Abstract:
A method for forming seamless tubular workpieces, such as vehicular wheel rim components. In the method, a flat circular blank having a central aperture is expanded into the interior of a hollow mandrel using a mushroom-shaped spinning roller. In this expansion operation, the blank is caused to take on a tubular shape having an exterior contour which conforms to the interior contour of the hollow mandrel.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to methods for forming metal workpieces and, more particularly, to methods for forming seamless tubular workpieces, such as wheel rim components. 
     BACKGROUND OF THE INVENTION 
     Seamless aluminum wheel rims for automobiles and other vehicles have become very popular. Such seamless wheel rims are generally held to be both structurally and aesthetically superior to conventional wheel rims. 
     Unfortunately, previously-known methods of making seamless wheel rims are unduly expensive, because such seamless wheel rims are either extruded or machined using external mandrels which produce large amounts of scrap metal waste. 
     Accordingly, there is a need for an improved method of forming seamless wheel rims without the problems associated with prior art processes. 
     SUMMARY 
     The invention satisfies this need. The invention is a method and an apparatus for forming a hollow annular work piece, such as a wheel rim component. The method comprises the steps of (a) providing a hollow mandrel with a forward end, a rearward end, a longitudinal axis and an internal surface typography, the forward end having a substantially circular cross-section with an internal diameter, the internal surface typography being the reverse of the desired typography, (b) providing a disc-shaped metallic blank having a centralized aperture, the centralized aperture having a center, (c) securing the blank to the forward end of the mandrel such that the center of the centralized aperture is aligned with the longitudinal axis of the mandrel, and (d) rotating the mandrel about the longitudinal axis of the mandrel while pressing the blank against the interior surface of the mandrel with a spinning roller, the spinning roller having a smooth rounded surface, the pressing of the blank against the interior surface of the mandrel being continued until the blank takes on a hollow annular shape having an external surface with the desired typography. 
    
    
     DRAWINGS 
     These features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims and accompanying figures where: 
     FIG. 1 is prospective of a wheel rim which can be constructed by the invention; 
     FIG. 2 is a cross-sectional side view of the wheel rim illustrated in FIG. 1 taken along line  2 — 2 ; 
     FIG. 3 is a cross-sectional side view illustrating a prior art process for making tubular work pieces using a solid mandrel; 
     FIG. 4 is a prospective view of a blank useable in the invention; 
     FIG. 5 is a top view of an apparatus having features of the invention; 
     FIG. 6A is a top view detail, in partial cross-section, of a hollow mandrel useable in the invention shown in the fabrication of a workpiece; 
     FIG. 6B is a side view of the hollow mandrel illustrated in FIG. 6A; and 
     FIG. 7 is a top view detail, in partial cross-section, of a hollow mandrel useable in the invention shown in the fabrication of a second workpiece. 
    
    
     DETAILED DESCRIPTION 
     The following discussion describes in detail one embodiment of the invention and several variations of that embodiment. This discussion should not be construed, however, as limiting the invention to those particular embodiments. Practitioners skilled in the art will recognize numerous other embodiments as well. 
     The invention is a method and apparatus for forming a hollow annular workpiece  20 . The apparatus  10  comprises a hollow mandrel  12 , a mandrel retaining assembly  14 , a spinning roller  16  and a spinning roller carriage  18 . 
     The invention can be used to manufacture hollow annular workpieces  20 , such as wheel rim components  22 . A typical wheel rim  24  is illustrated in FIGS. 1 and 2. The wheel rim  24  illustrated in FIGS. 1 and 2 is commonly termed a “three-piece” wheel rim because it comprises a forward moiety  26 , a rearward moiety  28  and a center plate  30 . Both the forward moiety  26  and the rearward moiety  28  have end flanges  32  to facilitate their connection to each other and to the center plate  30 . The three pieces are typically fastened together with bolts  34  (as illustrated in FIG. 2) or are welded together to form a completed wheel rim  24 . The apparatus of the invention  10  can be used to manufacture the forward moiety  26  of the wheel rim  24  and the rearward moiety  28  of the wheel rim  24 . In another embodiment of the invention, the apparatus of the invention  10  can be used to manufacture one-piece integral combinations  36  of the forward moiety  26  and the rearward moiety  28 . Such integral combinations  36  can be assembled with a center plate  30 , usually by welding. Such combination  36  is commonly termed a “two-piece” wheel rim. The forward moiety  26 , the rearward moiety  28  and the integral combination  36  of the forward and rearward moieties  26  and  28  are referred to herein as “wheel rim components  22 .” All such wheel rim components  22  have an external surface  38  with a desired typography. 
