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This application claims the benefit of U.S. Provisional Patent Application No. 60/569,787 filed May 10, 2004, hereby incorporated by reference in its entirety.
a. Field of Invention
The invention relates generally to the manufacture of aluminum wheels for automobiles and the like, and more particularly to an improved method of manufacturing aluminum wheels by forging the wheels with a casting blank instead of a raw forging.
b. Description of Related Art
Aluminum automobile wheels are typically manufactured by casting, forging or by spun-rim, flow-forming or rim rolling technology.
Existing casting technologies include, for example, gravity casting and pressure casting. Gravity casting generally involves the process of pouring molten aluminum into a mold utilizing gravity (without any additional pressure) to fill the mold. This casting technique offers reasonable production costs and is acceptable for casting designs that are more visually oriented or where weight reduction and strength is not a primary concern. Since the process relies on gravity to fill a mold, the aluminum is not as densely packed in the mold as compared to other casting or forging processes where increased pressure is used. Due to the limited compaction of the aluminum product, gravity cast wheels often have a higher weight due to the increased thickness requirement for enabling the wheels to achieve the required strength.
In order to achieve the higher strength and lower weight requirements desirable for wheels, compared to the aforementioned gravity casting technique, pressure casting uses positive pressure to move the molten aluminum into the mold to thus provide a denser finished product in a quicker manner as opposed to gravity casting. While the production cost for pressure casting is somewhat higher than the costs associated with gravity casting, and is typically a function of the degree of pressure associated with the process (i.e. the higher the pressure requirement, the higher the associated machinery cost), pressure casting is generally the most common process approved for aluminum wheels sold to the O.E.M. market or to the aftermarket.
Compared to gravity and pressure casting, for the aforementioned spun-rim, flow-forming or rim rolling technology, wheels formed by such technology begin with a low pressure type of casting and use a special machine that spins the initial casting, heats the outer portion of the casting and then uses steel rollers pressed against the rim area to pull the rim to its final width and shape. The combination of the heat, pressure and spinning creates a rim area with strength similar to that of a forged wheel, without the generally higher costs associated with forging.
Lastly, forging is the process of forcing a solid billet of aluminum between forging dies under an extreme amount of pressure to create a finished product that is very dense, very strong and therefore can be very light. The traditional method of manufacturing an aluminum wheel by forging includes the steps of (i) melting, (ii) casting the melt into a cylindrical blank, (iii) homogenizing of the material, (iv) extruding, (v) cutting, (vi) heating, (vii) raw forging, (viii) heating, (ix) primary forge forming, (x) heating, (xi) exact forging, (xii) removal of fins, (xiii) heat treatment, (xiv) fluoroscopy inspection, and (xv) machine forming. In following these fifteen steps, it becomes readily apparent that a great deal of time and material is expended in the traditional forging process.
Compared to the aforementioned casting and rolling processes, the costs of tooling, development and equipment associated with forging make a forged wheel very exclusive and usually demand a significantly higher price in the aftermarket. Further, due to the higher performance requirements for aluminum wheels in today's market, it is also becoming readily apparent that cast or rolled aluminum wheels cannot completely meet all of the high performance requirements.
It would therefore be of benefit to provide a cast forging process for aluminum wheels, which is simpler in operation than the aforementioned traditional forging process, and which provides a wheel product with the same or better performance than wheels made from existing forging technology. It would also be of benefit to provide a cast forging process which is repeatable in operation, which provides a significant reduction in the overall costs associated with the manufacture of a forged wheel, and which is relatively simple to implement.
The invention solves the problems and overcomes the drawbacks and deficiencies of existing cast or rolled aluminum wheel manufacturing technology by providing a cast forging method of manufacturing a disc for an automobile wheel and the like. The method may include the steps of producing a cast disc by low pressure casting, heating the cast disc to its material plasticity temperature, and placing the heated cast disc into a forging mold to forge the disc under high pressure. The method may further include the steps of inspecting the forged disc for defects, and thereafter machining the forged disc to produce a completed disc which may be attached to a rim to product a completed wheel product, as discussed below.
