JP3863591B2 - Method for producing sintered metal powder - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a metal powder sintered body having a hollow portion such as a through hole.
[0002]
[Prior art]
Conventionally, as a method for producing a metal powder sintered body having a hollow portion such as a through hole, as disclosed in JP-A-2-254104, a sintered part is obtained after preliminary sintering of the sintered part. The coefficient of thermal expansion is smaller than that of the sintered part in the hollow portion of the metal, there is no gap between the sintered part until the end of cooling of the sintering, and thermal deformation and seizure do not occur during sintering. A method of performing main sintering after inserting the insert and preventing the deformation of the hollow portion has been known.
[0003]
[Problems to be solved by the invention]
However, in the method described in Japanese Patent Application Laid-Open No. 2-254104, it is possible to obtain a metal powder sintered body that is free from seizure and thermal deformation of the insert and is free from deformation. When an insert with a smaller thermal expansion coefficient than the sintered part is inserted into the hollow part and sintered, the amount of thermal shrinkage when the insert fitted with the hollow part at the sintering temperature is cooled is the sintered part. Therefore, when it is taken out from the inside of the sintering furnace, the sintered part and the insert are in an interference fit state. In this case, even if the insert is not burned in, a process for removing such as punching is required, which increases the cost.
[0004]
In addition, inserts with a smaller coefficient of thermal expansion than sintered parts are used. Most of the materials with relatively large coefficients of thermal expansion are metals. When these metals are used as inserts, sintering is performed during sintering. One of the reasons is that it is fused and integrated with the parts.
[0005]
The present invention has been made in view of the above problems, those at low cost, to provide a method of manufacturing a metal powder sintered compact of high precision metal powder sintered body with no deformation can be manufacturing with a simple process It is.
[0007]
In the method of manufacturing a metal powder sintered body by degreasing and sintering a molded body of the metal powder and the organic binder kneaded mixture, the molded body is degreased under predetermined conditions, and then the molding is performed. The hollow portion formed in the body is made of a material having a coefficient of thermal expansion larger than that of the raw material metal of the metal powder and is not decomposed under the sintering conditions for sintering the sintered metal powder. And a dimension d satisfying the following formula when the dimensions of the sintered part before sintering, the sintering shrinkage rate of the sintered part, the thermal expansion coefficient of the sintered part, and the nested thermal expansion coefficient are determined in advance: The ceramic insert formed by the method is inserted into the hollow portion and sintered, and thereafter the insert is removed to produce a metal powder sintered body. .
d = b × (1 + nesting coefficient of thermal expansion)
Here, b = a × (1−sintering shrinkage ratio of sintered part), c = b / (1 + thermal expansion coefficient of sintered part), c> d. (However, d: dimension of at room temperature T2 of the insert, a: dimensions before sintering the sintered part, b: size during sintering of sintered parts (at temperature T1), c: bake sintered parts Dimensions after cooling ( at room temperature T2)
[0008]
The invention according to claim 2 is a method of manufacturing a metal powder sintered body by degreasing and sintering a molded body of a metal powder and an organic binder kneaded mixture, and then forming the molded body after degreasing the molded body under predetermined conditions. The hollow portion formed in the body is made of a material having a coefficient of thermal expansion larger than that of the raw material metal of the metal powder and is not decomposed under the sintering conditions for sintering the sintered metal powder. And a dimension d satisfying the following formula when the dimensions of the sintered part before sintering, the sintering shrinkage rate of the sintered part, the thermal expansion coefficient of the sintered part, and the nested thermal expansion coefficient are determined in advance: The insert made of a metal and coated with ceramic fine powder is inserted into the hollow portion and sintered, and then the insert is removed to produce a sintered metal powder. It is what.
d = b × (1 + nesting coefficient of thermal expansion)
Here, b = a × (1−sintering shrinkage ratio of sintered part), c = b / (1 + thermal expansion coefficient of sintered part), c> d. (However, d: dimension of at room temperature T2 of the insert, a: dimensions before sintering the sintered part, b: size during sintering of sintered parts (at temperature T1), c: bake sintered parts Dimensions after cooling ( at room temperature T2)
[0010]
Hereinafter, the present invention will be described in further detail. The following description will be given on the assumption that a sintered part 1 which is a rectangular parallelepiped metal powder sintered body having a hole 2 which is a hollow portion having a rectangular parallelepiped shape as shown in FIG. 1 is obtained. The sintered part 1 is manufactured by performing injection molding using a kneaded mixture of a fine metal powder such as SUS and an organic binder as a molding material, and degreasing and sintering the obtained molded body (green part). .
