JPH0788623A - Simple precision casting method for injection formation - Google Patents

Abstract

PURPOSE:To enable a simple casting having a little pin hole and blow hole and excellent dimensional precision by heating the inner part of a casting chamber fixing a mold to near the m.p. of molten metal, reducing the pressure, pouring the molten metal in the mold and slowly cooling while controlling. CONSTITUTION:The molten metal 13 is heated to the temp. at higher than the m.p. and held to a crucible 14. After arranging the mold 3 and a base board 4 into the casting chamber 1 by a lifting device 5, the casting chamber 1 is heated to near the m.p. of the molten metal 13 and the pressure in the casting chamber 1 is reduced through a vacuum pump 2. Before starting the casting, the opening part 24 of an upper fixed plate 18 in a melting chamber 11 is opened and impurity in the molten metal 13 is removed. Then, a control rod 20 is moved upward with a motor 19 to open the pouring hole 15, and after pouring the molten metal 13 containing the impurity at the time of starting casting into a receiving pan 21 through a trough 22, the molten metal is cast into the mold 3. After completing the casting, the temp. control in the casting chamber 1 is executed so as to become a prescribed temp. gradient. When the cast metal becomes the prescribed temp., the control circuit is cut off and the natural cooling is executed. Further, the reduced pressure in the casting chamber 1 is released at the time when a specific temp. is attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for precision casting an injection molding die under reduced pressure.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a casting under reduced pressure and an apparatus for carrying out the method, for example, Japanese Patent Publication No. 2-2
There is a method and apparatus for producing castings disclosed in Japanese Patent No. 5701. This equipment has a casting chamber with a furnace inside, an inlet through which the mold and crucible pass, a retractable space that can be retracted from the furnace to cool the cast mold, and the casting chamber and the retractable space are decompressed. A device for sealing the inlet, a suction pump for reducing the pressure in the casting chamber and the furnace,
The mold and the heating device for heating the molten metal in the crucible.

The manufacturing process using the apparatus having the above-described structure includes the steps of placing an empty mold and molten metal in the furnace of the casting chamber, sealing the casting chamber from the outside air, and heating the mold and molten metal. , A process of casting the casting and cooling the casting, and solidifying the casting to the extent that it will not be damaged even when exposed to air, and by inserting air into the furnace before the furnace cools significantly And the step of replacing the molten metal.

Further, as a conventional method for inexpensively manufacturing a mold for injection molding in a short time, for example, Japanese Patent Laid-Open No. 60-624.
There is a method for producing a simple mold for synthetic resin injection molding disclosed in Japanese Patent No. 4 publication. According to this production method, a step of molding a prototype of a product with silicone rubber and then curing it to form a silicone rubber mold, and injecting a gypsum slurry containing a refractory powder into the silicone rubber mold and then curing The step of forming a gypsum green mold, the step of firing the gypsum green mold to form a gypsum mold, and the gypsum mold on the shelf of the formwork with the suction exhaust port at the lower part and the aeration raw shelf plate above it. Placing, casting the molten metal of molten metal into the mold while sucking and exhausting from the suction exhaust port, casting based on the gypsum mold, and removing the mold after the molten metal cast is solidified by cooling and plaster The process consists of removing the mold and obtaining a simple mold for injection molding in which the master mold is taken.

[0005]

However, in each of the above-mentioned prior arts, the casting mold filled with the molten metal is naturally cooled after casting under reduced pressure, but there are drawbacks in the following points. That is, when there is a difference in the wall thickness of the castings to be produced, the cooling state of the molten metal is greatly different between the vicinity of the mold in contact with the interior and the interior separated from the mold. Therefore, the internal residual stress caused by the difference in the cooling rate of the casting causes warping and sinking, resulting in deterioration of dimensional accuracy as a cast product.

Therefore, the present invention has been made in view of the above-mentioned drawbacks of the prior art, in which the molten metal in the melting furnace is caused to flow into the mold in the casting chamber which is heated to near the melting point of the molten metal and depressurized, While depressurizing the casting chamber while controlling the temperature of the mold optimally to obtain a casting by cooling, the gas generated when the molten metal solidifies, while suppressing the occurrence of pinholes and cavities, An object of the present invention is to provide a simple precision casting method for injection molding in which dimensional accuracy is not deteriorated due to uniform shrinkage of molten metal.

[0007]

According to the present invention, a casting chamber in which a mold is fixed is heated to near the melting point of the molten metal to heat the mold to the melting point, and the casting chamber is depressurized, and then the molten metal is cast. It is a method of pouring into a mold in a room and gradually cooling while controlling the casting room near the melting point of the molten metal.

