JP6947625B2 - Manufacturing method of sintered magnet, graphite mold for hot press and graphite mold for hot press - Google Patents

Description

The present invention relates to a method for producing a sintered magnet, a method for producing a graphite mold for hot pressing, and a method for producing a graphite mold for hot pressing.

R-Fe-B-based rare earth magnets (R is a rare earth element, Fe is iron, and B is boron), which are typical high-performance permanent magnets, have R ₂ Fe ₁₄ B phase, which is a ternary square compound, as the main phase. It has a texture containing it and exhibits excellent magnetic properties. Such R-Fe-B-based rare earth magnets are roughly classified into sintered magnets and bonded magnets. Sintered magnets are manufactured by compression-molding fine powder (average particle size: several μm) of R-Fe-B-based magnet alloy with a press device and then sintering. On the other hand, a bonded magnet is usually manufactured by compression molding or injection molding of a mixture (compound) of an R-Fe-B magnet alloy powder (particle size: about 100 μm) and a bonding resin. NS.

In the case of a sintered magnet, since powder having a relatively small particle size is used, each powder particle has magnetic anisotropy. Therefore, when the powder is compression-molded by the press device, an orientation magnetic field is applied to the powder, whereby a green compact in which the powder particles are oriented in the direction of the magnetic field is obtained, and a magnet having a strong magnetic force is obtained. be able to. This is because a strong magnetic force can be obtained by applying a magnetic field from the outside and aligning the directions of the magnetic moments by crushing the magnet to the smallest unit (single magnetic domain particle size) that naturally magnetizes in the same direction. ..

Patent Document 1 describes a method for producing a rare earth sintered magnet.
In order to make the powder particles finer and obtain a stronger magnetic force, a step of preparing an R-Fe-B-based rare earth alloy powder having an average particle size of less than 10 μm and a step of molding the R-Fe-B-based rare earth alloy powder to obtain a compact powder. A step of preparing a body, a step of heat-treating the green compact in hydrogen gas at a temperature of 650 ° C. or higher and lower than 1000 ° C., thereby causing a hydrogenation and disproportionation reaction, and in a vacuum or an inert atmosphere. A method for producing an R-Fe-B-based porous magnet including a step of heat-treating the green compact at a temperature of 650 ° C. or higher and lower than 1000 ° C. to cause a dehydrogenation and recombination reaction has been proposed. ing. In this method, hydrogen is occluded once in the R-Fe-B-based rare earth alloy powder to make a fine powder, so that the directions of the magnetic moments can be easily aligned.

In Patent Document 1, the obtained R-Fe-B-based porous magnet is further pressurized at a temperature of 600 ° C. or higher and lower than 900 ° C., and the R-Fe-B-based porous magnet is increased to 95% or more of the true density. A method for manufacturing an R-Fe-B magnet including a step of densifying has been proposed. It is described that the R-Fe-B based porous magnet can be increased in density to 95% or more of the true density by this step.

International Publication No. 2007/135981

However, the above-described invention is a method for producing an R-Fe-B-based sintered magnet, and Nd, Dy, and the like are often used as rare earth elements. Therefore, in the manufacturing stage, it is important to reduce the amount of rare metals used in order to reduce the manufacturing cost.

In view of the above problems, the present invention provides a method for producing an R-Fe-B-based sintered magnet having high shape accuracy and little material loss, and a method for producing a graphite mold for hot pressing and a graphite mold for hot pressing. With the goal.

The method for producing an R-Fe-B-based sintered magnet of the present invention for solving the above problems has the following contents.

(1) A method for producing an R-Fe-B-based sintered magnet in which an R-Fe-B-based porous magnet is placed in a graphite mold for hot pressing and pressurized while heating, wherein the graphite for hot pressing is produced. The mold comprises a die and a punch whose direction is defined by a pressurizing axis direction and a direction perpendicular to the pressurizing axis direction, and the coefficient of thermal expansion (α _z ) of the die in the pressurizing axis direction is , It is larger than the coefficient of thermal expansion (α _x , α _{y) in the vertical direction of the die.}

Since the graphite used in the graphite mold for hot pressing requires high strength, isotropic graphite obtained by finely crushing the raw material, press molding, firing, and graphitizing is suitable. However, isotropic graphite is not completely isotropic, and the vertical direction during molding tends to be higher than the horizontal direction due to uniaxial pressure due to the gravity of the powder after crushing. When hot molding is performed using such a graphite material, deformation occurs due to a difference in thermal expansion depending on the cutting direction of the material.

In the method for producing an R-Fe-B-based sintered magnet of the present invention, irregular deformation of the material can be prevented by setting the cutting direction having the largest coefficient of thermal expansion to the pressure axis direction of the die. Since the irregular deformation of the material is small, the amount of processing after sintering can be reduced, and the material loss can be reduced.
In the present invention, the coefficient of thermal expansion is the elongation rate per 1 ° C. between 50 and 400 ° C.

