JPS6127166A - Die casting method - Google Patents

Abstract

PURPOSE:To improve the casting yield of an Al alloy by remelting the upper part of the molten metal poured into a die at the point of the time when the upper part begins to solidify so that the remelted metal fills shrinkage cavity. CONSTITUTION:Arc discharge is generated by a torch 5 disposed above a casting mold 1 and the upper region where the molten metal begins to solidify is remelted 4 by the arc heat thereof at the point of the time when the lower part of the molten metal in the die 1 is completed solidification and the upper part begins to solidify. The molten metal generated by remelting the upper part region just prior to the formation of the large shrinkage cavity 3 in the upper part fills the space to form the large shrinkage cavity and a small amt. of the molten metal solidifies. The casting 2 formed with the small shrinkage cavity 3 is thus produced. The part formed with the cavity 3 is then discarded as a riser part and since the cavity 3 is small, the part to be discarded is decreased.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a mold casting method with high casting yield.

[Conventional technology]

BACKGROUND ART Mold casting, in which metal is cast using a metal mold, is generally known as a casting method for mass production of small items.

In the case of this mold casting, the molten metal is rapidly cooled by the mold, so the cooling rate of the molten metal is extremely high compared to the case of conventional sand mold casting.

Generally, when casting cast iron, if the molten metal is rapidly cooled,
The above-mentioned mold casting method has not been used much because it is chilled and becomes a hard and brittle casting.
When casting Il-based alloys, rapid cooling of the molten metal yields dense and fine crystal grains, which improves the mechanical properties of the casting, and the temperature of the molten metal is relatively low at 600 to 800°C, making it easier to mold. The above-mentioned die casting is widely used because it does not cause the problem of shortening the service life.

[Problem that the invention seeks to solve]

However, in the case of mold casting, the molten metal solidifies rapidly, so the effect of the riser is not fully demonstrated, and the area containing the cavities formed in the upper part of the mold becomes extremely large. Casting yield is extremely low.

Such a decrease in casting yield is particularly noticeable when casting alloys that experience a large amount of shrinkage upon solidification, such as AE alloys.

One possible solution to this problem is to attach an insulating or heat-generating sleeve to the top opening of the mold to move the area where cavities occur upwards, but such a measure is a fundamental countermeasure. However, it is not possible to significantly reduce the amount of feeder and significantly improve the casting yield.

[Means for solving problems]

The present invention has been made to solve the above-mentioned problems, and its purpose is to minimize the area where cavities occur when the molten metal poured into the mold solidifies. The goal is to reduce the overall cost and significantly improve the casting yield.

The mold casting method according to the present invention generates an arc discharge directly above the molten metal when the lower part of the molten metal poured into the mold completes solidification and the upper part starts solidifying, and the molten metal is solidified by the arc heat. It is characterized in that the upper region where it started is remelted.

The method of the present invention will be explained in detail with reference to the accompanying drawings.

FIG. 1 shows AI! by the method of the present invention! FIG. 2 is a vertical cross-sectional view schematically showing the main process of casting products made of alloys, etc.; FIG. 2 is a vertical cross-sectional view schematically showing the state immediately after casting; FIG. 3 is a vertical cross-sectional view schematically showing the state immediately after casting. FIG. 2 is a vertical cross-sectional view schematically showing the state immediately after casting when a product made of an Aβ alloy or the like is cast by the method.

The molten metal poured into the mold (1) solidifies sequentially from the bottom to the top of the mold (1), and eventually a large cavity (31) is formed at the top, as shown in Figure 3. , made casting (2
) However, in the case of the method of the present invention, as shown in Figure 1, the lower part of the molten metal in the mold (1) has completed solidification and the upper part has started solidifying, in other words, the entire molten metal has solidified. Immediately before completion and the formation of a large cavity (31) at the top, a torch (5) is placed above the mold (1) to generate an arc discharge (6) directly above the molten metal, and the arc The upper region that has started to solidify due to heat is remelted (4). In addition,
The point at which the upper part of the molten metal in the mold (1) starts to solidify may be determined by the point at which a thin skin starts to protrude from the surface of the molten metal.

