Abstract:
In attempting to reduce deformity when joining vehicle frame components, a riveting/brazing process has been proposed. This process includes joining tubular members, such as hydroformed parts, by cutting at least one flange into one end of a first body member, shaped in conformance with the surface of a second body member. Location holes are formed into each flange as well as into the surface of the second member in suitable alignment with each other. A brazing filler material is fixed into a side of the flange, usually within a pocket, intending to lie on the surface of the second member when the two structures are attached. The flange(s) are initially attached to the surface of the second member by means of a rivet to formed an actual vehicle body assembly. Heat is then applied to the assembly to form a brazed T-joint.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates generally to forming tubular or channel parts in a T-joint. More specifically, this invention relates to a method of joining said parts by a riveting and brazing method. The invention is useful in joining, e.g., hydroformed parts, in vehicle body or frame assembly.  
         BACKGROUND OF THE INVENTION  
         [0002]    Automobiles, and other such motor vehicles, often include a frame and body assembly comprising several unique structures and/or shapes. In the past, vehicle body structures comprised panel and frame members, usually metallic such as steel. Steel has typically been used because of its relatively high strength, low cost and the ease by which it can be shaped into frame members or body panels. Recent studies have developed vehicular body structures that include relatively lighter materials, such as aluminum or magnesium, and/or irregularly shaped, thin-walled hydroformed structures that are designed to reduce the number of parts and the overall weight of the automobile.  
           [0003]    The driving force for the introduction of hydroformed parts into the automotive industry is the desire to reduce the manufacturing cost and weight by consolidating parts. However, the application of tubular hydroformed parts for vehicle structures creates problems in vehicle fabrication and assembly. The joining of two hydroformed parts in a T-like joint has proven difficult. Attaching two tubular parts, or a channel-shaped part and a tubular part, at a right or an acute angle can be done by conventional welding techniques, such as spot welding or other fusion welding. However, it is sometimes difficult to fit the parts together. Moreover, the application of welding heat to relatively small areas of the thin-walled bulky structures often produces distortion of the parts at the weld region. This distortion can occur in the joining of steel parts but is particularly problematic in the joining of lower melting, lighter weight parts, such as those of aluminum or magnesium alloys.  
           [0004]    Thus, it is an object of the present invention to provide a new method for joining tubular or tubular and channel-shaped components in a T-shaped joint. It is a further object to employ such a method that utilizes lower temperatures and less heat so as to minimize distortion of metal in the region of the T-joint. Such a method would have particular utility in joining thin-walled hydroformed parts or the like.  
         SUMMARY OF THE INVENTION  
         [0005]    This invention provides a riveting/brazing process, which results in less heat distortion than is usually encountered in welding thin-walled tubular and/or channel parts in a T-joint. In making such a joint, the end of a first tubular or channel member must be attached at an acute or right angle to the side surface of a second tubular or channel member.  
           [0006]    In accordance with the invention, one or more flanges are cut into one end of the first member. The purpose of the flange is to provide integral material of the first member to be attached to the surface of the second member. The flange is cut so that it can be shaped in conformance with the surface of the second member. Corresponding location holes are formed both in the flange(s) as well as in the intended joint surface of the second member. These location holes are made to achieve suitable alignment of the end of the first member with the joint surface of the second member. A brazing alloy is fixed to a side of the flange, or forming the flange to the surface of the second member. The flange(s) are attached to the surface of the second member by means of a rivet to form an assembly. Once completed, heat is applied to the assembly to form a brazed joint.  
           [0007]    The flanges are formed on one end of the first member by cutting them into shapes that will allow good contact with the surface of the second member. For more complex structures, such as cylindrical tubes, several flanges may be necessary to accomplish a secure fit among the parts. Accordingly, a flange is to be cut and shaped so that it can be pressed into suitable conformance with the shape of the second member.  
           [0008]    In a preferred embodiment of the invention, a pocket is formed in the surface of the flange(s) to receive a body of braze alloy filler material. The pocket can be shaped to accommodate the brazing alloy, which is suitably in the form of a rod, a ring, or a flat sheet. In a particularly preferred embodiment, the pocket is formed in the surface of the flange(s) so that the body of braze material protrudes about 0.01 to 0.5 millimeter. When the flange and protruding braze alloy is placed into contact with the forming surface, a space is provided for flow of molten braze alloy to bond the assembled flange and the surface of the second member.  
           [0009]    In another preferred embodiment of the invention, each flange is attached to the surface of the second member, prior to brazing, by placing a rivet through their corresponding location holes. The rivet is sized to allow a suitable connection between the flange and the second member to accommodate the above-described brazing gap between the parts. Thus, the brazing alloy can better flow, from the pocket into the brazing gap, upon application of heat.  