     The mandrel  12  is most conveniently seen in FIGS. 6 and 7. The mandrel  12  comprises a forward portion  39  having a forward end  40 , a rearward portion  41  having a rearward end  42  and a longitudinal axis  44 . The forward end  40  has a substantially circular cross-section with a forward end internal diameter between about 10 inches and about 24 inches. The rearward portion  41  is also substantially circular with a rearward portion internal diameter. In a typical embodiment, the mandrel  12  is made from steel. 
     The internal surface  46  of the mandrel  12  has an internal surface typography which is the reverse of the desired typography of the workpiece  20 . In some embodiments, the internal surface typography of the mandrel  12  defines a smooth right circular cylinder. In other embodiments, the internal surface typography can be a non-smooth, non-cylindrical surface, termed herein as a “contoured surface.” 
     The mandrel retaining assembly  14  allows the mandrel  12  to be rotated at a rate of rotation which is typically between about 100 rpm and about 800 rpm, most typically between 400 rpm and about 500 rpm. 
     The spinning roller  16  is disposed proximate to the forward end  40  of the mandrel  12  on a spinning roller shaft  48 . The spinning roller  16  is rotatable by the spinning roller shaft  48  at rates of rotation typically between about 50 rpm and about 1000 rpm, most typically between about 300 rpm and about 500 rpm. The spinning roller shaft  48 , in turn, is retained on the spinning roller carriage  18 . The spinning roller carriage  18  maintains the spinning roller shaft  48  in a spinning roller plane  50  which contains the linear extension  52  of the longitudinal axis  44  of the mandrel  12 . Typically, the spinning roller plane  50  is a substantially horizontal plane, although it can also be a vertical plane or a plane disposed neither horizontally or vertically. 
     The spinning roller carriage  18  is moveable between a forward most position, wherein the spinning roller  16  is disposed within the hollow mandrel  12 , and a rearward most position wherein the spinning roller  16  is disposed external of the mandrel  12 . The spinning roller carriage  18  is also capable of moving the spinning roller shaft  48  laterally within the spinning roller plane  50 . Preferably, the spinning roller carriage  18  is capable of “canting” the spinning roller shaft  48  with respect to the linear extension  52  of the longitudinal axis  44  of the mandrel  12 . In a typical embodiment, the spinning roller shaft  48  can be canted to angles A between about −5° and about +30° with respect to the linear extension  52  of the longitudinal axis  44  of the mandrel  12 . 
     In the embodiment illustrated in the drawings, the spinning roller carriage  48  includes a pair of longitudinal opposed track members  54  for allowing the movement of the spinning roller  16  between the forward most position and the rearward most position. The spinning roller carriage  48  further comprises a pair of lateral track members  56  for allowing movement of the spinning roller shaft  48  in opposed lateral directions. 
     The apparatus  10  is capable of spin forming disk-shaped metallic blanks into the completed annular workpieces  20 . FIG. 4 illustrates a typical disk-shaped metallic blank  58 . The blank  58  has a centralized aperture  60  with a center  62 . The blank  58  can be substantially flat across its entire diameter (as illustrated in FIG. 4) or it can have a non-flat perimeter  64 , such as illustrated in FIGS. 5,  6  and  7 . Such non-flat perimeters  64  are typically provided in a preliminary machining or forging operation. 
     The blank  58  can have a substantially uniform thickness, but this is not necessary. In some applications, the blanks  58  are non-uniform in thickness. In the formation of wheel rim components  22 , the thickness of the blank  58  is typically between about 0.2 inch and about 1.5 inches. 
     The blank  58  is typically made from a material comprising aluminum or aluminum alloy. In many applications, the blank  58  will consist essentially of aluminum or aluminum alloy. The apparatus  10  and the method of the invention can also be used with other metals. The centralized aperture  60  is typically circular and has a diameter between about 4 inches and about 16 inches. In most applications, the optimum diameter of the centralized aperture  60  will depend upon the thickness and the ductility of the blank  58  and upon the thickness of the workpiece  20  to be formed from the blank  58 . 
     Blanks  58  made from aluminums or other materials having high elongation characteristics are often preferred in the invention because such materials are less likely to crack during fabrication. 
     The blank  58  can be conveniently manufactured from inexpensive cast material, such as 7-inch diameter billets of cast material. Such cast material can then be machined into a substantially planar shape using, for example, a rotary forge. 
     The spinning roller  16  has a smooth, rounded surface  66 , such as the “mushroom-shaped” spinning rollers  16  illustrated in the drawings. 
