Abstract:
An extruded aluminum alloy tube for hydroforming into an automotive body component includes a wall defining a closed perimeter. The wall includes weld seams disposed in the wall and running longitudinally along the tube. An extruded pip is disposed on the wall and runs longitudinally along the tube. The pip is parallel to the seams and is configured to identify a location of the seams for alignment of the tube during manufacturing.

Description:
TECHNICAL FIELD 
     The present disclosure relates to aluminum extruded tubing for automotive applications. 
     BACKGROUND 
     Vehicle manufacturers are implementing lighter, stronger materials, such as aluminum alloys to meet emission reduction goals, meet fuel economy goals, reduce manufacturing costs, and reduce vehicle weight. Increasingly demanding safety standards must be met while reducing vehicle weight. One approach to meeting these competing interests and objectives is to hydro-form high strength aluminum alloy tubular blanks into strong, lightweight hydro-formed parts. 
     Aluminum tube types include seam-welded tube, extruded seamless tube, and extruded structural tube. Seam-welded tube and extruded seamless tube are expensive. Extruded structural tubes are lower in cost because they are formed in a continuous mill operation having a greater line and material utilization efficiency than extruded seamless tubes and seam-welded tubes. 
     Extruded structural tubes are formed by extruding an aluminum billet through an extrusion die at a high temperature and at high pressure. Discontinuous material flow across the section of the shape occurs when the flowing aluminum separates in the mandrel plate and re-converges in the cap section. A weld line, or joining line, is created where the flowing aluminum re-converges to form the extruded shape. Extruded structural tubes may have two or more weld lines that are an artifact of the porthole extrusion process. 
     Hydro-forming complex parts may require a series of bending, pre-forming, hydro-forming, piercing and machining operations. Bending and hydro-forming aluminum tubes is not currently in use in high volume production operations. (i.e., more than 100,000 units/year) Aluminum intensive vehicles (AIVs) are envisioned that use metal forming methods consistent with current conventional automotive manufacturing methods. 
     The above challenges and other challenges are addressed by this disclosure as summarized below. 
     SUMMARY 
     According to one aspect of this disclosure, an extruded aluminum alloy tube for hydroforming into an automotive body component includes a wall defining a closed perimeter. The wall includes weld seams disposed in the wall and running longitudinally along the tube. An extruded pip is disposed on the wall and runs longitudinally along the tube and between the seams. The pip is parallel to the seams and is configured to identify a location of the seams for alignment of the tube during manufacturing. 
     According to another aspect of this disclosure, a method is disclosed for forming an aluminum alloy vehicle body component. An aluminum alloy billet is extruded into an aluminum tube that includes longitudinal weld seams formed in a sidewall of the tube during extrusion. A weld seam locating pip is also formed on a sidewall of the tube during extrusion. The pip is substantially parallel to the weld seams and is used to locate the weld seams during manufacturing of the body component. The pip may be disposed between the weld seams. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exploded diagrammatical view of a porthole extrusion die made according to one embodiment of this disclosure. 
         FIG. 2  is a cross-section view of an extruded tube formed by the porthole extrusion die shown in  FIG. 1 . 
         FIG. 2A  is a detail view of a pip feature on the tube. 
         FIG. 2B  is a detail view of a pip feature on the tube according to an alternative design. 
         FIG. 3  is a diagrammatic representation of a rotary draw bending tool. 
         FIG. 4  is a cross-section view of a hydroforming die in the open position. 
         FIG. 5  is a cross-section view of the hydroforming die of  FIG. 4  in the closed position. 
         FIG. 6  is a fragmented perspective view of a hydro-formed vehicle body component. 
         FIG. 7  is a fragmented elevation view of a truck cab with the body panels removed. 
         FIG. 8  is a flowchart illustrating one example of a method of forming a hydro-formed body component that includes a pip locating feature. 
     
    
    
     DETAILED DESCRIPTION 
     The illustrated embodiments are disclosed with reference to the drawings. However, it is to be understood that the disclosed embodiments are intended to be merely examples that may be embodied in various and alternative forms. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components. The specific structural and functional details disclosed are not to be interpreted as limiting, but as a representative basis for teaching one skilled in the art how to practice the disclosed concepts. 
     Referring to  FIG. 1 , a porthole extrusion die  10  is shown that includes a container  12 . The container  12  includes a cavity  14  defining a cavity surface  16 . A mandrel plate  18  is received within the cavity  14 . The mandrel plate  18  includes an outer ring  20  and central element  22  that are connected to each other by a plurality of webs  24 . The outer ring  20  is disposed against the cavity surface  16 . The central element  22  includes an extended portion that projects axially in the downstream direction. The outer ring  20 , the central element  22  and the webs  24  define a plurality of openings  26 . 
