Abstract:
An apparatus includes a press with dies configured to deform a strip of material by drawing material primarily from a width direction, a slitter set to cut the deformed strip to a uniform desired width dimension, and a roll-former with rolls configured to shape linear portions of the deformed and now uniform-width strip into a continuous beam. The apparatus further includes a welder for welding abutting edges of the sheet together to form a permanent tube, a sweep station for imparting a longitudinal shape to the continuous beam, and a cut-off for cutting the continuous beam into segments useful as vehicle bumper beams. A controller controls timing of various components. The beam segments are optimized in specific regions for local strength and minimized weight, and features can be incorporated into the beam segments such as coplanar mounting surfaces.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims benefit of provisional application Ser. No. 60/723,393, filed Oct. 4, 2005, entitled CONTINUOUS PROCESS OF ROLL-FORMING PRE-STAMPED VARYING SHAPES 
     
    
     BACKGROUND  
       [0002]     The present invention relates to a continuous process of roll-forming pre-stamped varying shapes, and more particularly relates to a process combining a stamping/deforming process with a roll-forming apparatus to obtain advantages of both in a continuous process.  
         [0003]     The advantages associated with roll-forming have made roll-forming a preferred manufacturing method for many open structural sections and tubular structural sections.  
         [0004]     Automotive bumpers beams are one example of a product that has capitalized on the benefits of roll-forming to produce light weight, low cost, and performance based designs that are widely accepted and used commercially. Roll-formed tubular bumper beams represent a majority of the bumper beam market and continue to gain in popularity as bumper beams move from Class A surface designs such as stamped and chrome plated beams to structural beams that are positioned behind plastic fascias. Another style of bumpers are open sections (sometimes called “C” section bumpers) are also commonly used for bumper beam designs. These open sections typically require additional secondary processing to insert and weld strategically placed internal bulkheads and strapping. The use of bulkheads and strapping is to improve structural integrity of the section with the addition of a minimal amount of weight. These bulkheads and straps improve bending stiffness of the open section but achieve this increased performance at the cost of secondary processing.  
         [0005]     The roll-forming process has many benefits that make it a cost-effective method of manufacturing tubular beams. Some advantages of roll-forming include the abilities to form Ultra High Strength Steels (UHSS). Pre-pierce, mid-pierce, and/or post-pierce operations can be used on flat sections of the sheet material before roll-forming. Also, operations can be done in-line with the roll-forming process, such as in-line welding and cutoff. Some limitations of roll-forming include the inability to change material properties within the part and the inability to change the cross section along the length of the part. The inability to change the cross section along the length of the part typically results in excessive material being used in areas where it is not needed to meet performance requirements in other areas where it is needed. The excessive material also adds to the weight of the part and to material cost. Specifically, testing and computer analysis shows that a tubular beam that is constrained at its ends and loaded in the center will exhibit a free body diagram where greater section depth, (i.e., moment of inertia) at the beam&#39;s center produces a stiffer beam. The inability to change the cross section of a roll-formed tubular beam along its length results in a tubular beam with a constant moment of inertia. The constant moment inertia results in excess material and geometry in areas along the length of the tubular beam that do not contribute to the overall bending stiffness of the beam.  
         [0006]     Stamping processes have an advantage over roll-forming in that beams with non-uniform cross sections can be made. However, stamping operations are limited and generally less efficient than roll-forming since individual sheet blanks must be laterally moved and accurately positioned after each die stroke. Also, dies cannot make tubular beams. Further, UHSS sheet material is very wearing on dies depending on the amount of shape deformation being imparted onto the sheet material and depending on a strength of the material.  
         [0007]     It is noted that current roll-forming processes utilize relatively-lower-force, fast-acting stamping presses before the roll-forming process, but these presses are used to piece and cut features such as holes, slots, etc. into the material while it is flat and before roll-forming is used to shape the part.  
         [0008]     Thus, a system having the aforementioned advantages and solving the aforementioned problems is desired.  
       SUMMARY OF THE PRESENT INVENTION  
       [0009]     In one aspect of the present invention, an apparatus adapted to form a reinforcement beam includes a press with dies configured to deform a flat strip of material into a deformed strip with a three-dimensional shape by moving material primarily in a width direction, a slitter set to cut the deformed strip to a uniform width of desired constant dimension, and a roll-former with rolls configured to shape linear portions of the deformed and uniform-width strip into a continuous beam.  
