JPH04327356A - Low pressure casting method for mg alloy-made wheel in two wheeler - Google Patents

Abstract

PURPOSE:To improve running of molten metal and the yield of material, to save cutting and finishing, etc., in the following process and to reduce the cost at the time of manufacturing an Mg alloy-made wheel in two wheeler with low pressure casting method. CONSTITUTION:Excess thickness part is arranged at the whole periphery or spoke base parts at parts of cavity in a rim part 9 in a die having the cavity C for the wheel in the two wheeler and on the other part, sprues 10 having the same number as pieces of the spokes 8 are arranged at the joining parts between the rim part 9 and the spokes 8 to pour the molten Mg allay from these sprues 10.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-pressure casting method for two-wheel wheels made of magnesium or magnesium alloys (hereinafter referred to as Mg alloys).

0002

BACKGROUND OF THE INVENTION Mg alloys are the lightest among practical alloys and have excellent specific rigidity, so they are widely used in aircraft parts and the like. On the other hand, in recent years, it has been applied to automobile parts for the purpose of weight reduction, and it is estimated that the number of automobile parts made of Mg alloy will increase in the future.

[0003] Generally, in casting, molten metal shrinks during solidification, so that shrinkage cavities occur if the molten metal is not replenished. In order to prevent this shrinkage cavity, it is necessary to replenish the amount of molten metal commensurate with the shrinkage. Therefore, when creating a casting plan, it is necessary to partially attach a riser to the surface of the cast product. However, although this riser is cast together with the cast product, it is not part of the product, so it must be removed from the cast product. Also, the part where the riser was attached by this removal becomes a cut surface, so it is necessary to finish it. Therefore, from a cost perspective, it is preferable not to have a boiler.

By the way, when Mg alloy casting products are obtained by casting, the effect of a feeder is poor because Mg alloy has a wide solidification range and a low specific gravity. Therefore, compared to cast iron or foundry aluminum (Al) alloy, if the same size of riser is attached to a casting product with the same wall thickness, shrinkage cavities will occur, so a very large riser is required. It will be established. However, such a large boiler has traditionally been made of Mg.
This also causes an increase in the cost of alloy casting products, and M
This is one of the obstacles to applying g-alloys to automobile parts.

[0005] In general, die casting is a well-known method for casting Mg alloys. The die casting method is a method of casting by filling a mold with molten metal at high pressure and high speed. Since the molten metal is injected under high pressure, the mold cost of the die casting method is very expensive, but the mass production effect makes up for the mold cost and allows the casting method to significantly reduce the cost per piece. . For this reason, many conventionally produced automobile parts, such as four-wheel wheels, are manufactured using the die-casting method.

[0006]

[Problems to be Solved by the Invention] Under the circumstances in which Mg alloy castings are being applied to automobile parts as described above, the present inventors have investigated the application of Mg alloys to motorcycle wheels. As a result, two-wheeled wheels are produced in far fewer units than four-wheeled vehicles, and are also cheaper, so the mass production of two-wheeled wheels is lower than that of four-wheeled wheels, and when the die-casting method is applied, the mold cost can be covered. It was discovered that it was difficult to apply the die-casting method due to the cost and the mass production effect could not be obtained.

[0007] Therefore, the present inventors focused on a low-pressure casting method that requires relatively low mold costs. However, in this low-pressure casting method, the molten metal is filled quietly at low pressure, so the flow of the molten metal is poorer than that of the die-casting method, and the production volume per hour is smaller than that of the die-casting method. The reality is that it has hardly been applied to Mg alloys, which are difficult to handle.

[0008] In view of the above circumstances, the present invention targets two-wheel wheels, improves the flow of molten metal to increase material yield, and also aims to reduce costs by eliminating post-process cutting, finishing, etc. as much as possible. The object of the present invention is to provide a low-pressure casting method for two-wheel wheels made of Mg alloy.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the low-pressure casting method for a Mg alloy two-wheel wheel according to the present invention provides a method for casting a two-wheel wheel made of Mg alloy at a partial or full circumference of a rim cavity of a mold having a cavity for a two-wheel wheel. An extra wall portion is provided at the base of the spoke, and the same number of sprues as the number of spokes are provided at the joint between the rim portion and the spokes, through which molten Mg alloy is poured.

0010

[Operation] The structure and operation of the present invention will be explained below. The present inventors have determined that in order to apply the low-pressure casting method at low cost as a casting method for Mg alloy two-wheel wheels,
Keep the defective rate as low as possible. ■Maintain material yield as high as possible. ■Omit post-processes such as cutting and finishing as much as possible. We believe that a casting method that achieves the following three items is necessary,
In order to achieve these goals, we conducted extensive study and research.

