Abstract:
A thermoforming machine is provided having a frame, a first platen, a second platen, a platen load shaft, and a load shaft latch. The first platen supports a first mold. The second platen supports a complementary second mold and is carried by the frame for movement toward and away from the first platen to engage and disengage with the first mold. The platen load shaft has a lock ledge with an engagement surface transverse to the load shaft. The load shaft is supported by the frame and extends between the first platen and the second platen. The load shaft latch has an engagement surface transverse to a central axis of the load shaft and is movable to engage and disengage the lock ledge transverse engagement surface. A method is also provided.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application Ser. No. 61/559,231 which was filed on Nov. 14, 2011, the entirety of which is incorporated by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure pertains generally to thermoforming apparatus. More particularly, this disclosure relates to lock or latch mechanisms for securing together opposed platens and dies when male dies are received into respective female mold cavities as pneumatic pressure is applied on a male mold side of a heated thermoformable sheeting during an article forming operation. 
       BACKGROUND OF THE INVENTION 
       [0003]    The use of large tonnage thermoforming frames and drive mechanisms is known where pneumatic pressure is being applied to a heated sheet of thermoformable material during an article forming operation. Where large arrays of articles are provided on die plates on a platen, the surface area subject to pneumatic pressure generates very large loads on the kinematic drive linkages and frame of a thermoforming machine. Improvements are needed in order to enable very large loads without requiring further increases in the size and strength of traditional frames and linkages of a thermoforming machine, particularly when forming newer plastic sheet materials that require greater forming pressures and loads. 
       SUMMARY OF THE INVENTION 
       [0004]    A thermoforming machine is provided with a platen lock mechanism that reduces a need to further increase structural load capacity of a frame and plate drive linkages on a thermoforming machine. The platen lock mechanism provides structural support to the thermoforming machine capable of handling increased thermoforming pressures on the thermoforming machine during a thermoforming operation. 
         [0005]    According to one aspect, a thermoforming machine is provided having a frame, a first platen, a second platen, a platen load shaft, and a load shaft latch. The first platen supports a first mold. The second platen supports a complementary second mold and is carried by the frame for movement toward and away from the first platen to engage and disengage with the first mold. The platen load shaft has a lock ledge with an engagement surface transverse to the load shaft. The load shaft is supported by the frame and extends between the first platen and the second platen. The load shaft latch has an engagement surface transverse to a central axis of the load shaft and is movable to engage and disengage the lock ledge transverse engagement surface. 
         [0006]    According to another aspect, a thermoforming machine is provided having a frame, a first platen, a second platen, a first die, a second die, a cyclical drive mechanism, a thermoforming load lock rod assembly, a manifold, a seal, and a pneumatic pressure source. The first platen is supported by the frame. The second platen is movable to-and-fro relative to the first platen. The first die is supported by the first platen. The second die is supported by the second platen. The cyclical drive mechanism is carried by the frame and is configured to move at least one of the platens to-and-fro relative to another of the platens. The thermoforming load lock rod assembly has a plurality of elongate load shafts and complementary load shaft latches configured to lock the second platen proximate the first platen during a web forming operation. The manifold is provided for receiving forming pressure between a web of material and one of the dies. The seal is provided between the web and the one die. The pneumatic pressure source is provided for delivering forming pressure to one side of heated web of thermoformable material. 
         [0007]    According to yet another aspect, a method is provided for forming articles in a heated thermoformable web. The method includes: providing a heated thermoformable web, a pair of opposed platens each having a respective thermoforming die, a plurality of lock rod assemblies configured to lock together in engaged and sealed relation the dies, and a pneumatic pressure source; engaging together the dies in sealed relation on either side of the web by moving the platens toward one another; securing the platens by locking the plurality of lock rod assemblies to secure together in sealed relation the dies; and applying differential pneumatic pressure across opposite sides of the heated thermoformable web to form articles between the dies. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Preferred embodiments of the disclosure are described below with reference to the following accompanying drawings. 
           [0009]      FIG. 1  is a perspective view from above of a thermoforming machine with a platen lock assembly taken from a drive motor side in accordance with an embodiment. 