           [0010]    Other objects and advantages of this invention will become apparent from a detailed description of specific embodiments that follow. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a generic T-joint representative of welded pillar-to-rocker connection used in a vehicular body assembly;  
         [0012]    [0012]FIG. 2 shows a completed body assembly in accordance with the invention comprising a brazed T-joint using rectangular tubes;  
         [0013]    [0013]FIG. 3 is an exploded view prior to assembly and brazing for making the joint of FIG. 2;  
         [0014]    [0014]FIG. 4 is a view of a flange isolated from the FIG. 3 view, partially broken away and in section showing a location hole and the placement of a rod of braze alloy; and  
         [0015]    [0015]FIG. 5 is a cross sectional view of the pillar flange and underlying rocker side as shown in FIG. 4 in the direction of arrows  5 - 5  of that figure. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    This invention provides a new method of forming a joint between tubular or channel shaped members. Such members are often used in the manufacture of a vehicle body frame. Often vehicle frame members are preformed into complex shape to accommodate the design shape of the vehicle and the attachment of body panels and other vehicle components, such as door hinges, latches and seat belt anchors. Obviously, the joint must provide suitable strength. The joint between the central pillar and the rocker frame member of a vehicle is illustrative of a typical T-type joint in vehicle manufacture.  
         [0017]    [0017]FIG. 1 illustrates a welded T connection between a channel-shaped pillar member  10  and a tubular rocker member  12 . Pillar channel  10  has been formed with side flanges  14 ,  16  and an end flange  18 . A portion of flanges  14 ,  16  and end flange  18  are used in welding an end of pillar  10  to sides of rocker  12 . The respective weld beads are shown at  20 ,  22  and  26 . Also shown in FIG. 1 are a series of spot welds  24  by which channel member  10  is attached to a separately formed inner pillar member (not shown).  
         [0018]    The pillar  10  in FIG. 1 requires two members, which must be welded together in a separate operation. Moreover, the application of welding heat to small regions of a complex assembly often leads to distortion of the assembly. This invention provides a way of utilizing tubular frame members in attaching the end of one tube to the body of a second tube without the use of welding heat that results in distortion of the assembly.  
         [0019]    [0019]FIG. 2 shows a frame assembly comprising a vertical pillar tube  30  and a horizontal rocker tube  32 . The joint  100  that is formed is generally referred to as a T-joint and is made to join body members at angles of 90° or less. The frame members shown in FIG. 2 can include a variety of irregular shapes and conformations.  
         [0020]    As seen in FIG. 2, pillar, or first member,  30  is attached to rocker, or second member,  32  utilizing four flanges (three shown  34 ,  36  and  38 ). These flanges were formed by cutting along the corners  40  from the end of the pillar tube  30  to be attached to the side of rocker  32 . The cuts allow the separation of discrete, generally rectangular, flanges  34 ,  36 , and  38 . In forming the flanges on the pillar member  30 , flanges  34  and  38  are bent 90° away from the vertical direction of the pillar member  30 . Flange  36  and the rear flange (not shown) are bent as necessary to fit over the top surface of  102  and around sides  104 ,  106  of rocker  32 .  
         [0021]    Still referring to FIG. 2, each flange  34 ,  36  and  38  comprises a rivet  91 ,  93  and  94 , for temporarily securing the flange to an underlying surface  102 ,  104  or  106  as will be described below. Each flange  34 ,  36  and  38  also contains a pocket  50 ,  52  and  54  to contain a body of braze alloy. Thus, the T-joint  100  in FIG. 2 comprises brazed bonds between the several flanges and the underlying surfaces of the rectangular rocker tube  32 . The method of forming T-joint  100  will be better understood by reference to FIGS.  3 - 5 .  
         [0022]    Preparation of the individual body members is generally shown in an exploded view of the pillar-to-rocker assembly in FIG. 3. This view better shows pillar member  30  prior to it being riveted and brazed to rocker member  32 . As seen in the exploded view, one end of pillar tube  30  has been cut back along each of its corners  40  to form four flanges of which three  34 ,  36 , and  38  are seen in FIG. 3. The number of flanges needed will depend on the complexity of the rocker member&#39;s shape and conformation. Furthermore, additional cuts or shaping may be required in any given flange in order to bend it into conformation with the surface of the tube, or channel, member to which it is to be attached. In the relatively simple embodiment of attaching an end of a square tube to the side of another square tube, four square, or rectangular, flanges are suitable.  