[0008]

In the present invention, after the molten metal is poured into the mold in the casting chamber, the casting chamber near the melting point of the molten metal is gradually cooled while controlling the temperature gradient to minimize the residual stress inside the casting. Thus, the rapid cooling of the molten metal is prevented, and it is possible to prevent the difference in the cooling rate of the molten metal between the part in contact with the mold and the part away from the mold from increasing.

[0009]

Embodiment 1 FIGS. 1 to 9 show the present embodiment, FIG. 1 is a vertical sectional view of an apparatus used in a casting method, FIGS. 2 to 8 are sectional views showing a process of producing a mold, and FIG. 9 is a graph. is there. A casting chamber 1 is connected to a vacuum pump 2 so that the casting chamber 1 can be depressurized. Inside the casting chamber 1, a mold 3 is placed on a base 4, and both the mold 3 and the base 4 can be moved in and out of the casting chamber 1 by an elevating device 5. Lifting device 5
Has a seal member 6 at a portion in contact with the casting chamber 1 for maintaining airtightness in the casting chamber 1 during casting. A heating device 7 is provided inside the furnace body forming the casting chamber 1, and the heating device 7 is operated via a temperature control circuit 9 according to the temperature sensed by a thermocouple 8 installed in the casting chamber 1. Let casting room 1
The temperature inside can be controlled.

A melting chamber 11 is provided above the casting chamber 1, and the melting chamber 11 has a melting furnace 12 whose temperature can be controlled independently of the temperature of the casting chamber 1. Inside the melting chamber 12, molten metal is provided. Thirteen
Has a crucible 14 for holding. A pouring port 15 is provided below the crucible 14, and the molten metal 13 is poured from the pouring port 15 through the runner 16 into the mold 3 in the casting chamber 1. Runway 16
A nozzle 17 capable of adjusting the flow rate of the molten metal 13 is provided at the tip inside the casting chamber 1. When the molten metal 13 is not poured into the mold 3, the upper fixing plate 1 above the melting chamber 11
The control rod 20 can close the pouring port 15 by the motor 19 mounted on the motor 8. The pouring port 15 capable of pouring the molten metal 13 into the mold 3 by operating the motor 19 by an arbitrary operation is located slightly above the bottom surface of the crucible 14, and the impurities under the molten metal 13 are poured into the pouring port 15.
You can prevent it from flowing out.

In the casting chamber 1, when the casting is started, the pouring port 1
5. A toy 22 is provided which does not inject the molten metal 13 containing impurities adhering to the runner 16 and the nozzle 17 into the mold 3 but into a saucer 21 installed on the base 4 in the casting chamber 1. A portion where the runner 16 and the casting chamber 1 are in contact with each other has a sealing member 23 for keeping the casting chamber 1 airtight. Melting furnace chamber 1
The upper fixed plate 18 of No. 1 has an opening 24 for removing impurities floating in the molten metal 13. Casting chamber 1 and melting chamber 1
1 has a window 25 through which the internal state can be observed. Further, a knock pin 28 for preventing the mold 3 from moving is installed on the base 4.

A casting method using the apparatus having the above structure will be described below. The molten metal 13 is heated to a temperature higher than the melting point and held in the crucible 14 at a stable temperature. At the same time, after the mold 3 and the base 4 are installed in the casting chamber 1 by the lifting device 5, the inside of the casting chamber 1 is heated to near the melting point of the molten metal 13 to heat the mold 3 to near the melting point, and the vacuum pump 2 is used. The casting chamber 1 is placed in a reduced pressure state of at least 100 mmHg of mercury column.

Here, for example, the mold 3 is manufactured by the method shown in FIGS. First, as shown in FIG. 2, the parting line of the prototype 51 of the product is determined and the block 52 is determined.
Fix on top. Subsequently, the block 52 is surrounded on four sides by a mold 53 as shown in FIG. 3, silicone rubber 54 is injected into the mold 53, and the mold 53 is left to cure at 25 degrees for about 12 hours. By removing the prototype 51 of the product after removing it, the silicone rubber mold 55 shown in FIG. 4 is obtained.

Next, the four circumferences of the silicone rubber mold 55 are shown in FIG.
As shown in FIG. 3, the gypsum slurry 57 mixed with refractory powder is poured into the mold 56, and the mold 56 is left to cure at room temperature for about 1 hour. Here, in the gypsum slurry 57, gypsum JK-2 (manufactured by Taisei Chemical Co., Ltd.) of refractory powder was used.
A filling type that does not generate bubbles was obtained by mixing 0 wt% with 50 wt% of water. After that, the mold 56 is removed and pulled out from the silicone rubber mold 55 to obtain a gypsum green mold 58. Subsequently, as shown in FIG. 6, a mold 59 is assembled to the gypsum green mold 58, and this mold 3 is used as the above-mentioned mold 3. This mold 3 heats the casting chamber 1 to a temperature near the melting point of the molten metal 13 so that the gypsum raw The mold 58 is fired to form a gypsum mold 60.

