JPH0994632A - Aluminum alloy casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the shrinkage hole and the outside shrinkage by specifying the proportion of a hole part vol. as cast in a boss part to the total vol. SOLUTION: An aluminum alloy is cast in the columnar boss shape by using a metallic mold 3 and a sand mold 5. The thickness (t) of a thin thickness part is made to e.g. 3mm. In this case, (a) and (b) represent the diameters, and in the case of using V1 for the whole boss vol. containing the hole part vol. as cast and V2 for the hole part vol. as cast, the (V2 /V1 ) is defined as a vol. ratio of the hole vol. as cast. Then, this vol. ratio of the hole part vol. as cast is made to 10-20%. By this method, this aluminum alloy casting can be produced into the high quality as automoble engine parts of a manifold and chain case, etc., needed to the air tightness and the strength.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy casting which is required to have strength and airtightness such as automobile engine parts such as a manifold and a chain case.

[0002]

2. Description of the Related Art When a thick boss is present in a thin portion of a casting, solidification of the boss is delayed as compared with surrounding thin portions, so that the molten metal is not sufficiently replenished and a shrinkage is likely to occur. As shown in FIG. 1, when the mold is composed of only the molds 3 and 3, solidification starts from the surface portion, so that the shrinkage cavity 4 is formed inside the boss portion 1. Since the boss portion 1 is usually provided with a screw hole for assembly by cutting or the like, the presence of the shrinkage cavity 4 deteriorates the airtightness and causes a reduction in strength. Further, as shown in FIG.
If is a sand mold or resin mold that has a smaller cooling capacity than the mold 3,
Since the solidification on the side of the mold 4 with a small cooling capacity is delayed, the external drawing 6
Occurs. Even in such a case, the airtightness is deteriorated due to insufficient wall thickness, and the strength is reduced. Therefore, in the case of engine parts for automobiles, which require airtightness and strength, the boss portion 1 during solidification is locally pressurized to prevent shrinkage, and the boss portion is cast out. Measures are taken to reduce shrinkage by providing a pin to reduce the wall thickness of the boss.

[0003]

The above-mentioned partial pressurization may be successful in the casting method in which the solidification is slow, but in the casting method in which the solidification is fast, it is very difficult to control the timing of pressurization and the applied pressure. If the pressurizing timing is too early, the pressurizing step ends before the solidification and contraction, so that there is no pressurizing effect and the shrinkage cavity 4 is formed. If the pressure is too large,
There is also a problem that the solidified portion is deformed by the applied pressure. Further, if the pressurizing timing is too late, the coagulation contraction ends before the pressurization, so that there is no pressurizing effect, and if the pressurizing force is too small, there is no pressurizing effect.

The installation of the above-mentioned casting pin is effective when the boss portion 1 is large to some extent and a thick pin can be used, but it may not be effective when the boss portion 1 is small. The ratio of the size of the as-cast pin to the is not determined in particular, and the size of the as-cast pin is currently dependent on experience and is not fully utilized.

The present invention solves the above-mentioned conventional problems, and relates to a method of manufacturing a component used in a portion having a pressure difference between the inside and the outside, for example, an automobile engine component such as a manifold or a chain case. The object is to produce an aluminum alloy casting having excellent airtightness and strength without such casting defects.

[0006]

In order to solve the above-mentioned problems, the inventors of the present invention have made earnest studies, and as a result, the result is that the volume of the cast-out portion is close to the total volume of the boss portion. The inventors have found that it is possible to manufacture a casting without generating cavities and without lowering the strength, and arrived at the present invention. That is, the aluminum alloy casting of the present invention is characterized in that the volume of the cast-out portion of the boss portion of the aluminum alloy casting is 10 to 20% of the total volume of the boss portion.

[0007]

