Abstract:
A thermoforming trim press is provided with a frame, a punch plate, a die plate, and a bushing. The frame has a guide post including a tapered outer surface with increasing cross-sectional dimension toward a closing position. The punch plate has a male cutting die. The die plate has a female cutting die configured to scissor in intermeshing relation with the male cutting die. The bushing has a tapered inner surface complementary and reverse to the tapered outer surface of the guide post. The bushing is adjustable in cross-sectional dimension and is configured to guide one of the punch plate and the die plate for axial reciprocation along the guide post. A method is also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This patent application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/543,456, filed Feb. 9, 2004, entitled “Adjustable Thermoforming Trim Press Alignment System and Structure”, naming as inventor Jere F. Irwin., and which is incorporated by reference herein. 

   TECHNICAL FIELD 
   This invention pertains to apparatus and methods for severing thermoformed plastic articles from a sheet of plastic thermoformable material. More particularly, the present invention relates to platen posts, tool die posts and bushing assemblies for a thermoforming trim press. 
   BACKGROUND OF THE INVENTION 
   When severing thermoformed articles from a web of plastic material, there exists a need to ensure accurate coaction between male and female cutting dies in order to ensure accurate part removal, as well as to enhance maximum operating speeds of a thermoforming trim press. Accurate tolerancing and tight fit-up between moving components ensures accurate severing of articles so that flanges along a trim edge are uniform and precise. However, small tolerances between sliding parts and accurate fit-up can also result in increased working loads when stroking a trim press platen or die along a die post (or guide post). Accordingly, improvements are needed in the manner in which moving members of a trim press are axially guided and fitted for coaction during a cyclical article severing operation. 
   SUMMARY OF THE INVENTION 
   An improved platen die set and an improved trim tool die set are each provided for a thermoforming trim press with an adjustable bushing assembly. A tapered bushing is mated in complementary relation with a tapered die post for the platen die set as well as the trim tool die set. The taper on each die post decreases in diameter and in an opposite direction that the taper on an inner surface of the bushing increases. Hence, the bushing conforms with the taper on the die post. Adjustable bushing assemblies enable controlled compression of a bronze bushing onto the tapered die posts so that a tight fit-up is presented at the position of maximum stroke corresponding with a position where an article is severed from a web of thermoformed material. As the trim tool dies are moved apart and as the platens are also moved apart, the taper provides a relatively looser fit as the platens and the dies separate, which reduces friction between the moving die and platen, and the respective die post during most of the stroke cycle. However, by adjusting the corresponding bushing assemblies, a snug fit-up is provided between the bushing and the tapered die post at the corresponding positions of maximum displacement which correspond with the position at which an article is being severed. Accordingly, an accurate severing operation is provided while reducing frictional forces during the remaining portions of stroke that occur between the platen and its die post, as well as the male punch plate (or trim tool) and its corresponding die post. 
   According to one aspect, a thermoforming trim press is provided with a frame, a punch plate, a die plate, and a bushing. The frame has a guide post including a tapered outer surface with increasing cross-sectional dimension toward a closing position. The punch plate has a male cutting die. The die plate has a female cutting die configured to scissor in intermeshing relation with the male cutting die. The bushing has a tapered inner surface complementary and reverse to the tapered outer surface of the guide post. The bushing is adjustable in cross-sectional dimension and is configured to guide one of the punch plate and the die plate for axial reciprocation along the guide post. 
   According to another aspect, a trim tool guide assembly is provided for a thermoforming trim press. The trim tool guide assembly includes a guide post and a bushing assembly. The guide post has a forward-tapered outer circumferential dimension. The bushing assembly has a bushing with a reverse-tapered inner circumferential dimension and an adjustable support collar for retaining the bushing assembly and adjusting the inner circumferential dimension of the bushing relative to the outer circumferential dimension of the guide post. 
   According to yet another aspect, a method is provided for accurately severing an article from a web of thermoformed material using a thermoforming trim press. The method includes: providing a trim press with a guide post having a tapered outer surface that increases in cross-sectional dimension toward a closing position, a punch plate with a male cutting die, a die plate with a female cutting die configured to scissor with the male cutting die, and a bushing adjustable in cross-sectional dimension and having a tapered inner surface complementary and reverse to the tapered outer surface of the guide post; positioning the male cutting die in intermeshing relation with the female cutting die proximate the closing position; and concurrent with positioning, adjusting cross-sectional dimension of the bushing to realize a desired accurate fit-up between the bushing and the guide post. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention are described below with reference to the following accompanying drawings. 
