Abstract:
An electro-hydraulic forming tool for forming a sheet metal blank in a one-sided die has first and second rigid rings that engage opposite sides of a sheet metal blank. The rigid rings are contained within slots on a die portion and a hydraulic force applicator portion of the forming tool. The seals are either resiliently biased by an elastomeric member or inherently resiliently biased into contact with the blank.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to seals for tools that use fluid to form a part against a rigid forming surface. 
         [0003]    2. Background Art 
         [0004]    Fluid forming processes generally include processes in which a workpiece is formed in a tool where one side of the tool is provided by a liquid. The other side of the tool is generally a rigid die against which the part is formed. Examples of fluid forming processes include hydro-forming, bladder press forming, super-plastic forming, electro-hydraulic forming, and explosive forming. 
         [0005]    Traditional seals for such applications include elastomeric seals, such as O-rings. Elastomeric seals used in hydro-forming applications may feature an O-ring inserted in a circumferential groove that is pushed inside the tube that is to be hydro-formed. Such O-ring seals have a short useful life in hydro-forming applications. In sheet forming applications, sealing requirements are more stringent. Elastomeric seals resist drawing the flange of the sheet across the seal. 
         [0006]    Metal-to-metal seals are used in hydro-forming applications that include a mandrel that includes a conical surface that is inserted into the tube that is to be hydro-formed. The mandrel is axially moved to provide additional material for the forming process. This approach is not adaptable to sheet forming processes to permit the outer edge of the flange of the sheet metal blank to be drawn into the forming die. 
         [0007]    In hydro-mechanical drawing operations, metal-to-metal surface contact has been proposed in which ribs formed on the die directly contact the metal blank. This approach suffers from considerable leakage of fluid from the die cavity. With this approach, the pressure level used in the forming process must be limited. A disadvantage of this approach is excessive wear of the ribs formed on the die. 
         [0008]    In super-plastic forming operations, seals are used in which metal-to-metal contact is obtained by indenting seating elements or ribs into the body of the blank. With this approach, only minimal movement of the blank across the sealing line is permitted. 
         [0009]    In electro-hydraulic forming processes, elastomeric sealing elements, such as O-ring seals, are utilized. In electro-hydraulic forming, elastomeric seals have lives that are limited to forming several dozen parts and, in any event, are certainly not expected to exceed several hundred parts. As a result, electro-hydraulic forming is limited to low volume applications. The sealing requirements for electro-hydraulic forming are more stringent than for hydro-forming because the sealing system must be able to preserve the vacuum between the blank and the die, and another seal must be provided on the side of the blank facing the fluid filled chamber to contain the fluid. 
         [0010]    The above problems relating to sealing in fluid forming applications are addressed by Applicants&#39; development as summarized below. 
       SUMMARY 
       [0011]    Some fluid forming technologies, such as electro-hydraulic forming, have been limited to low volume production due, in part, to a need for the development of an effective sealing system. Applicants have discovered a long-standing problem relating to the use of elastomeric O-ring seals in laboratory testing of electro-hydraulic forming tools. If metal is permitted to move or flow across the elastomeric O-ring sealing surfaces, the sealing surfaces become severely deformed after several cycles. This problem severely limits or precludes the use of electro-hydraulic forming for high volume production applications. 
         [0012]    According to one aspect of the disclosure, a metal sealing element is placed in contact with the blank that is to be formed. In one embodiment, the metal sealing element is backed by an elastomeric element that spring biases the metal sealing element into engagement with one or both sides of the blank. In other embodiments, the metal sealing element is constructed to use the inherent resilience of the metal to provide an integral spring biasing action against one or both sides of the blank. 
         [0013]    These and other aspects of Applicants&#39; concept will be better understood in view of the attached drawings and the following detailed description of the disclosed embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a diagrammatic perspective view parts of an electro-hydraulic forming tool. 
           [0015]      FIG. 2  is a diagrammatic cross-sectional view of the electro-hydraulic forming machine shown in phantom lines with the forming tool in its open position with a blank disposed between the die and the force applicator. 
           [0016]      FIG. 3  is a diagrammatic fragmentary cross-sectional view showing an insert and a metal seal backed by an elastomeric seal prior to engaging the blank. 
           [0017]      FIG. 4  is a diagrammatic fragmentary cross-sectional view of the insert and the metal seal shown in  FIG. 3  in sealing engagement with the blank. 
