Apparatus for making accurate cuts in thermoformed articles

An apparatus for making accurate cuts in thermoformed articles projecting vertically above a generally planar sheet of thermoformable material includes a base plate having a lower surface, at least one pair of knives being mounted to the lower surface of the base plate to depend therefrom and being capable of limited movement, each knife having a cutting portion and a guiding portion, the guiding portion of each knife being angled relative to the longitudinal axis of each knife and being divergent from the adjacent knife. Each pair of knives is disposed on the base plate, and the base plate is disposed relative to the sheet of thermoformable material so that thermoformed articles advanced toward the apparatus will engage the guiding portions of the knives and cause the knives to slidingly contact sides of the articles, and upon lowering the base plate toward the sheet, the cutting portions of the knives are positioned to create score lines in the sheet which are substantially flush with the sides of the articles.

BACKGROUND OF THE INVENTION 
The present invention relates to machines used for die cutting thermoformed 
articles from sheets of thermoformable source material, and specifically 
to a cutting apparatus for making incisions such as cuts or score lines 
which are in alignment with vertical sides of the thermoformed articles. 
In a typical thermoforming operation, a sheet of plastic thermoformable 
material is drawn in a web from a roll to a first station where it is 
heated, and then to a thermoforming die station including a set of 
thermoforming dies. In the operation, the sheet is moved from one station 
to another by a conveyor system including a pair of generally parallel 
chain belts, as are known in the art. 
The die set includes the male member, which has a plurality of vertically 
projecting formations and shapes consisting of the desired final 
configuration of the thermoformed article, and the female member, which is 
basically a "negative" of the male member. The male and female dies are 
moveable in a vertically reciprocable fashion with the plastic sheet 
sandwiched between the two dies. As the dies come together, the heated 
plastic softens and forms around the vertically projecting formations and 
shapes of the male die. The female die assists the formation of the 
plastic about the male die. In some cases, the male die is equipped with a 
vacuum assist and the female die with a pressure assist to more 
effectively draw and shape the plastic about the formations of the male 
die. 
After forming, the male and female dies separate, leaving the sheet with at 
least one thermoformed article. The number of articles formed is 
determined by the number of cavities in the die set. After the forming 
process, the conveyor system is designed to index the sheet as it cools. 
This indexing moves the recently formed articles a specified distance away 
from the die set, and makes room at the die set for the next thermoforming 
cycle, during which a second portion of the sheet of plastic material is 
shaped by the dies. Through indexing, the use of the material is 
maximized. 
After two or three indexes or thermoforming cycles, the first set of molded 
articles reaches a knife or die cutting press station, where specially 
designed knives mounted to depend from an underside of a press block are 
pressed downward upon the sheet. This downward pressing action cuts the 
articles from the sheet. In some cases, instead of cutting the articles, 
the knives are configured to merely score the plastic around the articles, 
to create hinged seams. 
A common problem of such thermoforming operations is that the indexing is 
imprecise, and the knives improperly cut or even damage the thermoformed 
articles, creating wasted material. One attempted solution to this problem 
has been the mounting of the knife to the support block so that the knives 
are movable in a direction parallel to the direction of travel of the 
articles on the thermoforming apparatus. These so-called "floating" knives 
accommodate a certain amount of error in the indexing process, and are 
normally accurate to .+-. 0.030 inches. However, in some thermoformed 
articles, this degree of error is unsatisfactorily high. 
Another measure commonly taken to avoid misalignment of the thermoformed 
articles relative to the knives is to shape the articles to have a drafted 
forward surface which guides the knives to the proper cutting position. 
These measures are satisfactory for most thermoformed articles, but not 
for those articles used in packages where the longitudinal edges of the 
article are not cut by the die press, but instead are merely scored to 
form hinged flaps. Upon scoring, these hinged flaps are folded backward to 
support products carried behind the thermoformed article when the article 
and products are eventually enclosed in a container or box. 
In such packages, the score lines need to be located in substantially flush 
relationship with the corresponding sidewall of the thermoformed article. 
Conventional floating knives have proved incapable of accurately and 
reliably making the required score lines in the thermoformed articles. 
Consequently, it is an object of the present invention to provide an 
apparatus for making accurate cuts in thermoformed articles. 
It is another object of the present invention to provide an apparatus for 
accurately cutting thermoformed articles which accommodates misalignment 
of the thermoformed articles due to inaccurate indexing. 
It is still another object of the present invention to provide an apparatus 
for accurately cutting thermoformed articles which is capable of reliably 
making score lines in the articles which are substantially flush with the 
corresponding sidewall of the article. 
