JP4311674B2 - Vehicle wheel - Google Patents

Description

  The present invention relates to an aluminum alloy vehicle wheel obtained, for example, by low pressure casting in a mold cavity.

  There are various materials and structures for automobile road wheels, but the ratio of mounting aluminum wheels is increasing for the purpose of reducing the weight of automobiles and improving the appearance and design. This aluminum wheel is usually manufactured by a low pressure casting method. That is, in the low pressure casting method, the molten metal is filled into the mold cavity at a low speed, so that gas entrainment and oxide generation are suppressed as much as possible as compared with other casting methods.

  In general, the aluminum wheel 30 has a thick hub part 31 attached to an axle by bolts and nuts as shown in FIG. 4, a disk part 33 composed of a design part 32 in which a thick part and a thin part are mixed, and a tire attached. The thin rim portion 34 is formed. In FIG. 4A, 35 is a front flange portion, 36 is a rear flange portion, 37 is an outer peripheral portion of the design portion, and 38 is a rim center portion. In FIG. 4 (b), 39 is a spoke part, 39 'is a design hole. From the viewpoint of improving the fuel efficiency of vehicles, weight reduction by changing the shape of the wheel has been studied. In this case, the hub part and the rim part cannot be remarkably changed in terms of handling with the vehicle body or the tire, so the shape change of the design part (for example, the area of the design hole is increased or the spoke part is thinned). However, it is extremely difficult to reduce the weight significantly.

  When the wheel is manufactured by low-pressure casting, a pouring gate is provided in the hub portion 31 and molten metal is poured therefrom, and the design portion 32 and the rim portion 34 and the molten metal are poured in this order (center gate method) or the end of the rim portion. A method (side gate method) in which a plurality of (usually two) gates are provided in the portion (outer peripheral portion 37 of the design portion) and molten metal is injected therefrom is adopted. In the center gate method, directional solidification is performed in the order of the rim portion, the design portion, and the hub portion in order to sufficiently exhibit the effect of the hot water pouring as a solidification form after filling the molten metal. However, in this casting method, the design part has a complicated shape in which a thick part and a thin part are mixed, so that it is difficult to achieve directional solidification from the rim part to the disk part. On the other hand, in the side gate method, the design part itself functions as a molten metal replenishment passage to the hub part that is easily solidified, so that the design part is thick in order to ensure a good hot water flow in the design part. Even with this method, it is difficult to significantly reduce the weight of the entire wheel.

In order to eliminate the above-mentioned drawbacks of the conventional method, it has been proposed to provide pouring gates at the center of the disk (hub portion) and the rim, respectively, and to pour molten metal from these pouring gates into the mold (for example, Japanese Patent Laid-Open No. Hei 5- 269563, 6-269923). According to this casting method (3-gate method), directional solidification from the rim portion toward the disc portion can be achieved even if the thickness of the design portion is reduced, so that the weight of the wheel can be significantly reduced. Although the light weight aluminum wheel can be obtained by the above-described three-gate method, it is difficult to determine whether or not the aluminum wheel satisfies a predetermined safety standard. As an index indicating the safety of an aluminum wheel, it is common to use an impact value and rotational bending strength. Aluminum wheels are usually made of an Al-Si-Mg alloy, and α-Al dendrite crystals crystallize inside the cast product. By measuring dendrite arm spacing (hereinafter referred to as DAS), the aluminum wheel can be evaluated. It has been proposed to do. For example, in Japanese Patent Laid-Open No. 2-147401, attention is paid to a DAS measurement value as an index indicating the safety of an aluminum wheel, a DAS measurement value at the front end of the rim on the non-disk side <a DAS measurement value at the rim body, a disc center Satisfies safety standards by satisfying the following three conditions: DAS measurement value of disk> DAS measurement value of rim bearing part of disk part and DAS measurement value of rim bearing part of disk part ≤ DAS measurement value of rim body part It is said that an aluminum wheel can be obtained.
JP-A-5-269563 ((0014) to (0019), FIG. 1) JP-A-6-269923 ((0012) to (0014), FIG. 3)

  However, just because the above three conditions are satisfied, the aluminum wheel does not necessarily satisfy the safety standard. Simply defining the magnitude relationship between the DAS measurement values of the rim portion and the disk portion in one section does not guarantee the safety of the aluminum wheel.

  Accordingly, an object of the present invention is to provide a vehicle wheel that is high in strength and light in weight.