Immediately before starting the casting due to the reduced pressure in the casting chamber 1, the opening 2 in the upper fixed plate 18 of the melting chamber 11 is opened.
4 is opened, an additive for removing impurities of the molten metal 13 in the crucible 14 is charged, and stirring is performed. After stirring, impurities floating on the molten metal 13 are removed, and the opening 24
Close. After that, the motor 19 is operated and the control rod 2
Move 0 upwards. The molten metal 13 that has flowed out is the crucible 14
The path of the runner 16 and the nozzle 17 is traced from the pouring port 15 slightly above the bottom surface of the. Molten metal at the start of casting 13
Contains impurities in the route from the crucible 14,
It is poured into the saucer 21 via the toy 22. After pouring molten metal 13 containing impurities into the pan 21, the toy 22
Then, as shown in FIG. 7, the molten metal 13 is directly injected from the nozzle 17 into the casting mold 3 for casting.

After the injection of the molten metal 13 into the mold 3 is completed, the temperature control circuit 9 controls the temperature of the casting chamber 1 so that the temperature gradient shown in the graph of FIG. In this embodiment, a zinc alloy is used as the molten metal 13, and its melting point is about 3
It is 80 degrees. Immediately after casting, the casting chamber 1 is set at 400 degrees for 30
Then, the temperature in the casting chamber 1 is lowered at a rate of 50 degrees every 2 hours, and the temperature is lowered to 50 degrees and held for 30 minutes. Similarly, the temperature is lowered, and when the temperature reaches 200 degrees, the temperature control circuit 9 is de-energized to stop the operation of the heating device and perform natural cooling. Further, the pressure reduction in the casting chamber 1 is released when the temperature reaches 350 degrees.

Here, the temperature is controlled up to 200 ° C. because the residual stress inside the casting does not occur to a problem even if the casting is naturally cooled thereafter. After the natural cooling, the casting is taken out from the casting chamber 1 together with the casting mold 3, and the mold 59 and the gypsum casting mold 60 are removed to obtain a simple mold 61 for injection molding as shown in FIG.

According to the present embodiment, casting is performed by a casting apparatus having a simple structure in which only the casting chamber is depressurized, and the cooling rate is program-controlled, so that pinholes generated by the gas generated when the molten metal solidifies. It was possible to obtain a very simple mold for injection molding, in which defects such as cavities and cavities can be eliminated, and dimensional accuracy does not deteriorate due to uniform shrinkage of the molten metal.

[0019]

[Embodiment 2] FIGS. 10 and 11 show the present embodiment, FIG. 10 is a longitudinal sectional view of an apparatus used in a casting method, and FIG. 11 is a graph. In the present embodiment, only the points different from the first embodiment will be described, the same components will be assigned the same reference numerals, and the description thereof will be omitted. A sealing material 26 is provided in a portion in contact with the opening 24 of the upper fixing plate 18 and the melting chamber 11, and the melting chamber 11 can be shielded from the outside air and can be kept airtight. Further, the melting chamber 11 can be filled with an inert gas such as argon by the connected inert gas injection device 27.

A casting method using the apparatus having the above structure will be described below. In this embodiment, the melting point of the molten metal 13 is 3
An 80 degree zinc alloy was used. The steps until the impurities are removed immediately before casting are the same as those in the first embodiment. After closing the opening 24, the inside of the melting chamber 11 is filled with an inert gas by the inert gas injection device 27 so that the molten metal 13 is not deteriorated mainly by oxygen. After that, the molten metal 13 is injected into the mold 3 as in the first embodiment. After casting, the temperature of the casting chamber 1 is controlled by the cooling program shown in FIG. Immediately after casting, the casting chamber 1 is set to 40
Hold at 0 degrees for 30 minutes, then lower by 10 degrees at 15 minutes and hold for 10 minutes at the time of 10 degrees down. Similarly, the temperature is lowered, and when the temperature reaches 200 degrees, the temperature control board is de-energized to perform natural cooling.

According to the present embodiment, since the molten metal is held in the crucible in the inert gas atmosphere, the deterioration of the molten metal is suppressed, and more simple defect-free injection molding than in the first embodiment. I got the mold.