SUMMARY OF THE INVENTION 
Accordingly, the above-identified objects are met or exceeded by the 
present invention, which provides a floating knife type die cutting 
apparatus for cutting or scoring thermoformed articles. The present 
apparatus includes at least one pair of generally parallel knife blades 
which are configured to guide the thermoformed articles for accurate 
cutting. Furthermore, the knife blades are preferably maintained in a 
ready position which is at a height between the upper edge of the 
thermoformed article and the upper surface of the sheet from which the 
articles are formed. 
More specifically, the present invention provides an apparatus for making 
accurate cuts in at least one thermoformed article projecting vertically 
above a generally planar sheet from which the at least one article is 
formed. The apparatus includes a base plate having a lower surface, at 
least one pair of knives being mounted to the lower surface of the base 
plate to depend therefrom, each knife having a cutting portion and a 
guiding portion. Each pair of knives is disposed on the base plate so that 
thermoformed articles advanced with the sheet toward the cutting apparatus 
will engage the guiding portions of the knives and cause the knives to 
slidingly contact sidewalls of the articles. Upon lowering the base plate 
toward the sheet, the cutting portions of the knives are positioned to 
create incisions in the sheet which are substantially flush with the 
sidewalls of the articles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, FIG. 1 illustrates a portion of a 
thermoforming operation, generally designated 10, which includes a 
conveyor 12, such as a pair of endless chain belts, to which a generally 
planar sheet 14 of plastic material is advanced in a direction represented 
by the arrow 16. At the cyclical stage of the thermoforming process 
depicted in FIG. 1, a portion 18 of the sheet 14 has just been advanced 
past a pair of forming dies (not shown) which are located to the right of 
the portion of the operation 10 depicted in FIG. 1. The dies are used to 
create at least one thermoformed article 20 from the sheet 14, so that the 
article projects vertically from the sheet. In FIG. 1, two such articles 
20 are depicted, however the number of thermoformed articles created by a 
die set at each cycle depends on the number of cavities in the die set, as 
is well known to skilled practitioners. 
Each thermoformed article 20 includes a front end 22, a rear end 24, a top 
26, a bottom 28, and a pair of sidewalls 30. The front end 22 and the rear 
end 24 are preferably drafted to assist the separation of the articles 
from the dies and also to facilitate the separation of nested articles 
from each other. In the preferred embodiment, the thermoformed article 20 
is a portion of a point-of-purchase package, and a part 32 of the article 
is configured to take the shape of a portion of the product to be 
packaged. 
The cutting apparatus of the invention is generally designated 40, and 
includes a base plate 42 having an upper surface 44 and a lower surface 
46. The base plate 42 is secured to an upper platen 48 of a conventional 
die cutting press generally designated 50. The upper platen 48 is 
generally a horizontally disposed flat plate provided with preferably four 
vertically positioned sleeves 52 (only one illustrated), one located at 
each corner, which each slidably engage a vertical member 54. The vertical 
members 54 are each secured at a lower end to a lower platen 56 across 
which the sheet 14 is drawn by the conveyor chain 12. The upper platen 48 
is powered such as by conventionally known pneumatic or hydraulic power 
systems (not shown) so that knives 58 attached to the upper platen impact 
the lower platen 56 on a cyclical basis. 
Referring now to FIGS. 1 and 2, at least one pair of knives 58, designated 
58a and 58b are preferably disposed in spaced, parallel relation to each 
other and are mounted to the lower surface 46 of the base plate 42 to 
depend therefrom. In the preferred embodiment, each knife 58 is generally 
bar-shaped and has an upper edge 60, a lower edge 62, and is functionally 
partitioned into a cutting portion 64 and a guiding portion 66. 
The cutting portion 64 of each knife 58 is defined by the sharpened lower 
edge 62, which may be provided with serrations 68 as in FIGS. 1 and 2. The 
serrations 68 are employed in applications when a perforated incision such 
as a score line 70 (best seen in FIG. 4) is to be formed to create a 
hinged flap 72 from a portion of the surrounding sheet 14. Alternately, a 
straight, sharpened lower edge 62 may be used to completely separate the 
article 20 from the surrounding sheet 14 at the point of impact of the 
blade. 
In the preferred embodiment, the cutting portion 64 of each knife 58 is 
generally parallel to the cutting portion of the adjacent knife of the 
pair of knives, and the cutting portions of each pair of knives defines a 
cutting zone 74 which is configured to accommodate at least one 
thermoformed article 20 therein. The cutting portion 64 preferably extends 
at least as long as two articles 20 placed end-to-end. 
