Method for manufacturing an aluminum wheel

Abstract

To provide a casting method capable of enhancing productivity while ensuring the strength, toughness, and lightweight property of an aluminum wheel. 【Solution means】A manufacturing method of an aluminum wheel including a die-casting process, the casting process including a first vacuum stage of vacuum-sucking the inside of the mold 10 from an injection sleeve 21 with the sprue closed after pouring an Al alloy molten metal into the mold 10, and a second vacuum stage of vacuum-sucking the inside of the mold 10 from a cavity 14 where the aluminum wheel is formed after the first vacuum stage. A manufacturing method of an aluminum wheel.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an aluminum wheel.

Background Art

[0002] In the casting of conventional aluminum wheels, in order to ensure strength, toughness, and lightness, a method of performing heat treatment after gravity casting is adopted (see, for example, Patent Document 1). Gravity casting has a relatively slow pouring speed, and it is difficult for air to mix into the molten metal. Therefore, the internal quality of the aluminum wheel is good, and high toughness is ensured. In addition, by performing heat treatment after gravity casting, even if the cross-section of the spoke or rim of the aluminum wheel is reduced, the required strength can be maintained, so the lightness of the entire aluminum wheel can be improved.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, since gravity casting takes time for casting, it has the demerit of low productivity. In order to improve productivity, it is conceivable to adopt die-cast molding that fills the molten metal at high pressure and high speed. However, since air easily mixes into the molten metal in die-cast molding, the internal quality of the aluminum wheel tends to deteriorate compared to gravity casting. In addition, when heat treatment is performed after die-cast molding, there is a problem that blisters (defects caused by air mixed in the molten metal) occur and the toughness of the aluminum wheel further decreases, so it is difficult to improve the strength by heat treatment. Therefore, in order to ensure the strength and toughness of the aluminum wheel by die-cast molding, it is necessary to set the cross-sectional area of the spoke and rim of the aluminum wheel to a certain size, and the weight of the entire aluminum wheel increases.

[0005] As described above, in the casting of aluminum wheels, there has been a problem that it is difficult to increase productivity while ensuring the strength, toughness, and light weight of the aluminum wheels.

Means for Solving the Problem

[0006] The technical problem of the present invention is to provide a method for manufacturing an aluminum wheel that has been improved by considering the above-mentioned current situation.

[0007] The present invention is a method for manufacturing an aluminum wheel including a die-casting process. In the casting process, after pouring an Al alloy molten metal into a mold, a first vacuum stage is performed in which the inside of the mold is vacuum-sucked from an injection sleeve with the pouring port sealed, and after the first vacuum stage, a second vacuum stage is performed in which the inside of the mold is vacuum-sucked from a cavity in which the aluminum wheel is formed. After pouring the Al alloy molten metal into the mold, the inside of the mold is vacuum-sucked from the injection sleeve with the pouring port sealed, and after the first vacuum stage, the inside of the mold is vacuum-sucked from the cavity in which the aluminum wheel is formed. After the first vacuum stage, a second vacuum stage is performed in which the inside of the mold is vacuum-sucked from a cavity in which the aluminum wheel is formed. It includes. Look, in the second vacuum stage, vacuum suction is simultaneously performed from a plurality of vacuum device connection parts that are radially and equidistantly positioned from the central part of the cavity part. It is.

[0008] Also, in the method for manufacturing an aluminum wheel of the present invention, No heat treatment is performed after the casting process. it may be done in this way. .

[0009] The Al alloy for casting used in the method for manufacturing an aluminum wheel according to the present invention preferably contains 8.0 to 10.0% by mass of Si, 0.25 to 0.40% by mass of Mg, 0.30 to 0.50% by mass of Fe, 0.28 to 0.52% by mass of Mn, 0.08 to 0.22% by mass of Cu, 0.04 to 0.15% by mass of Ti, and 0.0075 to 0.028% by mass of Sr, and the balance contains Al.

[0010] The sum of the contents of the Fe and the Mn is limited to 1.0% by mass or less. Further, the Sr is not added in the melting process, and is added in the molten metal treatment process for removing Al oxides and H2 gas in the Al alloy molten metal obtained in the melting process. The Mg may not be added in the melting process and may be added in the molten metal treatment process.