[Effect]

When using the method of the present invention, the upper region is remelted by arc heat just before a large drag cavity (31) is formed in the upper part, so that the molten metal produced by the remelting does not cause a large drag cavity. (31), and the molten metal, that is, the amount of molten metal smaller than the initial amount, solidifies, resulting in small evacuation holes (as shown in Figure 2).
3) becomes the casting (2).

The part where this hikiwa nest (3) is formed will be cut away as the feeder part, but since the hikiwa nest (3) is smaller than in the case of the conventional method, the portion to be discarded is reduced. Casting yield is significantly improved.

Note that if the area that is remelted by arc heat is made larger than necessary, the amount of molten metal produced by the remelting will increase, and large shrinkage cavities will be formed again in the process of solidifying the molten metal. It should be avoided to make the area to be remelted larger than necessary. That is, the large shrinkage that would occur if the material were solidified without being remelted should be remelted to a depth that includes the portion directly below the cavity (31), and should not be remelted to a depth beyond that. The region to be remelted can be easily adjusted by controlling the heat input due to arc discharge.

In the present invention, it is usually sufficient to remelt the upper region once, but if necessary, it may be repeated two or more times as appropriate.

〔Example〕

Next, using the method of the present invention, AI2 alloy (C: 0.41%
, s i : 1.05%, Mn: 1.03%, Cr
: 25.36%, Ni: 21.22%, Aβ:
The results of casting a product (cylindrical body with a diameter of 50 fi) consisting of the remainder will be explained.

Table 1 summarizes the results of casting with various changes in heat input by arc discharge.

Note that H is the total length of the casting, and h is the length of a healthy part of the casting in which no cavities are formed (see FIGS. 2 and 3). Therefore, h/H corresponds to the casting yield.

Experiment No. 1 in Table 1 is a case in which arc discharge is not performed, that is, a conventional method is used, and h/H is extremely poor at 43%.

On the other hand, in Experiments N1112 to Experiment No. 5, arc discharge was performed, that is, the method of the present invention was used, but h/H
has significantly improved by 45-65%.

In particular, when the heat input due to arc discharge is 60,000 joules (experimental point 4), h/H is 65%,
The casting yield is improved by 22% compared to the conventional case.

As described above, it can be seen that in the case of the method of the present invention, the area where shrinkage cavities occur is reduced as much as possible, and the casting yield is significantly improved.

In addition, experimental point 5 shows an example in which the area to be remelted is larger than necessary, and h/H is 14% compared to experimental floor 4.
is also declining. This proves that it is necessary to avoid making the area to be remelted larger than necessary.

〔Effect of the invention〕

As detailed above, when performing mold casting using the method of the present invention, an arc discharge is generated directly above the molten metal when the upper part of the molten metal in the mold starts to solidify, and the arc heat causes The upper region that has started to solidify is remelted, so
The molten metal produced by the remelting fills the space that should form large cavities, and as a result of that small amount of molten metal solidifying, the cavities formed in the resulting casting are small, and the casting yield is greatly improved. do. Therefore, the present invention
It is suitable for mass production casting of small products made of alloys with a large amount of solidification shrinkage, such as '-based alloys, etc., and suitable for casting alloy castings such as Aβ-Mn magnets at a high yield.

[Brief explanation of drawings]

Fig. 1 is a vertical cross-sectional view schematically showing the main process of casting by the method of the present invention, Fig. 2 is a longitudinal cross-sectional view schematically showing the state immediately after casting, and Fig. 3 is a longitudinal cross-sectional view schematically showing the state immediately after casting by the conventional method. FIG. 3 is a vertical cross-sectional view schematically showing the state. 1: Mold, 2: Casting, 3.3t: Drill hole, 6: Arc discharge.

Claims (1)

[Claims] (1) When the lower part of the molten metal poured into the mold completes solidification and the upper part begins to solidify, an arc discharge is generated directly above the molten metal, and the arc heat remelts the upper region that has started solidifying. A mold casting method characterized by: