Abstract:
Apparatus and methods of forming sheets of material are disclosed. Profile plates may be placed atop the sheets. Tabs attached to clamp frames may apply uniform pressure on the perimeters of the profile plates during the formation process.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of and priority to U.S. Provisional Patent application Ser. No. 61/984,116, filed Apr. 25, 2014, entitled “Additional Apparatus for Controlling the Pressure of an Assist in Thermoforming” the entire contents of which are incorporated herein by this reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates principally to apparatus and methods for shaping heated polymeric materials in a mold and more particularly, although not necessarily exclusively, to devices assisting such thermoforming in manners improving uniformity of the resulting shaped products. 
       BACKGROUND OF THE INVENTION 
       [0003]    Commonly-owned U.S. Pat. No. 8,727,763 to Shanley, IV (the “&#39;763 Patent”), details apparatus and methods for, among other things, selectively thermoforming plastics. The apparatus may include a mold comprising “a generally planar upper surface from which one or more plugs protrude.” in use, the “plugs function as three-dimensional objects about which sheets of polymer material are formed.” See &#39;763 Patent, col. 3, 11. 33-37. 
         [0004]    Consistent with disclosure of the &#39;763 Patent, a to-be-formed sheet may be placed between the upper surface of the mold and an energy sink. One such sink may comprise a generally planar plate with one or more cut-outs existing through its depth. Preferably, each cut-out “is approximately the size and shape of an associated plug” protruding from the upper surface of the mold, See id., col. 3,11. 57-67; col. 4, 11. 29-32 and 49-51. To form portions of the sheet.
       [a]heater is repositioned closely above [the] sink and activated for a selected period of time . . . . Heat or other energy from [the] heater transfers to [the] sink and, where cut-outs in [the] sink exist, to . . . areas of the sheet therewith aligned, where it is absorbed by the polymeric material [of the sheet].       
 
         [0006]    As the exposed areas of the sheet absorb sufficient heat to reach their forming temperatures, [the] mold is evacuated so as to stretch (form) the material around [the] plugs. [The h]eater then may be repositioned away from [the] mold, the formed sheet of material may be allowed to cool, and [the] sink may be removed so as to expose the sheet of material. 
         [0000]    See id., col. 4, 11. 53-65 (numerals omitted). 
         [0007]    Commonly-owned U.S. Patent Application Publication No. 2013/0200551 to Shanley, IV, et al. (the “&#39;551 Application”) describes additional apparatus and methods for selective thermoforming. Included in apparatus of the &#39;551 Application is a spacing device initially separating a sheet from the mold surface. In some versions the spacing device may be “in the form of a grid or support rail” designed to “support [the] sheet of polymeric material a substantially uniform distance from the mold surface while enabling a profile plate to block heat or other energy from an energy source to effect the selective thermoforming.” See &#39;551 Application, p. 1, ¶ 0006. As described in the &#39;551 Application:
       The grid further may be supported by springs or other biasing mechanisms and accepted by a receiver groove or recesses in the mold. When compressed by vacuum pressure and the force of the clamps, the grid may retract flush into the mold.
 
See id. The entire contents of both the &#39;763 Patent and the &#39;551 Application are incorporated herein by this reference,
       
 
         [0009]    The apparatus, systems, and methods of the &#39;763 Patent and &#39;551 Application work well for their intended purposes. At times, however, to-be-formed polymeric sheets may lack uniform thicknesses. Also, the profile plates or other energy sinks may be subject to (generally slight) warpage or bowing. Either or both issues may cause distortion of the formed products, even in their unprinted areas. 
         [0010]    For example, unduly thick sheets may prevent satisfactory formation of the polymeric material around the plugs of the mold. By contrast, overly thin sheets may result in excessive thinning and consequent distortion of formed areas. Accordingly, sometimes need exists for enhancing uniformity of pressure placed on the sinks and sheets of polymeric material so as to help account for these issues. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention satisfies this need. At least some versions of the invention may incorporate tabs onto clamp frames for this purpose. After a sheet is placed in the forming location on a mold and the profile plate is positioned atop the sheet, the clamp frames may close so as to maintain the positioning of the sheet. The tabs attached to the clamp frames apply uniform pressure on the perimeter of the profile plate, holding the profile plate on top of the sheet. 
