Abstract:
A tool for modifying a workpiece by either trimming or joining the workpiece. The tool is an electro-hydraulic tool that uses a pulse transmitted through a liquid to trim a workpiece or to join two thicknesses of metal together. A method of trimming the workpiece includes the steps of providing a high voltage discharge in a liquid that drives a workpiece into engagement with a cutting edge of a tool steel insert. A method of joining two or more thicknesses of metal together includes the step of creating a high voltage discharge through an electrode that accelerates one panel or thickness of metal into a second panel that is held stationary by a backing plate while the first thickness of metal is accelerated into the second thickness of metal.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    The invention was made with Government support under Contract No. DE-FG36-08GO18128. The Government has certain rights to the invention. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates to electro-hydraulic tools for trimming or joining sheet metal panels. 
       BACKGROUND 
       [0003]    Manufacturing parts from sheet metal normally requires trimming and welding sheet metal panels. In conventional manufacturing processes, mild steel is used because of its ductility and because it is easy to trim and weld. Many new materials have been proposed for manufacturing sheet metal parts, such as deep drawing quality steels, drawing quality steels, bake hardenable steels, dual phase steels, boron sheets, and aluminum alloys. Lightweight material and high strength materials are now being proposed instead of mild steel in the manufacture of vehicles to increase fuel economy. Working with these types of lightweight materials using conventional sheet metal forming tools and welding processes causes substantial problems in manufacturing processes. 
         [0004]    In trimming operations, harder materials require more force to trim scrap from the metal panels. In addition, greater clearance may result when trimming higher strength metal panels because of greater forces being applied to the tool. With conventional mild steel, clearance of less than 10% of the material thickness is generally recommended. Additional clearance may result in the formation of burrs, splits and slivers along the trimmed edge of the metal panel. In addition, increased clearance also may result in increased wear of the tool steel edges. Wear of the tool steel edges can be addressed by resharpening the trimmed steel edges or by shimming the trimmed steel insert that increases manufacturing costs. 
         [0005]    Another solution proposed is to include elastic scrap support adjacent to trimmed steels to reduce bending and formation of burrs as proposed by Applicant in U.S. Pat. No. 7,197,970. The use of the elastic scrap supports according to Applicant&#39;s prior patent is well suited to perpendicular trimming operations. However, if large angle cuts are required to be made by cam operated trim steel tools that may require cutting angles of up to 60°, the effectiveness of the elastic scrap supports is reduced. 
         [0006]    In Applicant&#39;s prior U.S. Pat. No. 7,810,366, electro-hydraulic trimming, flanging and hemming a blank is proposed, but large volumes of liquid must be provided to the electro-hydraulic tool. The use of large volumes of liquid reduces machine cycle time because of the need to drain and fill the electro-hydraulic chamber. In addition, increased voltage is required to provide sufficient force for trimming, flanging and hemming panels with greater liquid volumes in larger electro-hydraulic chambers. Also, increasing the spacing between the multiple electrodes that are discharged and the location of the area of the panel that is acted upon reduces the pressure available from the electro-hydraulic pulse. 
         [0007]    In welding operations, welding aluminum or mixed metals may require applying an adhesive in the joined area to obtain the required bond strength. The addition of an adhesive adds weight and cost to the finished panel and also complicates the manufacturing process. Spot welding operations and other thermal welding techniques rely upon localized melting of the material of the sheet metal panels. Localized melting reduces the strength and may lower the performance of the finished parts. Electromagnetic welding has been proposed to bond aluminum and other mixed metal assemblies. However, electromagnetic welding relies upon coils that have a short life and are costly to replace. In addition, electromagnetic welding is not particularly effective when applied to materials having poor electrical conductivity. 
         [0008]    The above manufacturing challenges and problems relating to trimming and joining lightweight sheet metal panels are addressed by Applicant as summarized below. 
       SUMMARY 
       [0009]    This disclosure proposes replacing trimmed steel edges and inserts on sheet metal dies with small volume electro-hydraulic chambers that extend about the periphery of the die. The electro-hydraulic chambers are provided with a wire that is disposed in a liquid and is connected to a source of stored charge. Small volume electro-hydraulic chambers extend about the periphery of the die. A pressure pulse is generated in the liquid when the stored charge is discharged through the wire. The high voltage discharge disintegrates the wire. The pressure pulse drives the panel against trimmed steel edges of tool steel inserts disposed on the opposite side of the panel from the electro-hydraulic chamber. 
