60/044,510, filed on April 21, 1997.

BACKGROUND OF THE INVENTION This invention relates in general to vehicle wheels and in particular to a process for forming a wheel component by forging a near net casting of the component.

It is known in the art to cast vehicle wheel components, such as, for example, full face wheel discs, from alloys of light weight metals, such as aluminum, magnesium and titanium. The casting process typically is highly automated with multi-piece wheel molds which are mounted upon a rotating carousel. The carousel is indexed past a charging station. At the charging station, each wheel mold is filled with molten metal by a conventional gravity or low pressure casting process. As the molten metal cools, it solidifies to form a wheel component casting. The mold is opened and the casting removed. The casting is then quenched and heat treated. The heat treated wheel component casting is machined to final shape. Similarly, a complete one piece wheel can be cast. The one piece wheel casting is heat treated and then machined at a number of finishing stations to a final shape. Typical machining operations for finishing a wheel component or complete wheel casting include tuming, facing and boring.

Altemately, the wheel component can be forged. A typically forging operation involves a plurality of die sets. Each die set is used sequentially during successive forging operations and more closely approaches the final shape of the

component. During a forging operation, a disc shaped metal billet is heated to a temperature near the melting temperature of the metal. The billet is inserted between an open first set of dies, which are closed upon the billet. The billet is squeezed between the dies under high pressure and the metal is plastically deformed to fill any voids between the die set members. The dies are opened and the partially shaped forging moved to a second set of dies and the process repeated. The forging removed from the second set of dies more closely approaches the desired shape of the wheel component. The forging operation is repeated with successive sets of dies until the final shape of the component is achieved. It may be necessary to reheat the forging before pressing between successive die sets. Machining of the final forging is usually required; however, less machining is typically required for a forging than for a casting.

SUMMARY This invention relates to a process for forging a wheel component from a near net casting of the component.

As described above, a vehicle wheel component can be cast and the casting machined to final shape. Due to dimensional variations caused by the shrinking of metal during the casting process, it is necessary to cast a component oversize and machine the casting to a final shape. Such machining is time consuming and costly. Alternately, a wheel component can be forged to reduce the amount of required machining. However; forging requires a number of die sets which progressively shape the component. Such die sets are expensive.

Additionally, the successive multiple forging operations are time consuming.

Furthermore, a complete set of dies is required for each wheel design.

Thus, it would be. desirable to develop a process which reduces the amount of time required to form a wheel component.

The present invention contemplates a process for forming a wheel component which includes casting the wheel component to a near net size of the desired finished component shape. The casting is then placed into a single set of dies and the die set closed to forge the near net casting into the wheel component. Subsequent to the forging operation, the wheel component can be optionally machined to a final shape.

In the preferred embodiment, the wheel component is full face a wheel disc and the process can further include forming a partial wheel rim and attaching the wheel rim to the full face wheel disc to form a wheel assembly.

The partial wheel rim is attached to the full face wheel disc with a continuous circumferential air-tight weld. Additionally, the process can include forming at least one lightener pocket in the wheel disc which extends beneath the outboard tire bead seat.

Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a flow chart of a process for forming a two piece vehicle wheel in accordance with the invention.

Fig. 2 is a sectional view of a mold for casting a near net wheel disc.

Fig. 3 is a sectional view of a near net casting of a wheel disc formed in the mold shown in Fig. 2 placed in an open die set for the process illustrated in Fig. 1.

Fig. 4 is a sectional view of the die set shown in Fig. 3 in a closed position for forging the near net casting into a wheel disc.

Fig. 5 is a sectional view of a two piece wheel which includes the wheel disc shown in Fig. 3.

Fig. 6 is a sectional view of an alternate embodiment of the mold shown in Fig. 2.

Fig. 7 is a sectional view of an alternate embodiment of the die set shown in Fig. 3 and a near net casting of a wheel disc formed in the mold shown in Fig.

6.

Fig. 8 is a sectional view of the die set shown in Fig. 7 in a closed position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, there is illustrated in Fig. 1, a flow chart for forging a near net casting of a wheel component. In the preferred embodiment a full face wheel disc is formed; however, it will be appreciated that the invention also can be practiced to form a wheel spider or a complete one piece wheel. A near net casting is a casting of a component which is dimensionally close to the finished component.

In functional block 10, a wheel disc casting is cast in a multi-piece wheel disc mold 20, as shown in Fig. 2, by a conventional high volume casting process, such as gravity or low pressure casting. The wheel disc mold 20 includes a base member 21 which supports a plurality of side members 22. The side members 22 can be retracted and extended in a horizontal direction by a conventional mechanism (not shown). A top core 23 is disposed between the side members 22 and can be raised and lowered by a conventional mechanism (not shown). The top core 23 co-operates with the side and base members 22 and 21 to define a mold cavity 24. For simplicity, the mold gate and sprues are not shown in Fig. 2.