           [0010]      FIG. 2  is a perspective view from above of the thermoforming machine of  FIG. 1  taken from a kinematic drive linkage side, and with the die plates removed. 
           [0011]      FIG. 3  is an elevational side view of the thermoforming machine of  FIGS. 1-2  showing the upper and lower platens locked together in a fully closed position (but with the forming dies plates omitted). 
           [0012]      FIG. 4  is a perspective view from below of the thermoforming machine of  FIGS. 1-3  taken from a kinematic drive linkage side. 
           [0013]      FIG. 5  is an elevational side view of the thermoforming machine of  FIG. 3  showing the upper and lower platens unlocked and in a fully open, or separated position (but with the forming dies plates omitted). 
           [0014]      FIG. 6  is a component view from below taken along line  6 - 6  of  FIG. 5  and showing one side of the platen lock assembly. 
           [0015]      FIG. 7  is a component view taken along line  7 - 7  of  FIG. 5  and showing one lock plate assembly and load shaft in an unlocked and separated position corresponding with separation of the upper platen and lower platen. 
           [0016]      FIG. 8  is a vertical sectional component view taken along line  8 - 8  of  FIG. 5  and showing a pair of load shafts and corresponding lock plate in the unlocked and separated position depicted in  FIG. 7 . 
           [0017]      FIG. 9  is a vertical side view of the thermoforming machine of  FIG. 3 , but later in time and showing the upper platen lowered and the lower platen raised to positions that correspond with a position where die plates (not shown) would be fully engaged during a thermoforming operation. 
           [0018]      FIG. 10  is a component view from below taken along line  10 - 10  of  FIG. 9  and showing one side of the platen lock assembly in a locked position. 
           [0019]      FIG. 11  is a component view taken along line  11 - 11  of  FIG. 9  and showing one lock plate assembly and load shaft in a locked position corresponding with movement of the upper platen and lower platen to a position where die plates (not shown) would be fully engaged during a thermoforming operation. 
           [0020]      FIG. 12  is a vertical sectional component view taken along line  12 - 12  of  FIG. 10  and showing a pair of load shafts and corresponding lock plate in the locked and closed (die) position depicted in  FIG. 9 . 
           [0021]      FIG. 13  is a vertical side view of the thermoforming machine taken on an opposite side of the view in  FIG. 3  and corresponding with the same time and showing the upper platen lowered and the lower platen raised to positions that correspond with a position where die plates (not shown) would be fully engaged during a thermoforming operation. 
           [0022]      FIG. 14  is a vertical sectional view taken along line  14 - 14  of  FIG. 13 . 
           [0023]      FIG. 15  is a perspective view from above of the thermoforming machine of  FIG. 1  with upper and lower servo drive motors, gearboxes, and die plates removed. 
           [0024]      FIG. 16  is a fragmentary component perspective view of one corner of lower platen  26  with a respective pair of load shafts and lock plate assembly depicting the load shafts locked with the lock plate assembly corresponding with a closed platen position. 
           [0025]      FIG. 17  is an enlarge perspective view of the encircled region  17  of  FIG. 16  showing the lock plate assembly in a locked position about the pair of load shafts. 
           [0026]      FIG. 18  is a fragmentary component perspective view of one corner of lower platen  26  with a respective pair of load shafts and lock plate assembly corresponding with that shown in  FIG. 16 , depicting the load shafts with the lock plate assembly moving from a fully locked position towards an open position. 
           [0027]      FIG. 19  is an enlarged perspective view of the encircled region  19  of  FIG. 18  further showing the lock plate assembly. 
           [0028]      FIG. 20  is a component perspective view from above of the load shafts and lock plate assembly of  FIGS. 16-19 , but corresponding with the lock plate assembly unlocked from the lock shafts and with the upper platen and lower platen moved apart. 
           [0029]      FIG. 21  is a vertical side view of a portion of the lower platen, load shafts, and lock plate assembly depicted in  FIG. 18  in a fully locked position. 
           [0030]      FIG. 22  is a vertical sectional view taken along line  22 - 22  of  FIG. 21  showing the fully locked position. 
