Abstract:
A two step system or stage is provided to manufacturer a bumper of “B” shape cross section including a roll forming-welding stage where a straight cross member of a length to mount on the front or rear of various models of automobiles and the bending stage where any curvature or sweep is introduced into the cross member as required by the design of the automobile. The roll forming welding stage include the spot or tack welding of the front wall to the web followed immediately by welding together without any gaps therebetween the abutting longitudinal edges utilizing a high frequency welder. Thus, the “B” shaped cross section of the bumper may be used to make different bumpers of various lengths and curvatures.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is a divisional application of U.S. application Ser. No. 10/894,826 filed Jul. 20, 2004, now U.S. Pat. No. 6,948,749 issued Sep. 5, 2005, the entire disclosure of which is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   This invention relates to a roll formed tubular vehicle cross member, bumper beam or bar fabricated from high or ultra-high strength steel. The cross member may be either straight or provided with a sweep or curvature having a value of more than 10. The resulting tubular bumper has a high impact resistance, low weight and relatively low cost of manufacture. 
   BACKGROUND OF THE INVENTION 
   Bumper beams or cross members for vehicles, particularly automobiles, are made from high strength or ultra-high strength steel. It has been difficult to manufacture the bumper beam or bar out of some high strength steel because such bar requires a curvature to be placed therein. It is necessary to roll form the cross member to obtain the desired curvature. In the past, when high strength steel is roll formed into the desired sweep or curvature, the material of the cross members has been damaged during the process resulting in unacceptable quality. The high strength obtainable with such steels is desired in order to provide a bumper beam or bar which can be impacted at speeds of up to 5 mph without resulting damage. 
   It is desired for certain applications where high strength is needed to use higher carbon steels, frequently alloyed with other materials. Such steels are characterized as “high-strength steels”. Within this category, there is a class defined as “ultra-high strength steel”. Such steel has a minimum yield of 100 ksi (100,000 pounds per square inch). Chemical compositions for such steel vary from one producer to another. Different compositions and thermo-mechanical processing may produce equivalent results. Formability of high strength steel is difficult than with low carbon steels because of greater spring-back and reduced ductility. 
   Thus, industry requires that bumpers maintain a high level of strength and damage resistance to meet the expectations of the consumer and government regulations throughout the world concerning low speed vehicular impact. The bumper must be of low weight to minimize vehicle dead weight which reduces gas mileage and increases suspension requirements. Also, bumpers must have a low manufacturing cost and a high dimensional consistency. Thus, high strength-to-weight ratios and ease of manufacture are of importance to the automotive industry. 
   Various systems, methods and equipment have been employed to manufacture tubular roll-formed automotive bumpers or cross members such as disclosed in the Sturrus et al U.S. Pat. Nos. 5,306,058, 5,092,512 and 5,104,026, each relating to a tubular bumper beam, method and/or apparatus for roll forming an automotive bumper. The same equipment and methods employed in the foregoing patents have also been used to manufacture “B” section cross members as disclosed in the Sturrus&#39; U.S. Pat. No. 5,395,036 entitled “Method of Roll Forming an End Automotive Bumper”; and U.S. Pat. Nos. 5,454,504, 5,566,874 and 5,813,594, entitled “Apparatus For Forming an End Bumper for Vehicles”. 
   A disadvantage of the methods and apparatuses disclosed in the Sturrus and Sturrus et al patents is that the method and apparatus for forming the straight tubular “B” section cross member and the equipment for forming the sweep in the cross members are connected together in one line, with the severing of the cross member from the roll formed member being located down stream of the welding station. With such a process, the curvature or sweep is placed in the cross member prior to cutting the swept integral tube. 
