JPH0358824B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vacuum casting method and apparatus, and in particular,
The present invention relates to a vacuum casting method and apparatus suitable for casting thin-walled castings that have thick-walled parts in some parts of the product.

BACKGROUND ART Conventionally, when casting a product by a vacuum casting method, an apparatus as shown in FIG. 1 has been used. In this device, a cavity 3 is formed by an upper mold 1 and a lower mold 2 having air and heat retention properties, and a pair of presser plates 4 are provided so as to sandwich both molds 1 and 2. There are many pressure reducing grooves 5 on the inner surface of the holding plate 4.
is formed, and a decompression line 6 communicating with this depressurization groove 5 is attached to the outer surface of the holding plate 4. Further, a presser plate 4 attached to the upper mold 1 has a casting port 7 for pouring metal into the cavity 3 and is open to the atmosphere. With such a device, molten metal is injected from the pouring port 7 while reducing the pressure inside the mold (upper mold 1 and lower mold 2), improving the flow of the molten metal in the cavity 3 and achieving a degassing effect. It is something that exists.

However, the vacuum casting method using the conventional apparatus described above has a problem in that the mold and the vacuum mechanism (the holding plate 4 and the vacuum line 6) are not tightly sealed. That is, in the conventional apparatus, in order to simplify the structure of the apparatus, no means for sealing the area around the joint between the upper mold 1 and the lower mold 2 is provided. As a result, the depressurization function is impaired, and casting of thin-walled castings with a wall thickness of 1 mm or less is difficult due to poor hot water flow. Furthermore, in the case of thin-walled castings that have thick-walled parts in part of the cast product,
A chiller for directional solidification is used for the purpose of preventing shrinkage defects and improving mechanical strength, but there are problems when using this chiller. That is, a cold metal is embedded in the thick wall part of the mold cavity 3, but embedding this cold metal is extremely inefficient, making it impossible to manufacture molds efficiently, and also preventing the ventilation of the mold. It causes sexual deterioration. Furthermore, a mold in which a chill metal is embedded has the disadvantage that cracks may occur in the mold due to differences in coefficients of thermal expansion during casting.

Therefore, in the vacuum casting method using conventional equipment,
There is a problem in that it is difficult to carry out castings that have a wall thickness of 1 mm or less and require directional solidification.

Furthermore, there is a method called the V process as a gold-like vacuum casting method. This method uses vinyl as a sealing jig on the inner wall of the mold cavity and performs casting by reducing the pressure inside the mold except for the cavity. However, with this method, the pressure inside the cavity is not reduced, so the wall thickness is 1 mm or less. It is difficult to cast thin-walled, complex-shaped castings, and the same problems as in the above example arise.

Regarding the vacuum casting method that takes into consideration each of the above problems,
For example, there is an invention disclosed in Japanese Patent Application No. 55-139555. In this invention, a cooling metal is interposed between the mold and a pressure reducing tank for reducing the pressure inside the mold, and the inside of the mold is sealed by covering at least the casting opening of the mold with metal foil. After reducing the pressure inside the mold, molten metal is injected from above the metal foil in the casting hole, and the metal foil is melted by the heat of the molten metal, thereby filling the cavity with molten metal. do. According to the present invention, it is possible to carry out casting by solving each of the above-mentioned problems, but even with this invention, there are still the following problems. That is, in the invention, since the pressure inside the cavity is reduced, the molten metal flows into the cavity at once when the metal foil melts and breaks.
It is not possible to control the filling speed of the molten metal, and when casting products with thin walls or complex shapes, problems such as turbulent flow of the molten metal and entrainment of air or the mold may occur, resulting in internal defects in the product. be. In order to alleviate such rapid filling of molten metal, the vacuum level inside the mold is lowered in advance.
It is conceivable to increase the degree of vacuum after pouring, but in that case, in order to eliminate internal defects in the product, it is necessary to lower the initial degree of vacuum to the same level as when opening the pouring hole. As a result, similar to the problem described above, a problem arises in that hot water flow in the thin wall portion is poor.

The present invention provides a vacuum casting method and apparatus that can stably produce complex-shaped thin-walled castings (thickness 1 mm or less) with thick-walled parts in some parts of the product, which were difficult to cast using conventional methods, without defects. The purpose is to provide.

In order to achieve the above object, the present invention provides heat retention,
A decompression mechanism is connected to an air-permeable mold through a chiller having depressurizing holes, and the chiller forms at least a part of the thick cavity part of the mold, and excludes the casting opening. The outer peripheral surface of the mold is surrounded by a sealing member, and the molten metal is injected from the casting port while reducing the pressure inside the cavity through the pressure reducing hole.