           [0031]      FIG. 23  is a vertical side view of a portion of the lower platen, load shafts, and lock plate assembly depicted in  FIG. 21  in a partially locked position. 
           [0032]      FIG. 24  is a vertical sectional view taken along line  24 - 24  of  FIG. 23  showing the partially locked position. 
           [0033]      FIG. 25  is a vertical side view of a portion of the lower platen, load shafts, and lock plate assembly depicted in  FIG. 21  in an unlocked position. 
           [0034]      FIG. 26  is a vertical sectional view taken along line  24 - 24  of  FIG. 23  showing the unlocked position corresponding with the upper platen raised and the lower platen lowered, as shown in  FIG. 5 . 
           [0035]      FIG. 27  is an exploded component perspective view from above of one lock plate assembly. 
           [0036]      FIG. 28  is an exploded component perspective view from below of the lock plate assembly of  FIG. 27 . 
           [0037]      FIG. 29  is an enlarged centerline sectional view taken from encircled region  29  of  FIG. 26 . 
           [0038]      FIG. 30  is a perspective view from above of an alternate embodiment upper platen and retrofit load shafts usable on a thermoforming machine similar to that depicted in  FIGS. 1-29 . 
           [0039]      FIG. 31  is an exploded and partial phantom view showing one retrofit load shaft of  FIG. 30 . 
           [0040]      FIG. 32  is a partial vertical sectional view of a thermoforming machine with the platen and retrofit load shafts of  FIGS. 30-31  taken through a centerline of the load shafts. 
           [0041]      FIG. 33  is a side elevational view of another alternative embodiment thermoforming machine similar to that depicted in  FIGS. 1-29 , but incorporating the upper platen and retrofit load shafts of  FIGS. 30-32 , and a control system. 
           [0042]      FIG. 34  is a vertical side view of thermoforming machine of  FIG. 33 , but taken from an opposite side. 
           [0043]      FIG. 35  is an enlarged partial perspective view of the upper platen and retrofit load shafts on the thermoforming machine of  FIGS. 30-34 . 
           [0044]      FIG. 36  is an enlarged partial side elevation view of the upper platen and retrofit load shafts on the thermoforming machine of  FIGS. 30-34  showing the load shaft splice connectors in partial breakaway. 
           [0045]      FIG. 37  is a simplified perspective view of yet another alternative embodiment thermoforming machine having lobbed stationary load shafts with rotating complementary locking collars for securing together engaged upper and lower die plates during a thermoforming operation. 
           [0046]      FIG. 38  is a perspective view from above in detail of the thermoforming machine of  FIG. 37  showing the upper and lower platens moved apart with the load shafts and locking collars unlocked and separated. 
           [0047]      FIG. 39  is an enlarged view taken from the encircled region  39  of  FIG. 38 . 
           [0048]      FIG. 40  is a perspective view from above in detail of the thermoforming machine of  FIG. 37  showing the upper and lower platens moved together with the load shafts and locking collars locked together in a position where the die plates (not shown) would be engaged together during a thermoforming operation. 
           [0049]      FIG. 41  is an enlarged view taken from the encircled region  41  of  FIG. 40 . 
           [0050]      FIG. 42  is an enlarged view taken in vertical section through the load shafts and corresponding with the view of  FIG. 41 . 
           [0051]      FIG. 43  is a perspective view of yet even another embodiment thermoforming machine having rotating load shafts each with a pair of dog legs, or arms that rotate to lock together the platens during a thermoforming operation and showing the dog legs rotated to a closed, or locked position. 
           [0052]      FIG. 44  is a perspective view of the thermoforming machine of  FIG. 43  showing the dog legs rotated to an open, unlocked position. 
           [0053]      FIG. 45  is a die elevational view of an even further embodiment thermoforming machine showing a hydraulic lock system for locking and releasing upper and lower platens. 
           [0054]      FIG. 46  is a vertical sectional view of the hydraulic lock system of  FIG. 45  taken along line  46 - 46  of  FIG. 45 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0055]    This disclosure is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts” (Article 1, Section 8). 
