JPH09253826A - Die for low pressure casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the directional solidification in the production of a wheel for vehicle by fastening a lower die with die constituting parts cooled with coolant and an outer peripheral part. SOLUTION: Molten metal is filled up into a cavity for the vehicle wheel in the dies constituted with an upper die 8, lower die 7 and side dies 9, 10 from near the center of the lower die 7. Then, the lower die 7 is fastened with the die constituting parts of a lower die base 11 arranging cooling water courses 13 and a lower platen 16, etc., and the outer peripheral part. By this constitution, the lower die 7 can indirectly and uniformly be cooled from the outer periphery and casting cycle can be shortened while promoting the directional solidification toward a sprue. Further, this die is inferior at the point of the cooling efficiency in comparison with the ordinary direct cooling, but since the directional solidification is not obstructed and further, the uniformity of the temp. distribution in the die is kept, a sound casting can be produced.

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 mold used for casting a light alloy vehicle wheel by a low pressure casting method.

[0002]

2. Description of the Related Art In a low-pressure casting method generally used for casting a light alloy, a molten metal is laminar-flow-filled at a low speed into a cavity (mainly a combination of an upper mold, a lower mold, and a horizontal mold) formed in a mold. Entrapment of gas and generation of oxides are suppressed as much as possible in other casting methods. Therefore, it is widely used when manufacturing a cast product having high soundness. However, in order to produce a sound product by the low-pressure casting method, it is necessary to maintain the mold surface temperature to a certain high level in order to secure the flow of molten metal at the time of filling the molten metal. Therefore, it takes time for the mold temperature to drop to the product take-out temperature after solidification of the product is completed after filling the molten metal. Therefore, in order to shorten the casting cycle, the mold is actively cooled with gas, water, etc. after the molten metal is filled.

[0003]

Most of the light alloy vehicle wheels, as shown in the sectional view of FIG. 6, have a thick disk portion 4 attached to the axle by bolts and nuts, and a mixture of thick and thin walls. And a thin rim portion 6 to which the tire is attached. Currently, from the viewpoint of improving the fuel efficiency of vehicles, weight reduction of wheels is required. In order to achieve this weight reduction, the shape of the disc and rim cannot be changed significantly due to the mounting relationship with the vehicle body and tires. It is being appreciated. The method of changing the shape of the design portion is mainly to increase the number of openings and thin portions in the design portion, and the design portion has a complex shape in which openings, thin portions, and thick portions are mixed.

Usually, when manufacturing a vehicle wheel by low pressure casting, the molten metal is injected from the disk portion 4 in the central portion, and then the design portion 5 and the rim portion 6 are sequentially filled with the molten metal. As for the solidification form after the molten metal is filled, directional solidification is performed in the order of the rim portion, the design portion, and the disc portion in order to fully exert the effect of pushing the molten metal at the gate. As described above, under the current situation where the shape of the design part in which the thick part and the thin part are mixed is complicated, it is very difficult to achieve the directional solidification from the rim part toward the gate.

When water cooling of a mold is introduced for the purpose of shortening the casting cycle, there is a high-temperature holding furnace for holding the molten metal below the lower mold, and it is difficult to cool naturally. A method of providing a cooling path or embedding a chill provided with a water cooling path in a lower mold has been proposed. However, as described above, there is a thin portion in the design part that is in contact with the lower mold, and when water cooling of the lower mold is performed,
In some cases, the solidification of the design part was completed significantly earlier than the thick disk part on the gate side. If there is a solidified portion that breaks the balance of the directional solidification toward the gate, the effect of pressurizing from the gate becomes insufficient and casting defects occur. Therefore, when water cooling is introduced into the lower mold by a conventional method, casting defects may be induced.

Further, since the surface temperature of the mold is entirely lowered by introducing water cooling of the mold, the temperature of the molten metal in the cavity is lowered, and the molten metal flow tends to be deteriorated. Therefore, in order to improve the temperature drop of the molten metal, it is necessary to maintain the mold surface temperature around the tip of the rim portion farthest from the sprue in the thin-walled rim portion by raising it more than before when water cooling is applied. is there. If the temperature of this portion falls below the optimum temperature, a casting defect may occur at the tip of the thin rim portion. In order to raise the mold surface temperature, a method such as reducing the mold wall thickness or keeping it warm with a heat insulating material can be considered. However, in most cases, the upper mold is originally fixed to the movable upper mold platen (upper mold base) by bolting, and the heat of the upper mold that is in contact with the periphery of the rim tip where defects easily occur is However, there is a problem in that it is difficult to raise the mold surface temperature in this portion because it flows by heat conduction to the upper platen (upper base) side that is bolted to fix. Therefore, when water cooling is applied,
It was difficult to prevent the occurrence of defects near the tip of the thin rim portion farthest from the sprue.

