Abstract:
A bumper beam and a method of fabrication. In a preferred embodiment, the bumper beam has a generally trussed-shaped section. The method generally comprises stamping a blank to form a front shell portion and rear plate portion; apertures in appropriate positions in the blank to accommodate vehicle rails or components of the bumper; folding the blank along a longitudinal interface line the separates the rear plate portion from the front shell portion so that at some part of the rear plate portion contacts at least some part of the interior side of the front shell portion; and welding parts of the rear plate portion and the front shell portion that are in contact.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to vehicle bumpers. In one aspect, the invention relates to a stamped folded vehicle bumper beam. This application claims priority of provisional U.S. Patent Application Ser. No. 60/302,534, filed Jul. 2, 2001. 
   2. Description of the Related Art 
   Bumpers are an integral part of any motor vehicle. The primary function of a bumper is to absorb and distribute impact loading during a collision, thus providing an important safety feature of the vehicle. While a bumper can assume a variety of configurations for providing the safety function, it is desirable that the shape of the bumper conform to the overall styling of the vehicle. Additionally, reducing the bumper weight is an important consideration in meeting fuel efficiency standards. 
   Bumpers have traditionally been roll formed or stamped from a single blank of material such as steel, and are rigidly attached to the vehicle frame. A roll formed bumper generally takes the shape of an arch with the apex of the arch facing forward toward the direction of travel. The bumper absorbs impact loading through the deformation, i.e. flattening, of the arch. However, flattening of the bumper under impact loading will tend to push the vehicle frame elements outward, thus causing considerable structural damage. Resistance of the bumper to deformation under impact loading is generally a function of the size, shape and strength of the material forming the bumper. Since the strength of the bumper is directly related to its size, it is difficult to obtain a bumper of sufficient strength while at the same time minimizing its weight and thus improving the vehicle&#39;s fuel efficiency. Furthermore, roll formed bumpers are typically mounted to the end of the vehicle frame elements, which involves a bumper-to-frame connection which has somewhat less rigidity and strength than a connection which is set back from the end of the vehicle frame elements. Mounting the roll formed bumper to the end of the vehicle frame elements effectively moves the bumper significantly forward of the vehicle chassis with resulting limitation on the vehicle aesthetic design considerations. 
   One such design consideration is impact performance. It is preferable that the front beam meet vehicle manufacturer specifications, such as managing a bather and a pendulum impact, without damaging adjacent systems. 
   Other important considerations involve noise, vibration, and harshness (NVH) considerations. The front beam is the first cross member of the vehicle frame and is an integral component of front end frame characteristics. The bumper beam design must also accommodate studio design constraints, which can include such aesthetic characteristics as a highly swept front end and an increased frame length of the front rails for improved crash performance. 
   Since the top surface of the front bumper beam can be visible in a lower air opening for the vehicle front end, the appearance of a bumper should meet design studio intent for a styled and integrated look with the front fascia for the bumper. In addition, the front beam cannot affect air intake for engine cooling by interfering with airflow in the lower air opening. 
   Past attempts to solve these functional and aesthetic design constraints have fallen short. One such past prior art attempt was to form the bumper beam as a roll formed beam with a B-shaped cross-section therein. This B-section roll formed beam was attached to a bracket welded to the end of the frame rails. The roll form beam could not meet several of the design objectives. First, the beam could not meet the sweeped appearance required for vehicle aesthetics, it could not accommodate the extra length of the frame rails, and it was positioned relatively high in the lower air opening, which affected both air intake and appearance. 
   Another past attempt was to form the bumper beam as a roll formed beam with stamped end cap portions. This second attempt included a roll formed section welded to two stamped end caps. The end caps would accommodate the sweep and extra length of the frame rails, but the roll form center section was still visible in the lower air opening of the vehicle. 
   Another prior art bumper was formed as a stamped open section with a back plate welded thereto to form a closed section beam. While this option proved least costly to manufacture, it was still desirable to reduce the number of parts and forming operations for a fully functional, high-strength and aesthetically-pleasing bumper design. 
   Further prior art attempts included a hot stamping process to form the bumper beam that proved costly to manufacture but can achieve the higher strengths needed in bumper applications. One standard option for this prior art system of this type was to form the bumper beam out of roll formed B-sections and box sections which include a swept bumper portion to satisfy aesthetic requirements. Ultra high strength steel was used to form this beam and also employed EPP filler pieces to match geometry of whatever bumper fascia assembly was employed. 