Effect of the Invention

[0011] The invention of the present application is a die-cast casting with high productivity, which can sufficiently ensure the strength and toughness of an aluminum wheel. Also, even if the cross-sections of the spokes and rim of the aluminum wheel are reduced, the required strength can be maintained, so that the weight reduction of the entire aluminum wheel can be improved. Furthermore, since heat treatment after die-cast casting is not performed, productivity can be further improved. Therefore, the method for manufacturing an aluminum wheel according to the invention of the present application enables improvement of productivity while ensuring the strength, toughness, and weight reduction of the aluminum wheel.

Brief Description of the Drawings

[0012]

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Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments embodying the present invention will be described with reference to the drawings. As shown in FIG. 2, the compositions of the Al alloy for casting and the Al alloy casting according to the present invention contain, by mass, 8.0% by mass or more and 10.0% by mass or less of Si (silicon), 0.25% by mass or more and 0.40% by mass or less of Mg (magnesium), 0.30% by mass or more and 0.50% by mass or less of Fe (iron), 0.28% by mass or more and 0.52% by mass or less of Mn (manganese), 0.08% by mass or more and 0.22% by mass or less of Cu (copper), 0.04% by mass or more and 0.15% by mass or less of Ti (titanium), and 0.0075% by mass or more and 0.028% by mass or less of Sr (strontium), and the balance contains Al (aluminum) and inevitable impurities.

[0014] Si is an important alloy component (element) that contributes to improving the castability, particularly the fluidity of the molten metal. The content of Si in the Al alloy for casting as a whole is preferably in the range of 8.0% by mass or more and 10.0% by mass or less as described above. When the Si content is too low (less than 8.0% by mass), the fluidity is insufficient and the fluidity of the molten metal cannot be ensured, and casting cracks and the like are likely to occur. Conversely, when it contains excessive Si exceeding 10.0% by mass, the elongation rate of the Al alloy casting will be decreased.

[0015] Mg mainly exists in a state dissolved in the Al base material in the Al alloy for casting or as Mg2Si, and is an alloy component effective for improving the tensile strength and yield strength. The content of Mg in the Al alloy for casting as a whole is desirably 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 the tensile strength and yield strength of the Al alloy casting can be improved without significantly affecting the castability and the elongation rate of the Al alloy casting. When the Mg content is too low (less than 0.25% by mass), sticking to the mold is likely to occur, and when the Mg content is too high (exceeding 0.40% by mass), the elongation rate of the Al alloy casting tends to decrease.

[0016] Fe is an alloying element that exhibits the effect of preventing seizure to the mold during casting. The content of Fe in the entire Al alloy for casting is preferably in the range of 0.30 mass% or more and 0.50 mass% or less. When the Fe content is too high (exceeding 0.50 mass%), Al-Si-Fe acicular crystals (ternary compounds) are formed, significantly reducing the elongation rate of the Al alloy casting. If the Fe content is 0.50 mass% or less, the formation of acicular crystals is suppressed, and the adverse effect on the elongation rate of the Al alloy casting is suppressed.

[0017] Mn is an alloying element added to prevent seizure to the mold during casting and to suppress the formation of acicular crystals composed of Al-Si-Fe, ensuring the elongation rate of the Al alloy casting. The content of Mn in the entire Al alloy for casting is preferably in the range of 0.28 mass% or more and 0.52 mass% or less. If the Mn content is set to 0.39 mass% or less, the mold release property is improved. Also, when the Mn content exceeds 0.52 mass%, the Al crystal grains coarsen and the elongation rate decreases. Therefore, by containing Mn in the range of 0.39 mass% or less, it is possible to improve the mold release property while suppressing the decrease in the elongation rate of the Al alloy casting.

[0018] As described above, Mn exhibits the effect of suppressing the formation of Al-Si-Fe acicular crystals in relation to Fe. According to the research of the present inventors, it has been found that if the sum of the contents of Fe and Mn is 1.0 (mass%) or less (Fe + Mn ≤ 1.0), the effect of suppressing acicular crystal formation is extremely high.

[0019] Cu is an alloying element that is dissolved in the Al base material and is effective in improving the mechanical properties, particularly the tensile strength and yield strength, of the Al alloy casting. The content of Cu in the entire Al alloy for casting is preferably in the range of 0.08 mass% or more and 0.22 mass% or less. If Cu is contained within the above range, the solid solution strengthening effect in the Al alloy can be effectively exerted without impairing the corrosion resistance. When the Cu content is too high (exceeding 0.22 mass%), it causes a decrease in the corrosion resistance and elongation rate of the Al alloy casting.

