Abstract:
A method and apparatus for forming flanges on a panel. The flanges may be weld flanges or hem flanges. The flanges stretch to reduce spring back and may be trimmed. The trimming operation is performed after the flange area is formed on the panel.

Description:
BACKGROUND 
     1. Technical Field 
     This disclosure relates to sheet metal forming tools and processes that are used to form and trim a hem flange or weld flange. 
     2. Background Art 
     Vehicle body panels such as deck lids, hoods, doors and the like frequently include a flange that extends about their periphery. Such body panels have traditionally been manufactured from mild steel sheet metal. Mild steel is very ductile and is easily formed in a hem forming operation. Increasingly, automotive manufacturers are turning to aluminum or advanced high strength steel (AHSS) alloys to obtain weight savings for vehicle body panels. Aluminum alloys and AHSS alloys offer high strength/low weight alternatives to mild steel. 
     Aluminum and AHSS alloys do not, however, have the same degree of ductility and resistance to work hardening offered by mild steel. Forming a flange on a sheet metal body panel made of aluminum or AHSS alloys is more difficult than forming the same flange on a mild steel panel due to the reduced ductility of aluminum or AHSS alloys. One proposed solution to this problem is to form a larger radius hem when making body panels of aluminum sheet metal. Larger radius hems result in lower fit and finish ratings because larger radius hems may cause gaps to appear larger between door closure panels and their openings. 
     The low ductility of aluminum may cause tears or splits starting from the outer surface of a hem. Tears and splits result in high part rejection rates and unacceptable scrap rates. 
     Substantial work hardening may occur during the hem flange formation process. The hem flange formation process is the initial step in forming a hem wherein a peripheral portion of a blank or drawn part is bent to about 90 degrees. Forming a 90 degree bend in an aluminum sheet around a relatively tight radius causes substantial amounts of deformation. Stretching the trimmed surface may lead to edge cracking. This amount of strain may result in splits and even tears as the hem flange is further formed in pre-hem and final hem forming steps. 
     Flanging and hemming of aluminum panels often requires larger radii due to insufficient formability of aluminum alloys (6111-T4; 6022-T4; 6016-T4), advanced high strength steel (AHSS) (DP500 steel) and similar materials for outer skin panels. One of the major problems for implementation of AHSS and aluminum alloys for outer skin panels is splitting of the sheet material from the trimmed surface in stretch flanging and stretch hemming areas. Attempts to reduce the radius of a hem or flange have resulted in splits along the flanging line. Applicants have proposed a two-step flanging operation in which a large radius bend is first made and then a smaller radius bend is made on the larger radius bend. A cam former that requires a complex tooling arrangement may be used to form a smaller radius bend after a larger radius bend is made in a normal flange forming die. 
     A simpler tooling configuration would be preferable that could obtain sharp flanging in a single step. A tooling solution would be preferred that would facilitate combining and simplifying the steps of drawing, trimming and flanging. There is a need for a flange forming and trimming tool that can form a sharper peripheral radii on a flange in one step without employing an expensive cam mechanism and without requiring an extra stamping operation. 
     Flange splitting from the sheared surface is a barrier to implementation of higher strength lower guage AHSS steels, such as DP500, for outer skin panels in auto industry. It is also a reason for the limited implementation of aluminum on vehicles. The use of aluminum in vehicle body parts has frequently been limited to hoods, with substantial difficulties being encountered when it is attempted to use aluminum for fenders and decklids. 
     In conventional sheet metal forming operations a flange is first trimmed and then flanged. Tooling dies may become contaminated with slivers that are formed when a flange splits. Slivers can be spread to the subsequent operations from the trimming operation because it is usually not a final part forming operation. Elimination of slivers is important for outer skin panels that must have a high quality class A surface. 
     Another problem is that aluminum or AHSS alloy panels tend to spring-back elastically after cold forming. Spring-back can be accommodated and remedied by re-striking the panel to eliminate stresses in the metal that cause spring-back. 
     These and other problems are addressed by Applicant&#39;s disclosure as summarized below. 
     SUMMARY 
     A method of forming a flange on a sheet metal panel to reduce spring back in a drawn panel is disclosed. A part is drawn in a die that includes a part forming area and a draw panel clamping flange. A flange is formed in a flange forming area that is outboard of the part. The flange forming area includes an inner clamping ring and an outer clamping ring on opposite inner and outer sides of a flange forming member. The drawn part is stretched by clamping the inner clamping ring and the outer clamping ring against the flange while the flange forming member stretches the flange. 
