Abstract:
A method of making a structural connection in a metallic tubular assembly is provided. It comprises providing a node having at least two legs and forming a radially extending rib extending from an exterior surface of each of the legs by deforming a corresponding interior portion of each of the legs. At least one tube is provided having a radially extending flange adjacent an open end. The tube is placed over the exterior surface of one of the legs abuts the radially extending flange and the radially extending rib. By applying opposing forces to one of the legs and one tube to hold the radially extending flange and the radially extending rib in abutting contact at a joint, resistance welding can take place at the joint when at least one electrode is applied to the joint.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 61/196,933 filed Oct. 22, 2008, the contents of which are incorporated by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    The subject matter disclosed herein relates to a method for preparing tubular structure frames and tubular support structures for deformation resistance welding. 
       BACKGROUND OF THE INVENTION 
       [0003]    Resistance welding of a first metal member to a second metal member (also known as electric-resistance welding) is a known metallurgical process in which the first and second metal members are heated by their own electrical resistance to a semi-fused or a fused state by the passage of very heavy electrical currents through the members for very short lengths of time. By forcing the first and second members together under pressure while the welding current is applied across the members, the members are then welded together. Resistance welding has many advantages in efficiently and effectively providing consistently reliable welds in high-volume manufacturing operations, when compared to alternative brazing or welding methods using gas torches or electrical arcs. 
         [0004]    In order to achieve a complete resistance weld of the interface between the two mating members, the members must fit together very tightly at the interface at the time welding current is applied. It has been difficult to economically resistance weld together thin-walled metal members together, due to the need for having the members fit together tightly. Metal members where this was difficult include metals in the form of sheets, tubes, or similar shapes. In high-volume production, even where the configuration of the members is fairly simple, such members have been typically brazed or arc welded together rather than being resistance welded. 
         [0005]    For example, in order to resistance weld a metal sheet or tube to another tube, the mating edges or surfaces of the members to be joined had to be cut or prepared along a three-dimensional contour so that the intersection between the members would fit together tightly enough before welding—to allow a good weld joint to be made. This can be difficult to achieve in thin-walled members that tend to flex under the pressure of the tooling used for preparing the mating edges or surfaces. The manufacturing costs for preparing the edges of the members to achieve an acceptably tight fit before welding, together with the cost of engineering for designing the members themselves and the equipment used for machining the members to achieve a tightly filling interface has been expensive. In addition to the cost associated with machining the members, complex fixtures were required to hold the members in position and to apply pressure along an interface, which is often three-dimensional, during resistance welding of the interface. 
         [0006]    U.S. Pat. No. 6,552,294, to Ananthanarayanan, et al, and U.S. Pat. No. 6,693,251 to Ananthanarayanan, et al, each of which is hereby incorporated by reference herein, provide methods for attaching tubular assemblies using resistance welding. These and other methods require forming processes, sometimes complicated, to prepare the parts for welding. For instance, forming kinks in thin walled tubing can result in uneven stresses in the tubing, or uneven kinks that do not line up well with a mating flange in the successive welding step. As such, some parts are subject to being scrapped. Further improvement of the resistance welding of annular shapes would be accomplished with a more uniform formation of the joint in preparation for welding parts together. 
       SUMMARY OF INVENTION 
       [0007]    A method of making a stand-alone node structure to connect tubular structure frames and tubular support structures that are welded together using the deformation resistance welding (DRW) process is provided. A collapsible element of the node allows for relative motion between the node and tubes parts during welding. 
         [0008]    According to one aspect of the invention, a method of making a structural connection in a metallic tubular assembly is provided. It comprises providing a node having at least two legs and forming a radially extending rib extending from an exterior surface of each of the legs by deforming a corresponding interior portion of each of the legs. At least one tube is provided having a radially extending flange adjacent an open end. The tube is placed over the exterior surface of one of the legs abuts the radially extending flange and the radially extending rib. By applying opposing forces to one of the legs and one tube to hold the radially extending flange and the radially extending rib in abutting contact at a joint, resistance welding can take place at the joint when at least one electrode is applied to the joint. 
