Abstract:
An apparatus and method is described to form and join a short flange on a periphery of a sheet material supported in a nest ( 30 ). The apparatus includes a positional pressure forming steel (PPFS) assembly ( 50 ) located on the end of a robotic arm ( 42 ). The PPFS assembly ( 50 ) includes a hub ( 52 ) slidably supported in a cylinder ( 56 ). At least one tool steel ( 70, 70′, 70 ″) is located on an extension ( 68, 68 ′) from the hub ( 52 ). A biasing element ( 58 ) interposed between the cylinder ( 56 ) and the hub ( 52 ) enables precise control of the forming pressure by defining a tool path control program which maintains a relative relationship between the PPFS assembly ( 50 ) and the nest ( 30 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/526,559, filed Dec. 3, 2003. The disclosure of the above application is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to systems that form and join sheet material. More particularly, the present invention describes a tool and method of use in forming and joining the short flanges of a first sheet material to a second sheet material.  
       DESCRIPTION OF THE RELEVANT ART  
       [0003]     One of the earliest operations required in the history of automobile assembly was the joining of an inner panel to an outer panel to form any of a variety of body parts, including doors, engine hoods, fuel tank doors and trunk lids, all referred to as “swing panels” which encase the vehicle frame. Known machines for the forming and joining of sheet materials include the press-and-die set, the tabletop and the roller-forming tool, the latter being the most-recently introduced device.  
         [0004]     An unfortunate feature of joining sheet materials is the difficulty of forming short flanges where required by the design. A certain approach has been undertaken to overcome this problem.  
         [0005]     One known effort to form short flanges is to use a roller tool and perform multiple rolling passes or nudges to push the flange over from a generally upright configuration to a folded configuration or seam. Though it is an inexpensive approach, repeated roller passes requires an excessive amount of time to perform and does not always form shorter flanges in a satisfactory manner.  
         [0006]     Another known effort to form short flanges is to use mechanically pushed forming steel known in the art as a corner unit. This unit mounts on a linear slide normal to the direction the flange is to be form. The corner unit which carries the forming steel is extended by pneumatics or by cam action in a direction normal into the flange to form the flange. The corner unit then retracts to a non-contact position. While this style of forming is fast, the unit gets in the way during other necessary operations, thereby restricting movement of the roller tool. Moreover, the slide must be oriented generally perpendicular to the direction of the seam. It is also relatively expensive to operate and maintain in that it requires independent mechanisms and energy sources for each corner unit.  
         [0007]     Accordingly, prior approaches to address short flanged sheet material forming and joining have failed to overcome all the aforementioned problems.  
       SUMMARY OF THE PRESENT INVENTION  
       [0008]     It is thus a general object of the present invention to provide an apparatus and method that overcomes the problems of known techniques for forming and joining the short flanges of a first sheet material to a second sheet material to form a swing panel for an automobile.  
         [0009]     It is a particular object of the present invention to provide propelled tooling to form and join a first sheet material to a second sheet material.  
         [0010]     Another object of the present invention is to provide such propelled tooling that is flexible enough to accommodate panels of various sizes, shapes, and contours.  
         [0011]     A further object of the present invention is to provide such propelled tooling that may be used in conjunction with a robotic arm in operation with a variety of machine cells.  
         [0012]     Yet another object of the present invention is to provide a method of forming and joining a pair of sheet materials with a short flange seam.  
         [0013]     In accordance with the present invention an apparatus to form and join sheet materials with a short flange includes a positional pressure forming steel (PPFS) assembly is operatively associated with a programmable positioning apparatus in the form of a robotic arm and a machine cell which includes a holder for a first panel in the form of a lower nest, and a holder for a second panel in the form of an upper gate. The PPFS assembly includes a cylinder head with a captured reciprocating piston. A biasing element in the form of a compression spring operably disposed within the cylinder and atop the piston. The biasing element urges the piston to an extended position. A shaft extends through an end of the piston opposite the cylinder and supports a roller. At least one forming steel is located on an extension of the piston between the roller and the cylinder. The forming steel is oriented generally perpendicular to the axis of the shaft.  