     According to another aspect of the disclosure, method of forming a sharp flange on a sheet metal panel is disclosed. A part is drawn in a die. A clamping flange includes a flange forming area that is outboard of the part. A flange forming member is disposed in the flange forming area. An inner clamping ring is provided on an inner side of the flange forming member, and an outer clamping ring on an outer side of the flange forming member. A flange is formed on the panel with the flange forming member in a die cavity that is larger than the flange forming member. The die cavity defines a gap between the panel and the die cavity. A liquid is pumped under pressure through a channel in the flange forming member to expand the flange to fill the gap defined between the panel and the die cavity. 
     According to another aspect of the disclosure, a tool for flanging and trimming a sheet metal blank is disclosed. An upper draw die has a punch for forming a part. An inner clamping ring, an outer clamping ring, and a flange forming tool that is disposed between the inner and outer clamping rings is provided in the draw operation or in a subsequent operation. A first shearing edge is provided on the flange forming die. A lower die defines a part drawing cavity, a flange forming recess and a second shearing edge. The first and second shearing edges engage opposite sides of the blank to trim the flange. 
     According to another aspect of the disclosure, a method is disclosed for forming a tight radius flange on a sheet metal panel with a reciprocating ram that has an elastomeric former. A clamped portion of a part is clamped in a die between an upper member and a lower member with freestanding lip portion extending from between the upper and lower members. The lip portion is engaged and formed in a first direction that is parallel to the direction that the ram reciprocates to engage the lip portion to form the lip into a flange that extends in the first direction. The elastomeric former is compressed to expand the former in a second direction that is perpendicular to the first direction, wherein expansion of the former causes the flange to be formed in the second direction. 
     These and other aspects of the disclosure will be better understood in view of the attached drawings and the following detailed description of the illustrated embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a fragmentary diagrammatic cross-section view of a flanging tool that clamps a flange forming area of a partially formed panel while a flange former stretches out spring back in a previously drawn panel; 
         FIG. 2  is a diagrammatic cross-sectional view of a flanging tool prior to engaging a blank disposed on a lower die; 
         FIG. 3  is a diagrammatic cross-sectional view of the flanging tool shown in  FIG. 2  in a first stage of forming a flange having a large radius; 
         FIG. 4  is a diagrammatic cross-sectional view of the flanging tool shown in  FIGS. 2 and 3  after a liquid is pumped into a space between the panel and the flange former to hydro-form the flange to form a smaller radius; 
         FIG. 5  is a diagrammatic cross-section view of a hem flange trimming tool for trimming and stretching out spring back prior to engaging the blank with a trimming tool; 
         FIG. 6  is a diagrammatic cross-section view of the hem flange trimming tool of  FIG. 5  engaging the panel in the flange area prior to trimming; 
         FIG. 7  is a diagrammatic cross-section view of the hem flange trimming tool shown in  FIGS. 5 and 6  after completion of the trimming step; 
         FIG. 8  is a diagrammatic cross-section view of a weld flanging and trimming tool showing the tool engaging the weld flange, but before beginning the trimming step; 
         FIG. 9  is a diagrammatic cross-section view of the weld flanging and trimming tool shown in  FIG. 8  after completing the trimming step; 
         FIG. 10  is a diagrammatic cross-section view of a flanging tool that includes an elastomeric former that initially forms a flange to a larger radius and is then compressed to expand the former and form the flange to a smaller radius with the tool being shown in its initial position; 
         FIG. 11  is a diagrammatic cross-section view of the flanging tool of  FIG. 10  shown initially engaging the panel to begin forming the flange; 
         FIG. 12  is a diagrammatic cross-section view of the flanging tool shown in  FIGS. 10 and 11  with the flange formed to a large radius; 
         FIG. 13  is a diagrammatic cross-section view of the tool shown in  FIGS. 10 through 12  just prior to compressing the elastomeric flange former; and 