         [0012]    In these versions, the sheet may then be heated to forming temperature and the mold evacuated so that the sheet forms onto the mold surface. During this process, the tabs assist the profile plate by applying a downward pressure. The pressure helps ensure the profile plate remains in full contact with the sheet so as to assist its formation. The tabs additionally help prevent warping and bowing of the profile plate in the heating process. 
         [0013]    The tabs may be made of spring steel or any other suitable material. Spring steel is presently preferred, however, based on its modulus of elasticity. The elasticity allows the profile plate to be retained in place without unduly straining or stressing the sheet material during the forming process. 
         [0014]    It thus is an optional, non-exclusive object of the present invention to provide apparatus and methods for thermoforming polymeric materials. 
         [0015]    It is also an optional, non-exclusive object of the present invention to provide apparatus and methods for enhancing uniformity of formation of polymeric materials, 
         [0016]    It is a further optional, non-exclusive object of the present invention to provide apparatus and methods for employing assistive devices to promote such uniform formation. 
         [0017]    It is an additional optional, non-exclusive object of the present invention to provide apparatus and methods in which the assistive devices may comprise tabs attached to clamp frames. 
         [0018]    It is, moreover, an optional, non-exclusive object of the present invention to provide apparatus and methods in which the tabs are made of spring steel, 
         [0019]    Other objects, features, and advantages of the invention will be apparent to persons skilled in the relevant art with reference to the remaining text and the drawings of this application. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a perspective view of exemplary thermoforming apparatus useful as part of or in connection with the present invention. 
           [0021]      FIG. 2  is a close-up view of part of a mold portion of  FIG. 1  illustrating especially various plugs protruding upward from its surface onto which a formable sheet may be placed. 
           [0022]      FIG. 3  is a generally elevational view of an exemplary profile plate that may be used as part of or in connection with the present invention. 
           [0023]      FIG. 4  is a close-up view illustrating a formed polymer sheet contacting the mold part of  FIG. 2   
           [0024]      FIG. 5  is a perspective view of portions of the mold of  FIGS. 2 and 4  comprising part of the apparatus of  FIG. 1   
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Depicted in  FIG. 1 . is exemplary thermoforming apparatus  10 . Apparatus  10  may be a conventional thermoforming machine, any number of which are available commercially. Preferably included as part of apparatus  10  are mold  14  (see also  FIGS. 2 and 5 ) and heater  18 . A computerized controller including actuating means  22 . may, if desired, be connected to heater  18  to control aspects of its operation. Actuating means  22  may comprise one or more manual switches as shown in  FIG. 1 . Those skilled in relevant fields will recognize, however, that other manners of actuating heater  18  may be employed instead and that no controller is required. 
         [0026]    Heater  18  preferably is positionable above mold  14  so as to supply heat only to one side of the mold  14 , which itself may be heated.  FIGS. 2 and 5  show aspects of an exemplary version of mold  14 , which preferably (although not necessarily) is made of aluminum. Alternatively, mold  14  may be of composite type with both male and female components. As illustrated particularly in  FIG. 2 , mold  14  may comprise a generally planar upper surface  26  from which one or more plugs  30  protrude. In use of apparatus  10 , plugs  30  function as three-dimensional objects about which sheets of polymer material are formed. 
         [0027]    Also detailed in  FIGS. 2 and 5  as part of mold  14  are clamps  34  and alignment pins  38 . Clamps  34  surround some or all of perimeter  42  of mold  14  and retain to-be-formed material in place relative to upper surface  26 . Pins  38 , which like plugs  30  extend upward from upper surface  26 , facilitate alignment of the to-be-formed material relative to the plugs  30 . 
         [0028]    An exemplary profile plate or sink  46  appears in  FIG. 3 . Sink  46  may be sized and shaped in any appropriate manner and may of any suitable heat-absorbing (or -reflecting) material. Preferably, however, sink  46  conforms to the shape of the corresponding mold or surface to be heated; as shown in  FIG. 3 , exemplary sink  14  is in the form of a generally rectangular, generally planar aluminum plate. Consistent with the present invention, sink  46  may include one or more cut-outs  50  through its depth, each of which preferably is approximately the size and shape of an associated plug  30 . Sink  46  additionally may include openings  54  for receiving alignment pins  38 . 