         [0010]     In another aspect of the present invention, an apparatus adapted to form a reinforcement beam includes a press with dies configured to deform a continuous strip of material by moving the material primarily in a direction perpendicular to a feed direction defined by a length of the strip. The apparatus further includes a roll-former positioned in-line with the press and having rolls configured and arranged to receive the strip in the feed direction and shape edge portions of the deformed strip into a reinforcement beam.  
         [0011]     In another aspect of the present invention, a method comprises steps of providing a single elongated sheet defining a plane and including first, second, and third strip portions integrally connected together. The method further includes stamping the first strip portion to deform the first strip portion by moving material primarily in a direction perpendicular to the plane, and roll-forming the second and third strip portions by use of a roll-forming mill.  
         [0012]     In still another aspect of the present invention, a tubular reinforcement beam includes a sheet of material formed into a tubular beam having a length with a center section, opposing mounting sections, and intermediate sections connecting outboard ends of the center section and to associated ones of the mounting sections. A first transverse cross section taken through the center section defines a first wall length around its perimeter that is a first length dimension. A second transverse cross section through an inboard edge of the mounting sections defines a second wall length around its perimeter that is a second length dimension. A third transverse cross section taken through a middle of the intermediate sections defines a first wall length around its perimeter that is a third length dimension. The second length dimension is different than the first and third length dimensions, and wherein the first, second, and third length dimensions are selected to optimize local beam strength and minimize weight and minimize wasted material.  
         [0013]     In another aspect of the present invention, a method of forming a reinforcement beam includes steps of providing a press including dies at a location in-line and upstream of a roll-former having rolls, operating the dies to deform a continuous strip of material by moving the material primarily in a direction perpendicular to a feed direction defined by a length of the strip, and operating the rolls to receive the strip in the feed direction and shape edge portions of the deformed strip into a reinforcement beam.  
         [0014]     The concepts of methods and bumpers related to the above are also contemplated to be a part of the present invention, including their novel appearance/design.  
         [0015]     The present inventive concepts focus on tubular sections, but it should be noted that the concepts and their uniqueness can also be applied to open sections.  
         [0016]     These and other aspects, objects, and features of the present invention will be understood and appreciated by those skilled in the art upon studying the following specification, claims, and appended drawings. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0017]      FIG. 1  is a flow chart showing a process embodying the present invention.  
         [0018]      FIG. 1A  is a side view of an apparatus incorporating a roll-forming mill, a stamping station, a welding station, and a sweeping station for the process of  FIG. 1 .  
         [0019]      FIG. 2  is a side view of a vehicle bumper beam embodying the present invention.  
         [0020]      FIGS. 3-6  are cross sections taken through  FIG. 2 .  
         [0021]      FIG. 7  is a side view of the vehicle bumper beam after being roll-formed but prior to being longitudinally swept.  
         [0022]      FIG. 8  is an end view of the beam of  FIG. 7  moving through an exemplary roll-forming station, the view showing the beam, the rolls, and a weld joint. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0023]     The current invention defines a way to produce roll-formed tubular beams with varying cross sections from high-strength sheet material, such as materials of over 120 ksi, ultra-high-strength steel of over 160 ksi, and martinsite materials of over 220 ksi.. The ability to change cross sections along the length of the beam is achieved by combining a pre-forming process via stamping with the roll-forming. The stamping process and roll-forming operations are done in-line and sequentially. Sequential processes in-line without the need for secondary handling results in a very cost efficient manufacturing process. The stamping press is used to pre-form material as well as pre-pierce the sheet material and add features before it travels through the roll-forming tooling. The stamping of the material while it is in the flat produces a shape with varying depth and geometry across the length of the part. For example, the formed shape could represent the rearward section of a tubular bumper section. The stamping press that combines the stamping of features and forming of varying shapes would have a greater tonnage than a typical pre-piece press that stamps features into the material. The present stamping press would also have to include stamping dies beyond the required punches and buttons necessary for the stamping of features. Since it is envisioned that material grades above mild steel such as UHSS material would be used to fabricate tubular bumper systems, it is assumed that a one-hit stamping operation must be sufficient to form the shape. Higher grade materials such as UHSS undergo a sizable amount of work hardening which makes the material susceptible to cracking if multiple hits are required to produce the desired final shape. If the stamping process requires a large amount of forming and in turn causes the materials to significantly work harden, it is likely that the stamped shape would be formed in a one-hit operation to avoid any material cracking that might result from multiple stamping of the work hardened material. Aggressive forming via stamping can be done in multiple hits if caution is exercised in speed of forming to keep work hardening at a minimum. A good understanding of the application of design guidelines with respect to bend radii should be exercised when stamping UHSS. It should also be noted that the shape when formed by UHSS material is formed primarily by moving material and not stretching or extruding the material. Materials such as UHSS have high yield and tensile strengths and in turn a low elongation. The low elongation translates directly to low ductility which prohibits the forming through material thinning, i.e., extrusion/drawing.  