Embodiments of the vacuum casting method and apparatus according to the present invention will be described in detail below with reference to the drawings.

FIG. 2 shows a sectional view of the vacuum casting apparatus according to this embodiment. As shown in this figure, the vacuum casting apparatus is comprised of a mold 10, a chiller 12, and a vacuum tank 14.

The mold 10 is made of foamable or non-foamable gypsum material and has heat retention and air permeability. A mold 10 having a cavity 16 corresponding to the product shape is manufactured from this material. This cavity 1
Reference numeral 6 is formed at a position close to the lower end surface side in the figure, and consists of a thin wall portion 18 corresponding to a blade having a product wall thickness of 1 mm or less, and a thick wall portion 20 corresponding to a boss portion. In such a mold 10, a part of the thick wall portion 20 is opened at the lower end surface, and this opening portion is closed by the chiller 12, and the chiller 12 is connected to a portion of the thick wall portion 20. It is formed to form a section. This is to achieve directional solidification of the thick wall portion 20 during casting to prevent shrinkage defects in the product. Further, the mold 10 is provided with a pouring port 22 that opens to the outside, and a runner portion 24 that communicates the pouring port 22 with the cavity 16 is formed. This casting port 2
2 is formed on the opposite end surface (the upper end surface in the figure) of the thick portion 20. As shown in FIG.

Such a mold 10 includes a cold metal 1 that closes the opening of the thick wall portion 20 to form a part of the thick wall portion 20.
2 are bonded and arranged so as to cover the entire lower end surface of the mold 10. This cooling metal 12 is provided with a depressurizing hole 26 that opens at a joint surface with the mold 10 other than the cavity 16 forming portion. This decompression hole 26 is opened into the inside of the decompression tank 14 which is connected to the mold 10 with the cooling metal 12 sandwiched therebetween.
Communication between the mold 10 and the decompression tank 14 is provided.

The decompression tank 14 connected to the chiller 12 has a box shape with one plane open, and the opening is closed by the chiller 12 to be hermetically sealed. A sealing jig 28 made of heat-resistant rubber or the like is provided at the joint between the decompression tank 14 and the chiller 12 to seal the joint and ensure the decompression function. Also,
The pressure reducing tank 14 is connected to a pressure reducing device such as a compressor, and is provided with a nozzle 30 for extracting air from the tank 14 .

The mold 10 in which the chiller 12 and the decompression tank 14 are connected in this way is fitted with a frame 32 that surrounds the outer periphery of the side thereof. This frame body 32 is formed from a metal material, and has a cold metal 1 at its lower edge.
It is joined to 2. A sealing jig 34 made of heat-resistant rubber or the like is also interposed at the joint between the frame 32 and the chiller 12 to provide a seal between the two. Further, the upper edge of the frame 32 is raised up to the same plane as the upper end surface of the mold 10, and the entire outer part of the mold 10 is sealed. The upper end surface of the mold 10 is open to the atmosphere, but the upper end surface except for the casting port 22 is sealed with a metal foil 36 made of aluminum or the like.

A vacuum casting method using such a vacuum casting apparatus is performed as follows. In advance, a pressure reducing device connected to the reduced pressure tank 14 is activated to bleed air from the reduced pressure tank 14. Due to this bleed action, the pressure reducing hole 26
The entire mold 10 is brought into a slightly reduced pressure state. At this time, the mold 10 is connected to the casting opening 2 by a sealing jig 34 and a metal foil 36 between the mold 10 and the cold metal 12.
The parts other than 2 are sealed, and the space between the decompression tank 14 and the chiller 12 is also sealed by a sealing jig 28. However, since the casting port 22 is open, the inside of the cavity 16 is not in a reduced pressure state.
Thereafter, molten metal made of aluminum material, which is a raw material for casting, is poured from the pouring port 22. When the casting hole 22 is blocked by molten metal, the mold 10
Since the upper end surface is completely sealed, the cavity 16
The pressure inside is suddenly reduced. As a result, the molten metal in this example can quickly and reliably fill even thin-walled parts with a wall thickness of 1 mm or less, compared to the molten metal in a conventional device that does not use a sealing member.
Compared to the molten metal in a device such as the invention of Japanese Patent Application No. 139555/1983, in which the casting opening is sealed with metal foil, the filling speed of the molten metal is controlled, and the molten metal flows smoothly and stably into the thin walled portion. It is filled around the hot water. Therefore, when pouring molten metal, the molten metal can flow smoothly without turbulence or air entrainment, and although some gas is sucked in due to the reduced pressure in the cavity 16, this is removed from the cavity. Therefore, it is possible to improve the quality of the product. There is no possibility that the hot water filled in the cavity 16 will undergo directional solidification in the thick wall portion 20 by the chiller 12 and cause shrinkage defects.

