Abstract:
A roll-forming process for the manufacture of a structural member can be used in the manufacture of an automotive vehicle. The roll-forming process creates a component that has multiple cells with an integral internal web separating the cells, enhancing the strength, rigidity and stiffness of the component for any given size and shape. The roll-forming process starts with a piece of sheet metal and rolls the sheet metal into a desired shape and then rolls the tube back over on itself to create a second cell with the internal reinforcing web positioned between two structural cells of the beam. The rolled form is then welded into the formed shape to create the structural beam. The two cells of the beam can be the same general size or be formed as completely disparate sizes, depending on the design requirements of the structural member.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates generally to the manufacturing of structural members for use in automobiles and, more particularly, to a process for roll-forming sheet metal into a structural beam having an internal web to increase strength of the beam. 
       BACKGROUND OF THE INVENTION 
       [0002]    Manufacturing processes for automobiles have evolved from one that utilized primarily stamped and bent sheet metal pieces that were welded together through a MIG welding processes, i.e. a welding process in which a line of molten material is deposited by the welder in joining two pieces of metal together. Now, conventional automobile manufacturing processes incorporate in a greater degree hydroformed tubular members that are shaped to fit into the chassis of an automobile in a desired manner. The hydroformed members are particularly conducive to being welded through a spot-welding process, which involves the passage of electrical current between two electrodes to melt and join two pieces of metal placed between the electrodes. Spot-welding requires a frame design having appropriate access holes that is conducive to being manufactured using the spot-welding process. For example, if two tubular members are being spot-welded together, access to the adjoining walls of the two tubular members by the spot-welder electrodes must be provided. Other welding techniques, such as gas metal arc welding (GMAW), are also be utilized for welding tubular designs. 
         [0003]    Roll-forming is a process for forming a structural tubular member involving the transformation of a piece of flat sheet metal into the structural beam by passing the sheet metal through a series of rollers arranged to bend the sheet metal into the structural beam. Generally, tubular members are formed through the roll-forming process. These tubular members can be used directly in the manufacture of an apparatus, such as an automobile, or be used in a subsequent manufacturing process called hydroforming to create a specially shaped and bent structural member that roll-forming cannot by itself create. 
         [0004]    Hydroforming is a process by which a standard tubular stock member is placed into a form shaped to correspond to the particular member to be formed. A liquid is then introduced into the interior of the tubular stock and pressurized until the tubular stock expands to assume the shape defined by the configured form. The expanded and re-shaped tubular stock now has a substantially different shape. By forming cutouts and other access openings into the re-shaped tubular member, spot-welding electrodes can gain access to opposing adjacent sides to create a weld bond between juxtaposed members. In this manner, a frame, as an example, for an automobile can be created using in large part hydroformed tubular members. Once the hydroformed part is formed, attachment brackets are attached to the part to permit other components of the automobile to be mounted. Typically, these attachment brackets are welded to the hydroformed part by either a MIG or spot-welding process, whereupon the other components can then be bolted or welded to the attachment brackets. 
         [0005]    Whether hydroformed or merely roll-formed, the structural tubular member is not conventionally formed with any internal reinforcement and, thus, the walls of the tubular member must carry the entire load placed on the structural member and provide the requisite stiffness needed for the structural member to perform its operative function. The load carrying ability of the tubular member is a limiting factor in the design of hydroformed or roll-formed structural members and can result in a non-optimized beam design having increased material thickness in the walls of the beam or increased tube diameter. Either of these enhanced load carrying characteristics leads to an expensive overweight design. Furthermore, the increasing of the tube diameter causes problems in the packaging of the enhanced design, making automotive design more difficult. 
         [0006]    Accordingly, it would be desirable to provide a manufacturing process by which the structural beam can be formed with multiple tubular cells that provide a single structural member having an integral internal reinforcement to increase structural strength for a roll-formed beam of a given size and shape. 