         [0024]     The material that is used to form the shape during the stamping process draws from the width of the coil and not down the length of the coil. This will require that the width of the coil that feeds the stamping press to be oversized to allow for shape forming via stamping and still provide sufficient blank width for the roll-forming operation which is used to finish the shape into a tubular geometry. It is also envisioned that relief slots will need to be introduced at the ends of the formed shape. These slots will assist in forcing material from the edges of the blank width and not down the length of the formed shape. The relief slots also will maintain blank flatness of the unstamped non-deformed areas of the blank before and after the shape is stamped into each part. The forming operation in the press will produce an irregular width blank since material moves across the coil width and will need to be resized before the material can pass through the roll-former. Roll-forming uses the edges of the material to guide the material from pass to pass and to trap the material while bending is being performed at each of the passes. The resizing of the blank width can be done at one or more locations along the manufacturing process. It is contemplated that the irregular blank will be slit immediately after the material leaves the stamping press. The slitting operation may have to be offset where one edge is slit and then used as a reference edge to slit the other edge. The material can also be slit after one or more of the early passes of the roll-former operation. It is contemplated that there may be some advantages to begin some initial forming in the roll-form mill before the irregular blank is resized with a slitting operation and before the roll-forming process is finalized. An additional option is to resize the irregular blank in a station of a multiple station stamping operation. One option would be to have the bed of the stamping press be at least twice the length of a typical part, or the other option would be to use two presses in-line. It is envisioned that the first station of the stamping press or the first press would stamp the relief slots needed at the ends of the part length and form the complete shape. The second station of the press or the second press would stamp features (holes, slots, etc . . . ) into the formed shape and trim the irregular blank to a size appropriate for the roll-forming process which will finish the part into a tubular beam section with varying cross-sectional geometries along the length of the part.  
         [0025]     Due to the amount of forming that is required for the part, it may be necessary to accumulate material after the press and before the roll-forming process. In a typical pre-pierce operation where features are added to the material while it is flat, the die is configured to travel with the material, (i.e., flying pre-pierce die). Preferably, the forming die would be configured to stamp while moving longitudinally along with the moving material, i.e., flying die configuration. Alternatively, if the shape-forming die is too heavy to move with the material, it may become necessary to accumulate the material after the press and before the roll-forming process. , Another option for excessively heavy dies would be to forgo the accumulation of material after the press and use a stop-start process with the roll-forming operation. Roll-form mills can be run successfully and efficiently using a stop-start repetitive motion, but stop-start motion is not a very complimentary process if in-line high frequency induction welding is used. A stop-start process may be more suited for either laser welding or contact welding.  
         [0026]     The formed shape and either the untrimmed blank or the trimmed blank can now be fed into the roll-forming process. The roll-form tooling would be designed to provide clearance for the formed shape. It is envisioned that only upper roll tooling be used to complete constant part geometry via roll forming, with the stamp formed perimeter of the part would be supported while the rest of the perimeter is roll formed. It is envisioned that the depth of the formed shape and the shape itself would change along the length of the part. The width at some given location and most preferably a location near the transition between the stamped formed section and the roll-formed section would remain constant along the length of the part. This common width is important because it provides a location where the material can be constrained as the remaining material is formed in the roll-forming process. The ability to constrain the formed part as the roll-forming process continues will cease because at some point along the roll-forming process, the individual legs of the part will converge to form a tubular shape. At this point, internal mandrels may be necessary to constrain the shape formed from stamping while the roll-forming process completes the tubular geometry.  
