JP2000271720A - Method for injection-forming metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection-forming method of a metal, with which the durability of an injection-forming die is improved by preventing the oxidation of DLC film (diamond-like carbon film) and thus, the maintainability can be improved and also, the quality of a formed product can be improved. SOLUTION: The DLC film is coated on a core block 1 and a cavity block 2 in the injection-forming die. Before starting the filling of molten metal (magnesium alloy) into a cavity 3, dry nitrogen gas is supplied into the cavity 3 through a chilling vent 16. Thereafter, the molten metal is poured into the cavity 3 in the state in which the atmosphere in the cavity 3 is replaced with the dry nitrogen gas, and also, the dry nitrogen gas in the cavity is exhausted to the outside of the injection forming die through a chilling vent 20 and the chilling vent 16 with the injection pressure of the molten metal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal injection molding method, and more particularly, to an injection molding method capable of improving the quality of a molded product and shortening a molding cycle.

[0002]

2. Description of the Related Art Conventionally, for the purpose of improving the durability of a metal injection mold, preventing seizure of an alloy onto the injection mold and preventing welding, the surface of the injection mold is nitrided or the injection mold is used. Of a coating film of TiN, TiC, CrN or the like on the surface of the substrate by PVD or CVD. In addition, attention has been given to coating a diamond-like carbon film (DLC film) on the surface of an injection mold with attention to the non-adhesiveness to soft metals and low friction characteristics of soft metals. This DLC film exhibits low friction against soft and easily adhered materials such as Al alloys and lead alloy magnesium alloys, and is expected to be used as a coating material for die casting and thixo molding dies for forming soft alloys. I have.

[0003]

As described above, if the surface of the injection molding die is nitrided or coated with a TiN, TiC, CrN film or the like, the life of the injection molding die is improved, and seizure and wear are reduced. It has been confirmed that remarkable effects such as prevention can be obtained.However, this method cannot obtain sufficient mold releasability of the injection mold for soft metal, and takes out the molded product when soft metal is formed. At the time of the deformation, there is a fear that deformation occurs. For this reason, the surface of the injection mold is usually spray-coated with a release agent of various liquids or powders for each molding shot.

[0004] Coating of a release agent on the surface of such an injection mold includes the following steps. 1. Surface defects such as hot wrinkles are likely to occur on the molded product surface. 2. Long molding cycle. Since the release agent adheres to the sliding portion of the mold and the divided surface of the mold and causes malfunction of the injection mold, there is a problem that maintenance such as division and cleaning of the injection mold is frequently required.

According to the above-mentioned method of coating a DLC film, molding without a release agent can be expected due to a small friction coefficient between the DLC film and the soft metal. If heated over, it will gradually graphitize and wear will increase significantly; Since the adhesion between the film and the base material of the injection mold decreases, it is recommended to use the film at a temperature of 450 ° C. or lower in the atmosphere, which limits the use temperature.

In fact, regarding the heat resistance of a DLC film formed by an ion plating method, it has been reported that the weight change starting at 600 to 700 ° C. in a nitrogen gas atmosphere and starting at 450 to 500 ° C. in the air. ing.

When a magnesium alloy is injection-molded (thixo-molded), the temperature of the molten metal in the heating cylinder is set to 550 to 580 ° C. and the temperature of the mold is set to about 200 ° C. The temperature of the molding die wall surface may exceed 450 ° C. The structural change (graphitization) of the DLC film is determined by the product of temperature and time, and when used in a mold for magnesium alloy injection molding, etc., it can withstand molding in a short time, but is durable. There is a problem that the property is insufficient.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to prevent the oxidation of a DLC film, improve the durability of an injection molding die, and prevent the surface of a molded product from being oxidized. It is an object of the present invention to provide a metal injection molding method that can be performed.

