Abstract:
A beam article for a vehicle includes a plurality of separate elongated metal sheets attached together to form generally planar walls of an elongated tubular structure. At least one of the plurality of separate elongated metal sheets has a shear wall that is disposed along a hollow interior of the elongated tubular structure and is attached at opposing walls of the elongated tubular structure. At least one of the plurality of separate elongated metal sheets comprises an edge that abuts a side surface of an adjacent one of the plurality of separate elongated metal sheets to define a non-radiused perpendicular weld corner along the elongated tubular structure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 15/173,797, filed Jun. 6, 2016, which is a continuation-in-part of U.S. patent application Ser. No. 14/692,327, filed on Apr. 21, 2015, now U.S. Pat. No. 9,381,880, which claims the benefit and priority of U.S. provisional application Ser. No. 62/089,334, filed Dec. 9, 2014, and U.S. provisional application Ser. No. 62/024,751, filed Jul. 15, 2014, and U.S. provisional application Ser. No. 61/985,029, filed Apr. 28, 2014, which are hereby incorporated herein by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to beam-forming apparatus and methods, and elongated beams manufactured using same, and more particularly relates to multi-strip beams and related apparatus and methods for forming automotive bumper reinforcement beams from multiple strips. However, a scope of the present invention is not limited to bumper reinforcement beams nor automotive uses. 
         [0003]    Modem vehicles include bumper systems with reinforcement beams that must pass stringent performance requirements (e.g. test standards that measure torsional and bending impact strengths, various barrier impacts, vehicle to vehicle and pedestrian impacts), but also meet industry standards that place a premium on minimizing weight (e.g. mpg standards). Also, the competitiveness of the industry requires minimizing manufacturing cost while providing high dimensional consistency, reliability of manufacture, and design and manufacturing flexibility. 
         [0004]    Bumper reinforcement beams are used to provide cross car structure to bumper systems, and are often made by roll forming and/or extrusion processes. Roll forming can provide a competitive process cost with good part quality when used in high volume runs. However, most high-volume commercial roll forming processes are limited to constant cross-sectional shapes, are limited to forming a single sheet of material, require significant lead time to develop the forming rolls, and require substantial investment in heavy-duty roll forming equipment. Secondary processes have been used to reshape portions of roll formed beams, but secondary processes are expensive, slow, often not dimensionally consistent, require multiple handling of in-process parts, and can be manually intensive. 
         [0005]    Extruded aluminum beams are sometimes specified by original equipment manufacturers (called OEMs) due to their light weight, high strength-to-weight ratio, and the ability of extruded aluminum beams to have walls with different thicknesses located for optimal performance. However, aluminum is an expensive material, and further extrudable grades of aluminum are limited in tensile strength and are generally high in cost. Also, aluminum beams have constant cross sections along their full length, due to the extruding process. Also, beams made using extrusion processes require secondary operations, such as beam-curving (i.e. “sweeping”), hole-punching (e.g. for bracket attachment or for attachment holes or clearance holes), and aging/thermal-treatment of the material (for strength and stability). 
         [0006]    An improvement is desired that provides flexibility of part design (including use of optimally-placed wall materials, varied wall thicknesses and shapes), but that also provides process savings/improvements in terms of low cost, relatively lower capital investment, high efficiency of manufacture, good reliability, high dimensional consistency, and low in-process inventory. It is desirable to use forming and bonding processes that are known and non-exotic. 
       SUMMARY OF THE PRESENT INVENTION 
       [0007]    In one aspect of the present invention, a beam article for a vehicle includes a plurality of separate elongated metal sheets attached together to form generally planar walls of an elongated tubular structure. At least one of the plurality of separate elongated metal sheets has a shear wall that is disposed along a hollow interior of the elongated tubular structure and is attached at opposing walls of the elongated tubular structure. At least one of the plurality of separate elongated metal sheets comprises an edge that abuts a side surface of an adjacent one of the plurality of separate elongated metal sheets to define a non-radiused perpendicular weld corner along the elongated tubular structure. 
         [0008]    In another aspect of the present invention, a beam article for a vehicle includes a plurality of separate metal sheets each having a planar shape and attached together to form an elongated tubular structure enclosing a hollow interior area. At least two of the plurality of separate metal sheets are arranged horizontally and comprise a non-linear edge that attaches along a side surface of a generally vertical wall of the elongated tubular structure to define a non-radiused corner of a cross section taken transversely to a length of the elongated tubular structure and to provide a non-constant width along the elongated tubular structure. 
         [0009]    In yet another aspect of the present invention, a beam article for a vehicle includes a plurality of separate pre-formed sheets attached together to form generally planar walls of an elongated tubular structure. At least two of the plurality of pre-formed sheets comprise vertical walls and at least three of the plurality of pre-formed sheets comprise horizontal walls. The horizontal walls each comprise opposing edges edge that attach at inside surfaces of the vertical walls to each define a non-radiused perpendicular weld corner. 
         [0010]    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 THE DRAWINGS 
         [0011]      FIGS. 1-3  are exploded perspective, assembled perspective, and cross-sectional views of a beam made of five aluminum sheets, two forming front and rear walls, and three forming horizontal shear walls, the front and rear walls having frame-attachment holes and having up flanges and down flanges extending above and below the shear walls, all corners of the beam being non-radiused perpendicular corners. 
           [0012]      FIGS. 4-5  are perspective and cross-sectional views of a beam similar to  FIG. 2 , but with channel ribs in its front wall. 
           [0013]      FIGS. 6-8  are perspective and cross-sectional views of a beam similar to  FIG. 4 , but with channel ribs and a varied cross section along its length. 
           [0014]      FIG. 9  is an exploded perspective view of a multi-sheet beam made from five preformed sheets, similar to  FIG. 2 , but the beam having a rear wall with thicker/different material in a center region and thinner/different material in end regions. 
           [0015]      FIG. 10  is an exploded perspective view of a multi-sheet beam similar to  FIG. 9  but made from seven preformed sheets, including a short center sheet and two shorter end sheets forming the rear wall of the beam (with gaps between the center sheet and two shorter end sheets), and the intermediate horizontal shear wall being similar in length to the center sheet in length but having outwardly angled end surfaces. 