         [0056]    Attention is now directed towards embodiments of the device.  FIGS. 1 and 2  are left and right perspective views illustrating a thermoforming machine  10  with a platen lock assembly  12  in accordance with an embodiment. More particularly, thermoforming machine  10  includes a structural frame  18 , stationary die posts  20  and  22  supported by frame  18 , an upper platen  24 , and a lower platen  26 . Upper platen  24  and lower platen  26  are supported for vertical reciprocation via pairs of respective bronze bushings  28 ,  29  and  30 ,  31 , respectively. A kinematic drive linkage drives upper platen  24  and lower platen  23  using upper kinematic linkage assembly  34  and lower kinematic linkage assembly  36 , respectively, each driven by a respective servo motor  38  and  40  (see  FIG. 1 ) via gearboxes  39  and  41 , respectively. A third motion platen, or assist platen  16  is supported for movement relative to lower platen  26  by bushings that slide over respective die posts. 
         [0057]    A set of platen load shafts  48 - 51  and  52 - 55  are provided on either side of mold plates  44  and  46 , extending between upper platen  24  and lower platen  26 . More particularly, platen lock assembly  12  comprises set of shafts  48 - 51  attached to platen  24  along a top end and lock plate assemblies  70  and  71  (see  FIG. 9 ), as well as set of shafts  52 - 55  attached to platen  24  along a top end and lock plate assemblies  72  and  73  (see  FIG. 13 ). A top end of each shaft  48 - 55  is mounted in vertically adjustable relation relative to top platen  24  with an adjustable rod end assembly  14 , thereby enabling adjustment of each shaft when locked to lock plate assemblies  70 - 73  to obtain uniform engagement and fit-up between contact surfaces (and seal) between upper die plate  44  and lower die plate  46  when brought together and locked via platens  24  and  26 . 
         [0058]    As shown in  FIG. 2 , third motion platen  27  of plug assist drive assembly  16  is carried for reciprocating movement relative to lower platen  26  on an array of drive shafts (not shown). 
         [0059]    As shown in  FIG. 1 , upper kinematic linkage assembly  34  and lower kinematic linkage assembly  35  cooperate to drive upper and lower platens  32  and  34 , respectively. Respective modern rotary electric servo drive motors  38  and  40  (see  FIG. 2 ) independently drive linkages  34  and  36  via gearboxes  39  and  41  to reciprocate platens  24  and  26  respectively. Such motors are driven by a computer control system, as is presently understood in the art. Other kinematic linkages and drive motor arrangements can be used in the alternative. 
         [0060]    More particularly, kinematic linkages  34  and  36  of  FIG. 3  each comprise drive linkages that are formed from a pair of top and bottom crank arm assemblies, respectively. Each assembly is formed from a crank arm linkage and a four-bar linkage. The crank arm linkage drives the four-bar linkage in an oscillating motion. Each kinematic linkage  34  and  36  is driven via servo motor  38  and  40  and respective gearbox  39  and  41  through a rotary cross shaft  56  and  58 , respectively. Each platen  24  and  26  is driven by kinematic linkage  34  and  36 , respectively, in substantially non-rotating linear, vertical motion. Guide posts  20  and  22  further limit such motion to vertical reciprocating motion. This vertical reciprocating motion causes coacting engagement of female cavities, or female dies  45  in an upper die plate  44  mounted on the upper platen  24  with mating male dies or plugs  47  in a lower die plate  46  mounted on the lower platen  26  on opposed sides of thermoformable web, or sheet  21  (see  FIG. 1 ). 
         [0061]    More particularly, each drive system, including the motor and associated drive controller, forms the motor of an associated rotary press. This rotary press attaches to a rotating crank arm assembly that moves the associated four-bar linkage. The linkage causes the attached platen to move up and down in response to rotation of the drive. Accordingly, a single revolution of shafts  56  and  58  caused by drive motors  38  and  40  and gearboxes  39  and  41  will produce a corresponding complete press cycle of both the upper and lower platens  24  and  26 , respectively. Hence, a complete cycle of each drive will return the press to a starting, or closed position. For example, when lower drive motor  40  is at an initial rotated position of zero degrees, the lower platen  26  is closed, or upwardly raised against the thermoformable sheet, or web. Similarly, when lower driven motor  40  is rotated to 180 degrees, the lower platen  26  is lowered, or completely opened. Likewise, the same holds true for upper drive motor  38  and upper platen  24 . 
