JPH04354807A - Production of sintered body - Google Patents

Abstract

PURPOSE:To prevent the generation of defects in degreasing and sintering and to enhance the degree of freedom in shaping a sintered body when an injection- molded body is sintered. CONSTITUTION:The previously formed compacts 1 and 2 are inserted into an injection-molding die and injection-molded to form a composite molded body to be degreased and sintered later.

Description

[Detailed description of the invention]

0001

FIELD OF THE INVENTION This invention relates to an injection molding sintering process. More specifically, the present invention increases the degree of freedom in the shape of the sintered body, and eliminates cracks and blisters that occur during degreasing and sintering.
This invention relates to an injection molding sintering method that suppresses the occurrence of defects such as deformation.

0002

BACKGROUND OF THE INVENTION The injection molding sintering method is capable of producing sintered parts with complex shapes, and is said to have the highest degree of freedom in the shape of sintered bodies in the production of sintered parts.

[0003] In the usual injection molding sintering method, raw material powder and a binder are kneaded, injection molded to produce a molded body, and further degreased and sintered to obtain a sintered body. Up until now, in this method, an injection molded body has been produced as close as possible to the final shape of the part (taking into account the shrinkage rate during sintering), and this has been degreased and sintered. Also, in this case, it is necessary to suppress defects such as cracks, blisters, and deformation that occur during degreasing and sintering, so improvements have been made mainly to the binder system to prevent the occurrence of these defects. Ta.

0004

Generally speaking, in the injection molding and sintering method, the protrusions of the molded body are likely to be deformed during degreasing, and cracks and bulges are likely to occur in the thick parts. If we try to prevent these problems by improving the binder system, we have to sacrifice the moldability of the kneaded product to some extent because it is necessary to keep the fluidity of the kneaded product of raw material powder and binder low in order to avoid defective degreasing. I don't get it.

[0005] As described above, the moldability and degreasing properties expected in the injection molding sintering method are contradictory properties, and hitherto this method has been carried out by searching for a compromise between the two. However, this limits the advantage of this method, which is the ability to manufacture parts with complex shapes. Furthermore, with injection molding, it is difficult to produce good molded bodies for parts with thin walls and large areas, so it is difficult to manufacture parts with such parts using the conventional injection molding sintering method. Met. In other words, although the injection molding sintering method has been evaluated as having the highest degree of freedom in shape in the production of sintered parts, it still has limitations in terms of mold production and the fluidity of the kneaded material. It is expected that the degree of freedom in shape will be further increased.

An object of the present invention is to provide a method for manufacturing a sintered body that prevents defects such as cracks, blisters, and deformation during degreasing and sintering, and increases the degree of freedom in the shape of the sintered body. .

[0007]

[Means for Solving the Problems] The method of manufacturing a sintered body of the present invention is a method of manufacturing a sintered body by injection molding a molding material, then degreasing and sintering the molded body. The method is characterized in that the previously prepared molded body is inserted into an injection mold and then injection molded to produce a composite molded body which is to be subsequently degreased and sintered.

[0008] The prefabricated compact in the method of the present invention eliminates areas in the finished sintered body that are prone to defects using conventional injection molding and sintering methods, such as protrusions, thick wall areas, and thin wall areas with large areas. Configure.

Methods for producing the preform include injection molding, powder molding, and green sheet molding. Powder compaction is suitable for producing preforms that make up protrusions and thick-walled parts because it requires a small amount of binder. Green sheet molding is suitable because it can easily produce large molded bodies. Furthermore, injection molding is suitable for producing preformed products with complex shapes that are difficult to produce using methods such as powder compacting. It goes without saying that the method for producing the preform is not limited to these methods.

[0010] The molding material for producing the preform is:
Contains the same kind of raw material powder as that used for later injection molding. Examples of raw material powder include metal materials such as soft magnetic materials (Fe-50%Co alloy, Fe-Si
metal alloys, etc.), stainless steel, cemented carbide, and ceramic materials such as silconia, silicon nitride, and silicon carbide. The molding material is
In addition to such raw material powder, it contains components such as a binder, which are generally contained in molding materials used for producing molded bodies in the production of injection molded sintered bodies.

