JP7708465B1 - Aluminum wheel manufacturing method - Google Patents

Abstract

A casting method is provided that can increase productivity while ensuring the strength, toughness, and light weight of an aluminum wheel.
[Solution] A method for manufacturing an aluminum wheel including a die-casting process, in which the casting process includes a first vacuum stage in which molten aluminum alloy is poured into a mold 10, and then the inside of the mold 10 is suctioned by vacuum from an injection sleeve 21 with a sealed pouring port, and a second vacuum stage in which, after the first vacuum stage, the inside of the mold 10 is suctioned by vacuum from a cavity 14 in which the aluminum wheel is formed.
[Selection] Figure 13

Description

This invention relates to a method for manufacturing aluminum wheels.

In conventional aluminum wheel casting, a method of performing heat treatment after gravity casting has been adopted to ensure strength, toughness, and light weight (see, for example, Patent Document 1). Gravity casting has a relatively slow pouring speed, and air is less likely to be mixed into the molten metal. This ensures good internal quality and high toughness of the aluminum wheel. In addition, by performing heat treatment after gravity casting, the necessary strength can be maintained even if the cross section of the spokes and rim of the aluminum wheel is reduced, improving the light weight of the entire aluminum wheel.

JP 2006-103577 A

However, gravity casting has the disadvantage of low productivity because it takes a long time to cast. In order to increase productivity, it is possible to adopt die casting, which fills the molten metal at high pressure and high speed. However, die casting is prone to air being mixed into the molten metal, so the internal quality of the aluminum wheel is more likely to be poor than gravity casting. In addition, if heat treatment is performed after die casting, blisters (defects caused by air mixed into the molten metal) will occur, further reducing the toughness of the aluminum wheel, so it is difficult to improve the strength by heat treatment. Therefore, in order to ensure the strength and toughness of aluminum wheels using die casting, the cross-sectional area of the spokes and rim of the aluminum wheel needs to be made to a certain size, which increases the weight of the entire aluminum wheel.

As a result of the above, there has been a problem with aluminum wheel casting: it is difficult to increase productivity while ensuring the strength, toughness, and light weight of the aluminum wheels.

The technical objective of the present invention is to provide an improved method for manufacturing aluminum wheels based on the current situation described above.

The present invention relates to a method for manufacturing an aluminum wheel that includes a die-casting process, and the casting process includes a first vacuum stage in which, after pouring molten aluminum alloy into a mold, the inside of the mold is suctioned by vacuum from an injection sleeve with a sealed pouring port, and a second vacuum stage in which, after the first vacuum stage , the inside of the mold is suctioned by vacuum from a cavity in which the aluminum wheel is formed. In the second vacuum stage, vacuum is simultaneously suctioned from multiple vacuum device connection parts positioned at equal radial intervals from the center of the cavity .

In the method for manufacturing an aluminum wheel according to the present invention, the heat treatment after the casting step may be omitted .

The casting Al alloy used in the manufacturing method of the aluminum wheel according to the present invention preferably contains 8.0-10.0 mass% Si, 0.25-0.40 mass% Mg, 0.30-0.50 mass% Fe, 0.28-0.52 mass% Mn, 0.08-0.22 mass% Cu, 0.04-0.15 mass% Ti, and 0.0075-0.028 mass% Sr, with the balance being Al.

The sum of the contents of Fe and Mn is limited to 1.0 mass% or less. The Sr is not added in the melting step, but is added in the molten metal treatment step for removing Al oxides and _H2 gas from the molten Al alloy obtained in the melting step. The Mg may not be added in the melting step, but is added in the molten metal treatment step.

The present invention uses highly productive die casting to ensure sufficient strength and toughness of the aluminum wheel. In addition, the necessary strength can be maintained even if the cross section of the spokes and rim of the aluminum wheel is made small, improving the overall lightness of the aluminum wheel. Furthermore, since no heat treatment is required after die casting, productivity can be further improved. Therefore, the manufacturing method for aluminum wheels of the present invention makes it possible to increase productivity while ensuring the strength, toughness, and lightness of the aluminum wheel.

