Abstract:
A method of manufacturing a hollow structural frame rail includes rotating a tube relative to a tool to reduce an outside diameter of the tube at predetermined positions along the length of the tube. An elastomeric insert is positioned within the tube. The tube is bent at a location containing the insert. The bent tube is hydroformed to define a finished shape of the frame rail.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This patent application claims the benefit of International Application No. PCT/CA2010/000370 filed Mar. 12, 2010 entitled “Method Of Producing Tailored Tubes” and U.S. Provisional Application Ser. No. 61/161,483 filed Mar. 19, 2009, the entire disclosures of the applications being considered part of the disclosure of this application, and hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates to a method of forming a tubular structural member for a vehicle. More particularly, a method of producing a hollow metal tube having certain portions expanded sixty percent more than other portions of the same tube is described. 
     BACKGROUND OF THE INVENTION 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Due to ever increasing concerns relating to vehicle fuel efficiency, increased efforts are being expended to reduce the overall weight of a vehicle. Improved vehicle handling and stability are also desired in combination with the reduction in weight. 
     Some vehicle manufacturers have successfully constructed a number of vehicle structural components from lighter weight materials including magnesium or aluminum alloys. Carbon fiber and reinforced plastic panels have also been incorporated within the vehicle design. This approach, however, may not be possible for certain applications where the component is subjected to substantial mechanical loading. Examples of such components may include vehicle frame members, suspension components, and axle housings. 
     Some vehicle frame members are constructed from “C”-shaped channels welded to one another. The channels are constructed from a relatively low carbon steel. Several brackets, gussets, flanges, and cross-members may be attached to the vehicle frame rail to provide attachment points for various vehicle body and suspension components that are not exactly aligned with the longitudinally extending frame rails. 
     Attempts have been made to hydroform hollow steel tubes to produce vehicle frame rails. While some of these attempts have been successful, limits on the amount of expansion that may be obtained by hydroforming exist. Some manufacturers have added additional procedural steps and off-line machines to bend, crush or otherwise deform a portion of the frame rail. While these additional sets of tools and process steps may more closely define a frame rail to a desired shape, the costs associated with these manufacturing techniques may be exorbitant. Accordingly, a need exists in the art to provide a manufacturing process for cost efficiently providing a reduced weight structural member having relatively complex geometry. 
     SUMMARY OF THE INVENTION 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     A method of manufacturing a hollow structural frame rail includes rotating a tube relative to a tool to reduce an outside diameter of the tube at predetermined positions along the length of the tube. An elastomeric insert is positioned within the tube. The tube is bent at a location containing the insert. The bent tube is hydroformed to define a finished shape of the frame rail. 
     The present disclosure also relates to a method of manufacturing a hollow structural frame rail including obtaining a tube having a substantially circular cylindrical outer surface. The tube is rotated and circumferentially spaced apart rollers are engaged with the outer surface to reduce an outside diameter of the tube at predetermined positions along the length of the tube. An elastomeric insert is positioned within the tube. The tube is bent at a location containing the insert. The bent tube is hydroformed to define a finished shape of the frame rail. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a perspective view of an exemplary frame rail constructed by a method of the present disclosure; 
         FIG. 2  is a cross-sectional view of the frame rail taken at the intersection portion A and portion B; 
         FIG. 3  is a cross-sectional view of the frame rail taken at the intersection between portion B and portion C; 
         FIG. 4  is a perspective view of a tube; 
         FIG. 5  is a perspective view of a work-in-process tapered tube; 
         FIG. 6  is a perspective view of a work-in-process bent and tapered tube; 
         FIG. 7  is a perspective view of a work-in-process hydroformed tube; 
         FIG. 8  is a perspective view of a hydroformed and hydropierced tube; 
         FIG. 9  is a schematic depicting a tool for rotating the tube and reducing its outer diameter; 
         FIG. 10  is a schematic depicting actuator roller assemblies for reducing the diameter of the tube; 
         FIG. 11  is a perspective view of an insert positioned within the tube prior to bending; 
         FIG. 12  is a cross-sectional view of the insert in an undeformed state; 
         FIG. 13  is a cross-sectional view of a portion of the insert in a deformed state; 
         FIG. 14  is a cross-sectional view of an alternate insert in an undeformed state; 
         FIG. 15  is a cross-sectional view of the alternate insert in a deformed state; 
         FIG. 16  is a schematic of a bending machine as well as a bending and hydroforming machine; and 
         FIG. 17  is a side view of an alternate tapered tube assembly. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     With reference to  FIGS. 1-2 , an exemplary frame rail constructed by a method of the present disclosure is identified at reference numeral  10 . Frame rail  10  includes a monolithic tube  12  having differently sized and shaped first through fifth portions A, B, C, D, and E, respectively. Each portion of frame rail  10  includes a top wall  14  and a bottom wall  16  interconnected by first and second side walls  18 ,  20 , respectively. The Figures depict each of the walls having a suffix letter corresponding to one of the first through fifth portions. For example, first portion A has a substantially rectangular cross-sectional shape including top wall  14 A and bottom wall  16 A having substantial equal lengths and extending substantially parallel to one another. First side wall  18 A has substantially the same size as second side wall  20 A. The first and second side walls  18 A,  20 A extend substantially parallel to one another. For reference purposes, the perimeter of first portion A is defined as a distance P. 
