Abstract:
A mechanism for hemming the beltline of a vehicle door panel is combined with a mechanism for hemming the outside perimeter of the door panel, and the two mechanisms are driven by a common drive. The beltline hemming steel acts on the beltline hem before the outside perimeter hemming steel acts on the outside perimeter hem, and lost motion in the actuation of the beltline hemming steel allows the beltline hemming steel to complete the beltline hem before the outside perimeter hem is completed. The lost motion mechanism provides reduced interaction or sensitivity between the steels, and the delay in the completion of the outside perimeter hem allows the entire hemming apparatus to be more easily tuned during set-up. The lost motion allows the entire mechanism to be less sensitive to variations in workpiece thickness.

Description:
FIELD OF THE INVENTION 
   This invention relates to a drive arrangement for hemming steels that are driven by a common actuator for hemming the beltline and the outside perimeter of a vehicle door panel. 
   BACKGROUND OF THE INVENTION 
   In the field of automobile manufacture, hemming is the process of folding over the edge of a body panel to form a finished edge. Hemming is also used to join two body panels together, such as the inner and outer panels of a door. The hem provides a secure mechanical joint, and the resulting edge of the hemmed joint is neat and finished. 
   The lower edge of a window opening in a vehicle door panel is called the beltline. A reinforcing plate, normally called a beltline reinforcement, is usually attached to the inside of the outer panel along the beltline. The beltline reinforcement provides added strength to the door in the event of a side impact. Until the present time, the beltline reinforcement was attached to the outer panel by a series of spot welds. Although spot welds provide a secure mechanical connection between the beltline reinforcement and the outer panel, the welds show through on the Class A surface of the outer panel. As automobile fit and finish has become more refined, it has become increasingly important to mask over or otherwise obliterate any marks or indentations caused by the spot welding process so that they will not be visible on the outside panel surface. The normal solution is to cover welds of the beltline joint with a piece of trim material that is usually in the form of a chrome or rubber strip. 
   Hemming would be a desirable way to join the beltline reinforcement to the outer panel, since the hemming process inherently leaves the outer panel without impressions or marks that need to be masked over with trim material. A beltline hemming mechanism would be less expensive than weld guns, and if the beltline hemming could be performed at the same time as other hemming operations were being performed on the same panel, the overall processing time for the panel could be reduced. Until recently, hemming has not been used to join the beltline reinforcement to the outer panel, and there are various reasons for this. If hemming is being used to hem the inside perimeter of the window opening, the space in the window opening is already occupied by that hemming mechanism, and there is not enough room for a separate beltline hemming machine. If the beltline hemming mechanism is combined with the mechanism for hemming some other portion of the window opening or the door panel, the timing and synchronization of the motion of all of the hemming steels, if they are driven by a single actuator, becomes an almost impossible task, and it is very difficult to set-up the hemming steels so that they all reach a Final Hem Complete position at the same time. Even if the steels are perfectly timed relative to one another, any variation in the thickness of the workpiece in a production run, or in the stroke or timing of the steels, results in a final hem that is not completely closed, or a hemming mechanism that becomes overly stressed because it is being driven past the Final Hem Complete position. One solution is to provide a second hemming machine at its own station in order to do the beltline hemming. This eliminates the timing and synchronization issues between the beltline hemming steels and the other hemming steels and allows the beltline hemming machine to be set up and tuned independently of the other hemming machines. The second hemming machine requires additional floor space however, and, because a second dedicated drive is required, the second hemming machine represents a substantial additional cost. 
   It would accordingly be desirable to provide a hemming machine that would hem the beltline of a vehicle door panel in the same station that is performing other hemming on the panel, using a single machine and a single drive mechanism, but would allow the hemming tools to finish their respective hemming strokes at different times. 
   OBJECTS OF THE INVENTION 
   It is accordingly an object of the invention to provide hemming mechanism for hemming the beltline of a vehicle door panel in the same machine that hems the outside perimeter of the panel. 
   It is another object of the invention to provide a hemming mechanism for hemming the beltline and the outside perimeter of a vehicle door panel in which the beltline hem steel and the outside perimeter hem steel are driven by the same mechanism, but are able to have independent movements. 
   It is another object of the invention to provide a hemming mechanism for both the beltline and the outside perimeter of a vehicle door panel in which the beltline hem is finished prior to the time that the outside perimeter hem is finished. 