FIG. 3 shows a second embodiment of the vacuum casting apparatus.
This device connects the runner section 24A to the side of the cavity 16, and connects the cavity 1 with the chiller 12.
In this embodiment, not only the thick wall portion 20 of No. 6 but also a part of the runner portion 24 is formed.

Further, FIG. 4 shows a third embodiment of the same device.
In this device, the mold 10 and the decompression tank 14 are inverted, and the pouring port 22B is provided at the upper end of the runner 24B passing through the chiller 12, and is arranged on the side of the decompression tank 14. It is configured as follows.

The apparatuses according to the second and third embodiments also make it possible to cast thin-walled products with a thickness of 1 mm or less, and
Attaching the chiller can also be done extremely easily.

In the first and second embodiments of the present invention,
Although an example has been shown in which the metal foil 36 is attached to the upper end surface of the mold 10, this portion does not particularly need to be melted with molten metal, so it may be formed of a metal plate or other heat-resistant plate-like material. When using metal plates and heat-resistant plates,
It is desirable to interpose a sealing member such as heat-resistant rubber between the casting member 32 and the outer peripheral edge of the casting port 22.

Specific examples of such a method are shown below.

Example 1 Using a mold 10 made of non-foaming gypsum material, a thin-walled casting (wall thickness of 1 mm or less, depending on the position, a wall thickness of 0.5
mm) was cast in aluminum material (AC4C). In this case, both the present example and the gravity casting method were compared and studied.

In the gravity casting method, the mold temperature is 500℃ and the pouring temperature is 850℃.
℃, chilled metal temperature of 400℃, and riser height of 200mm, but it was impossible to cast a product without defects such as poor hot water circulation and surface pinholes.

On the other hand, in the vacuum casting method, the mold temperature is 250
℃, pouring temperature 700℃, cooling metal temperature 250℃, riser height
30 mm and a vacuum of -300 mmHg or more, the product was cast without any defects.

In this embodiment, the mold 10 excluding the casting port 22
The top surface of the was sealed with an aluminum film with a thickness of 20 to 100μ. This is because if the film thickness is less than 20 μm, the aluminum film will be torn by mold temperature, etc., and if it is more than 100 μm, the sealing function against the mold will be impaired.

Example 2 A mold 10 made of foamable gypsum material was used, the mold temperature was 200°C, the casting temperature was 700°C, the chiller temperature was 250°C,
The above Example 1 was carried out under conditions of a degree of reduced pressure of −100 mmHg or more.
As a result of performing vacuum casting in the same manner, it was possible to cast a product with no defects.

As described above, according to the vacuum casting method and apparatus according to the present invention, it is possible to ensure the sealing of the mold except for the casting opening, and to prevent turbulent flow of the molten metal or air during pouring, which improves the depressurized state in the cavity during pouring. The hot water can flow well without any entrainment, and the chiller can be easily placed and assembly workability is good, making it possible to produce thin-walled castings with complex shapes that have some thick parts without defects. It can be manufactured stably.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a conventional vacuum casting device, Fig. 2 is a sectional view of a vacuum casting device according to the present embodiment, Fig. 3 is a sectional view showing a second embodiment of the same device, and Fig. 4 is a sectional view of the same device. FIG. 7 is a sectional view showing a third embodiment. 10... Mold, 12... Chilled metal, 14... Decompression tank, 16... Cavity, 18... Thin wall part, 20
. . . Thick wall portion, 22 . . . Casting port, 26 . . . Decompression hole, 32 .

Claims (1)

[Scope of Claims] 1. A mold having heat retaining properties and air permeability is connected to a pressure reducing mechanism via a chiller having holes for reducing pressure, and at least a part of the thick walled part of the cavity of the mold is connected by the chiller. and surrounding the outer peripheral surface of the mold except for the casting port with a sealing member, and injecting molten metal from the casting port while reducing the pressure inside the cavity through the pressure reducing hole. . 2 Equipped with a pressure reduction mechanism connected to a mold having heat retention and breathability via a chiller having pressure reduction holes,
A vacuum casting apparatus characterized in that the cooling metal forms at least a part of a thick cavity part of the mold, and the outer circumferential surface of the mold except for the casting opening is surrounded by a sealing member.