JP2001247904A - Method for producing metallic sintered product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a metallic sintered product by which the friction resistance between a molded body and a sintering stand is reduced, and the deformation of the molded body caused by the friction resistance can be prevented. SOLUTION: A molding material obtained by mixing metal powder and a binder is subjected to injection molding into a die to produce a molded body. Next, a degreasing stage of removing the binder from the molded body is performed, and, thereafter, a sintering stage of sintering the above metal powder is performed to produce a metallic sintered product. In the above sintered stage, in a sintering furnace 2, the above molded body 1 subjected to the degreasing stage is placed on a sintering stand 3, further, a rollable inclusion 4 is interposed between the above molded body 1 and the above sintering stand 3, and sintering is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintering step for sintering a metal powder after removing a binder when manufacturing a metal sintered product by a metal powder injection molding method.

[0002]

2. Description of the Related Art In recent years, metal powder injection molding (MIM: Metal
Powder Injection Molding) is used as a method for manufacturing metal parts. In this method, a metal powder is mixed with a binder so as to have fluidity, the mixture is injection-molded, and a large amount of the binder is removed from the obtained molded body by heating or the like. This is a method of obtaining a desired product by performing a firing step of sintering the metal powder.

As shown in FIG. 6A, generally, in a firing step, a firing table 93 is used to mount the compact 9 thereon. Since the inside of the baking furnace 2 is heated to a high temperature in the baking step, a baking table 93 made of a material having high thermal stability such as alumina is used. By the way, since most of the binder of the compact 9 is removed in the degreasing step, the compact 9 shrinks in the firing step as much as the powder sinters. Since the binder is uniformly interposed in the molded body 9, the molded body 9 contracts uniformly as a whole. At this time, the firing table 9 with high thermal stability
3 hardly shrinks, so that the molded body 9 and the baking table 93
A frictional resistance is generated between them, and their contraction is hindered. Therefore, as shown in FIG. 6B, the surface of the metal sintered body 91 after the firing step cannot be shrunk in contact with the firing table 93, and has a shape with a large bottom area.

[0004] Regarding the knowledge of the firing table, see
As disclosed in Japanese Patent Publication No. 305842, there is a method in which sintering is performed using a firing jig adapted to a compact. According to this method, it is possible to prevent deformation of the molded body due to its own weight. Also, as disclosed in Japanese Patent Application Laid-Open No. 10-158070, there is a method in which unevenness or through holes are provided in a firing jig and sintering is performed. According to this method, it is possible to prevent the compact from sticking to the firing jig.

[0005]

However, the conventional method cannot be expected to be effective in preventing deformation due to frictional resistance between the compact and the sintering fixture.

The present invention has been made in view of such a conventional problem, and reduces the frictional resistance between a compact and a baking table in a baking process, thereby preventing deformation of the compact due to the frictional resistance. It is an object of the present invention to provide a method for manufacturing a sintered metal product that can be used.

[0007]

According to a first aspect of the present invention, there is provided a degreasing method in which a molding material in which a metal powder and a binder are mixed is injection-molded into a mold to produce a molding, and then the binder is removed from the molding. After performing the step, a sintering step of sintering the metal powder is performed to produce a sintered metal product,
In the firing step, the compact having undergone the degreasing step is placed on a firing table, and sintering is performed with a rollable inclusion interposed between the compact and the firing table. A method of manufacturing a metal sintered product characterized by the above.

In the present invention, it is most remarkable that the compact having undergone the degreasing step is placed on a firing table, and a rollable inclusion is provided between the compact and the firing table. Sintering with the interposition.

Next, the operation and effect of the present invention will be described.
In the firing step according to the present invention, a rollable inclusion is interposed between the compact and the firing table. For this reason, deformation of the compact during sintering can be prevented. That is, in the firing step, when the entire molded body is about to shrink, parts other than the contact surface with the firing table can be shrunk freely without frictional resistance. On the other hand, on the contact surface with the baking table, the frictional resistance with the baking table hinders shrinkage. Here, in the present invention, the above-mentioned inclusion is interposed between the compact and the firing table. Therefore, when the compact shrinks,
The compact can roll and shrink the inclusions.

That is, on the contact surface, a rolling motion that generates only a very small frictional resistance is performed instead of a sliding motion that can generate a large frictional resistance as in the related art. Therefore, the frictional resistance generated on the contact surface when the compact shrinks can be significantly reduced. Therefore, deformation of the molded body due to frictional resistance can be prevented. In addition,
The inclusion does not need to have a special shape, and various shapes can be used. Further, not all of the inclusions need to be rolled, and even if a part of the inclusions roll, the frictional resistance can be significantly reduced.