In order to achieve the above object, in the present invention, a height difference is provided in the height of the gate between the center gate and the side gate, and the side gate is provided at a position avoiding the rim end to perform low pressure casting. Accordingly, in a vehicle wheel having a rim portion including a rear flange portion and a disk portion including a hub portion and a design portion and cast from an aluminum alloy, a dendrite arm by a secondary technique of an arbitrary longitudinal section including a shaft is used. When the pacing measurement value is measured, the dendrite arm spacing measurement value of the rear flange part is D ₁ , the dendrite arm spacing measurement value of the center part of the rim part is D ₂ , and the dendrite arm spacing measurement value of the outer peripheral part of the design part the D _3, when the dendrite arm spacing measurement of the hub portion and D _4, D _2> D ₃ composed has a relationship, and longitudinal section of the 90 ° apart regions from the regions in the longitudinal section of the region where the gate is present _D 3> together with the _{D 2} the relationship, the _{D 4} and _{D 3} over the entire circumference D in > Has a D ₃ the relationship, to obtain a vehicle wheel is not generated cold shuts the design surface. In the present invention, measurement of DAS (Dendrite Arm Spacing) was performed using a secondary technique. In the secondary technique, the interval between secondary arms of dendrites grown on both sides of the main axis in the microstructure of the aluminum alloy casting is obtained as a DAS measurement value, and the intervals between the secondary arms included in the intervals are included in the secondary. It is calculated as a value (μm) divided by the number of arms.

  As described above, according to the present invention, a DAS measurement value in an arbitrary longitudinal section including an axis has a specific distribution, so that a vehicle wheel having a complete design surface, high strength and light weight can be obtained. Can do.

Hereinafter, the details of the present invention will be described with reference to the drawings. For example, when the DAS of the arbitrary longitudinal section including the shaft is measured for the aluminum wheel cast by the above-mentioned three-gate method, the distribution of the DAS measurement value due to the difference in solidification rate between the part with the gate (pouring gate) and the part without it. Is different. In the aluminum wheel of FIG. 4, the DAS measurement value of the rear flange portion 36 is D ₁ , the DAS measurement value of the rim center portion 38 is D ₂ , the DAS measurement value of the outer peripheral portion 37 of the design portion 32 is D ₃ , and the hub portion 31. When the DAS measurements and D _4, DAS measurements of region a gate there becomes a curve X in FIG. 1, DAS measured value of the gate is not the region b is a curve Y in FIG. That is, in region a, D ₂ ≧ D ₃ , and in region b approximately 90 ° away from region a, D ₃ ≧ D ₂ > D ₁ . Further, over the entire circumference, D ₄ and D ₃ have a relationship of D ₄ > D ₃ , and the difference between D ₄ and D ₃ may be 15 μm or less. D ₁ and D ₃ are 35 μm or less over the entire circumference, but are preferably 30 μm or less from the viewpoint of mechanical strength, and are preferably 20 μm or more in consideration of ease of manufacture. In particular, D ₃ is more preferably 25 μm or more. In the present invention, by cooling the lower mold with water, the DAS measurement value in the region a having the gate becomes a curve X 'in FIG. 2, and the DAS measurement value in the inner region b having no gate is the curve Y in FIG. 'become that way. That is, in the region a, D ₂ > D _{3 is} satisfied, and in the region b that is approximately 90 ° away from the region a, D ₃ > D ₂ > D ₁ is satisfied. Further, over the entire circumference, D ₄ and D ₃ have a relationship of D ₄ > D ₃ , and the difference between D ₄ and D ₃ may be 15 μm or less. D ₁ and D ₃ are 35 μm or less over the entire circumference, but are preferably 30 μm or less from the viewpoint of mechanical strength, and are preferably 20 μm or more in consideration of ease of manufacture. In particular, D ₃ is more preferably 25 μm or more. The present invention is not limited to the aluminum wheel having the design shape shown in FIG. 4, and for example, an aluminum wheel having a symmetrical design hole as shown in FIGS. 5A and 5B or an aluminum wheel having a mesh-like design. Of course, it can also be applied. The aluminum wheel having the above-described distribution of DAS measurement values can be cast by, for example, the apparatus shown in FIG. FIG. 3 is a sectional view showing a main part of a casting apparatus for carrying out the present invention. In FIG. 3, reference numeral 1 denotes a mold, which is a cavity formed by fitting the lower mold 2 having various surface shapes corresponding to the wheel design, the upper mold 3 positioned above the lower mold 2, the lower mold 2 and the upper mold 3. Horizontal molds 4 and 5 are provided so as to form 6. The lower mold 2 is installed on a lower mold base 8 fixed to the lower mold platen 7. The upper die 3 is fixed to the upper die base 9 with bolts 10. The cavity 6 includes a disk part cavity 60 and a rim part cavity 61. The cavity 60 includes a hub part cavity 62 and a design part cavity 63. The cavity 61 includes a peripheral part cavity 64 and a central part cavity 65 of the design part. The hub cavity 62 and the outer peripheral cavities 64 and 64 of the design section are formed with gates 11a, 11b and 11c, respectively, and the gates communicate with the stalks 13a, 13b and 13c via the runners 12a, 12b and 12c. ing. The gates 11b and 11c are arranged symmetrically on both sides of the gate 11a as viewed from above, that is, the centers of the gates are located on the same straight line. The lower end portions of these stalks are inserted into a sealed container (not shown) in which the molten metal is accommodated. The lower mold 2 is provided with the lower mold cooling passage 14 at a position corresponding to the design portion cavity 62.

