Abstract:
Method and apparatus of forming articles includes a press having a pair of opposite platens. An articulated clamping frame is mounted between the platens, each of which are moveable toward and away from the clamping frame. Material to be formed is clamped into the clamping frames and the articulated clamping frame is wrapped around the die as the die forms the material. The formed article is extracted from the die by moving the clamping frame away from the die.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation of U.S. patent application Ser. No. 09/267,965, entitled “PRESS MECHANISM,” filed Mar. 12, 1999, which claims the benefit of U.S. Provisional Patent Application Serial No. 60/079,606, entitled “METHOD AND APPARATUS FOR FORMING LARGE ARTICLES,” filed Mar. 27, 1998. The entire disclosures of U.S. patent application Ser. No. 09/267,965 and U.S. Provisional Patent Application Serial No. 60/079,606 are hereby incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention relates to a method and apparatus for forming large articles having curved surfaces from plastic sheet material.  
           [0003]    Vacuum forming methods for forming large articles having curved surfaces from sheets of vinyl or plastic material are well known in the art. These processes are commonly used to form large automotive body members, such as bumper facia, and may also be used to form tank halves and similar articles. According to a known process, a plastic sheet is mounted in a clamping frame, heated, and then formed by forcing a die into the sheet and then sucking the sheet against the die by use of vacuum. The product is then cooled, the die extracted, and the finished product removed from the clamping frame. This and similar processes have been widely used to manufacture such articles at a relatively low cost.  
           [0004]    However, prior art processes, depending upon the shape and complexity of the article being formed, require larger sheets than would otherwise be necessary to accommodate stretching as the mold enters the sheet. Accordingly, the thickness of the product cannot be easily controlled, and “chills” and other defects in the product are common. Furthermore, dies must be carefully designed when complex shapes are formed to avoid die locks in which it is impossible to remove the die from the finished part.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention is directed to a press mechanism that includes a clamping frame, a die for forming an article and engaging members. The clamping frame is profiled to receive and retain a sheet of material to be formed and has articulable joints along opposite sides which allow the frame to articulate about at least one axis. The engaging members are shaped to receive and retain the clamping frame while allowing the clamping frame to articulate. At least one of the die and the engaging members are capable of movement with respect to each other and a sheet of material to be formed is held by the clamping frame when engaged with the die.  
           [0006]    These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    In the drawings:  
         [0008]    [0008]FIG. 1 is a flow chart describing the process according to the present invention;  
         [0009]    [0009]FIG. 2 is a view in perspective of the clamping frame used in the present invention;  
         [0010]    [0010]FIGS. 3 and 4 are enlargements, partly in section, of the corresponding circumscribed portions of FIG. 2;  
         [0011]    [0011]FIG. 5 is a schematic elevational view, with the die illustrated in cross-section, of the apparatus used in the present invention positioned to perform an initial step of the molding process of the present invention; and  
         [0012]    FIGS.  6 - 11  are views similar to FIG. 5 but illustrating additional steps in the process according to the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0013]    According to the present invention, a plastic sheet is mounted in an articulated frame that is wrapped around a mold as the mold enters the sheet. Accordingly, material savings of one-third or more can be realized by using smaller sheets than are required in the prior art processes. Because the sheet is wrapped around the mold as the mold enters the sheet, better quality formed products are realized, without chills and other defects in the product, and die locks are more easily avoided.  
         [0014]    Referring now to FIG. 1, a commercially available plastic or vinyl sheet of a size sufficient to be vacuum molded into the desired component is loaded onto a clamping frame and clamped to the frame as indicated at  10  in FIG. 1. Loading of the sheet on the frame may be effected by a conventional sheet loader onto which the sheet is placed and which then elevates the sheet so that it may be clamped on the clamp frame. The frame is then transferred to an oven, as indicated at  12 , and heated until the sheet sags below the frame a distance sufficient to actuate an electric eye, all as well known in the prior art. After the sheet is heated, it is transferred to the forming station, as indicated at  16  on FIG. 1 and as illustrated in FIG. 5. The upper platen of the press, which carries the vacuum forming die, is then forced into the sheet, as indicated at  18  in FIG. 1, and the lower platen is raised to bend the clamping frame about the mold carried on the upper platen, as indicated at  20  in FIG. 1, and also as illustrated in FIG. 6. A vacuum is then pulled through the die to form the sheet around the die, as indicated at  22 . A cooing cycle is then initiated, as indicated at  24 . The cooling cycle may, for example include the circulation of ambient air around the product to cool the product until the product becomes rigid. Toggle clamps on the lower platen are then closed onto the clamp frame as indicated at  26  in FIG. 1 and in FIG. 7. The lower platen is then lowered, as indicated at  28  and in FIG. 8, to pull the formed sheet away from the mold. The upper platen is then raised to remove the mold from the formed article as indicated at  30  in FIG. 1 and as also illustrated FIG. 9. The lower platen is then raised and the toggle clamps are released, as indicated at  32  in FIG. 1 and in FIG. 10. The lower platen is then fully lowered, as indicated at  34  in FIG. 1 and in FIG. 11. The part is then unloaded as indicated at  36  in FIG. 1, by raising a conventional unloader to support the part and then releasing the clamps and then lowering the completed component out of the forming station.  