In the firing step according to the present invention, it is only necessary to interpose inclusions between the compact and the firing table. Therefore, it is easy to implement and inexpensive. Therefore, it can be used for molded articles of various shapes.

It is preferable that the inclusions have good thermal stability. For example, ceramics such as alumina and silicon nitride, metals having a melting point higher than the sintering temperature,
It can be an intermetallic compound or the like. Thus, the inclusion does not deform even when exposed to high temperatures in a furnace, and when the compact shrinks, the compact can roll over the inclusion.

As described above, according to the present invention, there is provided a method for producing a metal sintered product capable of reducing the frictional resistance between a compact and a firing table and preventing deformation of the compact due to the frictional resistance. be able to.

Next, as in the second aspect of the present invention, it is preferable that the inclusions are spherical. This allows the compact to roll over the inclusion without difficulty. Therefore, the frictional resistance due to the rolling of the inclusion between the molded body and the baking table can be reduced.

Next, as in the third aspect of the present invention, it is preferable that the spherical particles have a particle size equal to or larger than that of the metal powder of the compact. This allows the compact to roll over the inclusion without difficulty. Therefore, the frictional resistance due to the rolling of the inclusion between the molded body and the baking table can be reduced. The particle size of the inclusions is
If the particle size is smaller than that of the metal powder of the compact,
When the compact shrinks, it may not be able to roll over the inclusions because it enters the gaps between the compacts. Therefore, the particle size of the inclusions is preferably equal to or larger than the particle size of the metal powder of the compact.

Next, as in the invention according to a fourth aspect, it is preferable that the spherical object has a particle size capable of contacting four or more pieces with the bottom surface of the sintered metal body. . This allows the compact to roll over the inclusion without difficulty. Therefore, the frictional resistance due to the rolling of the inclusion between the molded body and the baking table can be reduced.

As described above, in the firing step, the compact shrinks as much as the powder sinters. This shrinkage is, for example, as shown in FIG.
Shrink to% length. In this case, the diameter R of the spherical object 4 is
It is preferable to determine under the following conditions. That is, assuming that the length of each side of the bottom surface of the compact 1 before sintering is a and b, the length of each side of the sintered metal 11 after sintering is about 8
Since the length is shortened to 0%, when the area before sintering is ab, the area after sintering is about 0.64ab. On the other hand, when the diameter of the spherical object 4 is R, the spherical object 4 preferably intervenes four or more in order to support the metal sintered body 11 and roll in any direction.

[0018] More specifically, the area 4R ² where spheres 4 of diameter R to form two side by side each side is equal to the area 0.64ab formed by sintered metal 11 after sintering 4R ² = 0.64ab. Therefore, in this case, the diameter R of the spherical object 4 is 0.4 (ab)
It is preferable to be ^0.5 or less.

Next, as in the fifth aspect of the present invention, it is preferable that the spherical objects are interposed in a state of being stacked in a plurality of stages. Thereby, an inclusion can be easily interposed between the compact and the firing table. For example, the inclusions can be previously spread on the baking table before placing the compact on the baking table. At this time, it is not necessary to arrange the inclusions in a more orderly manner, and the work of laying down can be omitted.

Next, as in the sixth aspect of the present invention, it is preferable that the spherical material has a particle size of 0.05 to 1 mm. This allows the compact to roll over the inclusion without difficulty. Therefore, the frictional resistance due to the rolling of the inclusion between the molded body and the baking table can be reduced.

When the particle diameter of the spherical object is less than 0.05 mm, since the particle diameter of the metal powder has a distribution, the particle diameter may exceed the average particle diameter, and the rolling of the spherical object may occur. It may be worse. In addition, when the particle diameter is small, the surface energy is large, so that the rolling of the spherical object may be deteriorated. On the other hand, if it exceeds 1 mm,
Since the contact distance between the molded body and the spherical body becomes long, the molded body may be deformed depending on the shape of the molded body.

Next, as in the invention as set forth in claim 7, the inclusion may be a rod-shaped object. In this case, the frictional resistance at the contact surface can be significantly reduced as in the case where the inclusion is the spherical object.

Next, as in the present invention, it is preferable that the diameter of the rod is equal to or larger than the particle diameter of the metal powder of the compact. Thereby, the molded body can be rolled on the rod-shaped object without difficulty for the same reason as described in the case of the spherical object.

Next, as in the ninth aspect of the present invention, it is preferable that the rod has a diameter that allows two or more pieces to contact the bottom surface of the sintered metal body. Thereby, the molded body can be rolled on the rod-shaped object without difficulty for the same reason as described in the case of the spherical object.