         FIG. 14  is a diagrammatic cross-section view of the toll shown in  FIGS. 10-13  after compression of the elastomeric former to cause the flange to be formed with a smaller radius. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a flange tool  10  that is used to form a flange  12  on a peripheral portion  14  of a partially formed part  16 . The flange tool  10  includes a lower die set  20  and an upper die set  22  that act on opposite sides of the partially formed part  16 . A lower part forming die  26  and an upper part forming die  28  form the partially formed part  16  to a desired shape and contour. A lower flange forming die  30  defines a flange forming cavity  32 . An actuator  34 , such as a hydraulic cylinder, pneumatic cylinder, or press drive linkage, drives a flange former  36  into engagement with the partially formed part to stretch the previously drawn area to form a flange and stretch out spring back in the flange  12 . An inner clamping ring  38  and an outer clamping ring  40  clamp the peripheral portion  14  of the partially formed part  16 , while the flange former  36  stretches the hem flange area  42 . A flange bend  44  is provided at the transition between the peripheral portion  14  that is clamped between the inner clamping ring  38  and the lower flange forming die  30 . The hem flange area  42  extends generally perpendicular to the peripheral portion  14  and is the type of flange that is later formed in a reversely turned hem to secure an outer panel to an inner panel. A flange bend  44  is provided at the transition between the peripheral portion  14  and the hem flange area  42 . A weld flange area  46  is also shown that is the type of flange that is welded to one or more other parts. Offal  48  is created in the course of the flange forming process that may be trimmed away from the part  16  in the course of the part forming process. A bevelled wall  50  may be provided on the outer portion of the flange forming cavity  32  to facilitate drawing metal from between the outer clamping ring  40  and the lower flange forming die  30  as the flange is stretched into its desired shape. 
     Referring to  FIGS. 2-4 , an alternative embodiment of a flange tool  10  is shown. For brevity, reference numerals are carried over where possible in the embodiment disclosed in relation to  FIG. 1 . The flange tool  10 , shown in  FIGS. 2-4 , includes a lower die set  20  and an upper die set  22 . A lower flange forming die  30  defines a flange forming cavity  32 . The flange former  36  is part of the upper die set  22  and includes an inner seal  52  and an outer seal  54 . A fluid supply port  56  is provided through the flange former  36  through which hydrostatic forming pressure is applied to complete the process of forming the flange. The flange former  36  is reciprocally driven by a press, or other actuator, into engagement with a blank  58  or more specifically is driven into a peripheral portion  14  of the blank  58 . 
     Referring to  FIG. 2 , the lower die set  20  and upper die set  22  are shown with the blank  58  being disposed on top of the lower die set  20 . 
     Referring to  FIG. 3 , the flange former  36  is shown bottomed out in the flange forming cavity  32 . The peripheral portion  14  is shown formed into the flange forming cavity  32 . 
     A sharp radius bend tool edge  60  is provided at the inner edge of the cavity  32 . As shown in  FIG. 3 , a wide radius bend  62  is initially formed in the peripheral portion  14  and a partially formed flange area  64  is formed into the flange forming cavity  32 . A fluid cavity  66  is defined between the partially formed flange area  64 , the flange former  36  and the seal  52 . An expansion cavity  68  is defined between the partially formed flange area  64  and the cavity  32 . 
     Referring to  FIG. 4 , fluid  70  is provided under pressure through the fluid supply port  56  that is used to hydroform the partially formed flange area  64 , shown in  FIG. 3 , into a flange having a sharp radius bend against the sharp radius bend tool edge  60 . 
     In an alternative embodiment, the fluid may be ported through a fluid supply port  56  to other areas of the flange forming cavity  32 . 
     Referring to  FIGS. 5-7 , a tool  72  is shown forming and trimming a hem flange  74  in a panel  76 . The portion of the panel  76  that is cut off from the panel is referred to as offal  78 . The tool  72  includes a lower trim die  80  that has a lower shearing edge  82 . An upper trim die  86  has an upper shearing edge  88 . The upper and lower shearing edges  88  and  82  cooperate to trim the offal  78  from the panel  76  in the area of the hem flange  74 . A spring pad  90  is provided in the lower trim die  80 . The spring pad is preferably an elastomeric spring pad. Alternatively, it could be a mechanical spring pad. The panel  76  is retained on the lower trim die  80  by an inner clamping ring  92  and an outer clamping ring  94 . 
     As shown in  FIG. 5 , the upper trim die  86  is shown disposed above the lower trim die  80  before the trimming operation. The flange may be partially pre-formed, as shown in  FIG. 5 , so that is received within the lower trim die  80 . The flange can also be fully formed and trimmed in one operation starting from the drawn panel. 