         [0014]     In accordance with the present invention a method of forming and joining sheet materials with a short flange includes holding a first sheet material in a nest such that a periphery of the first sheet material is supported on a material contacting portion of the nest. A robotic arm locates a positional pressure forming steel relative to the nest and adjacent a short flange on the first sheet material. The robotic arm is manipulated to move the positional pressure forming steel along a tool path such the forming steel forms the short flange over a periphery of said first sheet material. The method may further be employed to join a second sheet material to the first sheet material.  
         [0015]     These and other objectives are accomplished by the provision of an apparatus and method for the forming and joining of sheet material as set forth hereinafter.  
         [0016]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The present invention will be more fully understood by reference to the following detailed description of the preferred embodiments when read in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout the views, and in which:  
         [0018]      FIG. 1  is a perspective view of a machine cell incorporating a positional pressure forming steel (PPFS) assembly according to the preferred embodiment of the present invention;  
         [0019]      FIG. 2  is a sectional view of the PPFS assembly of the present invention taken along lines  2 - 2  of  FIG. 1  and viewed from the side of the main roller illustrating a first forming steel in its pounce position;  
         [0020]      FIG. 3  is a sectional view of the PPFS assembly of the present invention similar to that of  FIG. 2  but illustrating the first forming steel in its engaged position;  
         [0021]      FIG. 4  is a sectional view of the PPFS assembly of the present invention similar to that of  FIG. 2  illustrating a second tiered forming steel in its pounce position;  
         [0022]      FIG. 5  is a sectional view of the PPFS assembly of the present invention similar to that of  FIG. 4  but illustrating the second tiered forming steel in its engaged position; and  
         [0023]      FIG. 6  is a sectional view similar to that of  FIG. 2  but illustrating an alternate embodiment of the PPFS assembly in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]     The drawings disclose the preferred embodiment of the present invention. While the configurations according to the illustrated embodiment are preferred, it is envisioned that alternate configurations of the present invention may be adopted without deviating from the invention as portrayed. The preferred embodiment is discussed hereafter.  
         [0025]     With reference first to  FIG. 1 , the preferred embodiment of a machine cell  10  is illustrated in a perspective view. The machine cell  10  includes an upper gate  20  and a lower nest  30  for precisely locating a sheet material A. The first sheet material A may be precision positioned by means of an array of crowders  34 . The machine cell  10  holds sheet material A so that a forming process may be undertaken without the sheet material being caused to shift or otherwise move out of position. As illustrated, first sheet material A has a generally square configuration. In some instances, two sheet materials may be included for purposes of forming and joining the two sheets, in a combination resulting from seaming, to form an integrated component. Accordingly, and as illustrated, an optional second sheet material B may be placed on top of the first sheet material A and aligned with the upper gate  20 . Thus, it is to be understood that the shape and number of sheet material being formed may vary without departing for scope of the present invention. It should also be understood that the configuration of the machine cell  10  as illustrated is preferred, but is not to be interpreted as limiting as other configurations conceivable to those skilled in the art may also be suitable. However, a presently preferred nest and gate configuration is disclosed in PCT/US04/34238, which is expressly incorporated by reference herein.  
         [0026]     A positional pressure forming steel (PPFS) assembly  50  is operatively associated with a robotic arm  42 . The PPFS assembly  50  rigidly mounts to a robotic arm faceplate  44  that is rotatably connected to the robotic arm  42 . The robotic arm  42  is itself operatively associated with a computer  46  which executes a run-time program for moving the PPFS assembly  50  along a pre-defined tool path. The PPFS assembly  50  may be selectably rotated to perform a desired operation with a given forming steel. The PPFS assembly  50  includes forming steels  70 ,  70 ′,  70 ″ as dictated by the particular forming and joining operation to be performed.  