         [0027]     The individual legs of the part are brought to a point of contact via the roll-forming process and at this point, the two individual legs are welded to form a one-piece tubular part with varying cross sections along the length of the part. Welding can be done in various ways where the type of the welding process used is based on numerous factors, i.e., geometry, desired cycle time, etc. . . . Options for welding may include high frequency induction welding, contact welding, or laser for tubular section. Other welding options such as impulse seam welding (rotary spot), plasma arc welding, or laser may be more suitable for irregular shaped geometries. All of these welding methods are widely used today to produce commercially available tubular and irregular shapes of constant cross section.  
         [0028]     An automotive bumper beam typically requires some degree of curvature which is complimentary to vehicle styling. As styling changes and becomes more aggressive, a bumper beam with multiple radii becomes easier to package in the available envelope. Imparting of multiple radii in a bumper beam is referred to as a compound swept bumper. This ability to produce compound swept bumper beams in-line and during the manufacturing process can be accomplished with an apparatus that uses servos, is driven, and is computer controlled. This type of apparatus allows for real time adjustment of a bending roller which is used to impart curvature into the beam. Because of the real time adjustment of the bending roller, multiple radii can be imparted at given locations along the length of the beam. The last in-line operation is to cut the beam section to length. The cutoff operation can be done in various ways. The most common method of cutting bumper beams to length is to use a flying cutoff apparatus. A flying cutoff will travel with the part and perform the cut-off operation as the part is moving at line speed. A typical flying cut-off apparatus would include part clamping steel forms, air or hydraulic cylinders, and shearing blade.  
         [0029]     The uniqueness of the present invention is the ability to produce a one-piece roll-formed structural beam or an open section roll-formed structural beam that has varying cross section along the length of the part. The ability to change the cross section along the length of the beam is achieved by the use of a forming die and a stamping press positioned upstream and in-line with the roll-forming process. The innovative design of the roll tooling allows the stamped pre-formed shape to move its coplanar flat edge sections through the individual roll-forming passes freely without distortion or shape change of its now-stamp-formed center section. Each pass of the roll-forming process continues to form the material of the edge sections into a final shape that incorporates the stamped form. Current roll-forming processes utilize relatively-lower-force, fast-acting stamping presses before the roll-forming process, but these presses are used to piece and cut features such as holes, slots, etc. into the material while it is flat and before roll-forming is used to shape the part. The present invention increases the tonnage of the upstream stamping press and incorporates forming dies into the stamping press. The stamping press or presses are used to form the steel with a shape that when closed in geometry with the use of roll-forming, produces a tubular beam section with varying cross-sectionals along the length of the part. The same concept can be applied to open sections where the stamping operation imparts an irregular shape across the length of the part and the roll-forming operations process the rest of the part shape. The varying of cross sections along the length of the part provides the opportunity to efficiently use material and geometry to achieve performance requirements. The result is a weight and performance optimized structural member that is produced in a continuous cost-effective manufacturing process.  
         [0030]      FIG. 1  is a flow chart showing a process embodying the present invention, and  FIG. 1A  shows a corresponding apparatus. As noted, the process starts with a step  30  ( FIG. 1 ) where a coiled sheet  31  ( FIG. 1A ) is unrolled and the uncoiled strip/sheet  32  is fed forward. The process proceeds to a step  33  to pre-pierce and shape form the sheet  32  through the use of a stamping press  34  that actuates dies  35  and  36  together against the sheet  32 . The press  34  and/or dies  35  and  36  preferably are movable laterally along with the sheet  32  during the stamping process and also are relatively fast-acting. Alternatively, the roll-forming operation can be slowed or stopped during the stamping operation. The dies  35  and  36  are configured and designed to stamp the sheet material, primarily pulling and moving material from a width direction and not from a longitudinal direction of the sheet  32 . It is noted that a preferred material is ultra high strength steel (UHSS), which can be bent but basically not drawn or stretched. Accordingly, pulling and moving material laterally (rather than longitudinally) is a significant concept when USHH material is used. Slits in the sheet at each end of a (future) bumper section can be used to reduce longitudinal movement of sheet material during the three-dimensional deformation process of step  33 .  
         [0031]     The process proceeds in a step  38  through slitter  39  that slits/cuts edges of the formed sheet  32  to a particular known width dimension, with edge portions of the sheet  32  still in a coplanar flat condition.  
