Abstract:
A tool and method of hemming a panel wherein the tool engages a flange to apply a compressive force with a stop initially preventing a distal end of the flange from moving inwardly. The hemming tool bends the intermediate portion of the flange between the flange bend and the distal end toward the panel. The stop is withdrawn to allow the flange to be progressively formed toward the panel until the distal end is aligned with the intermediate portion.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to flanging and hemming sheet metal panels that have sharp edges. 
       BACKGROUND 
       [0002]    Flanging and hemming processes for sheet metal parts formed of aluminum alloys and AHSS have been under development for more than a decade. One problem is caused by the reduced ability of aluminum alloys and AHSS to bend around sharp radius. 
         [0003]    Several techniques have been proposed to address this problem. For example U.S. Pat. No. 6,257,043 discloses a press hemming process in which the hemming area is compressed while forming the hem. This process was further developed as roll hemming process in U.S. Pat. No. 6,810,707. In the roll hemming process, the local pressure applied to the blank is better controlled than in press hemming process. However, the roll hemming process is substantially slower and is only feasible for low volume or mid-volume applications. Several rolls are required on a hemming tool to provide high volume production. Further development of roll hemming technology is disclosed in U.S. Pat. No. 7,347,072. that proposes making three passes of a hemming roller to form the hem. An alternative technique is disclosed in U.S. Pat. No. 6,928,848 in which the main emphasis is to form a sharp flanging radius during the flanging process by controlling the inner radius of the die instead of the displacement of the punch as proposed in the previously mentioned patents. 
         [0004]    One problem not addressed by the above patents is creep of the outer panel during later hemming steps. The “creep” phenomenon occurs due to continued bending of the flange during hemming process. The flanging radius undergoes changes during hemming process that result is a loss of sharpness in the flange after hemming. The continued deformation of the area of flange during following hemming process is caused by the movement of flanged material from outer side of the flange towards inner area of the hem that changes the overall radius of the hem and also adds strain to the previously formed flange area. 
         [0005]    This disclosure is directed toward solving the above identified problems and other problems that will be apparent to one of ordinary skill in the art as summarized below. 
       SUMMARY 
       [0006]    The disclosed embodiments are directed towards providing a press hemming process and tools that provide sharp hems and also increase productivity compared to the roll hemming processes. 
         [0007]    In one disclosed embodiment, a flange is formed on a panel that extends inwardly from the flange bend on the panel at an angle to a distal end of the flange. The panel is placed in a hemming tool that includes a stop that initially engages the distal end of the flange. The panel may be an outer panel and an inner panel may be placed on the outer panel inboard of the flange. The hemming tool engages the flange to apply a compressive force with the stop initially preventing the distal end of the flange from moving inwardly. The hemming tool bends the intermediate portion of the flange between the flange bend and the distal end toward the panel. The stop is then moved inwardly or otherwise withdrawn to allow the flange to be progressively formed toward the panel until the distal end is aligned with the intermediate portion. 
         [0008]    According to one aspect of the disclosure, a tool is provided for forming a hem on a panel. The tool comprises a first hem die defining a cavity having a perimeter edge. The panel has a flange at an outer edge at a base of the flange. A second hem die engages a distal end of the flange to compress the flange through the length of the flange into the perimeter edge while forming a hem bend on the flange. 
         [0009]    According to additional aspects of the disclosure as it relates to the tool, a stop is provided on the second hem die that initially engages the flange and prevents the flange from moving inwardly while the second hem die moves towards the first hem die. The stop may be a block that moves inwardly as the second hem die moves inwardly. The block may have a face that extends parallel to the direction that the second hem die moves. 
         [0010]    The second hem die may have an inner portion and an outer portion that move independently toward the first hem die, wherein the outer portion initially engages the distal edge of the flange, and wherein the inner portion includes the stop that prevents the flange from moving inwardly as the outer portion bends an intermediate portion of the flange inwardly of the distal edge. The outer portion may clamp the intermediate portion of the flange while the inner portion forms the distal edge inwardly and into alignment with the intermediate portion of the flange. 