         [0027]     Cross-sectional views of the PPFS assembly  50  are shown in  FIGS. 2 and 3 . With respect to these figures, the PPFS assembly  50  includes a reciprocating hub  52  having a piston end  54  mounted in a cylinder  56 . The cylinder  56  is fitted rigid to the faceplate  44  (shown in  FIG. 1 ) of the robotic arm  42  as is known in the art. The piston end  54  is captured within the cylinder  56  such that the hub  52  slides or reciprocates along an axis relative to the cylinder  56 . Hub  52  has extensions  68 ,  68 ′ extending outwardly therefrom on the end opposite piston end  54 . Forming steels  70 ,  70 ′,  70 ″ are secured to the extensions  68 ,  68 ′.  
         [0028]     The number and configuration of the extensions  68 ,  68 ′ and the forming steels  70 ,  70 ′,  70 ″ will be dictated by the particular forming and joining operation as mentioned above. For example, and as presently illustrated, the hub  52  includes a first extension  68  extending to the left (as seen in  FIGS. 2 and 3 ) which has a first forming steel  70  disposed on the lower surface  72  thereof. The hub  52  also has a second extension  68 ′ extending to the right (also as seen in  FIGS. 2 and 3 ). The lower surface  72 ′ of the second extension  68 ′ is stepped or tiered such that a second forming steel  70 ′ is disposed at an outer portion of extension  68 ′ and a third forming steel  70 ″ is disposed at an inner portion of extension  68 ′. Although generally shown to have a tapered or wedged face shape, each forming steels  70 ,  70 ′,  70 ″ is adapted with a shape formed into its face that closely resembles the preformed shape of the short flange to be formed. Thus, one skilled in the art will recognize that the details of the face shape for each of the forming steel  70 ,  70 ′,  70 ″ will depend on the geometry of the short flange F to be formed and that the present invention affords the ability to perform multiple short flange forming operations with a single PPFS assembly.  
         [0029]     A biasing element or spring  58  is interposed between the cylinder  56  and the piston end  54  to bias the hub  52  away from the cylinder  56 . As an alternative to the use of the illustrated spring biasing element  58 , a gas-charged cylinder may be placed in the position of the spring  58  to provide the needed biasing. In this manner, the PPFS assembly  50  provides a positional pressure forming tool whereby the position of the robot arm faceplate  44  relative to the lower nest  30  dictates the applied pressure at the interface between the short flange F and the forming steel  70 ,  70 ′,  70 ″.  
         [0030]     The characteristics of the biasing element are such that the pressure applied at the forming steel  70 ,  70 ′,  70 ″ is linearly proportional to the position of the piston end  54  relative to the cylinder  56  and the faceplate  44 . Each unit of linear distance the piston end  54  moves into cylinder  56  will increase the bias of element  58  in a linear proportion. In the event that a gas-filled cylinder is used in lieu of the spring  58 , a charge is built up therein and the piston end  54  moves into cylinder  56 . This linear relationship is the basis for the positional pressure variance programming that the robotic arm plays.  
         [0031]     A roller  62  is rotatably supported from the hub  52  by an axle  60  fixedly mounted in the hub  52  in a direction generally perpendicular to the extensions  68 ,  68 ′. The roller  62  operates in conjunction with the robotic arm  42  and a set of guide surfaces  32  formed on the lower nest  30  to provide positional pressure variance of the forming steel  70 . When no pressure is applied to the roller  62 , the biasing element  58  urges the piston end  54  in its outwardly extended position. Conversely, when pressure is selectively applied to the roller  62  by means of the robotic arm  42  positioning the roller  62  into engagement with the guide surface  32 , the piston end  54  is urged into the cylinder  56  causing the biasing element  58  to resist the inward movement of the piston end  54  and generate a counteracting force. In this manner the force applied at the face shape on the forming steel  70  can be precisely controlled when requiring force feedback from the end of the robotic arm  42 . The robotic arm  42  can be manipulated to rotate the PPFS assembly  50  through  1800  such that extension  68 ′ is directed toward the short flange F, thereby enabling formation with forming steels  70 ′,  70 ″.  