  The operation of the above configuration will be described. First, by pressurizing the molten metal in the sealed container, the molten metal is filled into the cavity 6 from the gates 11a, 11b and 11c through the runners 12a, 12b and 12c from the stalks 13a, 13b and 13c. Here, since there is a height difference between the gate 11a and the gates 11b, 11c, the molten metal passing through the gate 11a fills the design portion cavity 63, and the molten metal passing through the gates 11b, 11c enters the rim portion cavity 61. Fill. That is, the molten metal joins at the rim cavity 61. When the pressurization is released after a lapse of a predetermined time, the molten metal in each stalk returns to the sealed container, and the molten metal in the cavity 6 is solidified to obtain the wheel shown in FIG.

  It is as follows when the solidification process of the molten metal in said casting process is explained in full detail. The molten metal poured into the cavity 6 from the gates 11b and 11c (side gates) is solidified from the upper end of the rim portion cavity 65 toward the lower end thereof. On the other hand, the molten metal injected from the gate 11a (center gate) into the disk portion cavity 60 is solidified from the design portion cavity 63 toward the hub portion cavity 62. In this way, directional solidification is reliably performed. Therefore, it is not necessary to provide the design portion cavity 63 with a hot water flow function or a molten metal replenishment function, and the wheel design portion can be made thinner in terms of the casting method. In addition, since the solidification starts from the design part, the structure of the design part becomes fine and high strength can be maintained. Moreover, in the apparatus of FIG. 3, since the side gates (pouring gates 11b and 11c) are provided at a position avoiding the rim end, the structure of a portion requiring high strength such as the front flange or the center of the rim becomes fine. From the viewpoint of strength, the design part can be made thinner.

  Further, in the apparatus of FIG. 3, since there is a difference in height between the center gate and the side gate as described above, the molten metal merges at a position (rim portion) away from the design portion, thereby obtaining a complete design surface. be able to. Of course, according to the present invention, the flow length from each gate is shortened and the solidification time is shortened, so that there is an effect of improving productivity such as shortening of the casting cycle time.

  In the above description, the side gate is provided at a position above and in contact with the outer peripheral cavity 64 of the design part, but may be provided at a position away from the outer peripheral cavity 64 of the design part. However, it is inconvenient if a side gate is provided at the end of the rim cavity 61 or the side surface of the outer peripheral cavity 64 of the design portion because a hot water boundary is generated on the design surface.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.
Example 1 Using a casting apparatus shown in FIG. 3, a molten Al-Si-Mg-based alloy (JIS AC4CH) (about 450 ° C.) was poured into a mold (heated to about 480 ° C.) (pressure 0 0.5 to 0.7 kg / cm ² ), an aluminum wheel having the shape shown in FIG. 4 was cast.
(Example 2) An aluminum wheel having the design shape shown in Fig. 5 (a) was cast under the same conditions as in Example 1.
Example 3 An aluminum wheel having the design shape shown in FIG. 5B was cast under the same conditions as in Example 1.
Comparative Example 1 An aluminum wheel having the shape shown in FIG. 4 was cast under the same conditions as in Example 1 except that the molten metal was injected into the mold only from the side gate. As a result of measuring DAS measurement values for the aluminum wheels of the above examples, all the wheels of Examples 1 to 3 were distributed as shown in FIG. In addition, the design of each wheel was visually observed for the presence of a hot water boundary and subjected to an impact test. The results are shown in Table 1. Also, the weight of each aluminum wheel was measured, and the results (however, the ratio is shown by the ratio when Comparative Example 1 is 1) are also shown in Table 1.

  From Table 1, it can be seen that according to the low pressure casting method of the 3 gate method (Examples 1 to 3), the aluminum wheel can be reduced by 10% or more than the side gate method (Comparative Example 1). In either case, there is no occurrence of a hot water boundary in the design, and the result of the impact test is also good.

It is a figure which shows DAS measurement value distribution of the aluminum wheel which concerns on one Example of this invention. It is a figure which shows DAS measurement value distribution of the aluminum wheel which concerns on the other Example of this invention. It is sectional drawing which shows an example of the apparatus for casting the aluminum wheel of this invention. It is the longitudinal cross-sectional view (a) and the top view (b) of an aluminum wheel. It is the schematic (a) and (b) which show the design part of an aluminum wheel.

Explanation of symbols

1 mold, 2 lower mold, 3 upper mold, 4,5 horizontal mold, 6 cavity 11a, 11b, 11c gate, 30 wheel

Claims (1)

It has a rim part including a rear flange part and a disk part including a hub part and a design part, and a pouring hole is provided in a mold cavity for forming the rim part and the hub part to pour molten aluminum alloy. a cast vehicle wheel, when measured dendrite arm spacing value measured by secondary techniques any longitudinal section containing the axis, D ₁ the dendrite arm spacing measurement of the rear flange _portion, the central portion of the rim portion In the longitudinal section of the region where the gate is present, the measured dendritic arm spacing is D ₂ , the measured dendritic arm spacing at the outer periphery of the design portion is D ₃ , and the measured dendritic arm spacing at the hub portion is D ₄ . D _{2> D 3} composed has a relationship, and _{D 3} in the longitudinal section of the 90 ° apart from the region area While have a D ₂ the relationship, vehicle wheel and having a _{D 4} and _{D 3} is _D 4> _{D 3} the relationship over the entire circumference.

Images