JP3089697B2 - Injection molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method.About
You.

[0002]

2. Description of the Related Art For example, a method for manufacturing an injection-sintered member includes injection molding of a molding material obtained by kneading a powder made of a metal or ceramic and a binder made of a resin or the like, and the injection molding obtained by this method. There is a method in which the binder is degreased from the body, then sintered, and the resulting sintered body is subjected to post-processing to increase the dimensional accuracy and thus produce an injection-sintered member. In the injection molding process, a molding material obtained by kneading a powder and a binder is injected from a nozzle of an injection molding machine body into a mold cavity through a mold gate.
With the gate of the mold opened, pressure is applied to the molding material in the cavity of the mold by the injection molding machine body to perform molding.

[0003]

However, in such a conventional injection molding method, pressure is intensively applied to the molding material in the cavity of the mold via the gate of the mold by the main body of the injection molding machine. As a result, a pressure gradient is generated in the cavity of the mold, which causes a difference in the density of the powder made of metal, ceramic, or the like in the injection-sintered member, which is the final product, and deforms the injection-sintered member, which is the final product. There was a problem that this would be the cause. In addition, because of the small ballasting effect of the molding material obtained by kneading a powder made of metal or ceramic and a binder made of resin,
The molding material injected into the mold cavity spreads anisotropically, that is, the molding material is injected in a string shape, and the string-shaped molding material is filled into the mold cavity while being folded and overlapped. Therefore, there is a problem that air in the cavity of the mold and volatile components of the binder are caught in the overlap of the string-shaped molding materials, which causes cracks, swelling, and the like in the injection-sintered member as the final product. . An object of the present invention is to make it possible to uniformly pressurize the mold cavity so that a pressure gradient is not generated in the mold cavity, and to at least prevent air in the mold cavity from being caught in the overlap of the string-like molding material. It is an object of the present invention to provide an injection molding method which can be used. Another object of the present invention is to provide an injection molding method capable of preventing volatile components of a binder in addition to air in a cavity of a mold from being caught in an overlap of a string-like molding material.

[0004]

According to the first aspect of the present invention,
In an injection molding method of injecting a molding material into a mold, the mold is evacuated before the molding material is injected into the mold, and the gate of the mold is injected after the molding material is injected into the mold. Is closed, and then the mold is clamped and pressurized. According to a second aspect of the present invention, the inside of the mold is evacuated before and during the injection of the molding material into the mold.

[0005]

According to the first aspect of the present invention, since the inside of the mold is evacuated before the molding material is injected into the mold, at least the air in the cavity of the mold is filled with the string-like molding material. The mold can be prevented from being caught in the overlap, and after injecting the molding material into the mold, the mold gate is closed and then the mold is clamped and pressurized. can be pressure gradient is pressurized in other words uniform without causing the. According to the second aspect of the present invention, since the inside of the mold is perceived before and during the injection of the molding material into the mold, the volatile component of the binder is also contained in addition to the air in the cavity of the mold. It can be prevented from being caught in the overlapping of the string-shaped molding materials.

[0006]

FIG. 1 shows an injection molding step of an injection molding method according to an embodiment of the present invention, and FIG. 2 shows a main part of an injection molding machine. First, the injection molding machine shown in FIG. 2 will be described. This injection molding machine is a hopper (not shown) in which a molding material obtained by mixing a powder made of metal or ceramic and a binder made of resin or the like is stored. The molding material 2 sent from the hopper into the injection molding machine main body 1 is heated to melt the binder therein, and the molten molding material 2 of the binder is passed through the nozzle 3 and the gate 5 of the female mold 4. The injection is performed into a cavity 7 formed by the female mold 4 and the male mold 6.

The gate 5 is openable and closable. The male mold 6 is provided with a communication passage 8 communicating with the inside of the cavity 7. One end of the communication passage 8 is connected to a central portion of a T-shaped pipe 9. A first valve 10 is interposed on one side of the T-shaped pipe 9, and a distal end on the same side is connected to a vacuum pump 11. A second valve 12 is interposed on the other side of the T-shaped pipe 9, and the tip on the other side is open to the atmosphere.

In this injection molding method, the first valve 10 and the second valve 12 are closed, and the vacuum pump 11
Is driven, first, in the mold closing step 21, as shown in FIG. 1, the male mold 5 is closed as shown in FIG.
Let the space occupied by the cavity 7 be the desired amount. Next, in the temporary mold opening step 22, as shown in FIG. 2, the male mold 5 is opened by a predetermined amount, that is, an amount capable of obtaining the pressing force required in the subsequent mold clamping step 27, and the cavity 7 is opened.
Is occupied by a predetermined amount larger than an expected amount.