FIG. 2 is a flow diagram showing the manufacturing process of the present invention. FIG. 2 is a diagram showing the composition ranges of alloys of other companies and the present invention, and the component compositions of examples and comparative examples. FIG. 1 is a diagram showing the results of measuring the tensile strength, yield strength, and elongation of a casting obtained by a die casting method. 1 is a graph showing the relationship between the temperature of molten Al alloy during die casting and the tensile strength and yield strength of the casting. 1 is a graph showing the relationship between the temperature of molten Al alloy during die casting and the elongation rate of the casting. 1 is a graph showing the relationship between the die temperature during die casting and the tensile strength and yield strength of the casting. 1 is a graph showing the relationship between the die temperature during die casting and the elongation rate of a casting. 1 is a graph showing the relationship between the degree of vacuum in a die during die casting and the tensile strength and yield strength of a casting. 1 is a graph showing the relationship between the degree of vacuum in a die during die casting and the elongation rate of a casting. FIG. 1 is a diagram showing the component compositions of a heat-treatment-free casting and a T6-treated casting produced by a low-pressure casting method. FIG. 1 is a diagram showing the results of measuring the tensile strength, yield strength, and elongation of a heat-treatment-free casting obtained by a low-pressure casting method and a T6-treated casting. FIG. 2 is a flow diagram showing the casting process of the present invention. FIG. 1 is a schematic diagram showing a cross section of a casting apparatus 1 according to an embodiment, illustrating a casting process (step 1). FIG. 2 is a schematic diagram showing a cross section of the casting apparatus 1 according to the embodiment, illustrating the casting process (step 2). FIG. 2 is a schematic diagram showing a cross section of the casting apparatus 1 according to the embodiment, illustrating the casting process (step 3). FIG. 2 is a schematic diagram showing a cross section of the casting apparatus 1 according to the embodiment, illustrating the casting process (step 4). FIG. 2 is a schematic diagram showing a cross section of the casting apparatus 1 according to the embodiment, illustrating the casting process (step 5). FIG. 2 is a schematic diagram showing a cross section of the casting apparatus 1 according to the embodiment, illustrating the casting process (step 6). FIG. 2 is a schematic diagram showing a cross section of the casting apparatus 1 according to the embodiment, illustrating the casting process (step 7). 1 is a schematic plan view showing an intermediate mold 12 of a casting apparatus 1 according to an embodiment of the present invention. FIG. 21 is an enlarged view of a main part of FIG. 20 .

The following describes an embodiment of the present invention with reference to the drawings. As shown in FIG. 2, the composition of the casting Al alloy and Al alloy casting according to the present invention includes, by mass, 8.0% to 10.0% Si (silicon), 0.25% to 0.40% Mg (magnesium), 0.30% to 0.50% Fe (iron), 0.28% to 0.52% Mn (manganese), 0.08% to 0.22% Cu (copper), 0.04% to 0.15% Ti (titanium), and 0.0075% to 0.028% Sr (strontium), with the balance being Al (aluminum) and unavoidable impurities.

Si is an important alloy component (element) that contributes to improving castability, especially fluidity. As mentioned above, the Si content in the entire Al alloy for casting should be in the range of 8.0% by mass to 10.0% by mass. If the Si content is too low (less than 8.0% by mass), the fluidity will be insufficient and the fluidity will not be ensured, and casting cracks will be more likely to occur. Conversely, if the alloy contains excessive Si, exceeding 10.0% by mass, the elongation of the Al alloy casting will be reduced.

Mg exists mainly in the form of a solid solution in the Al matrix in the casting Al alloy or as Mg ₂ Si, and is an alloy component effective for improving tensile strength and yield strength. The content of Mg in the entire casting Al alloy is preferably 0.25% by mass or more and 0.40% by mass or less. If Mg is contained within the above range, the mechanical properties such as tensile strength and yield strength of the Al alloy casting can be improved without significantly affecting the castability or elongation of the Al alloy casting. If the Mg content is too low (less than 0.25% by mass), seizure to the mold is likely to occur, and if the Mg content is too high (more than 0.40% by mass), the elongation of the Al alloy casting tends to decrease.

Fe is an alloy component that acts to prevent seizure on the mold during casting. The Fe content in the entire Al alloy for casting is preferably in the range of 0.30% by mass to 0.50% by mass. If the Fe content is too high (over 0.50% by mass), Al-Si-Fe needle-like crystals (ternary compound) are generated, significantly reducing the elongation of the Al alloy casting. If the Fe content is 0.50% by mass or less, the generation of needle-like crystals is suppressed, and the adverse effect on the elongation of the Al alloy casting is suppressed.

Mn is an alloy component added to prevent seizure on the mold during casting, and to suppress the formation of needle-like crystals made of Al-Si-Fe, thereby ensuring the elongation of the Al alloy casting. The Mn content in the entire Al alloy for casting is preferably in the range of 0.28% by mass to 0.52% by mass. Setting the Mn content to 0.39% by mass or less improves the mold releasability. Furthermore, if the Mn content exceeds 0.52% by mass, the Al crystal grains become coarse and the elongation decreases. Therefore, if Mn is added in the range of 0.39% by mass or less, the mold releasability can be improved while suppressing the decrease in the elongation of the Al alloy casting.

As mentioned above, Mn, in combination with Fe, acts to suppress the formation of Al-Si-Fe-based needle-like crystals. According to the inventors' research, it was found that if the sum of the Fe and Mn contents is 1.0 (mass%) or less (Fe+Mn≦1.0), the effect of suppressing the formation of needle-like crystals is extremely high.

