KR20140137614A - A method for powder injection molding - Google Patents

Abstract

Disclosed is a powder injection molding method which can manufacture a hemispheric or cylindrical object of tungsten heavy metal. The powder injection molding method comprises the steps of: forming mixed powder by mixing a certain ratio of nickel (Ni) powder to iron (Fe) powder with tungsten (W) powder; forming a feedstock by mixing a binder with the mixed powder; forming a hemispheric injection-molded object wherein a multitude of notch parts are formed on an inner circumferential surface by injection-molding the feedstock; degreasing the injection-molded object; and inserting a degreased object in which the degreasing is completed into a sintering tool of a ceramic material, sintering the same, and then forming a sintering object.

Description

METHOD FOR POWDER INJECTION MOLDING

The present invention relates to a powder injection molding method for producing a semi-spherical or cylindrical tungsten-polymerized gold product.

In general, tungsten-polymerized gold is a kind of composite material containing tungsten (W) as its main raw material and containing nickel (Ni) and iron (Fe) or nickel and copper (Cu). Tungsten-polymerized gold has high density and excellent tensile strength and is widely used for radiation shielding materials, mobile phone vibrators, high density penetrators for war cars, warheads and high-density debris. In particular, tungsten-polymerized gold (W-Ni-Fe) containing 90 to 97% by weight of tungsten and containing nickel and iron is the most widely used tungsten-polymerized gold composition because of its excellent mechanical strength.

For reference, the shell is designed to scatter already formed fragments or scatter debris generated by the violent pressure. In addition, the shells can be formed into notches having a uniform size inside the shell, thereby forming debris having a desired size and shape at the time of explosion. The envelope of the shell can be made in a variety of ways. For example, a steel or tungsten heavy alloy plate as the material of the shavings is notched to a suitable size, and then a hemispherical shell is formed by a press forming process, or the plate is rolled to form a cylindrical sheath Can be produced. Alternatively, notches may be formed in the hemispherical or cylindrical shells manufactured by using machining or the like.

Here, when the hemispherical shell is manufactured by press molding, residual stress is generated because the material is plastic deformed, and the amount of deformation varies depending on the region, which results in a disadvantage that the size of the debris varies. Further, in the case of manufacturing a cylindrical shell by rolling a plate material, since the joint surface is required to be welded, generation of debris is not uniformly generated in the 360 degree direction when the debris is generated by the extreme pressure due to the inhomogeneity of the weld.

On the other hand, when machining is used, it has a disadvantage in that machining is difficult and the machining time is long and machining cost is high.

Therefore, a powder injection molding method can be used as a manufacturing method for overcoming the disadvantages of the above-described methods of forming shells of shells.

In the production of tungsten-polymerized gold, high-density tungsten-polymerized gold having a theoretical density of 98% or more can be obtained by a solid phase sintering method. However, in the case of tungsten-polymerized gold in which mechanical properties such as strength and elongation are required, And is manufactured using a liquid phase sintering method. This is because the formed body is usually prepared by mixing tungsten, nickel and iron powder present as powder in a certain ratio, and sintered at a high temperature through a sintering furnace which maintains a temperature condition higher than the process point of nickel and iron, During the sintering process, a liquid phase is formed to form a tungsten-polymerized gold material having two different phases of tungsten and liquid phase.

On the other hand, in the production of tungsten-polymerized gold, when a liquid phase is formed due to the melting of nickel and iron contained in the tungsten-polymerized gold, a severe deflection phenomenon and a change in thickness occur due to gravity during sintering. Particularly, in the case of a tungsten-plated gold spherical body having a small thickness, sagging due to gravity during sintering is severely generated, so that the hemispherical shape can not be maintained.

According to the embodiments of the present invention, it is intended to manufacture a precision hemispherical or cylindrical tungsten-polymerized gold sintered body having a notch inside.

The powder injection molding method according to the above-described embodiments of the present invention includes the steps of: mixing nickel (Ni) powder and iron (Fe) powder with tungsten (W) powder at a certain ratio to form a mixed powder; Forming a hemispherical injection molded body having a plurality of notched portions formed on its inner peripheral surface by injection molding the feedstock, degreasing the injection molded body, and removing the degreased body from a ceramic And sintering the sintered body to form a sintered body.

According to one aspect, the sintering jig may be formed of alumina (Al 2 O 3) material having a purity of 95% or more. The sintering jig may have an inner circumferential surface having the same size as the outer diameter of the sintered body having been sintered.

According to one aspect, the mixed powder may have a content of tungsten of 90 to 97%. The mixed powder is formed by mixing tungsten, iron, and nickel. The mixed powder may contain tungsten in an amount of 90 to 97%, and iron and nickel in an amount of 3 to 10% based on the tungsten content.