For the method described above, the high pressure may compress the heated cast disc from approximately 5-20 mm. The low pressure may include pressure of approximately 0.1-1 mpa, and the high pressure may include pressure of approximately 500 mpa. The inspection may be performed by fluoroscopy and other known techniques in the art. The machining may include machining of the disc to its final dimensional specifications, and further include machining of assembly fitments, such as hubs, valve stem holes etc. The method may further include attaching the machined disc to a rim to form a wheel by bolts and/or welding. The disc may be formed of an aluminum composition, with an exemplary composition including elements having the following ratio: Si—approximately 6.58%, Mg—approximately 0.3%, Ti—approximately 0.2%, Sr—approximately 0.18%, L—approximately 0.2%, C—approximately 0.2%, Fe—approximately 0.16%, Al—Remainder.
Additional features, advantages, and embodiments of the invention may be set forth or apparent from consideration of the following detailed description, drawings, and claims. Moreover, it is to be understood that both the foregoing summary of the invention and the following detailed description are exemplary and intended to provide further explanation without limiting the scope of the invention as claimed.
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate preferred embodiments of the invention and together with the detail description serve to explain the principles of the invention. In the drawings:
FIG. 1 is a flow chart of the manufacturing steps for a related forging process;
FIG. 2 is an illustration of the various processes associated with the cast forging manufacturing method of the present invention;
FIGS. 3a-e are various illustrations of the forged disc according to the present invention being connected to a spun rim; FIG. 3c being an illustrative cutout view of the disc and rim assembly being connected by bolts; and
FIG. 4 is an illustration of the manufacturing steps for the cast forging manufacturing method of the present invention, including the process from casting blank to raw forging.
Turning now to the drawings wherein like reference characters refer to like and corresponding parts throughout the several views, FIGS. 2-4 illustrate various manufacturing steps and schematics for the cast forging process according to the present invention.
Specifically, referring to FIG. 1, a traditional method of manufacturing an aluminum wheel by forging may include the steps of (i) melting at 10, (ii) casting the melt into a cylindrical blank at 12, (iii) homogenizing of the material at 14, (iv) extruding at 16, (v) cutting at 18, (vi) heating at 20, (vii) raw forging at 22, (viii) heating at 24, (ix) primary forge forming at 26, (x) heating at 28, (xi) exact forging at 30, (xii) removal of fins at 32, (xiii) heat treatment at 34, (xiv) fluoroscopy inspection at 36, and (xv) machine forming at 38.
Generally, the present invention aims to simplify and incorporate the aforementioned first eight steps (i-viii) of manufacturing an aluminum wheel, and directly uses the casting blank to heat and forge. Thereafter, the forged wheel may be machined to reach the product size specifications. Based upon testing performed herein, it has been shown that the cast forged wheel produced by the cast forging process of the present invention includes mechanical properties superior to those of traditionally cast or forged wheels.
Specifically, referring to FIG. 2, the present invention cast forging process may first use low pressure casting to produce a cast disc 40 with a partial rim 42. The low pressure casting may be performed using air pressure field technology with an air pressure range of approximately 0-0.1 mpa (0-1 kg/cm2) as shown at 43. Upon completion of the low pressure casting step, cast disc 40 may then be heated to its plasticity temperature as shown at 44, which is the temperature at which the aluminum material becomes plastically distorted, as is known in the art. Once at the plasticity temperature, cast disc 40 may then be placed into a forging mold 45, where the heated disc is forged under high pressure into the exact desired shape. A screw pressure machine (not shown) capable of approximately 8000 tons of pressure may be used to forge cast disc 40 under high pressure. Depending on the structural and performance requirements of the wheel, the amount of compression for the high pressure step may vary from 5-20 mm as shown at X in FIG. 4. Compared to the aforementioned low pressure casting which uses air pressure of approximately 0.1-1 mpa, the high pressure casting may use the aforementioned screw press to product a piston pressure of approximately 500 mpa. After a predetermined time interval to enable the cast disc to solidify, forged disc 46 may be removed from the mold with the forging press rod.
Forged disc 46 may then be inspected for inner defects using fluoroscopy, which involves the use of X-rays to carry out the inspection of the forged disc, as is known in the art. It should be noted that other inspection techniques known in the art may be used for inspection of the forged disc, without departing from the scope of the present invention.
