JPS63168266A - Pressure casting method - Google Patents

Abstract

PURPOSE:To prevent the deformation of core caused by molten metal pressure and to obtain product having excellent quality by araising the molten metal pressure to the specific pressure after forming the initial solidified layer having the prescribed thickness on the surface of core. CONSTITUTION:The disintegratable cores 3, 4 are set at the prescribed state in a cavity (a) formed at the parting part of upper die 1 and lower die 2 and the plunger tip 6 in an injection sleeve 5 is shifted toward (c) direction, to fill up the molten metal (b) in the sleeve 5 into the cavity (a). Next, in case of pressurizing the molten metal by the plunger tip 6, the pressure applied to the molten metal (b) is held to <=100kg/cm<2>, to form the initial solidified layer (d) having the prescribed thickness on the surfaces of cores 3, 4. And, at the time of forming the solidified layer (d), the pressurized force by the tip 6 to the molten metal (b) is increased to raise at >=100kg/cm<2> and the molten metal (b) is solidified by holding the pressurized condition till the prescribed time.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is an improvement of a pressure casting method such as a die casting method or a molten metal forging method, particularly a pressure casting method that is performed after placing a collapsible core in a mold. Regarding.

(Prior art) As a type of casting method, the pressure casting method, which is mainly used for casting light alloys, involves injecting molten metal into a molten metal passage formed directly below the cavity of a mold, and then passing the molten metal through a plunger tip. The material is forced into a cavity and solidified under pressure. According to this method, since the molten metal is solidified under pressure, it is possible to obtain a cast product having a high density and uniform structure without casting defects, in other words, a cast product having excellent mechanical strength. For this reason, when trying to reduce weight by manufacturing the rotor, cylinder block, and cylinder head of a rotary piston engine from aluminum alloy casting, for example, the pressure casting method described above tends to be adopted as the forming method. .

By the way, in conventional pressure casting methods, it has been customary to pressurize the molten metal in a pattern as shown in the graph of FIG. 8, for example. In other words, as shown in the same graph, at time T1 when the filling process of filling the mold cavity with molten metal is completed, the molten metal pressure is immediately increased to a predetermined pressure P1, and the molten metal is kept at that pressure P1 for a predetermined time (chill time). It was kept under pressure to solidify it.

On the other hand, when attempting to use such a pressure casting method to produce a molded product with a relatively complex shape, such as the rotor mentioned above, which has a cavity or an undercut, the shape inevitably results in a collapsible core. However, the core in this case must be able to sufficiently withstand the above-mentioned pressing force and must also be able to easily collapse after casting. Therefore, conventionally, as shown in Japanese Patent Publication No. 60-15418, for example, sand cores (shell cores) having a coating layer provided on the surface to prevent molten metal insertion (molten metal intrusion) have been used.
This is used to set the mold in a mold, then fill it with molten metal and pressurize it for pressure casting.

(Problems to be Solved by the Invention) However, in the conventional pressure casting method, as described above, the molten metal is immediately pressurized with a predetermined large force by the plunger tip after filling the mold cavity. However, there was a problem in that the collapsible core was easily deformed or damaged due to the large pressing force.

The present invention addresses the above-mentioned problems in the pressure casting method, and effectively utilizes the so-called initial solidification layer that is formed on the surface of the core at the beginning of the pressure casting process. It is an object of the present invention to provide a pressure U-immersion method that can prevent or reduce such problems.

(Means for Solving the Problems) In order to achieve the above object, the pressure casting method according to the present invention is characterized in that it is configured as follows.

That is, with the collapsible core placed in the mold, the cavity of the mold is filled with molten metal using an injection means such as a plunger tip, and then a pressing force is applied to the molten metal in this state.
maintained at 100 K9/cd or less for a predetermined time until an initial solidified layer of a predetermined thickness is formed on the surface of the core;
Thereafter, the pressurizing force is increased to a predetermined pressure exceeding 100 kg/CIA to solidify the molten metal.

(Function) According to the above configuration, the molten metal in the mold cavity is exposed to relatively high pressure (pressure exceeding 100 kg/cA) only after an initial solidified layer of a predetermined thickness is formed on the surface of the collapsible core. Since it is pressurized, when that large pressurizing force is applied to the molten metal, the surface of the collapsible core is protected by the initially solidified layer of the predetermined thickness. This results in
The molten metal pressure acting on the collapsible core is reduced, and deformation or breakage of the core due to the molten metal pressure is prevented.

(Example) Examples of the present invention will be described below.

First, the rotor material of the rotary piston engine manufactured according to this embodiment and the pressure casting device used in this embodiment will be briefly explained.