       FIG. 1  is a simplified schematic perspective view of a machine trim press having alignment and guide features in accordance with the preferred embodiment of the invention. 
       FIG. 2  is a vertical side view of the trim press of  FIG. 1  and illustrates alignment features on a machine platen die post and a trim tool die post. 
       FIG. 3  is an end view for an alignment structure on a machine platen die post. 
       FIG. 4  is a centerline sectional view of the alignment structure for the machine platen die post of  FIG. 3  taken along line  4 — 4  of  FIG. 3 . 
       FIG. 5  is an end view of the alignment structure for use with the trim tool die posts of  FIGS. 1–4 . 
       FIG. 6  is a vertical centerline sectional view of the one alternative construction alignment structure of  FIG. 5  taken along lines  6 — 6  of  FIG. 5 . 
       FIG. 7  is a partial exploded perspective view of the one alternative construction alignment structure of  FIGS. 5–6  for use with the trim tool die posts. 
       FIG. 8  is a plan view of the trim tool die assembly used within the trim press and corresponding with the end view of the alignment structure for the trim tool die post of  FIGS. 5–7 . 
       FIG. 9  is a side view of the trim tool die assembly of  FIG. 8 . 
       FIG. 10  is a cross-sectional view of the trim tool die assembly taken along line  10 — 10  of  FIG. 8 . 
       FIG. 11  is a vertical sectional view taken along line  11 — 11  of  FIG. 8  illustrating configuration of the male and female cutting die components. 
       FIG. 12  is an isometric view of the trim tool die assembly of  FIGS. 8 and 9 . 
       FIG. 13  is an isometric view corresponding with the view taken in  FIG. 12  of the trim tool die assembly, but illustrating separation between the male and female die members. 
       FIG. 14  is a vertical centerline sectional view of the bronze bushing used within the alignment structure of  FIGS. 5–14 . 
       FIG. 15  is an enlarged view of the bronze bushing from the encircled region  15  of  FIG. 14 . 
       FIG. 16  is an end view of an alternative construction for an alignment structure for a trim tool die post corresponding with the view taken in  FIG. 5 . 
       FIG. 17  is a vertical centerline sectional view of the alternative construction for an alignment structure of  FIG. 16 , corresponding with the view taken in  FIG. 6 . 
       FIG. 18  is a partial exploded perspective view of the alternative construction for an alignment structure of  FIGS. 16–17 , corresponding with the view depicted in  FIG. 7 . 
       FIG. 19  is a simplified perspective view of a second alternative construction for an alignment structure for a trim tool die post over the two embodiments depicted in  FIGS. 1–18 . 
       FIG. 20  is a sectional view taken along lines  20 — 20  of  FIG. 19  and illustrating the alternative construction for the alignment structure of  FIG. 19 . 
       FIG. 21  is a simplified, partial exploded perspective view of the alternative construction for an alignment structure of  FIGS. 19–20 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   This disclosure of the invention 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). 
   A preferred embodiment of an improved machine trim press is generally designated with reference numeral  10  in  FIG. 1 . Trim press  10  includes a frame  12  that supports a moving platen  14  and a stationary platen  16 . A trim tool assembly  18  is mounted between moving platen  14  and stationary platen  16 . 
   Frame  12  includes a base  20  comprising a ballast tank in which ballast material is placed to stabilize frame  12  while trim press  10  is cycled in operation. For example, gravel can be placed inside base  20 . 
   It is understood that trim press  10  is shown in simplified form in order to prevent obscuring the invention at hand. More particularly, trim press  10  comprises one of a number of thermoforming trim press constructions. One exemplary construction is disclosed in U.S. Pat. No. 6,067,886, herein incorporated by reference, having counterbalanced crank arm assemblies configured to drive a moving platen in reciprocation. The commercial version of this trim press is available from Irwin Research and Development, of Yakima, Wash., Model No. 44 Vertical Trim Station (VTS). Such a trim press supports moving platen  14  on a pair of die posts, such as die posts  26  and  28 , with four counterbalanced crank arm assemblies. Hence, four counterbalanced kinematic linkages (not shown) drive each corner of moving platen  14  within frame  12 . Details of the kinematic linkages that oscillate platen  14  along die posts  26  and  28  are not shown in  FIGS. 1 and 2  in order to simplify the drawings and not obscure the invention at hand. However, any of a number of techniques presently known in the field for driving a moving platen to and fro can be utilized to drive trim press  10  and can benefit from the improvements presented by the present invention. 