         [0011]    The stop may be a block that has an inwardly angled surface and the block may be refracted into the second hem die as the second hem die moves toward the first hem die. The second hem die may have an inner portion and an outer portion with the stop being provided on the outer portion, and wherein the inner portion advances towards the first hem die while the outer portion remains stationary relative to the first hem die. The inner portion may have a plurality of inner portion ribs separated by a plurality of inner portion grooves, and the outer portion may have a plurality of outer portion ribs that are received in the inner portion grooves and a plurality of outer portion grooves that receive the inner portion ribs to guide the movement of the inner portion relative to the outer portion. 
         [0012]    According to another aspect of the disclosure, a method of forming a hem on a sheet metal panel comprises placing the panel in a first part of hemming tool, wherein the panel has a flange that extends inwardly from a body portion of the panel. A second part of the hemming tool advances toward the first part and engaging a distal end of the flange with a stop that prevents the distal end of the flange from moving inwardly and compressing the flange, wherein an intermediate portion of the flange between the body portion and the distal end is formed inwardly. The stop disengages the distal end of the flange after a first portion of the flange is formed to extend parallel to the body. A second portion of the flange that is contiguous with the distal end of the flange is formed to extend parallel to the panel after the first portion of the flange is formed. 
         [0013]    According to other aspects of the method, the intermediate portion of the flange may be formed into a concave cross-section in the outwardly facing direction as the intermediate portion is formed inwardly in the advancing step. The stop may be moved inwardly as the second part of the hemming tool moves inwardly. The second part of the hemming tool may include an inner portion and an outer portion that move independently, wherein the inner portion includes the stop, and wherein during the advancing step the stop prevents the distal edge of the flange from moving inwardly as the outer portion bends an intermediate portion of the flange inwardly of the distal edge. The outer portion may clamp the intermediate portion of the flange while the inner portion forms the distal edge inwardly and into alignment with the intermediate portion of the flange. 
         [0014]    According to other aspects of the method, the stop may be a block that has an inwardly angled surface, wherein the block is retracted into the second part of the hemming tool as the second part of the hemming tool moves toward the first part of the hemming tool. The second part of the hemming tool may have an inner portion and an outer portion with the stop being provided on the outer portion, and wherein the inner portion advances towards the first part of the hemming tool while the outer portion remains stationary relative to the first part of the hemming tool. 
         [0015]    The inner portion may have a plurality of inner portion ribs separated by a plurality of inner portion grooves. The outer portion may have a plurality of outer portion ribs that are received in the inner portion grooves and a plurality of outer portion grooves that receive the inner portion ribs. The method may further comprise guiding the movement of the inner portion relative to the outer portion with the respective ribs and grooves being received in each other. 
         [0016]    Other aspects of the disclosure will be more fully described with reference to the attached drawings and the following detailed description of the disclosed embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a diagrammatic cross-sectional view of a first embodiment of a tool for hemming a flange with compression to form a sharp edge at the beginning of the hemming process; 
           [0018]      FIG. 2  is a diagrammatic cross-sectional view of the embodiment shown in  FIG. 1  in an early intermediate point in the process; 
           [0019]      FIG. 3  is a diagrammatic cross-sectional view of the embodiment of  FIG. 1  at a late intermediate point in the forming process; 
           [0020]      FIG. 4  is a diagrammatic cross-sectional view of the embodiment of  FIG. 1  with the tool in its final position; 
           [0021]      FIG. 5  is a diagrammatic cross-sectional view of a second embodiment of a tool for hemming a flange with compression to form a sharp edge shown in its initial engagement position; 