           [0018]      FIG. 5  is a diagrammatic fragmentary cross-sectional view of a hollow tubular seal that may be used with the electro-hydraulic forming tool shown in  FIG. 1  prior to engaging the blank. 
           [0019]      FIG. 6  is a fragmentary cross-sectional view of the hollow tubular seal shown in  FIG. 5  shown in sealing engagement with the blank. 
           [0020]      FIG. 7  is a diagrammatic fragmentary cross-sectional view of an integral open cross-section seal that may be used with the electro-hydraulic forming tool shown in  FIG. 1  prior to engaging the blank. 
           [0021]      FIG. 8  is a diagrammatic fragmentary cross-sectional view of the seal shown in  FIG. 7  shown in sealing engagement with the blank. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Referring to  FIGS. 1 and 2 , an electro-hydraulic forming (“EHF”) tool is generally designated by reference numeral  10 . The EHF tool  10  includes a die  12  that includes a forming surface  14 . An electro-hydraulic force applicator  16  is shown disposed below the die  12 . It should be understood that the EHF tool  10  would also include a mechanism for clamping the die  12  and electro-hydraulic force applicator  16  together. A blank  18  comprising a sheet metal blank of steel, aluminum, or another metal. The EHF tool  10  of the present invention is particularly well suited for performing operations on high-strength steel or high-strength aluminum alloys. 
         [0023]    The die  12  includes a die cavity  20  which is evacuated prior to a forming operation. The electro-hydraulic force applicator  16  includes a liquid chamber  22 . When the EHF tool  10  is closed, the die cavity  20  is aligned with the liquid chamber  22 . The liquid chamber  22  is filled with a liquid, such as oil or water, when the EHF tool is closed. 
         [0024]    A first metal seal  26  is provided on the electro-hydraulic force applicator  16  and extends around the periphery of the liquid chamber  22 . A second metal seal  26 ′ is provided in the die  12  and extends around the periphery of the die cavity  20 . The first and second metal seal elements are held in place by inserts  30  and  30 ′, as will be more specifically described with reference to  FIGS. 2-4  below. 
         [0025]    A pair of electrodes  32  are provided in the liquid chamber  22  that are connected to a capacitor circuit  36 , or charge storage device, by leads  38 . 
         [0026]    In operation, the blank  18  is inserted between the die  12  and the electro-hydraulic force applicator  16 . The EHF tool  10  is closed forcing the first metal seal element  26  into engagement with the lower side of the blank  18 , as shown in  FIG. 1 , while the second metal seal element  26 ′ is brought into sealing engagement with the upper side of the blank  18 . The die cavity  20  is evacuated by drawing a vacuum through ports (not shown) in the die  12 . The liquid chamber  22  is filled or refilled with liquid that is provided to the liquid chamber  22  in the electro-hydraulic force applicator  16  through fluid fill/evacuation ports (not shown). The liquid chamber  22  is preferably completely filled with liquid. The capacitor circuit  36  is selectively discharged through the electrodes  32  to create an arc that generates a shockwave that drives the blank  18  into engagement with the forming surface  14  of the die  12 . The first metal seal element  26  seals the fluid with the liquid chamber  22 . The second metal seal element  26 ′ provides a seal to maintain the vacuum within the die cavity  20 . 
         [0027]    Referring to  FIG. 2 , the die  12  is shown in the EHF tool  10  above the electro-hydraulic force applicator  16  on the opposite side of the sheet metal blank  18 . The die cavity  20  is aligned with the liquid chamber  22 . A slot  40  is provided in the electro-hydraulic force applicator  16  that receives the first metal seal element  26 . A slot  40 ′ is provided in the die  12  that receives the second metal seal element  26 ′. In each slot, a resilient backing ring  42 ′ is provided that biases the respective first and second seal elements  26  and  26 ′ toward the blank  18 . The cross section of  FIG. 2  is taken through the inserts  30  and  30 ′ that will be more particularly described with reference to  FIGS. 3 and 4  below. 