As for the binder, one that is suitable for the preform, in other words, one that is highly effective in preventing defects from occurring during subsequent degreasing, is used. Specifically, a material that satisfies both moldability and degreasability of the preform is used. Examples of materials that meet this requirement for compaction are polystyrene and acrylic binders (e.g., polymethyl methacrylate, polybutyl methacrylate, etc.), which both facilitate the shaping of the preform and are extremely resistant to degreasing. The fluidity does not improve or the viscosity decreases, and there is little risk of rapid decomposition and scattering, causing defects. In addition to these binders, paraffin-based binders and polyolefin-based binders such as polyethylene can also be used as the binder for the preform. However, it must be noted that these binders may have better fluidity or lower viscosity at higher temperatures than polystyrene or acrylic binders, which may cause deformation of the preform. Probably. Further, an example of a binder suitable for green sheet molding is polyvinyl butyral.

[0012] A molding material for injection molding using a mold into which a preform is inserted also contains, in addition to the raw material powder, other components such as a binder that are normally contained in such molding materials. The conditions for the binder of this injection molding material are different from those for preforms, and a greater specific gravity is placed on moldability. Therefore, it is preferable to use a paraffin-based binder or a binder such as polyethylene. More specifically, polyethylene is the more preferred binder since polyethylene has less lubricity than paraffin, making it more difficult for the preform to separate from the injection molded body, taking into account subsequent sintering.

[0013] The binder used may be a mixture of a plurality of types of binders, both for preforming and for subsequent injection molding.

Both the above-mentioned production method of the preform and the subsequent injection molding method are known molding methods,
There is no need to explain any of them in detail here. However, when sintering a green body obtained by injection molding with a mold into which a preform is inserted, the shrinkage rate between the preform and the subsequently injection molded part is If they are different, it is inconvenient to obtain a desired integrated finished sintered body. Therefore, the difference in shrinkage rate during sintering between the two should be eliminated.

For example, the linear shrinkage rate of a normal powder compact during sintering is 10% or less, which is smaller than the approximately 18% of an injection molded product. In order to match this, in order to reduce the amount of binder in the kneaded material for injection molding and make the linear shrinkage rate 10% or less, it is necessary to reduce the amount of binder to 30% or less, but with this amount of binder, injection molding is extremely difficult. but,
By adjusting the particle size distribution of the raw material powder, injection molding is possible even with a small amount of binder, and the shrinkage rate during sintering can be kept low, so the shrinkage rate during sintering of the compacted product can be reduced. Can be matched. The particle size distribution of the raw material powder for injection molding can be adjusted by mixing powders with different particle sizes so that the tap density of the raw material powder is a certain constant value, and by doing this, it is possible to adjust the particle size distribution of the raw material powder for injection molding by mixing powders with different particle sizes. The amount of binder in the injection molding material can be adjusted so that the shrinkage rates of the injection molded parts during sintering are the same. The technique of adjusting the particle size distribution and binder amount of the raw material powder in this way is disclosed in Japanese Patent Application No.
-241824.

[0016] The finished molded product produced by injection molding in a mold into which the preform is inserted has only to have the same composition as a whole. Therefore, for example, if the composition of the finished molded body is to be 50% Fe and 50% Co, Fe with an average particle size of 20 μm is used as the raw material powder for injection molding.
It is also possible to use -50% Co alloy and use a combination of Fe-20% Co alloy with an average particle size of 20 μm and Co powder with an average particle size of 3 μm as the raw material powder for the preform. . In the case of this example, there is an advantage that the press forming of the preform can be made easier than when Fe-50%Co alloy is used as the raw material powder.

[0017]

[Function] Before producing the injection molded product to be sintered, the prefabricated molded product inserted into the mold has protrusions and thick parts that are generally difficult to produce using the normal injection molding sintering method. , it is possible to produce thin-walled parts with large areas. this is,
This is because the preforms constituting such parts can be produced using materials and molding methods suitable for them. For example, powder molding, which can be used to create protrusions and thick-walled parts that are prone to defects during degreasing, does not require as much fluidity of the material as injection molding, so it requires less binder.
Moreover, it is possible to use a molding material using a binder that is less likely to cause deformation due to rapid decomposition and scattering during degreasing. Also, for example, green sheet molding, which can be used to create large-area, thin-walled parts, facilitates the molding of such parts that are difficult to successfully create by injection molding.