   SUMMARY OF THE INVENTION 
   According to the invention, a pressure plate is used to drive hem steels that pre-hem and hem the beltline of a vehicle door panel. The same pressure plate drives the steel that is used to final hem the outside perimeter of the panel. The beltline hemming steels and the outside perimeter hemming steels are actuated at different times, providing reduced interaction or sensitivity between the steels. The different actuation times allows the entire hemming apparatus to be more easily tuned during the set-up and run-off process, and to be less sensitive to variations in workpiece thickness. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects, features and advantages of this invention will be apparent from the following detailed description, appended claims and accompanied drawings in which: 
       FIG. 1  is a plan view of a typical vehicle door panel having a window opening. 
       FIG. 2  is a cross sectional view of a hemming mechanism for hemming the beltline and the outside perimeter of a door panel showing the beltline hemming steel in both the Open and the Pre-Hem Complete positions. 
       FIG. 3  is a cross sectional view of a hemming mechanism for hemming the beltline and the outside perimeter of a door panel showing the beltline hemming steel in the Final Hem Complete position and the outside perimeter hemming steel in the Pre-Hem Complete position. 
       FIG. 4  is a cross sectional view of a hemming mechanism for hemming the beltline and the outside perimeter of a door panel showing the beltline hemming steel in the Final Hem position and the outside perimeter hemming steel in the Final Hem position. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Turning now to the drawing figures,  FIG. 1  shows the exterior of a typical vehicle door panel generally designated by the reference numeral  8 . The door panel has a window opening  9  and a beltline  10  along its lower edge. A beltline reinforcement  11  is normally attached to the inside of the outer panel, just below the window opening  9 . The inside and outside panels that comprise the complete door panel  8  may be joined together by an inside the window hem around the top and sides  13  of the window opening  9 . To further join of the inner and outer panels together, the outside perimeter  14  of the inner and outer panels may be joined together by an outside perimeter hem. 
     FIG. 2  is a side view partly in section of a hemming mechanism that is used to hem the beltline  10  and the outside perimeter  14  of a vehicle door panel  8 . The hemming mechanism includes a pressure plate  15  that is actuated by the force  16  from a press (not shown). The pressure plate  15  is located generally above a portion of a vehicle body panel  8  that has been loaded into the hemming apparatus. The vehicle body panel  8  includes an inner panel  17 , an outer panel  18 , and a beltline reinforcement  11 . A flange  21  from the outer panel is folded over the beltline reinforcement  11  to form a beltline hem that attaches the beltline reinforcement  11  to the outer panel  18 . A second reinforcement plate  19  similar to the beltline reinforcement  11  may be attached to the inner panel  17  by welding or other conventional means. The attachment of the second reinforcement plate  19  to the inner panel  17  does not form a part of the present invention. Spring loaded hold-down tooling (not shown) that is part of the hemming apparatus is conventionally used to engage the inner panel  17  to hold the workpiece securely in place. Such hold-down tooling is well known in the art and does not form a part of the present invention. The hold down tooling engages the workpiece prior to and during the pre-hemming and final hemming operation, but is not shown in the drawing figures for the sake of clarity. 
   An angled cam surface  23  that acts as a first actuator and a vertical cam surface  24  are formed on the side of a first extension foot  26  on the pressure plate  15 . A pressure pad  27  that acts as a second actuator is slideably mounted in a pressure pad pocket  28  on the underside of the pressure plate  15 . A spring  29  such as nitrogen gas spring is located in the pressure pad pocket  28  between the pressure pad  27  and the pressure plate  15 . The stiffness of the spring is chosen so that it will drive the pressure pad  27  into the beltline hem flange  21  with sufficient force to fold the flange and complete the hem, but will allow the pressure pad  27  to be driven into the pressure pad pocket  28  in response to continued downward motion of the pressure plate  15 . An outside perimeter hemming tool or steel  31  is mounted on the bottom of a second extension foot  32  on the pressure plate  15  in vertical alignment with the outside perimeter flange  33  on the outer panel  18 . 
   A beltline hemming tool  35  is mounted on a fixture head  36  that is attached to a rocker arm  37 . The hemming tool  35  comprises a pre-hem tool surface  38  and a final hem tool surface  39 . The two surfaces  38  and  39  may be formed on a single piece of tool steel, or may be formed on two separate pieces of tool steel that are mounted adjacent to one another on the fixture head  36 . The rocker arm  37  is pivotably mounted on a pivot  41 , and a compression spring  42  is used to bias the rocker arm and fixture head to the left against a stop  43  as shown in the drawing figure. The pivot  41  for the rocker arm  37  is supported by a spring  44  so that the fixture head  36  and the rocker arm can be driven downward in order to close the beltline hem as described more fully below. The pivot  41  is mounted on a base  46  by means of a post  47  with an end stop  48  that is slideably received in the base  46 . A roller  51  or other cam follower mechanism is mounted on one end of the fixture head  36 , and the angular position of the rocker arm  37  and the fixture head  36  is determined by the portion of the cam surface  23  and  24  that is in contact with the cam follower  51 . 
