JP2021074746A - Die for powder molding, and method of manufacturing the same - Google Patents

Abstract

To provide a die for powder molding, which is hardly broken by the powder molding under high pressure and which can be inhibited from being broken due to a delayed crack.SOLUTION: A die for powder molding comprises: an inside cylinder part; an intermediate cylinder part that is shrinkage-fitted into the outer periphery of the inside cylinder part; and an outside cylinder part that is shrinkage-fitted into the outer periphery of the intermediate cylinder part. The shrinkage fit ratio of the intermediate cylinder part to the inside cylinder part is set to be a first shrinkage fit ratio, and the shrinkage fit ratio of the outside cylinder part to the intermediate cylinder part is set to be a second shrinkage fit ratio. In this case, the first shrinkage fit ratio is higher than the second shrinkage fit ratio, and the second shrinkage fit ratio is 0.15% or more and less than 0.25%.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a powder molding die and a method for manufacturing a powder molding die.

Patent Document 1 discloses a stepped die including an inner ring and an outer ring that is shrink-fitted on the outer periphery of the inner ring. During powder molding, the die may be damaged due to the generation of tensile stress due to the internal pressure applied to the die. In particular, the vicinity of the inner peripheral surface of the die constituting the space filled with the molding powder may be damaged. In Patent Document 1, a compressive stress that cancels the tensile stress generated in the inner ring is previously applied to the inner ring. Specifically, in Patent Document 1, the shrinkage fitting ratio of the outer ring to the inner ring is set to 0.12% or more and 0.25% or less.

Japanese Unexamined Patent Publication No. 2015-182124

It is desired that the die can be prevented from being damaged even when powdered at a higher pressure than before. The higher the pressure during powder molding, the greater the tensile stress generated in the inner ring. Therefore, when powder molding is performed at high pressure, it is necessary to increase the compressive stress applied to the inner ring in advance. In order to increase the compressive stress, it is possible to increase the shrinkage fitting ratio of the outer ring with respect to the inner ring.

On the other hand, the die may be provided with a machined hole. For example, a medium for adjusting the temperature of the die passes through the machined hole. When the die is provided with a machined hole, if the compressive stress applied to the inner ring is too large, the die may be placed from the machined hole as a starting point and crack may occur due to the stress.

Therefore, one of the purposes of the present disclosure is to provide a powder molding die that is not easily damaged by powder molding at high pressure and can suppress damage due to cracking. Another object of the present disclosure is to provide a method for manufacturing a powder molding die, which can obtain a powder molding die that is not easily damaged by powder molding at high pressure and can suppress damage due to cracking. To do.

The powder molding die of the present disclosure is
Inner cylinder and
An intermediate cylinder portion that is shrink-fitted on the outer circumference of the inner cylinder portion, and
An outer cylinder portion that is shrink-fitted on the outer circumference of the intermediate cylinder portion is provided.
When the shrink fit ratio of the intermediate cylinder portion with respect to the inner cylinder portion is defined as the first shrink fit ratio and the shrink fit ratio of the outer cylinder portion with respect to the intermediate cylinder portion is defined as the second shrink fit ratio.
The first shrink-fitting rate is larger than the second shrink-fitting rate,
The second shrink fit ratio is 0.15% or more and less than 0.25%.

The method for producing the powder molding die of the present disclosure is as follows.
The process of preparing the inner cylinder, intermediate cylinder, and outer cylinder, and
A step of shrink-fitting the intermediate cylinder portion to the outer circumference of the inner cylinder portion and integrating the inner cylinder portion and the intermediate cylinder portion.
A step of shrink-fitting the outer cylinder portion to the outer periphery of the integrated object is provided.
When the shrink fit ratio of the intermediate cylinder portion with respect to the inner cylinder portion is defined as the first shrink fit ratio and the shrink fit ratio of the outer cylinder portion with respect to the integrated object is defined as the second shrink fit ratio.
The first shrink-fitting rate is set to be larger than the second shrink-fitting rate, and the second shrink-fitting rate is set to 0.15% or more and less than 0.25%.

The powder molding die of the present disclosure is not easily damaged by powder molding at high pressure, and can suppress damage due to cracking. Further, the method for producing a powder molding die of the present disclosure provides a powder molding die that is not easily damaged by powder molding at high pressure and can suppress damage due to cracking.

FIG. 1 is a schematic plan view showing a powder molding die of the embodiment. FIG. 2 is a schematic cross-sectional view showing the powder molding die of the embodiment. FIG. 3 is a schematic perspective view showing an inner cylinder portion provided in the powder molding die of the embodiment.

[Explanation of Embodiments of the present disclosure]
First, the contents of the embodiments of the present disclosure will be listed and described.

(1) The powder molding die according to the present disclosure is
Inner cylinder and
An intermediate cylinder portion that is shrink-fitted on the outer circumference of the inner cylinder portion, and
An outer cylinder portion that is shrink-fitted on the outer circumference of the intermediate cylinder portion is provided.
When the shrink fit ratio of the intermediate cylinder portion with respect to the inner cylinder portion is defined as the first shrink fit ratio and the shrink fit ratio of the outer cylinder portion with respect to the intermediate cylinder portion is defined as the second shrink fit ratio.
The first shrink-fitting rate is larger than the second shrink-fitting rate,
The second shrink fit ratio is 0.15% or more and less than 0.25%.

The powder molding die of the present disclosure has a three-layer structure consisting of an inner cylinder portion, an intermediate cylinder portion, and an outer cylinder portion. Since the powder molding die has a three-layer structure, the first shrink-fitting ratio of the intermediate cylinder with respect to the inner cylinder and the second shrink-fitting ratio of the outer cylinder with respect to the intermediate cylinder are different. Can be done. Specifically, the first shrink fit rate can be made larger than the second shrink fit rate. Since the first shrink fit ratio is larger than the second shrink fit ratio, the compressive stress applied to the inner cylinder portion can be increased, while the compressive stress generated in the outer cylinder portion can be set to a predetermined value or less. By increasing the compressive stress applied to the inner cylinder, the pressure during powder molding can be increased. This is because the tensile stress generated in the powder molding die during powder molding is mainly generated in the vicinity of the inner peripheral surface of the inner cylinder portion. The internal pressure applied to the powder molding die during powder molding is relieved by the compressive stress applied to the inner cylinder portion.

The compressive stress generated in the outer cylinder portion is mainly due to the second shrinkage fitting ratio. When the second shrinkage fitting ratio is less than 0.25%, the compressive stress generated in the outer cylinder portion can be set to a predetermined value or less. By setting the compressive stress generated in the outer cylinder portion to a predetermined value or less, it is possible to suppress the occurrence of cracks on the powder molding die. In particular, even when a machined hole is provided in the outer cylinder portion, it is possible to suppress the occurrence of cracks by placing the machined hole on the powder molding die as a starting point. On the other hand, when the second shrink fit ratio is 0.15% or more, the outer cylinder portion can be appropriately shrink fit on the outer circumference of the intermediate cylinder portion.