More specifically, as shown in FIG.
Is preferably determined by the following conditions. That is, when the length of the side in the rolling direction of the rod 4 on the bottom surface of the sintered metal body 11 after sintering is B, the rod 4
In order to stably support the metal sintered body 11, it is preferable that two or more are interposed. Therefore, the length 2R formed by arranging the two rod-shaped objects 4 having the diameter R is equal to the side length B, and 2R = B. Therefore, it is preferable that R be B / 2 or less.

Next, a tenth aspect of the present invention is a degreasing method in which a molding material in which a metal powder and a binder are mixed is injection-molded into a mold to produce a molding, and then the binder is removed from the molding. After performing the step, a firing step of sintering the metal powder is performed to produce a sintered metal product. In the firing step, the compact having undergone the degreasing step is placed on a firing table. The surface roughness of the sintering table on the contact surface between the compact and the sintering table, which is placed on top, has a ten-point average roughness Rz of 6.5 or less. In the manufacturing method.

The most remarkable point in the present invention is that the surface roughness of the baking table at the contact surface between the compact and the baking table is positively set to the specific value. As a result, the frictional resistance between the compact and the firing table can be reduced, and the compact can be prevented from being deformed.

That is, by making the surface roughness fine so that the ten-point average roughness Rz of the baking table becomes 6.5 or less, the contact surface of the contact surface can be made finer than in the case where the surface roughness is rougher than this. Friction resistance can be greatly reduced (see FIG. 4). Therefore, in this case, the same operation and effect as when the above-described inclusions are interposed are obtained, and deformation during sintering can be suppressed.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 A method for manufacturing a sintered metal product according to an embodiment of the present invention will be described with reference to FIG. In this example, first, a molding material in which a metal powder and a binder are mixed is injection-molded into a mold to produce a molded body. Next, after performing a degreasing step of removing a binder from the molded body, a firing step of sintering the metal powder is performed to manufacture a sintered metal product. In the firing step, the compact having undergone the degreasing step is placed on a firing table, and sintering is performed by interposing a rollable inclusion between the compact and the firing table. I do. The details are described below.

In this example, a mixture of SUS316 powder having an average particle diameter of 10 μm and a binder was used as a molding material for the molded body. Then, as shown in FIG. 1A, a rectangular parallelepiped molded body 1 was molded by a metal injection molding method, and then a degreasing step and a firing step were performed.

Here, in the firing step, as shown in FIG. 1A, in the firing furnace 2, the compact 1 after the degreasing step is placed on a firing table 3 and the compact 1 Sintering was carried out with a rollable inclusion 4 interposed between 1 and the firing table 3. In addition, as the inclusion 4, a spherical material made of an alumina material having an average particle diameter of 0.3 mm was used. The sintering was performed under the condition that the temperature was maintained at 1300 ° C. in a vacuum. As a result of performing the above steps, FIG.
As shown in the figure, the compact 1 shrunk uniformly by about 20% as a whole, and became a metal sintered body 11 having an excellent shape.

Next, the operation and effect of this embodiment will be described. In the firing step in this example, between the compact 1 and the firing table 3,
Rollable inclusions 4 are interposed. Therefore, deformation of the compact 1 during sintering can be prevented.

That is, in the firing step, when the entire molded body 1 is about to shrink, portions other than the contact surface 14 with the firing table 3 can be shrunk freely without frictional resistance. On the other hand, on the contact surface 14 with the baking table 3, the frictional resistance between the baking table 3 and the baking table 3 hinders contraction. Here, in this example,
The inclusion 4 is interposed between the molded body 1 and the firing table 3. Therefore, when the compact 1 shrinks, the compact 1
Can roll and shrink the inclusions 4.

That is, the contact surface 14 is not a sliding motion that can generate a large frictional resistance as in the related art, but a rolling motion that generates a very small frictional resistance. Therefore, when the molded body 1 contracts, the frictional resistance generated on the contact surface 14 can be significantly reduced. Therefore, deformation of the molded body 1 due to frictional resistance can be prevented. The inclusions 4 do not need to have a special shape, and various shapes can be used.
Further, not all of the inclusions 4 need to be rolled, and even if a part of the inclusions 4 can be rolled, the frictional resistance can be significantly reduced.

In the firing step according to this embodiment, the inclusions 4
Need only be interposed between the compact 1 and the firing table 3.
Therefore, it is easy to implement and inexpensive. Therefore, it can be used for molded articles of various shapes.