     The extrusion die  10  also includes a cap  30 . The cap  30 , when installed is disposed inside the cavity  14  and adjacent to the mandrel plate  18  on the downstream side of the mandrel plate  18 . The cap  30  defines an opening  32 . The extended portion projects into the opening  32 . The extended portion  34  includes an inside diameter (ID) forming surface  36 . Forming surface  36  includes a marking element  28 . The cap  30  includes an outside diameter (OD) forming surface  38 . The ID forming surface  36  and the OD forming surface  38  cooperate to define an orifice though which the extruded tube exits the die  10 . 
     The aluminum alloy billet  40  is extruded at high temperature and pressure through the extrusion die  10 . In a first stage, the billet  40  is extruded through the mandrel plate  18 . The mandrel plate  18  separates the billet  40  into a plurality of tube sections  42  as the billet passes through the openings  26 . 
     In a second stage, the forming surfaces  36 ,  38  cause the tube sections  42  to re-converge at the cap  30  forming a structural tube  44 . Re-convergence of the tube sections  42  creates weld seams  48  where the tube sections are joined to each other. (The weld seams are not welds in the traditional sense but rather are seams where pressure and heat forces two metal bodies together.) The marking element  28  creates a pip  52  in the aluminum as the aluminum passes over the forming surface  36 . The pip  52  is formed near in time with the formation of the weld seams and is located at a fixed position relative to the weld seams. Forming the pip  52  and the weld seams  48  near in time ensures a constant spatial relationship between the weld seams  48  and the pip  52  despite any twisting of the tube  44  that may occur during extrusion. The pip  52  is a locating feature that allows a person or machine to determine weld seam location. 
     As illustrated, the marking element  28  is located on the ID forming surface  36  and the pip  52  is located on an interior surface of the tube. Alternatively, the marking element may be located on the OD forming surface  38  and the pip  52  may be located on an exterior surface of the tube. 
     Referring to  FIG. 2 , the aluminum alloy, porthole extruded, structural tube  44  is shown. The tube  44  may be a circular tube with a hollow circular center or may be another shape. The tube includes a sidewall  46  that has an interior surface  54  and an exterior surface  56 . The weld seams  48  are formed in the sidewall  46 . The weld seams  48  extend longitudinally along the length of the tube  44  and completely through the sidewall  46 . The pip  52  is disposed on the interior surface  54 . The pip  52  runs longitudinally along the length of the tube  44 . The pip  52  may be located between the weld seams  48  or may be located on one of the weld seams. The pip  52  and the seams  48  are substantially parallel to each other in a fixed spatial relationship. The pip  52 , as shown, is disposed on the interior surface  54  but the pip  52  may be disposed on the exterior surface  56 . The location and size of the pip  52  is determined by the location and size of the marking element  28 . The pip  52  as shown is enlarged for better visibility in the drawing. 
     The pip  52  may be a raised portion of the sidewall  46  as is shown in  FIG. 2A . The raised pip  52  may be a ridge formed into the sidewall  46 . The ridge is formed by a recessed marking element  28 . For example, the marking element  28  may be a groove machined into the ID forming surface  36 . During extrusion, aluminum is forced into the groove forming the ridge. 
     Alternatively, the pip  53  may be a recessed portion in the sidewall  46  as is shown in  FIG. 2B . The recessed pip  53  may be a groove formed into the sidewall  46 . The groove is formed by a raised marking element  28 . For example, the raised marking element may be a tooth disposed on the ID forming surface  36 . During extrusion, the tooth cuts a groove into the aluminum. The pip  53  defines a pair of opposing sidewalls  55  that extend from the interior surface  54  towards the exterior surface  56 . A floor  57  of the pip  53  connects between the sidewalls  55 . 
     The structural tubes  44  are formed into a finished part by hydroforming the tube into a desired shape. Prior to hydroforming the tubes may go through a series of processes such as pre-bending, pre-forming and cutting. The weld seams have slightly different material properties than the rest of the tube. Consistent placement of the weld seams is necessary to ensure a consistent finished part in mass production. Damage can occur if the weld seams are not placed in a proper location during processing. For example, the tube can crack, split or blowout if misaligned in the hydroforming die. Aside from the problem of potential physical part damage, it is very desirable to provide an extruded tube that has consistent properties. Having final parts with different weld seam locations can lead to inconsistent part performance. For example, the weld seam location can affect the strength of the part. To mitigate this issue, the weld seams must be placed in the appropriate position within the manufacturing dies. Unlike steel tubes, that have visible welds, the weld seams on extruded aluminum tubes are almost undetectable with the naked eye and are very difficult to locate. 