As described above, according to the embodiments of the present invention, a hemispherical tungsten-polymerized gold-sintered body can be manufactured by using a sintering jig.

Further, it is possible to manufacture a sintered body of tungsten-polymerized gold having excellent dimensional accuracy and a well-formed notch.

1 is a flowchart illustrating a powder injection molding process according to an embodiment of the present invention.
2 is a perspective view of a sintering jig according to an embodiment of the present invention.
3 is a perspective view illustrating a state in which a hot deaerated hot deaerator is inserted into a sintering jig according to an embodiment of the present invention.
FIG. 4 is a photograph of a recessed portion showing a state in which sintering is completed in FIG.
5 is a photograph of a sintered body according to Comparative Example 1 of the present invention.
Fig. 6 is a photograph showing the main part of the sintered body according to Comparative Example 2 of the present invention. Fig.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments will be described in detail with reference to the accompanying drawings, but the present invention is not limited to or limited by the embodiments. In describing the embodiments, a detailed description of well-known functions or constructions may be omitted so as to clarify the gist of the present invention.

Hereinafter, a powder injection molding method according to an embodiment of the present invention will be described with reference to FIGS. 1 to 6. FIG. For reference, FIG. 1 is a flowchart for explaining a powder injection molding process according to an embodiment of the present invention. FIG. 2 is a perspective view of a sintering jig 10 according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of a sintering jig 10 according to an embodiment of the present invention, And Fig. 4 is a photograph of a recess showing the sintered body 22 in a state where sintering is completed in Fig. FIG. 5 is a photograph of a sintered body according to Comparative Example 1 of the present invention, and FIG. 6 is a photograph showing a recessed portion of the sintered body 32 according to Comparative Example 2 of the present invention.

An embodiment of the present invention relates to a method of manufacturing hemispherical or cylindrical products using tungsten powder.

Referring to the drawings, a tungsten-polymerized gold product is formed of a mixed powder (S1, S2) in which tungsten powder is mixed with at least one powder selected from the group consisting of nickel (Ni) powder, iron (Fe) powder and copper (Cu) powder.

For example, the content of tungsten in the mixed powder is 90 to 97%. The mixed powder can be formed by mixing nickel and iron in a predetermined weight ratio (nickel / iron weight ratio: 1 to 10) to tungsten in order to form tungsten-polymerized gold, which requires high density and high strength. May be contained in an amount of 3 to 10% based on the tungsten content.

Next, a mixed powder is mixed with a binder and a solvent to produce a feedstock (S3).

For example, the feedstock is a fluid filled in a mold during injection molding and having a predetermined viscosity such that the injection molded body after injection has a predetermined strength. For this purpose, the feedstock is formed by mixing an appropriate amount of binder in the mixed powder. For example, the binder may be used with various kinds of binders having different melting points. For example, a binder mixed with paraffin wax, polyethylene, polypropylene, stearic acid or the like may be used.

Next, injection molding is performed on the feedstock prepared as described above to mold the injection molded body (S4).

Here, the injection body is formed in a hemispherical shape, and a plurality of notches 220 are formed along the inner circumferential surface, as shown in Fig. For example, the notch 220 may have a lattice shape with a predetermined spacing. However, the present invention is not limited by the drawings, and the notch 220 may have substantially various sizes and shapes.

Next, a degreasing step for removing the binder from the injection-molded body is performed (S5, S6).

Here, when a plurality of binders having different properties (for example, melting points) are included in the feedstock, the degreasing process can be performed over various stages. For example, in the degreasing step, solvent degreasing (S5) and hot degreasing (S6) can be performed.

Then, the degreased body 21 having been degreased is sintered at a predetermined temperature to form a sintered body 22 (S8). Here, in the sintering step, sintering is performed in a state where the degreasing body 21 having been degreased is inserted into the sintering jig 10 (S7).

According to these embodiments, sintering is performed in a state in which the notch portion 220 is not in contact with the sintering jig 10 during sintering by using the sintering jig 10. Since the temperature of the notch 220 is relatively low in comparison with the ambient temperature during sintering, the liquid phase is first generated on the outer circumferential surface of the degreasing body 21 and the liquid phase is not filled in the notch 220, Lt; RTI ID = 0.0 > 220 < / RTI >

The sintering jig 10 is formed so that its inner diameter is equal to the outer diameter of the sintered body 22 to be finally produced. The sintering jig 10 is manufactured using a powder injection method in order to increase the dimensional accuracy. The material of the sintering jig 10 is formed of high purity alumina (Al 2 O 3) having a purity of 95% or more.