From the above, the powder molding die of the present disclosure is not easily damaged by high pressure powder molding, and can suppress damage due to cracking.

(2) As an example of the powder molding die of the present disclosure,
The first shrink fit ratio may be 0.25% or more and less than 0.35%.

When the first shrink fit ratio is 0.25% or more, the compressive stress applied to the inner cylinder portion can be made larger than before. If the first shrink fit ratio is too large, cracks may occur during shrink fit. Therefore, when the first shrink-fitting rate is less than 0.35%, cracks at the time of shrink-fitting can be suppressed.

(3) As an example of the powder molding die of the present disclosure,
The inner cylinder portion
The first inner peripheral surface into which the lower punch is fitted,
The second inner surface on which the upper punch is fitted, and
An example includes a form including a stepped surface connecting the first inner peripheral surface and the second inner peripheral surface.

When the inner cylinder portion is provided with a stepped surface, the tensile stress generated in the powder molding die during powder molding is concentrated on the second inner peripheral surface or the corner portion composed of the first inner peripheral surface and the stepped surface. easy. As described above, the powder molding die of the present disclosure has a large compressive stress applied to the inner cylinder portion in advance. Therefore, even if the tensile stress is concentrated on the corner portion, it is easy to prevent the powder molding die from being damaged.

(4) As an example of the powder molding die of the present disclosure,
The intermediate cylinder portion and the outer cylinder portion are provided with processing holes through which a medium for adjusting the temperature of the powder molding die flows.
The machined hole is
Vertical holes provided along the axial direction of the powder molding die, and
It is provided with a horizontal hole provided in a direction intersecting the vertical hole.
The vertical hole is provided in the outer cylinder portion and is provided.
Examples of the lateral hole include a form provided in the outer cylinder portion and the intermediate cylinder portion.

By providing the intermediate cylinder portion and the outer cylinder portion with processing holes, the temperature of the powder molding die can be adjusted. For example, when the pressure during powder molding is increased, the temperature of the powder molding die becomes higher. Therefore, by flowing the refrigerant through the processing holes, it is possible to suppress the temperature rise of the powder molding die.

When a machined hole is provided in the powder molding die, cracks are likely to occur by placing the intersection of the vertical hole and the horizontal hole as the starting point. In the powder molding die of the present disclosure, as described above, the compressive stress generated in the outer cylinder portion can be set to a predetermined value or less. Therefore, since the intersection is provided on the outer cylinder portion, it is easy to prevent the occurrence of cracks by placing the intersection as the starting point.

(5) As an example of the powder molding die of the present disclosure,
Examples thereof include a form in which the intermediate cylinder portion and the outer cylinder portion are made of the same type of material.

Since the intermediate cylinder and the outer cylinder are made of the same material, the mechanical and thermal characteristics of the intermediate cylinder and the outer cylinder can be the same or similar. When the above characteristics are the same or similar, it is easy to perform a step of shrink-fitting the outer cylinder portion to the outer circumference of the intermediate cylinder portion at the time of manufacturing the powder molding die. In addition, it is easy to reduce variations in mechanical properties and thermal properties when using a powder molding die.

(6) As an example of the powder molding die of the present disclosure,
The thickness of the outer cylinder portion may be thicker than the thickness of the intermediate cylinder portion.

Regarding the relationship between the thickness of the outer cylinder and the compressive stress acting on the outer cylinder due to shrink fitting, when the shrink fit ratio is constant, the thicker the outer cylinder, the smaller the compressive stress, and the outer cylinder The thinner the thickness, the larger the compressive stress tends to be. Therefore, when the total thickness of the intermediate cylinder and the outer cylinder is constant, the thickness of the outer cylinder is thicker than the thickness of the intermediate cylinder, so that the compressive stress of the outer cylinder is set to a predetermined value or less. easy.

(7) The method for manufacturing a powder molding die according to the present disclosure is as follows.
The process of preparing the inner cylinder, intermediate cylinder, and outer cylinder, and
A step of shrink-fitting the intermediate cylinder portion to the outer circumference of the inner cylinder portion and integrating the inner cylinder portion and the intermediate cylinder portion.
A step of shrink-fitting the outer cylinder portion to the outer periphery of the integrated object is provided.
When the shrink fit ratio of the intermediate cylinder portion with respect to the inner cylinder portion is defined as the first shrink fit ratio and the shrink fit ratio of the outer cylinder portion with respect to the integrated object is defined as the second shrink fit ratio.
The first shrink-fitting rate is set to be larger than the second shrink-fitting rate, and the second shrink-fitting rate is set to 0.15% or more and less than 0.25%.

The method for manufacturing a powder molding die of the present disclosure is to manufacture a powder molding die having a three-layer structure consisting of an inner cylinder portion, an intermediate cylinder portion, and an outer cylinder portion. By forming the powder molding die with a three-layer structure, the first shrink-fitting ratio of the intermediate cylinder with respect to the inner cylinder and the second shrink-fitting of the outer cylinder with respect to the integral body obtained by shrink-fitting the intermediate cylinder with the inner cylinder. It is possible to make the shrinkage fitting rate of. Specifically, the first shrink fit rate can be made larger than the second shrink fit rate. Since the first shrink fit ratio is larger than the second shrink fit ratio, the compressive stress applied to the inner cylinder portion can be increased, while the compressive stress generated in the outer cylinder portion can be set to a predetermined value or less. By increasing the compressive stress generated in the inner cylinder, the pressure during powder molding can be increased. This is because the tensile stress generated in the powder molding die during powder molding is mainly generated in the vicinity of the inner peripheral surface of the inner cylinder portion. The internal pressure applied to the powder molding die during powder molding is relieved by the compressive stress applied to the inner cylinder portion.

The compressive stress generated in the outer cylinder portion is mainly due to the second shrinkage fitting ratio. By setting the second shrinkage fitting ratio to less than 0.25%, the compressive stress generated in the outer cylinder portion can be set to a predetermined value or less. By setting the compressive stress generated in the outer cylinder portion to a predetermined value or less, it is possible to suppress the occurrence of cracks on the powder molding die. In particular, even when a machined hole is provided in the outer cylinder portion, it is possible to suppress the occurrence of cracks by placing the machined hole on the powder molding die as a starting point. On the other hand, by setting the second shrink fit ratio to 0.15% or more, the outer cylinder portion can be appropriately shrink fit to the outer periphery of the integral body in which the intermediate cylinder portion is shrink fit into the inner cylinder portion.

From the above, the method for producing a powder molding die of the present disclosure is less likely to be damaged by high pressure powder molding and can suppress damage due to cracking.