[0020] Ti is an alloying element effective in refining Al crystal grains. When the Ti content is too low (less than 0.04% by mass), the Al crystal grains coarsen, resulting in a decrease in elongation, tensile strength, and yield strength. On the other hand, when the Ti content is too high (exceeding 0.15% by mass), the Si crystal grains (eutectic Si) concentrate too much at the grain boundaries and become defective parts, also leading to a decrease in elongation, tensile strength, and yield strength in this case. Therefore, it is desirable that the Ti content in the entire Al alloy for casting be in the range of 0.04% by mass or more and 0.15% by mass or less. By doing so, the degree of refinement of the Al crystal grains is adjusted to the extent that the dendrite shape remains in the Al crystal grains, and the Si crystal grains are finely dispersed throughout the casting structure, resulting in a stable and uniform casting structure.

[0021] Sr is an alloying element effective in refining Si crystal grains and improving elongation, tensile strength, and yield strength even without post-casting heat treatment (casting without heat treatment). Such an effect is significantly exhibited when Sr is added at 0.0075% by mass or more. In contrast, when an excessive amount of Sr exceeding 0.028% by weight is added, an Al-Si-Sr ternary compound is formed, resulting in over-improvement and an increased tendency to produce casting defects, leading to a decrease in mechanical properties such as elongation, tensile strength, and yield strength. The addition of Sr exhibits the effect of spheroidizing and refining Si crystal grains without post-casting heat treatment. If the Si crystal grains are spheroidized, stress concentration will be suppressed. Therefore, when Sr is included in the composition of the Al alloy for casting, due to its effect, heat treatment such as solution treatment can be omitted. Despite being a heat treatment-free state after casting, an Al alloy casting with sufficient mechanical properties such as elongation, tensile strength, and yield strength can be obtained. Therefore, it is preferable that the Sr content in the entire Al alloy for casting be in the range of 0.0075% by mass or more and 0.028% by mass or less.

[0022] In the present invention, alloying elements such as Zn, Ni, Sn, Pb, Ca, Cr, and Cd are treated as inevitable impurities. For Zn, if the content is too high, it will act to impair the corrosion resistance like Cu, so the content is limited to 0.15% by mass or less. Ca is a harmful alloying element that makes the casting structure unstable and deteriorates the molten metal flow, so the content is limited to 0.005% by mass or less. It is desirable to keep the content of other inevitable impurities at 0.1% by mass or less.

[0023] There is no particular limitation on the purity (quality) of the Al raw material used. If sufficient purification is carried out, it becomes easy to obtain an Al alloy casting having good mechanical properties. However, since a great deal of cost is required for purification, it does not matter if other inevitable impurities are included. For example, a high-purity Al ingot and recycled materials may be blended at an appropriate ratio.

[0024] Now, when manufacturing the Al alloy for casting and the Al alloy casting of the present invention, first, raw materials containing each alloying element other than Mg and Sr among the main alloying elements Al, Si, Mg, Fe, Mn, Cu, Ti, and Sr are charged into a melting and holding furnace, and these raw materials are melted (melting step, see Figure 1). Here, a flux for slag removal is added and slag removal treatment is performed. The temperature of the Al alloy molten metal in the melting step is controlled within the range of 730°C ± 10°C. The raw materials containing Mg and Sr are not charged into the melting and holding furnace.

[0025] Next, the molten Al alloy in the melting and holding furnace is transferred to a ladle preheated within the range of 750 °C ± 50 °C, and Al oxides and H2 gas in the molten Al alloy are removed by rotary bubbling using N2 gas (molten metal treatment process). The molten metal treatment process is carried out for approximately 10 to 15 minutes, although it depends on the amount of the molten Al alloy. Then, raw materials (secondary alloy ingots) containing Mg and Sr during the molten metal treatment process are charged into the ladle so that the composition of the Al alloy for casting becomes the predetermined ratio described above (secondary alloy charging process). A flux is added 5 minutes after the start of the molten metal treatment process, and rotary bubbling with N2 gas is performed to remove Al oxides and H2 gas in the molten Al alloy.

[0026] When the treatment time of the molten metal treatment process is, for example, 12 minutes, it is necessary to ensure sufficient time to uniformly stir Mg and Sr in the molten Al alloy. Also, temperature control of the molten metal is extremely important, and the temperature of the molten Al alloy after the completion of the molten metal treatment process is controlled within the range of 680 °C ± 10 °C. Alloy components such as Mg and Sr are easily burned out by the heat of the molten Al alloy, so in the present invention, they are added in the molten metal treatment process instead of the melting process to prevent burning out of Mg and Sr.