   A pair of adjustable platen die sets  22  and  24  provide for adjustable sliding fit-up and engagement of moving platen  14  relative to die posts  26  and  28 . More particularly, die posts  26  and  28  are tapered such that each die post has a larger diameter when platen  14  is moved into engagement with stationary platen  16  during a severing operation. According to one construction, each die post  26  and  28  decreases in diameter by 1.5/1000ths of an inch for each inch of length along the respective posts  26  and  28 . Accordingly, fit-up in the platen die sets  22  and  24  increases the snugness therebetween as the platen  14  is moved into engagement with platen  16 . As platen  16  moves away from platen  14 , fit-up loosens, which provides for less friction when moving platen  14 . However, the taper in die posts  26  and  28  ensures that there exists accurate and tight fit-up between the platen die sets  22  and  24  as platens  14  and  16  come together during a severing operation. It is during the severing operation (closest positioning between the platens) that precise fit-up is most needed in order to maintain accurate severing of articles from a web of thermoformable material (not shown). 
   In operation, trim press  10  receives a web of thermoformable plastic material in which an array of cups has been previously formed within a thermoforming machine (not shown). The web is intermittently fed between moving platen  14  and stationary platen  16  by a conveyor (not shown) which intermittently progresses the web through a molding machine where articles are formed in the web, and into position between trim press platens  14  and  16  where the articles are severed from the web. Trim tool assembly  18  includes male and female cutting members in respective punch plates  34  and die plates  36  that coact to sever articles from the web. 
   Each platen die set  22  and  24  includes an adjustable bushing assembly  30  and  32 , respectively. Adjustable bushing assemblies  30  and  32  can be tightened to ensure that each bushing assembly  30  and  32  remains tight about tapered die posts  26  and  28  when moving platen  14  is positioned at a fully extended position towards stationary platen  16 . Accordingly, as bushings within bushing assemblies  30  and  32  wear, the bushings can be tightened by adjusting bushing assembly  30  and  32  in order to maintain accurate alignment along tapered die posts  26  and  28 . 
   Trim tool assembly  18  includes a plurality of punches that are provided within a male punch plate  34  and a plurality of dies provided within a female die plate  36 . Male punch plate  34  is rigidly affixed to moving platen  14 , whereas female die plate  36  is rigidly affixed to stationary platen  16 . Accordingly, male punch plate  34  moves in reciprocation with moving platen  14  by way of kinematic linkages (not shown) that drive moving platen  14  to and fro along tapered die posts  26  and  28 . Additionally, a pair of trim tool die sets  38  and  40  provide for alignment between male punch plate  34  and female die plate  36 . Trim tool die sets  38  and  40  are somewhat similar in construction to platen die sets  22  and  24 . The adjustable bushing assemblies  30 ,  32  and  46 ,  48  are likewise similar in operation and set-up. 
   Trim tool die sets  38  and  40  each have a tapered trim tool die post  42  and  44 , respectively. Each trim tool die post increases in diameter as the male punch plate and the female die plate are brought together, and taper in decreasing diameter as the male punch plate  34  and female die plate  36  are brought apart. Preferably, respective trim tool die posts  42  and  44  are tapered to decrease in diameter by 15/1000ths of an inch for each axial inch of length along posts  32  and  34 . Other alternative constructions are also possible. An adjustable bushing assembly  46  and  48  has a complementary internal surface taper that substantially complements the taper on posts  42  and  44 . 
   As shown in  FIGS. 1 and 2 , a pair of accessory guideposts  50  and  52  are also provided along moving platen  14 . However, moving platen  14  does not mount onto guideposts  50  and  52 . Instead, guideposts  50  and  52  serve to provide axial guide ways for accessory devices, such as a treadle or a part handling machine (not shown) that is associated with the trim press. 
     FIG. 3  illustrates an outer, left end view of stationary platen  16  coincident with tapered platen die post  26 . 