As shown in FIG. 1, the rotor material A is a substantially triangular aluminum alloy casting having a cavity inside.
A hollow portion A1, which serves as a bearing portion for supporting the engine output shaft, is formed to penetrate through the center portion. On the other hand, the above pressure V
As shown in FIG. 2, the I-making apparatus includes a mold set consisting of an upper mold 1 and a lower mold 2, and a pair of upper and lower collapsible cores 3.4 arranged in a cavity a of this mold set. , the above lower mold 2
The injection sleeve 5 has an injection sleeve 5 connected to the injection sleeve 5, and a plunger tip 6 slidably fitted within the sleeve 5. Then, the molten metal 1b injected into the injection sleeve 5 is forced into the cavity a by the plunger tip 6, and the molten metal can be solidified under pressure.

The collapsible core 3.4 is molded using so-called shell sand (coated sand), and has two coating layers formed on its surface to prevent molten metal from entering. The first coating layer is a slurry layer for smoothing the surface of the core, and is coated with a slurry liquid containing metal oxides etc. on the surface of the core and dried. It is formed to have a layer thickness of 100 to 350 μm. The second coating layer is a graphite layer, which is formed by applying a solution containing graphite particles with an average particle size of 0.5 to 10 μm onto the slurry layer and drying it.
It is formed to have a layer thickness of 0 to 50 μm.

Next, the pressure casting method according to this embodiment will be described.

First, the collapsible cores 3 and 4 are set in a predetermined state in the cavity a formed at the joint of the upper mold 1 and the lower mold 2, and a predetermined amount of the melt 1b is injected into the injection sleeve 5. .

In this state, the plunger tip 6 in the injection sleeve 5 is moved in the direction of arrow C in FIG. 2, and the cavity a is filled with the molten metal in the sleeve 5 as shown in the figure.

In this filling process, the molten metal in the injection sleeve 5 is simply filled into the mold cavity a by the upward movement of the plunger tip 6, so the molten metal pressure at that time is as shown in the graph of FIG. , at the start of filling t1
No pressure is applied (OK9/aA) from to t2 when filling is completed.
) is maintained.

Next, after filling the cavity a with molten metal, the layer zb is pressurized with the plunger tip 6. In this case, in the present invention, the pressure applied to the layer 1b is first applied for a predetermined time t3. By keeping the temperature at 100Ary/cm2 or less, an initial solidified layer 1fid of a predetermined thickness is formed on the surface of the core 3.4. Then, at time t4, when the initial solidification 1fid of a predetermined thickness is formed on the surface of the cough core, the pressure of the plunger tip 6 against the molten metal is increased relatively rapidly to reduce the pressure of the layer WAb to 1fid.
By increasing the pressure to a predetermined pressure p of 00 kg/d or more and further maintaining this pressurized state until a predetermined time (at the end of the chill time) ts, the molten metal in the cavity a is completely solidified, as shown in Fig. 1. We manufacture rotor materials such as ' According to the above configuration, after the filling of the molten metal into the cavity a is completed, an initial solidified layer d of a predetermined thickness is formed on the surface of the collapsible core 3.4.
During the predetermined time t3 until the molten metal is formed, only a relatively small pressure (10 lv/cm2 or less) is applied to the melt 1b, so the core 3.4 is deformed by the molten metal pressure during that time. There is no such thing as the above predetermined time t3.
The molten metal is removed by the plunger tip 6.
When the core 3.4 is pressurized at a pressure exceeding 9/cd, the initial solidification W1d of the predetermined thickness is formed on the core surface, so the molten metal pressure no longer acts directly on the core 3.4. In other words, since the molten metal pressure applied to the core 3.4 is reduced by the presence of the initial solidification vJd formed on the core surface, the pressing force by the plunger tip 6 can be reduced by 10
Even if the pressure is increased to a relatively large predetermined pressure p of 0 Kv/d or more, the core 3.4 can sufficiently withstand the large pressing force. This prevents the collapsible core 3.4 from being deformed or damaged by the pressure of the molten metal during pressure casting.

In the above embodiment, as shown in the graph of FIG. 3, after the filling of the melt 1b into the cavity a is completed, the predetermined time t
However, as shown in the graph of FIG. 4, as another example, as shown in the graph of FIG. Time point I a when a solidified layer is formed on the surface of the core
The molten metal in the cavity may be maintained in an unpressurized state for a predetermined time t3' up to l. In this case, in addition to the effect of preventing core deformation due to the formation of the above-mentioned initial solidified layer, it is possible to obtain the effect of avoiding molten metal intrusion into the core (because no pressure is applied). However, when casting a product with a thin wall part, the thin wall part is completely solidified within the above predetermined time (time until an initial solidified layer of a predetermined thickness is formed on the core surface), resulting in a dense structure. Since there is a possibility that the product will not be obtained, in such a case, the molten metal bath should be
The first embodiment, in which the pressure is maintained at a low pressure of g/crJ or less, is more desirable.

Here, the predetermined time (ts or t3') for forming the initial solidified layer and the molten metal pressure (100N9 / c
The relationship between pressure (pressure below tA) will be described.

The predetermined time (ts or t3') is generally about 10% of the chill time (the time from when the molten metal is filled into the cavity until it completely solidifies). This is because, while the required initial solidified layer is formed within 10% of the chill time, if it exceeds 10%, the initial solidified layer becomes too thick and tends to form so-called cavities.