Further, the method for producing an R-Fe-B-based sintered magnet of the present invention of the present invention preferably has the following aspects.

(2) The coefficient of thermal expansion (α _x , α _y , α _z ) of the die is
1.05 ≤ α _z / α _x ≤ 1.3 ... (1)
1.05 ≤ α _z / α _y ≤ 1.3 ... (2)
The relationship between equations (1) and (2) is satisfied.

_{When the anisotropy ratio (α z} / α _x or α _z / α _y ) in the equations (1) and (2) is 1.05 or more, it is sufficiently larger than the error of the measuring instrument and the direction in which the anisotropy ratio is high. Can be easily detected, and the cutting direction of the material can be selected correctly. When the heterogeneous ratio is 1.3 or less in the equations (1) and (2), the coefficient of thermal expansion in the pressurizing axis direction can be suppressed to a small value, so that the generation of thermal stress can be reduced.

(3) thermal expansion coefficient of the pressure axis direction of the die (alpha _z) is ^{3.5 × 10 -6 /℃~5.0×10 -6 / ℃} .

In graphite, the crystal size of hexagonal crystals increases as graphitization progresses, the coefficient of thermal expansion decreases, and the material itself becomes soft. When graphitized graphite is used as a graphite mold for hot pressing, it is easy to rub and it is difficult to obtain the shape accuracy of the sintered magnet. On the other hand, in graphite that has not been graphitized, since the coefficient of thermal expansion is large, the dimensional change becomes large during hot pressing, and it is difficult to obtain shape accuracy.

In the method for producing a sintered magnet of an R-Fe-B based the present invention, the thermal expansion coefficient of the pressure application shaft direction (alpha _z) is 3.5 × ^{10 -6} /℃~5.0×10 ^-6 / Since graphite at ° C. is used, an R-Fe-B-based sintered magnet can be obtained with high accuracy.

(4) The coefficient of thermal expansion (β _z ) of the punch in the pressure axis direction is larger than the coefficient of thermal expansion (β _x , β _{y) of the punch in the vertical direction.}

Since the graphite used in the graphite mold for hot pressing requires high strength, isotropic graphite obtained by finely crushing the raw material, press molding, firing, and graphitizing is suitable. However, isotropic graphite is not completely isotropic, and the vertical direction during molding tends to be higher than the horizontal direction due to uniaxial pressure due to the gravity of the powder after crushing. When hot molding is performed using such a graphite material, deformation occurs due to a difference in thermal expansion depending on the cutting direction of the material.

In the method for manufacturing an R-Fe-B-based sintered magnet of the present invention, irregular deformation of a material such as burrs is prevented by setting the cutting direction having the largest coefficient of thermal expansion to the pressure axis direction of the punch. Can be done. Since the irregular deformation of the material is small, the amount of processing after sintering can be reduced, and the material loss can be reduced.

(5) The coefficient of thermal expansion (β _x , β _y , β _z ) of the punch is
1.05 ≤ β _z / β _x ≤ 1.3 ... (3)
1.05 ≤ β _z / β _y ≤ 1.3 ... (4)
The relationship between equation (3) and equation (4) is satisfied.

_{When the anisotropy ratio (α z} / α _x or α _z / α _y ) in the equations (3) and (4) is 1.05 or more, it is sufficiently larger than the error of the measuring instrument and the direction in which the anisotropy ratio is high. Can be easily detected, and the cutting direction of the material can be selected correctly. When the heterogeneous ratio is 1.3 or less in the equations (3) and (4), the coefficient of thermal expansion in the pressure axis direction can be suppressed to a small value, so that the generation of thermal stress can be reduced.

(6) thermal expansion coefficient of the pressure axis direction of the punch (beta _z) is ^{3.5 × 10 -6 /℃~5.0×10 -6 / ℃} .

In graphite, the crystal size of hexagonal crystals increases as graphitization progresses, the coefficient of thermal expansion decreases, and the material itself becomes soft. When graphitized graphite is used as a graphite mold for hot pressing, it is easy to rub and it is difficult to obtain the shape accuracy of the sintered magnet. On the other hand, since graphitization of graphite has a large coefficient of thermal expansion, the dimensions become large during heating, and it is difficult to obtain shape accuracy.

In the method for producing a sintered magnet of an R-Fe-B based the present invention, the thermal expansion coefficient of the pressure application shaft direction (beta _z) is 3.5 × ^{10 -6} /℃~5.0×10 ^-6 / Since graphite at ° C. is used, an R-Fe-B-based sintered magnet can be obtained with high accuracy.