           [0016]      FIG. 11  is an exploded perspective view of a multi-sheet beam similar to  FIG. 2  and made from five sheets, including a preformed front wall having rearwardly-deformed end sections starting at noticeable bends at outer edges of the center region (and optionally including channel ribs), and an intermediate horizontal shear wall foreshortened and having concavely shaped end portions. 
           [0017]      FIG. 12  is a cross section of a multi-sheet beam, where the intermediate horizontal shear wall has edges extending to front and rear surfaces of the beam, and where upper and lower front sheets combine with the front tip of the intermediate horizontal shear wall to form the front wall of the beam, where upper and lower rear sheets combine with the rear tip of the intermediate horizontal shear wall to form the rear wall of the beam, and where top and bottom horizontal shear walls abut inward surfaces of the combination front wall and combination rear wall. 
           [0018]      FIG. 13  is an enlarged view of a circled area (a T corner) in  FIG. 12 . 
           [0019]      FIG. 14  is an enlarged view similar to  FIG. 13  but where the various sheets forming the T corner have three different thicknesses. 
           [0020]      FIGS. 15-17  are exploded, perspective, and center cross-sectional views of a variable depth multi-sheet aluminum beam, the beam having a constant cross section across its center region and rearwardly narrowing end cross sections, with all cross sections having a shallower depth than the beams in  FIGS. 1-8  and having shallower channel ribs in its front wall. 
           [0021]      FIG. 18  is a front view of a multi-sheet beam where the front wall has a constant height and the top and bottom horizontal shear walls extend in having planes rearward from upper and lower edges of the front wall, but where the intermediate horizontal shear wall has an undulating non-planar shape (shown in dashed lines). 
           [0022]      FIGS. 19-21  are front, and cross-sectional views of a double-tube beam where one tube has a varied shape along a length of the beam. 
           [0023]      FIG. 22  is a front view of a multi-sheet beam where the front wall has an arching upper edge that extends vertically well above a top of ends of the beam. 
           [0024]      FIG. 23  is an exploded view of a multi-sheet beam, the front and rear walls having fixturing holes and wall-locating slots, with one or more of the three shear walls having slot-engaging tabs that locate into the wall-locating slots, and the fixture having pins engaging the fixturing holes. 
           [0025]      FIG. 24  is a cross-sectional view of a multi-sheet beam, where the intermediate and bottom horizontal shear walls form non-radiused perpendicular corners with the front and rear walls, but the illustrated top horizontal shear wall forms non-radiused corners that are 5-10 degrees off from a perpendicular angle, or more preferably 2-5 degrees off from a perpendicular angle. 
           [0026]      FIGS. 25-26  are perspective and cross-sectional views of a prior art extruded aluminum beam with double tube design and front up flange. 
           [0027]      FIGS. 27-28  are perspective and cross-sectional views of a prior art roll formed steel beam with double tube design and radiused corners. 
           [0028]      FIG. 29  is a view similar to  FIG. 28  but after initial impact where radiused corners are beginning to collapse. 
           [0029]      FIG. 30  is a perspective view of a prior art, reinforcement beam with a cross section profile matching the beam in  FIG. 28  (which is roll formed from a single steel sheet), the beam having end caps welded onto angle-cut ends to define outboard ends of the front wall. 
           [0030]      FIG. 31  is a perspective view of a beam dimensionally similar to  FIG. 30 , but where the outboard ends are formed by pre-forming the outboard ends of the front wall and shear walls (instead of using secondary cutting and welding operations). 
           [0031]      FIGS. 32-34  are prior art beam tests,  FIG. 32  showing a three-point bending test,  FIG. 33  showing a zero offset centerline bumper impact test (also called an “HHS 100% overlap impact test”), and  FIG. 34  showing a 73.2 mm offset centerline overlap impact test. 
           [0032]      FIGS. 35-36  are charts comparing mass savings of a multi-sheet aluminum beam (see  FIGS. 4 and 6 ) over an extruded aluminum beam (see  FIG. 25 ),  FIG. 35  comparing mass for beams fitting into a same package space and equivalent HHS bumper impact test performance;  FIG. 36  comparing beam mass for beams fitting into a same package space and having similar bending test results. 
           [0033]      FIGS. 37-39  are charts comparing mass savings of a multi-sheet steel beam of constant cross section (see  FIG. 4 ) and a multi-sheet steel beam of varied cross section (see  FIG. 6 ) over a roll formed steel beam (see  FIG. 27 ),  FIG. 37  comparing mass savings for beams fitting into a same package space and having equivalent bending moment;  FIG. 38  comparing mass savings for beams fitting into a same package space and having an equivalent IIHS 100% overlap impact test performance; and  FIG. 39  comparing mass savings for beams fitting into a same package space and having an equivalent IIHS 73.2 mm offset overlap impact test performance. 
           [0034]      FIGS. 40-41  are plan and side views of a traditional MIG weld in prior art, the view showing a weld bead and a heat-affected-zone (also called a “HAZ region”) extending 5-15 mm (or more) from the edge, the HAZ region having material properties significantly reduced due to heat generated during the welding process, leading to significantly reduced impact performance characteristics. 
           [0035]      FIG. 42  is a perspective view of a typical prior art laser weld, which includes a smaller HAZ region. 
           [0036]      FIGS. 43-44  are 1st and 2nd side views, and  FIG. 45  is a perspective view, of a cold metal transfer (CMT) welding process using a laser beam to weld a cold wire fed into the weld area, the CMT welding process minimizing the heat-affected-zone around the weld to less than about 3 mm, and potentially less than about 1.5 mm. 
           [0037]      FIGS. 46-47  are side views of a friction stir welding (FSW) process using a spinning/moving tool that causes solid state welding, the FSW process eliminating or nearly eliminating the heat-affect-zone around the weld. 
           [0038]      FIGS. 48-50  show fixturing and welding of the multiple sheets to form a beam,  FIG. 48  showing welding of a first shear wall to front and rear walls,  FIGS. 49-50  showing welding of additional shear walls. 
           [0039]      FIGS. 51-52  are perspective end views of a swept double-tube bumper reinforcement beam with a 12-18 inch hat-shaped internal reinforcement centered on a “flat” front wall of the beam&#39;s lower tube. 
