Patent Publication Number: US-7587825-B2

Title: Method for producing a wheel disc

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is related to co-pending U.S. application Ser. No. 10/836,828 and co-pending U.S. application Ser. No. 11/345,530. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to vehicle wheels and, more specifically, to an improved method for producing a wheel disc adapted for use in such a vehicle wheel. 
     One type of conventional fabricated vehicle wheel comprises a two-piece construction having an inner disc and an outer rim. The disc includes an inner wheel mounting portion and an outer annular portion. The wheel mounting portion defines an inboard mounting surface and includes a center pilot or hub hole, and a plurality of lug receiving holes formed therethrough for mounting the wheel to an axle of the vehicle. The rim is fabricated from steel, aluminum, or other alloys, and includes an inboard tire bead seat retaining flange, an inboard tire bead seat, an axially extending well, an outboard tire bead seat, and an outboard tire bead seat retaining flange. The outer annular portion of the disc is typically secured to the inner radial surface of the rim by welding. 
     Some preferred materials for the disc are steel and other alloys which can be cold worked from a flat blank into the desired final shape of the disc. Using several stages of die stamping and punching, a wheel disc of sufficient dimensional accuracy and strength can be economically produced. An example of progressive die stamping to manufacture wheels discs with multi-stage, high speed transfer press equipment is shown in U.S. Pat. No. 5,568,745, issued to Daudi on Oct. 29, 1996, which is incorporated herein by reference in entirety. 
     In addition to stringent requirements for strength and shape of both the wheel disc and rim, an attractive styling of the wheel disc is desired. Windows are formed in a typical wheel disc in order to give the wheel a spoked appearance by forming a single spoke between each pair of adjacent windows. The windows also function to provide a flow of cooling air to brake units installed inboard of the wheel. 
     To further improve styling of a stamped wheel disc, cladding of various shapes and finishes may be applied to the outboard side of the wheel disc after it is assembled to the rim. The cladding shape may conform to the shape of the wheel disc or it may provide a very different appearance. Regardless of actual styling, it is preferable that enough “see-through” area remains after installing the cladding to allow sufficient air flow to cool the wheel and brake. 
     Recent trends in wheel styling have made it desirable to provide large windows so that the unitary spokes between windows are as small as possible. When a cladding is used, a large window size in the wheel disc provides greater flexibility in styling the cladding such that the cladding windows can be located in more arbitrary locations. 
     Using conventional techniques for fabricating stamped wheel discs from flat blanks, it has not been possible to obtain larger window sizes. During manufacture, the blank is typically bent over to form the outer band prior to punching the windows because if the windows were to be punched first then they would distort to an unacceptable degree during bending. With larger window sizes, a punching operation becomes increasingly difficult because of the need to provide the space to receive the slugs as they are punched out. 
     In order to obtain larger window sizes, other forming processes such as casting of aluminum have been employed. However, these other processes and materials are less well suited to low cost, mass production. Therefore, it would be desirable to obtain increase window sizes with a stamped wheel disc. 
     Co-pending U.S. application Serial No. 11/345,530 filed concurrently herewith, entitled “Disc Forming Process for Wheels with Large Windows,” teaches an improved disc forming process that enables increased window size while maintaining disc strength and avoiding distortions even though the outer band is bent over after punching the larger windows. An intermediate camming operation performs a preliminary shaping prior to final shaping with a wipe die so that the disc may be formed without introducing stresses that would weaken the disc or distorting the window shape. 
     A potential problem associated with both the preliminary and final shaping of the outer band is unintended undulations. Due to the presence of the large windows, cyclic variations in the radial length of the outer band may be produced. The unintended length variations can produce undulations in the final outer band that run in a direction parallel with the wheel axis and/or perpendicular to the wheel axis. When the formed wheel disc is placed within the rim for welding, any undulations parallel to the wheel axis cause the seam for welding to be wavy, making it more difficult to perform the welding operation. Undulations perpendicular to the wheel axis result in discontinuous contact between the wheel disc and rim along the seam, preventing the formation of a strong welding joint. Therefore, it would be desirable to reduce undulations. 