Next, in the in-mold deaeration step 23, the first valve 10 is opened, and the air in the cavity 7 is removed by the driven vacuum pump 11. When the inside of the cavity 7 reaches a predetermined degree of vacuum, the molding material 2 obtained by kneading the powder and the binder is injected from the nozzle 3 of the injection molding machine body 1 to the gate 5 of the female mold 5 in an injection step 24. A predetermined amount is injected into the cavity 7 through the cavity. At this time,
The first valve 10 is opened as it is, so that the vacuum pump 11 removes volatile components of the binder in the molding material 2 in the cavity 7.

Next, in a mold release step 25, the first valve 10 is closed and the second valve 12 is opened to return the inside of the cavity 7 to the atmospheric pressure. Next, in a gate closing step 26, the gate 5 is closed. Next, in the mold clamping step 27, as shown in FIG. 3, the male mold 5 is closed, and the space occupied by the cavity 7 is set to a desired amount.
A predetermined amount of the molding material 2 injected into the cavity 7 is pressed and molded. At this time, the air and the like in the cavity 7 are discharged into the atmosphere via the second valve 12 in the open state. Next, in a mold opening step 28, the male mold 6 is opened, and then in an ejection step 29, an injection molded body formed by press-molding a predetermined amount of the molding material 2 is taken out. Hereinafter, after the binder degreasing step, the sintering step, and the post-processing step, an injection-sintered member as a final product is obtained.

As described above, in this injection molding method, since the inside of the cavity 7 is evacuated before and during the injection of the molding material 2 into the cavity 7, the air in the cavity 7 and the volatile components of the binder are removed. It can be prevented from being caught in the overlap of the string-shaped molding materials 2, so that cracks, blisters and the like can hardly be generated in the injection sintered member as a final product. Further, since the gate 5 of the female mold 4 is closed after the molding material 2 is injected into the cavity 7 and the male mold 6 is closed and pressurized thereafter, the pressure gradient is prevented from being generated in the cavity 7. Uniform pressure can be applied, so that there is little difference in the density of the powder made of metal, ceramic, etc. in the injection-sintered member, which is the final product, so that the injection-sintered member, which is the final product, is not easily deformed. be able to. Further, from the above, the dimensional accuracy of the injection-sintered member is improved, so that a post-processing step for improving the dimensional accuracy can be omitted or simplified.

[0012]

As described above, according to the first aspect of the present invention, since the inside of the mold is perceived before the molding material is injected into the mold, at least the inside of the cavity of the mold is provided. Air can be prevented from being trapped in the overlap of the string-like molding material, so that the final product is an injection-sintered part
In this case, it is possible to prevent cracks and swelling from occurring in the injection sintered member, and close the gate of the mold after injecting the molding material into the mold, and then clamp the mold. Since the pressure is applied, the pressure can be uniformly applied without generating a pressure gradient in the cavity of the mold, that is, when the final product is an injection- sintered member, the metal, ceramic, etc. in the injection-sintered member is used. Therefore, it is possible to make it difficult for a difference in the density of the powder made of the powder to be generated, and to make it difficult for the injection sintered member, which is the final product, to be deformed. Claim 2
According to the described invention, since the inside of the mold is evacuated before and during the injection of the molding material into the mold, the volatile components of the binder as well as the air in the cavity of the mold are string-shaped. In the overlap of the molding materials of the molds, and is therefore suitable when the final product is an injection-sintered part.
Cracks, blisters, and the like can be made more difficult to occur in the injection-sintered member.

[Brief description of the drawings]

FIG. 1 is a view showing an injection molding step of an injection molding method according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a state in which a molding material is injected into a cavity in an injection molding machine used in the injection molding method.

FIG. 3 is a cross-sectional view showing a state where the molding material injected into the cavity is molded by pressurization in the injection molding machine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Injection molding machine main body 2 Molding material 3 Nozzle 4 Female mold 5 Gate 6 Male mold 7 Cavity 11 Vacuum pump

Claims (3)

(57) [Claims] The method according to claim 1] formed form material in an injection molding method for molding by injection into the mold, pre-Symbol molding was degassed in the mold prior to injection into the mold, the molding material An injection molding method, characterized in that after injection into the mold, the gate of the mold is closed, and then the mold is clamped and pressurized. 2. The injection molding method according to claim 1, wherein the molding material is injected into the mold while the inside of the mold is persuaded. 3. The molding material is made of metal, ceramic or the like.
Powder and a binder made of resin etc. are kneaded
3. The injection molding according to claim 1, wherein
Shape method.