(7) The pressurization method is pulse energization sintering in which uniaxial pressurization is performed while applying heat and DC pulse voltage to the graphite mold for hot pressing.

By applying the DC pulse voltage, the interface of the particles of the R-Fe-B-based porous magnet is activated, and sintering is promoted.

The graphite mold for hot pressing of the R-Fe-B-based sintered magnet of the present invention for solving the above problems has the following contents.

(8) A graphite type for hot pressing of an R-Fe-B-based sintered magnet that pressurizes an R-Fe-B-based porous magnet while heating, and the graphite type for hot pressing is pressurized. A die and a punch whose direction is defined by an axial direction and a direction perpendicular to the pressure axis direction are provided, and the coefficient of thermal expansion (α _z ) of the die in the pressure axis direction is the same as that of the die. It is larger than the coefficient of thermal expansion in the vertical direction (α _x , α _y).

Further, the graphite type for hot pressing of the R-Fe-B-based sintered magnet of the present invention preferably has the following aspects.

(9) The coefficient of thermal expansion (α _x , α _y , α _z ) of the die is
1.05 ≤ α _z / α _x ≤ 1.3 ... (1)
1.05 ≤ α _z / α _y ≤ 1.3 ... (2)
The relationship between equations (1) and (2) is satisfied.

The isotropic graphite material has an isotropic ratio in the coefficient of thermal expansion depending on the site due to the influence of gravity before molding. Therefore, it is preferable to use a portion having a small anisotropic ratio, but material loss occurs when sorting by the magnitude of the anisotropic ratio. Rather, by utilizing the fact that the anisotropic ratio of the isotropic graphite material appears regularly according to the direction at the time of molding of the material and using it as the pressure axis direction after confirming the direction in which the coefficient of thermal expansion is large. The deformation of the obtained R-Fe-B-based sintered magnet can be reduced.

_{Further, when the anisotropic ratio (α z} / α _x or α _z / α _y ) in the equations (1) and (2) is 1.05 or more, it is sufficiently larger than the error of the measuring instrument, and the anisotropic ratio is large. The high direction can be easily detected, and the cutting direction of the material can be selected correctly. When the heterogeneous ratio is 1.3 or less in the equations (1) and (2), the coefficient of thermal expansion in the pressurizing axis direction can be suppressed to a small value, so that the generation of thermal stress can be reduced.

(10) the thermal expansion coefficient of the pressure axis direction of the die (alpha _z) is ^{3.5 × 10 -6 /℃~5.0×10 -6 / ℃} .

(11) The coefficient of thermal expansion (β _z ) of the punch in the pressure axis direction is larger than the coefficient of thermal expansion (β _x , β _{y) of the punch in the vertical direction.}

(12) The coefficient of thermal expansion (β _x , β _y , β _z ) of the punch is
1.05 ≤ β _z / β _x ≤ 1.3 ... (3)
1.05 ≤ β _z / β _y ≤ 1.3 ... (4)
The relationship between equation (3) and equation (4) is satisfied.

The isotropic graphite material has an isotropic ratio in the coefficient of thermal expansion depending on the site due to the influence of gravity before molding. Therefore, it is preferable to use a portion having a small anisotropic ratio, but material loss occurs when sorting by the magnitude of the anisotropic ratio. Rather, by utilizing the fact that the anisotropic ratio of the isotropic graphite material appears regularly according to the direction of material molding, the direction in which the coefficient of thermal expansion is large is confirmed and then used as the pressure axis direction. The deformation of the obtained R-Fe-B-based sintered magnet can be reduced.

_{Further, when the anisotropic ratio (α z} / α _x or α _z / α _y ) in the equations (3) and (4) is 1.05 or more, it is sufficiently larger than the error of the measuring instrument, and the anisotropic ratio is large. The high direction can be easily detected, and the cutting direction of the material can be selected correctly. When the heterogeneous ratio is 1.3 or less in the equations (3) and (4), the coefficient of thermal expansion in the pressure axis direction can be suppressed to a small value, so that the generation of thermal stress can be reduced.

(13) a coefficient of thermal expansion of the pressure axis direction of the punch (beta _z) is ^{3.5 × 10 -6 /℃~5.0×10 -6 / ℃} .

The method for producing a graphite mold for hot pressing of an R-Fe-B-based sintered magnet of the present invention is as follows.

(14) The graphite material is cut out so that the direction having the highest coefficient of thermal expansion is the pressure axis direction.

(15) The coefficient of thermal expansion in the x, y, and z directions of the graphite material is measured, and the direction having the highest coefficient of thermal expansion is cut out so as to be the direction of the pressurizing axis and processed.

Irregular deformation of the material can be prevented by setting the cutting direction having the largest coefficient of thermal expansion to the pressure axis direction of the die. Since the irregular deformation of the material is small, the amount of processing after sintering can be reduced, and the material loss can be reduced.