     The pip  52  is a locating feature that allows a person or machine to determine locations of the seam welds without being able to see the seams. The pip can be identified by a person with the naked eye and can be identified by an optical scanner or eddy current machine. The pip and weld seam are formed during extrusion and have a fixed spatial position relative to each other. By knowing the location of the pip, the location of the weld seams can be determined. The location, size, type and shape of the pip may vary. The pip  52  may also be used to measure the amount of twist that is occurring during the extrusion process. Different amounts of twist are desired for different extrusion operations. The pip provides an convenient visible indicator that can be monitored during the extrusion process to ensure that proper twist is occurring. 
     Referring to  FIG. 3 , a rotary draw bending tool  62  is shown. The tube  44  may go through a series of pre-bending stages to roughly shape the part prior to hydroforming so that the tube  44  will fit into the die. The tube  44  must be properly aligned in the bending tool  62 . If the weld seams  48  are not properly aligned during the pre-bending phase, then they will not be properly aligned during hydroforming. The pip  52  is used to properly align the tube  44  in the bending tool  62 . For example, the pip  52  is aligned with markings located on the bending tool  62  when the tube is loaded in the tool  62 . Alternatively, a robot may be programed to place the pip  52  in a specific location relative to the tool  62 . After proper alignment, the tube  44  is bent to form a pre-bent tube  66 . The pre-bent tube  66  may be pre-formed before hydroforming. The pre-forming may take place after the tube  44  is pre-bent. 
     Referring to  FIGS. 4 and 5 , a hydro-forming die  64  is shown. The die  64  includes a first die half  68  and a second die half  70 . The pre-bent tube  66  is loaded into the hydro-forming die  64  between the first and second die halves  68 ,  70 . End plugs (not shown) are inserted into the open ends of the tube  44 . A pressurizing medium (such as water) is pumped into the tube  66  to pressurize the interior of the tube. The die halves are clamped together to form a hydro-formed part  72 . The tube  66  may be hydro-pierced in the hydroforming die  64 . In another embodiment, the pre-bent tube  66  is pre-formed prior to hydroforming. 
     Referring to  FIG. 6 , the hydro-formed part  72  is shown to have weld seams  48  at specific locations. For example, the seams are located away from holes and curved portions of the part  72 . The pip  52  may be utilized throughout the pre-bending and hydroforming stages to ensure that the weld seams are in the design locations. Alternatively, the pip  52  may only be used at selected stages. For example, the pip may only be used at the pre-bending stage and thereafter the bends on the tube may be used to locate the weld seams. Proper alignment of the weld seams provides repeatable final parts with uniform strength, characteristics and performance. Variations in weld seam location may cause undesirable variations in the manufacturability, dimensional, or functional performance of the final product. 
     Referring to  FIG. 7 , a side view of a truck cab  74  is shown with the body panels removed. The cab  74  includes a hydro-formed roof rail  76 . The roof rail  76  is a porthole extruded structural tube that may be manufactured using the previously described die and manufacturing process. The roof rail  76  attaches to the cab  74  at the hinge pillar  78  and at additional locations. The roof rail  76  provides rigidity to the cab and supports the body panels. The roof rail  76  must be strong to provide acceptable performance as tested in roof-crush, side impact, and other tests. Proper alignment of the weld seams in an extruded tube assures uniform strength and reduced variation in part performance. 
       FIG. 8  is a flowchart illustrating a method of forming an aluminum body part for a vehicle. References to the components parts in the following description of the method are illustrated in  FIGS. 1 to 7 . At step  100  an aluminum alloy structural tube  44  is formed with a porthole extrusion die  10 . The extrusion die  10  forms weld seams  48  in a sidewall  46  of the tube  44 . The extrusion die  10  also forms a pip  52  in the sidewall  46  of the tube  44  near in time with the formation of the weld seams  48 . For example the pip  52  and the weld seams  48  are formed essentially simultaneously. The tube  44  is extruded in a continuous operation. The tube  44  may be stretched after extrusion. At step  102 , the extruded structural tube  44  is cut into desired lengths. At step  104  the tubes  44  are aligned in a bending tool  62  using the pip  52  to place the weld seams  48  at a desired location relative to the bending tool  62 . The tube  44  is pre-bent with the tool at step  106 . The pre-bent tube  66  is placed into a hydroforming die  64  and hydro-formed into a finished part  72  at step  108 . Alternatively, the pre-bent tube is pre-formed prior to hydroforming. The finished part  72  is then installed onto a vehicle, such as a truck, at step  110 . 
     The embodiments described above are specific examples that do not describe all possible forms of the disclosure. The features of the illustrated embodiments may be combined to form further embodiments of the disclosed concepts. The words used in the specification are words of description rather than limitation. The scope of the following claims is broader than the specifically disclosed embodiments and also includes modifications of the illustrated embodiments.