[Details of Embodiments of the present disclosure]
Details of the embodiments of the present disclosure will be described below with reference to the drawings. The same reference numerals in the figures indicate the same names. It should be noted that the present invention is not limited to these examples, and is indicated by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

<Die for powder molding>
The powder molding die 1 of the embodiment will be described with reference to FIGS. 1 to 3. The powder molding die 1 includes an inner cylinder portion 2 and an outer cylinder portion 4 provided on the outside of the inner cylinder portion 2. One of the features of the powder molding die 1 of the embodiment is that it includes an intermediate cylinder portion 3 provided between the inner cylinder portion 2 and the outer cylinder portion 4. Specifically, in the powder molding die 1 of the embodiment, the intermediate cylinder portion 3 is shrink-fitted to the outer periphery of the inner cylinder portion 2, and the outer cylinder portion 4 is shrink-fitted to the outer circumference of the intermediate cylinder portion 3. It is one of the features. Further, one of the features of the powder molding die 1 of the embodiment is that the shrinkage fit ratio of the intermediate cylinder portion 3 with respect to the inner cylinder portion 2 is larger than the shrink fit ratio of the outer cylinder portion 4 with respect to the intermediate cylinder portion 3. .. Further, the powder molding die 1 of the embodiment is characterized in that the shrinkage fitting ratio of the outer cylinder portion 4 with respect to the intermediate cylinder portion 3 is 0.15% or more and less than 0.25%. Hereinafter, the detailed configuration of the powder molding die 1 will be described, and then a method for manufacturing the powder molding die 1 will be described.

FIG. 1 is a schematic plan view of the powder molding die 1 as viewed along the axial direction. In FIG. 1, for convenience of explanation, the machined holes 5 provided in the intermediate cylinder portion 3 and the outer cylinder portion 4 are shown by dotted lines. FIG. 2 is a schematic cross-sectional view cut along the (II)-(II) cutting line shown in FIG.

[Inner cylinder]
As shown in FIG. 2, the inner cylinder portion 2 includes a through hole 20 into which the lower punch 8 and the upper punch 9 are fitted. The through hole 20 is composed of a first inner peripheral surface 21, a second inner peripheral surface 22, and a stepped surface 23. The lower punch 8 is fitted into the first inner peripheral surface 21. The upper punch 9 is fitted into the second inner peripheral surface 22. The step surface 23 connects the first inner peripheral surface 21 and the second inner peripheral surface 22. The stepped surface 23 is composed of a single plane intersecting the first inner peripheral surface 21 and the second inner peripheral surface 22. The stepped surface 23 of this example is composed of a plane extending in a direction orthogonal to both the first inner peripheral surface 21 and the second inner peripheral surface 22. Of the through holes 20, the space formed by the upper surface of the lower punch 8, the first inner peripheral surface 21, the second inner peripheral surface 22, and the stepped surface 23 is a cavity filled with molding powder. It is 200. By pressing the molding powder 100 filled in the cavity 200 with the upper punch 9, a powder molded body having a stepped surface can be obtained.

In this example, of the through hole 20, the first region 210 composed of the first inner peripheral surface 21 has a cross-sectional shape cut along a plane orthogonal to the axial direction of the through hole 20, as shown in FIG. Is circular. Further, in the through hole 20, the second region 220 composed of the second inner peripheral surface 22 has a rectangular cross-sectional shape cut by a plane orthogonal to the axial direction of the through hole 20, as shown in FIG. The shape. The cross-sectional shape in the first region 210 and the second region 220 can be appropriately selected. For example, the cross-sectional shapes in the first region 210 and the second region 220 may be circular shapes having different diameters. Further, the cross-sectional shape in the first region 210 is circular, and the cross-sectional shape in the second region 220 is elliptical. The combination described above may be reversed between the cross-sectional shape in the first region 210 and the cross-sectional shape in the second region 220.

The thickness of the inner cylinder portion 2 is considered as follows. In the inner cylinder portion 2, a circle centered on the central axis of the inner cylinder portion 2 and passing through the second inner peripheral surface 22 located most radially outward from the center is referred to as a virtual circle P2. FIG. 1 shows the virtual circle P2 as a chain double-dashed line. The length between the virtual circle P2 and the outer peripheral surface of the inner cylinder portion 2 is defined as the thickness t2 of the inner cylinder portion 2. The thickness t2 of the inner cylinder portion 2 is 3 mm or more and 40 mm or less. When the thickness t2 of the inner cylinder portion 2 is 3 mm or more, it is easy to suppress the occurrence of cracks when the intermediate cylinder portion 3 is shrink-fitted on the outer circumference of the inner cylinder portion 2. On the other hand, when the thickness t2 of the inner cylinder portion 2 is 40 mm or less, the increase in size of the inner cylinder portion 2 can be suppressed, and the increase in size of the powder molding die 1 can be suppressed. The thickness t2 of the inner cylinder portion 2 may be further 3 mm or more and 30 mm or less, particularly 5 mm or more and 20 mm or less.

The inner cylinder portion 2 may be made of cemented carbide. Examples of cemented carbide include WC-Co-based alloys and WC-TiC-Co-based alloys.

[Intermediate cylinder]
As shown in FIGS. 1 and 2, the intermediate tubular portion 3 is shrink-fitted on the outer periphery of the inner tubular portion 2. The shrinkage fitting ratio of the intermediate cylinder portion 3 with respect to the inner cylinder portion 2 will be described later.

As shown in FIGS. 1 and 2, the intermediate cylinder portion 3 includes a machined hole 5. In this example, the intermediate cylinder portion 3 includes two machined holes 5. The machined hole 5 in the intermediate cylinder portion 3 includes lateral holes 55 and 56. The lateral holes 55 and 56 penetrate the outer peripheral surface and the inner peripheral surface of the intermediate tubular portion 3. As shown in FIG. 1, the lateral holes 55 and 56 are provided at positions shifted in the circumferential direction of the intermediate cylinder portion 3. Further, as shown in FIG. 2, the lateral holes 55 and 56 are provided at positions shifted in the axial direction of the intermediate cylinder portion 3. As shown in FIG. 2, the intermediate cylinder portion 3 is provided with a spiral groove 57 on the inner peripheral surface. The spiral groove 57 is provided so as to connect the two lateral holes 55 and 56. The lateral holes 55, 56 and the spiral groove 57 are connected to a machined hole 5 provided in the outer tubular portion 4, which will be described later.

The thickness t3 of the intermediate cylinder portion 3 shown in FIG. 1 is 5 mm or more and 40 mm or less. When the thickness t3 of the intermediate cylinder portion 3 is 5 mm or more, it is easy to suppress the occurrence of cracks when the outer cylinder portion 4 is shrink-fitted on the outer circumference of the intermediate cylinder portion 3. On the other hand, when the thickness t3 of the intermediate cylinder portion 3 is 40 mm or less, it is possible to suppress the increase in size of the intermediate cylinder portion 3, and thus the increase in size of the powder molding die 1. The thickness t3 of the intermediate cylinder portion 3 may be further 5 mm or more and 30 mm or less, particularly 10 mm or more and 25 mm or less.

