JP4134876B2 - Vehicle wheel and casting apparatus thereof - Google Patents

Description

  The present invention relates to a vehicle wheel that is cast by a low-pressure casting apparatus having a plurality of gates including side gates and is entirely formed of a light alloy such as an aluminum alloy, and the casting apparatus.

As a vehicle wheel mounted on an automobile (passenger car or the like), in order to reduce the weight of the vehicle body, for example, an aluminum wheel formed entirely of an aluminum alloy by a low-pressure casting technique is used. The aluminum wheel is composed of a rim portion on which a tire is mounted, a disk portion mounted on an axle, and a cross portion that forms a portion where both intersect. Various methods have been put to practical use as a casting method for this aluminum wheel. Recently, for example, a casting method in which pouring from a multi-gate including side gates described in Patent Document 1 and Patent Document 2 has attracted attention. Has been. According to this casting method, a wheel material having a rim portion, a disc portion and a cross portion is cast by pouring from a side gate provided in the rim portion forming cavity and a center gate provided in the disc portion forming cavity. By removing the non-product part including the side gate from the aluminum wheel, an aluminum wheel is manufactured. According to this casting method, since the disk portion is thinned and directional solidification from the rim portion toward the disk portion is performed, there is an advantage that a light weight wheel can be obtained. Moreover, in addition to being lightweight, vehicle wheels including aluminum wheels are required to satisfy predetermined safety standards, so that they have a predetermined mechanical strength through impact tests and rotational bending tests. Confirmed to be shipped. Even if these tests are passed, if there is a minute casting defect inside the wheel, it may not be detected, and in order to guarantee higher safety, casting of each part of the wheel Considering the organization and adopting a casting strategy that meets certain relationships. For example, Patent Document 3 focuses on dendrite arm spacing (hereinafter referred to as DASII) as an indication of the size of the microstructure of a casting, and the knowledge that the smaller the DASII, the finer the structure and the higher the mechanical strength. (1) DASII of the rim barrel> DASII of the rim tip, (2) DASII of the center of the disc> DASII of the disc support, and (3) DASII of the rim barrel and rim support are the same or It is described that by setting DASII of the rim trunk portion> DASII of the rim support portion, an aluminum wheel satisfying safety can be obtained in terms of vehicle safety.
JP 2000-254766 A (page 3-5, FIG. 1) JP 2001-287014 A (page 2-3, FIG. 1) Japanese Patent No. 2817925 (page 3-5, FIG. 1)

  Aluminum wheels also have a wide range of diameters, and the casting method (mold shape / structure) varies depending on the diameter. In other words, when casting a large wheel having a diameter of 17 inches or more, the same casting method as that for casting a small diameter wheel does not yield a thin and lightweight cast product, and a casting defect occurs. The mold shape and cooling structure are determined by examining the solidification form. Therefore, when the mold shape and cooling structure are changed, the cast structure of the aluminum wheel also changes, so that safety can be guaranteed even if the relationship described in Patent Document 3 is satisfied for all caliber wheels. Not necessarily. In order to ensure the strength of the large-diameter wheel, it is necessary to increase the cooling speed of the disk surface, and in particular, the strength at the spoke part is required to be high. It is important to optimize the cooling rate at this point. However, simply lowering the lower mold temperature tends to cause casting defects, and there is room for improvement.

  Accordingly, an object of the present invention is to provide a vehicle wheel having a large diameter, a light weight and high mechanical strength using a side gate.

As described above, in order to ensure the strength of the large-diameter wheel, it is necessary to increase the cooling rate of the disk surface part, but the volume of the molding space is small at the part facing the window part of the rim part. Therefore, the cooling rate is faster than other portions of the disk portion such as the spoke portion. As a result, the cooling rate of the rim part in the part away from the side gate along the circumferential direction is slower than the rim part in the part facing the window part, and directional solidification along the circumferential direction of the rim is not performed, It was found that casting defects such as shrinkage nests occurred. This phenomenon becomes more prominent as the distance from the side gate increases.
Therefore, the present inventors have intensively studied a casting method for realizing optimal directional solidification, and as a result, found that directional solidification toward the side gate can be realized by partially delaying solidification at the cross portion. The present invention has been conceived.
That is, the present invention includes a rim portion on which a tire is mounted, a disk portion mounted on an axle, and a cross portion that forms a portion where both intersect, and a vehicle wheel cast in a molding space connected to at least a pair of side gates. The vehicle wheel is manufactured by a casting apparatus having a structure that keeps heat from the side of the shoulder of the cross portion over a range of 10 ° to 60 ° to the left and right along the circumferential direction from the side gate, and the outer periphery of the cross portion. DASII (D _O ) on the side has a value equal to or greater than DASII (D _i ) on the inner periphery side, and the position of the side gate and the position farthest from the side gates in the rim portion The difference between D _O and D _i at the intermediate position is larger than the difference between D _O and D _i at the side gate position.

