Abstract:
A method and device is provided for measuring springback of a vehicle panel within a deformation press. This avoids the need for removing the panel from the press and fabricating a dedicated measuring fixture. A trim die in the deformation press is retrofit to perform an additional function, namely securing a deformed panel in a position such that a measurement of the panel can be made. The trim die is retrofit by modifying existing apertures and adding additional aperture(s) in required positions. In the process, after bending the panel into the press and, using the trim die, undesired material is trimmed from the deformed panel. The panel is raised and at least three fixture posts are placed in apertures in the trim die. The panel rests on the posts with one post securing the panel in either one, two or three directions. The panel is then scanned or otherwise measured to determine springback in the panel.

Description:
BACKGROUND OF THE INVENTION 
     Manufacture of vehicle panels such as fenders etc. requires one or more sheet metal forming operations such as bending, drawing, trimming etc., referred to, in general herein, as stamping operations. Such operations include the use of dies wherein a first die comes in close proximity with a second die to deform sheet metal, located in between, into a desired shape. However, because sheet metal parts are thin and are subjected to relatively small strains, they are subject to the phenomenon of springback (i.e. the sheet metal deflects slightly back toward its original shape). The degree of springback in a particular panel must be determined so the dies and forming operations can be designed such that the desired final shape is met, with the effects of springback taken into account. 
     Springback in a part can be approximated by computer simulation of a metal forming operation, but eventually the simulation should be confirmed by deforming an actual part. Whether the confirmation test is performed in a lab or on the factory floor, typical practice includes deforming the panel within a stamping press, and then moving the deformed panel out of the press and to a dedicated fixture, where the panel is secured, and where the springback of the panel is then measured using a CMM (Coordinate Measuring Machine) or laser scanning measuring process. 
     When measuring springback, it is important to secure one portion of the panel in a known position so the measured deformation in another position is representative of actual springback. 
     Fabricating several dedicated measuring fixtures for securing and measuring a deformed part is expensive, especially when a large number of significantly different shaped panels are formed. What is desired is a way to avoid having to manufacture a dedicated fixture and move a deformed panel to the dedicated fixture in order to measure springback. 
     BRIEF SUMMARY OF THE INVENTION 
     A method and device is provided for measuring springback of a vehicle panel within or outside of a deformation press. A trim die, used in the deformation press, is retrofit to perform an additional function, namely for acting as a fixture to secure a deformed panel in a position such that a measurement of springback of the panel can be made. The trim die is retrofit by modifying existing apertures and adding additional aperture(s) in required positions. In the process, after drawing the panel in the press, using the trim die, undesired material is trimmed from the deformed panel. The trim die is then either removed from the press for fixturing of the panel or fixturing is performed with the trim die remaining in the stamping press. The panel is raised and at least three fixture posts are placed in the new/modified apertures in the trim die. The panel rests on the posts with one post securing the panel in either one, two or three directions. The panel is then scanned or otherwise measured to determine springback in the panel. 
     These and other features, aspects and advantages of the present invention will be fully described by the following description, appended claims, and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a multi-purpose trim die according to the invention; 
         FIG. 2  is a perspective view of a vehicle panel supported on the multi-purpose trim die; 
         FIG. 3  is a perspective view of a vehicle panel alone; 
         FIG. 4A  is side elevational view of a first fixture post; 
         FIG. 4B  is a cross sectional view of the first fixture post; 
         FIG. 5  is a side elevational view of a second fixture post; and 
         FIG. 6  is flowchart illustrating the method of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings, specifically  FIGS. 1 and 2 , a multi-purpose trim die  10  according to the present invention is illustrated. The trim die  10  includes at least three apertures  12 ,  22  that receive fixture posts  14  that support a vehicle panel  16  or other stamped work part. The trim die  10  and fixture posts  14  facilitate measurement of springback in the vehicle panel  16  as described in more detail below. 