     FIG. 2  uses phantom and solid lines to show the rocker arm  37 , the fixture head  36 , and the hem flanges  21  and  33  in two positions. The rocker arm and fixture head shown in phantom are in the Open position in which the fixture head  36  is retracted from the beltline of the door panel  8  so that the door panel may be loaded or removed from the hemming machine. At the time the door panel  8  is first loaded, the beltline hem flange  21  is in the Open position as shown in phantom. A flange in the Open position allows the inner panel to be placed into the outer panel, and can normally be closed with two strokes of the hemming machine. The first stroke partially closes the Open flange to the Pre-Hem Complete position, and the second stroke completely closes the flange to the Final Hem Complete position. A flange in the Open position normally has to be rotated no more than 105 degrees to bend it to the fully closed or Final Hem Complete position. 
     FIG. 2  also shows in phantom the outside perimeter flange  33  formed on the edge of the outer panel  18  in the Open position. As a downward force  16  is applied by the press, the pressure plate  15  starts its vertical stroke. The angled cam surface  23  causes the rocker arm  37  and fixture head  36  to pivot to the right to the Pre-Hem Complete position in which the pre-hem steel  38  of the fixture head engages the beltline hem flange  21  and bends it from the Open position shown in phantom to the Pre-Hem Complete position as shown in solid. In the Pre-Hem Complete position, the pressure pad  27  is not yet in engagement with fixture head  36 , and the outside perimeter hemming tool  31  has not yet engaged the outside perimeter hem flange  33 . The outside perimeter hem flange  33  has been bent from the Open position shown in phantom to the Pre-Hem Complete position shown in solid by a separate pre-hem mechanism, not shown, as well known to those skilled in the art. 
     FIG. 3  shows the beltline hemming mechanism after the beltline hem has been completed. The downward force  16  of the press on the pressure plate  15  acts through the spring  29  and the pressure pad  27  to depress the fixture head  36  and the final hem steel  39  so that the beltline hem flange  21  is bent by the final hem steel  39  to its Final Hem Complete position. With the pressure plate  15  in this vertical position, the outside perimeter hemming tool  31  has come into contact with the open flange  33  of the outside perimeter hem, but the outside perimeter hem has not yet been bent to the Final Hem Complete position. 
     FIG. 4  shows the beltline hemming mechanism after the outside perimeter flange  33  has been bent to its Final Hem Complete position. The downward force  16  of the press on the pressure plate  15  has acted through the second extension foot  32  to drive the outside perimeter hem steel  31  against the open flange  33  to bend it to the Final Hem Complete position. At the same time, since the beltline hem flange  21  was already bent to its closed position against the beltline reinforcement  11 , the spring force of the spring  29  has been overcome to allow the pressure pad  27  to be driven into the pressure pad pocket  28 , allowing the necessary downward travel of the pressure plate  15  and the outside perimeter hem steel  31  on the second extension foot  32  to close the outside perimeter flange  33 . 
   Through the use of the invention, the beltline hem in a vehicle door panel can be bent to the Pre-Hem Complete and Final Hem Complete positions in one operation and using the same drive mechanism that is used to hem the outside perimeter hem to the Final Hem Complete position, by driving both hemming tools with a common pressure plate. In addition, variations in workpiece thickness or high spots on the workpiece are accommodated by coupling at least one of the hemming tools to the pressure plate through a spring. The spring between the pressure plate and the pressure pad provides a lost motion and allows the pressure plate to continue its downward stroke to bend the outside perimeter hem to the Final Hem Complete position, although the beltline hem flange is already bent to the Final Hem Complete position. This also allows the beltline hemming steels to be set-up independently of the outside perimeter hemming steels, thus simplifying the set-up process, and the making the mechanism less sensitive to variations in the workpiece thickness, since the position of one of the hemming steels in the Final Hem Complete position is not dependent on the position of the other hemming steel. For this reason, the invention is also applicable to any hemming operation where it is desired to hem two distinct areas of a workpiece, such as the inside and outside of a window opening, using two hemming mechanisms that are driven by a single press. 
   Having thus described the invention, various alterations and modifications will occur to those skilled in the art, which modifications and alterations will be deemed to be within the scope of the invention as defined by the appended claims.