   SUMMARY OF THE PRESENT INVENTION 
   A feature of the present invention is to provide a tubular cross member of “B” shape which is roll formed from a single sheet of high strength or ultra-high strength steel. With such a construction, two side-by-side longitudinally extending tubular sections are connected by a web, with each section having a front wall, a rear wall, an outer side wall and an inner side wall. The inner side walls are spaced one from the other and are connected together by the web roll formed integrally with the inner side walls. As the roll formed cross member leaves the last roll former, the front wall overlies the web and is spot or tact welded to the web at longitudinally spaced areas and thereafter the pair of abutting longitudinal edges are welded together by a high frequency welder. 
   Another further feature of the present invention is to provide an in-line system of standard metal forming and welding equipment to produce a straight tubular cross member which later on can be swept at a remote bending station to provide a bumper with a curvature. The in-line system includes a roll mill with a series of roll formers where the “B” shaped cross section of the cross member is provided, a spot welder and a high frequency welder followed by a cut-off machine. After the spot or tact welding has taken place, the steel strip continues to move and the abutting longitudinal edges are moved through the high frequency welder where the abutting longitudinal edges are welded together without any gaps therebetween. After the welding steps have been completed, the cut-off machine cuts the straight tubular cross member to a predetermined length. 
   Still another feature of the present invention is to provide a method and equipment of the aforementioned type wherein after the cross member has been severed by the cut-off machine, it is manually or automatically placed in a gravity stacking system that is palletized. 
   A further feature of the present invention is to provide a method for placing a curvature or sweep in a cross member of B shape cross section by moving the stacking system or pallet to a remote work station where a curvature or sweep is placed in each cross member independent of and separate from the in-line roll mill and equipment. 
   The present invention provides a vehicle bumper bar and method of making the bumper bar from high strength or ultra-high strength steel and roll formed into a tubular cross section of B shape. The cross member may be made from a variety of steels of varying thickness, cut to different lengths and bent to different curvatures for various automobiles. The equipment utilized in the system remain the same since the cross section remains the same for different length and different curvature bumpers. This system thus provides an economical advantage over the prior art methods and equipment discussed previously where the steel is fabricated in tubular form and swept in one apparatus since there will be no additional tooling costs for providing bumpers of various lengths. 
   With the present invention, the method and equipment employed may be used to make bumpers or cross members of different lengths and curvatures without changing the roll formers since the same cross section is utilized. Thus, a less costly tooling system is provided for making various bumpers for different manufacturers which is extremely important because of the competitiveness of the industry. 
   A final feature of the present invention is to provide a unique method of forming a straight tubular cross member by using a rolling spot or tact weld process to connect portions of the cross member to the web followed by the in-line high frequency butt welding process to join the longitudinal edges. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an automobile, in dotted lines, with a novel bumper beam made from a “B” section blank mounted on the front of the automobile. 
       FIG. 2  is a top view of the tubular straight cross member, bumper or bumper beam. 
       FIG. 2A  is a “B” shape cross section taken on the line  2 A— 2 A of  FIG. 2   
       FIG. 2B  is a fragmentary perspective view of one end of the cross member. 
       FIG. 3  is a schematic view of the roll-forming apparatus and related equipment for practicing the process of the present invention. 
       FIG. 4  illustrates a flower pattern of the steel sheet as the rollers of the roll-forming apparatus form the sheet into the “B” section blank. 
       FIGS. 4A–4Q  inclusive shows the consecutive steps for progressively forming the flat steel sheet ( FIG. 4A ) into the “B” section blank of  FIG. 4Q . 
       FIG. 5  is a perspective view of the bender or bumper sweep apparatus in a hydraulic press for placing a sweep or a longitudinal curvature in the “B” section blank to form a swept or curve bumper beam. 
       FIG. 6  illustrates the bumper sweep apparatus in the hydraulic press which is in an open position, with a “B” section blank securely mounted at the center on a contour cut male sweep mandrel. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The bumper  10  of the present invention is illustrated in  FIG. 1  mounted on the front of an automobile  12  although it should be understood that the bumper, with or without a sweep, may be mounted either on the front or rear of the automobile  12 . 