         [0015]    Referring now to FIG. 2, a clamping frame used in the present invention is generally indicated by the numeral  38 . Clamping frame  38  includes side clamps  40 ,  42 ,  44  and  46  extending along one side of the frame, and corresponding clamps,  48 ,  50   52  and  54  extending along the other side of the frame. The frame  38  includes opposite end clamps  56 ,  58 . The side clamps  40  and  48  are tied to the end clamp  58  for movement therewith by bar assembly  60 . Similarly, the clamps  46  and  54  are tied to the end clamp  56  by bar assembly  62  at the end of the frame  38  opposite the bar assembly  60 . Clamp  48  is pivotally attached to clamp  50  through pivot connector  64 ; clamp  40  is pivotally connected to clamp  42  by a pivot connector  66 ; clamp  44  is pivotally connected to clamp  46  by a pivot connector  68 ; and clamp  52  is connected to clamp  54  through a pivot connector  70 . The pivot connectors  70 ,  64  are attached to a side rail extending substantially parallel to the clamps  48 ,  50 ,  52  and  54 , a portion of which is shown at  72  in FIG. 2. The pivot connectors  64 ,  70  allow the corresponding clamps  48 ,  50  and  52 ,  54  to pivot both upwardly and downwardly with respect to one another. The pivot connectors  66  and  68  are connected to a similar rail extending along the other side of frame  38  (not shown in FIG. 2, but illustrated schematically at  74  in FIGS.  5 - 11 ).  
         [0016]    The contiguous ends of the clamps  50  and  52  are supported by a mechanism mounted on the rail  72  and generally indicated by the numeral  76 . A similar mechanism (only a few components being shown as at  78 ) supports the contiguous ends of the clamps  42  and  44 . The support member  78  is also illustrated schematically in FIGS.  5 - 11 . Since the support mechanisms  76  and  78  are identical, only the support mechanism  76  will be described in detail.  
         [0017]    Referring now to FIG. 3, support mechanism  76  includes a first upright  80  which is mounted on the rail  72  adjacent the end of the clamp  52  which is contiguous with the corresponding end to the clamp  50 , and a second upright  82 , which is mounted in a similar position adjacent the end of the clamp  50 . Springs  84 ,  86  extend downwardly from the uprights  80 ,  82  and are secured to their corresponding clamps  52 ,  50  and are adjusted so that the contiguous ends of the clamps  50 ,  52  are biased to a position in which the ends are in a substantial axial alignment with one another. Brackets  88 ,  90  are also mounted on rail  72  adjacent the ends of the clamps  52  and  50 . The brackets  88  and  90  each include an upper transverse member  92 , a lower transverse member  94  and a vertical member  96  that is received within an aperture defined in a corresponding bracket  98 ,  100  mounted adjacent to the ends of the clamp  52  and  50 , respectively. Accordingly, the clamps are biased by the springs  84  and  86  into a position in which they are in substantial axial alignment, but each of the clamps  52  and  50  can move relative to one another about their correspondent pivot connections  70  and  64 , the range of movement being limited by engagement of the corresponding bracket  98  or  100  with its corresponding upper and lower transverse members  92  and  94 .  
         [0018]    Referring to FIG. 4, each of the side clamps  40 - 46  and  48 - 54  are actuated by a pair of double acting pneumatic actuators indicated by the numeral  102 , and each of the end clamps  56  and  58  are actuated by three such pneumatic actuators  102 . Each of the actuators are connected with other actuators and with a supply of compressed air by flexible hoses  104 . Since all of the actuators are the same, only one of the actuators  102  will be described in detail. Each of the actuators  102  are mounted on a longitudinally extending support member  106  upon which upper jaw  108  of each of the clamps  40 - 58  is mounted. A lower jaw  110  of each clamp is pivotally connected to the upper jaw  108  at a pivot connection  112 . The actuator  102  is conventional and includes an output rod  114  which is connected to the lower jaw by a pivot connection  116  and a linkage  118 . When a sheet is to be clamped in a clamping frame  38 , air pressure is admitted into the actuator  102  in a direction which urges the output rod  114  in a direction biasing the lower jaw  110  to a position closing with the jaw  108 . When the clamp is to be released, air is admitted into the actuators  102  in a direction which drives the output rod  114  in the reverse direction, thereby opening the lower jaw  110  from the upper jaw  108 .  