     Die stamping operations to form a wheel disc are typically performed using a series of press stations with partially finished pieces being transferred between stations. In addition to the multiple stations, each station can be set up to perform more than one compatible metal forming operation such as bending some sections of the piece while a hole in another area of the piece is pierced. In order to produce a part most economically using the least equipment and factory floor space, it is desirable to use a fabrication process needing a minimal number of stations. Manufacturing costs are also dependent upon the complexity of the forming operations performed by each set of dies, both in terms of original cost of the tooling and maintenance during the useful lifetime of the tooling. Thus, it is further desirable to find a sequence of operations to form a desired wheel disc using less complicated steps without increasing the number of stations required. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved wheel disc forming process that enables an increased window size. The process reduces undulations while avoiding complex piercing operations and reducing the number of press stations. 
     In one aspect of the invention, a method is provided for forming a wheel disc. A flat disc blank is formed into a bowl shaped wheel disc. The bowl shaped wheel disc is formed to form spoke-forming regions adjacent window-forming regions. A window is formed in each of the window-forming regions in a substantially vertical direction, wherein each window has a respective outer edge proximate with a continuous outer band around a periphery of the wheel disc. The windows define a plurality of spokes between adjacent windows. An angular size of each of the windows along the outer band is preferably greater than an angular size of each of the spokes. The outer band is partially closed toward a cylindrical shape by engaging a cam die against at least a portion of the outer band, wherein the cam die comprises an engagement surface having an intermediate ledge for receiving a peripheral edge of the outer band to reduce undulations of the outer band. The outer band is fully closed substantially into a cylindrical shape by axially wiping the outer band. 
     Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the invention, when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a wheel disc fabricated according to an embodiment of the present invention. 
         FIG. 2  is a perspective view of the wheel disc of  FIG. 1  joined with a wheel rim. 
         FIGS. 3 and 3A  are cross-sectional views of a closed press after processing a wheel disc according to a first operation of a first embodiment of the present invention. 
         FIGS. 4 ,  4 A, and  4 B are cross-sectional views of a closed press after processing a wheel disc according to a second operation of the first embodiment of the present invention. 
         FIGS. 5 ,  5 A, and  5 B are cross-sectional views of a closed press after processing a wheel disc according to a third operation of the first embodiment of the present invention. 
         FIGS. 6 ,  6 A, and  6 B are cross-sectional views of a closed press after processing a wheel disc according to a fourth operation of the first embodiment of the present invention. 
         FIGS. 7 and 7A  are cross-sectional views of a closed press after processing a wheel disc according to a fifth operation of the first embodiment of the present invention. 
         FIG. 8  is a cross-sectional view of an open press before processing a wheel disc according to a sixth operation of the first embodiment of the present invention. 
         FIG. 8A  is a top plan view of a portion of the die set of the sixth operation. 
         FIGS. 8B and 8C  are cross-sectional views of a closed press after processing a wheel disc according to the sixth operation. 
         FIGS. 9 and 9A  are cross-sectional views of a closed press after processing a wheel disc according to a seventh operation of the first embodiment of the present invention. 
         FIGS. 10 ,  10 A, and  10 B are cross-sectional views of a closed press after processing a wheel disc according to an eighth operation of the first embodiment of the present invention. 
         FIG. 11  is a cross-sectional view of a closed press after processing a wheel disc according to a fourth operation of a second embodiment of the present invention which may replace the fourth operation shown in  FIGS. 6 ,  6 A and  6 B in connection with the first embodiment of the present invention. 
         FIGS. 12 and 12A  are cross-sectional views of a closed press after processing a wheel disc according to a fifth operation of a second embodiment of the present invention which may replace the fifth operation shown in  FIGS. 7 and 7A  in connection with the first embodiment of the present invention. 