   This stamping prior art process achieved its strength through the use of geometry of the bumper beam cross sections, ultra high strength steel, and the sweep curvature of the bumper. Because this is still a roll formed bumper assembly, this process did not allow the bumper beam to fit closely to the vehicle and include bumper fascias with multiple geometry features as required for many bumper systems. Finally, these types of bumper systems that include swept roll formed sections also include an open arch geometry or a curved beam. When a front centerline impact is encountered, the impact force works to flatten these swept sections out. As a result, the only features of this prior art design resisting this impact force are the strength of the bumper beam material and the vehicle frame rails. 
   SUMMARY OF THE INVENTION 
   The invention comprises a stamped, folded, one-flange bumper beam and a fabrication method therefore. A flat steel blank proceeds through a series of stamping and folding operations to provide a bumper beam of the desired shape, which is then welded into a closed, one-flange structure. The forward portion of the vehicle frame elements is received for mounting within the interior of the bumper beam thereby providing a bumper-to-frame connection of increased rigidity and strength, and a bumper beam configuration readily conformable to the overall styling of the vehicle. The bumper beam conforms to the overall styling of the vehicle, is lightweight, and has a high strength-to-weight ratio. The use of a stamped form provides design flexibility to fit the fascia design and interface with other systems. The one-piece beam has an integral back plate that is folded over and welded to the top surface, resulting in a closed section beam that creates a very rigid structural member. The elimination of a bottom welding flange necessary for a separate back plate saves weight and material, and reduces the amount of clearance required for the bottom of the beam. The integral back plate also reduces the need for extra fixturing, welding equipment, and handling, and reduces overall cycle time, thereby reducing overall manufacturing costs. 
   This concept uses conventional stamping technology without additional extraordinary manufacturing processes. The stamping process can follow any required geometry including the shape of an external bumper fascia employed therewith, eliminating or reducing the need for foam fillers thereby reducing cost. 
   In addition, the cross sectional design developed for use on the inventive system herein allows use of lower strength steel, gaining strength through geometry thereby reducing cost by using a less expensive material (i.e., not ultra high strength steel). The inventive bumper beam described herein uses the geometry of a truss, which is stronger than an open arch design of prior art roll formed beams. In this design, the curved arch of the bumper beam front face is a longer line than the back plate of closed sections. In centerline impact, the force trying to flatten the arch defined by the front face is resisted by the integral strength of the back plate being in tension. Prior art roll formed beams do not have this advantage. With this design feature, it is not necessary to rely on the vehicle frame rails to resist side thrust caused from flattening of the arch as with prior art roll formed beams. 
   In addition, no complicated mounting brackets are required thereby reducing costs as well. The inventive front bumper beam described herein meets all applicable design and safety requirements while also being substantially less expensive to manufacture. 
   The bumper beam meets impact performance requirements, has a closed section and minimum number of fasteners to meet NVH requirements, accommodates both aesthetic considerations and receives the bumper beam frame rail extensions for improved impact performance, and is positioned so that it is visually integrated with the lower air opening at the front end of the vehicle so that it does not impede air flow. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
       FIG. 1  is a perspective view of a completed bumper beam according to the invention. 
       FIGS. 2A-D  are front, top, rear, and perspective side views, respectively, of the completed bumper beam of FIG.  1 . 
       FIG. 3  is a front view of one-half of the bumper beam of  FIG. 1  showing the locations of cross-section views of  FIGS. 3A-L . 
       FIGS. 3A-L  are cross-sectional views of the completed bumper beam shown in FIG.  15 . 
       FIG. 4  is an exploded view of the bumper beam of FIG.  1  and vehicle frame rails showing the components for mounting the bumper beam to the frame rails. 
       FIGS. 5A-E  are perspective views of the bumper beam of  FIG. 1  at intermediate steps in the fabrication process. 
       FIG. 6  is a flowchart of a bumper beam fabrication process according to the invention. 
       FIG. 7  is a schematic view of the various steps comprising the bumper beam fabrication process of FIG.  6 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIGS. 1 and 2 , a stamped folded bumper beam  10  is shown for mounting to the frame rails of a vehicle (not shown) to absorb and distribute impact loads to vehicle frame rails in the event of a collision. The bumper beam  10  is adapted for the mounting of a fascia and other aesthetic or design elements and accessory items such as a license plate and lights, e.g. fog lights, as hereinafter described. The bumper beam  10  is an elongated member comprising a front shell  12  and a rear plate  14  enclosing a beam-interior  16 . In the preferred embodiment, the front shell  12  and rear plate  14  are fabricated from a single flange of sheet metal, such as steel, which is stamped and folded to form the finished bumper beam  10 . The front shell  12  and rear plate  14  are attached along respective longitudinal edges by a folded web  62  (see FIG.  5 D). In the preferred embodiment, the finished bumper beam  10  comprises a center crosspiece  18  extending between a pair of frame rail pockets  20 . Extending laterally outwardly of the frame rail pockets  20  are end pockets  22 . 