   The bumper beam  10  is made in two manufacturing stages. The first manufacturing stage is illustrated in  FIG. 3  where the method and apparatus is demonstrated and illustrated for making a straight tubular cross member  14  as illustrated in  FIG. 2  with a B shaped cross section as shown in  FIG. 2A . The equipment and method utilized for manufacturing the straight tubular cross member  14  includes an in-line system of standard metal forming and welding equipment including a steel roll holder  20  rotatably supporting a steel roll  21  of strip steel S; a straightener system or straightener  22  and a pair of guide posts  24  located on opposite sides of a punch press  26  for directing steel strip as it moves along the line. Downstream from the punch press  26  where mounting openings are placed is a roll mill  28  having a series of roll formers where the B shaped cross section of the straight cross member  14  is shaped. There are sixteen (16) roll formers identified by the even numerals  42 – 72  inclusive. Downstream of the roll former  72  is a tack or spot welder  76  followed immediately inline by a high frequency welder  78 , where the longitudinal edges of the roll formed tubular section are welded together from one end to the other end. The cut off machine  80  is located downstream of the welder  78  and severs the cross member  14  at the requisite length. 
   Each straight tubular cross member  14  is a roll formed, single sheet of high or ultra-high strength steel having a pair of longitudinal edges which abut and are welded together. The B shaped cross member  14  of  FIGS. 2A and 2B  includes two side-by-side longitudinally extending tubular sections  90  and  92  which are connected together by a web  94 , each section  90  and  92  having a front wall  86 , a rear wall  88 , outer side wall  96  and an inner side wall  97 . Inner side walls  97  are spaced one from the other and are connected together by the web  94  roll-formed integrally with the inner side walls  97 . As the roll formed cross member  14  leaves the last roll former  72 , the front wall  86  which overlies the web  94  is spot welded to the web  94  at longitudinally spaced areas  95 . The spot weld  95  may be placed, as an example, from eight to twelve inches apart along the length of the cross member  14 . As the welded tubular structure continues to move along the line, the high frequency welder  78  butt welds the longitudinal edges  104  and  106  together from one end to the other. The abutting longitudinal edges  104  and  106  are welded together as represented by the weld line  107 . 
   After the welding steps have been completed, the cut off machine  80  cuts the straight tubular cross member  14  to a predetermined length and thereafter the cross member  14  is placed either manually or automatically in a gravity stacking system  82  that is palletized. With such a construction and procedure, the B shaped cross member  14  which is severed by the cut off machine  80  is straight from one end to the other. The cross member  14  can be utilized as a straight bumper and mounted on an automobile in place of the curved bumper of  FIG. 1 . The palletizer or collection container  82  is spring loaded and the cross members  14  are automatically or manually stacked on the gravity stacking system or apparatus  82 . 
   Referring now to  FIG. 4  where steel sheet S is illustrated in a flower diagram or pattern folded or bent by the roll formers  42 – 72  inclusive. Each roll former places a predetermined bend or pattern in the strip S as it proceeds along the line. Thus,  FIGS. 4A–4Q  illustrate seventeen different patterns, with the straight sheet S being illustrated in  FIG. 4A . The first roller or roll former  42  of the roll mill  16  places several bends in sheet S as shown in  FIG. 4B . As the strip of steel S continues to proceed downstream of the roll formers, the roll formers continue to progressively bend and shape the metal. Thus each  FIGS. 4B–4Q  represents roll formers  42 – 72  inclusive and the metal cross sections designated by the correspondence roll former plus the --′-- designation. The last roll former  72  closes the gap between the longitudinal edges as shown in  FIG. 4P . After the straight tubular cross member  14  is formed, it proceeds to a two step welding process where the front walls  86  overlie the web  94  and are spot welded thereto along the length of the cross member  14  at longitudinally spaced areas  95 . It is followed almost simultaneously by the inline high frequency welding of the longitudinal edges  104  and  106  to form the butt weld  107  throughout the length of the cross member  14 . Thus, the edges  104  and  106  have an abutment weld represented by the numeral  107 . Generally the abutment weld will be located at the bottom of the bumper  10  as it is mounted on the vehicle  12  although it could be located at the top. The longitudinal edges  104 ,  106  are butt welded and do not overlap any other portion of the cross member  14 . 