[0009]

According to a first aspect of the present invention, there is provided an injection molding method for molding a metal using an injection molding die having a diamond-like carbon film coated on a core block and a cavity block. Before starting the filling of the molten metal into the cavity, a step of replacing the atmosphere in the cavity with an inert gas, and injecting the molten metal into the cavity with the inside of the cavity replaced by the inert gas. And discharging the inert gas in the cavity to the outside of the injection mold by the injection pressure of the molten metal.

[0010] The metal injection molding method according to the second aspect of the present invention is characterized in that:
The method of injection molding a metal according to claim 1, wherein the inert gas is supplied and discharged through a path provided on a side of a molten metal injection side and a side opposite to the side of the cavity.

[0011]

FIG. 1 is a sectional view showing the structure of an injection mold used in the present embodiment. Here, molding of an alloy containing magnesium as a main component (hereinafter, referred to as a magnesium alloy) will be described.

In FIG. 1, 1 is a cavity block,
Reference numeral 2 denotes a core block, which forms a cavity 3. A runner (a sprue 4, a runner 5, a side gate 6) and a pool 7 are formed by the cavity block 1, the core block 2, the sprue bush core 12, and the sprue bush 10, and are connected to the cavity 3.

The cavity block 1, the core block 2, the sprue bush core 12, the sprue bush 10
Are configured such that a cavity 17 connected to the sprue 4 is formed by a mold dividing surface formed by the above. A chill vent 16 is connected to the space 17. The chill vent 16 is an air vent formed by forming a lot of irregularities on a mold dividing surface, and is generally known as a large-volume degassing method, and allows only a gas to pass without passing a molten metal having a large flow resistance. Has a function. A supply line is connected to the chill vent 16 so that nitrogen can be supplied via a pressure reducing valve 14 and a direction control valve 15 from a nitrogen gas supply source provided outside the injection molding die. The chill vent 16 has a directional control valve 19.
, And exhaust through the chill vent 16 is enabled.

Further, a chill vent 20 is provided in the pool 7.
(An air vent formed by forming a lot of irregularities on the mold dividing surface in the same manner as the chill vent 16).
Degassing through it is possible.

Cavity block 1, core block 2,
The sprue bush 10 and the sprue bush core 12 are SKD
-61 (hot die steel). In addition, a mold release film having a low coefficient of friction is provided on the mold release surfaces with magnesium such as the cavity forming surfaces 8, 9 of the core block 2, the core block 2, the inner surface 11 of the sprue bush 10, and the outer peripheral surface 13 of the sprue bush core 12. DLC film is coated. The coating film has an average thickness of about 1 μm.

The production of the DLC film utilizes a known film forming method, namely, (1) P-CVD (chemical vapor deposition) using glow discharge plasma by high frequency or DC power, (2) sublimation and deposition of solid carbon. P such as ion plating
VD (physical vapor deposition) and the like can be used.

The DLC film and the mold base material (SKD-6)
In order to prevent the peeling of the DLC film or the deformation of the film due to the difference in hardness and coefficient of thermal expansion from 1), TiN, TiC or the like may be provided as a base film of the DLC film.

Hereinafter, the injection molding method of the present invention using the injection molding die configured as described above will be described.

(Step 1) First, with the fixed mold 31 and the movable mold 30 provided with the cavity block 1 closed, dry nitrogen gas is supplied from an external nitrogen gas supply source via the pressure reducing valve 14 and the direction control valve 15. Supply inside the mold. Specifically, the dry nitrogen gas reduced in pressure to 1 to ² kg / cm ² by the pressure reducing valve 14 is supplied from the directional control valve 15 in an energized state to the cavity 17 through the chill vent 16 and the gap 17 in the mold dividing surface. Introduce to 3. At this time, the direction control valve is in a non-energized state, that is, in a closed state.

In this step 1, at the same time as the dry nitrogen gas starts to fill the cavity 3, the air in the cavity 3 (and the sprue 4, the runner 5, and the side gate 6) is discharged through the chill vent 20 to the outside of the injection mold. Cavities 3 (and sprues 4, runners 5,
The inside of the side gate 6) can be replaced with dry nitrogen gas.