     Referring to  FIG. 1 , a trim die  10  for a vehicle panel  16  is shown. The trim die  10  is located in a dedicated stamping press  18 , a portion of which is illustrated, or in one position within a multi-stage stamping press. A blank of sheet metal that was first deformed within another press or another position within the multi-stage press is moved to a position on the trim die  10  to have extraneous material trimmed therefrom. Thus, trimming is performed before springback within the vehicle panel  16  is measured. 
     The trim die  10  has a shape determined by the shape of the vehicle panel  16  being trimmed. Outer edges  20  of the trim die  10  form one cutting surface that trims extraneous material. The other cutting surface is on a mating die (not illustrated) supported on a ram portion of the press  18 . The trim die  10  includes several apertures  12  used to support tools, often referred to as buttons (not illustrated). The button acts in conjunction with a punch tool on the press ram portion to form an aperture within a panel. Two apertures  12  within the trim die  10  serve a dual purpose, both for supporting buttons in prior/later operations and for supporting a fixture post  14  in the measuring operation. As illustrated, the apertures  12  are modified by machining to have a unique shape. Flats  25  are defined within the aperture  12  that match the specific shape of a fixture post  14  that is supported in the aperture  12 . A cylindrical portion below the machined portion supports a cylindrical portion of the fixture post  14 , or a button in other operations. A third aperture  22  is provided in the trim die  10 , dedicated only to holding a fixture post  14  for measurement of springback.  FIG. 2  shows a laser scanning device  23  used in the measurement of springback. 
       FIGS. 4A and 4B  show a first type  24  of fixture post  14  that is supported in the trim die apertures  12 . The first post  24  includes a generally cylindrical main body  26 . Projecting from a proximal end  28  of the main body  26  is a cylindrical projection  30  having a smaller diameter than the adjacent portion of the main body  26 . This projection  30  fits into the cylindrical portion of the aperture  12  on the multi-purpose trim die  10 . The main body  26  of the first type of fixture post  24  includes two flat surfaces  35 . These surfaces  35  act as an alignment and locking mechanism. As described below the distal end  34  of the first fixture posts  24  are specifically shaped to match the vehicle panel  16 . A first fixture post  24  must, therefore, be aligned properly when inserted into the trim die  10 . The apertures  12  in the trim die include matching flats  25  previously described therein, thus allowing only one type of first fixture post  24  to be inserted into each aperture on the upper portion of the trim die  10 . Herein, the flats  35  on the first fixture posts  24  are offset by 180 degrees and have different widths, as clearly shown in  FIG. 4B  to allow insertion in only one orientation. When the first fixture post  24  is installed in the trim die  10 , the flat surfaces  35  of the main body  26  lock into matching flats  25  around the apertures  12  of the trim die  10 . Thus, the first fixture post  24  can not rotate and only the correct post can be placed in each hole. The width of the flats  35  can be varied between different first fixture posts  24  so the posts  24  are distinguishable from one another. 
     The distal end  34  of the first fixture post  24  is shaped in a manner that matches a corresponding position on the underside of the vehicle panel  16 . Thus, when the vehicle panel  16  is supported on the first fixture post  24 , almost the entire contact surface  36  at the distal end  34  of the first fixture post  24  contacts the underside of the vehicle panel  16 . The distal end  34  of the first fixture post  24  also includes an axial threaded aperture  38  therein. The aperture  38  is countersunk. A screw  40  with a head  42  having an interior tapered surface  44  is threadingly engagable within the threaded aperture  38  of the first fixture post  24 . 
     The second type of fixture post  50  also includes a generally cylindrical main body  52 . Projecting from a proximal end  54  of the second post is also a cylindrical projection  56  having a smaller diameter than the adjacent portion of the main body  52 . This projection  56  fits into an aperture  22  on the multi-purpose trim die  10 . When the second fixture post  50  is installed in the trim die  10 , the transition  58  between the projection  56  and the remainder of the main body  52  seats on the exterior surface of the trim die  10 . 
