Abstract:
A method of rollforming one-piece tubular doorbeams. The method includes the steps of drawing a continuous metal strip, creating cut-outs in the edges of the strip at spaced locations, rollforming the strip into a tube so that the unindented edges engage one another, welding the engaged edges together, cutting the tube in the areas of the cut-outs to create pre-forms, and opening the ends of the pre-forms to create end brackets. Additional optional steps provide customization of the end brackets.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/217,790 filed Jul. 12, 2000 entitled “One (1) Piece Tubular Doorbeam”. 
    
    
     BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     The present invention relates to the forming of a tubular beam and more particularly to a one-piece tubular beam. 
     II. Description of the Art 
     Vehicle doorbeams are widely used in the automotive industry to enhance the impact strength of vehicle doors and thereby to enhance passenger safety. Typically these beams are fabricated from multiple pieces including a metal tube and brackets welded on the opposite ends of the tube. The brackets are used in securing the beam within the door frame. Such beams are not without their drawbacks. First, the multi-piece beams require numerous manufacturing steps, and therefore are relatively labor-intensive and expensive. Second, the structural integrity of these doorbeams greatly depends on weld consistency and weld quality. Third, any welding splatter left on the beam may cause a squeak if the splatter contacts another interior door component. 
     The doorbeams also can be manufactured as a single-piece or one-piece beam. A method for roll-forming such a beam is illustrated in U.S. Pat. No. 5,756,167 issued May 26, 2998 to Tamura et al. The Tamura process rollforms continuous strip stock into one-piece beams using specially designed rollers. The rollers have a circumference that corresponds to the length of the beam. The rollers create alternating rolled body portions and flat end brackets joined together by curving transition portions. This process also is not without its drawbacks. First, the tooling is extraordinarily expensive. Second, the separate set of tooling is required for each doorbeam. Third, extensive set up time is required when a new/different doorbeam is to be manufactured. As part of the set up, different circumference rollers require different distances between the axes of opposing and adjacent rollers. 
     One-piece beams also can be manufactured using stamping or pressing methodologies. Examples of such processes are illustrated in U.S. Pat. No. 5,183,718 issued Sep. 29, 1998 to Masuda et al and Japanese Patent Publication 4-238725 published Aug. 26, 1992. These methods form individual metal blanks into beams, and also are not without their drawbacks. First, these methods are relatively labor intensive resulting in relatively high manufacturing costs because individual blanks must be press formed. Second, stamping often utilizes less of the sheet than rollforming, thereby creating more waste. Third, different doorbeams require different tooling. 
     SUMMARY OF THE INVENTION 
     The aforementioned problems are overcome in the present application wherein a one-piece doorbeam is rollformed from continuous stock using relatively simple tooling and producing relatively little waste. More specifically, the process includes the steps of removing material from the edge of a continuous metal stock at spaced locations, rollforming the entire stock into a tubular shape so that the opposite edges engage one another except where material has been removed, welding the engaged edges, severing the tubular shape in the area where material was removed to create a rollformed piece having two ends, and opening at least one of the ends to create an end bracket. 
     The present invention has a variety of advantages over the prior techniques. First, highly specialized and unique tooling is not required. Second, virtually any length doorbeam can be created using a single set of tooling. Third, the integral end brackets can be uniquely shaped and processed following the basic forming steps. Consequently, the present invention is relatively labor efficient and inexpensive. Further, the quality and consistency of the tubular beam is improved. 
     These and other objects, advantages and features of the invention will be more fully understood and appreciated by reference to the detailed description of the preferred embodiment and the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a flow diagram of the process of the present invention; 
     FIG. 2 is a schematic view of the process; 
     FIG. 3 is a block diagram of four different processing options all using the process; 
     FIG. 4 is a perspective view of a door beam formed using the process and broken to show indeterminate length; 
     FIG. 5 is a top view of a portion of the continuous metal strip showing the area of the pierced indentations; 
     FIG. 6 is a view of a portion of the continuous rolled tube showing the area of pierced indentations; 
     FIG. 7 is a view of the individual door beam cut to length in the area of cut-outs, broken to show indeterminate length; 
     FIG. 8 is an end view of the beam in FIG. 7; 
     FIG. 9 is a perspective view of the beam pre-forms in a progressive press in which the ends of the pre-forms are opened and flattened; 
     FIG. 10 is a perspective view of the end of a door beam with reinforcement gussets; and 
     FIG. 11 is a perspective view of the end of a door beam with rolled-in reinforcements in the transition area. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The manufacturing process of the present invention is illustrated in FIGS. 1-3; and a tubular doorbeam fabricated using the process is illustrated in FIG.  4  and generally designated  10 . The beam  10  is a single piece and includes a tubular body  12 , a transition area  14 , and end brackets  16 . 
     I. Manufacturing Process 
     As illustrated in FIGS. 1-3 the tubular beam starts as a continuous web of flat stock drawn from a coil. As seen in FIG. 5 (which shows the stock after the pre-piercing step), the stock includes a pair of opposite edges  24 . In the preferred embodiment, the edges as the stock are linear and uniformly spaced from one another so that the stock has a uniform width. In the preferred embodiment, the material is martinsitic steel (i.e. Martinsite) such as Inland M 220  ultra high strength low alloy steel. Of course, other materials could be used that have suitable properties for the performance requirements of the doorbeam. 