Each DASII is a numerical value measured at three or more positions at equal intervals along a straight line inclined by 45 ° with respect to the central axis of the wheel, and is a cross-sectional view along the window portion of the disk portion shown in FIG. To explain, D _O is the measured value at the outermost peripheral side and the substantially central part of the shoulder of the cross part, and D _i is measured along the direction inclined 45 ° from D _O (the cast surface of the window part). It is a measured value at a depth of 0.5 mm from the surface). To describe in cross-sectional view along the spoke portion of the disk portion illustrated in FIG. 3, the inner circumferential side DASII (D _i) is a value measured at sites along the peripheral circle of the window portion. However, the same tendency can be observed even if measurement is performed along a straight line inclined within a range of 30 to 60 ° with respect to the central axis. As described above, DASII measured on a straight line inclined by a predetermined angle (for example, 45 °) with respect to the central axis of the wheel has a cross portion which is a portion where a casting defect is likely to occur in a casting method using a side gate. This is a numerical value indicating the degree of soundness of the shoulder, and serves as an index indicating that directional solidification has been performed obliquely toward the central axis. In the present invention, D _O is almost equal to D _{i at} the side gate position (H1 in FIG. 2). For example, the difference between D _O and D _i is less than 10 μm. The difference between D _O and D _i at the intermediate position (H ₃ ) between the position of the side gate and the position farthest from the side gates is larger than the difference between D _O and D _i at the side gate position (H ₁ ). It is preferable to have the following value. Furthermore, the difference between D _O and D _i at the position (H ₅ ) farthest from the side gates has a larger value than the difference between D _O and D _i at the side gate position (H ₁ ). , the difference between _{D O} and _{D i} of the in intermediate position preferably has a small becomes a value than the difference between _{D O} and _{D i} in _{(H 3),} for example, the middle position _{(H 3)} is a 10μm or more . Moreover, it is preferable that DASII of the cross part tends to increase as it goes to the outer peripheral side.

  In order to manufacture the vehicle wheel of the present invention, a casting method having a structure in which heat is maintained from the shoulder side of the cross portion over a range of 10 ° to 60 ° to the left and right along the circumferential direction with respect to the side gate is applied. It is preferable. If the range to keep warm is less than 10 °, the directional solidification in the circumferential direction of the rim portion becomes insufficient, and the above DAS distribution cannot be obtained. On the other hand, if the range to keep warm exceeds 60 °, the coagulation time is long. Since the casting cycle time increases, both are inconvenient.

  In the present invention, the value of DASII is the average value (unit: μm) of the distance between a plurality of secondary arms existing on both sides of the main axis in the aluminum alloy structure mainly composed of α-Al dendrite phase. It is shown.

According to the present invention, the DASII of the cross portion that forms a portion where the rim portion on which the tire is mounted and the disk portion that is mounted on the axle intersects has a value that is equal to or greater than the inner peripheral side on the outer peripheral side. By adopting the wheel structure, the quality of the part away from the side gate can be secured while keeping the DASII of the disk surface small, and as a result, a lightweight vehicle wheel with a large diameter and a thin wall thickness is obtained. be able to. In addition, since the casting method of keeping the temperature from the shoulder side of the cross portion over the range of 10 ° to 60 ° to the left and right along the circumferential direction with the side gate as a reference, the directivity in the circumferential direction of the rim portion is applied. Solidification can be realized.

  Details of the present invention will be described below with reference to the accompanying drawings. 1 is a cross-sectional view of a mold apparatus used in the present invention, FIG. 2 is a cross-sectional view taken along line AA of FIG. 1, FIGS. 3 and 4 are cross-sectional views schematically showing main portions of an aluminum wheel, FIG. These are figures which show DASII distribution of a cross part.