     The distal end  60  of the second fixture post  50  has a semi-spherical cap  62  thereon. Thus, when the vehicle panel  16  is supported on the second fixture post  50 , there is simple point contact between the distal end  60  of the second fixture post  50  and the underside of the vehicle panel  16 . The spherical cap  62  can be manufactured of a magnetic material, thus contact with the underside of a steel vehicle panel  16  is maintained. Alternatively, the spherical cap  62  is steel and a separate magnet  63  is used on the opposite side of an aluminum vehicle panel from the spherical cap  62  to hold the panel  16  in place as shown in  FIG. 2 . 
     The vehicle panel  16  illustrated in  FIGS. 2 and 3  is a fender, although any vehicle panel may be used. For springback testing purposes, the vehicle panel  16  is provided with at least two apertures  70  and  72  therein. In the left side of the vehicle panel, a generally circular aperture  70  is placed. When this generally circular aperture  70  is placed over the distal end of a first post  24  supported in the trim die  10 , the screw  40  can be secured within the threaded aperture  38  in the post  24 . The tapered inner surface  44  of the screw  40  contacts the circular aperture  70  around its entire perimeter and, thus, restrains movement of the vehicle panel  16  within the X, Y, and Z directions. 
     In the right side of the vehicle panel  16 , a generally rectangular aperture  72  with rounded ends is placed. When this aperture  72  is placed over the distal end of a first type post  24  supported in the trim die  10 , a screw  40  can be secured within the threaded aperture  38  in the first type post  24 . The tapered inner surface  44  of the screw  40  contacts only a portion of the rectangular aperture  72  and, thus, restrains movement of the vehicle panel within the Y and Z directions (or X and Z directions depending on the orientation of the rectangle). If screws  40  are not secured in either position near the first and second apertures  70  and  72  formed in the vehicle panel, then only movement of the panel in a Z direction is constrained, by the magnet used as a part of or in conjunction with the second type post  50 , holding the metallic panel. 
     A method of operation is illustrated within a flowchart in  FIG. 6 . Beginning with a metal blank, drawing operations are performed in a first step  100 . Trim operation(s) are next performed in step  110 . The formed vehicle panel  16  is placed over the trim die and the press activated in order to bring two dies together. When the dies are brought together excess material on the vehicle panel is trimmed off the vehicle panel  16 . In step  115 , any required bending operations are performed. The vehicle panel  16  is then returned to the trim die  10 . 
     In step  120 , the vehicle panel  16  is lifted slightly in order to put at least three fixture posts  14  into position  130  between the vehicle panel  16  and the trim die  10 . Depending on the direction of restraint desired, in step  140  zero, one or two screws  40  are secured into fixture posts  24  of the first type supported on the trim die. In step  150 , the vehicle panel is then scanned with a laser scanner  80  to determine to position of the panel with respect to a predicted position which is the result of a computer simulation process. 
     The fixture posts are shown as all being linearly insertable and removable from the trim die. Alternatively, the projections from the proximal ends of the second fixture posts  50  may be threaded and the fixture posts  50  screwed into position within the trim die. Flats on the exterior surface of the second fixture post  50  may be provided to facilitate tightening and loosening the second fixture post  50  with a wrench. 
     The flats  35  on the first fixture posts  26  are shown as being offset by 180 degrees, but other offset configurations, such as 90 degrees are also possible with the apertures  12  on the trim die being machined accordingly. 
     Although vehicle panel parts are described herein, any stamped part may be scanned using the device and method described herein. Although measurement is described after completion of bending operations, measurement may be performed directly after trimming of the vehicle panel. Measurement is disclosed as taking place while the modified trim die is still within the stamping press. However, the trim die may be removed from the press before measurement is performed. 
     Although the invention has been shown and described with reference to certain preferred and alternate embodiments, the invention is not limited to these specific embodiments. Minor variations and insubstantial differences in the various combinations of materials and methods of application may occur to those of ordinary skill in the art while remaining within the scope of the invention as claimed and equivalents.