JPH04179501A - Removing method of placement core in molding method of powder injection - Google Patents

Abstract

PURPOSE:To enable an article having complicate inner configurations to be manufactured relatively easily at low cost by immersing a green body injection- molded in a state of being incorporated with a placement core into an organic solvent and then dissolving the placement core therein. CONSTITUTION:A placement core 3 is disposed in a mold 5 for injection molding, and the kneaded body of alumina powder and binder is injection-molded in order to be a green body 6 in a state of including the placing core 3. Then the green body 6 is immersed in an organic solvent 7, such as e.g. methylene chloride, and after the lapse of time of 10 hours at a room temperature of 25 deg.C, the green body is taken out for excluding the placing core 3 therefrom perfectly. Next, it is placed in a heating furnace and degreasing is effected therefor, following this, baking is performed therefor, resulting in obtaining a non-defective article 1.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for removing a dropped core in a powder injection molding method, and particularly relates to a powder injection molding method for producing a product having a complex-shaped cavity inside. The present invention relates to a method for removing a dropped core in a molding method.

[Prior Art] In recent years, plastic injection molding technology has developed into injection molding of ceramic powders and metal powders, and parts in various fields are manufactured by injection molding of ceramic powders and metal powders.

In such powder injection molding, a powder made of fine particles of metal or the like is heated and kneaded with a binder such as an organic material (wax, wood such as polyethylene) to obtain a kneaded body. This kneaded body is injection molded into a predetermined mold using an injection molding machine as in the case of plastics to obtain a powder injection molded body called a green body.

Since this green body contains a binder, it is necessary to extract this binder by heating, for example. The process of removing the binder (debinding) through such a heating process is called degreasing.

The degreased body (brown body), which is a powder injection molded body after degreasing, is fired or sintered to fill the countless spaces left after the binder has come out, to obtain a final product that is a shrunken sintered body with a similar shape. .

However, when manufacturing a product that has a cavity inside, this kneaded body is injection molded with a core placed in an injection mold to produce a green body, and the green body is then molded into a green body. After removing the green body, the green body is degreased, for example, by heating.

If the above-mentioned cavity has a linear shape that communicates with the outside of the product, a mold with a sliding member as the core is used, so this sliding member is removed when the mold is opened, and a green body with a linear cavity is used. obtain.

On the other hand, in the case of a cavity with a linear shape, a cavity with a complicated connection of fins, a curved cavity, or another complex shape, it is virtually impossible to remove the slide member. Conventionally, post-processing was performed after forming a green body or in the form of a sintered body.

Powder injection molding methods generally have better workability than machining and are suitable for mass production.

When the above-mentioned post-processing is required, there is a problem that workability is reduced.

In order to solve these problems, patent application No. 1-22026
A method according to No. 0 has been proposed. In this method, a core is created from a material that can be volatilized by heating, and the core is removed together with the binder in the degreasing process.

However, in this method of removing the placed core by heating, the temperature increase rate during heating must be extremely slow to prevent defects such as cracks and blisters in the green body. Another problem is that it requires a much longer degreasing time.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned problems, and when manufacturing a product that has a complex-shaped cavity inside, it is difficult to perform work using conventional machining or the like. In addition to solving the problem of poor performance, it also solves the problem that it takes a lot of time to remove the left core by heat treatment, and makes it possible to easily remove the left core, making it possible to produce products of any shape relatively easily. It is an object of the present invention to provide a method for removing a placed core in a powder injection molding method that can take advantage of the advantages of the powder injection molding method.

[Means for solving the problem] In other words, the present invention involves kneading a material powder such as ceramic powder or metal powder with a binder to form a kneaded body, and placing the kneaded body in a mold for injection molding and placing a core thereon. A method for removing a core in a powder injection molding method, which comprises injection molding the kneaded body to form a green body, removing the core from the green body, and annealing the green body. , a resin soluble in an organic solvent is adopted as the material of the placing core, and the placing core is dissolved by immersing the green body in the organic solvent;
This is a method for removing a dropped core in a powder injection molding method, which is characterized by removing this core.