         [0029]    Apparatus  10  may be utilized with any thermoformable material. For certain purposes identified herein, however, the material beneficially is polyethylene terephthalate (“PET”), a polymeric plastic resin. Additionally beneficial for various of these purposes is that the PET be transparent. Again, though, the thermoformable material need not necessarily be clear or transparent, nor need it be PET. For ease of handling, the material advantageously may be preformed into a generally planar sheet of predetermined size and shape. 
         [0030]    Among products usefully created using the present inventive techniques are plastic. display holders for coins or souvenirs. Collector-quality versions of such holders may, and indeed typically, include color printing, art work, and text in unformed regions. By contrast, formed regions—into which coins are placed—preferably remain clear so as not to impede viewing of the coins. In some cases the holders may be combined back-to-back or placed within clear housings for further protection of the coins. Objects other than coins or souvenirs may be displayed, and products other than display holders may be created, however, as should be apparent to persons skilled in the art. 
         [0031]    According to at least one method of the present invention, mold  14  may be heated to a preset temperature. The temperature may he selected so as to allow thermoformable material to be formed by the mold  14  and so as to be sufficient to remove heat from the material. Preferably, however, the selected temperature is such that warping or chill marks will not be formed on or in the material. 
         [0032]    After mold  14  is heated adequately, a sheet of material containing undistorted color printing, art work, or text (or combinations thereof) may be laid onto upper surface  26  of mold  14 . For at least some display holders, up to six colors may be printed on each side of the sheet, with opaque material (text and art work) then printed over the printed colors. Of course, any or all of the printed matter may be omitted if not needed in the final product. Nevertheless, when present, the printed matter need not be pre-distorted, as it is not subject to material distortion during the forming process. 
         [0033]    Assuming the above-described coin display holders are to be created, the sheet preferably contains openings through its depth for receiving alignment pins  38 , with the openings themselves positioned so that, when pins  36  are received, unprinted (clear) areas of the sheet are positioned on upper surface  26  atop some or all of plugs  30 . Clamps  34  may be employed to secure the periphery of the sheet against upper surface  26 . Also, sink  46  may be placed atop the sheet, with its openings  54  likewise receiving alignment pins  38  and at least some of its cut-outs  50  aligned with clear areas of the sheet. So placing sink  46  effectively sandwiches the sheet between mold  14  and sink  46 , precluding its longitudinal and lateral movement. 
         [0034]    Illustrated in  FIG. 5  is that one or more tabs  56  may be attached to one or more clamps  34 . Such attachment may utilize bolts  57  or any other suitable fastener or connecting device. If more than one tab  56  is attached to a particular clamp  34 , the tabs  56  preferably are spaced; FIG,  5 , for example, depicts two such tabs  56  spaced along a particular clamp  34 . 
         [0035]    Although tabs  57  may be made of any appropriate material, they preferably are formed of spring steel. After the sheet is in place and sink  46  is positioned atop it, clamps  34  may dose. This closure causes tabs  56  to contact upper surface  59  of sink  46 , with the tabs  56  applying uniform (or substantially uniform) pressure on the perimeter area of sink  46  while assisting the clamps  34  in maintaining sink  46  atop the sheet. Downward pressure supplied by tabs  56  helps ensure sink  46  maintains complete contact with the sheet during forming. Tabs  56  additionally aid in preventing sink  46  from warping or bowing by holding it flat. 
         [0036]    Following placement of the sheet relative to mold  14 , heater  18  is repositioned closely above sink  46  and activated for a selected period of time. Continuing with the display holder example, heater  18  may be activated for approximately thirty seconds, Heat or other energy from heater  18  transfers to sink  46  and, where cut-outs  50  in sink  46  exist, to (clear) areas of the sheet therewith aligned, where it is absorbed by the polymeric, material. 
         [0037]    As the exposed areas of the sheet absorb sufficient heat to reach their forming temperatures, mold  14  is evacuated so as to stretch (form) the material around plugs  30 . Heater  18  then may be repositioned away from mold  14 , the formed sheet of material may be allowed to cool, and sink  46  may be removed so as to expose the sheet of material.  FIG. 4  illustrates material  58  in this exposed state, with the material  58  including (in this example) both unformed portions  62  and formed portions  66 . The sheet of material  58  thereafter may be removed from mold  14  and, if appropriate, divided into display holders. Moreover, because only the periphery of material  58  was clamped during the forming process and need be trimmed, the vast remaining majority of the material  58  was available to create products. The processes of the invention may be repeated for any number of sheets of material. 
         [0038]    The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of the present invention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of the invention.