If no inner defects are found in forged disc 46, the disc may be heat treated according to its material properties to improve its machining properties. Thereafter, the heat treated disc may be machined to the required wheel size specifications. The machining may include machining of assembly fitments such as the hub, valve hole and bead seat, while taking into account parameters such as offset, pitch circle diameter to automobile and tire installation requirements.
In order to form a completed wheel, a wheel rim 48 may be formed by conventional spinning stroke rotary formation, which involves the spinning of an aluminum plate in a spinning stroke rotary formation mold. It should be apparent that other methods may be used for rim formation without departing from the scope of the present invention. For example, an aluminum tube may be simply cut off to form the rim, or an aluminum plate may be rolled and then welded to form a rim.
Referring next to FIGS. 3a-e, once the spun wheel rim 48 is formed, forged disc 46 and spun wheel rim 48 may be connected together by bolts 50 for ensuring balanced performance for the wheel assembly, as is known in the art (see FIGS. 3a-c). It should be noted that other methods known in the art may be used for connecting disc 46 to rim 48, as would be apparent to those skilled in the art. For example, disc 46 may be connected to rim 48 by welding and the like, which would provide a yet further lighter wheel product. In addition to the bolts, the forged disc and spun wheel rim may be bonded together by using a conventional sealing gum (i.e. an hermitic glue at 49) for preventing leakage of air between the disc and the rim upon tire installation. Once assembly of wheel 52 is completed, the wheel may be inspected as shown in FIG. 3(d), and thereafter prepared for delivery as shown in FIG. 3(e).
In order to meet the performance criterion for forged wheels, the aluminum material used for the cast forging process of the present invention may use a special chemical composition for facilitating the casting process and for enabling the finished wheel product to meet the required forging performance. The alloy material may be composed of Al—Si—Mg and other elements in the following ratio (Si—6.58%, Mg—0.3%, Ti—0.2%, Sr—0.18%, L—0.2%, C—0.2%, Cu 0.0%, Sb-0.0%, Fe—0.16%, Al—Remainder). By using this composition of material, a wheel product produced by the cast forging process of the present invention is able to meet and/or exceed the strength, weight and performance requirements of today's forged wheels.
Based upon the cast forging process discussed above, the forged aluminum wheel of the present invention also provides several distinct benefits over wheels formed by conventional casting, rolling or forging techniques. For example, compared to the traditional forging process which requires the manufacturing steps of (i) melting, (ii) casting the melt into a cylindrical blank, (iii) homogenizing of the material, (iv) extruding, (v) cutting, (vi) heating, (vii) raw forging, (viii) heating, (ix) primary forge forming, (x) heating, (xi) exact forging, (xii) removal of fins, (xiii) heat treatment, (xiv) fluoroscopy inspection, and (xv) machine forming, the cast forging process of the present invention eliminates several of the aforementioned manufacturing steps, which results in a significant reduction in the machining time, increase in metal material usage, and reduction in the overall manufacturing and end-product cost by as much as 40%. Since the present invention uses the casting blank as the raw material for forging, this use provides unlimited design freedom for the disc. Because of the use of the Al—Si—Mg composition of the present invention in combination with the cast forging process disclosed herein, the invention provides an improved wheel product having fewer defects, such as pin holes and the like. Further, because of the use of the Al—Si—Mg composition of the present invention in combination with the cast forging process disclosed herein, the aluminum wheel product can achieve up to 10% elongation even in the region of the hub and have a tensile strength of up to 250 N/mm2, thus providing a superior wheel product as required for today's automobiles.
As discussed throughout the description, various modifications may be made to the cast forging steps discussed above, without departing from the scope of the present invention. For example, while the forged disc is described as including a partial rim and being attached to a spun rim, it is conceivable that the forged disc may be produced with or without a partial rim for enabling attachment to a rim. Additionally, while the present invention describes a method of producing a cast forged disc, those skilled in the art would readily appreciate in view of this disclosure that the present invention manufacturing process is not restricted to use with a wheel disc, but may be used with any conceivable product which may be forged.
Although particular embodiments of the invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those particular embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.