         [0023]    In the pre-assembled embodiment of FIG. 3, securing pillar member  30  to rocker member  32  in position is essential to obtain a perfected brazed joint. The preferred embodiment uses rivets that are placed through location holes  44 ,  46  and  48  that are formed in flanges  34 ,  36  and  38  and their corresponding location holes  56 ,  58  and  60  formed in rocker member  32 . Depending upon the shape and conformation of the flange, positioning of the location holes on the flange surface can be tailored to obtain an optimum brazed joint among frame members. Once the optimum position of the location hole formed in a flange is determined, a respective location hole can be formed on rocker member  32 . Location holes that are formed into the second member can be completed during hydroforming operation.  
         [0024]    According to FIG. 3, when lining up the location holes from the pillar member  30  to the rocker member  32 , corner  72  of flange  38  will end up at point  84  on the rocker member  32 , while corner  70  of the flange will end up at point  82  of the rocker member  32 . Accordingly, corners  62 ,  64  of flange  34  will end up at points  74 ,  76 , respectively, and corners  66 ,  68  of flange  36  will end up at points  78 ,  80 , respectively. Once attached, flanges  34 ,  36  and  38  will lie on surfaces  102 ,  104  and  106  of rocker member  32 .  
         [0025]    An isolated view of flange  38  and the underlying surface of rocker  32  is depicted in FIG. 4. Flanges  34 ,  36  and  38  includes pocket  50 ,  52  and  54  that have been formed under the surface of the flanges. A pocket is a continuous recess that can be made by hydroforming or alternative methods, such as stamping. The shape of the pocket should conform to the shape of braze material  92  that will soon be placed inside it. The suggested braze alloy  92  for this embodiment is either a silver-copper-zinc base alloy for brazing steel or an aluminum-silicon alloy for brazing aluminum. In the process of brazing steel with a silver-copper-zinc alloy, a white flux is generally used. Since capillary attraction between the steel and the filler material is much higher than that between the steel and the flux, the flux is displaced by filler material. Braze alloy  92  is shown as a rod bent to the shape of pocket  54  and press fit into it. Obviously, braze alloys could take other shapes as well. Typically, the braze alloy  92  has a thickness in the range of 0.1 to 3 millimeters.  
         [0026]    Referring to FIGS. 4 and 5, flange  38  is initially attached to rocker  32  with a rivet  94  placed inside of location hole  48  centered on the a flange surface  120 . The rivet is placed through location hole  48 &#39;s respective location hole  60  that is formed on the surface  102  of rocker member  32 . Though a selection of rivets can be used in this process, the rivet used in this embodiment is a blind rivet that includes a head  114 , a hollow body  112 , a mandrel  116 , and a collapsible blind end  110 . Using a suitable rivet gun, the hollow body  112  of rivet  94  is inserted through overlying location holes  44 ,  60  until rivet head  110  engages flange surface  120 . The gun then upsets hollow body  112  to form rivet head  114  against rocker  32 . As seen in FIG. 5, rivet  94  snugly attaches flange  38  to rocker member  32  where then conforming surfaces can be brazed. A portion of braze rod  92  protrudes from flange pocket  54  defining a gap  96  for flow of molten braze material. The optimum brazing gap  96  is generally in the range of 0.1 to 1 millimeters. In general, the rivet is used as a “net” locator to fix pillar member  30  and rocker member  32  in proper position before commencing the brazing process.  
         [0027]    In general, the method of brazing comprises the application of heat to join two structures. The brazing technique is analogous to that of welding but is performed at temperatures that will mitigate deformity of the vehicle body part. Brazing joins materials by heating them in the presence of a braze alloy while having a liquidus temperature above 450° C. but below the solidus temperature of the base material(s) used. Since melting of the base material is not involved and the peak temperature is controllable, the brazing process reduces the residual stress and distortion of the components.  
         [0028]    Once pillar member  30  and rocker member  32  have been joined using rivets, heat is then applied to the frame assembly by application of a heat source, such as a torch, laser, or induction heating. When the brazing temperature is reached, the braze alloy is melted between the surfaces of the joint area, also known as the brazing gap  96 . As a result of capillary attraction, the molten filler material flows into gap  96  between flanges  34 ,  36  and  38  and the fourth flange (not shown) and the second member  32 , and is consequently distributed between the closely fitted-surfaces of the joint  100 . To achieve mechanically sound joints, various process variables (e.g., brazing temperature, time, thickness of the filler material, and spacing between the parts) for each application need to be tested and tried.  
         [0029]    The method and procedure described above may be used for attaching various automotive components that have sheet metal or tubular flange portions. Examples include sheet-to-extrusions, sheet-to-cast parts and tube-to-tube parts, various vehicle components such as roof rail-to-cast node applications and roof rail to pillar application and the like.  
         [0030]    While the invention has been described in the context of the preferred embodiments, it is not intended to be limited to the above description, but rather only to the extent set forth in the following claims.