According to these embodiments, it is possible to mass-produce a high-purity sintered jig 10 having excellent surface roughness and high dimensional accuracy by using the powder injection method. For reference, high-purity alumina having a purity of 95% or more is usually made of a material having a purity of about 90% and containing about 10% of silica (SiO 2) because press molding is difficult. However, when the sintering jig is made of a material containing silica, the silica contained in the sintering jig reacts with hydrogen to generate silicon (Si) in a sintering process performed in a hydrogen atmosphere with poor surface roughness, The silicon component thus produced can contaminate the sintering furnace. In addition, when silicon is produced, pores may be generated in the sintering jig as the silicon escapes from inside the sintering jig. As a result, the surface of the sintering jig gradually becomes rough and the porosity becomes high, So that the service life of the sintering jig is shortened. However, according to the present embodiment, since the sintering jig 10 is manufactured from a high-purity alumina material having a purity of 99% or more, the sintering furnace is contaminated with silicon in the sintering process or the sintering jig (10) 10 can be prevented from being generated.

Referring to FIG. 5, in Comparative Example 1, a hemisphere of tungsten-polymerized gold was produced without using a sintering jig. During the preparation of the tungsten-polymer gold spheres, the liquid phase is formed as the nickel and iron contained in the tungsten-polymerized gold are melted, and the thickness is changed along with the sagging phenomenon due to the influence of gravity during sintering. However, as shown in FIG. 5, when the sintering jig is not used, it can be seen that sagging due to gravity during sintering is severe and the shape of the hemispherical shape is not maintained and the shape is deformed.

And FIG. 6 shows a hemisphere of tungsten-polymerized gold produced by sintering the sintered jig while inserting a sintered jig therein. Specifically, Comparative Example 2 of Fig. 6 is a photograph of a sintered body 32 which is sintered in a state where a sintering jig corresponding to the inner diameter of the hemisphere to be sintered is inserted into the degreasing body. Referring to FIG. 6, when the sintering jig is inserted into the degreasing body and sintered, the semispherical shape of the sintered body 32 is maintained after sintering. However, when the inner peripheral surface of the sintered body 32 is examined in FIG. 6, it can be seen that the notch 320 is filled. In the case of Comparative Example 2, since the sintering jig is inserted into the debris body, sintering proceeds in a state where the sintering jig and the notch portion 320 are in contact with each other, and the temperature of the notch portion increases due to the sintering jig This is because the resulting liquid phase fills the notch 320. If the notch 320 is filled in this way, it is difficult to form the debris, so that the performance of the can is deteriorated. However, since the notch portion 220 and the sintering jig 10 are not in contact with each other in the present invention, a liquid phase is not formed in the notch portion 220 during the sintering process. Therefore, 220 may be formed.

In the case of Comparative Example 2, since the sintering jig is inserted into the sintered body, the sintered body is shrunk as the sintering progresses. Therefore, it is difficult to remove the sintered body from the sintered body 32 after sintering. The sintering jig may be damaged because it impacts the sintering jig.

In contrast, in the case of the present invention, since the degreasing body 21 is inserted and sintered in the sintering jig 10, when the sintered body 22 is shrunk after the sintering, 22) is contracted), so that the sintering jig 10 and the sintered body 22 can be easily separated from each other.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. For example, it is to be understood that the techniques described may be performed in a different order than the described methods, and / or that components of the described systems, structures, devices, circuits, Lt; / RTI > or equivalents, even if it is replaced or replaced.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

10: sintering jig 21: hot debris body
22: sintered body 220: notch

Claims (5)

In the powder injection molding method,
Mixing tungsten (W) powder with at least one powder selected from the group consisting of nickel (Ni) powder, iron (Fe) powder and copper (Cu) powder to form tungsten (W) powder;
Mixing the mixed powder with a binder to prepare a feedstock
Forming a hemispherical injection molded body having a plurality of notches formed on its inner peripheral surface by injection molding the feedstock;
Degreasing the injection body; And
Inserting the degreased body into the sintering jig of ceramic material and sintering the sintered body to form a sintered body;
Wherein the powder injection molding method comprises the steps of:
The method according to claim 1,
Wherein the sintering jig is formed of high purity alumina (Al 2 O 3) material having a purity of 95% or more.
The method according to claim 1,
Wherein the sintering jig has an inner circumferential inner circumferential surface having the same size as the outer diameter of the sintered body having been sintered.
The method according to claim 1,
Wherein the mixed powder has a tungsten content of 90 to 97%.
5. The method of claim 4,
The mixed powder is formed by mixing tungsten, iron and nickel,
Wherein the mixed powder contains tungsten in an amount of 90 to 97%, and iron and nickel in an amount of 3 to 10% based on the tungsten content.

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