     Second portion B has a first end  24  seamlessly joined to first portion A. First end  24  has substantially the same cross-sectional shape as first portion A. Second portion B includes a second end  28  having a substantially rectangular cross-section. As shown in  FIG. 3 , the outer perimeter of portion B at second end  28  is reduced to approximately 0.63 P. Top wall  14 B and bottom wall  16 B are substantially the same size as top wall  14 A and bottom wall  16 A. The reduction in perimeter is accomplished by reducing the height of first side wall  18 B and second side wall  20 B. In the example depicted in the Figures, first side wall  18 B and second side wall  20 B taper substantially the same amount from first end  24  to second end  28 . It should also be appreciated that second portion B extends at an angle relative to first portion A. 
     Third portion C has a substantially constant rectangular cross-sectional shape having an outer perimeter of approximately 0.37 P. Third portion C extends at an angle relative to second portion B. 
     Fourth portion D is a tapered portion similar to portion B in that top wall  14 D and bottom wall  16 D are substantially the same size as the top and bottom walls  14 ,  16  of portions A, B, and C. First side wall  18 D and second side wall  20 D taper from a first end  30  to a second end  32 . At second end  32 , the perimeter of portion D is approximately 0.72 P. Fourth portion D may extend at an angle relative to third portion C as the final design of frame rail  10  requires. 
     Fifth portion E has the cross-sectional size and shape of second end  32  of fourth portion D. The cross-sectional shape of fifth portion E is substantially constant along its length. The perimeter of portion E is approximately 0.72P. Based on the above description, it should be appreciated that portion A has an approximate 60% expansion when compared to portion C. Similarly, portion E exhibits approximate 15% expansion when compared to portion C. 
     With reference to  FIGS. 4-8 , a method of producing frame rail  10  includes beginning with a work-in-process component or tube  40  having an outer surface  42  with a substantially circular cylindrical shape. An inner surface  44  of tube  40  also has a substantially circular cylindrical shape. Tube  40  is rotatably mounted within a machine such as a lathe  46  depicted in  FIG. 9 . A first end  48  of tube  40  is temporarily drivingly mounted to a spindle  50  of lathe  46 . Spindle  50  is driven by a motor  52 . A second end  54  of tube  40  is rotatably supported by a tail stock  56 . By energizing motor  52 , tube  40  may be rotated relative to a tool  58 . 
     As shown in  FIG. 10 , tool  58  may include three circumferentially spaced apart pressure roller assemblies  60 . Each pressure roller assembly  60  includes an actuator  62  operable to radially translate a roller  64  into and out of contact with outer surface  42  of tube  40 . The set of pressure roller assemblies  60  are also longitudinally moveable parallel to an axis of rotation  66  of tube  40 . By varying the force applied to each roller  64  in concert with the longitudinal position of the set of pressure roller assemblies  60 , outer surface  42  may be shaped. Once the pressure assemblies are no longer engaged with outer surface  42 , an intermediate level work-in-process tapered tube  70  is defined. Tapered tube  70  includes portions A, B, C, D and E but the outer shape of each portion is either substantially cylindrical or frustoconical. Other shapes may also be defined. Furthermore, the outer surface of each portion is aligned along the common axis of rotation  66 . Tapered tube  70  is now removed from lathe  46 . 
     One or more inserts  74 , depicted in  FIGS. 11-15 , may be positioned within tapered tube  70  at predetermined axial locations. Insert  74  is preferably constructed from an elastomeric material such as urethane or rubber. Insert  74  functions to restrict buckling, creasing or kinking of a localized portion of tapered tube  70  during a subsequent bending process. Insert  74  will likely have an outer surface  76  shaped to compliment at least a portion of the shape of inner surface  44 . In a first configuration shown in  FIGS. 11 and 12 , insert  74  includes an axially extending aperture  78  formed in the shape of an elongated slot. The shape of aperture  78  may be varied to maintain a desired shape of inner surface  44  and outer surface  42  after the bending process.  FIG. 13  depicts the shape of insert  74  after a compressive load has been applied. 