           [0040]      FIGS. 53-54  are perspective end views of a swept double-tube beam with an internal reinforcement similar to  FIGS. 51-52  but where the front wall includes stiffening channel ribs. 
           [0041]      FIG. 55  is a top view of an impacted beam with buckle-type failure, and  FIG. 56  is a chart showing energy absorption by the beam of  FIG. 51  compared to a beam without internal reinforcement. 
           [0042]      FIG. 57  is a cross section of a beam with welded non-radiused corners, and having localized annealing of welds at the non-radiused corners. 
           [0043]      FIGS. 58-59  are charts relating to  FIG. 57 ,  FIG. 58  showing hardness variations in the beam&#39;s (vertical) front wall across the weld, and  FIG. 59  showing similar hardness variations in the shear wall abutting the front wall, where annealing can reduce a size of the hardness variations by 50% or more, depending on the time period and temperature of the annealing process and depending on materials of the beam. 
           [0044]      FIGS. 60-61  are cross sections of two similar double-tube beams, where the beam includes a vertically-flat front wall, a (horizontal) mid-level shear wall, and one or more sheets forming top, rear and bottom walls. 
           [0045]      FIG. 62  is an exploded cross section of a double-tube beam, the beam including a vertical “flat” front wall (which may be longitudinally swept or linear) and including a horizontal mid-level shear wall, and including (upper and lower) L-shaped walls that form the rear and top (or rear and bottom) walls of the beam, the figures also showing an optional internal reinforcement. 
           [0046]      FIG. 63  is an exploded cross section similar to  FIG. 62 , but with the front wall including channel ribs across the two tubes, the figures also showing an optional internal reinforcement. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0047]    It should be understood that many of the present innovative concepts are inter-related, and can be combined in different ways to generate a wide variety of different beam designs. Concurrently, persons skilled in the art will understand that it is not possible to illustrate every single possible beam that could be constructed using these principles. Accordingly, skilled artisans will understand that the wide variety of beams can be constructed using characteristics selected from any of the various illustrated embodiments. Thus, the present illustrations are not intended to be exhaustive, nor limiting. 
         [0048]    In the following figures, multi-sheet beams (also called “multi-strip beams” or “bumper reinforcement beams” or “beam segments”) are described as made from high strength material (aluminum or steel sheets) welded together. The beams typically have optimally-placed wall thicknesses and properties at strategic locations to give them excellent impact strengths while minimizing weight as needed for specific vehicle applications. Novel welding processes are also discussed for forming low heat-affect-zones around the welded area of beams, particularly around the non-radiused perpendicular corners formed by abutting adjacent sheets, and a related novel fixturing system is described for holding the sheets together during welding. As used herein, the term “non-radiused corner” (or “zero radiused corner”) is used to mean a corner formed by an edge of a first sheet abutting a non-edge (body) of a second sheet, where the abutting structure at the corner defines an angle of about 90 degrees (e.g. within 5-10 degrees of perpendicular), and where the abutting structure at the corner does not include a radius formed by sheet material that would “roll” or become unstable during a side impact into the beam at the corner. 
         [0049]    The beam  100  ( FIGS. 1-3 ) is made from five sheets of aluminum, including sheets forming its front wall  101 , rear wall  102 , top horizontal shear wall  103 , intermediate horizontal shear wall  104 , and bottom horizontal shear wall  105 . The shear walls  103 - 105  are generally planar, (but are pre-formed to have non-linear front and rear edges). The front and rear walls  101  and  102  matingly engage and are secured to the edges by continuous welds, such as welds located at the six non-radiused corners  106  ( FIG. 3 ) formed when orthogonally-related sheets abut. The front and rear walls  101  and  102  are pre-formed to include attachment holes  107  in the rear wall  102  (also called “attachment structure” herein, and is intended to include welded-on brackets with holes) and access holes  108  in the front wall  101 , and any other features desired such as accessory mounting hole  109 . It is contemplated that the front and rear walls  101  and  102  (or other walls) can be pre-formed (i.e. roll formed, pierced, punched, or stamped), and can be non-planar or planar (e.g. when unstressed) but sufficiently flexible to take on the shape of the edges when biased into engagement by the welding fixture. (See for example the fixture in  FIGS. 50-52 .) Up flanges  110  and down flanges  111  on the front and rear walls  101  and  102  extend above and below the top and bottom shear walls  103  and  105 , respectively. 
         [0050]    The illustrated beam  100  ( FIG. 3 ) can, for example, have thicker sheets forming the front wall  101  and the rear wall  102 , and thinner sheets forming the shear walls  103 - 105 . For example, when aluminum is used, the front and rear walls  101 - 102  can be 2 mm-5 mm thick material, or more preferably 2 mm-3 mm thick, and can be 80 ksi tensile strength material, or more preferably 120 ksi tensile strength (or more, especially the front wall); while the shear walls  103 - 105  can be 1.5 mm-3 mm thick material, or more preferably 1.5 mm-2.2 mm thick, and can be 60 ksi tensile strength material or more preferably 72 ksi to 87 ksi yield strength. It is noted that the aluminum can be selected from very high strength aluminum, including aluminum that is much higher in strength than extrudable grades of aluminum. When steel is used instead of aluminum, the front and rear walls  101 - 102  can be 1.0 mm-4 mm thick material, or more preferably 1.2-2.0 mm thick, and can be 190 ksi tensile strength material, or more preferably 220 to 250 ksi tensile strength or more (e.g. Martensite materials and ultra-high strength materials); and the shear walls  103 - 105  can be 0.8-3 mm thick material, or more preferably 1-1.5 mm thick, and can be 190 ksi tensile strength material, or more preferably 220 to 250 ksi material or more. A ratio of thicknesses of the front and rear walls  101 - 102  to the shear walls  103 - 105  can be important to total cost and/or beam function. For example, strips thickness ratios of front and rear walls  101 - 102  to the shear walls  103 - 105  is preferably in a range between a ratio 2:1 down to a ratio of almost 1:1. An outer dimension of the beam segment  100  can be 90 mm-150 mm high and 30 mm-80 mm fore-aft (deep), but it is noted that the beam can be made to be any size or shape for its intended function or intended environment. A length of the illustrated beam segment  100  matches a cross car dimension of a vehicle for which it is intended. 