         [0028]    Referring to  FIGS. 3 and 4 , the structure of the inserts  30  and  30 ′ and seals  26  and  26 ′ will be described in greater detail.  FIG. 3  shows a pair of inserts  30 ,  30 ′ on opposite sides of the blank  18  prior to engagement with the blank  18 . Seal element  26  is below the blank  18 , while seal element  26 ′ is disposed above the blank  18 . The seal elements are each backed up by the resilient backing ring  42 . The first seal element  26  and backing ring  42  are disposed in a slot  40  within the insert  30 . Second seal element  26 ′ and backing ring  42 ′ are disposed in a slot  40 ′. A protruding portion  46  of the first seal element  26  protrudes from the slot  40 . The first seal element  26  is retained by retaining lips  50  formed on the insert  30 . No retaining lips are provided in the portions of the slot  40  that are between the inserts  30 . A protruding portion  46 ′ of the second seal element  26 ′ protrudes from the insert  30 ′. Retaining lips  50 ′ provided by the insert  30 ′ retain the second seal element  26 ′ within the slot  40 ′. No retaining lips are provided in the portions of the slot  40 ′ that are between the inserts  30 ′. 
         [0029]    The elastomeric rings  42  and  42 ′ as illustrated have a circular cross-section, however, they could have a rectangular or other cross-section if desired. 
         [0030]    Referring to  FIG. 4 , the inserts  30 ,  30 ′ shown in  FIG. 3  are shown with the first and second seal elements engaging the blank  18 . The first and second seal elements  26  and  26 ′ are pushed into their respective slots  40  and  40 ′ and no longer protrude from the slots. The resilient backing rings  42 ,  42 ′ are compressed by the first and second seal elements  26  and  26 ′. 
         [0031]    The seal  26  for the chamber shown in  FIG. 2  that prevents liquid from flowing out of the chamber  22  is established by the contact of the seal element  26  with the blank  18 . A seal is also created between seal element  26  and the resilient backing ring  42  that prevents liquid from passing through the slot  40 . The second seal element  26 ′ also establishes a seal with the blank  18  and the resilient backing ring  42 ′ forms a seal within the slot  40 ′ that prevents loss of vacuum in the die cavity  20 . 
         [0032]    The blank  18  may be drawn into the die cavity  20  when the electro-hydraulic force applicator  16  is discharged to form a portion of the blank  18  into the die cavity  20 . An effective seal is provided by the first and second seal elements and their biasing backing rings  42 ,  42 ′ while the metal seal elements  26  and  26 ′ are not damaged by the blank  18  being drawn into the die cavity  20 . The resilient backing rings  42 ,  42 ′ are not destroyed by the movement of the blank  18  because they do not contact the blank  18 . 
         [0033]    Referring to  FIGS. 5 and 6 , an alternative embodiment is shown to include a hollow tubular seal  52 . The hollow tubular seal  52  is preferably formed of metal. It should be understood that a hollow tubular seal would be provided on both sides of the blank  18  similar to that shown in  FIGS. 3 and 4 . The hollow tubular seal  52  is disposed in a slot  54  and held in place by means of retainers  56 . A protruding portion  58  of the hollow tubular seal  52  is shown protruding from the slot  54  prior to engaging the blank  18 . 
         [0034]    Referring to  FIG. 6 , the hollow tubular seal  52  is shown within the slot  54 . The protruding portion  58  is compressed upon engagement with the blank  18  and a compressed wall portion  60  is shown as a flattened side on the hollow tubular seal  52 . The hollow tubular seal  52  is preferably formed of steel or other metal that is resilient and has high fatigue resistance. The blank  18  may be drawn into the die cavity  20  during the forming process and the hollow tubular seal  52  is not believed to be substantially adversely affected by the drawing movement of the blank  18  across the compressed wall portion  60 . 
         [0035]    Referring to  FIGS. 7 and 8 , another alternative embodiment is illustrated in which an integral open cross-section seal  64  is provided in a slot  65 . The open seal  64  includes a protruding portion  66  that extends from the slot  65 . Retaining lips  67  are provided to retain the seal  64  in the slot  65 . A first and second leg  68  and  70  extend into the slot  65  and away from the protruding portion  66 . First and second flanges  72  and  74  are provided on the opposite ends of the first and second legs  68  and  70 , respectively, from the protruding portion  66 . As shown in  FIG. 7 , the protruding portion  66  extends from the slot  65  toward the blank  18  prior to contacting the blank  18 . 
         [0036]    Referring to  FIG. 8 , the integral open cross-section seal  64  is shown after engaging the blank  18  to form a seal between the protruding portion  66  and the blank  18 . The open seal  64  is also sealed within slot  65  by the contact of the first and second leg  68  and  70  with the sides of the slot  65 . The blank  18  is permitted to be drawn towards the die cavity  20  across the protruding portion  66  that is pushed into the slot  65  by the blank  18 . 
         [0037]    While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.