Cu is an alloying component that dissolves in the Al base material and is effective in improving the mechanical properties of Al alloy castings, particularly tensile strength and yield strength. The Cu content in the entire Al alloy for casting is preferably in the range of 0.08% by mass to 0.22% by mass. If Cu is contained within the above range, it can effectively exert its solid solution strengthening effect in the Al alloy without impairing corrosion resistance. If the Cu content is too high (exceeding 0.22% by mass), it will result in a decrease in the corrosion resistance and elongation of the Al alloy casting.

Ti is an alloying component that is effective in refining Al crystal grains. If the Ti content is too low (less than 0.04 mass%), the Al crystal grains become coarse, reducing the elongation, tensile strength, and yield strength, whereas if the Ti content is too high (more than 0.15 mass%), the Si crystal grains (eutectic Si) are concentrated too much at the grain boundaries, resulting in defects, which also reduces the elongation, tensile strength, and yield strength. Therefore, it is desirable to set the Ti content in the entire casting Al alloy to a range of 0.04 mass% to 0.15 mass%. In this way, the degree of refining of the Al crystal grains is adjusted to the extent that a dendrite shape remains within the Al crystal grains, and the Si crystal grains are finely dispersed throughout the cast structure, resulting in a stable and uniform cast structure.

Sr is an alloying component that refines the Si crystal grains and is effective in improving the elongation, tensile strength, and yield strength even in the as-cast state (without heat treatment after casting). This effect is remarkable when 0.0075 mass% or more of Sr is added. In contrast, when excess Sr is added in an amount exceeding 0.028 wt%, an Al-Si-Sr ternary compound is generated, resulting in over-improvement, and casting defects are more likely to occur, resulting in a decrease in mechanical properties such as elongation, tensile strength, and yield strength. The addition of Sr has the effect of spheroidizing and refining the Si crystal grains in the as-cast state. Since the stress concentration is suppressed by spheroidizing the Si crystal grains, if Sr is included in the composition of the casting Al alloy, heat treatment such as solution treatment can be omitted due to its effect, and an Al alloy casting that sufficiently secures mechanical properties such as elongation, tensile strength, and yield strength can be obtained, even though it is in the as-cast state without heat treatment. Therefore, it is preferable that the Sr content of the entire casting Al alloy be in the range of 0.0075 mass% or more and 0.028 mass% or less.

In the present invention, alloy components such as Zn, Ni, Sn, Pb, Ca, Cr, and Cd are treated as inevitable impurities. The Zn content is limited to 0.15 mass% or less because, like Cu, excessive Zn content impairs corrosion resistance. Ca is a harmful alloy component that makes the casting structure unstable and deteriorates the flow of molten metal, so its content is limited to 0.005 mass% or less. It is desirable to keep the content of other inevitable impurities to 0.1 mass% or less.

There are no particular restrictions on the purity (quality) of the Al raw material used. Sufficient refining makes it easier to obtain Al alloy castings with good mechanical properties. However, because refining is very costly, it is acceptable for other unavoidable impurities to be included. For example, high-purity Al ingots and recycled materials may be mixed in an appropriate ratio.

Now, when manufacturing the casting Al alloy and Al alloy castings of the present invention, first, raw materials containing each of the main alloy components Al, Si, Mg, Fe, Mn, Cu, Ti, and Sr, except for Mg and Sr, are charged into a melting and holding furnace and melted (melting process, see Figure 1). Here, a flux for removing slag is added to perform a slag removal process. The temperature of the molten Al alloy in the melting process is controlled within the range of 730°C ± 10°C. Raw materials containing Mg and Sr are not charged into the melting and holding furnace.

Next, the molten Al alloy melted in the melting and holding furnace is transferred to a ladle preheated to within a range of 750°C ± 50°C, and Al oxides and _H2 gas in the molten Al alloy are removed by rotary bubbling with _N2 gas (molten metal treatment process). The molten metal treatment process is carried out for approximately 10 to 15 minutes, depending on the amount of molten Al alloy. During the molten metal treatment process, raw materials (secondary alloy ingots) containing Mg and Sr are added to the ladle so that the composition of the casting Al alloy is the above-mentioned predetermined ratio (secondary alloy addition process). After 5 minutes, flux is added and rotary bubbling with _N2 gas is performed to remove Al oxides and _H2 gas in the molten Al alloy.

If the processing time of the molten metal treatment process is, for example, 12 minutes, it is necessary to ensure that there is enough time to uniformly mix the Mg and Sr into the molten Al alloy. In addition, management of the molten metal temperature is extremely important, and the temperature of the molten Al alloy after the molten metal treatment process is controlled within the range of 680°C ± 10°C. Since alloy components such as Mg and Sr are easily burned by the heat of the molten Al alloy, in the present invention, they are added in the molten metal treatment process rather than the melting process to prevent the Mg and Sr from burning.