         [0062]    A control system is configured to move upper platen  24 , lower platen  26 , and third motion, or plug assist platen  27  via respective servo motors, such as servo motors  38 ,  40 . According to one construction, upper platen  24  and lower platen  26  are each drive platens, and plug assist platen  27  is also a moving platen. The control system includes a controller comprising processing circuitry and memory configured to precisely regulate motion of platens  24 ,  26  and  27  in desired, timed synchronization such that individual plugs, or male dies  47  are driven upwardly with a greater combination of speed and force than would be capable by merely moving platens  24  and  26  together. In operation, platens  24  and  26  are driven together into a heated web of thermoformable material that is captured between upper platen  24  and lower platen  26  during a thermoforming operation. A seal  65  is provided around each male plug  47 , while a vacuum is applied to the bottom of mold plate  44  (top of the thermoformable web) via a vacuum source through vacuum ports  69 , and pneumatic form pressure is applied along the top of mold plate  46  (bottom of the thermoformable web) to help form the web. However, this generates considerable loads, which are countered by using platen lock assembly  12 . For the case of some mold designs, an entire periphery along top surface of mold plate  46  is encircled by a seal, which generates considerable loads when vacuum and pressure are applied to respective top and bottom surfaces of a thermoformable web, or sheet  21 . Third motion platen  27  is subsequently moved upwardly relative to moving platen  26  so as to cause forming of a thermoformed article in a heated plastic web between each individual pair of complementary male plugs  47  and female die cavities  45 , while platen lock assembly  12  is locked. As shown in  FIG. 1 , numerous rows of complementary, interacting male plugs  47  and female die cavities  45  are provided in die plates  46  and  44  affixed to respective platens  26  and  24 , respectively. Subsequently, platens  24 ,  26  and  27  are withdrawn, or retracted apart in order to start the cycle all over again, and third motion platen  27  is lowered relative to lower platen  26 . The cyclical process is then repeated. 
         [0063]    Preferably, a modern rotary electric servo drive motor, or actuating device, is used for drive motors  15  and  17  (see  FIG. 2 ). Such a drive includes an AC servo motor and an associated servo drive motor controller. For example, one suitable AC motor is sold by Siemens AG, Automation Group, Automation Systems for Machine Tools, Robots and Special-Purpose Machines, P.O. Box 31 AD, D-91050, Erlangen, Federal Republic of Germany. Additionally, one suitable servo drive motor controller is sold by Siemens as an analog feed drive system including the SIMO DRIVE 611-A Transistor PWM Inverters and Motors for AC FV Drives. Such a drive will provide a predictable motor device that can very accurately position a machine element to a desired position at a given time. Accordingly, the associated servo motor is a brushless servo motor. Using suitable control software, activation of associated machine components can also be triggered based on velocity or position of a drive, by using a velocity profile or an integrated displacement of the drive. Furthermore, one suitable servo drive motor used for servo drive motor  58  is also a Siemens AC servo motor, model number 1FT5132-OSC71-1-ZH27, also available from Siemens AG. Automation Group, Automation Systems for Machine Tools, Robots and Special-Purpose Machines, P.O. Box 31 AD, D-91050, Erlangen, Federal Republic of Germany. 
         [0064]    As shown in  FIG. 2 , plug assist drive assembly  12  reciprocates third motion platen  36  up and down relative to lower platen  34 . Platen  36  is guided for axial reciprocation by a rectangular array of bronze bushings  28 - 31 , each contained within a housing, that are slidably received over respective cylindrical die posts  24 - 27  mounted rigidly to lower platen  34 . Optionally, plug assist drive assembly can be mounted to upper platen  32 , with the third motion platen being driven in a downward direction while the upper platen is being driven downwardly. Further optionally, a third motion platen can be mounted to a stationary platen, when an opposing platen is moved to and fro. Further optionally, a third motion platen can be mounted for horizontal movement relative to a moving platen from a pair of opposed moving platens that move together and apart along a horizontal direction. Finally, a third motion platen can be affixed to any one of a pair of platens that move together and apart along a contact plane in any angular orientation. 