The vehicle wheel has a design property as one of its functions. Therefore, the design surface that faces outward when mounted on a vehicle has a number of complicated shapes such as spoke type, fin type, and disk type, in which thick and thin are mixed. Therefore, the surface shape of the lower die, which is in contact with the design surface, is complicated according to the shape of the design surface of each wheel. In order to obtain the optimum cooling, it is necessary to change the cooling plan of the lower mold variously depending on the design of each wheel, but the lower mold with the cooling path or the lower mold with the cooling path embedded Designing a mold for each item was expensive. The present invention has been made to solve the above problems, in a mold for producing a vehicle wheel made of a light alloy by low pressure casting, without shortening the directional solidification, the cycle time can be shortened. An object of the present invention is to provide a low-pressure casting mold that can be formed and has no casting defects in the rim portion.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies on the heat flow of a low-pressure casting mold in order to solve the above problems. As a result, by indirectly cooling the lower die instead of directly cooling it with a water cooling path, the temperature gradient of the lower die due to cooling becomes gentle, and directional solidification toward the sprue may be hindered. The present invention was discovered, and the present invention was conceived. That is, the present invention is a low-pressure casting mold used in a low-pressure casting method for filling a molten metal from the vicinity of the center of the lower mold into a vehicle wheel cavity composed of an upper mold, a lower mold, and a horizontal mold, wherein the lower mold is cooled. A low pressure casting mold characterized in that it is fastened to at least one mold component cooled by a medium at an outer peripheral portion.
The mold component parts are a lower mold base and a lower platen for fixing the lower mold. Further, it is preferable to fasten the lower mold and the mold component with bolts.

The low-pressure casting mold of the present invention is a low-pressure casting mold used for a low-pressure casting method in which a cavity for a vehicle wheel composed of an upper mold, a lower mold and a horizontal mold is filled with molten metal from near the center of the lower mold. In the mold, since the lower mold is fastened to the mold component such as the lower mold base or the lower mold platen that fixes the lower mold cooled by the cooling medium at the outer peripheral portion, the lower mold is indirectly and uniformly distributed from the outer periphery. It can be cooled, and the casting cycle can be shortened while promoting the directional solidification toward the gate. Usually, when cooling the die, a method of directly cooling the high temperature portion, that is, in the case of such a lower die, the vicinity of the sprue portion in the central portion is adopted. However, such cooling not only hinders directional solidification, but also makes the temperature distribution in the lower mold non-uniform, which may cause casting defects. On the other hand, since the low-pressure casting mold of the present invention is indirectly cooled, it is inferior in terms of cooling efficiency as compared with direct cooling, but it does not inhibit directional solidification, and the mold temperature is further decreased. Since the uniformity of the distribution is also maintained,
It is possible to produce sound castings. Further, since the contact area of the contact portion between the outer periphery of the lower die and the lower die base or the lower platen can be changed arbitrarily, the cooling amount can be controlled in proportion to the contact area. Also, by fastening the lower mold and the lower mold base or lower mold platen with bolts, the lower mold and the lower mold base or lower mold platen can be easily removed, and they can be in close contact with each other to improve thermal conductivity. .