[0027] As the secondary alloy ingot, for example, AlMn20 (containing 20 mass% Mn) or AlSr10 (containing 10 mass% Sr) may be used. Of course, it goes without saying that AlSi50 (containing 50 mass% Si), AlCu50 (containing 50 mass% Cu), Mg99.9%, AlTi5B1 (containing 5 mass% Ti and 1 mass% B), etc. may be added to the ladle for adjustment of the alloy components. In addition, dross removal treatment may be performed during the molten metal treatment process. Although only the Sr-containing raw material may be added in the molten metal treatment process and the Mg-containing raw material may be added in the melting process, it is desirable to add both in the molten metal treatment process.

[0028] Next, the refined Al alloy melt that has undergone the melt treatment process is transferred from the ladle to the in-house holding furnace (in-house holding process). The temperature of the Al alloy melt in the in-house holding furnace is controlled within the range of 665°C ± 5°C. Then, the refined Al alloy melt is poured into a predetermined mold (casting mold) from the in-house holding furnace by applying pressure with a die-casting machine or a low-pressure casting machine and solidified, thereby forming a casting Al alloy or an Al alloy casting (casting process). Here, the mold temperature is set within the range of 180°C to 220°C so that the temperature of the Al alloy melt poured into the mold from the in-house holding furnace is maintained at about 665°C ± 5°C. When the die-casting method is adopted, the degree of vacuum in the mold is set within the range of 50 mbar to 100 mbar.

[0029] The Al alloy casting of the present invention can be manufactured by a conventionally known die-casting method, low-pressure casting method, or gravity casting method. Therefore, the present invention will be specifically described in each example. Note that the present invention is not limited to the content of the following examples, and various modifications can be made without departing from the spirit of the present invention.

[0030] Figure 2 shows the composition ranges of an Al alloy for casting from another company (hereinafter referred to as the other company's alloy) and the Al alloy for casting of the present invention (hereinafter referred to as the present invention's 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 rate as accuracy values by cutting out test pieces from large castings (gigadiecast) obtained by the die-casting method using the same mold for the other company's alloy, the examples, and the comparative examples. The values in Figure 3 are the average values measured using five test pieces each.

[0031] Figure 3 also shows the results of evaluating the fluidity of the molten metal during die casting, the sticking to the mold, and the cracking of the casting. The other company alloys shown in Figures 2 and 3 are casting Al alloys called C370 manufactured by Alcoa, which is understood to correspond to AlSi10MnMg. Comparative Example 1 is the case where the Sr content rate is near the lower limit of the alloy of the present application, and Comparative Example 2 is the case where the Sr content rate is near the upper limit of the alloy of the present application. The other company alloys, the examples, and the comparative examples are all in the as-cast state without performing heat treatment.

[0032] As is clear from Figure 3, both Examples 1 and 2 of the present invention in the as-cast state show a tensile strength of around 280 MPa, a yield strength of around 140 MPa, and an elongation rate of around 14%, greatly exceeding the mechanical properties of the other company alloys and Comparative Examples 1 and 2. The mechanical properties of Examples 1 and 2 far exceed the required levels for structural parts in the automotive field, for example, and it was found that they can sufficiently withstand use despite being in the as-cast state without heat treatment. Also, Examples 1 and 2 had good fluidity of the molten metal during casting and no sticking occurred. Furthermore, no cracking was observed in large castings, and overall, they showed extremely good castability. In Comparative Examples 1 and 2, cracking in large castings was observed as a result.

[0033] Figure 4 shows the relationship between the molten Al alloy 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 4, if the molten Al alloy temperature is within the range of 665°C ± 5°C, the Al alloy casting can obtain extremely high tensile strength and yield strength. Figure 5 shows the relationship between the molten Al alloy temperature during die casting in the present invention and the elongation rate of the Al alloy casting. Also in this case, if the molten Al alloy temperature is within the range of 660°C to 670°C, the Al alloy casting can obtain an extremely high elongation rate.

[0034] Figure 6 shows the relationship between the mold 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 mold temperature is within the range of 180°C to 220°C, the Al alloy casting can obtain extremely high tensile strength and yield strength. Figure 7 shows the relationship between the mold temperature during die-casting in the present invention and the elongation rate of the Al alloy casting. Also in this case, if the mold temperature is within the range of 180°C to 220°C, the Al alloy casting can obtain an extremely high elongation rate. Although the details are unclear, it is considered that if the mold temperature is within the range of 180°C to 220°C, it becomes easier to maintain the temperature of the Al alloy molten metal during die-casting within the range of 660°C to 670°C. Thanks to the mold temperature, the temperature of the Al alloy molten metal hardly decreases. Since the temperature of the Al alloy molten metal is within the range of 660°C to 670°C, it is understood that the Al alloy casting has obtained good mechanical properties.