  In FIG. 1, reference numeral 1 denotes a low pressure casting mold, which includes a lower mold 11 and an upper mold 12 having surface shapes corresponding to a wheel design, horizontal molds 13 a and 13 b that are fitted to form a molding cavity 14, and a lower mold 13 A base 15a for fixing the mold 11 and a base 15b for supporting the upper mold 12 are provided. The cavity 14 includes a disk part cavity 14a and a rim part cavity 14b, and each cavity communicates with a molten metal supply part via a gate (pouring gate). In other words, the rim cavity 14b communicates with the stalks 18a and 18b connected to the molten metal holding furnace (not shown) via the side gates 16a and 16b. The side gates 16a and 16b are arranged so as to exist at symmetrical positions with respect to the wheel shaft center (see FIG. 2). The disk portion cavity 14a communicates with a stalk 18c connected to a holding furnace (not shown) via a center gate 17. Although not shown, in order to realize the directional solidification in the circumferential direction of the rim portion, means for delaying the solidification of the cross portion of the rim cavity 14a, 14b is provided in the mold 1. . In order to keep the upper part of the cloth warm and delay the solidification of the part, for example, a heat retaining means or a heating means is provided in a part of the horizontal molds 13a and 13b, or the rim cavities 14a and 14b are provided on the upper part of the cross part. What is necessary is just to make it the shape which added.

  According to the mold apparatus 1, low pressure casting is performed as follows. After the molten metal in the holding furnace is pressurized and the stalks 18a and 18b are raised, the molten metal is injected from the side gates 16a and 16b into the molding cavity 14, and then filled into the rim cavity 14b. The molten metal that has risen through the continuous stalk 18c is filled from the center gate 17 into the disk portion cavity 14a. After the predetermined time has elapsed, the molten metal remaining in the stalks 17a, 17b, and 17c is returned to the holding furnace by releasing the pressurization. The molten metal injected into the cavity 14 undergoes directional solidification from the inner flange side (upper end portion of the rim portion) to the outer flange side (lower end portion of the rim portion), and then along the circumferential direction of the outer flange portion. Solidification is performed to form a disk portion. In this casting process, the mold is opened after solidification is completed, and the cast product (wheel material) shown in FIG. 2 is taken out. After the non-product parts (side gate parts 16a and 16b) are removed from the wheel material, the design surface is processed, hermetic inspection, and surface treatment (painting) is applied, and the aluminum wheel has the shape shown in FIGS. Is obtained. FIG. 3 is a longitudinal sectional view along the center of the spoke portion, and FIG. 4 is a longitudinal sectional view along the center of the window portion. The aluminum wheel 20 includes a disk-shaped disk portion 21 attached to an axle (not shown), a rim portion 22 to which a tire (not shown) is attached, and an inner flange portion 23 formed on the upper end side thereof. The outer flange portion 24 formed at the lower end portion of the rim portion 22 and the cross portion 25 serving as a portion where the disc portion 21 and the rim portion 22 intersect. The shoulder portion 26 of the cross portion is a portion of a surface substantially parallel to the design surface formed on the outer peripheral surface of the cross portion.

A molten metal (about 450 ° C.) of an Al—Si—Mg-based alloy (corresponding to an AC4CH material defined in JIS H 5202) is injected into a mold (about 450 ° C.) shown in FIG. The wheel material shown in FIG. 2 was produced by casting at 0.063 MPa. The mold used here is provided with heat retaining means adjacent to the outer peripheral side of the cross portion on the horizontal molds 13a and 13b, and the heat retaining means is in a range of 45 ° along the circumferential direction on both sides of the side gates 16a and 16b. The configuration was positioned. The non-product part including the side gate is removed from the wheel material, and the aluminum wheel 20 having _five spokes S _{1 to} S ₅ arranged at equal intervals in the circumferential direction on the disk part 21 (see FIG. 2, For 18 inches). With respect to the aluminum wheel 20, the disk portion 21 and _five portions (H _{1 to} H ₅ , equiangular intervals) immediately below the side gate 16 a along the circumferential direction and to a position spaced by 90 ° in the counterclockwise direction therefrom. DAS II was measured at five locations (C _{1 to} C ₅ , a direction inclined by θ = 45 ° with respect to the central axis) from the inner periphery side to the outer periphery side of the cross portion 25 at the portion where the rim portion 22 intersects. . The result is shown in FIG. 5, each curve shows equi DASII line, the area under the curve _{D 1} is DASII = 30~35μm, the area between the curves _{D 1} and curve _{D 2} is DASII = 35~40μm, curve _{D 2} a region between the curve _{D 3} is DASII = 40~45μm, the outer region of the curve _{D 3} is DASII = 45~50μm.