     The first step  101  is the feeding of the continuous metal stock into a pre-piercing press. 
     The second step  102  is the trimming of the opposing linear edges  24  by the pre-piercing press at regularly spaced or period intervals forming indentations or cut-outs  22  (see FIG.  5 ). The pre-pierced, but still flat, stock is designated  20 . The spaced points  25  define the opposite ends of each indentation  22 . The distance between the points  25  corresponds to the length L of the tubular body  12  of the finished beam  10 . Depending on the implementation of the fourth step  104  of welding, this second step may be omitted. 
     The third step  103  is the rollforming of the pre-pierced stock  20  within a tube rolling mill. The flat stock  20  is rollformed into a tubular shape generally designated  30  (see FIG.  6 ). In the continuous tubular shape  30 , the opposite edges  24  of the stock engage one another in areas other than the cut-outs  22 . Preferably, the edges  24  abut one another, but they also could overlap one another. The cut-outs  22  create elongated gaps or spaces  32 . The edges of the cut-outs  22  do not engage one another. The rolling mill operates at a speed at which the subsequent steps are able to accept material. 
     The fourth step  104  is to weld the lateral edges  24  together between the elongate spaces  32 . The welding apparatus may operate continuously as the stock moves through the welder (because the spaced cut-outs  22  will not be joined), or the welding apparatus may be operated only in the areas between the elongate spaces  32  (i.e. only where the edges  24  engage one another. Further, if the second step  102  of pre-piercing has been omitted, the welding apparatus must be operated intermittently to create areas of joined edges separated by areas of unjoined edges. The preferred welder is a laser welder to obtain high weld quality. Any suitable welding technique, such as induction welding, also could be used. The welding seam  36  results from the welding (see FIG.  7 ). 
     The fifth step  105  is to size and straighten the welded tubular shape to increase the uniformity of the final beams  10 . 
     The sixth step  106  is to anneal the continuous stock. In the preferred embodiment, annealing performed only in the approximate area of the elongate spaces  32 . Annealing also can be performed before or after other steps in the process depending on the desired qualities and characteristics to be imparted to the doorbeam both for processing (e.g. pre-piercing) and/or as a final product. 
     The seventh step  107  is to cut the continuous tubular form into lengths creating individual items or pre-forms  40  (see FIGS.  7 - 8 ). This step occurs at the end of the rollforming line. The cuts occurs in the area of the elongate spaces  32  (if the stock has been pre-pierced) or in the area of unjoined edges (if the stock has not been pre-pierced), so that an unwelded portion remains at each end of the pre-form  40 . 
     In the eighth step  108 , the end of each pre-form  40  is opened to create a relatively flat end. The progressive press used to perform this step is illustrated in FIG.  9 . Preferably, the opening step includes a plurality of forming steps but may be done with only one step. In the preferred embodiment the elongate space  32  is initially opened as illustrated at  42  and is further opened as illustrated at  44 ,  45 , and  46 . After stamping in the final die, the end bracket  48  is fully formed. 
     The subsequent steps (i.e. those after the opening step  108 ) occur on various lines to perform different processes as illustrated in FIGS. 2 and 3. The particular processes or steps  110  utilized in each line will depend on the desired shape and features to be imparted to the ultimate doorbeam. The four process options illustrated in FIG. 3 are exemplary, and other process options can be readily developed depending on the desired result. 
     One alternative forming step  111  is to pierce at least one hole  52  (see FIG. 4) in the end bracket  16 . As many holes as are needed may be pierced. A second alternative forming step  112  is to add bends or angles  54  (see FIGS.  4  and  10 - 11 ) to the end bracket  16 . The angles  54  can be any one of a variety of shapes, and the angle may vary greatly depending upon the installation needs of the tubular beam  10 . A third alternative forming step  113  is to add reinforcement gussets  56  (see FIG. 10) to the angles  54  on the end bracket  16  to strengthen the bracket  16 . A fourth alternative forming step  114  is the rolling in of reinforcements  58  (see FIG.  11 ). In this step the edges of the trimmed cut-outs  22  are rolled over and into the center of the transition area  14 . This doubling back of the edges of the cut-outs  22  strengthens the transition area  14 . This rolling may also be done to reduce the profile of the transition area  14  to enable installation in areas with little clearance. A fifth alternative step  115  is to trim the end bracket  16  to a final shape and size. The trimming of the edges after all forming steps have completed provides improved consistency of the resulting doorbeams  10 . The alternative steps may be preformed in virtually any order or in any combination. 
     After all forming, shaping and trimming steps have been completed the door beam may be laser marked with the company name, date, shift, customer part number, or bar code to identify and track the beam for quality control reasons. Preferably each doorbeam is inspected  116  to confirm that has been made to specification. After the doorbeam is inspected  116  it is packaged  118  for shipment. 
     Four exemplary process options  201 ,  202 ,  203 , and  204  are illustrated in FIG.  3 . Each includes a various combination of the above-described steps, as well as other steps that will be recognized and understood by those skilled in the art. 
     The invention can be used to create a wide, and indeed limitless, variety of one-piece tubular doorbeams  10  wherein the tubular body  12  is integral with the end brackets  16  through a transition area  14 . The present invention results in an improved product at a lower cost. 
     The above descriptions are those of preferred embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents.