Abstract:
A method of flange trimming a sheet metal panel to form a part including flanges for subsequent hemming or weld operation is disclosed. The method utilizes an electro-hydraulic forming (EHF) tool to form a channel within which a flange is cut out in a trimming operation. A combined flange/trim die may be provided in which both a channel forming operation and a flange trimming operation may be performed. A manufacturing system for fabricating a part by forming a channel in a peripheral portion and cutting the channel area to form a flange. The method also relates to a die for an EHF tool that defines a channel-shaped recess and has a trim edge for cutting a flange into the channel.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to sheet metal manufacturing processes that include trimming and flanging sheet metal parts. 
         [0003]    2. Background Art 
         [0004]    Sheet metal manufacturing processes are used to manufacture interior panels, exterior panels and other structural parts of manufactured products. Sheet metal manufacturing processes originally focused on manufacturing parts from mild steel. Mild steel is a preferred material for sheet metal manufacturing processes because of its favorable material properties that allow parts to be drawn, formed, flanged, trimmed and welded relatively easily. 
         [0005]    In an effort to increase strength and reduce the weight of some sheet metal parts, such as those used in the manufacture of vehicles, considerable effort has been devoted to using light-weight, high performance materials. Examples of such light-weight materials include Bakehardenable Steels, Dual Phase Steels, Boron Steels and high strength aluminum alloys. Unfavorable material properties of these high strength, light-weight materials pose a wide variety of technological problems for conventional sheet metal forming processes. 
         [0006]    One problem area encountered when using high strength, light-weight materials in sheet metal forming processes relates to the trimming operation. Trimming, as used herein, refers to shearing off extra material from a drawn panel. In many instances, especially when the geometry of a part being trimmed is rather complicated, it may be necessary to perform two trimming operations. Conventional trimming dies usually incorporate an upper trim steel and a lower trim steel that shear extra material from the drawn panel while the panel is retained on the lower die by a clamping pad that holds the panel against the lower trim steel cutting member. 
         [0007]    Advanced high strength steels require applying substantially greater forces to the trimming dies. In conventional trimming dies, clearance between the upper trim steel and lower trim steel should be less than 10% of the material thickness. However, with advanced high strength steel and aluminum, visible burrs may be formed which typically indicates that the die has excessive clearance. Burrs may form even if the die is manufactured to the normal clearance of less than 10% of the blank thickness if the die has insufficient stiffness against expanding the clearance between shearing edges driven by trimming forces. Trimming advanced high strength steels and aluminum may also result in increased die wear and, more specifically, increased wear of the trimming edges of the upper and lower trim steels. Wear may also add to increased clearance, decreased sharpness and other problems relating to the trim operation. 
         [0008]    Another problem relating to sheet metal forming operations on less ductile advanced high strength steel and aluminum alloys relates to the reduced formability as it impacts flanging operations. Splits emanating from a trimmed surface may be created during a stretch flanging operation. Stretch flanging operations can also be adversely impacted by reduced sharpness of trim die tool steel. To address this issue, it has been proposed to combine trimming operations and one flanging operation in one electro-hydraulic forming (EHF) tool. However, this approach does not eliminate the issue of stretch flange splitting especially after the trim steels become worn, splits may subsequently occur in the flanging operation. Another problem encountered when the panels are trimmed and then flanged may include generation of wrinkles in transition zones and waviness of the flange. Transition zones may be created when sequential discharges of the EHF tool are required to trim and flange the part. 
         [0009]    The trim die may require a cam-driven trimming tool if a large cutting angle is required. Cam-driven trimming tools make the trim die more expensive and require additional maintenance. Trim dies must be maintained by resharpening the trim steel edges or by compensating for wear by shimming the trim steels. The trim die may require adjustment to prevent or eliminate splits created in stretch flanging operations. Trimmed parts may require additional metal finishing if the material forms slivers or localized splits created along a trimmed edge during subsequent stretch flanging operations. 
         [0010]    These and other problems are addressed by Applicant&#39;s development of an improved sheet metal manufacturing process. 
       SUMMARY 
       [0011]    According to one aspect of the present development, sheet metal parts are formed initially in a drawing operation. After the part is drawn to the desired shape, a channel is then formed around the periphery of the drawn part. Following the formation of the channel, the partially formed part is placed in an EHF tool for a trimming operation to trim flanges of the parts in the channel. Parts of the panel outboard of the flanges are trimmed from the panel. 
         [0012]    The channel forming operation may be performed subsequent to drawing. The drawing operation may be a conventional drawing operation or may be an EHF operation. Similarly, the channel forming operation may be performed in a conventional forming die or may be performed in an EHF operation. 
         [0013]    The electro-hydraulic trimming operation is performed in a one-sided die that has a single set of sharp trim steels in areas where the trimming operation is to be performed. Generally, the trimming operation is performed around the entire periphery of the panel. The trimming operation may be performed in a single step or may be performed by a series of sequential discharges of the EHF trimming machine, especially if the size of the area to be trimmed is substantial. 
         [0014]    According to another aspect of the development, a method is provided for making a sheet metal part from a blank of sheet metal. The method includes the steps of drawing the blank of sheet metal to form a partially formed sheet metal panel including a part-shaped portion within a peripheral edge portion that is provided around at least part of the part-shaped portion. A flange is formed in a first part of the peripheral edge portion. The partially formed sheet metal part is then placed into a one-sided trim die of an EHF trimming machine. The trim die has at least one trim steel that provides the cutting edge for the trimming operation. An EHF trimming machine is discharged to trim a second portion of the peripheral edge portion from the first part after the flange is formed by shearing the partially formed sheet metal part with the trim steel. 
         [0015]    According to another aspect of the present invention, a manufacturing system is provided for fabricating a part from a sheet metal blank. The manufacturing system comprises a part forming tool for forming the blank into a part-shaped portion and a peripheral portion. A flange forming tool forms the peripheral portion into a flange area and an offal area. An EHF trim tool including a one-sided die, a vessel that contains a fluid, and at least two electrodes disposed in the fluid that are electrically connected to a capacitor circuit. The capacitor circuit provides a high voltage pulse of electrical energy to the electrodes that creates a shockwave in the fluid. The shockwave drives the peripheral portion of the blank into engagement with the one-sided die to trim the offal area from the flange area. 
         [0016]    According to another aspect of this development, a one-sided die for an electro-hydraulic forming tool is provided in which a channel is first formed and then trimmed to create a flange on a sheet metal part. The die defines a channel-shaped recess in which a channel is formed about a shaped part in a sheet metal blank. A trim edge is provided in the channel-shaped recess and an insert is assembled to the die adjacent to the trim edge to partially define the channel-shaped recess. The insert is moved to a recessed position in the die to expose the trim edge for cutting a flange from the channel. The insert may be formed of an elastomeric material or may be a movable steel insert. 
         [0017]    These and other aspects of Applicant&#39;s development will be better understood in view of the attached drawings and the following detailed description of the illustrated embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    Embodiments of the present invention described herein are recited with particularity in the appended claims. However, other features will become more apparent, and the embodiments may be best understood by referring to the following detailed description in conjunction with the accompanying drawings, in which: 
           [0019]      FIG. 1  is a fragmentary perspective view of a sheet metal panel that has a part portion that is drawn to a part shape and a peripheral area outboard of the part portion; 
           [0020]      FIG. 2  is a perspective cross-sectional view of an EHF tool set-up to form a channel in a sheet metal panel; 
           [0021]      FIG. 3  is a perspective cross-sectional view of an EHF forming tool after a discharge forms the channel in the sheet metal panel; 
           [0022]      FIG. 4  is a fragmentary diagrammatic view of an EHF trim tool set-up to trim a weld flange in the channel; 
           [0023]      FIG. 5  is a fragmentary diagrammatic view of an EHF trim tool after a discharge trims the weld flange in the channel formed in  FIG. 4 ; 
           [0024]      FIG. 6  is a fragmentary diagrammatic view of an EHF flange/trim tool forming a channel in a sheet metal panel; 
           [0025]      FIG. 7  is a fragmentary diagrammatic view of an EHF flange/trim tool trimming a weld flange in the channel formed in  FIG. 6 ; 
           [0026]      FIG. 8  is a fragmentary diagrammatic view of a flange/trim tool forming a channel in a sheet metal panel; 
           [0027]      FIG. 9  is a fragmentary diagrammatic view of an EHF flange/trim tool trimming a hem flange in the channel formed in  FIG. 8 ; 
           [0028]      FIG. 10  is a fragmentary diagrammatic view of an EHF flange/trim tool forming a channel in a sheet metal panel; and 
           [0029]      FIG. 11  is a fragmentary diagrammatic view of an EHF flange/trim tool trimming a channel in the channel formed in  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary 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. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0031]    Referring to  FIG. 1 , a sheet metal panel  10  is shown to include a part-shaped portion  12  that is surrounded by a peripheral edge portion  16 . The sheet metal panel  10  may be formed of mild steel, high strength steel or aluminum alloy. A blank of the sheet metal is initially formed in a drawing operation to the shape illustrated in  FIG. 1 . The panel may be drawn in a conventional draw press or may be formed by an electro-hydraulic forming process. A draw bead  18  is shown in  FIG. 1  in the peripheral edge portion  16 . The draw bead  18  serves to hold the blank in the peripheral edge portion  16  while the part-shaped portion  12  is drawn into the sheet metal panel  10 . 
         [0032]    Referring to  FIG. 2 , a one-sided electro-hydraulic forming (EHF) die  20  that is used with an EHF tool is generally indicated by reference numeral  22 . Only part of the EHF tool  22  is shown. An EHF charge source  24  is a capacitive charge storing device that is discharged to provide the electro-hydraulic discharge that may be used to form or trim the sheet metal panel  10 . Other components of the EHF tool  22  include a vessel  26  in which a first electrode  28  and a second electrode  30  are disposed in a spaced relationship. A volume of fluid  32  is provided within the vessel  26  and separates the first and second electrodes  28 ,  30 . When the EHF charge source  24  is discharged, the first and second electrodes  28  and  30  arc across the gap between their end through the fluid  32  which creates a powerful shockwave in the fluid  32  that is sufficient to form or cut the sheet metal panel  10 . 
         [0033]    The one-sided die  20  defines a channel shaped recess  36  that is placed over the vessel  26 . The channel-shaped recess  36  is located on the opposite side of the peripheral edge portion  16  of the sheet metal panel  10  from first and second electrodes  28  and  30  in the vessel  26 . 
         [0034]    Referring to  FIG. 3 , the sheet metal panel  10  is shown in the one-sided EHF die  20  after discharge of the EHF tool  22 . The peripheral edge portion  16  is driven into the channel shaped recess  36  in the one-sided EHF die  20 . A channel  38  is formed within the channel shaped recess  36  upon discharge of the EHF charge source  24  (shown in  FIG. 2 ). The EHF charge source  24  is only shown in  FIG. 2 , but it should be understood to be connected to the electrode shown in  FIG. 3  and in the other views of the alternative embodiments disclosed below. 
         [0035]    Referring to  FIG. 4 , a one-sided EHF trim die  40  is illustrated that includes a cutting edge  42 . The cutting edge  42  is preferably formed by a tool steel insert that is secured to the EHF trim die  40  to improve durability. However, the cutting edge  42  could also be provided as an integral sharp edge defined by the trim die  40  as illustrated. A recess  44  is provided adjacent to the cutting edge  42  to provide relief for the trimming operation. The sheet metal panel  10  is partially shown with the previously formed channel  38  shown as received in the trim die  40 . The channel  38  includes two side walls  48  that are interconnected by a base wall  50 . As shown in  FIG. 4 , the channel  38  is in place in the die  40  and the first and second electrodes  28  and  30  are disposed in the fluid  32  in the vessel (as shown in  FIGS. 2 and 3 ). 
         [0036]    Referring to  FIG. 5 , the trim die  40  is shown after the EHF tool  22  is discharged between the first and second electrodes  28  and  30  in the fluid  32 . The fluid  32  exerts force on the panel  10  to cut the base wall  50  to form a weld flange  52  by driving part of the base wall  50  into the recess  44 . 
         [0037]    Referring to  FIG. 6 , an alternative embodiment is shown wherein a one-sided flange/trim die  54  is shown to include a movable insert  56 . The sheet metal panel  10  is disposed in the one-sided flange/trim die  54  with the channel  38  including the side walls  48  and the base wall  50  driven into contact with the one-sided die  54  to form the channel  38 . The electrodes  28  and  30  are shown after discharge in which the channel  38  is formed into the channel-shaped recess  36 . The insert  56  is shown flush with the channel-shaped recess  36 , and the channel  38  is formed against the channel-shaped recess  36  and the insert  56 . 
         [0038]    Referring to  FIG. 7 , a trimming operation is illustrated in conjunction with the one-sided flange/trim die  54 . After the channel  38  has been formed, as shown in  FIG. 6 , the EHF tool  22  is subsequently discharged to perform the trimming operation. The insert  56  is retracted to provide a recess  58  between the base wall  50  of the channel  38  and the insert  56 . The EHF tool  22  is discharged through the electrodes  28  and  30  creating a shockwave within the fluid  32  that drives a portion of the base wall  50  into the recess  58 . A weld flange  52  is formed when the base wall  50  is trimmed against the cutting edge  42 . 
         [0039]    Referring to  FIG. 8 , an alternative embodiment of a one-sided flange/trim die  60  is shown that sequentially discharges the EHF tool  22 . The EHF tool  22  includes a first stage electrode  62 , a second stage electrode  64  and a ground  66 . The EHF tool is connected to the first stage electrode  62 , second stage electrode  64  and ground  66  so that an EHF discharge may occur between the first stage electrode  62  and the ground  66  to partially form the channel  38  in the flange/trim die  60 . 
         [0040]    Referring to  FIG. 9 , the successive discharge between the second stage electrode  64  and ground  66  is used to perform a trimming operation. A cutting edge  68  is provided adjacent to a recess  70 , as shown in  FIGS. 8 and 9 . The discharge between the second stage electrode  64  and the ground  66  drives a portion of the side wall  48  into the recess  70 . A hem flange  72  is formed by the remainder of the side wall  48  when the EHF tool  22  is discharged between the second stage electrode  64  and the ground  66 . 
         [0041]    Referring to  FIG. 10 , an alternative embodiment comprising a one-sided flange/trim die  78  is shown with the channel  38  being formed into the flange/trim die  78 . An elastomeric insert  80  is received within the flange/trim die  78 , and pressure is applied by a pressure foot  82  that compresses the elastomeric insert  80  to form a portion of the flange/trim die  78  against which the sheet metal panel  10  is formed. The EHF tool provides a stored charge from the EHF charge source  24  (not shown in  FIG. 10 ) that is similar to the arrangement of  FIGS. 2-7  above. The discharge travels through the fluid  32  to form the channel  38  including the side wall  38  and base wall  50 . 
         [0042]    Referring to  FIG. 11 , the trimming operation is illustrated that is performed after the channel forming operation shown in  FIG. 10 . The trimming operation may be performed by withdrawing the pressure foot  82  and relieving pressure on the elastomeric insert  80  to create a recess  84  that is located adjacent to the cutting edge  86 . As shown in  FIG. 11 , the EHF tool  22  again discharges through the first and second electrodes  28  and  30  to drive the side wall  48  against the cutting edge  86  with part of the side wall being driven into the recess  84 . The other part of the side wall forms a hem flange  72  on the sheet metal panel  10 . 
         [0043]    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.