A charge of molten metal is poured into the mold cavity 24. In the preferred embodiment, an alloy of a light weight metal, such as aluminum, titanium or magnesium is used to charge the mold cavity 24; however, alloys of other metals, such as a steel alloy also can be used. The molten metal cools and

solidifies to form an annular wheel disc casting 25 which is dimensionally close to the final size of the wheel disc. Such a casting is commonly referred to as a "near net" casting. The invention contemplates that the near net casting formed in the mold 20 is sufficiently close to the final dimensions of the wheel disc that the casting can be subsequently forged into its final shape by a single forging operation. As shown in Figs. 2 through 5, the wheel disc being formed by the process includes an outboard tire bead seat. Such a wheel disc is commonly referred to as a "full face wheel disc".

The wheel disc casting 25 is removed from the mold 20 in functional block 26. If the casting 25 has cooled, the casting 25 is placed in a reheat oven (not shown) before proceeding and heated to near the melting temperature of the metal forming the casting 25, as shown in functional block 27. For example, an alloy ofthe aluminum-silicon-magnesium family, such as alloy 6061, would typically be heated to approximately 475"C. to assure that the metal is ductile for the forging process. Reheating would typically be needed only if the casting foundry is not co-located with the forge. The reheating step is optional, because, in the preferred embodiment, the forge is located near the casting machine and the process proceeds to the forging operation while the casting 25 retains sufficient heat for the forging operation.

In functional block 28, the heated casting 25 is loaded into a two piece die set 30, as illustrated in Figs. 3 and 4, for a single warm forge operation to form a wheel disc. The die set 30, which is shown in an open position in Fig. 3, includes an upper die 31 and a lower die 32. The upper die 31 co-operates with the lower die 32 to define a die set cavity 33. The die set 30 is generally equivalent to the final set of dies used in a conventional forging process where a heated forging blank is squeezed within a successive series of die sets with each of the die sets more closely approaching the desired final shape of the wheel disc.

The die set 30 shown in Figs. 3 and 4 is intended to be exemplary and,

accordingly, is simplified. It will be appreciated that the die set can include additional components. For example, the upper die 31 may include multiple pieces which are movable to allow removing the forged wheel disc after forming an outboard tire safety bead thereon.

The die set 30 is mounted upon a conventional pressure forging machine which, for clarity, is not shown in Figs. 3 and 4. In functional block 35, the upper and lower dies 31 and 32 are closed over the heated wheel disc casting 25 and then squeezed together on the casting 25 with high pressure by the forging machine. The metal in wheel disc casting 25 is extruded by the dies 31 and 32 to completely fill the die set cavity 33 and form a wheel disc forging 40.

Alternately, a drop forge (not shown) can be utilized in which the upper die 31, which is weighted, is dropped or projected with high force against the heated casting 25 and the lower die 32. As a result of the pressure or the impact of the upper die 31 upon the casting 25 and the force transmitted to the casting 25 which presses the casting 25 onto the lower die 32, the heated metal forming the casting 25 is plastically deformed into the voids within the die cavity 33 to form a wheel disc forging 40.

As described above, the invention contemplates using only one forging operation, because the casting 25 has a near net shape to the final component.

The die set 30 is opened and the wheel disc forging 40 removed.

If necessary, the forging 40 is heat treated in functional block 30; however, this step is optional. Depending upon the tolerances required and the structure of the mold 20 and die set 30, the forging is machined in functional block 31; however, this step also is optional. For example, it may be necessary to drill lug holes thorough the wheel hub or to finish the pilot hole. If the lug holes are formed during the casting and forging operations, it may be necessary to couterbore the lug holes with a machining operation. Additionally, depending upon the die set used, it may be necessary an turn outboard tire bead seat into the

sidewall portion of the forging 40 to form an outboard tire safety bead. It is the intent of the invention that any machining be minimal or not required at all.

As shown in the flow chart in Fig. 1, the invention also contemplates forming a partial wheel rim in functional block 47. The partial wheel rim is formed in a conventional manner. For example, a strip of an alloy of a light metal or steel is rolled into a hoop. The ends of the hoop are butt welded together. The hoop is then rolled into an annular partial wheel rim having a cylindrical inboard end. The finished wheel disc forging 40 is attached to the inboard end of the partial wheel rim in functional block 48. A conventional means of attachment is utilized. In the preferred embodiment, a continuous circumferential air-tight weld is formed between the wheel disc forging 40 and the wheel rim. The weld can be formed by friction welding or arc welding techniques. As a final step, which is optional, the assembled wheel receives final machining in functional block 49. For example the inboard and outboard tire bead seats may be turned to assure that they are concentric.