           [0022]      FIG. 6  is a diagrammatic cross-sectional view of the embodiment shown in  FIG. 5  in an early intermediate stage in the forming process; 
           [0023]      FIG. 7  is a diagrammatic cross-sectional view of the embodiment of  FIG. 5  shown in a late intermediate step in the forming process; 
           [0024]      FIG. 8  is a diagrammatic cross-sectional view of the embodiment shown in  FIG. 5  at the final point in the hem forming process; 
           [0025]      FIG. 9  is a diagrammatic cross-sectional view of a third embodiment of a tool for hemming a flange with compression to form a sharp edge shown in the initial contact position; 
           [0026]      FIG. 10  is a diagrammatic cross-sectional view of the embodiment of  FIG. 9  shown in an early intermediate stage of the process; 
           [0027]      FIG. 11  is a diagrammatic cross-sectional view of the embodiment of the tool shown in  FIG. 9  at a late intermediate point in the process of forming the hem; 
           [0028]      FIG. 12  is a diagrammatic cross-sectional view of the embodiment of  FIG. 9  shown at the final stage in the hem forming process; 
           [0029]      FIG. 13  is a diagrammatic side elevation view of the tool made according to the third embodiment shown in  FIG. 9 ; 
           [0030]      FIG. 14  is a diagrammatic exploded perspective view of the tool shown in  FIG. 9  disposed above a flange of a panel that is in position to be hemmed over an inner panel; 
           [0031]      FIG. 15  is an exploded perspective view of one part of a hem forming tool disposed above a panel ready to be hemmed over an inner panel; and 
           [0032]      FIG. 16  is an exploded perspective view of a second part of the tool shown in  FIG. 15  disposed above a panel ready to be hemmed over an inner panel. 
       
    
    
     DETAILED DESCRIPTION 
       [0033]    A detailed description of the illustrated embodiments of the present invention is 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. 
         [0034]    Referring to  FIGS. 1-4 , a panel  10  is shown with a flange  12  that is to be formed over an inner panel  16  to form a hem. The panel  10  is disposed in a first part of a hemming tool  18  that also may be referred to as a first hem die. The first part of the hemming tool defines a cavity  20  that includes a perimeter edge  22 . The perimeter edge  22  may be on a movable side support structure  24  that may be moved by a cylinder  25 , or the like. 
         [0035]    A base  26  of the flange  12  is formed at an outer edge  28  of the panel  10 . A second part of the hemming tool  30 , which may also be referred to as a second hem tool, is disposed above the first part of the hemming tool  18 . A distal end  32  of the flange  12  is engaged by the second part of the hemming tool  30  that exerts a compressive force through the length of the flange  12 . The distal end  32  engages a face  34  of a stop  36  that is provided on the second part of the hemming tool  30 . A clamping member  46  holds the inner panel  16  against the panel  10  during the hemming process. An intermediate portion  48  of the flange  12  bends to form an outwardly concave surface, as shown in  FIGS. 2 and 3 , as a result of the compressive force exerted by the second part of the hemming tool  30  on the flange  12 . The intermediate portion  48  is formed to fold over and engage an upper surface  50  of the inner panel  16 . The distal end  32  of the flange  12  is prevented from moving inwardly by the stop  36 , as shown in  FIG. 1 . In  FIG. 2 , the intermediate portion  48  has been formed inwardly while the distal end  32  is prevented from moving inwardly by the stop  36 . In  FIG. 3 , the stop, which is maintained in the track (not shown) in the second part of the hemming tool  30 , moves inwardly after the intermediate portion  48  is formed into the convex shape to allow the flange  12  to be formed into a parallel orientation relative to the upper surface  50  of the inner panel  16 . 
         [0036]    The compressive force applied through the flange  12  keeps the outer edge  28  of the panel  10  in firm engagement with the perimeter edge  22  of the cavity  20 . By maintaining the compression in flange  12  as it is hemmed over the inner panel  16 , the outer edge  28  of the panel  10  maintains a sharp edge on the panel  10  and prevents the flange  12  from creeping inwardly as a result of the hemming operation. 