The perspective view which shows one Embodiment of the graphite type for hot press housed in the chamber of the hot press apparatus which concerns on this invention. Sectional drawing of another embodiment of the graphite type for hot press which concerns on this invention.

(Detailed description of the invention)
In the method for producing an R-Fe-B-based sintered magnet of the present invention for solving the above problems, an R-Fe-B-based porous magnet is placed in a graphite mold for hot pressing and pressurized while heating. A method for manufacturing an R-Fe-B-based sintered magnet, the graphite mold for hot pressing has a die whose direction is defined by a pressurizing axis direction and a direction perpendicular to the pressurizing axis direction. With a punch, the coefficient of thermal expansion (α _z ) of the die in the pressure axis direction is larger than the coefficient of thermal expansion (α _x , α _{y) of the die in the vertical direction.}

Since the graphite used in the graphite mold for hot pressing requires high strength, isotropic graphite obtained by finely crushing the raw material, press molding, firing, and graphitizing is suitable. However, isotropic graphite is not completely isotropic, and the vertical direction during molding tends to be higher than the horizontal direction due to uniaxial pressure due to the gravity of the powder after crushing. When hot molding is performed using such a graphite material, deformation occurs due to a difference in thermal expansion depending on the cutting direction of the material.

In the method for producing an R-Fe-B-based sintered magnet of the present invention, irregular deformation of the material can be prevented by setting the cutting direction having the largest coefficient of thermal expansion to the pressure axis direction of the die. Since the irregular deformation of the material is small, the amount of processing after sintering can be reduced, and the material loss can be reduced.

Further, the method for producing an R-Fe-B-based sintered magnet of the present invention of the present invention preferably has the following aspects.

The coefficient of thermal expansion (α _x , α _y , α _z ) of the die is
1.05 ≤ α _z / α _x ≤ 1.3 ... (1)
1.05 ≤ α _z / α _y ≤ 1.3 ... (2)
The relationship between equations (1) and (2) is satisfied.

_{When the anisotropy ratio (α z} / α _x or α _z / α _y ) in the equations (1) and (2) is 1.05 or more, it is sufficiently larger than the error of the measuring instrument and the direction in which the anisotropy ratio is high. Can be easily detected, and the cutting direction of the material can be selected correctly. When the heterogeneous ratio is 1.3 or less in the equations (1) and (2), the coefficient of thermal expansion in the pressurizing axis direction can be suppressed to a small value, so that the generation of thermal stress can be reduced.

Thermal expansion coefficient of the pressure axis direction of the die (alpha _z) is ^{3.5 × 10 -6 /℃~5.0×10 -6 / ℃} .

In graphite, the crystal size of hexagonal crystals increases as graphitization progresses, the coefficient of thermal expansion decreases, and the material itself becomes soft. When graphitized graphite is used as a graphite mold for hot pressing, it is easy to rub and it is difficult to obtain the shape accuracy of the sintered magnet. On the other hand, in graphite that has not been graphitized, since the coefficient of thermal expansion is large, the dimensional change becomes large during hot pressing, and it is difficult to obtain shape accuracy.

In the method for producing a sintered magnet of an R-Fe-B based the present invention, the thermal expansion coefficient of the pressure application shaft direction (alpha _z) is 3.5 × ^{10 -6} /℃~5.0×10 ^-6 / Since graphite at ° C. is used, an R-Fe-B-based sintered magnet can be obtained with high accuracy.

The coefficient of thermal expansion (β _z ) of the punch in the pressure axis direction is larger than the coefficient of thermal expansion (β _x , β _{y) of the punch in the vertical direction.}

Since the graphite used in the graphite mold for hot pressing requires high strength, isotropic graphite obtained by finely crushing the raw material, press molding, firing, and graphitizing is suitable. However, isotropic graphite is not completely isotropic, and the vertical direction during molding tends to be higher than the horizontal direction due to uniaxial pressure due to the gravity of the powder after crushing. When hot molding is performed using such a graphite material, deformation occurs due to a difference in thermal expansion depending on the cutting direction of the material.

In the method for manufacturing an R-Fe-B-based sintered magnet of the present invention, irregular deformation of a material such as burrs is prevented by setting the cutting direction having the largest coefficient of thermal expansion to the pressure axis direction of the punch. Can be done. Since the irregular deformation of the material is small, the amount of processing after sintering can be reduced, and the material loss can be reduced.

The coefficient of thermal expansion (β _x , β _y , β _z ) of the punch is
1.05 ≤ β _z / β _x ≤ 1.3 ... (3)
1.05 ≤ β _z / β _y ≤ 1.3 ... (4)
The relationship between equation (3) and equation (4) is satisfied.