(Step 2) The interior of the cavity 3 and the like is filled with dry nitrogen gas by Step 1,
Here, a molten magnesium alloy is injected into the cavity 6 at high speed from an injection molding machine and filled into the cavity 6 through a runner.
At this time, the directional control valve 19 is set to the energized state (open state), and the dry nitrogen gas filled in step 1 is discharged from the chill vent 20 and through the chill vent 16 by the injection pressure of the magnesium alloy. 19
From the injection mold.

At this time, dry nitrogen gas is supplied to the pressure reducing valve 1
4. The supply may be continued through the direction control valve 15 to the inside of the injection mold. However, in this case, the supply pressure of the dry nitrogen gas (the outlet side of the pressure reducing valve 14) must be lower than the injection pressure of the magnesium alloy.

(Step 3) After filling the molten metal, the cavity 3
When the molten metal inside is solidified, the movable mold 30 is opened.

(Step 4) Then, the molded product is released from the core block 2 by, for example, an extrusion pin (not shown). Thereby, the molding of one shot is completed.

As described above, in the injection molding method of the present invention, since the atmosphere in the cavity is replaced with nitrogen before filling with the molten metal, the DLC film is used. Can be prevented from being graphitized by high-temperature oxidation. In addition, it is possible to prevent oxidation of a molded product (a magnesium alloy in the present embodiment).

Since the supply and exhaust of the dry nitrogen gas are performed through the paths provided on the side of the molten metal injection side and the side opposite to the cavity 3, the atmosphere in the cavity 3 can be quickly replaced. .

Although dry nitrogen gas was used here,
Any inert gas such as Ar gas can be used instead.

[0028]

According to the present invention, since injection molding can be performed in an atmosphere containing no oxygen, when a DLC film is coated on a mold wall surface, graphitization due to high-temperature oxidation can be prevented. Therefore, the durability of the injection mold can be improved, and the maintainability can be improved.

Further, since the DLC film can be used, it is not necessary to use a release agent, and it is possible to eliminate surface defects such as hot wrinkles on the surface of the molded article due to the release agent, and it is also necessary to use the DLC film frequently. This eliminates the need for cleaning the mold, and shortens the molding cycle due to the elimination of the release agent spraying operation.

Further, it is possible to suppress the generation of magnesium oxide on the surface of the molded product, and it is possible to reduce the number of secondary processing steps and coating steps after molding.

Further, if dry nitrogen gas is supplied and exhausted through a path provided on the molten metal injection side and the opposite side to the cavity 3, the atmosphere in the cavity 3 can be quickly replaced. .

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating a configuration of an injection mold used in an embodiment.

FIG. 2 DL by temperature change in air and nitrogen gas
It is a figure explaining the weight change of C film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cavity block 2 Core block 3 Cavity 4 Sprue 5 Runner 7 Hot water pool 8, 9 DLC film 14 Pressure reducing valve 15, 19 Direction control valve 16, 20 Chill vent 17 Void

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B29C 45/34 B29C 45/34 45/37 45/37 (72) Inventor Masafumi Tokiwa Atobe Honcho, Yao City, Osaka Prefecture 4-Chome 1-33 Sharp Manufacturing Co., Ltd. F-term (reference) 4F202 AJ09 CA11 CB01 CM73 CP04

Claims (2)

[Claims] A diamond-like carbon film as a core block;
In an injection molding method for molding a metal using an injection molding mold coated on a cavity block, a step of replacing an atmosphere in the cavity with an inert gas before starting filling of the molten metal into the cavity; Injecting the molten metal into the cavity while the inside is replaced by the inert gas, and discharging the inert gas in the cavity out of the injection mold by the injection pressure of the molten metal. A metal injection molding method, characterized in that: 2. The metal injection molding method according to claim 1, wherein the inert gas is supplied to and discharged from a cavity through a path provided on a molten metal injection side and an opposite side thereof. Metal injection molding method.