       SUMMARY OF THE INVENTION 
       [0007]    It is an object of this invention to overcome the aforementioned disadvantages of the known prior art by providing a roll-forming process to create a tubular structural member that has an internal web reinforcement. 
         [0008]    It is another object of this invention to provide a roll-forming process for manufacturing a structural tubular member having multiple cells. 
         [0009]    It is still another object of this invention to roll-form a flat sheet of metal into a shaped tubular beam by rolling the sheet metal on top of itself to form an internal reinforcement web between two structural cells. 
         [0010]    It is an advantage of this invention that a roll-formed structural member can have increased strength for a given size and shape due to an integral internal reinforcement separating the cells of the structural member. 
         [0011]    It is another advantage of this invention that the cost of manufacturing automobiles can be reduced. 
         [0012]    It is a feature of this invention that the roll-formed structural beam is manufactured with an internal rib forming a reinforcement along the entire length of the beam. 
         [0013]    It is another feature of this invention that the roll-formed structural beam is formed in a fashion that creates two cells with a rib member separating the two cells. 
         [0014]    It is still another advantage of this invention that the roll-formed component, manufactured into multiple cells with an internal rib separating the cells to reinforce the component, increases strength, rigidity and stiffness of the structural component, while maintaining a predetermined size and shape. 
         [0015]    It is another advantage of this invention that the improved roll-forming process enhances the structural properties of the component without adding additional parts or external reinforcements to the component. 
         [0016]    It is a further object of this invention to provide a roll-forming process that creates an automotive component with multiple cells having an integral internal rib reinforcement that is durable in construction, inexpensive of manufacture, carefree of maintenance, facile in assemblage, and simple and effective in use. 
         [0017]    These and other objects, features and advantages are accomplished according to the instant invention by providing a roll-forming process for the manufacture of a structural member that can be used in the manufacture of an automotive vehicle. The roll-forming process creates a component that has multiple cells with an integral internal web separating the cells, enhancing the strength, rigidity and stiffness of the component for any given size and shape. The roll-forming process starts with a piece of sheet metal and rolls the sheet metal into a desired shape and then rolls the tube back over on itself to create a second cell with the internal reinforcing web positioned between two structural cells of the beam. The rolled form is then welded into the formed shape to create the structural beam. The two cells of the beam can be the same general size or be formed as completely disparate sizes, depending on the design requirements of the structural member. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The advantages of this invention will become apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein: 
           [0019]      FIG. 1  is a representative cross sectional view of a pillar forming part of an automotive frame manufactured from a piece of sheet metal using a roll-forming process according to the principles of the instant invention; 
           [0020]      FIG. 2  is a perspective view of a piece of sheet metal from which the pillar of  FIG. 1  is formed according to the principles of the instant invention; 
           [0021]      FIG. 3  is an end view of the structural member following a first formation stage of the roll-forming process to create the pillar of  FIG. 1 ; 
           [0022]      FIG. 4  is an end view of the structural member following a second formation stage and welding overlapping portions to form the pillar depicted  FIG. 1 ; 
           [0023]      FIG. 5A  is an end view of a second embodiment of the roll-formed beam having an internal web showing a first stage of formation according to the principles of the instant invention; 
           [0024]      FIG. 5B  is an end view of a second embodiment of the roll-formed beam having an internal web after the final stage of formation, this second embodiment being particularly adapted for further formation through a subsequent hydroforming process; 
           [0025]      FIG. 6A  is an end view of a third embodiment of the roll-formed beam having an internal web showing a first stage of formation according to the principles of the instant invention; 
           [0026]      FIG. 6B  is an end view of a third embodiment of the roll-formed beam having an internal web after the final stage of formation, this third embodiment also being particularly adapted for further formation through a subsequent hydroforming process; 