     FIG. 4  illustrates a vertical sectional view of the construction of platen die set  22 . Platen die set  24  is similarly constructed. Platen die set  22  is mounted between stationary platen  16  and moving platen  14 . Die post  26  is tapered to have a larger diameter on the left side and a smaller diameter on the right side. Adjustable bushing assembly  30  is formed from a right half shell  54  and a left half shell  56  that bolt together with a plurality of threaded fasteners  66  in regions that form a pair of clamp rings. Shells  54  and  56  leave a pair of end gaps when assembled together. One shell has clearance bores for the fasteners, while the other shell has a threaded bore that mates with the threaded fastener. A pair of bronze bushings  58  and  60  are provided spaced apart within bushing assembly  30 . Each cylindrical bronze bushing  58  and  60  has an inner surface that is frustoconical and complements (or mates with) the tapered outer surface of tapered platen die post  26 . A pair of cylindrical wicking washers (wool or felt)  62  and  64  are provided adjacent each bronze bushing  58  and  60 , respectively, for holding lubricating oil that is dispensed along die post  26  during reciprocation of bushing assembly  30  therealong. 
     FIG. 5  illustrates a left end view of female die plate  36  and corresponds with the trim tool die set  38 . 
     FIG. 6  illustrates tapered trim tool die post  42  which is rigidly affixed at one end to female die plate  36 . Tapered trim tool die post  42  has a larger diameter adjacent female die plate  36 , and tapers towards a reduced diameter in a direction towards male punch plate  34 . Die post  42  reciprocates within adjustable bushing assembly  46 . 
   Adjustable bushing assembly  46  includes a tapered bushing housing  68  that is affixed to plate  34  via a plurality of cap screw fasteners  70 . Housing  68  includes a tapered male threaded portion  74  that includes a plurality of axial slots  72 . A tapered lock nut  78  is then tightened onto tapered male threaded portion  74  via tapered female threads  76  of nut  78 . By advancing nut  78  onto thread  74  and towards plate  34 , axial slots  72  accommodate compression on an inner surface of tapered male threaded portion  74  which compresses a bronze bushing  100  onto tapered die post  42 . Bronze bushing  100  has an inner surface that is tapered so as to complement the opposite taper on die post  42 . Bushing  100  can optionally have an axial slot to enhance compression. When plates  34  and  36  are brought to their closest position (during a trim operation), nut  78  is tightened onto thread  74  so as to compress bushing  100  radially about die post  42 . Subsequently, a lock ring  80  is also threaded onto male tapered threaded portion  74  via female threads  82 . Once lock ring  80  is threaded onto threaded portion  74 , a plurality of fasteners  83  are engaged with lock nut  78  so as to lock the positioning of lock nut  78  onto male threaded portion  74 . 
   A cap  84  is mounted onto tapered bushing housing  68  to entrap bronze bushing  100  radially therein via a plurality of threaded fasteners, such as cap screws  86 . 
   Trim tool die post  42  also includes a radially outwardly extending shoulder  88  which engages with female die plate  36  when an end cap  98  is affixed thereto via a plurality of fasteners  96  (such as cap screws). A lubrication feed fitting  94  communicates with an axial lubricating feed port  90 . Feed port  90  communicates with a plurality of radially extending ports  92 . An oil lubrication line is then connected onto feed fitting  94  to deliver lubricating oil (or grease) via ports  90  and  92  to outer surfaces of trim tool die post  42  to lubricate axial sliding movement between an inner surface of bronze bushing  100  and an outer surface of trim tool die post  42 . 
     FIG. 7  illustrates in greater detail the construction of trim tool die set  38 . Punch plate  34  and die plate  36  are shown in simplified form as a rectangle (with remaining portions omitted). Exploded view construction of trim tool die set  38  illustrates the components and assembly of tapered, bronze bushing  100  onto tapered trim tool die post  42 . Tapered bushing housing  68  is affixed onto plate  34  using a plurality of threaded cap screw fasteners  70 . Bronze bushing  100  is entrapped within tapered bushing housing  68  via a cap ring  84  and a plurality of threaded cap screw fasteners  86 . 
     FIG. 8  illustrates in plan view the trim tool assembly  18 .  FIG. 9  illustrates the trim tool assembly  18  in side view.  FIG. 10  illustrates trim tool assembly  18  taken along line  10 — 10  of  FIG. 8 . 
     FIG. 11  illustrates a cross-sectional view of trim tool assembly  18  taken through line  11 — 11  of  FIG. 8  corresponding with a cross-sectional view taken through a punch and die of punch plate  34  and die plate  36 , respectively. 