         [0037]    Referring to  FIGS. 5-8 , a panel  60 , including a flange  62 , is shown as the flange  62  is formed over an inner panel  66  to form a hem. The hem is fully formed, as shown in  FIG. 8 . A first hem die  68 , or first part of a hemming tool, defines a cavity  70  that includes a perimeter edge  72 . A base  76  of the flange  62  is formed at an outer edge  78  of the panel  60 . A second hem tool  80 , or second part of a hemming tool, engages the distal end  82  of the flange  62 . As shown in  FIG. 6 , a notch  84  is provided that receives the distal end  82  of the flange  62 , as shown in  FIG. 6 . The notch  84  prevents the distal end  82  of the flange  62  from moving outwardly as the intermediate portion  90  is formed inwardly by the downward movement of the outer portion  88  of the second hem tool  80 . The outer portion  88  bends the flange  62  until it contacts the inner panel  66  at which point the distal end  82  slips from the notch  84 . The process continues with the inner portion  86  of the second hem tool  80  continuing to fold the flange inwardly against the inner panel  66  until the flange is fully seated against the upper surface  98  of the inner panel  66 . Clamping member  96  holds the inner panel  66  against the panel  60  throughout the forming process. As shown in  FIG. 8 , the flange  62  is formed fully into engagement with the upper surface  98  of the inner panel  66 . 
         [0038]    Referring to  FIGS. 9-16 , a panel  110  includes a flange  112  that is intended to be hemmed over an inner panel  116 . The panel  110  and inner panel  116  are loaded into a first hemming die  118 , or first part of a hemming tool, that defines a cavity  120 . The cavity  120  defines a perimeter edge  122 . A base  126  of the flange  112  is provided at an outer edge  128  of the panel  110 . 
         [0039]    A second hem tool  130 , or second part of a hemming tool, engages a distal end  132  of the flange  112 . An inwardly angled surface  134  of a stop  136  engages the distal end  132  of the flange  112 . The stop  136  prevents the distal end  132  of the flange  112  from moving inwardly until initially as the flange  112  is hemmed over the inner panel  116 . The inner panel  116  is held in place relative to the panel  110  by a clamping member  146 . 
         [0040]    An intermediate portion  148  of the flange  112  is first formed into a convex outwardly facing shape, as shown in  FIG. 10 , because the distal end  132  of the flange  112  contacts the inwardly angled surface  134  of the stop  136 . The intermediate portion  148  is formed against the upper surface  150  of the inner panel  116  to complete the hem forming process. During the hem forming process, the second hem tool  130  exerts a compressive force through the flange  112  forcing the base  126  of the flange  112  into engagement with the perimeter edge  122  of the cavity  120 . In this way, a sharp edge is maintained at the outer edge  128  of the panel  110 . 
         [0041]    Referring to  FIGS. 13-16 , the panel  110  is shown with the flange  112  extending upwardly and inwardly toward the inner panel  116 . A distal end  132  of the flange  112  engages inwardly angled surface  134  of the stop  136 . As shown in  FIG. 13 , the distal end is spaced from the inwardly angled surface  134  and is shown prior to the step illustrated by  FIG. 9  wherein the second hem tool  130  has been moved downwardly to engage the distal end  132 . The second hem tool  130  includes an inner portion  152  and an outer portion  154  that are moveable relative to each other to perform the operation described with references to  FIGS. 9-12 . A plurality of ribs  156  are formed on the inner portion  152  of the second hem tool  130 . A plurality of grooves  160  are provided between the ribs  156  on the inner portion  152  of the second hem tool  130 . A plurality of ribs  162  are also formed on the outer portion  154  of the second hem tool  130 . The ribs  162  are spaced apart by grooves  164  defined by the outer portion  154  of the second hem tool  130 . The ribs  156  and  162  are inter-engaged with the ribs  156  being received in the grooves  164  and the ribs  162  being received in the ribs  156 , as shown in  FIG. 14 . 
         [0042]    Referring to  FIG. 15 , the inner portion  152  is shown in isolation to more clearly illustrate the relationship of the ribs  156  and the grooves  160 . Referring to  FIG. 16 , the outer portion  154  of the second hem tool  130  shown in  FIGS. 13 and 14  is shown in isolation to illustrate the relationship between ribs  162  and grooves  164 . The ribs  162  terminate in the stops  136  upon which the inwardly angled surface  134  is provided, as previously described. 
         [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.