The intermediate cylinder portion 3 may be made of hardened steel.

[Outer cylinder]
As shown in FIGS. 1 and 2, the outer tubular portion 4 is shrink-fitted on the outer periphery of the intermediate tubular portion 3. The shrinkage fitting ratio of the outer tubular portion 4 with respect to the intermediate tubular portion 3 will be described later.

The outer tubular portion 4 includes a machined hole 5 as shown in FIGS. 1 and 2. In this example, the outer tubular portion 4 includes two machined holes 5. The machined hole 5 in the outer tubular portion 4 includes vertical holes 51 and 52 and horizontal holes 53 and 54. The vertical holes 51 and 52 are provided along the axial direction of the outer tubular portion 4. The horizontal holes 53 and 54 are provided in a direction intersecting the vertical holes 51 and 52. The horizontal holes 53 and 54 of this example are provided in a direction orthogonal to the vertical holes 51 and 52. In the machined hole 5, the vertical hole 51 and the horizontal hole 53 located on the right side of FIG. 2 communicate with each other, and the vertical hole 52 and the horizontal hole 54 located on the left side of FIG. 2 communicate with each other. As shown in FIG. 1, the machined hole 5 composed of the vertical hole 51 and the horizontal hole 53 located on the right side of FIG. 2 and the machined hole 5 composed of the vertical hole 52 and the horizontal hole 54 located on the left side of FIG. The outer tubular portion 4 is provided at a position shifted in the circumferential direction. Further, the machined hole 5 composed of the vertical hole 51 and the horizontal hole 53 located on the right side of FIG. 2 and the machined hole 5 composed of the vertical hole 52 and the horizontal hole 54 located on the left side of FIG. 2 are as shown in FIG. Is provided at a position deviated in the axial direction of the outer tubular portion 4. The lateral holes 53 and 54 penetrate the outer peripheral surface and the inner peripheral surface of the outer tubular portion 4. The lateral holes 53 and 54 communicate with the lateral holes 55 and 56 of the intermediate tubular portion 3 in a state where the outer tubular portion 4 is shrink-fitted into the intermediate tubular portion 3. The ends of the outer tubular portions 4 on the outer peripheral surface side of the lateral holes 53 and 54 are closed by the set screws 59.

A medium for adjusting the temperature of the powder molding die 1 flows through the processing holes 5 provided in the intermediate cylinder portion 3 and the outer cylinder portion 4. Examples of the medium include a refrigerant that cools the powder molding die 1. Examples of the refrigerant include cooling water. Further, as the medium, a high temperature fluid for heating the powder molding die 1 can be mentioned. Examples of the high temperature fluid include hot air and hot water.

Cooling water is circulated in the powder molding die 1 of this example. The cooling water is supplied to the powder molding die 1 from the vertical hole 51 located on the right side of FIG. 2, flows through the vertical hole 51 and the horizontal holes 53 and 55, and is guided to the inner peripheral surface of the intermediate cylinder portion 3. The cooling water guided to the inner peripheral surface of the intermediate cylinder portion 3 flows through the spiral groove 57 and is guided to the lateral hole 56 located on the left side of FIG. After that, it flows through the horizontal holes 56, 54 and the vertical holes 52 located on the left side of FIG. 2, and is discharged from the vertical holes 52 to the outside of the powder molding die 1. When the pressure during powder molding is increased, the temperature of the powder molding die 1 becomes higher. Therefore, by circulating the cooling water through the powder molding die 1, it is possible to suppress the temperature rise of the powder molding die 1. In the powder molding die 1 of this example, the inner cylinder portion 2 does not have a processed hole through which cooling water or the like passes.

The powder molding die 1 may be provided with a hole into which a heater can be arranged, in addition to the processing hole 5 through which the medium is distributed.

The thickness t4 of the outer tubular portion 4 shown in FIG. 1 is 10 mm or more and 60 mm or less. Here, regarding the relationship between the thickness of the outer cylinder portion 4 and the compressive stress acting on the outer cylinder portion 4 by shrink fitting, when the shrink fit ratio is constant, the thicker the thickness of the outer cylinder portion 4, the higher the compressive stress. As the size becomes smaller and the thickness of the outer cylinder portion 4 becomes thinner, the compressive stress tends to increase. Therefore, when the thickness t4 of the outer cylinder portion 4 is 10 mm or more, it is easy to set the compressive stress generated in the outer cylinder portion 4 to a predetermined value or less. On the other hand, when the thickness t4 of the outer cylinder portion 4 is 60 mm or less, it is possible to suppress the increase in size of the outer cylinder portion 4, and thus the increase in size of the powder molding die 1. The thickness t4 of the outer tubular portion 4 is further 20 mm or more and 60 mm or less, particularly 20 mm or more and 50 mm or less.

The thickness t4 of the outer tubular portion 4 may be thicker than the thickness t3 of the intermediate tubular portion 3. Regarding the relationship between the thickness of the outer cylinder 4 and the compressive stress acting on the outer cylinder 4 by shrink fitting, as described above, when the shrink fitting ratio is constant, the thicker the outer cylinder 4, the more compression is performed. The stress tends to be small. Therefore, when the total thickness of the intermediate cylinder 3 and the outer cylinder 4 is constant, the thickness t4 of the outer cylinder 4 is thicker than the thickness t3 of the intermediate cylinder 3, so that the outer cylinder 4 is compressed. It is easy to set the stress below a predetermined value. When the total thickness of the intermediate cylinder portion 3 and the outer cylinder portion 4 is constant, the thickness t4 of the outer cylinder portion 4 is 1.2 times or more and 5.0 times or less of the thickness t3 of the intermediate cylinder portion 3. Can be mentioned. Since the thickness t4 of the outer cylinder portion 4 is 1.2 times or more the thickness t3 of the intermediate cylinder portion 3, the compressive stress of the outer cylinder portion 4 can be easily set to a predetermined value or less. On the other hand, since the thickness t4 of the outer cylinder portion 4 is 5.0 times or less of the thickness t3 of the intermediate cylinder portion 3, the thickness t3 of the intermediate cylinder portion 3 can be made an appropriate thickness, and the thickness of the intermediate cylinder portion 3 can be adjusted to an appropriate thickness. It is easy to prevent cracks from occurring when the outer cylinder portion 4 is shrink-fitted to the outer periphery. The thickness t4 of the outer cylinder portion 4 is 1.5 times or more and 4.0 times or less, particularly 1.5 times or more and 3.0 times or less of the thickness t3 of the intermediate cylinder portion 3.