_{When the anisotropy ratio (α z} / α _x or α _z / α _y ) in the equations (3) and (4) is 1.05 or more, it is sufficiently larger than the error of the measuring instrument and the direction in which the anisotropy ratio is high. Can be easily detected, and the cutting direction of the material can be selected correctly. When the heterogeneous ratio is 1.3 or less in the equations (3) and (4), the coefficient of thermal expansion in the pressure axis direction can be suppressed to a small value, so that the generation of thermal stress can be reduced.

Thermal expansion coefficient of the pressure axis direction of the punch (beta _z) is ^{3.5 × 10 -6 /℃~5.0×10 -6 / ℃} .

In graphite, the crystal size of hexagonal crystals increases as graphitization progresses, the coefficient of thermal expansion decreases, and the material itself becomes soft. When graphitized graphite is used as a graphite mold for hot pressing, it is easy to rub and it is difficult to obtain the shape accuracy of the sintered magnet. On the other hand, since graphitization of graphite has a large coefficient of thermal expansion, the dimensions become large during heating, and it is difficult to obtain shape accuracy.

In the method for producing a sintered magnet of an R-Fe-B based the present invention, the thermal expansion coefficient of the pressure application shaft direction (beta _z) is 3.5 × ^{10 -6} /℃~5.0×10 ^-6 / Since graphite at ° C. is used, an R-Fe-B-based sintered magnet can be obtained with high accuracy.

The pressurization method is pulse energization sintering in which uniaxial pressurization is performed while applying heat and DC pulse voltage to the graphite mold for hot pressing.

By applying the DC pulse voltage, the interface of the particles of the R-Fe-B-based porous magnet is activated, and sintering is promoted. Examples of such a pressurizing method include SPS (Spark Plasma Sintering).

Further, the graphite type for hot pressing of the R-Fe-B-based sintered magnet of the present invention for solving the above problems is

A graphite type for hot pressing of an R-Fe-B-based sintered magnet that pressurizes an R-Fe-B-based porous magnet while heating, and the graphite type for hot pressing is in the pressurizing axial direction. A die and a punch whose direction is defined by a direction perpendicular to the pressure axis direction, and the coefficient of thermal expansion (α _z ) of the die in the pressure axis direction is the direction of the die in the vertical direction. It is larger than the coefficient of thermal expansion (α _x , α _y).

Further, the graphite type for hot pressing of the R-Fe-B-based sintered magnet of the present invention preferably has the following aspects.

The coefficient of thermal expansion (α _x , α _y , α _z ) of the die is
1.05 ≤ α _z / α _x ≤ 1.3 ... (1)
1.05 ≤ α _z / α _y ≤ 1.3 ... (2)
The relationship between equations (1) and (2) is satisfied.

The isotropic graphite material has an isotropic ratio in the coefficient of thermal expansion depending on the site due to the influence of gravity before molding. Therefore, it is preferable to use a portion having a small anisotropic ratio, but material loss occurs when sorting by the magnitude of the anisotropic ratio. Rather, by utilizing the fact that the anisotropic ratio of the isotropic graphite material appears regularly according to the direction at the time of molding of the material and using it as the pressure axis direction after confirming the direction in which the coefficient of thermal expansion is large. The deformation of the obtained R-Fe-B-based sintered magnet can be reduced.

_{Further, when the anisotropic ratio (α z} / α _x or α _z / α _y ) in the equations (1) and (2) is 1.05 or more, it is sufficiently larger than the error of the measuring instrument, and the anisotropic ratio is large. The high direction can be easily detected, and the cutting direction of the material can be selected correctly. When the heterogeneous ratio is 1.3 or less in the equations (1) and (2), the coefficient of thermal expansion in the pressurizing axis direction can be suppressed to a small value, so that the generation of thermal stress can be reduced.

Thermal expansion coefficient of the pressure axis direction of the die (alpha _z) is ^{3.5 × 10 -6 /℃~5.0×10 -6 / ℃} .

The coefficient of thermal expansion (β _z ) of the punch in the pressure axis direction is larger than the coefficient of thermal expansion (β _x , β _{y) of the punch in the vertical direction.}

The coefficient of thermal expansion (β _x , β _y , β _z ) of the punch is
1.05 ≤ β _z / β _x ≤ 1.3 ... (3)
1.05 ≤ β _z / β _y ≤ 1.3 ... (4)
The relationship between equation (3) and equation (4) is satisfied.

The isotropic graphite material has an isotropic ratio in the coefficient of thermal expansion depending on the site due to the influence of gravity before molding. Therefore, it is preferable to use a portion having a small anisotropic ratio, but material loss occurs when sorting by the magnitude of the anisotropic ratio. Rather, by utilizing the fact that the anisotropic ratio of the isotropic graphite material appears regularly according to the direction of material molding, the direction in which the coefficient of thermal expansion is large is confirmed and then used as the pressure axis direction. The deformation of the obtained R-Fe-B-based sintered magnet can be reduced.