[1] Lower the defective rate as much as possible. ] In conventional Mg alloy four-wheel wheel die-casting or Al alloy four-wheel wheel low-pressure casting, a sprue is provided at one location in the hub portion, and molten metal is filled from there. In this case, the molten metal flows from the hub portion, passes through the spoke portions, and is filled up to the rim portion. However, in the case of Mg alloy two-wheel wheels, the spoke portions have a thin wall thickness, and there is a high risk that molten metal flowing from the hub portion will solidify in the spoke portions and cause the wheels to spin incorrectly. Furthermore, since the material itself is an Mg alloy that has poor melt flow, this tendency is strong. For this reason, manufacturing becomes difficult with the usual method of providing a sprue at one location in the hub portion.

The present invention focuses on this point, and in order to sufficiently fill the molten metal, a sprue is provided in the rim part, and in order to expect the effect of pushing the water from the sprue, the number of sprues is the same as the number of spokes. A casting method was adopted in which the molten metal directly filled the inside of the mold with multiple stalks, by providing them at the joints between the rim and the spokes. In conventional low-pressure casting methods, there are few casting methods with multiple sprues like this, and in normal cases, the molten metal is filled into a reservoir called a ball feeder using a single stalk, and the molten metal is passed through the reservoir. The method used was to fill the mold with molten metal. However, when this sump is used, the temperature of the molten metal in the sump decreases, which makes it more likely to cause non-spinning, and the molten metal is disturbed in the sump, generating oxides, which deteriorates the quality of the casting. Therefore, in the present invention, for these reasons, it was decided to directly fill the mold with molten metal using multiple stalks without using a molten metal reservoir, thereby improving the circulation of the molten metal and improving the quality of the casting. was completed.

[1] Make the material yield as high as possible. ]
Material yield is expressed as the ratio of casting weight to product weight. As mentioned above, casting requires a feeder, etc., so it is impossible to achieve a 100% material yield. However, increasing material yields has positive effects on all aspects of the manufacturing process, from lower melting costs to lower finishing costs.

[0014] In the present invention, in order to improve the material yield, an excess wall portion is provided on a part of the entire periphery of the rim portion or at the base of the spokes, thereby eliminating the need for a riser. In conventional methods for casting Mg alloys, there have been cases in which a riser is provided in the rim portion in order to produce the rim portion soundly. but,
As a result of the coagulation analysis conducted by the present inventors, it has been found that a riser is not necessarily necessary in order to produce a sound rim part, and soundness can be ensured by providing extra thickness in the rim part. Furthermore, it has been found that the extra wall thickness of the rim needs to be about 8 to 16 mm if it is attached only between the spokes, and around 4 mm is sufficient if it is attached all around the spokes. Adding extra meat also improves the circulation of hot water.

[■ Eliminate post-processes such as cutting and finishing as much as possible. ] Since the rim is generally machined, the extra thickness added to the rim can be cut off at the same time as the rim is machined. In particular, the extra thickness added to a portion of the rim around the entire circumference can be continuously cut, making it possible to cut more efficiently than interrupted cutting when added only between the spokes. Furthermore, since a smaller amount of excess metal is required in the present invention than in the case where a conventional riser is provided, the casting yield is also improved.

[0016]

[Examples] Examples of the present invention will be described below. Figure 1 shows
1 is a schematic cross-sectional view of a low-pressure casting apparatus applied to a low-pressure casting method for a two-wheel Mg alloy wheel according to the present invention.

[0017] The cavity C of the two-wheel wheel is formed by the upper mold 1,
It is formed by a lower mold 2, a horizontal mold 3, and a core 4. The upper die 1 is provided on a movable platen 5 and can be moved up and down. The lower mold 2 is provided on a fixed platen 6. Further, the horizontal mold 3 is formed into six parts and pressed by a pressing means (not shown) into an annular shape, and is provided on the upper surface of the lower mold 2. The core 4 is made of upper and lower molds 1 to form the axle of the hub part 7.
, 2 is buried in the center of the hub portion.

A sprue 10 is provided in the rim portion 9 corresponding to the base of the spoke portion 8 of the cavity C, passing through the lower mold 2, and a stalk 11 is connected to the sprue 10. The stalk 11 is inserted through the lid 12 and immersed in the molten metal 15 of the crucible 14 installed in the pressurizing chamber 13 .

The pressurizing chamber 13 is provided with a pressurizing port 16 and an exhaust port 17 connected to a pressurizing valve and an exhaust valve (not shown) for low-pressure casting. In addition, there is a crucible 1 on the inner peripheral surface.
A heater 18 is provided between the two.