The outer tubular portion 4 may be made of hardened steel. It can be mentioned that the intermediate cylinder portion 3 and the outer cylinder portion 4 are made of the same kind of material. Since the intermediate cylinder portion 3 and the outer cylinder portion 4 are made of the same material, the mechanical characteristics and the thermal characteristics of the intermediate cylinder portion 3 and the outer cylinder portion 4 can be the same or similar. When the above characteristics are the same or similar, it is easy to perform the step of shrink-fitting the outer cylinder portion 4 to the outer circumference of the intermediate cylinder portion 3 at the time of manufacturing the powder molding die 1. In addition, it is easy to reduce variations in mechanical properties and thermal properties when the powder molding die 1 is used.

As shown in FIGS. 1 and 2, the outer tubular portion 4 includes a flange portion 40 that projects radially outward from the outer peripheral surface. The collar portion 40 is provided over the entire circumference of the outer tubular portion 4. The collar portion 40 engages with the die plate 7. When the powder molded body is molded using the powder molding die 1, the powder molded body after molding is a relatively powder molded body with the powder molding die 1 lowered together with the die plate 7 and the lower punch 8 in the fixed state. Die-cutting is performed by pushing up. In order to facilitate the lowering of the powder molding die 1, it is difficult to arrange a support for supporting the powder molding die 1 in the space below the powder molding die 1. Therefore, the powder molding die 1 of this example is supported by the die plate 7 by the flange portion 40 in the outer tubular portion 4.

[Burning rate]
In the powder molding die 1 of the embodiment, the shrinkage fit ratio of the intermediate cylinder portion 3 with respect to the inner cylinder portion 2 is larger than the shrink fit ratio of the outer cylinder portion 4 with respect to the intermediate cylinder portion 3. The shrink-fitting ratio of the intermediate cylinder portion 3 with respect to the inner cylinder portion 2 is called the first shrink-fitting ratio. Further, the shrink fit ratio of the outer cylinder portion 4 with respect to the intermediate cylinder portion 3 is referred to as a second shrink fit ratio.

Here, the shrink fit ratio is expressed by the following equation.
Shrink fit rate = {(d-D) / d} x 100
In the above formula, d is the outer diameter of the cylinder portion located inside among the adjacent cylinder portions. D in the above formula is the inner diameter of the cylinder portion located on the outer side of the adjacent cylinder portions.

≪First shrink fit rate≫
The first shrink fit ratio is expressed by the following equation when the outer diameter of the inner cylinder portion 2 is d2 and the inner diameter of the intermediate cylinder portion 3 is D3.
First shrink fit rate = {(d2-D3) / d2} x 100

The first shrink-fitting ratio represented by the above formula is 0.25% or more and less than 0.35%. When the first shrink fit ratio is 0.25% or more, the compressive stress applied to the inner cylinder portion 2 can be made larger than before. If the first shrink fit ratio is too large, cracks may occur during shrink fit. Therefore, when the first shrink-fitting rate is less than 0.35%, cracks at the time of shrink-fitting can be suppressed. The first shrink-fitting rate may be further 0.28% or more and 0.33% or less, particularly 0.30% or more and 0.33% or less.

≪Second shrink fit rate≫
The second shrink fit ratio is expressed by the following equation, where the outer diameter of the intermediate cylinder portion 3 is d3 and the inner diameter of the outer cylinder portion 4 is D4.
Second shrink fit rate = {(d3-D4) / d3} x 100

The second shrink fit ratio represented by the above formula is 0.15% or more and less than 0.25%. When the second shrinkage fitting ratio is less than 0.25%, the compressive stress generated in the outer cylinder portion 4 can be set to a predetermined value or less. Therefore, since the second shrink fit ratio is less than 0.25%, even if the outer cylinder portion 4 is provided with the machined hole 5, the powder molding die 1 is placed from the machined hole 5 as a starting point and cracks occur. Can be suppressed. On the other hand, when the second shrink fit ratio is 0.15% or more, the outer cylinder portion 4 can be appropriately shrink fit on the outer periphery of the intermediate cylinder portion 3. The second shrink-fitting rate may be further 0.15% or more and 0.22% or less, particularly 0.18% or more and 0.22% or less.

<Manufacturing method of powder molding die>
The method for producing a powder molding die of the embodiment includes a preparatory step, a first shrink-fitting step, and a second shrink-fitting step.

[Preparation process]
In the preparation step, the inner cylinder portion 2, the intermediate cylinder portion 3, and the outer cylinder portion 4 described above are prepared. At this time, the inner cylinder portion 2, the intermediate cylinder portion 3, and the outer cylinder portion 4 are appropriately prepared with dimensions such that the first shrink fit ratio and the second shrink fit ratio are desired values.

[First shrink fitting process]
In the first shrink-fitting step, the intermediate cylinder portion 3 is shrink-fitted on the outer circumference of the inner cylinder portion 2. By the first shrink-fitting step, an integral product in which the intermediate cylinder portion 3 is shrink-fitted on the outer periphery of the inner cylinder portion 2 is obtained. The shrink fit rate in the first shrink fit step is defined as the first shrink fit rate. The first shrink-fitting rate may be 0.25% or more and less than 0.35%. By setting the first shrink fit ratio to 0.25% or more, the compressive stress applied to the inner cylinder portion 2 can be made larger than before. If the first shrink fit ratio is made too large, cracks may occur during shrink fit. Therefore, by setting the first shrink fit ratio to less than 0.35%, cracks during shrink fit can be suppressed. The first shrink-fitting rate may be further set to 0.28% or more and 0.33% or less, particularly 0.30% or more and 0.33% or less.

[Second shrink fitting process]
In the second shrink-fitting step, the outer cylinder portion 4 is shrink-fitted to the outer periphery of the integral product obtained by the first shrink-fitting step. By the second shrink-fitting step, a powder molding die 1 in which the outer cylinder portion 4 is shrink-fitted on the outer periphery of the one piece is obtained. The shrink fit rate in the second shrink fit step is defined as the second shrink fit rate. The second shrink fit rate is set smaller than the first shrink fit rate. In other words, the first shrink fit rate is set higher than the second shrink fit rate. The second shrink fit ratio is 0.15% or more and less than 0.25%. By setting the second shrinkage fitting ratio to less than 0.25%, the compressive stress generated in the outer cylinder portion 4 can be set to a predetermined value or less. Therefore, by setting the second shrink fit ratio to less than 0.25%, even if the outer cylinder portion 4 is provided with the machined hole 5, the powder molding die 1 is placed from the machined hole 5 as a starting point and cracks occur. Can be suppressed. On the other hand, by setting the second shrink fit ratio to 0.15% or more, the outer cylinder portion 4 can be appropriately shrink fit to the outer periphery of the integral body in which the intermediate cylinder portion 3 is shrink-fitted to the outer circumference of the inner cylinder portion 2. The second shrink-fitting rate may be further set to 0.15% or more and 0.22% or less, particularly 0.18% or more and 0.22% or less.