           [0027]      FIG. 7  is a partial perspective view of the A-pillar beam to depict the formation of optional slots formed in the outer in the outer wall of the first cell to permit certain welding techniques, such as laser edge welding; 
           [0028]      FIG. 8  is a partial perspective view of the opposing side of the A-pillar shown in  FIG. 7  to depict an optional opening in the second cell for internal access for welding purposes; and 
           [0029]      FIG. 9  is a partial perspective view of the A-pillar to show an optional weld access opening. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0030]    Referring to  FIGS. 1-4 , a structural beam formed according to the principles of the instant invention can best be seen. The structural member  10  can be used in a variety of devices in known manners, such as is depicted in  FIG. 1 , which is the A-pillar  10  of an automobile. Generally, automotive frame design requires structural components with this particular shape, size and configuration, which when assembled together form the chassis of an automotive vehicle. The A-pillars  10  are generally vertical frame members located at the front corners of the automobile to support the front part of the roof (not shown), the windshield W, side glass (not shown), and the front doors (not shown). The envelope  11  in which the A-pillar is positioned has a limited size and certain characteristics relating to the strength, rigidity and stiffness for the component  10  have to be maintained. To increase the strength or other properties of this particular structural component  10 , external reinforcements (not shown) or additional parts (not shown) could be added strategically to the structural member  10  as needed. Such additional parts or reinforcements add manufacturing steps, and additional materials to attain the requisite structural properties, and thus, increase the cost of manufacturing the component and the automotive vehicle into which this component  10  is assembled. 
         [0031]    As is reflected in  FIGS. 2-4 , the A-pillar  10  is manufactured through a roll-forming process during which a flat piece of sheet metal  20  is passed through a series of properly arranged rollers (not shown), as is known in the art, to bend the sheet metal  20  into a first cell  12  during a first stage of formation of the structural member  10 . The first cell  12  has an outer wall  13 , a side wall  14  and an inner wall  15 . Because of the particular utilization of this structural member  10  as an A-pillar, the first cell is also formed with a first mounting flange  18  and a second cell flange  19 . 
         [0032]    The first cell  12  and the second cell flange  19  are then passed through a second stage of rollers (not shown) to effect a bending of the second cell flange into a second cell  22  that folds back over the first cell  12  such that the second cell  22  is formed with a first end wall  23  that is positioned against the first mounting flange  18 , and a second end wall  24  that overlaps the side wall  14  of the first cell  12  and terminates in a second mounting flange  28 . Because of the particular application of this structural beam  10  as an A-pillar the mounting flange  18  bends around a portion of the outer wall  13  of the first cell before extending outwardly therefrom for connection to supporting structure of the vehicle chassis. The first and second end walls  23 ,  24  are separated by an exterior wall  25 . In this particular configuration, the A-pillar is formed in a generally trapezoidal shape such that the first and second cells  12 ,  22  are also shaped generally as trapezoids with the outer wall  13  and the exterior wall  25  being the primary external walls of the A-pillar with the inner wall  15  defining a reinforcing web extending generally parallel midway between the two primary external walls  13 ,  25 . 
         [0033]    Welding the first end wall  23  to the first mounting flange  18  against which the first end wall  23  rests, as well as welding the overlapping areas of the second end wall  24  of the second cell  22  and the side wall  14  of the first cell  12 , and optionally the overlapping areas of the second mounting flange  28  and the outer wall  13  of the first cell  12 , as is represented by the “x” designators in  FIG. 4 , secures the beam  10  in the two cell configuration with an internal reinforcement web  15  and provides a structural member that can be used in the design of an automotive frame. One skilled in the art will readily recognize that the specific shape of the structural beam  10  can be designed to fit the strength and stiffness parameters associated with the utilization of the beam  10 . The principles of the instant invention would have the structural beam  10  formed with a first cell and then with a second cell that folds back onto the first cell to provide a two cell structural beam with one of the walls of the first cell  12  becoming the internal reinforcement web  15  for the beam  10 . 