         FIG. 12B  is a top plan view of a portion of the die set of the fifth operation of the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a wheel disc  10  having the shape shown is to be made from flat stock using cold stamping. After it is made, disc  10  may be welded, riveted or otherwise suitably secured to a suitable rim  11 , such as shown in  FIG. 2 , to produce a wheel W having a wheel or wheel disc axis X. Wheel rim  11  is fabricated from a suitable material, such as for example, steel, aluminum or alloys thereof, magnesium, or titanium. 
     Wheel disc  10  is fabricated or otherwise formed from a suitable material having the ductility necessary for cold working, such as for example, steel, aluminum or alloys thereof, steel, magnesium, or titanium. Wheel disc  10  includes a generally centrally located wheel mounting surface or contour  12 , a plurality of outwardly extending unitary spokes  13 , and an outer annular rim connecting band or flange  14 . In the illustrated embodiment, disc  10  includes five of such unitary spokes  13  which are integral with the wheel mounting surface  12  and outer band  14 . In the illustrated embodiment, the spokes are formed as solid spokes; however, one or more of the spokes  13  can have an opening(s) (not shown) formed therein if so desired. Also, as shown in the embodiment illustrated in  FIG. 1 , each spoke  13  defines a radial line R intersecting the wheel disc axis X and each spoke  13  is preferably symmetrical with respect to the radial line R. Alternatively, a different number, orientation and/or shape of spokes  13  can be employed if so desired. 
     Wheel mounting surface  12  is provided with a centrally located pilot aperture  15  and a plurality of lug bolt receiving holes  16  circumferentially spaced around pilot aperture  15 . Lug bolt receiving holes  16  receive lug bolts (not shown) for securing the finished wheel on an axle of a vehicle. 
     Wheel disc  10  also includes a plurality of openings or windows  17  formed between adjacent spokes  13 . As shown in the embodiment illustrated in  FIGS. 1 and 2 , the angular extent of windows  17  is preferably greater than the angular extent of unitary spokes  13 , in particular at the outer radial periphery of disc  10  proximate to outer band  14 . Alternatively, the angular extent of the windows  17  relative to the spokes  13  can be other than illustrated if so desired. 
     Outer band  14  extends in a generally axial direction and is joined to the remainder of disc  10  only by spokes  13 . Consequently, the transitions between each spoke  13  and outer band  14  should be formed without fractures, cracks, or other imperfections that could weaken the structural integrity of the disc  10  and therefore the wheel. Since outer band  14  defines an annular mounting flange for welding to rim  11 , it is bent down by approximately ninety degrees from the plane of the original blank during the stamping process. As shown in the embodiment illustrated in  FIGS. 1 and 2 , windows  17  are so large that a side edge surface  20  of windows  17  has its face generally perpendicular to the wheel axis X. In other words, outer band  14  is a generally flat cylinder with substantially no curvature (at least in the area of the circumferential center of each window  17 ) so as to extend in a generally axial direction and define a side edge surface  14 A extending between each pair of adjacent spokes  13  which extends in a generally axial outboard direction. This generally flat cylindrical shape gives the least amount of intrusion of outer band  14  into the view through windows  17  after disc  10  is joined to rim  11  which is desirable for styling purposes. However, the degree of bending and the narrowness of unitary spokes  13  would result in excessive material stress at the transition between spokes  13  and outer band  14  when using prior art stamping processes. 
       FIGS. 3 and 3A  show a tooling set, indicated generally at  21 , for performing a first operation on a wheel disc blank (not shown) to produce a wheel disc  20 . Tooling set  21  is adapted to be mounted to a punch press (not shown) and performs a metal stamping operation easily appreciated by those skilled in the art from an inspection of  FIG. 3 . A generally flat circular blank (not shown) is loaded into tooling set  21  and then the press is moved into its closed configuration depicted in  FIG. 3 . As a result of the closing of the press, the central portion of wheel disc  20  is drawn vertically upward with respect to the outer periphery of wheel disc  20 , creating a symmetrical bowl shape. This adds material volume needed for subsequent drawing steps and work hardens the material. 
     Preferably, a radius  22  is formed proximate to the outer edge of wheel disc  20 . After completing the first operation shown in  FIG. 3 , tooling set  21  is opened and wheel disc  20  is transferred to a subsequent press for the next operation. 