         [0051]    It is noted that only certain classes of aluminum material are extrudable. The aluminum materials having a highest tensile strength are not extrudable and generally considered not weldable. By using the present innovative concepts including welding techniques, beams can be made from aluminum stronger than the “extrudable” classes of aluminum. This allows beams to be made using a much wider range of aluminum materials than can be processed by extruding processes, including using stronger aluminum materials and/or thinner/thicker/multi-thickness aluminum sheet materials. In particular, higher strength aluminums lead to lower weight beams while maintaining strength properties. 
         [0052]    The present apparatus (and related methods) have many advantages, including relatively low capital cost for equipment, reduced lead times for equipment, is easy to automate (leading to lower manual labor costs), and potentially provides reduced in-process inventory and reduced secondary processing. At the same time, the present apparatus is flexible and able to produce a wide range of beam shapes, including beams having non-radiused perpendicular corners (also called “zero-radius corners”) well suited for optimal impact strength, beams having discontinuous walls, beams having strategically-located thicker and thinner sheets (or having strategically-located higher strength and lower strength sheets) at locations along the beam to provide best functional properties. It also allows formation of up (and down) flanges which extend above (or below) the beam, which is sometimes desired by vehicle manufacturers. Such flanges can help the manufacturer&#39;s vehicle pass impact testing, can support fascia, and can serve as mounting sites for various components, sensors and accessories. 
         [0053]    The illustrated beam segment  100  ( FIG. 3 ) has an up flange  110  extending above the front wall  101 . This is sometimes specified by the vehicle manufacturer in order to provide support to adjacent components, such as support for the front end fascia or for supporting an attachment clip or wire clip. It is noted that the up flange  110  can be a consistent height, or can be increased near a center of the vehicle or increased at selected locations along its length. 
         [0054]    Also, the illustrated beam  100  has non-radiused corners (also sometimes referred to as “square corners” or “T-shaped corners”) where an edge of one sheet abuts a side of another sheet at a perpendicular 90 degree angle. (The phrase “non-radiused corners” is used herein to refer to 90 degree corners formed by abutting planar sheets, but is intended to include corners that are slightly varied from 90 degrees, such as 85 degrees or even 80 or 75 degrees (see  FIG. 24 .) This contrasts to traditional roll formed beams which necessarily have radiused corners (see  FIGS. 27-28 , and  FIG. 29  where the radiused corners lead to early collapse upon impact). In roll formed beams having radiused corners, the inner radius typically has to be greater than at least about 4 times the thickness of the material to avoid shearing or fracturing the material at the corner as it is bent into the shape of the corner. The radiused corners tend to roll and provide a “softer” or lower initial resistance to impact, and hence a potential for a greater tendency of catastrophic collapse due to the existence of the radius (see  FIG. 29 ). In contrast, the illustrated beam  100  with non-radiused corners does not have any corner radius at all. This provides advantages when impacted, since square corners provide an immediate and sharp rise in its resistance to the impact (commonly referred to as “highly efficient impact resistance” since a generally higher amount of energy is absorbed than in impact beam systems having a lower efficiency of impact resistance). Hence, a beam&#39;s resistance against catastrophic collapse is improved by the existence of non-radiused corners. It is contemplated that, even though non-radiused corners are preferred in the present innovative beams, some beams could be developed with some radiused corners. For example, a beam could be formed using a single sheet to form front, top, and bottom walls (i.e. with radiused corners joining same), with additional sheets forming the rear wall and intermediate shear wall (and having non-radiused corners). 
         [0055]    Additional beams are described hereafter, with similar components, features, characteristics, and attributes being identified using the same number but with the addition of a letter such as “A”, “B”, and etc. This is done to reduce redundant discussion and not for another purpose. 
         [0056]      FIGS. 4-5  show a beam  100 A similar to beam  100 , but with channel ribs  114 A in its front wall  101 A, one channel rib  114 A being centered over each tubular section of the beam  100 A. Testing shows that channel ribs  114 A help stabilize the front wall during an impact, leading to an improved impact resistance and/or an improved bending strength over an identical beam ( 100 ) without the channel ribs  114 A. The channel ribs  114 A can be as deep or shallow as desired in the beam for functional purposes. (Compare ribs in  FIGS. 5 and 17 .) The illustrated preferred channel rib  114 A extends about 25% a width of the underlying tubular section, and the channel rib  114 A is about as deep as it is wide. However, different channel depths are contemplated, including making the channel rib  114 A so deep that a bottom of the channel rib  114 A rests on the sheet forming a rear wall  102 A of the beam  100 A. The illustrated shear walls  103 A- 105 A have edges that define a longitudinal shape of the beam, sometimes referred to as its sweep. The front wall  101 A is formed to match a shape of the edges of shear walls  103 A- 105 A. The rear wall  102 A can be relatively planar (when unstressed) and deformed during fixturing to a shape of the rear edge of the shear walls  103 A- 105 A (or can be pre-formed to shape). The illustrated edges of the walls  103 A- 105 A ( FIG. 4 ) are non-linear but generally parallel, such that a length of the beam defines constant cross-sectional dimensions. 
         [0057]    A modified beam  100 B ( FIGS. 6-8 ) is similar to the beam  100 A ( FIGS. 4-5 ) but the beam  100 B ( FIGS. 6-8 ) has shear walls  103 B- 105 B with non-parallel edges, such that its cross-sectional shape changes along a length of the beam  100 B. Thus, beam  100 B has a larger (deeper) cross-sectional dimension in a depth direction in its center region ( FIG. 8 ), and a narrower (shallower) cross-sectional dimension in a depth direction at its outboard ends ( FIG. 7 ). This beam  100 B provides a more aerodynamic appearance to the leading end of the vehicle. It is noted that bumper reinforcement do not require as high of bending strength at the structural mounts on ends of the beam where the beam is bolted to a vehicle frame or to vehicle crush tubes. Contrastingly, near a center of the beam  100 B, it is desirable to have a greater bending moment (i.e. larger cross-sectional shape) in order to pass IIHS offset overlap impact tests. (See  FIG. 34 .) The beam  100 B can have a lesser swept center section (i.e. a larger-radius when viewed from above) and more sharply swept end sections (i.e. smaller-radius when viewed from above). 