A sectional view of a two piece wheel formed by the above described process is shown in Fig. 5. In Fig. 5, the finished wheel disc forging 40 is attached to a partial wheel rim 50 by a continuous circumferential weld 55. The wheel disc 50 includes a central hub 56. A pilot hole 57 extends through the center of the hub 56 and a plurality of wheel lug holes 58 (one shown) are formed through the hub 56 on a bolt hole ring which is concentric with the pilot hole 57. A plurality of wheel spokes 60 extend radially from the hub 56 to an annular wheel disc sidewall 61. An outboard tire retaining flange 62 is formed in the outboard end of the sidewall 61. Inboard of the outboard tire retaining flange is an outboard tire bead seat 62 which terminates in an outboard tire safety bead 63. A deepwell wall 64 extends in a radially inward direction from the outboard tire safety bead 63. The deepwell wall 64 terminates in an annular ring 65 which

extends axially from the inboard face of the wheel disc forging 40. As shown in Fig. 5, the ring 65 forms a portion of a wheel deepwell 66.

As described above, the partial wheel rim 50 includes a cylindrical inboard end 70 which co-operates with the annular ring 65 portion of the wheel disc forging 40 to form the wheel deepwell 66. A leg portion 71 extends axially from the deepwell 66 toward the inboard end of the wheel rim 50. The leg portion 71 terminates in an inboard tire safety bead 72 which is adjacent to the inboard tire bead seat 73. An inboard tire retaining flange 74 is formed upon the inboard end of the wheel rim 50.

While the preferred embodiment has been illustrated and explained as forming a wheel having a wheel rim attached to a forged wheel disc in the deepwell area, it will be appreciated that the invention also can be practiced with the attachment formed in a different position. For example, the wheel rim can be formed to include the entire deepwell and a portion of the outboard tire bead seat (not shown). Accordingly, the weld would be formed in the outboard tire bead seat which would then be machined to assure a smooth surface.

Because the wheel disc is formed separately from the wheel rim, the invention further contemplates forming a lightener recess in the wheel disc sidewall to reduce the weight of the wheel. Accordingly, an alternate embodiment of the wheel disc mold is shown generally at 80 in Fig. 6.

Components of the mold 80 which are similar to components shown in Fig.2 have the same numerical designators. The mold 80 has a top core 81 which includes an annular core portion 82 which extends axially into the sidewall portion of the mold cavity 24. The core portion 82 can be either continuous or formed in a series of segments. Optionally, the continuous core can include a transverse gap, the purpose for which will be explained below. The core portion 82 forms a lightener pocket 83 in a near net wheel disc casting 84 formed in the

mold 80. As shown in Fig. 6, the lightener pocket 83 extends axially beneath the outboard tire bead seat of the wheel disc.

A sectional view of an alternate embodiment of a die set 85 which corresponds the wheel mold 80 is shown in Figs. 7 and 8. Components shown in Figs. 7 and 8 which are similar to components in Figs. 3 and 4 have the same numerical designators. The die set 85 includes an upper die 86 having an annular core portion 87 which extends axially into the sidewall portion of the die cavity 33. The die core portion 87 is shaped to correspond to the mold core portion 82 described above.

After heating, if necessary, the wheel disc casting 84 is placed in the lower die 32, as shown in Fig. 7. Similar to the description above, the upper and lower dies 86 and 32 are closed over the heated casting 84 and then squeezed together on the casting 84 with high pressure a forging machine. The metal in wheel disc casting 84 is extruded to completely fill the die set cavity 33 and form a wheel disc forging 88 having a lightener cavity 89 which extends axially beneath the outboard tire bead seat. Alternately, a drop forge (not shown) can be utilized in which the upper die 86, which is weighted, is dropped or projected with high force against the heated casting 84 and the lower die 32 to form the wheel disc forging 88.

Continuous cores in the mold 80 and die set 85 would form a continuous lightener recess which extends circumferentially beneath the outboard tire bead seat. As described above, the core may include an optional gap, which would form a narrow transverse metal bridge across the lightener recess. The narrow bridge would be bored to receive a tire valve. Alternately, a plurality of cores could be formed upon the mold and die set to form a corresponding plurality of lightener pockets within the wheel disc sidewall.

The above described process has the advantage of both reducing the time required to machine the wheel disc and the number of die sets required to forge

the wheel disc. Accordingly, the total time required to form the wheel disc is reduced from prior art methods. Additionally, the forging process produces a wheel disc having a smooth surface which may be satisfactory as a final finish.

The deformation of the near net casting during the forging process properly orients and refines the crystalline structure of the component metal. This increases the strength, ductility and resistance of the component to impact and fatigue of the component.

In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.