Abstract:
A hydroform die tube holding assembly and method of using same includes at least one seal unit for sealing an end of a tube. The hydroformed die tube holding assembly also includes a seal unit elevator for attachment to a lower die half to operatively support the at least one seal unit. The hydroformed die tube holding assembly further includes at least one upper gas spring for attachment to an upper die half to engage, the seal unit elevator to drive the seal unit elevator downward prior to the upper die half engaging the tube.

Description:
TECHNICAL FIELD 
     The present invention relates generally to hydroforming and, more particularly, to a hydroform die tube holding assembly and method of making same for automotive structures. 
     BACKGROUND OF THE INVENTION 
     It is known to hydroform tubular components or members. Hydroformed tubular members are becoming increasingly popular in automotive body structural applications. During vehicle body manufacturing, many of the hydroformed tubular members are used in vehicle body and chassis applications. However, vehicle strength, stiffness, and/or impactworthiness often necessitate the need for local areas of structural reinforcement to meet their design goals. 
     Tube sealing is a major factor in the tube hydroform process. Seal units may be mounted on nitrogen powered elevators. The tube is filled (fill pressure) and the round tube is stuffed into the die cavity to bottom. Press tonnage is applied and form pressure is initiated forming the tube to the cavity. This process eliminates the need for a pre-form die operation. 
     When the seal units do not directly oppose one another, the pneumatic clamp devices do not provide capability to hold the bent tube into proper position. When finish part geometry changes round tube near seals, the tubes tend to move within the sealing process (creating sealing inefficiencies). 
     As a result, it is desirable to provide a new hydroform die tube holding device. It is also desirable to provide a hydroformed tubular member that is locally and internally reinforced prior to the hydroforming process. It is further desirable to provide a method of locally and internally reinforcing a hydroformed tubular member. Therefore, there is a need in the art to provide a new hydroform die tube holding assembly and method of making same that meets these desires. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is a hydroform die tube holding assembly including at least one seal unit for sealing an end of a tube. The hydroformed die tube holding assembly also includes a seal unit elevator for attachment to a lower die half to operatively support the at least one seal unit. The hydroformed die tube holding assembly further includes at least one upper gas spring for attachment to an upper die half to engage the seal unit elevator to drive the seal unit elevator downward prior to the upper die half engaging the tube. 
     Also, the present invention is a method of hydroforming a tube using a hydroform die tube holding assembly. The method includes the steps of providing a seal unit for sealing an end of a tube and supporting the seal unit with a seal unit elevator on a lower die half. The method also includes the steps of providing at least one upper gas spring for attachment to an upper die half and engaging the seal unit elevator with the at least one upper gas spring. The method further includes the steps of driving the seal unit elevator downward prior to the upper die half engaging the tube, closing the upper die half and lower die half together, and hydroforming the tube to form a hydroformed tubular member. 
     One advantage of the present invention is that a hydroform die tube holding assembly is provided for hydroforming a tubular member. Another advantage of the present invention is that a method of making a hydroform die tube holding assembly is provided to form a hydroformed tubular member by holding the tubular member in position before the die closes to the bottom. Yet another advantage of the present invention is that the assembly and method adds the ability to manufacture products with additional form (sections) at the tube ends, near the seal units. Still another advantage of the present invention is that the assembly and method adds the ability to hold the round tube into position and improve sealing condition by not allowing the tube to move over the o-ring seal. A further advantage of the present invention is that the assembly and method reduces downtime and die maintenance. Yet a further advantage of the present invention is that the assembly and method adds design flexibility to locally and internally reinforce hydroformed tubular members for crashworthiness, strength, and/or stiffness improvements. 
     Other objects, features, and advantages of the present invention will be readily appreciated, as the same becomes better understood, after reading the subsequent description taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a fragmentary elevational view of a hydroform die tube holding assembly, according to the present invention. 
         FIG. 2  is an elevational view of the hydroform die tube holding assembly of  FIG. 1 . 
         FIG. 3  is a view similar to  FIG. 1  illustrating a first step of operation of the hydroform die tube holding assembly of  FIGS. 1 and 2 . 
         FIG. 4  is a view similar to  FIG. 1  illustrating a second step of operation of the hydroform die tube holding assembly of  FIGS. 1 and 2 . 
         FIG. 5  is a view similar to  FIG. 1  illustrating a third step of operation of the hydroform die tube holding assembly of  FIGS. 1 and 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings and in particular  FIGS. 1 and 2 , one embodiment of a hydroform die tube holding assembly  10 , according to the present invention, is shown for hydroforming a tube  12  used for assembly in automotive structures (not shown) of a vehicle (not shown). The hydroform die tube holding assembly  10  includes at least one, preferably a pair of seal units, generally indicated at  14 , to seal the ends of the tube  12 . Each seal unit  14  includes an axial protrusion  16 . One end of the tube  12  is placed over the protrusion  16  of the seal unit  14 . It should be appreciated that the other end of the tube  12  would also be placed over the protrusion  16  of the other seal unit  14 . It should also be appreciated that the seal units  14  do not oppose one another. It should further be appreciated that only the one seal unit  14  for the hydroform die tube holding assembly  10  will be subsequently described. It should still further be appreciated that the seal unit  14  is conventional and known in the art. 
     Each seal unit  14  is placed in a die set, generally indicated at  18 , comprised of an upper die half  20  and a lower die half  22 . The upper die half  20  includes a cavity portion (not shown) and the lower die half  22  includes a cavity portion (not shown) for receiving the tube  12 . It should be appreciated that the upper die half  20  and lower die half  22  are progressively closed so that the tube  12  is progressively deformed into the cavity portion of the die set  18 . 