         [0058]    The sheets in beams can have different thickness and strengths as desired for optimal performance, and also a particular sheet could have different sheet segments welded together end to end. For example, a beam  100 C ( FIG. 9 ) has a rear sheet  102 C with a center portion  102 C′ made of steel having a thickness of 2 mm and that is about 16-20 inches long. Outboard sheets  102 C″ for example could be a similar steel material but having a thinner thickness, such as 1.0-1.S mm thickness. The sheets  102 C′ and  102 C″ are welded together, such as along a laser weld line, to form a continuous “hybrid” sheet extending a length of the beam  100 C. The resulting hybrid rear wall  102 C could result in a large amount of material mass savings. A same arrangement can be done on a front wall  101 C, or on shear walls  103 C- 105 C. 
         [0059]    Beam  100 D ( FIG. 10 ) is similar to beam  100 C, but in beam  100 D, a rear center portion  102 D′ is not connected to a rear outboard portion  102 D″. Instead, there is a gap between the portions  102 D′ and  102 D″, such as gaps that are generally about 4-10 inches long. Also, an intermediate horizontal shear wall  104 D is similar in length to the center rear sheet  102 D′, but notably it may be somewhat longer than the center rear sheet  102 D′ in length so that the ends of the center rear sheet  102 D′ do not align with ends of the shear wall  104 D. This is done to avoid adversely affecting bending strength of the beam at that point. Outer ends of the intermediate horizontal shear wall  104 D extend at an outboard angle as they extend from the rear wall  102 D toward the front wall  101 D. Notably, it is contemplated that the ends of the intermediate shear wall  104 D can be linear, or curved, or otherwise any shape desired to optimize beam strength and impact properties while minimizing beam weight. 
         [0060]    Beam  100 E ( FIG. 11 ) includes a preformed front wall  101 E having rearwardly-deformed end sections  101 E′ defining a vertical bend line  101 E″. The bend line  101 E″ is not a sharp bend, but instead is a gradual curve formed to avoid concentration of stress and to provide a good transition from the center to ends of the beam. The front wall  101 E may or may not include channel ribs ( 114 A), and these may or may not extend a length of the beam. An illustrated intermediate horizontal shear wall  104 E is foreshortened and has concavely shaped end portions. Top and bottom horizontal shear walls  103 E and  105 E are relatively planar, but have a front edge matching a shape of the front wall  101 E. The rear edge of the shear walls  103 E- 105 E are non-linear and and non-parallel and generally curved to define a desired shape. The sheet for a rear wall  102 E is relatively planar and flexible, such that it is planar when unstressed, but so that it bends to match a shape of the rear edge of the shear walls  103 E- 105 E when fixtured and pressed thereagainst. (See  FIGS. 1, 4, 6, and 48-50 .) 
         [0061]    Beam  100 F ( FIGS. 12-13 ) is made of seven sheets of aluminum. An intermediate horizontal shear wall  104 F extends to and forms a part of the front and rear surfaces of the beam  100 F. Two upper and lower front sheets  101 F′ and  101 F″ combine with the front tip of the intermediate horizontal shear wall  104 F to form a front wall  101 F. Two upper and lower rear sheets  102 F′ and  102 F″ combine with the rear tip of the intermediate horizontal shear wall  104 F to form the rear wall  102 F of the beam  100 F. Top and bottom horizontal shear walls  103 F and  105 F abut inward surfaces of the combination front wall  101 F and the combination rear wall  102 F. It is noted that friction stir welding described below (see  FIGS. 46-47 ) is particularly well adapted to bond the center weld on the beam  100 F in a manner maintaining a smooth “flat” front surface.  FIG. 13  is an enlarged view of a circled area XIII in  FIG. 12  at the center of beam  100 F (a T corner). Notably, preferably a welding process is used so that no weld material extends away from the welded corner. Restated, there is essentially no weld bead. Instead, all of the weld material is captured within the corner as illustrated, and hence the front surface (and/or rear surface if a similar weld is used) is “flat”. 
         [0062]    In beam  100 F ( FIG. 13 ), all abutting sheets have a similar thickness. However, in a modified beam  100 G ( FIG. 14 ) the various sheets forming the corner each have different thicknesses. Thus, beam  100 G has dissimilar materials or dissimilar thickness materials top to bottom on a given sheet. This beam  100 G presents novel properties since it provides a lower (or higher) bending strength along the lower tubular section of the beam  100 G. 
         [0063]    Beam  100 H ( FIG. 15 ) is similar to beam  100 B ( FIG. 6 ), but beam  100 H has a generally thinner fore-aft dimension along its length, and a sharper bend on a front wall  101 H as it transitions from a first sweep (first curve) along the center of the front wall to a sharper second sweep (second curve) along the outboard ends of the front wall  101 H. Also, a channel rib  114 H is shallower than the rib  114 B in beam  100 B. (Compare  FIG. 17  and  FIG. 8 .) 
         [0064]    Beam  100 J ( FIG. 18 ) has a shape similar to beam  100  ( FIG. 1 ), but beam  100 J has an intermediate horizontal shear wall  104 J that is non-planar. Specifically, the shear wall  104 J has an undulating or wavy shape, with one wave on each side of center. More or less waves can be formed by the shear wall  104 J, or sharp zig-zag bends can be made, and also the waves can be consistent or inconsistent in width or height of undulation. 
         [0065]    Beam  100 K ( FIGS. 19-21 ) is similar to beam  100  ( FIG. 1 ), but beam  100 K has a top shear wall  103 K that is arch-shaped, and the front and rear walls  101 K and  102 K match its shape. Thus, the two tubes formed by beam  100 K are dissimilar in a center region (see  FIG. 21 ) but similar at the beam&#39;s ends ( FIG. 20 ). In particular, the illustrated bottom tube section maintains a constant shape, but the top tube varies from a largest shape in the center ( FIG. 20 ) to a narrower tube at the ends ( FIG. 21 ). 
         [0066]    Beam  100 L ( FIG. 22 ) is similar to beam  100 K, but a top shear wall  103 L has an even greater arcuate shape. It is noted that the top shear wall  103 L can follow a top edge of the front wall  101 L, or it could extend in a horizontal plane. 