         [0065]    As shown in  FIGS. 3-4 , a servo motor  60  drives a cross shaft  61  via a gearbox  62 , using a connecting rod  64  that is eccentrically mounted onto each end of cross shaft  61  to drive a respective drive bar  74  and  75  (see  FIG. 5 ) to-and-fro so as to lock and unlock platen lock assembly  12 . Accordingly, load shafts  48 - 55  of  FIG. 3  lock together platens  24  and  26  while vacuum and pressure are respectively applied to top and bottom surfaces of a thermoformable web presented between respective mold plates (see  FIG. 1 ). A pneumatic cylinder  43  is pressurized so as to counterbalance gravitational pull on lower platen  26 . 
         [0066]      FIG. 5  illustrates platens  24  and  26  is a fully open state via positioning of kinematic linkages  34  and  36 , with lock plate assemblies  70 - 73  of platen lock assembly  12  placed in an unlocked position via servo motor  60 , shaft  61 , gearbox  62 , rods  64  and drive bars  74  and  75 .  FIG. 6  further illustrates the open, or unlocked position between load shafts  48 - 51  relative to lock plate assemblies  70  and  71 . Likewise,  FIG. 7  further illustrates the position of load shaft  51  relative to lock plate assembly  71  when unlocked with the platens opened (or moved apart), and showing reduced diameter portion, or lock ledge  66  having a horizontal engagement surface, or circumferential shelf  68 . Furthermore,  FIG. 8  shows load shafts  50  and  51  in the unlocked and open position relative to lock plate assembly  71 , with lock ledges  66  raised relative to lock plate assembly  71 . 
         [0067]      FIGS. 9 and 15  illustrate thermoforming machine  10  on opposite sides, with  FIG. 13  showing the configuration of servo motors  38  and  40  with respective gearboxes  39  and  41 . An eccentric mount on each end of shaft  61  is positioned to place drive bars  74  and  75  in forward positions, locking each lock plate assembly  70 - 73  onto each respective load shaft  48 - 55 . In such locked configuration, load shafts  48 - 55  counter forming pressures imparted when applying vacuum and pressure to top and bottom surfaces of a thermoforming web during an article forming operation. 
         [0068]      FIG. 10  depicts lock plate assemblies  70  and  71  in a locked position on load shafts  48 - 49  and  50 - 51 , respectively.  FIG. 11  further illustrates load shaft  51  secured by lock plate assembly  71  along lock ledge  66 . Finally,  FIG. 12  illustrates load shafts  50  and  51  locked by lock plate assembly  71  while platens  24  and  26  are held in a closed position corresponding with respective mold plates (not shown) being urged together in sealed relationship. 
         [0069]      FIGS. 13 and 14  further illustrate platen lock assembly  12  of thermoforming machine  10  in a locked, or closed position.  FIG. 14  depicts third motion plug assist drive assembly  16  in a retracted position, corresponding with male plugs retracted before they are extended into a web during a forming operation. 
         [0070]      FIG. 16  depicts in component view exemplary load shafts  54  and  55  in a locked position relative to lock plate assembly  73 .  FIG. 17  further illustrates the configuration of lock plate assembly  73  is a closed, or locked position relative to lock ledges  66  and circumferential shelves  68  on load shafts  54  and  55 . A pair of apertures, or key slots  80  and  82  each have an elongate, narrow portion and an enlarged clearance portion. The narrowed portion locks onto ledges  66 . 