       FIGS. 4 ,  4 A, and  4 B show a second operation wherein a tooling set, indicated generally at  30 , performs further preliminary shaping of wheel disc  20 . Die details  31  and  32  perform preliminary shaping in an inner wheel mounting area of disc  20 . Die details  33  and  32  cooperate to stamp a spoke forming region  35 . Die details  34  and  32  cooperate to stamp a window forming region  36 . In the embodiment shown in  FIGS. 1 and 2 , a total of five spoke forming regions  35  and five window forming regions  36  are formed around the full periphery of wheel disc  20 . In the illustrated embodiment, window forming regions  36  are shown with a greater stamped height than spoke-forming regions  35 , but any other relative heights between the window and spoke forming regions are possible depending upon the desired final shape of the wheel disc. Although tooling set  30  is shown in cross section, one skilled in the art will appreciate that the die details have a three dimensional shape. 
     In the second pre-forming operation, the inner mounting area and regions  35  and  36  are preferably drawn downward with respect to the outer periphery of wheel disc  20  (i.e., in the opposite vertical direction). Consequently, further material redistribution and work hardening are achieved. 
       FIGS. 5 and 5A  show a tooling set, indicated generally at  40 , for a next operation conducted in a subsequent press to which wheel disc  20  is transferred for piercing windows in a substantially vertical direction. A punch detail  41  is driven into window forming regions  36  along a punch axis P which is generally parallel with respect to the wheel disc axis X, and the resulting slug is removed through a chute  42 . As shown in this embodiment, the outer edge of wheel disc  20  extends substantially horizontally and is retained by tooling set  40  during the piercing operation so that the pierce can be conducted vertically, which simplifies the tooling set as opposed to making an aerial pierce at an angle. 
     In the illustrated embodiment, the top side of the formed windows is preferably simultaneously coined as shown in  FIG. 5B  by providing a collar  43  on die detail  41  behind the leading or front cutting edge of die detail  41  (the collar  43  only being shown on die detail  41  in  FIG. 5B ). Collar  43  strikes along the edge of the pierced window as part of the same downward stroke of die detail  41 . Alternatively, the coining of the pierced windows can be performed by other methods subsequent to this operation if so desired. 
     The next operation shown in  FIGS. 6 and 6A  performs further disc shaping using a tooling set, indicated generally at  50 . Tooling set  50  includes an upper ring  51  and a die detail  52  providing an anvil  53 . Complementary sloped edges of upper ring  51  and anvil  53  shape outer band  55  into an angled leg. Preferably, the angled leg of outer band  55  is oriented at about twenty degrees from the wheel disc axis X (i.e., the central vertical axis). It is desirable to draw down outer band  55  no more than about twenty degrees to avoid stressing the spoke transitions or causing unwanted undulations. Additionally, in the illustrated embodiment, it is preferred that the upper ring  51  and anvil  53  are shaped so as to induce or produce counter undulations in the outer band  55  which are effective to reduce or cancel out the self induced undulations which occur during this operation. 
     In the illustrated embodiment, additional die details  56  and  57  are preferably provided to simultaneously perform a final shaping of wheel disc  20  to provide areas to receive a central hole and a plurality of lug bolt holes. Final shaping adjustments may also be obtained in the areas of the spokes and windows if desired. Alternatively, the final shaping of the wheel disc  20  in the areas to receive the central hole and the lug bolt holes can be performed by other methods subsequent to this operation if so desired. 
     In the subsequent operation shown in  FIGS. 7 and 7A , the central hole is pierced using a tooling set, indicated generally at  60 . Specifically, a die detail  61  is driven through wheel disc  20  and a resulting slug is removed through a chute  62 . 