         [0032]     The process then proceeds in a step  41  through a roll-forming operation, as illustrated by the roll mill  42  having roll-forming stations  43 - 48 ′. The particular illustrated roll mill  42  has rolls constructed to form the sheet into a tubular shape (see  FIG. 7 ) which is welded in process step  50  at abutting edges  51 ,  52  ( FIG. 8 ) and welded at location  82  in a welding station  53  ( FIG. 1A ). Where necessary or desirable, an internal mandrel can be positioned upstream or downstream to help maintain cross sectional shape or to provide support for bending or forming through the roll forming operation. For example, the internal mandrel can be anchored at location  54  and an anchoring tie-bar or cord can extend downstream (or upstream) to provide mandrel support. Due to the stamping operation, the middle or lower portion of the cross section changes shape longitudinally and laterally, causing the final cross section of the final beam  72  to vary in a depth dimension and shape along its length (see  FIGS. 3-6 ).  
         [0033]     The process then proceeds in a step  60  where the continuous welded tubular beam  61  is longitudinally swept as it moves through stabilizing/motivating rolls  49  and a sweep station  62  with adjustable external mandrels  63  and with (if needed) internal mandrels  64 . Thereafter, the continuous beam  61  is cut to length in step  70  by a cut-off apparatus  71  into individual beams  72  useful as impact reinforcement bumper beams on a vehicle. The entire process is controlled by a controller for optimal, coordinated, and simultaneous operation.  
         [0034]     Notably, one overall apparatus and process of rolling, welding, and sweeping a tubular beam of a constant cross section is shown and described in Sturrus U.S. Pat. Nos. 5,092,512 and 5,454,504, and an exemplary cut-off device is shown in Heinz U.S. Pat. No. 5,305,625. The reader is referred to these disclosures if additional detail about those processes are desired. Also, their teachings are incorporated herein in their entirety for the purpose of fully disclosing and teaching the present invention. The present concepts can be used with a power adjusted variable sweep station, such as those known in the art.  
         [0035]      FIG. 2  is a side view of a vehicle bumper beam embodying the present invention as it comes off the cut-off apparatus  71 .  
         [0036]      FIGS. 3-6  are cross sections taken through  FIG. 2 . Notably, these cross sections are similar to cross sections taken through similar locations in the continuous beam  61  (see  FIG. 7 ) prior to the step of sweeping the beam  61 .  
         [0037]      FIG. 7  is a side view of the vehicle bumper beam after being roll-formed but prior to being longitudinally swept. Notably, the top “half” section of the beam is linear and constant in cross section (compare the upper portion of  FIGS. 3-6  and also see  FIG. 8 ), while the bottom “half” section of the beam is deformed into different three-dimensional changing longitudinal shapes (compare the  FIGS. 3-6 ). It is contemplated that various features can be incorporated into the beams  72 . For example, the angled surfaces  73  ( FIG. 2 ) become coplanar and aligned mounting surfaces  74  when the beam  61  is swept to become individual beams  72 . The coplanar mounting surfaces  74  are adapted to be attached to a front of vehicle frame rails, such as by attachment bolts or fasteners, and can include pre-pierced holes for the attachment bolts and fasteners.  
         [0038]      FIG. 8  is an end view of the beam of  FIG. 7  moving through an exemplary roll-forming station, the view showing the beam  61  engaged by bottom forming roll  80  and side containment rolls  81 . A weld joint  82  found at station  53  is shown at abutting edges  51  and  52 . Sequential formation of the top “wings” or side flanges  84  of the sheet are illustrated by the positions  85 - 88 .  
         [0039]     It is contemplated that the present process can be used to manufacture sophisticated beams with non-uniform cross section along their length, allowing the beams to be “customized” and optimized for various applications, such as for interior cross car structural beam, frame components, exterior cross car structural beams, roof bows, windshield header, rocker panels/sills, door beams, engine cradles, and instrument panel supports. It is contemplated that the present concept would be more cost competitive and have a more efficient/higher through-put than hydro-forming processes and also provide design flexibility over stamping processes.  
         [0040]     It is to be understood that variations and modifications can be made on the aforementioned structure without departing from the concepts of the present invention, and further it is to be understood that such concepts are intended to be covered by the following claims unless these claims by their language expressly state otherwise.