[0011]
At this time, a rectangular parallelepiped shaped insert 3 made of a material having a thermal expansion coefficient larger than that of the metal material forming the sintered part 1 is inserted into the hole 2 of the brown part which is a molded body after degreasing. The insert 3 is made of a material that does not decompose or evaporate even under predetermined sintering conditions such as reduced pressure and reducing atmosphere in the sintering process.
[0012]
The sintered part 1 shrinks during sintering, and the amount of shrinkage at this time depends on the mixing ratio of the metal fine powder and the organic binder in the molding material, the sintering temperature, the physical properties of the metal fine powder, etc. It is fully possible to anticipate the desired dimensions after sintering shrinkage.
[0013]
On the other hand, the insert 3 is thermally expanded by being heated at the time of sintering, but the amount of expansion (an insert size after expansion) can be easily calculated from the coefficient of thermal expansion. Therefore, the insert 3 may be designed so that the inner diameter of the hole 2 of the sintered part 1 at the sintering temperature matches the outer diameter of the insert 3 during thermal expansion.
[0014]
FIG. 2 shows, as an example, a graph showing the dimensional change during sintering of the corresponding portion between the A dimension portion of the inner diameter of the hole 2 of the sintered part 1 of FIG. 1 and the A dimension portion of the insert 3 inserted therein. .
[0015]
The green part dimension a of the dimension A part of the sintered part 1 is shrunk by sintering and becomes b at a temperature T1. At this time, a relationship of b = a × (1−sintering shrinkage ratio) is established between the green part dimensions a and b.
[0016]
Further, after cooling after sintering, the green part size c is obtained at room temperature T2. At this time, a relationship of c = b / (1 + sintered component thermal expansion coefficient) is established between the green part dimensions c and b.
[0017]
On the other hand, the corresponding part of the insert 3 corresponding to the dimension A is d at room temperature, but becomes b when the temperature reaches T1 during sintering. At this time, d = b × (1 + insert (Thermal expansion coefficient) relationship is established, and the hole 2 is fitted. When the temperature returns to room temperature T2 by cooling after sintering, the dimension returns to d again. At this time, since the thermal expansion coefficient of the sintered part 1 is smaller than the thermal expansion coefficient of the insert 3, both of them are fitted at the sintering temperature, but the insert material is decomposed and evaporated under the sintering conditions. Since it is chemically stable and does not react with the sintered part 1, c> d at room temperature T2 after sintering, and a clearance of cd is generated between the two.
[0018]
As a result, the sintered part 1 and the insert 3 can be easily separated after sintering, and the shape of the hole 2 follows the shape of the insert 3 when the sintering temperature T1 is fitted. Since the shrinkage is completed, no deformation occurs after this, and it becomes possible to manufacture a highly accurate sintered part 1 without deformation.
[0019]
In addition, a material having a relatively large coefficient of thermal expansion is often a metal, and when this is used as the insert 3, it is welded to the sintered part 1 because the insert 3 and the sintered part are in direct contact with each other. This is because material exchange occurs between the two. Therefore, it is only necessary that the two are not in direct contact with each other, and this can be solved by providing a chemically stable ceramic film between the two. The ceramic film only needs to be coated (sprayed) with ceramic fine powder, and the ceramic fine powder has a particle size of about 1 μm and does not affect the dimensional accuracy of the sintered part 1.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
Embodiment 1 of the present invention will be described below. Description will be made assuming that the sintered part 5 having the outer diameter 20 mm × 20 mm (thickness t = 3 mm) shown in FIG. 3 and the hole 6 having an inner diameter of 16 mm × 16 mm is manufactured.
[0021]
The material of the part is SUS316L, and the thermal expansion coefficient at a sintering temperature of 1320 ° C. is 11.5 × 10 ⁻⁶ [/ ° C.]. The molding material used was a mixture of 11 parts by weight of an organic binder mainly composed of paraffin wax, polystyrene, acrylic and stearic acid with 100 parts by weight of SUS316L fine powder (average particle size 8 μm).
[0022]
The shrinkage ratio of the hole (inner diameter dimension) during sintering of the molding material is 18.2%. Therefore, the corresponding part dimension of the mold is finished to about 19.55 mm × 19.55 mm.
[0023]
On the other hand, MgO having a purity of 97% is used for the insert inserted after degreasing, and the thermal expansion coefficient at 1320 ° C. of this insert is 13.3 × 10 ⁻⁶ [/ ° C.]. Therefore, the outer diameter of the nesting at 1320 ° C. is finished at 15.72 mm × 15.72 mm at room temperature so that it becomes 16 mm × 16 mm.
[0024]
After molding with the molding material, this was heated and degreased at 330 ° C., and then inserted into the hole 6 and sintered at 1320 ° C. in a vacuum. After sintering, the sintered part 5 and the insert removed from the furnace are separated (the inner diameter of the sintered part is 16 mm × 16 mm, but the insert returns to the original size of 15.72 mm × 15.72 mm. Therefore, there is a clearance of 0.14 mm over the entire circumference between the sintered part 5 and the insert, and separation is easy.) After this, deformation was measured, but no deformation was seen. .