         [0067]    Beam  100 M ( FIG. 23 ) includes front and rear walls  101 M and  102 M with fixturing holes  130 M and wall-locating slots  131 M. The fixturing holes  130 M in the front (and rear) walls  101 M and  102 M engage pins  132 M in a fixture  133 M to accurately locate the sheets  101 M- 105 M when positioned in the fixture  133 M. One (or more) of the three shear walls  103 M- 105 M have tabs  135 M (note that tabs  135 M are only shown on the intermediate shear wall  104 M) that locate into mating wall-locating slots  131 M, thus accurately locating the horizontal shear walls  103 M- 105 M on the front (and rear) walls  101 M and  102 M during welding. The fixturing holes  130 M and slot-tab structures  131 M/ 135 M simplify the fixtures needed for assembly. It is noted that the fixtures can also include other securement devices, such as clamps and mechanical holders (engaging two sides of sheets to hold them), or vacuum cups and magnets (engaging one side of sheets to hold them), and/or can include other means known in the art for accurately locating adjacent parts for welded assembly. See  FIGS. 50-52  described below. 
         [0068]    Beam  100 N ( FIG. 24 ) has top, bottom and intermediate horizontal shear walls  103 N- 105 N that form non-radiused corners  106 N with front and rear walls  101 N and  102 N. The intermediate and bottom horizontal shear walls  104 N and  105 N form non-radiused perpendicular corners. However, the top horizontal shear wall  103 N extends at an angle to horizontal, such that it forms a non-radiused corner that is about 1-10 degrees off from a perpendicular angle, or more preferably 2-5 degrees off from a perpendicular angle (when used as a bumper reinforcement beam). It is contemplated that the beam  100 N could be “flipped” so that the angled wall is on a bottom of the beam when in a vehicle-mounted position. 
         [0069]      FIGS. 25-26  illustrate an extruded aluminum beam  500  in prior art used as a baseline for comparison to multi-sheet beams incorporating the various concepts noted above. The beam  500  includes front, rear, top, intermediate, and bottom walls  501 - 505  and a front up flange  506 . 
         [0070]      FIGS. 27-28  illustrate a roll formed steel beam  600  made of high strength steel in prior art used as a baseline for comparison to multi-sheet beams incorporating the various concepts noted above. The roll formed steel beam  600  includes front, rear, top, intermediate, and bottom walls  601 - 605  defining radiused corners  608  and includes channel ribs  606  over the tubes in the beam  600 . 
         [0071]      FIG. 29  illustrates an impact against the beam  600 , where it&#39;s cross-sectional shape changes as it begins to collapse during an impact. It is noted that deformation tends to start at the radiused corners, which leads to instability in all walls of the roll formed beam and hence leads to “early” catastrophic collapse of the beam. 
         [0072]    A beam  600 A ( FIG. 30 ) is similar to beam  600 , but its ends are angle cut in a secondary operation, and a cap  609 A is welded onto each end. The caps  609 A form a sharply rearwardly-cut rearwardly-extending end to a front wall  601 A, adding to side impact strength and desired properties. However, the caps  609 A also add to the bumper&#39;s total weight and cost from secondary processes. 
         [0073]    A multi-sheet beam  100 P ( FIG. 31 ) is similar to beam  100 A ( FIG. 4 ), but beam  100 P includes a front wall  101 P with an outboard end section  100 P″′ that is sharply bent rearwardly, and includes shear walls  103 P- 105 P with a matching front edge to abuttingly engage the front wall  101 P. Thus, the angle-cut shape of beam  100 P is integrated into the existing components, eliminating secondary operations, avoiding additional weight, yet providing a similar look and function to the roll formed beam  600 A described above. 
         [0074]      FIGS. 32-34  show tests commonly used to measure performance of bumper reinforcement beams.  FIG. 32  illustrates a three-point bending test used to test bumpers. We used an 880 mm span of support and targets of 7.6 kN-m bend strength when tested.  FIG. 33  illustrates an IIHS 100% overlap impact test.  FIG. 34  illustrates an IIHS 73.2 mm offset overlap impact test. Notably, the offset cause&#39;s significant torsional loading on the beam during impact, especially near a center of the beam which is spaced from the vehicle mounts (at ends of the beam). IIHS stands for Insurance Institute for Highway Safety, and has known bumper test standards widely used in the automotive industry. 
         [0075]    To summarize a related method of manufacturing, a method of manufacturing the bumper beam comprises providing multiple strips of selected (potentially different) material properties and thicknesses for forming front, rear, top, center and bottom walls of a beam; shearing edges of all sheets and forming holes in any sheet necessary (such as shearing edges of the top, center, and bottom walls to form a varied width along their length); shaping the walls as needed (such as to form a channel ribs or other feature in the front wall); fixturing the front and rear walls in abutting contact with one or more of the top, center, and bottom walls; welding the same together; and repeating the steps of fixturing and welding with the remaining of the top, center and bottom walls. 
         [0076]      FIG. 35  is a graph comparing beam mass for a constant-depth multi-sheet beam  100 A ( FIG. 4 ) and a varied depth multi-sheet beam  100 B ( FIG. 6 ) compared against a target extruded aluminum beam  500  ( FIG. 25 ). The beams  100 A,  100 B, and  500  fit into a same vehicle package space and have an equivalent HHS bumper impact test performance. The beams  100 A and  10 B used high strength (non-extrudable) aluminum optimally placed for strength and properties, and to minimize weight. This study suggested that there is a great opportunity for mass savings, since beam  100 AA offered a large mass savings, and beam  100 B offered an even greater potential mass savings (of about 20% mass savings) while maintaining a same HHS impact test performance. By optimizing material properties along a length of the beam and around a cross section of the beam, even greater mass savings can be achieved over the known prior art aluminum extruded beam, with mass savings being as much as 34%, as shown in  FIG. 36 . 
         [0077]      FIG. 37  is a chart comparing maximum bending moment per unit mass for three different beams, including a prior art roll formed (double tube) baseline monoleg beam  600  ( FIG. 27 ) made of steel material, a multi-sheet beam  100 A ( FIG. 4 ) with constant cross section and channel-ribbed face, and a multi-sheet beam  100 B ( FIG. 6 ) with varied cross section and channel-ribbed face. The test was to measure a maximum bending moment per kilogram. The test was not based on equal beam performance nor equal beam mass. As shown, the multi-sheet beam  100 B with varied cross section provided a much greater bending moment per unit mass by 27.4% over the prior art baseline monoleg beam  600 . Even the multi-sheet beam  100 A with constant cross section provided an improved bending moment per unit mass by 23% over the baseline prior art beam  600 . 