         [0009]    According to another aspect of the invention, a node for joining metallic tubes together in a structural assembly is provided. It comprises a first portion comprising three partial cylinder portions bounded by axially extending flanges. The three cylinders have a common intersection point and each of the three partial cylinders having at least one radially extending rib. A second portion comprises three partial cylinder portions bounded by axially extending flanges. The three cylinders also have a common intersection point and each of the three partial cylinders has at least one radially extending rib. The first portion is connected to the second portion at abutting radially extending flanges. 
         [0010]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0012]      FIG. 1  is an illustration of an exemplary embodiment of the invention; 
           [0013]      FIG. 2  is a cross-sectional detail view, taken along the line  2 - 2  of  FIG. 1 ; 
           [0014]      FIG. 3  is a detail view, partially in cross-section, taken along line  3 - 3  of  FIG. 1 ; 
           [0015]      FIG. 4  is an exploded view of a joint in accordance with an exemplary embodiment of the invention; 
           [0016]      FIG. 5  is an isometric view of an exemplary embodiment of the invention; 
           [0017]      FIG. 6 . is a side view of one aspect of the exemplary embodiment of  FIG. 5 ; 
           [0018]      FIG. 7  is a detail view taken along line  7 - 7  of  FIG. 6 ; 
           [0019]      FIG. 8  is an exploded view of the exemplary embodiment shown in  FIG. 5 ; 
           [0020]      FIG. 9  is an illustration of joints formed in accordance with an exemplary embodiment of the invention; 
           [0021]      FIG. 10  is a detail view of joints formed in accordance with an exemplary embodiment of the invention; and 
           [0022]      FIG. 11  is an illustration of the steps to carry out an exemplary embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    Referring now to the Figures, where the invention will be described with reference to specific embodiments, without limiting same, the invention provides a node to connect tubular structural frames and tubular support structures that are manufactured using a Deformation Resistance Welding process (DRW). 
         [0024]    An exemplary embodiment of a node  10 , useful as connection point or redistribution point for a structural frame (not shown) is shown in  FIGS. 1-4 . Node  10  is comprised of two generally equal halves, a first upper clamshell portion  11  and a second lower clamshell portion  12  forming an interior portion  17  of node  10 . As shown, node  10  is comprised of three equidistant node legs—first leg  14 , second leg  15  and third leg  16 . Each leg  14 ,  15  and  16  is generally cylindrical in shape and defined by an axis A, B and C, respectively and has an exterior diameter. As shown the arc angle, α, β, and γ, between adjacent axes A, B, C is 120 degrees. It will be appreciated that other alternative embodiments of node  10  may include elliptical or oval shaped tubing, when viewed in cross-section, or the arc angles, α, β, and γ, may be of varying angles such that only two are the same or that none of the angles are the same. Each of the varying embodiments fall within the scope of the invention, and the exemplary embodiment shown is not meant to limit the invention. 
         [0025]    The axes A, B and C each fall within a common plane, though it is contemplated that other embodiments may include one or more of axes A, B and C falling in different planes, though corresponding legs  14 ,  15  or  16  will still intersect at node intersection point  21 . Each of legs  14 ,  15  and  16  contain a circumferential recess  22 ,  23  and  24 , respectively within the inside surface wall  25  of node  10  and adjacent an outer uniform edge  27 . Node  10  also includes an outer surface wall  26  and the outer uniform edge  27  extending therebetween. Outer edge  27  has a generally uniform thickness extending between the inner and outer surface walls  25 ,  26 . Circumferential recesses  22 ,  23  and  24  form corresponding radially extending circumferential ribs  32 ,  33  and  34  on outer surface wall  26 . Each rib  32 ,  33  and  34  has a leading edge  35 ,  36  and  37 , respectively for purposes that will be described hereinafter. In one non-limiting embodiment, node  10  is comprised of a low carbon steel such as AISI 1008 to 1010 having a generally uniform edge  27  with a thickness of generally 2 millimeters. 