   Referring to FIG.  3  and the corresponding cross sections of  3 A- 3 L, in cross  10  section the front shell  12  defines a generally variably arcuate surface conforming generally to the styling of the vehicle to which the bumper beam  10  is to be mounted. The front shell  12  is comprised of a center ridge  80  forming a first portion of the center crosspiece  18 , a pair of domed cover flanges  82  forming first portions of the frame rail pockets  20 , and the end pockets  22 . The upper edge of the center ridge  80  terminates in a center crosspiece flange  24 . The upper edge of the domed cover flange  82  terminates in a frame rail pocket inner flange  26 , a frame rail pocket upper flange  28 , and a frame rail pocket outer flange  30 . The center crosspiece flange  24  transitions into the inner frame rail pocket flange  26 . The perimeter of the end pocket  22  terminates in an end pocket flange  32 . The front shell  12  can be provided with elongated indentations or ridges to form strengthening ribs  34 . The front shell  12  can also be provided with mounting apertures, such as license plate mounting apertures  36 . The frame rail pocket upper flanges  28  and the center crosspiece flange  24  are provided with rear plate locking tabs  38  extending outwardly from the plane of the flanges  24 , 28  which are adapted to secure the rear plate  14  to the front shell  12  as hereinafter described. 
   The rear plate  14  is a generally flat, elongated member extending between the end pockets  22  and adapted to matingly communicate along a first longitudinal edge with a first longitudinal edge of the front shell  12  to enclose the beam interior  16 , as hereinafter described. The rear plate  14  comprises a center crosspiece back portion  84  which, along with the center ridge  80 , forms the center crosspiece  18 , and frame rail pocket plates  86 , which, along with the domed cover flanges  82 , form the frame rail pockets  20 . 
   The rear plate  14  is provided with a plurality of openings. In the preferred embodiment, the rear plate  14  is provided with frame rail openings  40 , frame rail mounting bolt apertures  42 , hand hold apertures  44 , mounting apertures  46 , 48 , access ports  50 , and flag bolt apertures  52 . The function of the rear plate openings will be described hereinafter. 
   The first longitudinal edge of the rear plate  14  terminates in a rear plate center crosspiece flange  54 , a rear plate frame rail pocket inner flange  56 , a rear plate frame rail pocket upper flange  58 , and a rear plate frame rail pocket outer flange  60 , which extend upwardly in a somewhat inclined orientation from the rear plate  14 . The flanges  54 ,  56 ,  58  and  60  are brought into mating communication with the front shell flanges  26 ,  28  and  30  as hereinafter described. 
   The folded web  62  connecting the rear plate  14  to the front shell  12  extends longitudinally to terminate in folding notches  64 . During the fabrication process, the folded web  62  comprises a folding ledge  66  (See, FIG.  5 D). 
   The completed bumper beam  10  is mounted horizontally and transversely to the frame rails  88  of the vehicle. Referring to  FIG. 4 , the frame rails  88  are provided with frame rail brackets  70 , which can be an integral part of the frame rails or attached to the frame rails  88  through conventional fasteners, such as bolted connections or welding. 
   The frame rail brackets  70  are mounted somewhat rearwardly of the forward ends of the frame rails  88  so that the frame rails  88  extend through the frame rail openings  40  into the beam interior  16  when the bumper beam  10  is mounted to the frame rails  88 . Mounting bolts  72  are used to connect the bumper beam  10  to the frame rail brackets  70  by passing the mounting bolt  72  through the frame rail mounting bolt apertures  42  and mating apertures in the brackets  70 . Mounting bolt washers  76  can also be provided. A mounting bolt nut  76  is used to secure the mounting bolt  72  to the bumper beam  10  and frame rail brackets  70 . Mounting the frame rail brackets  70  rearwardly of the forward ends of the frame rails  88  so that frame rails  88  extend into the interior  16  of the bumper beam  10  provides a beam-to-frame connection of high rigidity and strength. Furthermore, such a connection moves the bumper beam  10  closer to the vehicle body, providing a bumper beam configuration more readily conformable to the overall styling of the vehicle. Finally, the brackets  70  can be selectively mounted along the frame rails  88  to vary the length of the frame rails  88  inserted into the bumper beam  10  for strength and aesthetic considerations. Hand hold cutouts  44  are provided to enable the bumper beam  10  to be easily lifted and manipulated for mounting the bumper beam  10  to the frame rails  88 . The flag bolt apertures  52  are adapted to receive conventional flag bolts (not shown) for mounting  10  the bumper beam  10  to the frame along with apertures  42 . Access ports  50  as well as apertures  46 , 48  are provided for mounting optional and additional accessory components to the bumper beam. Such accessories include, for example, fog lamps, heater plugs, temperature sensors, wiring clips/connectors, license plate brackets, spoilers and other aerodynamic body features and the like. The bumper beam  10  is fabricated in a series of steps that comprise progressively stamping a flange of flat stock, referred to as a “blank,” into a desired shape using a series of conventional machine presses and dies, and folding the rear plate  14  into the front shell  12 . The fabrication process is automated and comprises transferring the blank through a series of stamping and folding operations. The blank is transported through successive stages by the use of robotic arms. Fabrication of the bumper beam  10  begins with a blank that is initially cut to a size approximating that of the bumper beam  10 . 