For example, AlMn20 (containing 20% by mass of Mn) or AlSr10 (containing 10% by mass of Sr) can be used as the secondary alloy ingot. Of course, AlSi50 (containing 50% by mass of Si), AlCu50 (containing 50% by mass of Cu), Mg99.9%, AlTi5B1 (containing 5% by mass of Ti and 1% by mass of B) and the like can be added to the ladle to adjust the alloy composition. In addition, a slag removal process can be performed during the molten metal treatment process. Only the Sr-containing raw material can be added during the molten metal treatment process, and the Mg-containing raw material can be added during the melting process, but it is preferable to add both during the molten metal treatment process.

Then, the molten Al alloy refined through the molten metal treatment process is transferred from the ladle to a local holding furnace (local holding process). The temperature of the molten Al alloy in the local holding furnace is controlled within the range of 665°C ± 5°C. The refined molten Al alloy is then poured from the local holding furnace into a specified metal mold (casting die) under pressure using a die casting machine or low pressure casting machine and solidified to form an Al alloy for casting or an Al alloy casting (casting process). Here, the die temperature is set within the range of 180°C to 220°C so that the temperature of the molten Al alloy poured from the local holding furnace into the die is maintained at about 665°C ± 5°C. When the die casting method is adopted, the degree of vacuum in the die is set within the range of 50 mbar to 100 mbar.

The Al alloy casting of the present invention can be manufactured by the conventionally known die casting method, low pressure casting method, or gravity casting method. The present invention will be specifically explained in each example. Note that the present invention is not limited to the contents of the following examples, and various modifications are possible without departing from the spirit of the present invention.

Figure 2 shows the composition ranges of other companies' casting Al alloys (hereinafter referred to as "other companies' alloys") and the casting Al alloy of the present invention (hereinafter referred to as "the present alloy"), as well as the component compositions of the examples and comparative examples. Figure 3 shows the results of measuring the tensile strength, yield strength, and elongation percentage of test pieces cut from large castings (giga die casts) obtained by die casting using the same mold for the other companies' alloys, the examples, and the comparative examples as characteristic values. The values in Figure 3 are the average values measured using five test pieces for each.

Figure 3 also shows the results of evaluation of the fluidity of the die cast, the seizure on the mold, and the cracking of the casting. The other alloys shown in Figures 2 and 3 are Alcoa's casting Al alloy called C370, which is considered to be equivalent to AlSi10MnMg. Comparative Example 1 is a case where the Sr content is near the lower limit of the alloy of the present application, and Comparative Example 2 is a case where the Sr content is near the upper limit of the alloy of the present application. The other alloys, examples, and comparative examples are all in an as-cast state without undergoing heat treatment.

As is clear from FIG. 3, Examples 1 and 2 of the present invention, in the as-cast state, exhibited a tensile strength of about 280 MPa, a yield strength of about 140 MPa, and an elongation rate of about 14%, which greatly exceeded the mechanical properties of the other alloys and Comparative Examples 1 and 2. The mechanical properties of Examples 1 and 2 far surpass the required level for structural parts in the automotive field, for example, and it was found that they were fully durable in use despite being in the as-cast state without heat treatment. In addition, Examples 1 and 2 had good melt flow during casting and no seizure occurred. Furthermore, no cracks were observed in the large castings, and overall they showed extremely good castability. However, in Comparative Examples 1 and 2, cracks were occasionally observed in the large castings.

Figure 4 shows the relationship between the temperature of the molten Al alloy during die casting in the present invention and the tensile strength and yield strength of the Al alloy casting. As can be seen from Figure 4, if the temperature of the molten Al alloy is within the range of 665°C to ±5°C, the Al alloy casting can achieve extremely high tensile strength and yield strength. Figure 5 shows the relationship between the temperature of the molten Al alloy during die casting in the present invention and the elongation rate of the Al alloy casting. In this case as well, if the temperature of the molten Al alloy is within the range of 660°C to 670°C, the Al alloy casting can achieve an extremely high elongation rate.

Figure 6 shows the relationship between the die temperature during die casting in the present invention and the tensile strength and yield strength of the Al alloy casting. As can be seen from Figure 6, if the die temperature is within the range of 180°C to 220°C, the Al alloy casting can have extremely high tensile strength and yield strength. Figure 7 shows the relationship between the die temperature during die casting in the present invention and the elongation rate of the Al alloy casting. In this case, too, if the die temperature is within the range of 180°C to 220°C, the Al alloy casting can have an extremely high elongation rate. Although the details are unclear, it is believed that if the die temperature is within the range of 180°C to 220°C, it is easier to maintain the molten Al alloy temperature within the range of 660°C to 670°C during die casting, and it is believed that the molten Al alloy temperature is less likely to decrease due to the die temperature, and the Al alloy casting has good mechanical properties because the molten Al alloy temperature is within the range of 660°C to 670°C.

Figure 8 shows the relationship between the degree of die vacuum during die casting in the present invention and the tensile strength and yield strength of the Al alloy casting. As can be seen from Figure 8, if the degree of die vacuum is within the range of 50 mbar to 100 mbar, the Al alloy casting can achieve extremely high tensile strength and yield strength. Figure 9 shows the relationship between the degree of die vacuum during die casting in the present invention and the elongation rate of the Al alloy casting. In this case too, if the degree of die vacuum is within the range of 50 mbar to 100 mbar, the Al alloy casting can achieve extremely high elongation.