         [0019]    Referring now to FIGS.  5 - 11 , forming takes place in a vacuum forming press having an upper platen  120  and a lower platen  122 . A conventional vacuum forming die, which is illustrated in cross-section at  124 , is mounted on the upper platen  120 . Uprights  126 ,  128  extend upwardly from lower platen  122  and terminate in socket ends  130 ,  132  which receive the outer ends  134  (FIG. 2) of the bars  60 ,  62  as illustrated in FIG. 2. The ends  134  project beyond the ends of the corresponding clamps  56 ,  58 . Preferably, two additional uprights (not shown) are located behind the uprights  126 ,  128 . A toggle clamp  136 ,  138  is provided on each of the uprights and closes across the top of the corresponding socket, as will be described in detail hereinafter. The ends of the rails  72 ,  74  are received on tracks indicated schematically at  140 ,  142  which extend parallel to the end clamps  56 ,  58  when the clamping frame  38  is installed in the press. Accordingly, the clamping frame  38  is moveable transversely with respect to the Figures along the tracks  140 ,  142 .  
         [0020]    As discussed above, when a forming operation is initiated, a conventional plastic or vinyl sheet is placed on a conventional sheet loader (not shown) and elevated onto the clamping frame  38 . The clamps  40 - 56  are then operated to grasp the sheet and hold it in the clamping frame  38 . Preferably, the aforementioned oven is offset transversely from the press, so that the frame  38  can be transferred by movement along the tracks  140 ,  142  from the press into the oven. The frame and sheet are heated until the sheet sags as indicated at W on FIG. 5. The frame  38  and the sheet are then moved out of the oven and back into the position illustrated in FIG. 5, wherein the sheet, still being at an elevated temperature, sags as indicated at FIG. 5. The platens  120 ,  122  are then advanced toward one another. As the upper platen  120  is lowered, the die  124  passes through the frame  38  and engages the sheet W. As the die  124  engages the sheet W, the clamps  42 ,  44  and  50 ,  52  are deflected slightly around the corresponding pivot connections  64 ,  66  and  68 ,  70  and the contiguous ends of the clamps  42 ,  44  and  50 ,  52  are forced downwardly, in opposition to the springs  84 ,  86 . At the same time, lower platen  122  is raised until the socket  130 ,  132  engage the ends  134 , as illustrated in FIG. 6. Further upward movement of the lower platen  122  causes the uprights to pivot the side clamps  40 ,  48  and end clamp  58 , and the side clamps  46 ,  54  and end clamp  56 , about their corresponding pivot connections  64 ,  66  and  68 ,  70 , thereby wrapping the sheet about the die  124 . In the prior art, a flat, unarticulated frame was used, and the die  124  was forced into the sheet by movement of the die relative thereto. If complex shapes were formed, die locks were difficult and sometimes impossible to avoid, and substantial stretching also occurred. Usually the sheet had to be much larger than in the case of the present invention. By wrapping the sheet around the die due to the articulated clamping frame  38 , the size of the sheet required for a given end product size is substantially reduced, die locks can more easily be avoided, and a better quality product results, since defects due to stretching of the material are substantially reduced. After the sheet has been wrapped around the die as indicated by FIG. 6, a conventional vacuum forming cycle begins, in which vacuum is pulled through the die  124 , thereby pulling the sheet around the die, in a manner well known to those skilled in the art.  
         [0021]    After forming is complete, a cooling cycle is initiated, such as by turning on fans, etc., to cool the sheet into a rigid state. During the vacuum forming and cooling steps, the platens remain in the positions illustrated in FIG. 6. After the product has become rigid, the toggle clamps  134 ,  136  are engaged over the sockets  130 ,  132  as illustrated in FIG. 7. The lower platen  122  is then lowered slightly, as indicated in FIG. 8, thereby breaking the product away from the die  124 . The die  124  can then be extracted from the product as illustrated in FIG. 9. As also illustrated in FIG. 9, the lower platen is raised back into the FIG. 6 position to permit release of the toggle clamps, as illustrated in FIG. 10. The lower platen  122  is then lowered to the fully lowered position as illustrated in FIG. 11, while the product remains in the frame  38 , which remains in the articulated position illustrated in FIG. 11. The product is then removed from the frame by positioning a conventional unloader (not shown) under the product P, and then releasing the clamps  40 - 58  to release the product P onto the unloader. The unloader is then able to transfer the product out of the press.  
         [0022]    The above description is considered that of the preferred embodiment(s) only. Modifications of the invention will occur to those skilled in the art and to those who make or use the invention. Therefore, it is understood that the embodiments shown in the drawings and described above are merely for illustrative purposes and not intended to limit the scope of the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the doctrine of equivalents.