_{Further, when the anisotropic ratio (α z} / α _x or α _z / α _y ) in the equations (3) and (4) is 1.05 or more, it is sufficiently larger than the error of the measuring instrument, and the anisotropic ratio is large. The high direction can be easily detected, and the cutting direction of the material can be selected correctly. When the heterogeneous ratio is 1.3 or less in the equations (3) and (4), the coefficient of thermal expansion in the pressure axis direction can be suppressed to a small value, so that the generation of thermal stress can be reduced.

Thermal expansion coefficient of the pressure axis direction of the punch (beta _z) is ^{3.5 × 10 -6 /℃~5.0×10 -6 / ℃} .

In addition, the method for producing a graphite mold for hot pressing of an R-Fe-B-based sintered magnet of the present invention for solving the above problems includes the following contents.

It is cut out from the graphite material so that the direction with the highest coefficient of thermal expansion is the pressure axis direction.

The coefficient of thermal expansion in the x, y, and z directions of the graphite material is measured, and the direction having the highest coefficient of thermal expansion is cut out so as to be the pressure axis direction for processing.

(Form for carrying out the invention)
FIG. 1 is a perspective view showing a graphite mold for hot pressing housed in a chamber of a hot pressing apparatus. An embodiment of a method for manufacturing an R-Fe-B-based sintered magnet will be described with reference to FIG.

The graphite mold 1 for hot pressing includes punches 2, 2'and a die (die) 3. The graphite mold 1 for hot pressing is housed in the chamber of the hot pressing apparatus, and the R-Fe-B-based porous magnet 4 loaded (arranged) in the die 3 is heated by the upper and lower punches 2 and 2'. , Pressurize to manufacture R-Fe-B based sintered magnets.

The graphite constituting the graphite mold for hot pressing preferably has a shore hardness of 40 to 65. When the shore hardness is 40 or more, wear of the die or punch can be reduced due to friction with the R-Fe-B based porous magnet. When the shore hardness is 65 or less, graphitization has progressed sufficiently, so that dimensional changes are unlikely to occur even when heated.

The punches 2 and 2'have a substantially cylindrical shape, and the die 3 is a substantially cylindrical mold having an opening 5 in the center. An R-Fe-B-based porous magnet 4 is loaded into the opening 5, and for example, the die 3 is heated to raise the temperature of the R-Fe-B-based porous magnet 4 from 600 ° C. to 900 ° C. The porous magnet 4 is pressurized with punches 2 and 2'at a pressure of 1 to 3.0 ton / cm ² , and an R-Fe-B-based sintered magnet can be manufactured. The punches 2, 2'and the die 3 are preferably carbon, SiC, tungsten carbide, or the like, which can withstand the heating temperature and the applied pressure.

Further, a sleeve 6 made of a plurality of divided graphite pieces and having a tapered outer side may be inserted into the opening 5 of the die 3. The diameter of the opening 5 decreases from the upper surface to the lower surface of the die 3, and the diameter of the sleeve decreases accordingly. By making the opening 5 tapered, the R-Fe-B-based sintered magnet can be easily taken out from the die 3 together with the sleeve 6.
Further, the lower punch 2'has a flange portion, and has a structure in which the die 3 and the sleeve 6 do not fall when the die 3 and the sleeve 6 are set.

The pressurizing method is not particularly limited, but if the pulse energization sintering is performed by uniaxially pressurizing the DC pulse voltage while applying the DC pulse voltage, the DC pulse voltage can be applied, and the R-Fe-B system can be applied. The interface between the particles of the porous magnet 4 is activated, and sintering is promoted.
It should be noted that molding can be performed without applying a DC pulse voltage.
Further, by applying a magnetic field from the outside at the same time as molding, the magnetic field can be oriented to obtain a strong sintered magnet.

The pressing direction of the punches 2 and 2'is the pressure axis direction, and is shown as the Z axis in FIG. Further, the vertical direction perpendicular to the pressurizing axis is the X-axis or the Y-axis, but the direction perpendicular to the pressurizing axis direction is established in all directions around the pressurizing axis. The directions of the punches 2, 2'and the die 3 are defined by the vertical direction.

In the present invention, the coefficient of thermal expansion (α _z ) of the die 3 in the pressure axis direction is cut out to be larger than the _{coefficient of thermal expansion (α x} , α _y ) of the die 3 in the vertical direction. That is, since the die 3 is related to the overall shape of the R-Fe-B-based sintered magnet, it is important to specify the coefficient of thermal expansion of the die 3. Then, by setting the cutting direction having the largest coefficient of thermal expansion to the pressure axis direction of the die 3, irregular deformation of the material can be prevented. Since the irregular deformation of the material is small, the correction process after sintering becomes unnecessary or the correction amount is reduced, and the material loss can be reduced. Further, the R-Fe-B type sintered magnet is easily oxidized, and it is desirable to coat the surface immediately after sintering. Therefore, oxidation of the sintered magnet can be prevented if the correction process after sintering is unnecessary.