         [0026]    As discussed above, first upper portion  11  and second lower portion  12  are generally uniform in size and shape so that they may mate together in a clamshell type configuration to form node  10 . Each of first and second portions  11 ,  12  starts out as a flat piece of sheet metal. The portions  11  and  12  are generally identical in size and shape, and after stamping are a mirror image of each other. In one exemplary embodiment, first upper portion  11  is stamped to create a semi-cylindrical clamshell portion  11  with at least one partial cylinder bounded by axially extending flanges  42  on the outer edges. Each one half cylinder, when joined with second lower portion  12 , as described below, becomes one half of legs  14 ,  15  and  16 . One-half of the recesses  22 ,  23  and  24  are stamped on the inside surface wall  25  to create one-half of the radially extending ribs  32 ,  33  and  34 , while second lower portion  12  is stamped to create a semi-cylindrical clamshell portion  12  with at least one partial cylinder bounded by axially extending flanges  43  on the outer edges. Each one half cylinder, when joined with first upper portion  11 , becomes one half of legs  14 ,  15  and  16 . One-half of the recesses  22 ,  23  and  24  are stamped on the inside surface wall  25  of second lower portion  12  to create one-half of the radially extending ribs  32 ,  33  and  34 . When first upper portion  11  and second lower portion  12  are joined together at flanges  42  and  43 , node  10  is formed. 
         [0027]    It will be appreciated that flanges  42 ,  43  may be formed together with resistance welding, arc welding or the like to form single node receptacle  10 . By stamping recesses  22 ,  23  and  24  at the same time as node  10  is being stamped in first and second clamshell portions  11  and  12 , elimination of an additional forming step to create a kink in each of legs  14 ,  15  and  16  is eliminated. 
         [0028]    With reference now to  FIGS. 4 and 10 , and as best shown in the exploded view of  FIG. 4 , an example of the deformation resistance welding process as applied to node  10  is shown. A force F 1  is applied to leg  15  of node  10  and a corresponding opposite force F 2  is applied to thin walled tube  51 . Thin walled tube  51  has been formed with a radially extending circumferential flange  52  at a face edge  53 . Forces F 1  and F 2  cause rib  33  to circumferentially abut against flange  52  and outer surface wall  26  to slide within an inner surface wall  54  of thin walled tube  51 . Electrodes  55  and  56 , which may be circumferential or partially circumferential, abut each of ribs  33  and flange  52 , respectively, to cause deformation resistance welding and join leg  15  of node  10  to thin walled tube  51  circumferentially along the face edge  53  of flange  52  and the leading edge  36  of rib  33 . It will be appreciated that flange  51  is also useful to accommodate and support electrode  56  and the application of Forces F 1  and F 2  during the welding process. 
         [0029]    The resulting formed joint  60  is shown in  FIG. 10 . There it can be seen that recesses  22 ,  23  and  24  were useful to provide a collapsible element that allowed for relative motion between node  10  and tube  51  during welding to form joint  60 . While rib  33  remains it will be appreciated that the combination of resistance heating an plastic deformation causes recess  23  to generally collapse onto itself in the interior portion  17  of recess  23 . The resistance heating is due to the application of the welding current and the plastic deformation is due to the opposite Forces F 1  and F 2 . Legs  14  and  16  are welded in a like manner to tubes (not shown). 
         [0030]    In another exemplary embodiment, where like numerals will be used to show like elements, node  110  is illustrated in  FIGS. 5-9 . Node  110  is comprised of two generally equal halves, a first upper clamshell portion  111  and a second lower clamshell portion  112  forming an interior portion  117  of node  110 . As shown, node  110  is comprised of three equidistant node legs—first leg  114 , second leg  115  and third leg  116 . Each leg  114 ,  115  and  116  is generally cylindrical in shape and defined by an axis A 2 , B 2  and C 2 , respectively. As shown the arc angle, between adjacent axes A 2  B 2 , C 2  is 120 degrees. It will be appreciated that other alternative embodiments of node  110  may include elliptical or oval shaped tubing, when viewed in cross-section, or the arc angles, may be of varying angles such that only two are the same or that none of the angles are the same. Each of the varying embodiments fall within the scope of the invention, and the exemplary embodiment shown is not meant to limit the invention. 
         [0031]    The axes A 2 , B 2  and C 2  each fall within a common plane, though it is contemplated that other embodiments may include one or more of axes A 2 , B 2  and C 2  falling in different planes, though corresponding legs  114 ,  115  or  116  will still intersect at a common node intersection point (not shown). Each of legs  114 ,  115  and  116  contain a circumferential mating flange  72 ,  73  and  74 , respectively at a mating face edge  75 ,  76  and  77  of node  110 . Like node  10 , node  110  also includes an inside surface wall  25 , an outer surface wall  126  and a uniform edge  127  extending therebetween, and having a generally uniform thickness extending between the inner and outer surface walls  125 ,  126 . In one non-limiting embodiment, node  10  is comprised of a low carbon steel such as AISI 1008 to 1010 having a generally uniform edge  27  with a thickness of generally 2 millimeters. 