<Powder for molding>
The powder molding die 1 described above is used when molding a powder molded product using a molding powder 100 containing a soft magnetic powder.

The soft magnetic powder is composed of an aggregate of soft magnetic particles. Examples of the soft magnetic particles include those containing 50% by mass or more of iron. Specifically, the soft magnetic particles are made of pure iron or an iron-based alloy. The pure iron here has a purity of 99% or more, that is, an iron (Fe) content of 99% by mass or more. The iron-based alloy here contains an additive element, and the balance is composed of Fe and unavoidable impurities. Iron-based alloys contain one or more additive elements. Examples of the additive element include silicon (Si) and aluminum (Al). Specific examples of iron-based alloys include Fe-Si alloys, Fe-Al alloys, Fe-N alloys, Fe-Ni alloys, Fe-C alloys, Fe-B alloys, and Fe-Co alloys. Examples thereof include Fe-P-based alloys, Fe-Ni-Co-based alloys, and Fe-Al-Si-based alloys.

Each soft magnetic particle constituting the soft magnetic powder may have an insulating coating on the surface. By providing an insulating coating on the surface of the soft magnetic particles, it is easy to reduce the eddy current loss of the soft magnetic powder itself, and a low-loss powder molded product can be obtained. The insulating coating can be composed of an oxide containing one or more kinds of metal elements, a metal oxide such as a nitride or a carbide, a metal nitride, a metal carbide or the like. Examples of the metal element include iron, aluminum, calcium, manganese, zinc, magnesium, vanadium, chromium, barium, strontium, rare earth elements and the like. Further, the insulating coating may be composed of, for example, one or more compounds selected from a phosphorus compound, a silicon compound, a zirconium compound and an aluminum compound. In addition, the insulating coating may be composed of a metal salt compound, for example, a metal phosphate compound, a metal borate compound, a metal silicate compound, a metal titanate compound, or the like. Typical examples of the metal phosphate compound include iron phosphate, manganese phosphate, zinc phosphate, calcium phosphate and the like.

The thickness of the insulating coating is 10 nm or more and 1 μm or less. When the thickness of the insulating coating is 10 nm or more, it is easy to secure the insulation between the soft magnetic particles. On the other hand, when the thickness of the insulating coating is 1 μm or less, the presence of the insulating coating can suppress a decrease in the content ratio of the soft magnetic powder in the powder molded product. The thickness of the insulating coating is further 10 nm or more and 200 nm or less, particularly 10 nm or more and 100 nm or less.

The molding powder 100 can contain a lubricant. By containing a lubricant, friction during powder molding can be reduced. Since the friction during powder molding can be reduced, the powder molded body can be easily extracted from the mold using the powder molding die 1, and a powder molded body having excellent surface properties can be obtained. Further, by containing a lubricant, moldability can be improved. By improving the moldability, a powder molded product having excellent dimensional accuracy can be obtained. Examples of the lubricant include metal soaps such as lithium stearate and zinc stearate, fatty acid amides such as stearic acid amides, organic substances such as higher fatty acid amides such as ethylene bisstearic acid amides, and inorganic substances such as boron nitride and graphite. ..

<Effect>
The powder molding die 1 of the embodiment has a three-layer structure consisting of an inner cylinder portion 2, an intermediate cylinder portion 3, and an outer cylinder portion 4. Since the powder molding die 1 has a three-layer structure, the first shrink fit ratio of the intermediate cylinder portion 3 with respect to the inner cylinder portion 2 and the second shrink fit ratio of the outer cylinder portion 4 with respect to the intermediate cylinder portion 3. Can be larger than. Since the first shrink fit ratio is larger than the second shrink fit ratio, the compressive stress applied to the inner cylinder portion 2 can be increased, while the compressive stress generated in the outer cylinder portion 4 can be set to a predetermined value or less. ..

The tensile stress generated in the powder molding die 1 during powder molding is mainly generated in the vicinity of the inner peripheral surface of the inner cylinder portion 2. In particular, when the inner cylinder portion 2 is provided with the stepped surface 23, the tensile stress tends to be concentrated on the corner portion composed of the second inner peripheral surface 22 and the stepped surface 23. The powder molding die 1 of the embodiment can increase the compressive stress applied to the inner cylinder portion 2. Therefore, even when the corner portion where tensile stress is concentrated and easily cracked is provided, the pressure at the time of powder molding can be increased.

On the other hand, since the compressive stress generated in the outer cylinder portion 4 can be set to a predetermined value or less, the machined hole 5 can be provided in the outer cylinder portion 4. When the machined hole 5 is provided in the outer cylinder portion 4, cracks are likely to occur by placing the intersection of the vertical holes 51, 52 and the horizontal holes 53, 54 constituting the machined hole 5 as the starting point. In the powder molding die 1 of the embodiment, the second shrinkage fitting ratio is 0.15% or more and less than 0.25%, so that the compressive stress generated in the outer cylinder portion 4 is not more than a predetermined value. Therefore, by providing the above-mentioned intersection that can be the starting point of cracking in the outer tubular portion 4, it is possible to suppress the occurrence of cracking in the powder molding die 1 starting from the machined hole 5.

By providing the processing hole 5 in the powder molding die 1, the temperature of the powder molding die 1 can be adjusted. Specifically, the powder molding die 1 can be cooled, and the temperature rise of the powder molding die 1 can be suppressed. When the pressure during powder molding is increased, the temperature of the powder molding die 1 becomes higher. When the temperature of the powder molding die 1 becomes high, when the molding powder 100 contains a lubricant, the lubricant may be softened and the function of the lubricant may not be exhibited. If the lubricant does not function, the soft magnetic particles come into contact with each other, and the insulating coating provided on the surface of the soft magnetic particles is easily destroyed. Therefore, since the powder molding die 1 can be cooled, the function of the lubricant can be maintained and the destruction of the insulating coating can be suppressed. By doing so, it is easy to obtain a low-loss powder molded product.

[Test Example 1]
In Test Example 1, the stress distribution acting on the powder molding die when powder molding was performed using various powder molding dies was analyzed. That is, in Test Example 1, the stress distribution acting on the powder molding die under the pressure of powder molding was analyzed. Hereinafter, the conditions of various powder molding dies and the analysis conditions will be described, and then the analysis results will be described.