         [0010]    Utilizing similar small volume electro-hydraulic chambers, it has been found that the high pressure pulse transmitted through the liquid may drive one panel into another panel at a high velocity. A fixed electrode may be connected to a source of stored charge in a small liquid filled chamber to make a spot joint. Alternatively, the electro-hydraulic chamber may be provided with a wire that is connected to a stored charge source that is discharged through the wire to create the pressure pulse in the electro-hydraulic chamber. The electro-hydraulic chamber may be an elongated channel that is disposed adjacent to the surface of one of the panels that is to be joined to another panel or to a hemmed edge. 
         [0011]    Applicant&#39;s disclosure as summarized above will be better understood in view of the attached drawings and the following detailed description of the illustrated embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a diagrammatic plan view of a partially formed sheet metal part; 
           [0013]      FIG. 2  is a diagrammatic cross-sectional view of an electro-hydraulic forming tool at a location on the sheet metal part at line  2 - 2  in  FIG. 1 ; 
           [0014]      FIG. 3  is a diagrammatic cross-sectional view of an electro-hydraulic forming tool taken along the line  3 - 3  in  FIG. 2 ; 
           [0015]      FIG. 4  is a diagrammatic cross-sectional view showing an electro-hydraulic forming tool after an electro-hydraulic trimming operation is performed; 
           [0016]      FIG. 5  is a diagrammatic cross-sectional view of an alternative embodiment of an electro-hydraulic forming tool showing a blank disposed in the electro-hydraulic trimming tool prior to the trimming operation; 
           [0017]      FIG. 6  is a diagrammatic cross-sectional view of the electro-hydraulic trimming tool shown in  FIG. 5  after the trimming operation is performed; 
           [0018]      FIG. 7  is a diagrammatic cross-sectional view of a spot joining tool before joining; 
           [0019]      FIG. 8  is a diagrammatic cross-sectional view of the spot joining tool shown in  FIG. 7  after joining; 
           [0020]      FIG. 9  is a diagrammatic cross-sectional view of an elongated joining tool before joining; 
           [0021]      FIG. 10  is a diagrammatic cross-sectional view of the elongated joining tool shown in  FIG. 9  after joining; 
           [0022]      FIG. 11  is a diagrammatic view of an elongated joined area and clinch tool before joining; and 
           [0023]      FIG. 12  is a diagrammatic view of the elongated joined area and clinch tool shown in  FIG. 11  after joining. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    A detailed description of the illustrated embodiments of the present invention are provided below. The disclosed embodiments are examples of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale. Some features may be exaggerated or minimized to show details of particular components. The specific structural and functional details disclosed in this application are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art how to practice the invention. 
         [0025]    Referring to  FIG. 1 , a drawn blank  20  comprising a sheet metal blank that has been drawn to the form of a vehicle quarter panel is illustrated in its “as drawn” condition. The blank  20  has not been trimmed. The location of a trimmed edge  22  is illustrated as a dashed line. Portions of the blank  20  outboard of the trimmed edge  22  are trimmed from the blank  20  to create a trimmed panel  24 . The portion of the blank  20  outboard of the trimmed edge  22  is the scrap portion  28  that may also be referred to as offal. The draw bead  30  is shown in the scrap portion  28 . The draw bead  30  is removed with the scrap portion  28 . 
         [0026]    Referring to  FIG. 2 , a portion of a trimming tool  32  is diagrammatically illustrated. The trimming tool  32  includes a lower tool  36 , as shown in  FIG. 2 . It should be understood that references to the lower tool  36  are equally applicable to an upper die in the event that the tool is inverted. The terms “lower” and “upper” when used to describe the die parts should not be interpreted to limit the disclosed concept to the illustrated embodiment or any specific spatial orientation. A liquid chamber  38  is provided in the lower tool  36  that is filled with a liquid  40 . The liquid may be water with additives, such as a rust preventative. A wire electrode  42  is shown disposed in the liquid  40  in a spaced relationship relative to the size of the liquid chamber and is preferably centrally located within the liquid chamber  38 . The fluid chamber  38  may have a concave wall  39  that focuses the pulse created when a high voltage discharge is applied to the wire  42 . The blank  20  is shown disposed on the lower tool  36  with a first side  48  of the blank  20  enclosing the liquid  40  within the chamber  38 . An upper die  50 , which again could be a lower tool if the die is inverted and should not be construed as limiting the concept, is illustrated engaging a second side  52  of the blank  20 . A tool steel insert  54  that has a cutting edge  55  is provided in the upper die  50  that also engages the second side  52  of the blank  20 . In the trimming tool embodiment, the tool steel insert  54  may also be referred to as an anvil area in that the blank  20  is driven against the tool steel insert  54 . A trim clearance area  56  is provided on the opposite side of the blank  20  from the liquid chamber  38  and is adjacent to the tool steel insert  54 . A radiused edge  58  is provided on the upper die  50  on the opposite side of the trim clearance area  56  from the tool steel insert  54 . The radiused edge  58  is provided to avoid cutting or splitting the blank  20  in the area of the radiused edge  58 . 