         [0032]    Like the embodiment above, first upper portion  111  and second lower portion  112  are generally uniform in size and shape so that they may mate together in a clamshell type configuration to form node  10 . Each of first and second portions  111 ,  112  starts out as a flat piece of sheet metal. The portions  111  and  112  are generally identical in size and shape. In one exemplary embodiment, first upper portion  111  is stamped to create a semi-cylindrical clamshell portion  111  having flanges  142  on the outer edges. One-half of the mating flanges  72 ,  73  and  74  are formed by a stamping process, while second lower portion  112  is stamped to create a semi-cylindrical clamshell portion  112  having flanges  143  on the outer edges. One-half of the mating flanges  72 ,  73  and  74  are formed by a stamping process. When first upper portion  111  and second lower portion  112  are mated together at flanges  142  and  143 , node  110  is formed. 
         [0033]    It will be appreciated that flanges  142 ,  143  may be formed together with resistance welding, arc welding or the like to form single node receptacle  110 . By stamping mating flanges  72 ,  73  and  74  at the same time as node  110  is being stamped in first and second clamshell portions  111  and  112 , elimination of an additional forming step to create a flanges in each of legs  114 ,  115  and  116  is eliminated. 
         [0034]    It will be appreciated that node  110 , and specifically legs  114 ,  115  and  116  can be joined to tubes  81 ,  82  and  83 , respectively, as shown in  FIG. 9 , in a mirror image fashion to that shown in  FIGS. 4 and 10 . In other words, each of tubes  81 ,  82  and  83  will have a recess in the interior and a corresponding rib on the exterior surface of the tube for circumferential mating with the mating face edges  75 ,  76  and  77  of node  110  to form welded joints  160 . As shown in  FIG. 9 , a node  210  can be included to form a metallic tubular assembly  200  which allows four tubes to be joined at structural junction  200 . This is accomplished by the use of tube  83  which is a short length of tube having ribs on each end and additional tubes  84  and  85 . 
         [0035]    It will be appreciated that the details of the embodiments of  FIGS. 1-4  and  10  and  FIGS. 5-9  are interchangeable. For instance, two of nodes  10  can be substituted for nodes  110  and  210  and tubes  51  substituted for tubes  81 - 85 , shown in  FIG. 9 . Referring now to  FIG. 11 , an exemplary embodiment of the method  300  of constructing node  10  is illustrated. 
         [0036]    Tubular nodes  10  and  110  replace more conventional cast or stamped stand-alone tubular nodes that may not have such a recess or flange around a periphery. Forming the recess or flange by a stamping process at the same time as forming a node eliminates additional forming process to create a kink or flange in at node in preparation for the deformation resistance welding process. In addition, the geometry of the recess stamping or flange forming should be done in such a way to allow for an electrode to be applied for the welding process. The geometry of the recess deformation should also be done in such a way to allow for any tube material thickness and any tubular geometry of a node, or vice versa, to fit within the tube. It will also be appreciated that each of legs of node  10  or  110  need not be welded to a tube. Nodes  10  and  110  are intended to be generic connections in a large structural array. As such nodes  10  and  110  serve to connect tubes as dictated by the requirements of the structural array. 
         [0037]    In one exemplary embodiment, pulses (totaling ⅓ of a second) of electric current of generally 5,000 amperes (and in one variation 15,000 to 20,000 amperes) are applied while applying a force of generally 300 to 800 pounds to the electrodes which abut against ribs and flanges to form Forces F 1  and F 2  to bring node  10  together with tubes  51  and the like, or node  110  together with tubes  81 ,  82  and  83 . The joining of materials by the deformation resistance welding is not limited to specific materials, dimensions, electric current, and forces, as is understood by those skilled in the art. Any materials capable of being welded, such as copper, aluminum alloy, stainless steel, etc. can be used, as can be appreciated by the artisan. The particular choice of electric current, forces, and part dimensions, etc. are within the ordinary level of skill of the artisan. 
         [0038]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description.