Further, when manufacturing an R-Fe-B-based sintered magnet using a plurality of graphite molds for hot pressing, it is obtained that the directionality of the coefficient of thermal expansion of each graphite mold for hot pressing varies. The shape of the sintered magnets to be produced also varies, and it becomes necessary to correct them in post-processing.

Therefore, when a graphite material to be used as a material is selected in advance and a graphite mold for hot pressing is manufactured from the graphite material, the direction having the highest coefficient of thermal expansion is set so that the direction of the coefficient of thermal expansion does not vary. Cut out so that it is in the direction of the pressurizing axis. As a result, it is possible to reduce corrections due to post-processing. In this case, the coefficient of thermal expansion of the graphite material in the x, y, and z directions is measured using a known method so that the direction having the highest coefficient of thermal expansion is the direction of the pressurizing axis and the direction of the Z axis in FIG. Set in the cutting machine. The device is controlled by a preset NC program to cut out and process dies 3, punches 2, and 2'.

FIG. 2 is a cross-sectional view of the graphite mold 1 for hot pressing.

In the graphite mold 1 for hot pressing, the opening 5 of the die 3 is tapered, and in FIG. 2, the diameter of the opening 5 decreases from the upper surface to the lower surface of the die 3, and the sleeve corresponds to this. The diameter of is also smaller. By making the opening 5 tapered, the R-Fe-B-based sintered magnet can be easily taken out from the die 3 together with the sleeve 6. The illustration of the collar of the lower punch 2'is omitted.

Examples and comparative examples of the present invention will be described below.
3 the direction of thermal expansion coefficients, respectively, to create a die using an isotropic graphite material of ^{3.52 -6 /℃,3.64 -6 /℃,4.84×10 -6 / ℃} .
The inner diameter of the die is a circle having a diameter of 50 mm at 25 ° C. Using this die, the die is heated to 890 ° C. by a hot press to pressurize an R-Fe-B-based porous magnet to obtain a sintered magnet.

(Example)
In the embodiment, the die is processed so that the pressure axis direction α _z is 4.84 × 10 ^{−6 / ° C.} _{In this case, α x} perpendicular to the pressurizing axis direction is 3.52 × 10 ^-6 / ° C, and α _y is 3.64 × 10 ^-6 / ° C. That is, the pressure axis direction α _z is larger than the two directions perpendicular to the pressure axis direction.
In this case, _{the difference between α x} and α _y is 0.08 × 10 ⁻⁶ / ° C., and a difference in thermal expansion of 3.5 μm occurs under pressure by a hot press. That is, the difference between the major axis and the minor axis of the obtained circular sintered magnet is 3.5 μm (0.08 × ^10-6 × (890-25) × 50).

(Comparison example)
On the other hand, the die is processed so that the pressure axis direction α _z is 3.64 × 10 ^{−6 / ° C.} _{In this case, α x} perpendicular to the pressurizing axis direction is 3.52 × 10 ^-6 / ° C, and α _y is 4.84 × 10 ^-6 / ° C. That is, the pressure axis direction α _z is an intermediate value in the two directions perpendicular to the pressure axis direction.
In this case, _{the difference between α x} and α _y is 1.32 × 10 ⁻⁶ / ° C., and a thermal expansion difference of 57 μm occurs under pressure by a hot press. That is, the difference between the major axis and the minor axis of the obtained circular sintered magnet is 57 μm (1.32 × ^10-6 × (890-25) × 50).
The sintered magnet obtained in the comparative example is deformed by 50 μm or more, and if it exceeds the dimensional tolerance, further correction processing is required.
Since the magnet to be manufactured is an R-Fe-B system, it is easily oxidized, and during this period, oxygen and the atmosphere must be blocked for processing, and the risk of oxidation of the obtained sintered magnet increases.
If the graphite mold for hot pressing of the sintered magnet of the present invention is used, the sintered magnet is less deformed and the need for correction processing can be reduced.

The present invention is not limited to the above-described embodiment, and can be appropriately modified, improved, and the like. In addition, the material, shape, size, numerical value, form, number, arrangement location, etc. of each component in the above-described embodiment are arbitrary and are not limited as long as the present invention can be achieved.

The method for producing a sintered magnet and the graphite mold for hot pressing of the present invention can be applied to a field requiring an R-Fe-B-based sintered magnet having high shape accuracy and low material loss.