     The hydroform die tube holding assembly  10  includes at least one, preferably a plurality of mounting blocks  23  connected to the upper die half  20  by a suitable mechanism such as fasteners (not shown). The hydroform die tube holding assembly  10  includes at least one, preferably a plurality of gas springs  24  extending downwardly from the mounting blocks  23 . Preferably, four gas springs  24  are used (only two shown). The gas springs  24  are of a nitrogen gas type. Each of the gas springs  24  includes a cylinder  26 , a piston (not shown) disposed in the cylinder  26 , and a piston rod  28  connected to the piston and extending axially from one end of the cylinder  26 . One of the cylinders  26  is connected to one of the mounting blocks  23  by a suitable mechanism such as fasteners (not shown). It should be appreciated that the cylinders  26  are connected to a source of gas (not shown) via a suitable mechanism such as hoses (not shown). 
     The hydroform die tube holding assembly  10  includes at least one, preferably a plurality of locators  30  extending downwardly from the mounting blocks  23 . Preferably, four locators  30  are used (only two shown). The locators  30  are generally cylindrical in shape. The locators  30  engage the seal unit  12  for a function to be described. 
     The hydroform die tube holding assembly  10  includes a seal unit elevator  32  supported on the lower die half  22 . The seal unit  14  is connected to the seal unit elevator  32  by a suitable mechanism such as fasteners (not shown). The hydroform die tube holding assembly  10  also includes at least one, preferably a plurality of gas springs  34  extending upwardly from the seal unit elevator  32 . Preferably, four gas springs  34  are used (only one shown). The gas springs  34  are of a nitrogen gas type. Each of the gas springs  34  includes a cylinder  36 , a piston (not shown) disposed within the cylinder  36 , and a piston rod  38  connected to the piston and extending axially from one end of the cylinder  36 . The cylinders  36  are connected to the seal unit elevator  32  by a suitable mechanism such as fasteners (not shown). It should be appreciated that the cylinders  36  are connected to a source of gas (not shown) via a suitable mechanism such as hoses (not shown). 
     The hydroform die tube holding assembly  10  includes at least one, preferably a plurality of locators  40  extending upwardly from the lower die half  22  and into the seal unit elevator  32 . Preferably, four locators  40  are used (only two shown). The locators  40  are generally cylindrical in shape. The locators  40  engage the seal unit elevator  32  for a function to be described. 
     Referring to  FIGS. 3 through 5 , one embodiment of a method, according to the present invention, of operating the hydroform die tube holding assembly  10  is shown for hydroforming the tube  12  for assembly in automotive structures (not shown) of a vehicle (not shown). The method provides the ability to lock the tube  12  into its proper position and let the tube forming occur without allowing movement within the seal unit  14 . The method is used to add travel to the seal unit  14  such that the seal unit  14  is driven down square ahead of the finished part form for the tube  12 . 
     The method includes the step of providing a tubular member or tube  12 . The tube  12  is made of a metal material. In one embodiment, the tube  12  has a generally circular cross-sectional shape and extends axially. 
     The method includes the step of hydroforming the tube  12 . The tube  12  is placed in a die set, generally indicated at  18 , comprised of an upper die half  20  and a lower die half  22 . The upper die half  20  includes a cavity portion (not shown) and the lower die half  22  includes a cavity portion (not shown) for receiving the tube  12 . 
     The ends of the tube  12  are placed over the protrusions  16  of the seal units  14  and sealed. Hydraulic fluid is pumped into the tube  12  under pressure. The upper die half  20  and lower die half  22  are progressively closed so that the tube  12  is progressively deformed and the pressurized fluid captured therein expands the walls of the tube  12  into the cavity portions of the die set  18 . 
     In operation of the hydroform die tube holding assembly  10 , as the upper die half  20  moves toward the lower die half  22 , the gas springs  24  engage the seal unit elevator  32  to drive the seal unit elevator  32  downward ahead of the upper die half  20  engaging the lower die half  22  as illustrated in  FIG. 4 . The locators  30  engage the seal unit elevator  32  and drive the seal unit elevator  32  downward. The upper die half  20  continues to move toward the lower die half  22  until the upper die half  20  engages the lower die half  22  as illustrated in  FIG. 5 . When this occurs, the gas springs  24  take up or dwell, keeping pressure on the seal unit elevator  32 . It should be appreciated that the locators  30  allows for driving the seal elevator unit  32  square. It should be appreciated that an upper jaw (not shown) of the upper die half  20  grabs the tube  12  at the same time the seal unit elevator  32  is going down. 
     The die halves are fully closed upon one another with the tube  12  being tightly clamped between the die halves. During this closing of the die halves, a relatively constant hydraulic pressure may be maintained within the tube  12  by incorporating a pressure relief valve (not shown) into the seal unit  14  enclosing the ends thereof so that hydraulic fluid may be forced from the tube  12  as it collapses. 
     Once the die is closed, the tube  12  is then expanded to a final cross-sectional profile by increasing the hydraulic pressure sufficient to exceed the yield limit of the tube  12  so that the tube  12  is forced into conformity with the tubular forming cavity portions of the die halves  20  and  22 . The die halves  20  and  22  are then opened to permit removal of the finished tubular member from the die halves  20  and  22 . When the die halves  20  and  22  are open, the gas springs  34  drive the seal unit elevator  32  upwardly. It should be appreciated that the locators  40  allow for driving the seal elevator unit  32  square. 
     The present invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. 
     Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the present invention may be practiced other than as specifically described.