   The gravity stacking system or pallet  82  containing the straight tubular cross members  14  is moved to a remote work station where a curvature or sweep is placed in each cross member  14  to form the bumper  10  of  FIG. 1 . To place the sweep or curvature in the cross member  14 , bender  110  is employed. 
   The bender  110 , as shown in  FIGS. 5 and 6 , has a lower base plate  120  and an upper base plate  122 . The lower plate  120  is mounted on the base  114 , as an example of a conventional 100 ton hydraulic press  111 . The upper base plate  122  is secured to the press platen  123  and is movable therewith. The movement of plate  122  and platen  123  is guided by the posts  124  upon actuation of the hydraulic press  111 . The press  111  includes an upper support  125  spaced from the base  114  by corner posts  127 . 
   Mounted on the lower plate  120  of bender  110  is a curved contour swept male mandrel  130  having a top surface of arcuate configuration as viewed in  FIG. 5 . The male mandrel  130  is comprised of eleven segments numbered  132 – 152  inclusive. The center segment  142  is fixed to the lower plate  120  and forms a pedestal for a clamping mechanism  154  which is hydraulically operated for securing the straight cross member  14  on the male mandrel  130 . The clamping mechanism  154  is operated by a pair of hydraulic cylinders, not shown, to open the mechanism  154  to receive a cross member  14  and to close the mechanism  154  to clamp the cross member  14  in place on the curved mandrel  130  as shown in  FIGS. 5 and 6 . Each section of the male mandrel  130  as viewed from the end of  FIG. 5  includes an upstanding center support  160  located between a pair of grooves or channels  162 . The B shaped section cross member  14  when mounted on the male mandrel  130  has the center support  160  received in the space between the opposing inner walls  97  of the B shaped cross member  14 , with the web  94  opposite the top surface  161  of the support  160 . Tubular sections  90  and  92  of the B shaped cross members  14  are received in the channels, grooves or pockets  162  located on the opposite sides of the center support  160 . 
   The upper plate  122  of the bender  110  carries a pair of downwardly extending longitudinally spaced apart plates  170  and  172  for respectively mounting hydraulic cylinders  174  and  176  respectively. The hydraulic cylinders  174 ,  176  each includes a piston, not shown, and cylinder rods  178  and  180  extending from the cylinders  174  and  176  respectively as shown in  FIG. 6 . The cylinders  174 ,  176  are mounted on the same longitudinal axis, with the outer ends of each piston rods  178 ,  180  mounting support structures  179 ,  181  to respectively support wiper blocks  182  and  184 . Each wiper block  182 ,  184  has a profile which is cut to the profile of the opposing surface of the front walls  86  of the cross member  14 . The wiper blocks  182 ,  184  are driven outward from the center by the hydraulic cylinders  174  and  176 . Hydraulic cylinders  174 ,  176  are operated in sequence with the hydraulic press  111 . With the hydraulic press  111  energized and moving in a downward direction, the wiper blocks  182 ,  184  engage the top surface of the front walls  86  of the cross member  14  and thereafter the wiper blocks  182 ,  184  are moved in the “center out” direction, as represented by arrows A as the hydraulic press  111  continues to move downwardly as illustrated in  FIG. 6 . Thus, a curvature is placed in the cross member  14  to form the bumper  10  as represented by the solid line curved bumper  10  in  FIG. 5 . 
   It should be understood that various benders or apparatuses and presses may be used to place a sweep or curvature in the bumper  10 .