         [0071]    As shown in FIGS.  16  and  27 - 28 , lock plate assembly  73  comprises a stationary beveled clearance plate  76  and a movable beveled key plate  78 . Plates  76  and  78  each have top and bottom surfaces that are beveled at 2 degrees such that motion of plate  78  relative to plate  76  increases and decreases total thickness of lock plate assembly  73 . When locked, the total thickness increases. The ability to adjust thickness ensures that proper sealing occurs between the top and bottom mold plates when pressed together while applying vacuum and pressure. Threaded fasteners  90  secure plate  76  to platen  26  (see  FIG. 18 ), while threaded fasteners  94  secure retainer plates  84  and  86  onto plate  76  (see  FIG. 17 ). Finally, threaded fasteners  92  secure drive bar  75  onto plate  78 . A pair of parallel elongate grooves  88  provide a sliding surface along plates  84  and  86 , facilitating sliding to-and-fro of plate  78  relative to stationary plate  76  when locking and unlocking lock plate assembly  73  relative to load shafts  54  and  55 . 
         [0072]      FIG. 19  illustrates lock plate assembly  73  being moved towards an open position, decreasing thickness of assembly  73  while plate  78  slides relative to stationary plate  76 . 
         [0073]      FIG. 20  further illustrates lock ledges  66  and circumferential shelves  68  on load shafts  54  and  55 , as viewed from above which respective platens are pulled apart and lock plate assembly  73  is open. 
         [0074]      FIGS. 21 and 22  illustrate load shafts  54  and  55  when locked onto platen  26  via lock plate assembly  73 . Plate  78  is shown in a translated position that thickens lock plate assembly  73  by sliding the respective beveled surfaces between plates  76  and  78 . 
         [0075]    In contrast,  FIGS. 23 and 24  illustrate load lock plate assembly  73  in an open configuration corresponding with plate  78  being slide relative to plate  76  so as to reduce thickness of lock plate assembly  73  and open assembly  73  so that shafts  54  and  55  can subsequently be raised. 
         [0076]      FIGS. 25 and 26  show load shafts  48  raised while lock plate assembly  73  is held open. 
         [0077]      FIG. 29  illustrates in centerline sectional view an exemplary load shaft  54 . According to one construction, load shafts  25  and  26  are made of 4340 steel heat treated to 45 RC. Furthermore, slider plates  76  and  78  (see  FIG. 27 ) are made of 8620 case hardened steel at a 0.03 minimum depth to 58 RC. 
         [0078]      FIG. 30  is a perspective view from above of an alternate embodiment upper platen  130  and retrofit load shafts  148 - 155  usable on a thermoforming machine  124  similar to that depicted in  FIGS. 1-29 . Each shaft, such as shaft  148 , is configured in multiple pieces  189  and  193  with are joined together via a clamp collar assembly using threaded fasteners  199 . 
         [0079]      FIG. 31  is an exploded and partial phantom view showing one retrofit load shaft  148  of  FIG. 30 . More particularly, upper portion  189  and lower portion  193  of shaft  148  each have an array of annular ridges  183  and recesses  185  that interlock in assembly with complementary recesses  181  and ridges  179  (see  FIG. 36 ) within collar  191 . Splice collar  191  comprises a pair of semi-cylindrical shells  197  and  198  that are joined together over fastening ends  195  and  196  by receiving threaded fasteners  199  through bores in shell  198  into complementary threaded bores in shell  197 . Shaft  148  extends between upper platen  124  and lower platen  126  and is operative to lock together such platens in a manner previously described with respect to the embodiment depicted in  FIGS. 1-29 . 
         [0080]      FIG. 32  is a partial vertical sectional view of a thermoforming machine  110  with the platen and retrofit load shafts of  FIGS. 30-31  taken through a centerline of the load shafts. Splicing collars  191  are shown joining together shaft sections  189  and  193 , in assembly. 
         [0081]      FIG. 33  is a side elevational view of another alternative embodiment thermoforming machine similar to that depicted in  FIGS. 1-29 , but incorporating the upper platen and retrofit load shafts of  FIGS. 30-32 , and a control system. A control system  101  having processing circuitry  103 , memory  105 , a user interface  107 , and a control algorithm  109  control servo motors  138 ,  140  and  160 , and receive signals from position sensors  111 ,  113  and  115  to verify position of respective gearboxes  139 ,  141  and  162 , respectively. 
         [0082]      FIG. 34  is a vertical side view of thermoforming machine of  FIG. 33 , but taken from an opposite side. 