         [0027]    Referring to  FIGS. 2 and 3 , the blank  20  is shown with the tool steel insert  54  engaging the second side  52  of the blank  20 . The wire electrode  42  is supported by several spacers  60 , so that it does not engage the lower tool  36  in the liquid chamber  38 . The spacers may hold the wire electrode  42  at or near the focal point of the concave surface  39 . The wire electrode  42  is connected to a stored charge source  62  that may be a bank of capacitors that are charged to provide a high voltage discharge through the wire electrode  42 , as will be more fully described with reference to  FIG. 4  below. The wire electrode  42  is disposed in the liquid  40  that separates the wire electrode  42  from the blank  20  and the lower tool  36 . As shown in  FIGS. 2 and 3 , the blank  20  is in position to be trimmed by the tool steel insert  54  when the wire electrode  42  receives the high voltage discharge from the stored charge source  62 . 
         [0028]    Referring to  FIG. 4 , the blank  20  is shown after the wire electrode  42  (shown in  FIGS. 2 and 3 ) has received the high voltage discharge from the stored charge source  62  and has disintegrated during the electrical dischargeresulting in a pulse being generated through the liquid  40  against the first side  48  of the blank  20 . The pulse is also reflected off of the concave surface  39 . The blank  20  is driven by the pulse against the tool steel insert  54  to form the trimmed edge  22  on the trimmed panel  24 . The portion of the blank  20  outboard of the trimmed edge  22  is driven against the tool steel insert  54  into the trim clearance area  56 . Part of the blank is driven against the radiused edge  58 , but is not severed from the blank  20  and becomes the scrap portion  28 . Additional scrap cutters may be provided that extend transverse and outwardly from the tool steel insert  54  to cut the scrap portion, or offal, into segments. 
         [0029]    In  FIG. 4 , the liquid  40  remains substantially within the chamber  38  formed in the lower tool  36 . The upper die  50  engages the blank  20  and holds both the trimmed panel  24  and the scrap portion  28  in place during the high voltage discharge through the wire electrode  42 . 
         [0030]    Referring to  FIGS. 5 and 6 , an alternative embodiment of the trimming tool  32  is shown. In the alternative embodiment, the blank  20  is disposed on the lower tool  36  and covers the liquid  40  that is contained within the liquid chamber  38 . A wire electrode  42  is shown in  FIG. 5  that is supported by spacers similar to the spacers  60 , shown in  FIG. 3 . The upper die  50  supports a tool steel insert  54  and also defines a radiused edge  58 , as previously described with reference to  FIGS. 2-4 . In the embodiments of  FIGS. 5 and 6 , a scrap support block  64  is provided between the tool steel insert  54  and the radiused edge  58  of the upper die  50 . The scrap support block  64  may be made of a resilient polymer material such as polyurethane. The scrap support block  64  supports the scrap portion  28  during the trimming process. 
         [0031]    Referring to  FIG. 6 , the trimming tool  32  is shown after the wire electrode  42  receives the high voltage discharge from the stored charge source  62  (shown in  FIG. 3 ). The liquid  40  remains in the chamber  38  formed in the lower tool  36 . In  FIG. 6 , the trimmed edge  22  is formed by trimming the scrap portion  28  as a result of discharging the stored charge source through the wire electrode (shown in  FIG. 5 ) that is disintegrated in  FIG. 6 . The pulse transmitted through the liquid  40  causes the scrap portion  28  to be cut against the tool steel insert  54 . The scrap portion  28  compresses the scrap support block  64  which functions to control the movement of the scrap portion  28 . 
