherein the thickness of the green compact is 1/30 times or more and 1/2 times or less of the outer peripheral radius of the opening end face. 17. The compact according to any one of claims 12 to 16 , which contains magnet powder of a rare earth-iron alloy containing a rare earth element and iron.

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