As can be seen from the above explanation, according to the present invention, even in the as-cast state (without heat treatment after casting), it is possible to obtain an Al alloy for casting and an Al alloy casting that exhibits castability equivalent to that of an Al-Si-Mg alloy and good mechanical properties (elongation, tensile strength, yield strength, etc.), and it is possible to omit costly heat treatment and provide an Al alloy for casting and an Al alloy casting at low cost.

In particular, in the present invention, raw materials (secondary alloy ingots) containing Mg and Sr are added during the molten metal treatment process so that the composition of the casting Al alloy is in the specified ratio described above. This prevents alloy components such as Mg and Sr from being burned by the heat of the molten Al alloy, and ensures that the added effects of Mg and Sr are exerted in the casting Al alloy and Al alloy castings. This improves the quality and yield of the casting Al alloy and Al alloy castings.

The present invention does not intend to completely eliminate heat treatment after casting. For example, in low-pressure casting applications that require higher mechanical properties (particularly tensile strength and yield strength), it is possible to perform T4 treatment (natural aging after solution treatment), T5 treatment (artificial aging hardening after cooling from high-temperature processing), T6 treatment (artificial aging hardening after solution treatment), or T7 treatment.

Figure 10 shows the composition of the alloy of the present application in Example 3 (heat treatment-free) and Example 4 (T6 treated). The composition of Examples 3 and 4 is exactly the same. Figure 11 shows the results of measuring the tensile strength, yield strength, and elongation percentage as characteristic values for Examples 3 and 4, which were obtained by cutting test pieces from a heat treatment-free casting (Example 3) and a T6 treated casting (Example 4) obtained by low pressure casting using the same mold. The values in Figure 11 are the average values measured using five test pieces for each. Figure 11 also shows the results of evaluating the flowability of the alloy during die casting, the seizure on the mold, and the cracking of the casting.

As is clear from Figure 11, Example 3 of the present invention has a tensile strength of over 180 MPa and a yield strength of over 120 MPa even in the as-cast state during low-pressure casting. However, the elongation rate only showed a slightly low value of 5%. Example 3 had good fluidity during casting, no seizure occurred, and no cracks were observed in the casting. Overall, Example 3 showed extremely good castability. It was found that the results of Example 3 were almost equivalent to the performance (mechanical properties) after heat treatment of AC4C as specified in Japanese Industrial Standard JIS H5302.

In contrast, in Example 4, where a large low-pressure cast part was subjected to T6 treatment, the mechanical properties were significantly superior to those of Example 3, with a tensile strength of 300 MPa, a yield strength of 242 MPa, and an elongation of 8.0%. The mechanical properties of Example 4 far exceed the performance (mechanical properties) of AC4C after heat treatment, and far exceed the required standards for structural parts in the automotive field, for example. It was found that, depending on the application, heat treatment can make the part fully durable. Furthermore, in Example 4, the molten metal flow during casting was also good, there was no seizure, and no cracks were observed in the casting.

According to the present invention, even if giga die casting (large die casting) or large low pressure casting parts are cast in an as-cast state (without heat treatment after casting), a casting Al alloy and an Al alloy casting exhibiting good castability and mechanical properties (elongation, tensile strength, yield strength, etc.) can be obtained, and costly heat treatment can be omitted, so that a casting Al alloy and an Al alloy casting can be provided at a low cost. In particular, in the present invention, Sr is not added in the melting process, but is added during the molten metal treatment process in which Al oxides and _H2 gas are removed from the molten Al alloy obtained in the melting process, so that Sr can be prevented from being burned by the heat of the molten Al alloy, and the effect of adding Sr can be reliably exerted in the casting Al alloy and the Al alloy casting. Therefore, the quality and yield of the casting Al alloy and the Al alloy casting can be improved.

Furthermore, Mg is not added in the melting process, but is added in the melt treatment process to remove Al oxides and _H2 gas from the molten Al alloy obtained in the melting process, so that Mg can be prevented from being burned by the heat of the molten Al alloy, and the effect of adding Mg can be reliably exhibited in the casting Al alloy and Al alloy castings. Therefore, the quality and yield of the casting Al alloy and Al alloy castings can be improved. Note that the present invention does not exclude heat treatment after casting at all. In applications requiring higher mechanical properties, for example, heat treatment of parts after large-scale low-pressure casting can be performed without any problems, and the performance will be improved.

An aluminum wheel casting apparatus 1 according to an embodiment will be described. In the following, descriptions of the up, down, left and right directions will be based on the installation state of the casting apparatus 1 shown in Figures 13 to 19. Figure 13 is a schematic diagram showing a cross section of the casting apparatus 1. The casting apparatus 1 includes a mold 10 used for casting, an injection device 20 that injects molten metal into the mold 10, a first vacuum device 30 and a second vacuum device 40 that create a vacuum state inside the mold 10, and a runner cutting slide 50 for cutting off solidified excess molten metal (biscuit) 51.