Embodiment 2 In this embodiment, instead of using the inclusions 4 in Embodiment 1, the surface roughness of the firing table 3 is adjusted so that the distance between the compact 1 and the firing table 3 is reduced. When reducing the frictional resistance, a preferable range of the surface roughness of the firing table 3 was determined. That is, in the firing step, as shown in FIG. 5A, the compact 1 after the degreasing step was placed on the firing table 3 in the firing furnace 2. Then, the molded body 1
At the contact surface 14 between the sintering table 3 and the sintering table 3
The degree of deformation of the molded body 1 before sintering and the sintered metal body 11 after sintering were examined when the surface roughness was varied in several ways. Other configurations are the same as those of the first embodiment.

There are various methods for displaying the degree of deformation. In this example, the following deformation ratio difference [%] is used. Here, the deformation ratio difference [%] in FIG.
Is defined by: As shown in FIG. 5A, the length of the side at the contact surface 14 of the molded body 1 before sintering is a1, and the length of the side at the non-contact surface is b1. As shown in b), the length of the side on the contact surface 14 after sintering is a2, and the length of the side on the non-contact surface is b2. At this time, the deformation ratio difference [%] is
((B1-b2) / b1- (a1-a2) / a1) × 1
Represented by 00.

In this example, the surface roughness was changed from a ten-point average roughness of about 2 [μm] to about 12 [μm]. FIG. 4 shows a graph of the deformation ratio difference [%] obtained thereby. In the figure, the horizontal axis represents the ten-point average roughness Rz [μ
m] and the vertical axis represents the deformation rate difference [%]. As shown in the figure, it can be seen that the deformation ratio difference [%] is remarkably reduced below the boundary of the ten-point average roughness Rz of 6.5 [μm]. Therefore, in this case, the same operation and effect as those of the first embodiment can be obtained, and the deformation of the compact during sintering can be suppressed.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing (a) a molded body before sintering and (b) a metal sintered body after sintering in a first embodiment.

FIG. 2 is a view showing the arrangement of spherical objects, and is a bottom view showing (a) a molded body before sintering, and (b) a sintered metal body after sintering.

FIG. 3 is a perspective view showing an arrangement of a rod-shaped object on a metal sintered body.

FIG. 4 shows a ten-point average roughness Rz [μ in Embodiment 2;
Explanatory drawing showing the relationship between [m] and the difference in deformation ratio [%].

FIG. 5 is an explanatory view showing (a) a molded body before sintering and (b) a sintered metal body after sintering in a second embodiment.

FIG. 6 shows (a) a molded body before sintering,
(B) Explanatory drawing which shows the metal sintered compact after sintering.

[Explanation of symbols]

 1. . . Molded body, 11. . . 13. metal sintered body, . . 1. contact surface; . . Firing furnace, 3. . . Firing table, 4. . . Inclusion

Claims (10)

[Claims] 1. A molding material in which a metal powder and a binder are mixed is injection-molded into a mold to produce a molded body, and then a degreasing step of removing the binder from the molded body is performed. A method for producing a metal sintered product by performing a firing step of sintering, wherein in the firing step, the compact having undergone the degreasing step is placed on a firing table, and And sintering by interposing a rollable inclusion between the sintering table and the sintering table. 2. The method according to claim 1, wherein said inclusions are spherical. 3. The method for manufacturing a metal sintered product according to claim 2, wherein the spherical particles have a particle size equal to or larger than a particle size of the metal powder of the compact. 4. The metal sintering device according to claim 2, wherein the spherical object has a particle size capable of contacting four or more spheres with the bottom surface of the sintered metal body after sintering. Product manufacturing method. 5. The method according to claim 2, wherein:
A method for manufacturing a metal sintered product, wherein the spherical objects are interposed in a state of being stacked in a plurality of stages. 6. The method according to claim 2, wherein:
The method for producing a metal sintered product, wherein the spherical material has a particle size of 0.05 to 1 mm. 7. The method according to claim 1, wherein the inclusions are rod-shaped. 8. The method for producing a metal sintered product according to claim 7, wherein the rod has a diameter equal to or larger than a particle diameter of the metal powder of the compact. 9. A metal sintered product according to claim 7, wherein said rod-shaped object has a diameter capable of contacting two or more pieces with the bottom surface of the sintered metal body after sintering. Manufacturing method. 10. A molding is prepared by injection molding a molding material obtained by mixing a metal powder and a binder into a mold, and then performing a degreasing step of removing the binder from the molding. A method for producing a metal sintered product by performing a firing step of sintering, wherein in the firing step, the compact having undergone the degreasing step is placed on a firing table,
A method for producing a metal sintered product, wherein a surface roughness of the baking table at a contact surface between the molded body and the baking table has a ten-point average roughness Rz of 6.5 or less.