-Sample No. 1
Sample No. The powder molding die No. 1 is composed of a three-layer structure consisting of an inner cylinder portion, an intermediate cylinder portion, and an outer cylinder portion. The inner cylinder portion is the inner cylinder portion 2 shown in FIG. The inner peripheral surface of the inner cylinder portion includes a first inner peripheral surface, a second inner peripheral surface, and a stepped surface. The first inner peripheral surface is located on the side where the lower punch is fitted. The second inner peripheral surface is located on the side where the upper punch is fitted. The intermediate cylinder portion and the outer cylinder portion are the intermediate cylinder portion 3 and the outer cylinder portion 4 shown in FIGS. 1 and 2. The intermediate cylinder portion and the outer cylinder portion are provided with machined holes. The intersection of the vertical hole and the horizontal hole in the machined hole is provided in the outer tubular portion. The thickness t2 of the inner cylinder portion is 15 mm. The thickness t3 of the intermediate cylinder portion is 16 mm. The thickness t4 of the outer cylinder portion is 29 mm. The inner cylinder is made of cemented carbide. The intermediate cylinder and the outer cylinder are made of hardened steel having the same composition. The stress distribution is analyzed by setting the above dimensions and predetermined physical characteristics of each material. This point is the same for other samples and Test Example 2 described later.

Sample No. In the powder molding die of No. 1, the intermediate cylinder portion is shrink-fitted on the outer circumference of the inner cylinder portion, and the outer cylinder portion is shrink-fitted on the outer circumference of the intermediate cylinder portion. The first shrink fit ratio of the intermediate cylinder portion with respect to the inner cylinder portion is 0.35%. Further, the second shrink-fitting ratio of the outer cylinder portion with respect to the integral body in which the intermediate cylinder portion is shrink-fitted to the inner cylinder portion is 0.25%. Each shrink fit ratio is shown in Table 1.

-Sample No. 2
Sample No. The powder molding die of No. 2 has a sample No. The first shrink-fitting rate and the second shrink-fitting rate are different from those of the powder molding die 1. The first shrink fit rate is 0.30%. The second shrink fit rate is 0.20%. Other conditions are the sample No. Same as 1.

-Sample No. 3
Sample No. The powder molding die of No. 3 has a sample No. The positions of the machined holes are different from those of the powder molding die of 2. Sample No. The powder molding die of No. 3 has a sample No. With respect to the powder molding die No. 2, the vertical hole provided in the outer cylinder portion is located on the outer side in the radial direction by 2 mm, and the hole into which the set screw is fitted is 2 mm shallower. Other conditions are the sample No. Same as 2.

-Sample No. 4
Sample No. The powder molding die of No. 4 has a sample No. The first shrink-fitting rate and the second shrink-fitting rate are different from those of the powder molding die of 3. In addition, sample No. The powder molding die of No. 4 has a sample No. The thickness of the intermediate cylinder portion and the outer cylinder portion is different from that of the powder molding die of 3. The first shrink fit rate is 0.31%. The second shrink fit rate is 0.19%. The thickness t3 of the intermediate cylinder portion is 15 mm. The thickness t4 of the outer cylinder portion is 30 mm. Other conditions are the sample No. Same as 3.

-Sample No. 10
Sample No. The powder molding die of 10 has a two-layer structure consisting of an inner cylinder portion and an outer cylinder portion. The inner cylinder is the sample No. Same as 1. The outer tubular portion includes a machined hole and a spiral groove. The outer tubular portion includes an intersection of a vertical hole and a horizontal hole in a machined hole. A spiral groove connecting the lateral holes is provided on the inner peripheral surface of the outer tubular portion. The thickness of the inner cylinder portion is 15 mm. The thickness of the outer cylinder portion is 45 mm. The inner cylinder is made of cemented carbide. The outer cylinder is made of hardened steel. The composition of this cemented carbide and hardened steel is described in Sample No. Same as 1.

Sample No. In the powder molding die No. 10, the outer cylinder portion is shrink-fitted on the outer circumference of the inner cylinder portion. The shrink fit ratio of the outer cylinder portion with respect to the inner cylinder portion is 0.35%.

The stress distribution acting on the powder molding die when powder molding was performed using the powder molding die of each sample was analyzed by CAE (Computer Aided Engineering). The molding pressure at the time of powder molding is 14 ton / cm ² (about 1372 MPa). The configurations of the dies other than the powder molding die are all the same. From this analysis result, the maximum principal stress generated at a specific location in each cylinder was calculated. In the following, it may be simply referred to as stress. The specific portion of the inner cylinder portion was a corner portion composed of a second inner peripheral surface and a stepped surface. The specific location in the intermediate cylinder is the intersection of the lateral hole located on the lower side in the axial direction of the intermediate cylinder and the spiral groove. The specific location on the outer cylinder was the intersection of the vertical hole and the horizontal hole. Table 1 shows the maximum principal stress generated at a specific location in each cylinder.

First, the stress of the inner cylinder portion will be described. Sample No. In the powder molding die No. 10, the stress of the inner cylinder portion is as large as 987 MPa. Sample No. In the 10 powder molding dies, the stress of the inner cylinder portion is large because the powder molding die is composed of a two-layer structure consisting of an inner cylinder portion and an outer cylinder portion, and the molding pressure is concentrated on the inner cylinder portion. it is conceivable that. In particular, sample No. It is considered that the powder molding die of No. 10 has high rigidity because the thickness of the outer cylinder portion is as thick as 45 mm, and it is difficult for the molding pressure to be dispersed in the outer cylinder portion. That is, if the powder molding die is composed of a two-layer structure consisting of an inner cylinder portion and an outer cylinder portion and the shrinkage fitting ratio of the outer cylinder portion with respect to the inner cylinder portion is increased, the internal pressure applied to the inner cylinder portion during powder molding is applied. It is considered difficult to reduce. If the stress of the inner cylinder portion is large, the inner cylinder portion may be damaged such as cracks during powder molding.

Sample No. Sample No. 1 to sample No. The powder molding die of No. 4 has a sample No. The stress of the inner cylinder portion is smaller than that of the powder molding die of 10. Sample No. Sample No. 1 to sample No. It is considered that the reason why the stress of the inner cylinder portion is small in the powder molding die of No. 4 is that the powder molding die is composed of a three-layer structure consisting of an inner cylinder portion, an intermediate cylinder portion, and an outer cylinder portion. It is considered that the molding pressure was dispersed in each cylinder portion because the powder molding die was composed of the cylinder portion having a three-layer structure. In particular, sample No. The powder molding die of No. 1 is the sample No. From sample No. 2 Compared with 4, the stress of the inner cylinder portion is smaller. Sample No. It is considered that the powder molding die of No. 1 has a large first shrink-fitting ratio. That is, the sample No. It is considered that the powder molding die No. 1 was able to effectively relieve the internal pressure applied to the inner cylinder portion during powder molding by the stress due to the first shrink fitting.