     The next operation shown in  FIGS. 8 ,  8 A,  8 B, and  8 C partially closes the outer band using a tooling set, indicated generally at  65 . Tooling set  65  is shown in  FIG. 8A  in its open configuration holding wheel disc  20  in position to allow outer band  55  to be bent to a more nearly cylindrical shape following the closing of the tooling set  65 . Tooling set  65  includes a cam die detail  66  which can be driven radially inward by a cam driver  67 . Slanted surfaces  68  and  69  on cam die detail  66  and cam driver  67 , respectively, are oriented such that when cam driver  67  is forced downward, cam die detail  66  is driven radially inward. 
     Preferably, cam die detail  66  and cam driver  67  each comprise several separate circumferentially spaced segments to accommodate the change in radius as cam die detail  66  moves inward to simultaneously cam respective portions of outer band  55 . As shown in  FIG. 8A , relatively small gaps  70  between separate cam sections may be about one quarter of an inch at the smaller radius. Gaps  70  may preferably be located corresponding to points on the perimeter away from the spokes (i.e., juxtaposed with the windows) since no significant bending is needed there. 
     Cam die detail  66  has a slanted engagement surface  71  with an intermediate horizontal ledge  72  for receiving a peripheral edge of outer band  55  to reduce undulations which may be otherwise formed in outer band  55 . After wheel disc  20  is lowered into the tooling set  65  and cam die detail  66  begins to move radially inward, the peripheral edge of outer band  55  makes contact with engagement surface  71 . Outer band  55  bends downward while the peripheral edge slides down surface  71  until it makes contact with ledge  72 . As the peripheral edge of outer band  55  presses against ledge  72 , outer band  55  continues to bend downward and any undulations which may be present are evened out or removed because of the constraint in the leg length of the outer band  55  resulting from the presence of ledge  72 . 
       FIGS. 8B and 8C  show cam die detail  66  in its closed radially inward position after having driven outer band  55  radially inward to partially close it. After camming over outer band  55 , driver  67  is moved upward to withdraw cam die detail  65  to its radial outward position so that wheel disc  20  may be transferred to the next operation. 
       FIGS. 9 and 9A  show a tooling set, indicated generally at  75 , for fully closing the outer band into a generally cylindrical flange. More specifically as shown in the illustrated embodiment, a wipe die detail  76  moves downward to axially wipe outer band  55  so that it is drawn down to an approximately ninety degree angle from its original horizontal orientation. A generally cylindrical surface parallel with the wheel axis is formed for mating with the interior side of the rim. 
       FIGS. 10 ,  10 A, and  10 B show the next operation wherein the downward leg length of outer band  55  is calibrated to a more accurately controlled final length. In addition, any remaining undulations may be further reduced. A tooling set, indicated generally at  80  (shown closed), includes die details  81  and  82  for retaining wheel disc  20  in position while a calibration die detail  83  strikes the peripheral edge of outer band  55  in a direction generally parallel to the wheel disc axis X. Die detail  82  penetrates or is disposed within window  17  in order to accurately locate wheel disc  20  for the calibration. As shown in  FIGS. 10A and 10B , die detail  83  includes a ledge  84  for receiving the peripheral edge of outer band  44 . Die detail  83  may be segmented around the periphery of tooling set  80  provided that gaps between segments are sufficiently small so that all portions of outer band  55  are correctly calibrated. 
     Simultaneous with the outer band calibration, one or more “process holes” may be created around the periphery of the center hole by a punch die detail  85 . Slugs from the holes are removed via a chute  86 . The process hole(s) are used in locating and handling the wheel disc during subsequent machining steps. The number and location of the process holes depends upon the specific requirements of the subsequent processing steps. Preferably, the process holes coincide with lug bolt hole locations so that no process holes are remaining in the final wheel disc. 
     In the illustrated preferred embodiment, the forming of the wheel disc is completed after calibrating outer band  55  as shown in  FIG. 10 . Subsequently, the wheel disc is attached to the wheel rim by welding, riveting or other suitable attachment (e.g., adhesive or by other mechanical means) and then the rim and wheel disc are trued (e.g., squeezed in a true-centric machine at the bead seats thereby pressing the wheel into a round shape with very high accuracy). Thereafter, the wheel disc is machined (e.g., using a mill) in order to accurately locate the center hole. The center hole may then be expanded and/or coined in a press while final lug bolt holes are punched. In an alternative embodiment, the final center hole and lug bolt holes can be formed in the wheel disc in a punch press prior to attaching to the rim. 