   Referring to  FIGS. 5-7 , the blank is first trimmed to an initial configuration in a blank die operation  100  which is completed at a blank die station  130 , and leaves the operation in a generally plate-like shape. A robotic arm then transfers the blank to a draw die station  132  where the front shell  12  is stamped in the blank in a draw step  110  using a first die set. At the completion of the draw step  110 , only the general shape of the front shell  12  has been formed in the blank. See,  FIG. 5A. A  robotic arm then transfers the blank to a trim and pierce die station  134  for a trim and pierce step  112  where excess material from the perimeter of the blank is removed, and the various cutouts and apertures  36 ,  40 ,  42 ,  44 ,  46 ,  48 ,  50  and  52  are punched in the rear plate  14 . See,  FIG. 5B. A  robotic arm then, transfers the blank to a flange die station  136  where the flanges  54 ,  56 ,  58  and  60  are formed in the rear plate  14  in a flange formation step  114 . In the preferred embodiment, the same station, i.e. the same press, is used to complete both the flange formation step  114  and a straight wipe step  116 . Alternatively, the straight wipe step  116  can be completed in a separate station  138 . In the flange formation step  114 , the flanges  54 ,  56 ,  58  and  60  are folded upwardly so that, when the back plate  14  is folded toward the interior of the front shell  12 , the flanges  54 ,  56 ,  58  and  60  will be in contact with the interior of the front shell  12 . See, FIG.  5 C. In the straight wipe step  116 , the rear plate  14  is folded approximately 90 degrees toward the interior of the front shell  12  along a longitudinal line defining an interface between the front shell  12  and the folded web  62 , thus forming a folding ledge  66 . The folding ledge  66  provides a contact surface for a folding tool to further fold the rear plate  14  into the front shell  12 , thus eliminating the tendency of the rear plate  14  to spring away from the front shell  12  at the completion of the folding processes. 
   In the straight wipe step  116 , the center crosspiece flange  24  and frame rail pocket flanges  26 ,  28  and  30  are formed. See, FIG.  5 D. The blank is then transferred by a robotic arm to the  450  flange station  140  where the rear plate  14  is further folded toward the interior of the front shell  12  in the  450  flange formation step  118 . See, FIG.  5 B. The blank is then transferred to the flatten die station  142  where the final folding of the rear plate  14  is performed in the flatten step  120  to align the rear plate flanges  54 ,  56 ,  58  and  60  into contact with the front shell flanges  24 ,  26 ,  28  and  30 , and form the finished bumper beam  10 . In the flatten step  120 , the rear plate locking tabs  38  are folded downwardly to lock the rear plate  14  into the front shell  12 . See, FIG.  2 C. The bumper beam  10  is then transferred by a robotic arm to  25  the welding station  144  where the front shell flanges  24 ,  26 ,  28  and  30  are spot welded to the rear plate flanges  54 ,  56 ,  58  and  60  in a spot weld step  122  to complete the bumper beam  10 . 
   The bumper beam  10  according to the invention is an improvement over the prior art roll formed bumper. As opposed to the arch configuration of the roll formed bumper, the invention provides a bumper beam  10  with a truss configuration, which provides an increased straight-to-weight ratio. Additionally, impact loads which would be otherwise transferred as lateral loading to the vehicle frame with the prior art arch configuration are distributed by the bumper beam  10  to the vehicle frame with a greatly decreased, if not eliminated, lateral load component. The bumper beam  10  has a lower weight, which will improve fuel efficiency. Furthermore, the bumper beam  10  can be easily formed into complex shapes to conform to the overall styling of the vehicle, while satisfying impact specifications. Significantly, the folding of the rear plate  14  into the front shell  12  eliminates the need for forming two separate flanges and welding the flanges together along an additional mating flange structure, thus simplifying fabrication and reducing costs. 
   While the invention has been specifically described in connection with certain specific embodiments thereof it is to be understood that this is by way of illustration and not of limitation. Reasonable variation and modification are possible within the scope of the forgoing description and drawings without departing from the spirit of the invention.