     Referring to  FIG. 6 , the upper trim die  86  is shown in full contact with the panel  76 , but before commencement of the trimming operation. In this position, the upper trim die  86  stretches the panel  76  to relieve stresses and reduce the spring back effect in the panel  76 . 
     Referring to  FIG. 7 , the upper trim die  86  is shown at the point where the upper shearing edge  88  is driven into contact with the lower shearing edge  82 . The spring pad  90  is shown compressed as a result of the displacement of the offal  78  portion of the panel  76 . The hem flange  74  is formed to extend perpendicularly downwardly into the lower trim die  80 . 
     Referring to  FIGS. 8 and 9 , an alternative embodiment of a trim tool  100  is illustrated that is used to form a weld flange  102  in a panel  104 . The trim tool trims offal  106  from the panel  104 . The trim tool includes a lower trim die  108  that has a lower shearing edge  110 . The trim tool  100  also includes an upper trim die  114  that defines an upper shearing edge  116 . A spring pad  118  is provided in the lower trim die  108 . A spring pad  120  is provided in the upper trim die  114  and is adjacent to the upper shearing edge  116 . The spring pad  118  is adjacent to the lower shearing edge  110  of the lower trim die  108 . The spring pad  118  and spring pad  120  may be elastomeric pads, as illustrated, or alternatively may be made of another material or with other structure that is compressed with the upper trim die  114  is driven into the lower trim die  108  to trim the panel  104 . An inner clamping ring  122  and an outer clamping ring  124  clamp the panel  104  and the offal  106  against the lower trim die  108 . 
     Referring to  FIG. 8 , the upper trim die  114  is shown in contact with the panel  104  prior to trimming the offal  106  from the panel  104 . The upper trim die  114  continues to move toward the lower trim die  108 , as shown in  FIG. 9 . 
     Referring to  FIG. 9 , the upper trim die  114  is shown with the upper shearing edge  116  in engagement with the lower shearing edge  110  of the lower trim die  108 . The offal  106  is trimmed from the panel  104  and the spring pad  118  and spring pad  120  are shown in a compressed condition. 
     Referring to  FIGS. 10-14 , a flange tool  130  is illustrated that acts upon a panel  132 . A free standing portion  134  of the panel  132  extends from a lower die  136 . The flange tool  130  includes a flange former ram  140  that has a former  142  that may be formed from an elastomeric material or the like. A lower flange former die  144  is attached to the lower die  136  or integrally formed therewith to define a cavity  146 . 
     A radiused corner  148  is formed on the former  142 . A sharp flange bending edge  150  is formed on the lower die  136  at the edge of the cavity  146 . 
     Referring specifically to  FIG. 10 , the flange former ram  140  is shown with the former  142  just prior to engagement with the free standing portion  134  of the panel  132 . 
     Referring to  FIG. 11 , the flange tool  130  is shown with the radiused corner  148  of the former  142  engaging the free standing portion  134  (shown in  FIG. 10 ) to bend it at the sharp flange bending edge  150 . At this point, the former  142  is bending the free standing portion  134  (shown in  FIG. 10 ), but is not forming a sharp flange edge. 
     Referring to  FIG. 12 , the free standing portion  134  (shown in  FIG. 10 ) of the panel  132  is shown bent to a generally perpendicular orientation relative to the other portions of the panel  132 . A clearance gap  152  is defined between the perpendicularly bent free standing portion  134  and the lower die  136 . A large radius bend  156  (shown in  FIG. 13 ) is formed about the sharp flange bending edge  150 , but the flange is not sharply bent at this point. 
     Referring to  FIG. 13 , the flange tool  130  is shown with a bottom surface  158  of the former  142  engaging an end wall  160  of the lower flange forming die  144 . At this point in the process, the former  142  is not yet compressed against the end wall  160 . 
     Referring to  FIG. 14 , the flange tool  130  is shown with the flange former ram  140  compressing the former  142  so that it expands and engages the free standing portion  134  (shown in  FIG. 10 ) that was previously formed to be perpendicular to the panel  132 . Compression of the former  142  causes the free standing portion to be driven into engagement with the flange forming wall  164  thereby causing the free standing portion  134  (shown in  FIG. 10 ) to be stretched and formed about the sharp flange bending edge  150  thereby providing a flange with a smaller radius bend where the large radius bend  156  (shown in  FIG. 13 ) is formed in the intermediate steps of the flanging process.