     Turning now to  FIGS. 11 and 12  and  12 A and using like reference numbers to indicate corresponding parts, there is illustrated an alternate partial sequence of operations which can be used to produce the wheel disc of the present invention. Specifically,  FIG. 11  may be used in place of the operations shown in connection with  FIGS. 6 ,  6 A and  6 B above, and  FIGS. 12 and 12A  may be used in place of the operations shown in connection with  FIGS. 7 and 7A  above. 
     As shown in the illustrated embodiment of  FIG. 11 , a tooling set, indicated generally at  150  is provided. The tooling set  150  includes die details  151  and  152  to preferably simultaneously perform a final shaping of wheel disc  20  to provide areas to receive a central hole and a plurality of lug bolt holes. Also, tooling set  150  includes die details  153  and  154  which perform a coining of the backside of the windows. Thus, as can be seen, the operation in the embodiment illustrated in connection with  FIG. 11  does not initially draw down outer band  55  as occurred and described above in connection with the operation in the embodiment shown in connection with  FIGS. 6 ,  6 A and  6 B. 
     As shown in the illustrated embodiment of  FIG. 12 , a tooling set, indicated generally at  160  is provided. The tooling set  160  includes an upper ring  161  and a die detail  162  providing an anvil  163 . Complementary sloped edges of upper ring  161  and anvil  163  shape outer band  55  into an angled leg. Preferably, the angled leg of outer band  55  is oriented at about twenty degrees from the wheel disc axis X (i.e., the central vertical axis). It is desirable to draw down outer band  55  no more than about twenty degrees to avoid stressing the spoke transitions or causing unwanted undulations. In this embodiment as shown in  FIG. 12 , the die detail  161  (also schematically shown in  FIG. 12A ), is designed so that in the areas of the die detail  161  which are adjacent each of the window portions of the wheel disc a slight gap G exists between adjacent surfaces of the die detail  161  and the outer band  55  of the disc when the die detail  161  is in its fully lowered or extended working position. (The gap G shown exaggerated on the left side of  FIG. 12  for clarity). Also, in this embodiment, adjacent each the spoke portions of the wheel disc, the die detail  161  is designed with a inwardly curved or arched profile  161 A so that when the die detail  161  in its fully lowered position (as shown in  FIGS. 12 and 12A ), those portions of the outer band  55  which are adjacent each of the spoke portions are forced or deformed more inwardly than those portions of the outer band  55  which are adjacent each of the windows portions. (The inwardly curved profile portions  161 A of the die detail  161  shown exaggerated on the  FIG. 12B  for clarity). In this embodiment, the reason for the die detail  161  having this construction is for the purpose of preventing the outer band  55  from buckling or moving outwardly in the gaps  70  that exist in die detail  66  discussed above and best shown in connection with  FIGS. 8 and 8A , due the natural “spring back” inherency of the material during the leg camming operation discussed in connection with these figures. The amount or degree of the inwardly curved profile portions  161 A of die detail  161  is determined upon many factors, including but not limited to the particular characteristics of the wheel disc, such as type of material, the material thickness, the size of the wheel disc, and the like, and is generally believed to be about the thickness of the material of the wheel disc; however, the shape and/or amount of the inwardly curved profile portions  161 A of die detail  161  can be other than illustrated and described if so desired. In addition, in some wheel disc constructions, die detail  161  may be able to be formed with a continuous or uniform outer profile, i.e., not include the inwardly curved profile portions  161 A. Also, as shown in  FIG. 12 , a die detail  164  is provided for embossing the wheel disc in the area of the lug bolt apertures. 
     In view of the foregoing description, a stamping or metal forming process has been shown wherein relatively large windows can be formed in a wheel disc. A cylindrical flange for attaching the wheel disc to a rim is obtained without significant undulations in the outer band by virtue of an intermediate camming operation using a cam die with an intermediate ledge. 
     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.