[0025]
[Embodiment 2]
As in the first embodiment, description will be made assuming that the sintered part 5 having the outer diameter 20 mm × 20 mm (thickness t = 3 mm) shown in FIG. 3 and the hole 6 having an inner diameter 16 mm × 16 mm is manufactured.
[0026]
The material of the part is SUS316L, and the thermal expansion coefficient at a sintering temperature of 1320 ° C. is 11.5 × 10 ⁻⁶ [/ ° C.]. As the molding material, 100 parts by weight of SUS316L fine powder (average particle size 8 μm) was used by kneading and mixing 11 parts by weight of an organic binder mainly composed of paraffin wax, polystyrene, acrylic and stearic acid.
[0027]
The shrinkage ratio of the hole (inner diameter dimension) during sintering of the molding material is 18.2%. Therefore, the corresponding part dimension of the mold is finished to about 19.55 mm × 19.55 mm. On the other hand, a SUS304 melt is used for the insert inserted after degreasing, and its thermal expansion coefficient at 1320 ° C. is 12 × 10 ⁻⁶ [/ ° C.].
[0028]
Therefore, it is finished at 15.75 mm × 15.75 mm at room temperature so that the outer diameter of the nest at 1320 ° C. is 16 mm × 16 mm. After molding with a molding material, this is heated at 330 ° C. and degreased, and then the insert to be inserted into the hole is taken out after being embedded in h-BN powder having a particle size of 1 μm and inserted into the hole 6. Sintering was performed at 1320 ° C. in vacuum.
[0029]
After sintering, the sintered part 5 taken out of the furnace and the insert are separated (the inner diameter of the sintered part is 16 mm × 16 mm, but the insert returns to the original size of 15.75 mm × 15.75 mm. Since the sintered part 5 and the insert are not in direct contact with the h-BN powder around the insert, a clearance of 0.12 mm occurs between the sintered part 5 and the insert over the entire circumference. After this, deformation was measured, but no deformation was observed.
[0030]
[Embodiment 3]
A description will be given on the assumption that a sintered part 10 having a U-shaped groove 13 as shown in FIG. 4 is manufactured.
[0031]
The component material of the sintered component 10 is SUS316L, and the thermal expansion coefficient at a sintering temperature of 1320 ° C. is 11.5 × 10 ⁻⁶ [/ ° C.]. The molding material is a mixture of 9.5 parts by weight of organic binder mainly composed of paraffin wax, polystyrene, acrylic and phthalate ester with 100 parts by weight of SUS316L fine powder (average particle size 8 μm). Using.
[0032]
The shrinkage ratio of the hole (inner diameter dimension) during sintering of the molding material is 15.0%. Therefore, the dimension of the corresponding part of the mold is finished to about 5.9 mm × 5.9 mm. On the other hand, for the insert 12 to be inserted after degreasing, zirconia having a porosity of 30% is used, and its thermal expansion coefficient at 1320 ° C. is 11.7 × 10 ⁻⁶ [/ ° C.].
[0033]
Therefore, it is finished at 14.78 mm × 14.78 mm × 4.93 mm at room temperature so that the outer diameter of the insert is 15 mm × 15 mm × 5 mm at 1320 ° C. After molding with the molding material, as shown in FIG. 5, this is placed on the sintering jig 11, heated and degreased at 320 ° C., and then the insert 12 to be inserted into the groove 13 is inserted. Sintering was performed at 1320 ° C. under vacuum. After sintering, the sintered part 10 and the insert 12 taken out from the furnace are separated (the inner diameter of the sintered part 10 is 15 mm × 15 mm × 5 mm, but the insert 12 is the original 14.78 mm × 14. Since it is 78 mm × 4.93 mm, there is a clearance of about 0.1 mm between the sintered part 10, the groove width 5 mm and the insert 12, and the sintered part 10 and the insert 12 are not welded. Therefore, after that, the deformation of the sintered part 10 was measured, but the amount of deformation was not seen.
[0034]
(Comparative Example 1)
In the method of the first embodiment, after degreasing the green parts, sintering was performed under the same conditions without inserting an insert of MgO into the hole 21. Thereafter, the deformation of the sintered part 21 shown in FIG. 6 was measured. The edge around the hole 21 was deformed (fallen) to the inside of the hole 21 and the deformation amount was 0.05 mm at the maximum.