         [0083]      FIG. 35  is an enlarged partial perspective view of the upper platen and retrofit load shafts on the thermoforming machine of  FIGS. 30-34 . Splice collars  191  facilitate assembly of load shafts  151  on a thermoforming machine with having to totally disassemble the machine. Hence, a thermoforming machine can be retrofit with load shafts  151  by using splice collars  191 . 
         [0084]      FIG. 36  is an enlarged partial side elevation view of the upper platen and retrofit load shafts on the thermoforming machine of  FIGS. 30-34  showing the load shaft splice connectors, or collars  191  in partial breakaway. Complementary ridges  179  and recesses  181  are shown along an inner diameter of each splice collar  191 . 
         [0085]      FIG. 37  is a simplified perspective view of yet another alternative embodiment thermoforming machine  210  having lobbed stationary load shafts  248  with rotating complementary locking collars  266  for securing together engaged upper and lower platens  224  and  226 , respectively, and associated die plates (not shown) during a thermoforming operation. Servo motors  260  drive a common kinematic linkage  264  to rotate collars  45  degrees between locked and unlocked positions. 
         [0086]      FIG. 38  is a perspective view from above in detail of the thermoforming machine  210  of  FIG. 37  showing the upper and lower platens  224  and  226  moved apart with the load shafts  248 ,  249  and  252 ,  253  and locking collars  266  unlocked and separated. An array or radially outwardly extending engagement lobes  270  are integrally formed in each load shaft, configured to lock and unlock with a complementary respective array of lobes extending in a radially inward direction within each collar  266 . 
         [0087]      FIG. 39  is an enlarged view taken from the encircled region  39  of  FIG. 38  further showing collars  266  unlocked from respective radial arrays of engagement lobes on each load shaft  248  and  249 . 
         [0088]      FIG. 40  is a perspective view from above in detail of the thermoforming machine of  FIG. 37  showing the upper and lower platens  224  and  226  moved together with the load shafts  248  and  249  and locking collars  266  rotated 45 degrees and locked together in a position where the die plates (not shown) would be engaged together during a thermoforming operation. 
         [0089]      FIG. 41  is an enlarged view taken from the encircled region  41  of  FIG. 40  further showing each collar rotated into a locked position with each load shaft. 
         [0090]      FIG. 42  is an enlarged view taken in vertical section through the load shafts and corresponding with the view of  FIG. 41 . Top platen  224  supports load shafts  248  and  249 . Rotated collars  266  lock onto each load shaft so as to lock together (under load) platens  224  and  226 . 
         [0091]      FIG. 43  is a perspective view of yet even another embodiment thermoforming machine  310  having rotating load shafts  348  and  349  each with a pair of dog legs, or arms  366  and  367  that rotate to lock together the platens  324  and  326  during a thermoforming operation and showing the dog legs  366  and  367  rotated to a closed, or locked position. 
         [0092]      FIG. 44  is a perspective view of the thermoforming machine of  FIG. 43  showing the dog legs  366  and  367  rotated to an open, unlocked position. In this mode, platens  324  and  326  can be moved apart. 
         [0093]      FIG. 45  is a side elevation view of an even further embodiment thermoforming machine  410  showing a hydraulic lock system for locking and releasing upper and lower platens. More particularly, top platen  424  and lower platen  426  are moved together and apart using pairs of hydraulic pistons  470 .  471  and  472 ,  473  along shafts  448  and  450 . 
         [0094]      FIG. 46  is a vertical sectional view of the hydraulic lock system of  FIG. 45  taken along line  46 - 46  of  FIG. 45 . A stationary piston  474  is affixed to a respective shaft  448 - 451 . A hydraulic cylinder  470 - 473  is formed about each piston  474 . Movement of fluid between chambers above and below each fixed piston will move the respective platen  424  and  426  up and down. By closing a valve and stopping fluid flow, each platen  424  and  426  can be locked into a position, such as a closed position. 
         [0095]    In compliance with the statute, embodiments of the invention have been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the entire invention is not limited to the specific features and/or embodiments shown and/or described, since the disclosed embodiments comprise forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.