[0035] Figure 8 shows the relationship between the mold vacuum degree 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 mold vacuum degree is within the range of 50 mbar to 100 mbar, the Al alloy casting can obtain extremely high tensile strength and yield strength. Figure 9 shows the relationship between the mold vacuum degree during die-casting in the present invention and the elongation rate of the Al alloy casting. Also in this case, if the mold vacuum degree is within the range of 50 mbar to 100 mbar, the Al alloy casting can obtain an extremely high elongation rate.

[0036] As can be understood from the above description, according to the present invention, even in the as-cast state (without post-casting heat treatment), an Al alloy for casting and thus an Al alloy casting that exhibits casting properties equivalent to those of an Al-Si-Mg alloy system and shows good mechanical properties (such as elongation rate, tensile strength, and yield strength) can be obtained. The costly heat treatment can be omitted, and an Al alloy for casting and an Al alloy casting can be provided at a low cost.

[0037] Particularly in the present invention, since raw materials (secondary alloy ingots) containing Mg or Sr are added during the molten metal treatment step so that the composition of the Al alloy for casting becomes the predetermined ratio described above, it is possible to suppress the burning loss of alloy components such as Mg and Sr due to the heat of the Al alloy molten metal, and in the Al alloy for casting and the Al alloy casting, the addition effects of Mg and Sr can be surely exhibited. Therefore, the quality and yield of the Al alloy for casting and the Al alloy casting can be improved.

[0038] The present invention does not intend to completely eliminate the heat treatment after casting. For example, in the case of low-pressure casting applications that require higher mechanical properties (particularly tensile strength and yield strength), it is also possible to perform T4 treatment (natural aging after solution treatment), T5 treatment (artificial aging hardening treatment after cooling from hot working), T6 treatment (artificial aging hardening treatment after solution treatment), or T7 treatment.

[0039] FIG. 10 shows the component compositions of Example 3 (heat treatment-free) and Example 4 (T6-treated) of the alloy of the present application. Note that the component compositions of Examples 3 and 4 are exactly the same. FIG. 11 shows, for Examples 3 and 4, test pieces cut out from a heat treatment-free casting (Example 3) and a T6-treated casting (Example 4) obtained by the low-pressure casting method using the same mold, and the results of measuring the tensile strength, yield strength, and elongation rate as accuracy values. The values in FIG. 11 are the average values measured using five test pieces each. In addition, FIG. 11 also shows the results of evaluating the molten metal fluidity, mold sticking, and cracking of the casting during die casting.

[0040] As is clear from FIG. 11, Example 3 of the present invention has obtained a tensile strength exceeding 180 MPa and a yield strength exceeding 120 MPa even in the as-cast state during low-pressure casting. However, only the elongation rate showed a slightly low value of 5%. Example 3 had good molten metal fluidity during casting, no mold sticking occurred, and no cracking of the casting was observed. Example 3 showed extremely good castability as a whole. It was found that the results of Example 3 were almost equivalent to the performance (mechanical properties) after heat treatment of AC4C specified in Japanese Industrial Standard JIS H5302.

[0041] In contrast, in Example 4 where the large-sized low-pressure cast parts were subjected to T6 treatment, the tensile strength was 300 MPa, the yield strength was 242 MPa, and the elongation was 8.0%, far exceeding the mechanical properties of Example 3. The mechanical properties of Example 4 far exceed the performance (mechanical properties) after heat treatment of AC4C, and for example, greatly exceed the required level for structural parts in the automotive field. Depending on the application, it was found that by performing heat treatment, it can sufficiently withstand use. Regarding Example 4 as well, the fluidity of the molten metal during casting was good, no seizure occurred, and no cracks were found in the casting.