         [0032]    Referring to  FIG. 7 , a spot joining tool  70  is shown with a first sheet of metal  72 . The first sheet  72 , or thickness, of metal may be referred to as the accelerated sheet in the process description. A second sheet of metal  74  is also illustrated. The second sheet, or thickness, of metal  74  may also be referred to as the fixed blank or fixed tube wall in the process description. The first and second sheets may be two separate sheets or a single sheet with a reversely bent edge. Spacer block  76  is shown spacing the first sheet  72  from the second sheet  74 . A pulse tool member  78  is diagrammatically shown and may be part of a larger tool. The pulse tool member  78  defines a chamber  80  that is filled with a liquid  82 , such as water or water with rust preventative additives. An electrode  84  is disposed in the chamber  80  and immersed in the liquid  82 . The electrode  84  is electrically isolated from the pulse tool member  78  by an insulator sleeve  86 . A backing plate  88  is assembled to the second sheet  74  to hold the second sheet  74  in place during a joining operation. In the joining tool embodiment, the backing plate  88  may be referred to as an anvil area because the first sheet of metal  72  is driven against the second sheet  74  that is supported thereon. 
         [0033]    Referring to  FIG. 8 , a joint  90  is formed when a stored charge source  62 , similar to the stored charge source  62  shown in  FIG. 2 , is electrically connected to the electrode  84 . When the stored charge source  62  is discharged, a pulse of electrical energy is discharged from the electrode  84  to the pulse tool member  78 , or may alternatively be discharged to a second spaced electrode (not shown). When the high voltage pulse is discharged through the electrode  84 , a pulse is transmitted through the liquid  82  that displaces the first panel  72 , as shown in  FIG. 8 , causing it to be accelerated into the second panel  74 . The second panel  74  is held in place by the backing plate  88 . Acceleration of the first panel  72  into the second panel  74  creates the joint  90 . A joint formed by the pulse tool member  78  shown in  FIGS. 7 and 8  is similar to a spot weld in that it creates a single joined area in a spot location creating a substantially circular joined area the first and second sheets  72  and  74  together. 
         [0034]    Referring to  FIGS. 9 and 10 , a linear joining tool  92  is shown. Due to the similarities between the embodiment of  FIGS. 7-8 , similar reference numerals are used to refer to similar parts. The linear joining tool  92  includes a pulse tool member  78  that defines an elongated channel  96  in which an electrode wire  98  is disposed. The elongated channel  96  contains the liquid  82  that envelopes the electrode wire  98 . The electrode wire  98  is electrically connected to a source of stored charge  62 , as previously described with regard to  FIGS. 7 and 8 . The first sheet  72  includes a preformed local cavity  94 . The first sheet spans the elongated channel  96 , as shown in  FIG. 9 , until the stored charge source  62  is discharged through the electrode wire  98 . 
         [0035]    As shown in  FIG. 10 , after discharge, the electrode wire  98  shown in  FIG. 9  disintegrates as a pulse is transmitted through the liquid  82  to cause a joined area  90  to be formed in an elongated path that corresponds to the shape of the elongated channel  96 . The elongated channel may be straight or curved. The joined area  90  is formed by accelerating the preformed local cavity  94  formed on the first sheet  72  against the second sheet  94  formed that is held in place by the backing plate  88 . Spacer blocks  76  separate the pulse tool member  78  from the first sheet  72 . 
         [0036]    Referring to  FIGS. 11 and 12 , a crimp joining tool is illustrated that is similar in many ways to the embodiments of  FIGS. 7-10 . The same reference numerals will be used to refer to similar parts of the preceding embodiments. The joining crimp tool  100  includes a first sheet  72  that is disposed on the pulse tool member  78  to enclose the elongated channel  96  that is filled with liquid  82 . The electrode wire  98  is electrically connected to the stored charge source  62  in  FIG. 11 . A preformed local cavity  94  is formed in the second sheet  74  in  FIG. 11 . The second sheet  74  and preformed local cavity  94  are backed by the backing plate  88 . 
         [0037]    Referring to  FIG. 12 , the joined area  90  is formed as a result of the discharge of the stored charge source  62  through the electrode wire  98  (shown in  FIG. 11 ). The joined area  90 , as shown in  FIG. 12 , is augmented by the formation of two crimped areas  102  on either side of joined area  90 . The joined area  90  is formed by accelerating the first panel  72  into the second panel  74  that is held in place by the backing plate  88 . 
         [0038]    While exemplary embodiments are described above, it is not intended that these embodiments 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. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.