         [0078]      FIG. 38  is a chart comparing mass for the beams in  FIG. 37 , each having a similar performance in an HHS 100% overlap impact test. Specifically, the beams include the prior art roll formed (double tube) beam  600  ( FIG. 27 ), a multi-sheet beam  100 A ( FIG. 4 ) with constant cross section, and a multi-sheet beam  100 B ( FIG. 6 ) with varied cross section. The beam  100 B provided a 15.6% mass reduction, while the beam  100 A provided a 3.3% mass reduction, over the prior art baseline beam  600 . It is noted that different sheet thickness combinations were used to optimize performance. 
         [0079]      FIG. 39  is a chart comparing mass for the same three different beams compared in  FIG. 37 , each having a similar performance in an HHS 73.2 mm overlap impact test, but where the beams have a different mass to accomplish the offset impact performance. The chart shows that the beam  100 B had a 22.4% mass savings over the prior art roll formed beam  600  while providing an equivalent HHS 73.2 mm overlap impact test result. Again, it is noted that different sheet thickness combinations were used to optimize performance. 
         [0080]    It is contemplated that novel welding methods can be used to minimize (nearly eliminate) the heat-affect-zone around a weld. This can be particularly important in bumper reinforcement beams used in vehicle bumper systems, since bumper systems have numerous test standards set by HHS (Insurance Institute Highways Safety standards) and FMVSS (Federal Motor Vehicle Safety Standards) agencies. Notably, welding processes and welds that create high heat also degrade the physical properties of material around and adjacent the weld. It is noted that the impact and bending strengths and test standards for bumper reinforcement beams are very sophisticated, and relate to pole tests, pendulum tests, overlap (vehicle-to-vehicle simulating) impact tests, pedestrian impact/injury tests, occupant safety tests, and numerous other tests. 
         [0081]    Degraded material properties (i.e. areas of reduced strength in high strength steels or aluminums) generally have lower impact strengths and less consistency of properties and less predictable energy absorption during an impact.  FIG. 40  schematically shows the effect of heat-affect-zones around welds in traditional welding processes where heat is used to create molten metal that bonds adjacent components. The illustrated MIG weld (or could be TIG weld) adds weld material  700  (also called a “weld bead”) to bond adjacent sheets  701  and  702 . The weld bead  700  extends about 3-10 mm outward from the wall stock forming the corner (or flat) being welded. The weld bead  700  creates a puddle or pool of weld material at and along the corner, but further causes a high heat region  704  that extends much farther than the weld bead, such as 15-20 mm outward from a corner being welded. Still further, depending on a sensitivity of the material, an adversely affected region  705  (called a “heat-affected-zone” or “HAZ”) will extend even farther, such as 15-25 mm from the corner. Laser welding ( FIG. 42 ) is also a known welding process, where material  710  at the weld site is melted by laser energy  711  to create a pool of material that when cooled bonds adjacent material. 
         [0082]    We have found three welding processes that control the heat-affected-zone particularly well, in our opinion. These include cold metal transfer welding (CMT) ( FIGS. 43-45 ), friction stir welding (FSW) ( FIGS. 46-47 ), and homogenous laser welding (not illustrated). It is noted that each of these processes are publically known and commercially available, though their use is not widespread to our knowledge. In particular, we are not aware of any bumper reinforcement beams made using any of these processes, nor beams designed for crash impact made using any of these processes. 
         [0083]    Cold metal transfer (CMT) welding is a process promoted and commercially available from several companies, including for example a company named Fraunhofer.  FIGS. 43-45  illustrate one (of the several) cold metal transfer welding processes, and it includes an ability to minimize the heat-affect-zone around the weld to less than about 3 mm, and potentially less than about 1.5 mm. The process includes providing limited and focused energy for welding from a well-aimed well-calibrated laser  400  while feeding a cold (meaning non-electrically charged) wire stock  401  to the weld site as needed to initiate welding and for welding material (illustrated as sheets  104 F and  102 F′, from  FIG. 12 ). Notably, the amount of welding material added to the weld by the cold wire  401  is minimal (including a small size of the wire and potentially slow or oscillatingly movement/feeding of the wire), and further the laser  400  is closely controlled to minimize heat buildup. Thus, the heat-affect-zone around the weld site is minimal, such as less than 3 mm or even as low as 1 mm from the corner as noted above. There is essentially zero weld bead extending outside the welded corner. 
         [0084]      FIGS. 46-47  are side views of a friction stir welding process, which is a commercially available process promoted and sold by ESOB Company. Friction stir welding (FSW) is a solid state weld process so it nearly eliminates loss of properties from heat input from welding. In friction stir welding, a tool  420  moves cyclically or oscillatingly in a manner causing friction around a location closely associated with the weld site  421 , causing material from the sheets  104 F and  102 F′ and  102 F″ to bond without additional weld material, thus minimizing excess heat added to the welding site during welding. No exterior material is added to the weld site. Instead, material from immediately adjacent areas are made sufficiently mobile to bond adjacent sheets  104 F and  102 F′ and  102 F″. 
         [0085]    Homogenous laser welding (not illustrated) is a commercially known process that does not require a detailed explanation herein for an understanding by persons skilled in this art. It also can be used to minimize heat buildup during welding. 
         [0086]    In each of the above welding processes (cold metal transfer welding, friction stir welding, homogenous laser welding), minimal or zero material is added to the weld site. They do not leave a weld bead that extends 3-5 mm from the weld site. Concurrently, they minimize heat at the weld site, thus minimizing the heat-affect-zone to only a very short distance (e.g. a few millimeters) from the corner being welded. 