From FIG. 5, DASII of the cross part 25 shows an equivalent value on the outer peripheral side (C ₅ ) and inner peripheral side (C ₁ ) at the side gate position (H ₁ ) (the difference between the two is less than 10 μm), At the position (H ₅ ) farthest from the side gate, the difference becomes large, and at these intermediate positions (H ₃ ), the value of DASII is the difference between the inner peripheral side (C ₁ ) and the outer peripheral side (C ₅ ). Is considerably large (the difference between the two is 10 μm or more). In all the circumferential positions (H _{1 to} H ₅ ), DAS II increases from the inner peripheral side (C ₁ ) to the outer peripheral side (C ₅ ). Such distribution of DASII is such that directional solidification from the inner flange side (upper end portion of the rim portion 22) toward the outer flange side (lower end portion of the rim portion 22) is performed, and then along the circumferential direction of the outer flange portion. It is assumed that the disk portion 21 is formed by performing directional solidification. When such a two-stage directional solidification is performed, as a natural result, the DASII of the rim portion 22 has a lower value at the rim upper end than the value at the rim lower end, and at the rim lower end, There is no significant difference in the DAS II value between the vicinity of the gate and the position away from it, but the DAS II value tends to decrease as the distance from the side gate increases at the upper end of the rim.

  When casting an aluminum wheel using the mold shown in FIG. 1, the above two-stage directional solidification is performed by adopting a cooling structure provided with means for delaying solidification of a specific portion, so that a casting defect occurs. Even so, as shown in FIGS. 2 and 3, the spoke S <b> 2 and the rim portion 22 are present closer to the casting surface than the region B on the outer peripheral side of the cross portion 25. Therefore, by providing the DASII distribution of the present invention, casting defects can be easily removed by processing after casting. On the other hand, as practiced by the conventional casting method, for example, when pouring from only the center gate, casting is performed on the inner peripheral side region (shown by A in FIG. 2) at the lower end portion of the rim portion 22 that becomes the product portion. Since defects occur, it is necessary to increase the thickness of the rim portion and to remove the casting defects by processing after casting, which is accompanied by a problem that the casting yield is lowered.

It is sectional drawing which shows an example of the die apparatus for casting used by this invention. It is the sectional view on the AA line of FIG. It is a cross section which shows the principal part of an aluminum wheel typically. It is a cross section which shows the principal part of an aluminum wheel typically. It is a figure which shows DASII distribution of a cross part.

Explanation of symbols

1: Low pressure casting mold, 11: Lower mold, 12: Upper mold, 13a, 13b: Horizontal mold, 14: Cavity, 14a: Disk part cavity, 14b: Rim part cavity, 15a, 15b: Base, 16a, 16b: Side gate, 17: Center gate, 18a, 18b, 18c: Stoke 20: Aluminum wheel, 21: Disc part, 22: Rim part, 23: Inner flange part,
24: Outer flange part, 25: Cross part, 26: Shoulder part

Claims (5)

A vehicle wheel comprising a rim portion on which a tire is mounted, a disk portion mounted on an axle, and a cross portion forming a portion where both intersect, and is cast in a molding space connected to at least a pair of side gates . The wheel is manufactured by a casting apparatus having a structure that keeps heat from the shoulder side of the cross part over a range of 10 ° to 60 ° on the left and right sides along the circumferential direction from the side gate , and DASII (D _O) is have a similar to or larger than the value DASII the inner circumferential side (D _i), and, D at the intermediate position of the farthest from the side gates and position of the side gate at the rim portion the difference between the _O and D _i are vehicle wheel being larger than the difference between D _O and D _i at the position of the side gates. In the rim portion, the difference between D _O and D _i at the position farthest from the side gates has a value greater than the difference between D _O and D _i at the position of the side gate, and the intermediate vehicle wheel according to claim 1, than a difference between D _O and D _i at the position wherein the small again. In the rim portion, claim 1 difference D _O and D _i is the position of the side gate is less than 10 [mu] m, and in the intermediate position, wherein the difference between D _O and D _i is 10 [mu] m or more Or the vehicle wheel according to 2. 2. The vehicle wheel according to claim 1, wherein the DAS II is measured at three or more locations of the cross portion and increases from the inner peripheral side toward the outer peripheral side. A casting apparatus for a vehicle wheel, having a cavity for forming a cross part forming a portion where the rim part and the disk part intersect, and at least a pair of sides provided in the cavity for forming the rim part A casting apparatus comprising a gate and provided with means for keeping heat from the shoulder side of the cross portion over a range of 10 ° to 60 ° on the left and right sides along the circumferential direction from the side gate.

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