Furthermore, the reason for maintaining the molten metal pressure at 100 kg/d or less for this predetermined time is because the collapsible core 3 as described above
．． 4, the pressure acting directly on it is 100 Kg/
This is because if it is less than ctA, it will not be deformed or damaged.

By the way, when the molten metal is finally pressurized and pressure cast at a pressure of, for example, 300 K9/cd (this corresponds to the case of the rotor material A mentioned above), the pressure applied to the collapsible core is 100 Kg/d. In order to achieve the following state, it is necessary to form an initial solidified layer with a layer thickness of 4 mm or more on the surface of the core in advance, but it takes a predetermined time (t3
or t3') can be specifically determined, for example, as follows.

That is, as shown in FIG. 5, a sealed space e corresponding to a cavity formed by a mold 10, a sleeve 11, and a plunger tip 12 was filled with molten metal f, and this was held in an unpressurized state for a certain period of time. Afterwards, the mold is opened and the layer thickness of the solidified WJg formed on the inner surface of the mold is measured. The conditions in this case are as follows.

Mold temperature: 200°C, molten metal temperature = 750°C, molten aluminum alloy A04C, and if this operation is performed sequentially while changing the value of the above fixed time, the relationship between the layer thickness of the solidified Wig and its formation time will be obtained. A graph like the one shown in Figure 6 is obtained.

Therefore, using this graph, it is possible to maintain the predetermined time required to form an initial solidified layer with a layer thickness of 4 mm or more, or in other words, to maintain the molten metal pressure at 100:9/- or less (including a non-pressurized state). It is possible to specifically determine the predetermined time period.

In this case, from the graph of FIG.
Although a value of more than seconds can be obtained, the graph in Figure 6 was obtained under no pressure conditions, so the above
When it is decided to apply pressure at a pressure of 100 h/c4 or less instead of applying no pressure as in the example, the required thickness of the coagulated layer g will further increase. Next, the predetermined time required to form an initial solidified layer, in other words, the molten metal pressure is set to 100K.
g/d, and the final pressing force was 150 h/d, 2
0 (1 g/CIA, 300 tc9/ctA) The respective molten metal pressurization patterns are shown in Figure 7. The required initial solidification layer thickness and the time required for each of these pressurization patterns are shown in Table 1. It can be seen that as the final molten metal pressure increases, the thickness of the initial solidified layer must also increase.
1 Table In short, the thickness of the initial solidified layer formed on the core surface is:
It is determined by the mold temperature, melt-lifting wetness, pressurizing force, mold shape, etc. at that time, so if these factors differ, the thickness of the initial solidified layer will also change, but in general, as mentioned above, the thickness of the initial solidified layer is
It is considered that the required initial solidified layer can be obtained if the time is about 0%.

(Effects of the Invention) As described above, according to the present invention, in order to prevent deformation of the collapsible core, after forming an initial solidified layer of a predetermined thickness on the surface of the core, the molten metal pressure is increased to a predetermined pressure. Therefore, core deformation due to molten metal pressure is effectively prevented or reduced, and as a result, pressure cast products of excellent quality can be obtained.

[Brief explanation of the drawing]

Figures 1 to 4 show examples of the present invention. Figure 1 is a front view showing a rotor material manufactured according to the example, and Figure 2 is an initial solidification of a predetermined thickness on the surface of a collapsible core. FIG. 3 is a graph showing the relationship between molten metal pressure and process time in the first embodiment, and FIG. 4 is a graph showing the relationship between molten metal pressure and process time in the second embodiment. It is a graph showing a relationship. In addition, Fig. 5 is a process diagram showing the outline of an experiment conducted as an example to obtain the relationship between the layer thickness of the initial solidified layer and its formation time, Fig. 6 is a graph showing the experimental results, and Fig. 7 8 is a graph showing the relationship between molten metal pressure and process time in the third embodiment of the present invention, and FIG. 8 is a graph showing the relationship between molten metal pressure and process time in the conventional method. 1.2... Mold set (1... upper mold, 2... lower mold), 3.4... collapsible core, 6... injection means (plunger chip), a...・Cavity, b...molten metal,
d...Initial solidification layer. Figure 2 Figure 1 Figure 3 Figure 8 Light

Claims (1)

[Claims] (1) Using a mold set for pressure casting, a collapsible core placed in the cavity of this mold set, and an injection means for filling and pressurizing the cavity with molten metal, first, the mold is With the collapsible core placed in the cavity of the set, the cavity is filled with molten metal using an injection means, and then, in this state, a pressurizing force is applied to the molten metal to form an initial solidification of a predetermined thickness on the surface of the core. 1 for a predetermined time until a layer is formed.
00Kg/cm^2 or less, then 100Kg
A pressure casting method characterized by solidifying the molten metal by increasing the pressing force to a predetermined pressure exceeding /cm^2.