[0042] According to the present invention, for example, even if gigacast (large-sized die-cast products) or large-sized low-pressure cast parts are in the as-cast state (without post-casting heat treatment), a casting Al alloy and thus an Al alloy casting showing good castability and mechanical properties (elongation, tensile strength, yield strength, etc.) can be obtained, the costly heat treatment can be omitted, and the casting Al alloy and the Al alloy casting can be provided at low cost. Particularly in the present invention, Sr is not added in the melting process, but is added in the molten metal treatment process for removing Al oxide and H2 gas in the Al alloy molten metal obtained in the melting process. Therefore, burning loss of Sr due to the heat of the Al alloy molten metal can be suppressed, and the addition effect of Sr can be surely exhibited in the casting Al alloy and the Al alloy casting. Accordingly, the quality and yield of the casting Al alloy and the Al alloy casting can be improved.

[0043] Furthermore, if Mg is also not added in the melting process but is added in the molten metal treatment process for removing Al oxide and H2 gas in the Al alloy molten metal obtained in the melting process, burning loss of Mg due to the heat of the Al alloy molten metal can be suppressed, and the addition effect of Mg can be surely exhibited in the casting Al alloy and the Al alloy casting. Accordingly, the quality and yield of the casting Al alloy and the Al alloy casting can be improved. The present invention does not completely exclude post-casting heat treatment. In applications that require higher mechanical properties, for example, parts after large-sized low-pressure casting can be heat-treated without any problem and the performance will be improved.

[0044] The casting apparatus 1 for an aluminum wheel according to the embodiment will be described. Hereinafter, descriptions of the up, down, left, and right directions are based on the installation state of the casting apparatus 1 shown in FIGS. 13 to 19. FIG. 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 for injecting molten metal into the mold 10, a first vacuum device 30 and a second vacuum device 40 for making the inside of the mold 10 in a vacuum state, and a runner cutting slide 50 for cutting off the solidified excess molten metal (biscuit) 51.

[0045] FIG. 13 is a view showing a state in which the mold 10 (fixed mold 11, intermediate mold 12, movable mold 13) is clamped. The mold 10 is composed of a fixed mold 11, a movable mold 13 arranged to face the fixed mold 11, and an 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.

[0046] The intermediate mold 12 and the movable mold 13 move forward and backward in the left-right mold opening direction (the left-right direction in FIG. 13). Among the intermediate mold 12, the upper and lower slide molds 12a and 12b forming the side surface of the cavity 14 slide in the up-down mold opening direction (the up-down direction in FIG. 13).

[0047] The mold 10 (fixed mold 11, intermediate mold 12, movable mold 13) of the casting apparatus 1 opens the mold in two steps. 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 expands. That is, the mold parting surface (mold mating surface) of the intermediate mold 12 moves away from the mold parting surface (mold mating surface) of the opposing fixed mold 11. The movable mold 13 moves in conjunction with the intermediate mold 12.

[0048] In the second mold opening, the movable mold 13 is separated from the intermediate mold 12, and the space between the intermediate mold 12 and the movable mold 13 expands. 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 slide molds 12a and 12b sandwiching the side surface of the casting slide up and down to open.

[0049] The stationary 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 for extruding the molten metal in the injection sleeve 21 into the cavity 14.

[0050] The injection sleeve 21 is a cylindrical member provided in the longitudinal direction from the stationary mold 11 toward the intermediate mold 12. One end portion (the intermediate mold 12 side) of the injection sleeve 21 is fitted and fixed inside the stationary mold 11, and the other end portion protrudes from the stationary mold 11. The injection sleeve 21 is provided at the lower part of the stationary mold 11. A molten metal pouring port 21a is opened at the other end portion (the portion protruding from the stationary mold 11) of the injection sleeve 21.

[0051] The plunger 22 is inserted from the other end side (the side protruding from the stationary mold 11) of the injection sleeve 21 and can move forward and backward in the longitudinal direction inside the injection sleeve 21. The initial (standby) position of the plunger 22 may be on the other end side (the right side in FIG. 1) than the pouring port 21a as long as it is a position where the molten metal can be poured from the pouring port 21a into the injection sleeve 21. The outer diameter of the plunger 22 is matched with the inner diameter of the injection sleeve 21. Thereby, the plunger 22 can pump the molten metal in the injection sleeve 21 into the cavity 14.

[0052] A gate (opening) 12c for injecting molten metal into the cavity 14 is provided at the center of the mold split surface of the intermediate mold 12 facing the stationary mold 11. The so-called center gate method is adopted. A runner (passage portion) 11a for connecting the injection sleeve 21 fitted inside the stationary mold 11 and the gate 12c is provided on the mold split surface of the stationary mold 11 facing the intermediate mold 12.