     An alternate insert  74   a  is shown in  FIG. 14  as a solid, cylindrically-shaped member. When a compressive force is applied to an outer surface  76   a  of insert  74   a , the shape of the deformed outer surface  76   a , as shown in  FIG. 15 , is different than the shape of deformed outer surface  76 . Based on this characteristic behavior, specifically tailored cross-sectional shapes may be defined within portions of the workpiece. For example, use of insert  74  having elongated aperture  78  assures that the cross-sectional shape at a bend will be substantially rectangular. 
       FIG. 11  depicts insert  74  having three portions F, G, H that are sized and shaped to closely match the shape of internal surface  44  of tapered tube  70 . Accordingly, a first portion F includes the largest outer diameter. Second portion G has a tapered outer surface. Third portion H has a reduced diameter substantially cylindrical surface. Insert  74  may enter an aperture  92  formed at the end of tapered tube  70  including first portion A. The smallest diameter third portion H of insert  74  enters aperture  92  first. Insert  74  is axially translated until second tapered portion G engages inner surface  44  within tapered portion B of tapered tube  70 . 
     The process of producing frame rail  10  continues by placing the subassembly of tapered tube  70  and insert  74  within a tube bending machine  94  or a combination tube bending and hydroforming machine  94 ′ as shown in  FIG. 16 . Combination bending and hydroforming machine  94 ′ will be described in greater detail at a later point in this paper. 
     Bending machine  94  includes a clamp  100  operable to restrain tapered tube  70  from movement at a particular location. In the example depicted in  FIG. 16 , clamp  100  engages an outer surface of second portion B. Bending machine  94  also includes a first rotatable die  102  and a second rotatable die  104 . First die  102  includes a cavity  106  sized and shaped to complement the size and shape of outer surface  42  of tapered tube  70  at first portion A. First die  102  is rotatable about an axis  108 . A first cam surface  110  is formed on first die  102 . First cam surface  110  is engageable with outer surface  42 . A first actuator  112  applies a force to rotate first die  102  and bend tapered tube  70 . 
     Second rotatable die  104  includes a cavity  116  sized and shaped to complement outer surface  42  of tapered tube  70  at portions C, D, and E. Second rotatable die  104  is rotatable about an axis  118 . A second actuator  120  provides a force to move rotatable die  104  and bend tapered tube  70 . A second cam face  122  is formed on second rotatable die  104  and is selectively engageable with outer surface  42 . It should be appreciated that in the example depicted, third portion H of insert  74  is elongated to extend beyond third portion C and at least partially enter fourth tapered portion D. As such, only one insert  74  is required to produce the particular frame rail  10  shown in the Figures. As previously noted, additional inserts may be positioned within tapered tube  70  if the geometry of the tapers and the position of the desired bends so dictate. 
     If bending machine  94  is provided separately from a hydroforming machine, a bent and tapered work-in-process tube  128 , shown in  FIG. 6 , may be removed from bending machine  94  and positioned within a hydroforming apparatus. During hydroforming, pressurized fluid acts on inner surface  44  to radially outwardly expand outer surface  42  into contact with die surfaces of the hydroforming machine. It is contemplated that 80-90 percent of the finished part shape is defined after completing the bending operation. The hydroforming operation qualifies exterior surface  42  and causes bent and tapered tube  128  to expand approximately 2-4 percent to place the tube in final form thereby defining a work-in-process rail  130  as depicted in  FIG. 7 . A hydropiercing operation may also be performed at this time if additional features such as apertures  96 ,  97  and  98 , shown in  FIG. 8 , are desired. Completed frame rail  10  may now be removed from the hydroforming and hydropiercing die. 
     As previously mentioned, it is contemplated that a combination bending, hydroforming and hydropiercing apparatus be used in lieu of two separate machines as previously described. In particular, it is contemplated that combination bending and hydroforming machine  94 ′ performs each of the previously described bending and hydro processes without the need for physical transfer of work-in-process bent and tapered tube  128  between a bending machine and a hydroforming machine. 
     Another alternate process step may include induction heating bent and tapered tube  128  after the bending operation has been performed to introduce formability back into the tube. This step may be desired if the tube has been sufficiently work hardened during the bending process to preclude proper hydroforming and hydropiercing. 
     In an alternate form shown in  FIG. 17 , a multi-piece frame rail  200  may be formed by fixing a first work-in-process tapered tube  202  to a second work-in-process tapered tube  204 . The tubes may be coupled to one another by any one of several known processes including mig welding, laser welding, mechanical fastening, adhesive bonding, and the like. The remaining process steps previously described may be performed on tapered tube assembly  200 . 
     Furthermore, the foregoing discussion discloses and describes merely exemplary embodiments of the present disclosure. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations may be made therein without departing from the spirit and scope of the disclosure as defined in the following claims.