When the boss is cast out within the scope of the present invention, the following effects can be obtained. First, the shrinkage amount is reduced due to the decrease in the volume of the boss, and the shrinkage cavities are less likely to occur. Secondly, the difference in the solidification time from the thin wall around the boss becomes smaller due to the decrease in the boss volume and the increase in the boss surface area, and the strength of the boss, which is generally inferior to the surroundings of the boss because the solidification time is long Is improved. If the casting volume is less than 10% with respect to the volume of the boss, these effects are not only small, but also the casting pin is heated and may have an adverse effect. On the other hand, if the volume of the cast-out portion exceeds 20%, the boss becomes thin and the strength decreases.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to Examples. (Embodiment 1) Using a mold 3 and a sand mold 5 as shown in FIG. 4 and various cylindrical boss shapes shown in Table 1, (JIS) AC
An aluminum alloy equivalent to 4B was cast, and the relationship between the casting volume ratio and the shrinkage amount was investigated. The thickness t of the thin portion was 3 mm. It should be noted that a and b represent diameters, the total volume of the entire boss including the cast portion is the boss total volume V1, and the cast portion volume is V2.
The casting volume ratio is defined as (V2 / V1). Further, in this case, since the outer shrinkage occurs, the shrinkage amount is evaluated by the shrinkage depth. Table 1 shows the results. In Comparative Examples 11 to 13 in which casting is not performed, an outer shrinkage having a depth of 2 to 4 mm occurs. In Examples 1 to 5 having a casting volume ratio of 10% or more, the shrinkage is very small, less than 1 mm. On the other hand, in Comparative Examples 14 to 19 where the casting volume ratio (V2 / V1) is less than 10%, the depth is 1.1 to 1.4 mm.
There is a contraction.

[0009]

[Table 1]

(Example 2) By the gravity casting method, (JI
S) Molten aluminum alloy equivalent to AC4B is poured into a manifold type having a mold 3 on the outside and a sand core 5 on the inside, and two types of bosses (A) and (B) shown in FIGS. A manifold for a 2000 cc engine with a wall thickness of 3 mm was cast. Table 2 shows the result of the investigation of the shrinkage depth. Boss A that had 4mm shrinkage without casting
By setting the volume ratio of the casting to 14%, the shrinkage was 0.2 mm. Also, the boss B has a casting volume ratio of 1
By setting the content to 2%, the outer shrinkage was 0.6 mm, and the airtightness and smoothness were improved.

[0011]

[Table 2]

(Embodiment 3) (JIS standard) Molten aluminum equivalent to ADC12 is poured into a chain case mold whose outer and inner sides are all molds, and is shown in FIGS. 7, 8 and 9e by a die casting method. (C), (D) and (E)
2000cc of displacement with 3mm boss and 3mm thickness
A chain case for the engine was cast. Table 3 shows the results of an investigation of the size of shrinkage cavities inside the boss portion after casting.

[0013]

[Table 3]

By setting the casting volume ratio of the boss C, which had a shrinkage cavity of 4 mm in size without casting, to 11%, the shrinkage cavity was 0.4 mm. Further, the boss D has a cast-out volume ratio of 14%, and the boss E has a cast-out volume ratio of 13%.
The airtightness and strength were improved to 2 mm and 0.6 mm.

[0015]

As described above in detail, in the aluminum alloy casting according to the present invention, the volumetric rate of the boss portion is 10 to 20% of the volume of the boss portion, so that the shrinkage amount is reduced and the solidification rate is reduced. Shrinkage densities and shrinkage are reduced due to faster movement. And, by the aluminum alloy casting of the present invention,
We can manufacture high quality engine parts for automobiles such as manifolds and chain cases that require airtightness and strength.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a boss portion formed only by a mold and having a shrinkage cavity inside.

FIG. 2 is a cross-sectional view of a boss portion which is formed by a mold and a sand mold or a resin mold and in which external shrinkage occurs.

FIG. 3 is a cross-sectional view of a boss portion provided with a cast pin in the central portion.

FIG. 4 is a cross-sectional view of a boss portion of the mold used in Example 1.

5 is one of two types of manifolds used in Example 2. FIG.
It is sectional drawing of (A) boss part of a kind.

FIG. 6 is one of two types of manifolds used in Example 2.
It is sectional drawing of a kind (B) boss part.

FIG. 7 is a cross-sectional view of a (C) boss portion of one of three types of chain cases used in the third embodiment.

FIG. 8 is a cross-sectional view of a (D) boss portion of one of three types of chain cases used in the third embodiment.

FIG. 9 is a cross-sectional view of (E) boss portion of one of the three types of chain cases used in Example 3;

[Explanation of symbols]

1: Boss part, 2: Thin part, 3: Mold, 4:
Shrinkage cavity, 5: Sand type or resin type, 6: Outer shrinkage, 7: Cast pin.

Claims (1)

[Claims] 1. An aluminum alloy casting, characterized in that the volume of the cast-out portion of the boss portion of the aluminum alloy casting is 10 to 20% of the total volume of the boss portion.