[0035]
(Comparative Example 2)
In the method 3 of the embodiment, after the green part was degreased, sintering was performed under the same conditions without inserting a zirconia insert in the groove portion, and a sintered part 30 shown in FIG. 7 was obtained. Thereafter, deformation of the sintered part 30 was measured, and sagging occurred in one piece 30a of the sintered part 30, and the amount of deformation was 0.2 mm at the maximum at the most advanced portion.
[0036]
(Comparative Example 3)
In the method of Embodiment 3, the green part 41 was degreased by changing the installation method as shown in FIG. 8, and further sintered without inserting the insert therein to obtain a sintered part 40. Thereafter, the deformation of the sintered part 40 was measured. As shown in FIG. 9, the deformation was such that the piece 40a opened outward, and the amount of deformation was 0.1 mm at the maximum at the foremost part.
[0037]
As described above, the effect of the present invention in which the insert 12 is inserted into the hole 2 and the groove 13 and sintered is remarkable, and the thermal expansion coefficient is larger than the thermal expansion coefficient of the sintered parts 1, 5, and 10. Separation after sintering was easy by using an insert with an expansion coefficient.
[0039]
According to the first and second aspects of the invention, a metal powder sintered body with extremely high dimensional accuracy without deformation can be produced in a simple process and at a lower cost than conventional methods. Can provide a method.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a metal powder sintered body and a nest according to Embodiment 1 of the present invention.
FIG. 2 is a graph showing a dimensional change during sintering of the dimension part A of the hole of the sintered part and the corresponding part of the insert inserted into the hole in the first embodiment of the present invention.
FIG. 3 is a perspective view showing a metal powder sintered body according to Embodiment 2 of the present invention.
FIG. 4 is a perspective view showing a metal powder sintered body according to Embodiment 3 of the present invention.
FIG. 5 is a cross-sectional view showing a manufacturing process of Embodiment 3 of the present invention.
6 is a plan view showing a metal powder sintered body of Comparative Example 1. FIG.
7 is a plan view showing a metal powder sintered body of Comparative Example 2. FIG.
8 is a perspective view showing a process for producing a metal powder sintered body of Comparative Example 3. FIG.
9 is a plan view showing a deformation state of the metal powder sintered body of Comparative Example 3. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Sintered part 2 Hole 3 Insert 5 Sintered part 6 Hole 10 Sintered part 12 Insert 13 Groove part

Claims (2)

In a method for producing a metal powder sintered body by degreasing and sintering a molded body of a metal powder and an organic binder kneaded mixture,
After degreasing the molded body under a predetermined condition, the above-mentioned firing which has a larger coefficient of thermal expansion than the raw material metal of the metal powder and sinters the metal powder to be sintered is formed in the hollow portion formed in the molded body. It is made of a material that does not decompose under the sintering conditions.
When the shape corresponding to the hollow portion and the dimensions of the sintered part before sintering, the sintering shrinkage rate of the sintered part, the thermal expansion coefficient of the sintered part, and the nested thermal expansion coefficient are determined in advance, Inserting a ceramic insert formed in a dimension d satisfying the above into the hollow portion and sintering, and thereafter removing the insert to produce a metal powder sintered body,
A method for producing a sintered metal powder.
d = b × (1 + nesting coefficient of thermal expansion)
Here, b = a × (1−sintering shrinkage ratio of sintered part), c = b / (1 + thermal expansion coefficient of sintered part), c> d. (However, d: dimension of at room temperature T2 of the insert, a: dimensions before sintering the sintered part, b: size during sintering of sintered parts (at temperature T1), c: bake sintered parts Dimensions after cooling ( at room temperature T2) In a method for producing a metal powder sintered body by degreasing and sintering a molded body of a metal powder and an organic binder kneaded mixture,
After degreasing the molded body under a predetermined condition, the above-mentioned firing which has a larger coefficient of thermal expansion than the raw material metal of the metal powder and sinters the metal powder to be sintered is formed in the hollow portion formed in the molded body. It is made of a material that does not decompose under the sintering conditions.
When the shape corresponding to the hollow portion and the dimensions of the sintered part before sintering, the sintering shrinkage rate of the sintered part, the thermal expansion coefficient of the sintered part, and the nested thermal expansion coefficient are determined in advance, Insert a metal insert formed by applying a ceramic fine powder with a dimension d satisfying the condition d into the cutout portion and sinter,
After that, removing the insert to produce a metal powder sintered body,
A method for producing a sintered metal powder.
d = b × (1 + nesting coefficient of thermal expansion)
Here, b = a × (1−sintering shrinkage ratio of sintered part), c = b / (1 + thermal expansion coefficient of sintered part), c> d. (However, d: dimension of at room temperature T2 of the insert, a: dimensions before sintering the sintered part, b: size during sintering of sintered parts (at temperature T1), c: bake sintered parts Dimensions after cooling ( at room temperature T2)

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