Figure 13 shows the state when the mold 10 (fixed mold 11, intermediate mold 12, movable mold 13) is clamped. The mold 10 is composed of the fixed mold 11, the movable mold 13 arranged opposite the fixed mold 11, and the intermediate mold 12 arranged between the fixed mold 11 and the movable mold 13. When the mold 10 (fixed mold 11, intermediate mold 12, movable mold 13) is clamped, a cavity (female mold) 14 corresponding to the shape of the casting (aluminum wheel) is formed between the intermediate mold 12 and the movable mold 13.

The intermediate mold 12 and the movable mold 13 move forward and backward in the left-right mold opening direction (left-right direction in FIG. 13). Of the intermediate mold 12, the upper and lower sliding molds 12a and 12b that form the side surfaces of the cavity 14 slide in the upper and lower mold opening direction (up and down direction in FIG. 13).

The mold 10 (fixed mold 11, intermediate mold 12, movable mold 13) of the casting device 1 is opened in two stages. In the first mold opening, the intermediate mold 12 is separated from the fixed mold 11, and the space between the fixed mold 11 and the intermediate mold 12 is expanded. In other words, the mold parting surface (mold mating surface) of the intermediate mold 12 moves away from the opposing mold parting surface (mold mating surface) of the fixed mold 11. The movable mold 13 moves in conjunction with the intermediate mold 12.

In the second mold opening, the movable mold 13 separates from the intermediate mold 12, and the space between the intermediate mold 12 and the movable mold 13 widens. That is, the mold parting surface (mold mating surface) of the movable mold 13 moves away from the mold parting surface (mold mating surface) of the opposing intermediate mold 12. At the same time, the upper and lower sliding molds 12a and 12b that sandwich the sides of the casting slide up and down to open.

The fixed mold 11 is provided with an injection device 20 for injecting molten metal into the cavity 14. The injection device 20 is composed of a cylindrical injection sleeve 21 through which the molten metal flows, and a plunger 22 that pushes the molten metal in the injection sleeve 21 into the cavity 14.

The injection sleeve 21 is a cylindrical member arranged in the longitudinal direction from the fixed mold 11 toward the intermediate mold 12. One end of the injection sleeve 21 (the intermediate mold 12 side) is fitted and fixed in the fixed mold 11, and the other end protrudes from the fixed mold 11. The injection sleeve 21 is arranged at the bottom of the fixed mold 11. A molten metal pouring port 21a opens at the other end of the injection sleeve 21 (the part protruding from the fixed mold 11).

The plunger 22 is inserted from the other end side of the injection sleeve 21 (the side protruding from the fixed mold 11) and can move back and forth longitudinally within the injection sleeve 21. The initial (standby) position of the plunger 22 is on the other end side (the right side in FIG. 1) of the pouring port 21a, and can be a position where molten metal can be poured from the pouring port 21a into the injection sleeve 21. The outer diameter of the plunger 22 matches the inner diameter of the injection sleeve 21. This enables the plunger 22 to pressure-feed the molten metal in the injection sleeve 21 to the cavity 14.

A gate (opening) 12c for injecting molten metal into the cavity 14 is provided at the center of the parting surface of the intermediate mold 12 facing the fixed mold 11. The so-called center gate method is used. A runner (passage) 11a that connects the injection sleeve 21 fitted inside the fixed mold 11 and the gate 12c is provided at the parting surface of the fixed mold 11 facing the intermediate mold 12.

When the mold 10 (fixed mold 11, intermediate mold 12, movable mold 13) is clamped, the injection sleeve 21, runner 11a, gate 12c, and cavity 14 are connected. As a result, the molten metal poured from the pouring port 21a passes through the delivery path (injection sleeve 21, runner 11a, gate 12c) and is injected into the cavity 14.

In the aluminum wheel manufacturing method according to the present invention, vacuum suction is performed in two stages. The first vacuum device 30 is composed of a vacuum passage 31 that carries air or gas sucked in from a vacuum valve (not shown), a vacuum tank 32 that temporarily stores the air or gas carried from the vacuum passage 31, and a vacuum pump 33 that exhausts the air or gas stored in the vacuum tank 32.

The first vacuum device 30 is a part of the injection sleeve 21 that protrudes from the fixed mold 11, and is connected between the fixed mold 11 and the pouring port 21a (on the fixed mold 11 side of the pouring port 21a). That is, the first vacuum device 30 is connected to a vacuum device connection part 30a provided on the injection sleeve 21. In the first vacuum stage, the first vacuum device 30 connected to the first vacuum device connection part 30a operates to draw a vacuum inside the mold 10 (particularly inside the injection sleeve 21).