[0022]

Third Embodiment FIGS. 12 and 13 show the present embodiment, FIG. 12 is a vertical sectional view of an apparatus used in a casting method, and FIG. 13 is a graph. Also in this embodiment, the structure of the casting chamber 30 is
This is the same as the first embodiment. A melting chamber 31 is provided above the casting chamber 30, and the melting chamber 31 is connected to a suction pump 32 so that the melting chamber 31 can be decompressed together with the casting chamber 30. The melting chamber 31 has a melting furnace 33 whose temperature can be controlled independently of the temperature of the melting chamber 30, and inside the melting furnace 33, molten metal 34
Has a crucible 35 for holding. The crucible 35 is installed in the melting chamber 31 by a supporting device 36.

The molten metal 34 can be poured into the mold 38 inside the casting chamber 30 through the runner guide 37 by tilting the crucible 35 by any operation. Melting chamber 3
1 has an opening 39 at the top of which molten metal 34
Impurities floating on the surface can be removed. A seal member 40 is provided at a portion where the molten metal guide 37 and the opening 39 are in contact with the casting chamber 30 and the melting chamber 31, and the depressurized state of the casting chamber 30 and the melting chamber 31 can be maintained by the sealing member 40. The casting chamber 30 and the melting chamber 31 each have a window 41 for observing the internal state.

A casting method using the apparatus having the above structure will be described below. In this embodiment, the melting point of the molten metal 13 is 3
An 80 degree zinc alloy was used. The casting chamber 30 is filled with molten metal 34
The procedure is the same as in Example 1 until heating up to near the melting point of. Then, after removing impurities in the crucible 35 from the opening 39, the opening 39 is closed and the suction chamber 32 depressurizes the casting chamber 30 and the melting chamber 31. Next, the crucible 35 is tilted, and the molten metal 34 is poured into the molten metal guide 37.
It is injected into the mold 38 in the casting chamber 30 via. afterwards,
The temperature of the casting chamber 30 is controlled according to the cooling program shown in FIG. Immediately after casting, the casting chamber 1 is kept at 360 ° C. for 30 minutes, and then the temperature is lowered at a rate of 100 ° C. for 4 hours, and when the temperature drops 100 ° C., it is kept for 30 minutes. Similarly, the temperature is lowered, and when the temperature reaches 160 degrees, the temperature control is stopped and natural cooling is performed.

According to this embodiment, by reducing the pressure drop between the casting chamber and the melting chamber, air entrainment during casting is further reduced, deterioration of the molten metal is suppressed, and more defect-free injection is performed. A simple mold for molding can be obtained.

In each embodiment, the molten metal 13,
Although a zinc alloy having a melting point of 380 degrees was used as all 34 and the cooling program was explained, it goes without saying that the molten metal may be aluminum, tin or an alloy thereof, and the temperature control is performed by the molten metal to control the temperature of the casting chamber immediately after casting. It is clear that the cooling program can be changed. Also, the mold 3,
No. 38 is not limited to the method described in the first embodiment, and for example, a prototype of the product is made of a material that can sufficiently withstand the heating to the melting points of the molten metals 13 and 34, and the mold is formed in the same manner as in FIG. The molds 3 and 38 may be enclosed by 59.

[0027]

As described above, according to the method for precision casting of a simple mold for injection molding according to the present invention, a simple mold for injection molding having extremely few pinholes and cavities and extremely excellent dimensional accuracy is provided. Obtainable.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a first embodiment.

FIG. 2 is a cross-sectional view showing a first embodiment.

FIG. 3 is a cross-sectional view showing the first embodiment.

FIG. 4 is a cross-sectional view showing the first embodiment.

FIG. 5 is a cross-sectional view showing the first embodiment.

FIG. 6 is a cross-sectional view showing the first embodiment.

FIG. 7 is a cross-sectional view showing the first embodiment.

FIG. 8 is a cross-sectional view showing the first embodiment.

FIG. 9 is a graph showing Example 1.

FIG. 10 is a vertical sectional view showing a second embodiment.

FIG. 11 is a graph showing Example 2.

FIG. 12 is a vertical sectional view showing a third embodiment.

FIG. 13 is a graph showing Example 3.

[Explanation of symbols]

 1 Casting Chamber 2 Vacuum Pump 3 Mold 4 Substrate 5 Lifting Device 7 Heating Device 8 Thermocouple 9 Temperature Control Circuit 11 Melting Chamber 12 Melting Furnace 13 Molten Metal 14 Crucible 16 Top Station 18 Motor 20 Control Rod 22 Toy 24 Opening Part 25 window

Claims (1)

[Claims] 1. A casting chamber in which a mold is fixed is heated to near the melting point of the molten metal to heat the casting mold to the vicinity of the melting point, and after depressurizing the casting chamber, the molten metal is injected into the casting chamber to melt the molten metal. A simple precision casting method for injection molding, characterized by slowly cooling while controlling the casting chamber near the melting point of metal.