FIG. 2 shows a wheel with a diameter of 620 mm and a rim 9.
40 mm in thickness, 7 mm in spoke 8' thickness, and 6 spokes 8'. One is only at the base of the spoke 8
One mold has an extra thickness of 4 mm (example 1 of the present invention), and the other has an extra thickness of 4 mm all around the outer circumferential surface of the rim (example 2 of the invention). Casting was done.

[0021] Also, for comparison, a mold (conventional example) has a configuration in which one sprue is provided in the hub part, similar to conventional low-pressure casting, and a mold in which six sprues are provided in the base of the spokes in the rim part, as in the present invention. , and a mold with a configuration in which a riser is provided in the rim portion (Comparative Example 1), and a mold in which a riser is not provided in the rim portion (comparative example 1).
Comparative Example 2) were prepared and cast.

[0022] The results of evaluating the mold production, casting conditions, quality of the cast products, etc. are also shown in Table 1 below. In the table, ◎ means very good, ○ means good, △ means slightly bad, and × means very bad.

[0023]

[Table 1]

[0024] As is clear from Table 1, in the conventional example, since the mold has a structure in which a single sprue is provided in the hub portion, the casting weight can be reduced and the material yield is very high.
In actual casting, the molten metal solidifies at the spokes, causing the molten metal to spin around and not forming into a product.

In Comparative Example 1, the mold had six sprues at the bases of the spokes in the rim and a riser in the rim, which resulted in a large casting weight and a very poor material yield. Become. Also, since there is no extra wall on the rim, hot water tends to flow incorrectly. However, the internal quality was good as there was a hot water bath.

In Comparative Example 2, the mold was constructed without a sprue or riser in the rim part, so the casting weight was small and the material yield was very high.However, in actual casting, the molten metal flows at the spoke parts. It tends to solidify and cause hot water to flow, making it difficult to make into products. Furthermore, the rim part has no sprue or riser, and there is no extra wall, so it is easy to cut.

In contrast to the above-mentioned conventional examples and comparative examples, in Inventive Example 1, the mold was constructed such that only 8 mm of extra wall was provided at the base of the spoke, so the material yield was good, and during actual casting, the metal However, since the extra material was added between the spokes, the extra material could be cut at the same time as the rim cutting, but the extra material was cut intermittently. It took some time to cut.

In Example 2 of the present invention, the mold was constructed with an extra wall of 4 mm all around the outer circumferential surface of the rim, which improved the material yield, hot water circulation, and internal quality, as well as cutting the rim at the same time. The excess thickness could be cut, and unlike Example 1 of the present invention, the excess thickness was continuously cut, so the cutting time could be shortened.

As described above, in the example of the present invention, the bases of the spokes of the rim have the same number of sprues as the number of spokes, so the sprue area is large and the circulation of the molten metal is good. Moreover, since there is extra thickness that follows the shape of the product, the hot water circulation of the product is greatly improved, and the internal quality is also extremely excellent. In addition, since the amount of excess material can be applied thinly and appropriately, the material yield can be dramatically improved. In addition, the excess thickness can be removed by cutting according to the shape of the rim portion in a post-process, so post-processes such as cutting the rim portion can be performed very easily and in a short time.

[0030]

[Effects of the Invention] As explained above, the M according to the present invention
According to the low-pressure casting method for g-alloy two-wheel wheels, Mg-alloy two-wheel wheels can be made by low-pressure casting to improve the circulation of molten metal, without impairing internal quality, and with good productivity including post-processing. Can be manufactured at low cost.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a low-pressure casting apparatus according to the present invention.

FIG. 2 is an explanatory diagram of a two-wheeled wheel according to an embodiment of the present invention, in which (a) is an overall schematic diagram and (b) is a sectional view.

[Explanation of symbols]

1: Upper mold 2: Lower mold
3: Horizontal 4: Core 5: Movable platen 6: Fixed platen 7: Hub section 8: Spoke section 9: Rim section 10: Sprue 11: Stoke 12: Lid 13: Pressure chamber 14: Crucible
15: Molten metal 16: Pressurizing port 17: Exhaust port 8': Spoke 9': Rim C: Motorcycle wheel cavity W: Motorcycle wheel

Claims (1)

[Claims] Claim 1: In a mold having a cavity for a two-wheeled wheel, an excess wall portion is provided around a part of the rim cavity or at the base of the spokes, and the same number of sprues as the number of spokes are provided to join the rim part and the spokes. 1. A low-pressure casting method for a two-wheel wheel made of an Mg alloy, characterized in that the molten Mg alloy is poured from the sprue provided in the sprue.