1 Graphite type for hot press 2 2'Punch 3 Die 4 R-Fe-B type porous magnet 5 Opening 6 Sleeve 7 DC application device

Claims (15)

A method for producing an R-Fe-B-based sintered magnet in which an R-Fe-B-based porous magnet is placed in a graphite mold for hot pressing and pressurized while heating.
The graphite mold for hot pressing includes a die and a punch whose direction is defined by a pressure axis direction and a direction perpendicular to the pressure axis direction.
Manufacture of R-Fe-B-based sintered magnets in which the coefficient of thermal expansion (α _z ) of the die in the pressure axis direction is larger than the coefficient of thermal expansion (α _x , α _{y) of the die in the vertical direction.} Method. The coefficient of thermal expansion (α _x , α _y , α _z ) of the die is
1.05 ≤ α _z / α _x ≤ 1.3 ... (1)
1.05 ≤ α _z / α _y ≤ 1.3 ... (2)
The method for producing an R-Fe-B-based sintered magnet according to claim 1, which satisfies the relationship of the formulas (1) and (2). Thermal expansion coefficient of the pressure axis direction of the die (alpha _z) is as claimed in claim 1 or 2 is ^{3.5 × 10 -6 /℃~5.0×10 -6 / ℃} R-Fe -A method for manufacturing a B-based sintered magnet. The method according to any one of claims 1 to 3, wherein the coefficient of thermal expansion (β _z ) of the punch in the pressure axis direction is larger than the coefficient of thermal expansion (β _x , β _{y) of the punch in the vertical direction.} R-Fe-B system sintered magnet manufacturing method. The coefficient of thermal expansion (β _x , β _y , β _z ) of the punch is
1.05 ≤ β _z / β _x ≤ 1.3 ... (3)
1.05 ≤ β _z / β _y ≤ 1.3 ... (4)
The method for producing an R-Fe-B-based sintered magnet according to claim 4, which satisfies the relationship between the formula (3) and the formula (4). Thermal expansion coefficient of the pressure axis direction of the punch (beta _z) is any one of claims 1 to 5 is 3.5 × ^{10 -6} /℃~5.0×10 ^-6 / ℃ The method for manufacturing an R-Fe-B-based sintered magnet according to the above method. The R-Fe-B system according to any one of claims 1 to 6, wherein the pressurizing method is pulse energization sintering in which uniaxial pressurization is performed while applying heat and DC pulse voltage to the graphite mold for hot pressing. How to manufacture sintered magnets. A graphite type for hot pressing of an R-Fe-B-based sintered magnet that pressurizes an R-Fe-B-based porous magnet while heating it.
The graphite mold for hot pressing includes a die and a punch whose direction is defined by a pressure axis direction and a direction perpendicular to the pressure axis direction.
The coefficient of thermal expansion (α _z ) in the pressure axis direction of the die is larger than the coefficient of thermal expansion (α _x , α _{y) in the vertical direction of the die.} Graphite type for press. The coefficient of thermal expansion (α _x , α _y , α _z ) of the die is
1.05 ≤ α _z / α _x ≤ 1.3 ... (1)
1.05 ≤ α _z / α _y ≤ 1.3 ... (2)
The graphite mold for hot pressing of an R-Fe-B-based sintered magnet according to claim 8, which satisfies the relationship of the formulas (1) and (2). Thermal expansion coefficient of the pressure axis direction of the die (alpha _z) is, R-Fe- according to claim 8 or 9, which is 3.5 × ^{10 -6} /℃~5.0×10 ^-6 / ℃ Graphite type for hot pressing of B-based sintered magnets. The method according to any one of claims 8 to 10, wherein the coefficient of thermal expansion (β _z ) of the punch in the pressure axis direction is larger than the coefficient of thermal expansion (β _x , β _{y) of the punch in the vertical direction.} R-Fe-B type sintered magnet graphite type for hot pressing. The coefficient of thermal expansion (β _x , β _y , β _z ) of the punch is
1.05 ≤ β _z / β _x ≤ 1.3 ... (3)
1.05 ≤ β _z / β _y ≤ 1.3 ... (4)
The graphite mold for hot pressing of an R-Fe-B-based sintered magnet according to claim 11, which satisfies the relationship of the formulas (3) and (4). Thermal expansion coefficient of the pressure axis direction of the punch (beta _z) is to any one of claims 8 to 12 is 3.5 × ^{10 -6} /℃~5.0×10 ^-6 / ℃ The above-mentioned graphite type for hot pressing of an R-Fe-B type sintered magnet. The method for producing a graphite mold for hot pressing according to any one of claims 8 to 13, wherein the graphite material is cut out so that the direction having the highest coefficient of thermal expansion is the pressure axis direction. 6. Method for manufacturing graphite mold for hot press.

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