The organic solvent is preferably a halogenated hydrocarbon such as methylene chloride or trichloroethane, or a ketone such as acetone.

The material for the above-mentioned core is preferably acrylic, polystyrene, polyacetal, or a mixture thereof.

Furthermore, it is desirable to increase the contact area with the organic solvent by forming a solvent passage inside the core that communicates with the outside, thereby promoting dissolution of the core.

[Function] In the method for removing a placed core in the powder injection molding method according to the present invention, a resin soluble in an organic solvent is used as the material for the placed core, and the green material is injection molded with the placed core combined. By immersing the body in this organic solvent, the core is dissolved and removed, making it possible to perform the next degreasing process in a short time, making it possible to compare products with complex internal shapes or cavities. This makes it possible to manufacture products easily, at low cost, and with fewer defective products.

Note that with a mold having a normal sliding member, it was only possible to form a cavity with a linear shape, but the present invention not only makes it possible to manufacture products with a cavity with a complex shape, but also allows mold Since it can be made into a simple shape, manufacturing costs can be reduced.

[Example] Next, one embodiment of the present invention will be described.

Assume that a molded article 1 as shown in FIGS. 1 and 2 is manufactured using, for example, alumina powder as the ceramic material powder. This molded product 1 has a cylindrical outer diameter and has a complicated cavity 2 inside thereof as shown in FIG.

The placing core 3 has the male shape of the cavity 2, and is made of, for example, acrylic resin as shown in FIGS. 3 and 4. Note that a solvent passage 4 communicating with the outside is formed in the center thereof.

For injection molding, the core 3 is placed in a mold 5 for injection molding as shown in FIG. Let it be the green body 6. The outer diameter of this green body 6 is, for example, 20 mm.

As shown in FIG. 6, when this green body 6 was immersed in an organic solvent 7 such as methylene chloride and taken out after 10 hours at a room temperature of 25°C, the core 3 was completely removed. It had been.

Next, the molded product 1 was placed in a heating furnace and degreased for 45 hours, and then fired, resulting in a defect-free molded product 1.

As a comparative example, when the core 3 was not removed using the organic solvent 7 and degreased under the same conditions, the green body 6 cracked. The reason for this is thought to be that when the placed core 3 reaches its decomposition temperature, it violently generates decomposition gas, which generates an outward pressure.

[Effects of the Invention] As explained above, according to the present invention, since the placed core is dissolved in an organic solvent, it is possible to shorten the degreasing time in the next step, and also to reduce costs and reject rates. can be realized.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of a molded product 1 for explaining the method of removing a placed core in the powder injection molding method according to the present invention, Fig. 2 is a vertical front view of the molded product 1, and Fig. 3 is the same. , a perspective view of the placing core 3, and FIG. 4 is a longitudinal sectional view of the placing core 3. FIG. 5 is a cross-sectional view of the mold 5 for injection molding with the core 3 placed therein, and FIG. 6 is a cross-sectional view of the green body 6 immersed in the organic solvent 7. 1...Molded product 2...Cavity of complex shape 3...Placeable core 4...Solvent passage 5...For injection molding Mold 6, Green body 7, Organic solvent patent applicant Sumitomo Heavy Industries, Ltd. sub-agent Patent attorney Hiroshi Ikezawa

Claims (3)

[Claims] (1) A kneaded body is obtained by kneading a binder into material powder, and a green body is obtained by injection molding this kneaded body by placing it in an injection mold with a core placed therein;
A method for removing a core in a powder injection molding method in which the core is removed from the green body, and the green body is further degreased and fired. A method for removing a core in a powder injection molding method, characterized in that the green body is immersed in an organic solvent to dissolve the core and remove the core. (2) Removal of placed cores in the powder injection molding method according to claim (1), wherein the organic solvent is a halogenated hydrocarbon such as methylene chloride or trichloroethane, or a ketone such as acetone. Method. (3) The method for removing a placed core in a powder injection molding method according to claim 1, wherein the material of the placed core is acrylic, polystyrene, polyacetal, or a mixture thereof.