Next, the stress of the outer cylinder portion will be described. Sample No. From sample No. 2 The powder molding die of No. 4 has a sample No. 10 and sample No. Compared with the powder molding die of No. 1, the stress of the outer cylinder portion is small. Sample No. From sample No. 2 In the powder molding die of No. 4, the stress of the outer cylinder portion is small because the second shrinkage fitting ratio satisfies 0.15% or more and less than 0.25%, so that the stress of the outer cylinder portion is reduced to a predetermined value or less. It is thought that it was possible to set it. It is considered that since the stress of the outer cylinder portion is small, even if the outer cylinder portion is provided with the intersection of the vertical hole and the horizontal hole, it is possible to prevent the occurrence of cracks by placing the intersection as the starting point. The cracks that may occur in the powder molding die will be described in Test Example 2.

[Test Example 2]
Sample No. described in Test Example 1. Sample No. 1 to sample No. 4 and sample No. For each of the 10 powder molding dies, the stress distribution acting on the powder molding dies when no molding pressure was applied was analyzed. That is, in Test Example 2, the stress distribution of the powder forming die having only the stress applied by shrink fitting was analyzed. The analysis method is the same as in Test Example 1. Table 2 shows the maximum principal stress generated at a specific location in the intermediate cylinder portion and the outer cylinder portion in Test Example 2. The specific location of each cylinder is the same as in Test Example 1.

Sample No. In the powder molding die No. 10, the stress of the outer cylinder portion is as large as 1356 MPa. Sample No. In the 10 powder molding dies, the stress of the outer cylinder portion is large because the powder molding die has a two-layer structure consisting of an inner cylinder portion and an outer cylinder portion, and the outer cylinder portion is shrink-fitted to the inner cylinder portion. It is considered that the rate is as large as 0.35%. In addition, sample No. The powder molding die of No. 1 also has a large stress of 1551 MPa in the outer cylinder portion. Sample No. It is considered that the reason why the stress of the outer cylinder portion is large in the powder molding die of No. 1 is that the second shrinkage fitting ratio is as large as 0.25%. If the stress of the outer cylinder portion is large, the powder molding die may be placed and cracked starting from the intersection of the vertical hole and the horizontal hole provided in the outer cylinder portion.

Sample No. From sample No. 2 The powder molding die of No. 4 has a sample No. 10 and sample No. Compared with the powder molding die of No. 1, the stress of the outer cylinder portion is small. Sample No. From sample No. 2 In the powder molding die of No. 4, the stress of the outer cylinder portion is small because the second shrinkage fitting ratio satisfies 0.15% or more and less than 0.25%, so that the stress of the outer cylinder portion is reduced to a predetermined value or less. It is thought that it was possible to set it. In particular, sample No. The powder molding die of No. 3 has a sample No. Compared with the powder molding die of No. 2, the stress of the outer cylinder portion is further smaller. Sample No. The powder molding die of No. 3 has a sample No. On the other hand, it is considered that the stress at the intersection could be relaxed by changing the position of the machined hole in the outer cylinder. In addition, sample No. The powder molding die of No. 4 has a sample No. Compared with the powder molding die of No. 3, the stress of the inner cylinder portion is the same, and the stress of the outer cylinder portion is further smaller. Sample No. The powder molding die of No. 4 has a sample No. It is considered that the second shrinkage fitting rate is smaller than that of 3.

From the above, the powder molding die is composed of a three-layer structure consisting of an inner cylinder portion, an intermediate cylinder portion, and an outer cylinder portion, and when the first shrink fit ratio satisfies a specific range, the inner cylinder portion is large. It can be seen that stress can be applied. Further, the powder molding die is composed of a three-layer structure consisting of an inner cylinder portion, an intermediate cylinder portion, and an outer cylinder portion, and the stress of the outer cylinder portion is reduced by satisfying the second shrinkage fitting ratio within a specific range. It can be seen that it can be set to a predetermined value or less.

1 Powder molding die 2 Inner cylinder part 20 Through hole 21 First inner peripheral surface, 22 Second inner peripheral surface, 23 Stepped surface 200 Cavity, 210 First area, 220 Second area 3 Intermediate cylinder part 4 Outer cylinder 40 Brim 5 Machining hole 51, 52 Vertical hole 53, 54, 55, 56 Horizontal hole 57 Spiral groove 59 Set screw 7 Die plate, 8 Lower punch, 9 Upper punch 100 Molding powder P2 Virtual circle t2, t3 , T4 thickness

Claims (7)

Inner cylinder and
An intermediate cylinder portion that is shrink-fitted on the outer circumference of the inner cylinder portion, and
An outer cylinder portion that is shrink-fitted on the outer circumference of the intermediate cylinder portion is provided.
When the shrink fit ratio of the intermediate cylinder portion with respect to the inner cylinder portion is defined as the first shrink fit ratio and the shrink fit ratio of the outer cylinder portion with respect to the intermediate cylinder portion is defined as the second shrink fit ratio.
The first shrink-fitting rate is larger than the second shrink-fitting rate,
The second shrink fit ratio is 0.15% or more and less than 0.25%.
Die for powder molding. The powder molding die according to claim 1, wherein the first shrink fitting ratio is 0.25% or more and less than 0.35%. The inner cylinder portion
The first inner peripheral surface into which the lower punch is fitted,
The second inner surface on which the upper punch is fitted, and
The powder molding die according to claim 1 or 2, further comprising a stepped surface connecting the first inner peripheral surface and the second inner peripheral surface. The intermediate cylinder portion and the outer cylinder portion are provided with processing holes through which a medium for adjusting the temperature of the powder molding die flows.
The machined hole is
Vertical holes provided along the axial direction of the powder molding die, and
It is provided with a horizontal hole provided in a direction intersecting the vertical hole.
The vertical hole is provided in the outer cylinder portion and is provided.
The powder molding die according to any one of claims 1 to 3, wherein the lateral hole is provided in the outer cylinder portion and the intermediate cylinder portion. The powder molding die according to any one of claims 1 to 4, wherein the intermediate cylinder portion and the outer cylinder portion are made of the same material. The powder molding die according to any one of claims 1 to 5, wherein the thickness of the outer cylinder portion is thicker than the thickness of the intermediate cylinder portion. The process of preparing the inner cylinder, intermediate cylinder, and outer cylinder, and
A step of shrink-fitting the intermediate cylinder portion to the outer circumference of the inner cylinder portion and integrating the inner cylinder portion and the intermediate cylinder portion.
A step of shrink-fitting the outer cylinder portion to the outer periphery of the integrated object is provided.
When the shrink fit ratio of the intermediate cylinder portion with respect to the inner cylinder portion is defined as the first shrink fit ratio and the shrink fit ratio of the outer cylinder portion with respect to the integrated object is defined as the second shrink fit ratio.
The first shrink-fitting rate is set to be larger than the second shrink-fitting rate, and the second shrink-fitting rate is set to 0.15% or more and less than 0.25%.
A method for manufacturing a die for powder molding.

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