         [0032]     With reference now to  FIG. 6 , an alternate embodiment of a positional pressure forming steel (PPFS) assembly  150  is illustrated in which the placement of the hub  152  and the cylinder  156  are reversed relative to the robotic arm face plate  144 . Specifically, hub  152  extends from faceplate  144 . Cylinder  156  is slidably supported on the hub  152  by a bearing sleeve  154  interposed therebetween. A spring  158  is operably coupled between the hub  152  and the cylinder  156  to bias the hub  152  away from the cylinder  156 . An axle  160  extends through a lower portion of the cylinder  156 . A roller  162  is rotatably supported on the axle  160 . A pair of support flanges  164 ,  164 ′ extend from the sidewall of cylinder  156 . The support flanges  164 ,  164 ′ are adapted to retain forming steels  168 ,  168 ′ in a manner similar to that described with reference to  FIGS. 2-5 . The configuration of the embodiment illustrated in  FIG. 6  yields a more compact design than that illustrated in  FIGS. 2-5 , thereby enabling the use of PPFS assembly  150  in forming operations performed in more confined spaces. Rod  166  extends through hub  152  and slots  172 ,  172 ′ formed in cylinder  156 . The rod  166  cooperates with slots  172 ,  172 ′ to provide a stop or limit on the range of motions of the cylinder  156  relative to the hub  152 . It is to be understood that other aspects of the alternate embodiment of PPFS assembly  150  including its utilization in the forming operation are substantially similar to that of PPFS assembly  50 .  
         [0033]     With continued reference to the figures, the operation of forming a short flange F on the sheet assembly A in the machine cell  10  will now be generally described. The sheet material A is approximated onto the lower nest  30  and precision positioned by means of the crowders  34 . The first sheet material A and the second sheet material B are then securely held in place either by known means or by a vacuum system and upper gate such as disclosed in PCT/US04/34238. With the sheet material so fixed, a short flange forming operation is initiated to form a portion of the first sheet material A by means of a positional pressure forming steel (PPFS) assembly  50 .  
         [0034]     Initially, the robotic arm  42  orients the forming steel  70  to a pounce position which is normal to and within a close proximity of its associated flange F of interest. In other words, the forming steel  70  is adjacent to (but not in contact with) the upright flange F (as seen in  FIG. 2 ) on sheet A. When a pounce position is initiated, the main roller  62  may contact the guide surface  32 . As previously mentioned, the guide surface  32  or landing strip is a flat platform extending from the lower nest  30  that follows the approach path of the forming steel  70 . The guide surface  32  is positioned a distance below the forming steel  70  equal to the distance D between the forming steel  70  and the bottom of the roller  62 . The robotic arm  42  also preloads the biasing element  58  of the PPFS assembly  50  at this time to remove backlash from its system with enough static energy to prevent deflection of the forming steel  70  when it makes contact with the short flange F.  
         [0035]     Next, the robotic arm  42  rapidly manipulates the PPFS assembly  50  along a tool path which is substantially normal to the axis of the axle  60 . At this point the roller  62  rolls along the guide surface  32  and the forming steel  70  engages and crash forms the short flange F on sheet A. At this point, the flange F may be fully formed such that the PPFS assembly  50  can be moved to another location on the sheet A.  
         [0036]     However, the flange F may only be preformed (i.e. partially bent over) in which case, the roller  62  can be manipulated onto the flange F to finish the forming operation in an expedient manner such as disclosed in PCT Application No. PCT/US ______ entitled “Roller Tool and Positional Pressure Method of Use for the Forming and Joining of Sheet Metal” filed on Nov. 12, 2004 by the applicant of the present invention, the disclosure of which is hereby incorporated by reference.  
         [0037]     Alternatively, the additional forming steels  70 ′,  70 ″ may be used to perform the final forming operation. In this case the PPFS assembly  50  is rotated 180° to orient the forming steels  70 ′,  70 ″ to a pounce position which is normal to and within close proximity of the preformed flange. The robotic arm  42  rapidly manipulates the PPFS assembly  50  along a tool path to execute the final forming operation in a manner similar to the preforming operation.  
         [0038]     The robotic arm  42  manipulates the PPFS assembly away from the machine cell  10 . The upper gate  20  is moved away from the sheet materials A and B and the formed sheet material may be unloaded from the lower nest  30 .  
         [0039]     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with the particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification and following claims.