         [0087]    The sheets  101 - 105  can be fixtured in different manners, depending on a shape of the sheets and the type of welding used. Fixture  800  ( FIG. 48 ) uses a base  801  with upright block  802 , side clamps  803  and a top clamp  804  to hold sheets  101 ,  102 , and  104  together. The illustrated welding process is a CMT welding process with laser  400  and cold wire (not shown). The process is repeated in  FIG. 49  using an additional center block  805  to hold sheet  105 . Thereafter, in  FIG. 50 , the partial beam is inverted, and the last sheet  103  is fixtured by block  806  and welded. It is contemplated that many different fixturing methods and procedures can be used. For example, the beam may be welded from a bottom instead of being inverted (not illustrated, but see  FIG. 50 ), or the beam may be rotated 90 degrees and welded from a side (not illustrated). 
         [0088]      FIGS. 51-52  are perspective end views of a swept double-tube bumper reinforcement beam  900  formed by multiple sheets  901 - 905  to form adjacent tubes  906 - 907  (five sheets shown, though more or less could be used) sharing a common mid-level horizontal shear wall  903 . The beam  900  includes a 12-18 inch hat-shaped internal reinforcement  908  welded in a centered position on an inside of the “flat” front wall  901  of the beam&#39;s lower tube  907 . It is contemplated that the internal reinforcement  908  could be a same material and thickness and hardness as the front wall  901 , or could be a different material, thickness or hardness, or any variation thereof. For example, where the sheets  901 - 905  are 1.6 mm steel with tensile strength of 220 ksi, the internal reinforcement  908  could be 2.2 mm steel with 80 ksi tensile strength. Part of the advantage of using the internal reinforcement  908  is that the beam  900  can be tailored to provide optimal resistance to buckling along its center area when impacted, while still minimizing weight by strategically limiting a location of the reinforcement beam  900  to only the area where the additional buckling resistance is needed. (Specifically, it is noted that buckling strength in bumper reinforcement beams is most near a center of an unsupported section of a beam, while buckling strength is not as necessary in locations near the vehicle frame mounts at ends of the beam.) 
         [0089]    Part of the advantage of the internal reinforcement  908  is that the overall weight of the beam  900  can be minimized by optimally selecting thin-walled sheets making up the walls  901 - 905 . It is noted that very high strength materials allow the use of thinner walls, thus saving weight. However, our testing has shown that bumper beams made from thin-walled sheets (e.g. 1.6 mm or less) and using very-high-tensile-strength materials (e.g. 190 ksi tensile strength or more) can have a tendency to catastrophically and prematurely collapse (herein called “thin walled catastrophic failure from impact”). In thin walled catastrophic failure from impact, the thin wall loads up and then prematurely fails well ahead of the predicted theoretical failure load. The results are that the actual failure of an impacted beam occurs at impact energies far below the theoretical predicted impact energy, which is not a good thing. The addition of the internal reinforcement  908  helps reduce this premature failure of the thin-walled front wall of the beam. It is noted that the internal reinforcement ( 908 ) can be used on one or both tubes. The illustrated internal reinforcement  908  was only used on one of the tubes (such as the bottom tube as illustrated due to offset impactor location  999  as illustrated in  FIG. 52 ), thus further saving weight and yet it was found to provide adequate resistance to buckling on impact. 
         [0090]      FIGS. 53-54  are perspective end views of a swept double-tube beam with an internal reinforcement similar to  FIGS. 51-52  but where the front wall  901  includes stiffening channel ribs  909  over each of the tubes  906  and  907 . In  FIG. 53 , the internal reinforcement  908  is placed “on” the lower stiffening channel rib  909 , thus adding to its strength. It is noted that in some circumstances, the beam in  FIG. 51  can be designed with lower total weight than the beam in  FIG. 53  because the existence of the channel rib(s)  909  adds considerably to the overall amount of sheet material necessary to form the beam. By eliminating the channel rib(s)  909  and adding only a short internal reinforcement  908 , the total beam weight can be reduced, by up to 5%. 
         [0091]      FIG. 55  is a top view of an impacted beam (similar to beam  900 ) with buckle-type failure.  FIG. 56  is a chart showing load deflection curves for similar beams. The chart includes a first line  914  showing energy absorption by the beam  900  (with one internal reinforcement  908 ) of  FIG. 51  compared to a beam without internal reinforcement (referred to as a “no-internal-reinforcement beam” herein) (line  915 ). Notice that with the internal reinforcement  909 , the buckle is prevented and energy is absorbed with less displacement, as shown by the gap  916  identified on the chart. Specifically, the beam  900  with internal reinforcement  908  continues to rise in resistance to load up until about 130 mm displacement. Contrastingly, the line  915  falls off sooner, such as about 100 mm displacement, due to earlier buckling of the no-internal-reinforcement beam. 
         [0092]      FIG. 60  illustrates a double-tube beam  930  having a vertical front wall  931  made by a single sheet; top, mid, and bottom horizontal shear walls  932 ,  933 ,  934  made by single sheets; and a rear wall  935  made by a single sheet. Top and bottom edge sections  936  and  937  of the rear wall  935  are bent with a radius so that they overlap onto the top and bottom shear walls  932 ,  934  respectively. The front wall  931  includes an upper edge section  938  that extends well above the upper tube, thus forming a lip that can be used to support fascia, or for other mounting purpose on the beam. 
         [0093]      FIG. 61  is a cross section of a double-tube beam  940  similar to double-tube beam  930 . The beams  940  has a front wall  941 ; upper, mid, and lower shear walls  942 - 944 , and a rear wall  945 . However, an upper L-shaped component  946  has legs forming the top wall  942  and an upper part of the rear wall  945 . Also, a lower L-shaped component  947  has legs forming the top wall  944  and a lower part of the rear wall  945 . It is noted that the components of beam  940  facilitate welding during assembly of the beam  940 . 
         [0094]      FIG. 62  shows a beam  940 , but shows addition of an internal reinforcement  948  (previously described as reinforcement  908 ).  FIG. 63  illustrates a beam  950  with walls  951 - 955  similar to beam  940  with walls  941 - 945 , but where the front wall  951  includes two channel ribs  956 . The internal reinforcement  958  is welded internally to the front wall near a center section of the beam  950  for providing added buckling strength in the selected center section. The reinforcement  958  does not extend a full length of the beam  950 , but instead only extends a short distance as required by a particular bumper beam functional requirements, such as only 12 to 20 inches or so. 
         [0095]    Thus, 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.