[0018]

EXAMPLES Next, the present invention will be further explained by examples.

Example 1 φ5×20 mm and 20×20×10 mm were made from a molding material using Fe-50%Co alloy, a soft magnetic material, as the raw material powder and an acrylic binder.
100 pieces of the same sample were made by powder molding, and 100 pieces of the same sample were made by injection molding. A sample of φ5 x 20 mm that forms the protrusion and a 20 x sample that forms the thick part.
Insert a 20 x 10 mm sample into an injection mold, fill the mold with an injection molding material whose shrinkage rate is the same as the shrinkage rate during sintering, and perform injection molding. ,
Composite molded bodies having shapes shown in FIGS. 1(a) to 1(c) were produced. In this figure, 1 is a protrusion, 2 is a thick part, and 3 is a part that was injection molded later. The binder of the injection molding material after inserting the preform sample was not an acrylic binder but a binder mainly composed of polyethylene.

For comparison, the same material as the injection molding material after inserting the preform sample was injection molded without inserting the preform into the injection mold. A molded body having the same shape as the molded body shown was produced.

[0021] These molded bodies are degreased under normal conditions,
and sintered. Table 1 shows the results of examining the presence or absence of defects such as cracks, blisters, and deformation in the degreased molded bodies. In the comparative example, the protrusions of all samples collapsed (deformation rate: 100%), and cracks and bulges occurred in more than half of the thick parts (occurrence rate: 63%).
). On the other hand, although some cracks occurred in the thick wall portion into which the preform was inserted according to the method of the present invention (incidence rate: 8%), no other degreasing defects were observed. Moreover, no defects occurred even when these molded bodies were sintered.

[0022]

[Table 1]

Example 2 A 50×50×1 mm sample constituting a large-area thin-walled portion was prepared by the green sheet method. As the molding material, a mixture containing the same Fe-50%Co alloy as in Example 1, polyvinyl butyral (binder), and methyl ethyl ketone (solvent) was used. Each of these samples was inserted into an injection mold, and a molding material using a binder mainly composed of polyethylene was injection molded.
Composite molded bodies having the shapes shown in (a) to (c) were produced. In this figure, 11 is a thin-walled part, and 12 is a part injection-molded later.

For comparison, without inserting the preform,
A molded body having the same shape as the molded body shown in FIG. 2 was produced by injection molding the same molding material as above.

[0025] These compacts were degreased and sintered. When the method of the present invention was followed, no defects occurred during molding, degreasing, and sintering. However, in a partially sintered molded body prepared for comparison, filling defects occurred in the thin wall portion, and a satisfactory product could not be obtained.

[0026]

[Effects of the Invention] As explained above, according to the present invention,
It is now possible to prevent defects such as cracks, bulges, and deformation in protrusions and thick parts during degreasing and sintering of injection molded products, which was difficult with conventional methods. In addition, it has become possible to produce molded bodies with large-area thin-walled parts, and it has become possible to produce molded bodies with protrusions and thick-walled parts that do not cause defects.In addition, the shape of the completed sintered body The degree of freedom has improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a molded article produced in Example 1, which has protrusions and thick-walled parts, (a) is a top view thereof, (b)
is a front view, and (c) is a side view.

FIG. 2 is a diagram showing a molded article produced in Example 2 having a large-area thin-walled part, (a) is a top view thereof, (b)
is a front view, and (c) is a side view.

[Explanation of symbols]

1...Protrusion 2...Thick part 3... Part that was injection molded later 11...Thin wall part 12...Part injection molded later

Claims (3)

[Claims] Claim 1: In a method of manufacturing a sintered body by injection molding a molding material, then degreasing and sintering the molded body, the previously prepared molded body is placed in a mold for injection molding. A method for manufacturing a sintered body, which comprises inserting the molded body and then performing injection molding to produce a composite molded body to be degreased and sintered later. 2. The method of claim 1, wherein the prefabricated compact is a compacted compact. 3. The method according to claim 1, wherein the prefabricated molded body is a green sheet molded body.