[0053] When the mold 10 (fixed mold 11, intermediate mold 12, movable mold 13) is clamped, the injection sleeve 21, the runner 11a, the gate 12c, and the cavity 14 are in a communicating state. As a result, the molten metal injected from the pouring port 21a is injected into the cavity 14 through the delivery path (injection sleeve 21, runner 11a, gate 12c).

[0054] In the method for manufacturing an aluminum wheel according to the present invention, vacuum suction is performed in two stages. The first vacuum device 30 includes a vacuum passage 31 that transports air and gas sucked from a vacuum bubble (not shown), a vacuum tank 32 that temporarily stores the air and gas transported from the vacuum passage 31, and a vacuum pump 33 that discharges the air and gas stored in the vacuum tank 32.

[0055] The first vacuum device 30 is a portion that protrudes from the fixed mold 11 of the injection sleeve 21 and is connected between the fixed mold 11 and the pouring port 21a (on the fixed mold 11 side rather than the pouring port 21a side). That is, the first vacuum device 30 is connected to a vacuum device connection portion 30a provided on the injection sleeve 21. In the first vacuum stage, the first vacuum device 30 connected to the first vacuum device connection portion 30a operates to vacuum-suck the inside of the mold 10 (particularly inside the injection sleeve 21).

[0056] The second vacuum device 40 includes a vacuum passage 41 that transports air and gas sucked from a vacuum plate or a vacuum bubble (not shown), a vacuum tank 42 that temporarily stores the air and gas transported from the vacuum passage 41, and a vacuum pump 43 that discharges the air and gas stored in the vacuum tank 42.

[0057] As shown in FIGS. 20 and 21, the second vacuum device 40 is connected to the inside of the cavity 14 via four tilt vents 44 that are radially and equidistantly arranged from the central portion of the cavity 14. That is, the second vacuum device 40 is connected to the vacuum device connection portions 40a, 40b, 40c, and 40d provided in the cavity 14 (each tilt vent 44). In the second vacuum stage, the second vacuum device 40 connected to the vacuum device connection portions 40a to 40d operates to vacuum suck the inside of the mold 10 (particularly inside the cavity 14). Each tilt vent 44 attached to the tip of the cavity 14 is a cooling device for exhausting air and gas inside the mold (cavity 14).

[0058] The runner cutting slide 50 is installed on the mold split surface side of the intermediate mold 12 facing the fixed mold 11 and moves vertically along the mold split surface of the intermediate mold 12. The initial (standby) position of the runner cutting slide 50 only needs to be a 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.

[0059] The manufacturing method (casting process) of the aluminum wheel of the present invention using the casting device 1 will be described with reference to FIGS. 12 to 21. The manufacturing method (casting process) of the aluminum wheel of the present invention is an improvement based on a method called the conventional vacuum die casting method or the reduced-pressure die casting method, that is, a method of manufacturing a casting by evacuating or reducing the pressure inside a mold.

[0060] [Step 1] First, the mold 10 (fixed mold 11, intermediate mold 12, movable mold 13) is clamped (see FIG. 13). Thereby, a cavity 14 corresponding to the shape of the aluminum wheel is formed between the intermediate mold 12 and the movable mold 13. Also, a feed path (injection sleeve 21, runner 11a, gate 12c) for injecting the molten metal poured from the pouring port 21a into the cavity 14 is formed. The plunger 22 and the runner cutting slide 50 are in a standby state at their initial positions.

[0061] [Step 2] Pour the molten metal into the injection sleeve 21 from the pouring port 21a (see Fig. 14). For example, when the above Al alloy for casting 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. Also, the temperature of the mold 10 is preferably set within the range of 180°C to 220°C.

[0062] [Step 3] After the pouring is completed, the plunger 22 waiting on the other end side of the injection sleeve 21 moves, and the molten metal in the injection sleeve 21 is pumped into the runner 11a (see Fig. 15). When the plunger 22 reaches the position where it completely closes the pouring port 21a (after sealing the pouring port 21a), the first vacuum device 30 connected to the injection sleeve 21 operates, and the inside of the mold 10 (especially inside the injection sleeve 21) is evacuated. That is, it is evacuated by the first vacuum device 30 from the vacuum device connection part 30a provided in the injection sleeve 21 (first vacuum stage). For example, when the above Al alloy for casting is used as the molten metal, the vacuum time is preferably set within the range of 0.1 to 1.0 second. Also, the degree of vacuum is preferably set within the range of 50 mbar to 100 mbar.