     FIG. 12  illustrates a perspective view of trim tool assembly  18  when plates  34  and  36  are brought together. More particularly, plates  34  and  36  are temporarily held together with a plurality of cross-members that are removably fastened on opposite ends of plates  34  and  36  to facilitate insertion and removal of trim tool assembly  18  between platens on a trim press. 
     FIG. 13  illustrates trim tool assembly  18  when plates  34  and  36  are at a maximally spaced-apart position during a trim operation. Such positioning corresponds with trim tool die sets  38  and  40  being positioned at the most tapered, or reduced diameter, position on each respective die post  42  and  44 . 
     FIG. 14  illustrates a centerline sectional view of bronze bushing  100 . An outer diameter of bronze bushing  100  is uniform. However, a rightmost inner diameter portion is smaller than the leftmost inner diameter portion of bronze bushing  100 , corresponding with the inner diameter taper provided therein which complements the decreasing taper of the respective die posts extending from a leftmost position (larger diameter) to a rightmost position (smaller diameter). 
     FIG. 15  illustrates an array of circumferential grooves  101  that are provided on an inner surface of bronze bushing  100  to facilitate conveyance and retention of lubricating fluid, or oil, along an inner surface of bronze bushing  100  as bronze bushing  100  axially travels across a respective tapered die post. Optionally, grooves  101  can have a helical shape, or they can be eliminated. 
     FIGS. 16–18  provide an alternative construction for a trim tool die set  38  of  FIGS. 5–7 .  FIG. 16  illustrates a left end view of platen  16 . 
     FIG. 17  illustrates an alternative construction of trim tool die set  138  similar to die set  38  of  FIG. 6 . However, a tapered bushing housing  168  differs in that bushing housing  168  has a longitudinal slot  173  provided in a circumferential body  171  (see  FIG. 18 ). A threaded fastener  175  is used to compress housing  171  by threading fastener  175  into a threaded bore in housing  171  across slot  173  which closes slot  173  and clamps bronze bushing  100  onto tapered die post  142 . 
     FIGS. 19–21  illustrate a second alternative construction for an alignment structure for a trim tool die set  238  similar to die set  138  in  FIG. 17  and die set  38  in  FIG. 6 . More particularly, a tapered bushing housing  268  differs from tapered bushing housing  168  (of  FIG. 17 ) in that bushing housing  268  has a longitudinal slot  273  that is adjusted in thickness (or gap size) by tightening and loosening a pair of threaded cap head screws  275  in order to compress a bronze bushing  200 . By tightening threaded screws (or fasteners)  275 , bushing housing  268  is provided with an aperture that is adjustably reduced in diameter so as to compress bushing  200  by decreasing the thickness of slot  273  in order to clamp bronze bushing  200  onto tapered die post  242 . In response, bushing  200  deforms so as to adjust fit-up with guide post  242 . 
     FIGS. 20 and 21  further illustrate the construction and assembly of bearing  200  within housing  268 . An inner surface of bearing  200  has a tapered inner surface that mates in complementary and opposed relation with a corresponding tapered surface provided on an outer surface portion of tapered die post  242 . Post  242  is affixed onto a female die plate  36  (see  FIG. 19 ) via an end plate  298  using a plurality of threaded cap screws  293 . Housing  268  is affixed onto a male punch plate  34  via a ring backing plate  299  having a radial slot  291  via a plurality of threaded fasteners  297 . Additionally, a plurality of radially spaced-apart threaded fasteners  295  further secure housing  268  onto male punch plate  34 . 
   Although the embodiments depicted in  FIGS. 1–21  illustrate a lubrication system for delivering lubrication between a bearing and a guide post, such as a die post, it is understood that it is not necessary to deliver lubrication therebetween. For example, the bushing and/or the guide rod can be constructed of a relatively low friction material, such as by constructing the bushing from bronze material. 
   In the case where lubrication is used, one preferable lubrication comprises a oil which is delivered through a pressurized oil feed system between each bearing and guide rod. Alternatively, other lubrications can be utilized, such as grease, graphite, or other lubricating medium. 
   According to one construction, the collars or housings for each bushing assembly can be constructed from No. 836 standard steel, and the guide rods are constructed from pre-heat-treated 4130 steel that is induction hardened to approximately 60 Rockwell, and is then covered with a thin, dense chrome outer surface. 
   In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred 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.