The second vacuum device 40 is composed of a vacuum passage 41 that carries air or gas sucked from a vacuum plate or vacuum bubble (not shown), a vacuum tank 42 that temporarily stores the air or gas carried from the vacuum passage 41, and a vacuum pump 43 that exhausts the air or gas stored in the vacuum tank 42.

As shown in Figures 20 and 21, the second vacuum device 40 is connected to the inside of the cavity 14 via four chill vents 44 arranged at equal intervals radially from the center of the cavity 14. That is, the second vacuum device 40 is connected to vacuum device connectors 40a, 40b, 40c, and 40d provided in the cavity 14 (each chill vent 44). In the second vacuum stage, the second vacuum device 40 connected to the vacuum device connectors 40a to 40d operates to suction the inside of the mold 10 (particularly the cavity 14). Each chill vent 44 attached to the tip of the cavity 14 is a cooling device for removing air and gas from the inside of the mold (cavity 14).

The runner cutting slide 50 is installed on the side of the die parting surface of the intermediate die 12 that faces the fixed die 11, and is movable in the vertical direction along the die parting surface of the intermediate die 12. The initial (standby) position of the runner cutting slide 50 may be any position where the tip of the runner cutting slide 50 is above the gate 12c and the runner cutting slide 50 does not block the gate 12c.

The manufacturing method (casting process) of the aluminum wheels of the present invention using the casting device 1 will be described with reference to Figures 12 to 21. The manufacturing method (casting process) of the aluminum wheels of the present invention is an improvement on the conventional method known as the vacuum die casting method or reduced pressure die casting method, that is, a method of producing a casting by creating a vacuum or reduced pressure inside a mold.

[Step 1]
First, the mold 10 (fixed mold 11, intermediate mold 12, movable mold 13) is clamped (see FIG. 13). As a result, a cavity 14 corresponding to the shape of the aluminum wheel is formed between the intermediate mold 12 and the movable mold 13. Also, an injection path (injection sleeve 21, runner 11a, gate 12c) is formed for injecting the molten metal poured from the pouring port 21a into the cavity 14. The plunger 22 and the runner cutting slide 50 are in a standby state in the initial position.

[Step 2]
The molten metal is poured into the injection sleeve 21 from the pouring port 21a (see FIG. 14). For example, when the above-mentioned casting Al alloy is used as the molten metal, it is preferable to set the temperature of the molten metal poured into the mold 10 from the pouring port 21a to be maintained at about 665°C ± 5°C. In addition, it is preferable to set the temperature of the mold 10 within the range of 180°C to 220°C.

[Step 3]
After the pouring is completed, the plunger 22 waiting at the other end of the injection sleeve 21 moves and pressure-feeds the molten metal in the injection sleeve 21 to the runner 11a (see FIG. 15). When the plunger 22 reaches a position where it completely blocks the pouring port 21a (after sealing the pouring port 21a), the first vacuum device 30 connected to the injection sleeve 21 is activated and suctions the inside of the mold 10 (particularly the inside of the injection sleeve 21). That is, the first vacuum device 30 suctions the inside of the mold 10 (particularly the inside of the injection sleeve 21) from the vacuum device connection part 30a provided on the injection sleeve 21 (first vacuum stage). For example, when the above-mentioned casting Al alloy is used as the molten metal, it is preferable to set the vacuum time within the range of 0.1 to 1.0 seconds. It is also preferable to set the degree of vacuum within the range of 50 mbar to 100 mbar.

[Step 4]
When the plunger 22 reaches the runner 11a, the second vacuum device 40 connected via four chill vents 44 arranged radially and at equal intervals from the center of the cavity 14 is activated to suction the inside of the mold 10 (particularly the inside of the cavity 14) by vacuum suction (see FIG. 16). That is, the second vacuum device 40 simultaneously suctions the inside of the mold 10 (particularly the inside of the cavity 14) by vacuum device connection parts 40a to 40d (four places) arranged radially and at equal intervals from the center of the cavity 14 (second vacuum stage). For example, when the above-mentioned casting Al alloy molten metal is used, the vacuum time is preferably set within a range of 0.1 to 1.6 seconds. Also, the degree of vacuum is preferably set within a range of 50 mbar to 100 mbar. Air and gas are further removed from the casting (aluminum wheel) by each chill vent 44 attached to the tip of the cavity 14.

[Step 5]
When the molten metal filled in the mold 10 is solidified by cooling, the first mold opening is performed (see FIG. 17). In the first mold opening, the intermediate mold 12 is separated from the fixed mold 11 and moves backward, and the space between the fixed mold 11 and the intermediate mold 12 is expanded. In other words, the mold parting surface of the intermediate mold 12 moves away from the opposing mold parting surface of the fixed mold 11. The movable mold 13 moves in conjunction with the intermediate mold 12.