         [0034]    Welding can be accomplished through many known procedures, including MIG welding, spot welding, and other welding techniques, such as gas metal arc welding (GMAW). As can best be seen in  FIGS. 7-9 , these certain welding techniques can best be utilized if slots  42  or openings  40  are pre-punched into the sheet metal blank  20  to be properly positioned upon formation of the beam  10  to permit access into the interior of the cells  12 ,  22 . For example, as depicted in  FIG. 7 , the slots  42  formed into the outermost thickness of sheet metal at the overlap area on the first cell  12  allow the use of laser edge welding or GMAW welding techniques to join the layers of overlapping sheet metal. The access opening  40  in the exterior wall  25  of the second cell  22  would need to be aligned with a correspondingly located opening (not shown) in the internal reinforcing web  15  to permit access into the first cell for spot-welding the overlapping areas of the first cell  12 . Similarly, the weld access opening  40  in the end wall  24 , shown in  FIG. 9  would allow spot-welding techniques to be utilized at the end wall  23 . Accordingly, appropriately positioned openings  40 ,  42  will facilitate the welding of the cells  12 ,  22  to form the integral beam  10 . Preferably, the slots  40  are placed in the single thickness walls of the cells  12 ,  22 ; however, the slots can also be formed in the overlapping sections, though alignment of the slots  40  in one wall with the slots in the overlapping wall can be problematic. 
         [0035]    Referring now to  FIGS. 5A-6B , additional configurations of the two cell roll-formed structural member  30  can be seen. In  FIGS. 5A and 5B , the structural member  30  starts with a flat piece of sheet metal parent material, as depicted in  FIG. 2 , and rolls the sheet metal parent material into a cellular configuration that forms the first cell  36  from a portion of the sheet metal and then rolls the remaining parent sheet metal back against the first cell  36  to form the second cell  37 . While the two cells  36 ,  37  can be formed in a generally circular configuration or in a box-like configuration, as depicted in the drawings, the structural member  30  is formed so that the second end  32  mates against the side of the upper cell  36  with the second end  32  being welded to the outside of the second cell  36 . The first end  31  of the parent sheet metal is then welded to the outside of the lower cell  37  at a position that is spaced from the second end  32  with an intermediate strip  35  of the parent material extending between the first and second ends  31 ,  32 . Since the structural member  30  is formed from a continuous piece of sheet metal parent material extending from the first end  31  to the second end  32 , the strip  35  is an integral part of the blank  30 . Furthermore, the strip  35  forms the barrier between the upper and lower cells  36 ,  37  and creates an internal reinforcement web. 
         [0036]    An alternative configuration for the dual cell structural member  30  can be seen in  FIGS. 6A-6B  in which the first end  31  is rolled into the first cell  36  and then into the second cell  37 . The first end  31  is welded to a point on the sheet metal to define the first cell  36 , while the second end  32  is welded along the first cell  36  at a distance spaced from the first end  31  such that the strip of sheet metal becoming the barrier  35  between the first and second cells  36 ,  37  extends from the first end  31 , rather than along an intermediate strip of the sheet metal per the configuration of  FIG. 5A-5B . Either configuration of the dual cell structural member  30  works satisfactorily in a subsequent hydroforming process, particularly if the first and second cells  36 ,  37  are formed in a generally circular configuration; however, certain characteristics of one configuration may be desired over the other, as can be recognized below. 
         [0037]    Although the first and second cells  36 ,  37  of the structural member are depicted as being substantially the same size, the roll-forming process through which the structural members  30  are manufactured does not require that the cells  36 ,  37  be the same size or even the same shape. If the envelope in which the beam  30  is to be placed, or the operational characteristics desired for the beam, requires different sizes or shapes of the respective cells  36 ,  37 , such a configuration can be easily arranged. 
         [0038]    It will be understood that changes in the details, materials, steps and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description, may be employed in other embodiments without departing from the scope of the invention.