Further, among the lower die parts which come into contact with the design surface facing outward when mounted on a vehicle, a lower die base or a lower die platen provided with a water cooling path is provided in each lower die having various designs. However, it is common for wheels of different designs to be replaced by replacing only the lower mold. Therefore, there is no need to provide a water cooling path in the lower mold for each item or to embed a chill having a water cooling path, so that the cost of the mold can be reduced. Furthermore, by inserting a heat insulating material with high compressive strength between the upper mold and the mold components and tightening the bolts to increase the heat insulation effect, and suppressing the amount of heat flowing from the upper mold to the upper mold platen, the furthest from the gate By preventing the temperature of the upper mold surface in contact with the tip of the thin rim portion from decreasing, it is possible to prevent defects from occurring at the tip of the rim portion.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred mold structure of a vehicle wheel according to the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is a first embodiment. The first embodiment shows a case where the lower mold is bolted and fixed to a lower mold base as a mold component. The cavity of FIG. 1 has a lower mold 7 having various surface shapes depending on the wheel design, an upper mold 8 above it, and a horizontal mold which is arranged to fit the lower mold 7 and the upper mold 8 and slides left and right. It is basically composed of 9, 10. The molten metal stored in the holding furnace 1 is pressurized with a pressure gas to raise the stalk 2 and the sprue insert 3 and fill the cavity. The cavity is composed of a thick-walled disc portion 4, a thin-walled and thick-walled design portion 5, and a thin-walled rim portion 6 in order from the gate side. The design portion of the wheel facing outward when mounted on the vehicle has various shapes, and these are formed by the lower mold 7. This lower mold 7
The lower die base 11 fixed by a clamp (not shown) or the like on the lower die platen 16 of the casting machine is fastened by bolts 12. The lower mold base 11 is provided with a cooling water passage 13 through which cooling water flows, and the effect of this water cooling is conducted to the lower mold 7 only through the contact surface 14 between the lower mold 7 and the lower mold base 11 by bolting. It There is a gap 15 between the side surface of the lower die 7 and the lower die base 11, and there is no heat conduction from here. The cooling amount can be controlled by arbitrarily changing the area of the contact surface 14 between the lower mold 7 and the lower mold base 11. FIG. 5 shows an example of measuring the temperature distribution on the lower die surface of this example and the conventional example. It can be seen from FIG. 5 that the present example has a temperature gradient toward the sprue on the surface of the mold and promotes directional solidification, as compared with the conventional example.

Next, the contact surface 14 between the lower mold 7 and the lower mold base 11
FIGS. 3 and 4 show an embodiment in which the area is changed arbitrarily. These are obtained by changing the shape of the contact surface with the lower mold base 11 of the lower mold 7 to change the area of the contact surface 14 (hatched portion in the figure), and it is possible to obtain a cooling effect in proportion to the contact area. I understand. Further, the upper mold 8 is fastened to a vertically movable upper mold platen (upper mold base) 17 with bolts 19 via a heat insulating material 18 having high compressive strength in a high temperature range. With this configuration, the temperature of the rim portion can be increased by 20 to 30 ° C. as compared with the case where no heat insulating material is interposed, and a casting defect does not occur.

(Embodiment 2) The second embodiment shows a case where the lower die is fixed by bolting to the lower die platen as a part of the casting machine. In FIG. 2, the lower die 7 is directly fixed to the lower die platen 16 of the casting machine by bolts 12.
The lower mold platen 16 is provided with a cooling water passage 13, and the effect of this water cooling is transmitted to the lower mold 7 only by the bolted contact surface 14. Others are exactly the same as in the first embodiment.

[0014]

According to the present invention, when a light alloy vehicle wheel is manufactured by low pressure casting, the cycle time can be shortened without impeding directional solidification, and casting defects are generated in the rim portion. It was possible to obtain a low-pressure casting mold that does not.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a vehicle wheel mold structure according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a vehicle wheel mold structure according to a second embodiment of the present invention.

FIG. 3 is a plan view of a lower die base of a vehicle wheel die according to the first embodiment of the present invention.

FIG. 4 is a plan view of a lower mold base of a vehicle wheel mold according to the first embodiment of the present invention.

FIG. 5 is a surface temperature distribution of a lower mold before and after carrying out the first embodiment of the present invention.

FIG. 6 shows a cross-sectional view of a vehicle wheel.

[Explanation of symbols]

1 holding furnace, 4 disk section, 5 design section,
6 rim, 7 lower die, 8 upper die, 9, 10 horizontal type, 11 lower die base, 13 cooling water path, 14 contact surface, 16 lower die platen, 17 upper die base, 1
8 insulation

Claims (5)

[Claims] 1. A low-pressure casting mold used in a low-pressure casting method in which a cavity for a vehicle wheel made of a light alloy composed of an upper die, a lower die, and a horizontal die is filled with molten metal from near the center of the lower die, A low-pressure casting mold, wherein a lower mold is fastened to at least one mold component cooled by a cooling medium at an outer peripheral portion. 2. The low-pressure casting mold according to claim 1, wherein the mold component is a lower mold base for fixing the lower mold. 3. The low pressure casting mold according to claim 1, wherein the mold component is a lower platen. 4. The lower die and the die component are fastened together by bolts.
The low pressure casting mold according to any one of 1. 5. The low-pressure casting mold according to claim 1, wherein the upper mold is fastened to the mold component through a heat insulating material.