[STEP 6]
By opening the first mold, the molten metal (biscuit) 51 solidified in the runner 11a is removed from the fixed mold 11. The biscuit 51 protruding from the gate 12c is cut off by the runner cutting slide 50 (see FIG. 18). The runner cutting slide 50 slides downward along the mold parting surface of the intermediate mold 12 to cut the biscuit 51. By cutting the biscuit 51 that was caught in the L-shape on the gate 12c, it becomes possible to remove the casting (aluminum wheel) from the intermediate mold 12.

[STEP 7]
When the biscuit 51 is cut off, the second mold opening is performed (see FIG. 19). In the second mold opening, the movable mold 13 is separated from the intermediate mold 12 and moves backward, and the space between the intermediate mold 12 and the movable mold 13 is expanded. That is, the mold parting surface of the movable mold 13 moves away from the mold parting surface of the opposing intermediate mold 12. At the same time, the upper and lower slide molds 12a and 12b that sandwich the side surface of the casting (aluminum wheel) slide open (up and down direction in FIG. 19). In addition, during the second mold opening, an ejector pin (not shown) provided on the movable mold 13 extends into the cavity 14 and pushes the casting out of the movable mold 13. This makes it possible to remove the casting from the intermediate mold 12 and the movable mold 13.

The manufacturing method of the aluminum wheel according to the present invention is characterized by vacuum suction in the mold 10 in two stages (steps 3 and 4). In the first vacuum stage of step 3, after pouring, vacuum suction is applied to the inside of the mold 10 (particularly the inside of the injection sleeve 21) from the injection sleeve 21 with the pouring port 21a sealed, thereby preventing air or gas from being entrained when the molten metal is injected into the cavity 14. In the second vacuum stage of step 4, vacuum suction is applied all at once from four vacuum device connections (40a, 40b, 40c, 40d) positioned at equal radial intervals from the center of the cavity 14, so that the molten metal flowing in from the gate 12c (the center of the cavity 14) is uniformly filled into the cavity 14.

In this way, by vacuum suctioning specific parts at specific times, the air and gas contained within the die 10 and the molten metal can be removed efficiently and effectively. This makes it possible to produce castings (aluminum wheels) with good internal quality even when using die casting.

The aluminum wheel manufacturing method of the present invention makes it possible to manufacture aluminum wheels with sufficient strength and toughness using highly productive die casting. In addition, the necessary strength can be maintained even if the cross section of the spokes and rim of the aluminum wheel is made small, improving the overall lightness of the aluminum wheel. Furthermore, since no heat treatment is required after die casting, productivity can be further improved. Therefore, the aluminum wheel manufacturing method of the present invention makes it possible to increase productivity while ensuring the strength, toughness, and lightness of the aluminum wheel.

The configuration of each part in the present invention is not limited to the illustrated embodiment, and various modifications are possible without departing from the spirit of the present invention. Furthermore, the shape of the aluminum wheel (cast product) manufactured by the aluminum wheel manufacturing method according to the present invention is not limited to the embodiment.

The position of the vacuum device connection part 30a is not limited to the embodiment and can be changed as appropriate. As long as it is provided on the injection sleeve 21, it may be in a position different from the positions shown in Figures 13 to 15, and there may be multiple vacuum device connection parts.

The positions of the vacuum device connection parts 40a to 40d are not limited to the embodiment and can be changed as appropriate. As long as they are arranged radially at equal intervals from the center of the cavity 14, they may be located in positions other than the four locations (44a, 44b, 44c, 44d) shown in Figures 20 and 21, and there may be more than four vacuum device connection parts.

In the manufacturing method of the aluminum wheel according to the present invention, it is more preferable to use the above-mentioned casting Al alloy. By using the above-mentioned casting Al alloy, the strength, toughness, and light weight of the casting (aluminum wheel) can be further improved. However, the casting Al alloy and molten metal used in the manufacturing method of the aluminum wheel according to the present invention are not limited.

1 Casting device 10 Mold 11 Fixed mold 12 Intermediate mold 13 Movable mold 14 Cavity 20 Injection device 21 Injection sleeve 21a Pouring port 30 First vacuum device 30a Vacuum device connection part 31 Vacuum passage 32 Vacuum tank 33 Vacuum pump 40 Second vacuum device 40a to 40d Vacuum device connection part 41 Vacuum passage 42 Vacuum tank 43 Vacuum pump 44 Chill vent 50 Runner cutting slide 51 Biscuit

Claims (2)

A method for manufacturing an aluminum wheel including a die casting process,
The casting process includes:
a first vacuum stage in which the molten aluminum alloy is poured into the die and then the inside of the die is evacuated through an injection sleeve with a sealed pouring port;
a second vacuum stage in which the inside of the mold is suctioned by vacuum from a cavity in which an aluminum wheel is molded after the first vacuum stage;
Including,
In the second vacuum stage, a plurality of equally spaced radially extending portions of the cavity are provided.
At the same time, vacuum is sucked from the vacuum device connection part.
A method for manufacturing aluminum wheels. No heat treatment is performed after the casting process.
A method for manufacturing the aluminum wheel according to claim 1.