     In the method of the invention, hollow annular workpieces  20  having an external surface  38  with a desired typography are formed in the following steps. A disk-shaped metallic blank  58  is secured to the forward end  40  of the hollow mandrel  12  using a mechanical clamp  68  or equivalent device. The center  62  of the centralized aperture  60  of the blank  58  is aligned with the longitudinal axis  44  of the mandrel  12 . The mandrel  12  is then rotated about the longitudinal axis  44  of the mandrel  12  while the spinning roller  16  (rotating on the spinning roller shaft  48 ) is slowly pressed against the rotating blank  58 . The initial pressure applied to the blank  58  by the spinning roller  16  is made proximate to the centralized aperture  60  of the blank  58 . Using the forward/backward and lateral movement of the spinning roller carriage  18 , the spinning roller  16  can be moved forward and rearward as well as left and right within the spinning roller plane  50 . Also, the spinning roller shaft  48  can be canted with respect to the linear extension  52  of the longitudinal axis  44  of the mandrel  12 , so that the pressure of the spinning roller  16  on the blank  58  can be applied obliquely. 
     The entire operation can, in many instances, be carried out in a single “pass.” In other operations, two or more passes are used. 
     The operation is continued until the blank  58  is formed into a hollow annular workpiece  20  having an external surface  38  with the desired typography. 
     Typically, the blank is at ambient temperature during the operation. With certain metals and with certain thicknesses of metals, the operation is preferably carried out after the blank has been preheated up to about 650° F. 
     FIGS. 6A and 6B illustrate an embodiment of the invention  10  wherein a rearward moiety  28  of a wheel rim  24  is formed. The spinning roller  16  is pressed against the blank  58  until the centralized apertured  60  is expanded to substantially the same diameter as the rearward portion internal diameter and the blank  58  is expanded into an annular tubular configuration having a contoured external surface  38  which is the reverse of the internal contoured typography  46  of the mandrel  12 . In the embodiment illustrated in FIGS. 6A and 6B, an end flange  32  is provided on the rearward moiety  28  by pressing the blank  58  against an annular stop ring  70  disposed within the mandrel  12 . 
     FIG. 7 illustrates another embodiment of the invention. In this embodiment, an integral wheel rim combination  36  is formed. In a most typical embodiment, the internal typography  46  of the mandrel  12  defines a smooth, right circular cylinder. The spinning roller  16  presses the blank  58  against the internal typography  46  of the mandrel  12  until the blank  58  is expanded into an annular tubular configuration having a smooth exterior typography  38  in the shape of a right circular cylinder. Thereafter, the completed workpiece  20  is removed from the mandrel  12  and is machined in a separate post-invention step into the final configuration of the integral wheel rim combination  36 , typically by spin forming or press forming. 
     In an alternative embodiment, the integral wheel rim combination  36  can be wholly formed within the mandrel  12 . In this embodiment, the mandrel  12  must be separable along edges parallel with the longitudinal axis  44  so that the completed integral wheel rim combination  36  can be removed from the mandrel  12 . In one such embodiment, the mandrel  12  is separable in “clam-shell” fashion. In another embodiment, the mandrel  12  is separable in “chuck-like” fashion. 
     The invention  10  can be used to manufacture seamless wheel rims  24  in an efficient and far less expensive manner than methods and apparatuses of the prior art. The invention  10  is contrasted with methods and apparatuses  110  of the prior art for manufacturing seamless wheel rims  24  as illustrated in FIG.  3 . In such prior art methods and apparatuses  110 , a substantially flat blank  158  is machined into a wheel rim component  22  by pressing the blank  158  against the outside typography  180  of an external mandrel  112 . As can be readily appreciated, the flat blanks  158  used in such prior art methods must be considerable larger in diameter than blanks  58  used in the invention  10 . For example, in forming a 17-inch wheel rim  24 , a typical blank  58  used in the invention  10  is 19 inches in diameter, whereas a typical blank  158  used in prior art methods  110 , such as illustrated in FIG. 3, would be about 22½ inches in diameter. Since the circular blanks  58  and  158  in both cases are most conveniently cut from square sheets, it can be seen that the amount of waste material created in the preparation of a 22½ inch diameter blank  158  is considerably more than that which results from the creation of a 19-inch diameter blank  58 . Moreover, in methods of the prior art, the centralized aperture  160  of the blank  158  must be considerably larger than the centralized aperture  60  in blanks  58  used in the invention  10 . Accordingly, the method of the invention  10  entails a second considerable savings stemming from less wasted scrap metal from the formation of the centralized aperture  60  of the blank  58 . 
     Having thus described the invention, it should be apparent that numerous structural modifications and adaptations may be resorted to without departing from the scope and fair meaning of the instant invention as set forth hereinabove and as described hereinbelow by the claims.