[0063] [Step 4] When the plunger 22 reaches the runner 11a, the second vacuum device 40 connected via four chill vents 44 arranged radially and equidistantly from the central part of the cavity 14 operates, and the inside of the mold 10 (especially inside the cavity 14) is evacuated (see Fig. 16). That is, it is simultaneously evacuated by the second vacuum device 40 from the vacuum device connection parts 40a to 40d (four places) provided radially and equidistantly from the central part of the cavity 14 (second vacuum stage). For example, when the above Al alloy molten metal for casting is used, the vacuum time is preferably set within the range of 0.1 to 1.6 seconds. Also, the degree of vacuum is preferably set within the range of 50 mbar to 100 mbar. Each chill vent 44 attached to the tip of the cavity 14 further removes air and gas from the casting (aluminum wheel).

[0064] [Step 5] When the molten metal filled in the mold 10 solidifies by cooling, the first mold opening is performed (see FIG. 17). In the first mold opening, the intermediate mold 12 separates from the fixed mold 11 and moves backward, and the space between the fixed mold 11 and the intermediate mold 12 widens. 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.

[0065] [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.

[0066] [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). Also, 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.

[0067] The manufacturing method of the aluminum wheel according to the present invention is characterized by vacuum suction within the mold 10 over two steps (Step 3 and Step 4). In the first vacuum step of Step 3, after pouring the molten metal, by vacuum suction from within the mold 10 (particularly within the injection sleeve 21) with the injection port 21a sealed from the injection sleeve 21, it is possible to prevent air and gas from being entrapped when the molten metal is injected into the cavity 14. In the second vacuum step of Step 4, by suddenly performing vacuum suction from the four vacuum device connection parts (40a, 40b, 40c, 40d) radially and equidistantly positioned from the central part of the cavity 14, the molten metal flowing in from the gate 12c (the central part of the cavity 14) is uniformly filled within the cavity 14.

[0068] In this way, by performing vacuum suction on a predetermined part at a predetermined timing, it is possible to efficiently and effectively remove the air and gas contained within the mold 10 and the molten metal. Thereby, even in the die-casting method, it is possible to manufacture a casting (aluminum wheel) with good internal quality.

[0069] The manufacturing method of the aluminum wheel of the present invention enables the production of an aluminum wheel with sufficient strength and toughness by highly productive die-casting. Also, even if the cross-sections of the spokes and rims of the aluminum wheel are made smaller, the required strength can be maintained, so the lightness of the entire aluminum wheel can be improved. Furthermore, since heat treatment after die-casting is not performed, productivity can be further improved. Therefore, the manufacturing method of the aluminum wheel of the present invention enables the enhancement of productivity while ensuring the strength, toughness, and lightness of the aluminum wheel.

[0070] Note that 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 gist of the present invention. Also, the shape of the aluminum wheel (casting) manufactured by the manufacturing method of the aluminum wheel according to the present invention is not limited to the embodiment.

[0071] 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 a position different from the positions shown in FIGS. 13 to 15, or there may be a plurality of vacuum device connection parts.

[0072] 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 at equal intervals radially from the central part of the cavity 14, they may be positions different from the four locations (44a, 44b, 44c, 44d) shown in FIGS. 20 and 21, or there may be four or more vacuum device connection parts.

[0073] In the method for manufacturing an aluminum wheel according to the present invention, it is more preferable to use the above Al alloy for casting. By using the above Al alloy for casting, the strength, toughness, and light weight of the casting (aluminum wheel) can be further improved. Note that the Al alloy for casting and the molten metal used in the method for manufacturing an aluminum wheel of the present invention are not limited.

Explanation of reference numerals

[0074] 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~40d Vacuum device connection part 41 Vacuum passage 42 Vacuum tank 43 Vacuum pump 44 Chiller vent 50 Runner cutting slide 51 Biscuit

Claims

1. A method for manufacturing an aluminum wheel including a die-casting process, comprising: In the casting process, After pouring the Al alloy molten metal into the mold, a first vacuum stage of vacuum-sucking the inside of the mold from an injection sleeve with the pouring port sealed; After the first vacuum stage, a second vacuum stage of vacuum-sucking the inside of the mold from a cavity in which the aluminum wheel is formed; Including In the second vacuum stage, a plurality of Vacuum device connection parts located at equal intervals radially from the central part of the cavity are simultaneously vacuum-sucked; A method for manufacturing an aluminum wheel.

2. Not performing heat treatment after the casting process, The method for manufacturing an aluminum wheel according to Claim 1.

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