The guiding portion 66 of each knife 58 is located upstream of the cutting 
portion 64 so that the thermoformed articles 20 engage the guiding portion 
prior to engaging the cutting portion. In addition, the guiding portion 66 
is angled relative to the longitudinal axis of each knife 58, and is 
divergent from the adjacent knife of the pair of knives. Thus, the guiding 
portion 66 of knife 58a diverges from the knife 58b, and vice versa. The 
amount of angular divergence of the guiding portion 66 depends on the 
application and upon the configuration of the thermoformed article 20. 
The positioning of each knife 58a, 58b of the pair of knives 58 on the base 
plate 42 is designed so that thermoformed articles 20 advanced with the 
sheet 14 toward the cutting apparatus 40 will engage the guiding portions 
66 and cause inner surfaces of the cutting portions 64 of the knives to 
slidingly contact the sidewalls 30 of the articles. Thus, in the preferred 
embodiment, the knives 58a, 58b are spaced apart only slightly wider than 
the width of the thermoformed article 20. 
The knives 58 are secured to the base plate 42 by a plurality of fasteners 
74, such as bolts, which pass through linearly elongated openings 76 in 
the base plate. In the preferred embodiment, four such openings 76 are 
provided, however the number of openings may vary with the application. To 
engage the fasteners 74, the upper edge 60 of each knife 58 is provided 
with at least one eyelet 78 projecting transversely to the longitudinal 
axis of the knife, and each eyelet is disposed to be in register with a 
corresponding opening 76. The eyelets 78 are preferably supported by a 
gusset 80 on each side. 
A threaded wingnut 82 or equivalent fastener is provided to engage each of 
the fasteners 74 to secure the knife 58 to the base plate 42. When the 
wingnuts 82 are tightened upon the fasteners 74, the elongate shape of the 
openings 76 allows the knife 58 to move slightly or "float" relative to 
the base plate 42 along the longitudinal axis of the knife. 
An important feature of the invention is that during normal operation, the 
base plate 42 is adjusted on the die press 50 to be vertically movable 
between an upper position (best seen in FIG. 1) wherein the lower edges 62 
of the knives 58 are disposed at a height which is less than or equal to 
the height of the thermoformed article 20, and a lower position wherein 
the lower edges of the knives are in contact with the sheet 14. In some 
cases, the distance between the upper position and the lower position may 
be only 0.5 inch (1.25 cm). The upper position of the base plate 42 in the 
present invention is significantly lower than the uppermost position of 
the base plate in conventional thermoforming operations using the type of 
floating knives previously known in the art. 
The base plate 42 is moved from the upper position to the lower position 
under force to cause a desired cutting or scoring action in the sheet 14. 
Sufficient force may be generated by the die cutting press 50 to achieve 
adequate cuts or score lines even though there is a relatively short 
distance between the upper position and the lower position of the base 
plate 42. 
Referring now to FIG. 3A, the apparatus 40 of the invention is 
diagrammatically depicted in plan view, and is shown including two pair of 
knives 58, the knives of each pair being labeled 58a and 58b. It is 
evident that the pairs of knives are generally parallel to each other, 
with the diverging guiding portions 66 of each pair of knives 58 defining 
a generally "Y"-shaped configuration as seen from above. Furthermore, it 
is evident that the guiding portions 66 of adjacent knives 58a, 58b of 
adjacent pairs of knives converge toward each other. 
In FIG. 3A, a sheet 14 of thermoformable material is seen advancing in the 
direction indicated by the arrow 16 toward the present cutting apparatus 
40. There are four thermoformed articles 20 which have been formed by the 
thermoforming die set. The articles 20 are arranged upon the portion 18 of 
sheet 14 to maximize space. In the preferred embodiment, each thermoformed 
article 20 includes a pair of the laterally extending flaps 72 which are 
substantially coplanar with the sheet 14. In the final boxes into which 
the articles 20 are each inserted upon assembly, the flaps 72 fold 
backward to be coplanar with the side walls 30 and to protect portions of 
the packaged product. 
Due to the nature of the final use of the thermoformed article 20 depicted 
in FIGS. 1, 3A-3C and 4, it is especially desirable that the article be 
manufactured so that the flaps 72 fold backward along a seam 86 which is 
substantially flush with the sidewalls 30. The cutting apparatus 40 of the 
invention is specifically designed to achieve this goal. 
Referring now to FIG. 3B, the group of thermoformed articles 20 on the 
portion 18 has been indexed through one cycle, which has brought the front 
ends 22 of the articles into engagement with the guiding portions 66 of 
the knives 58. It will be seen here that the guiding portions 66 are 
configured to direct the articles 20 to a specified position directly 
between the knives 58a and 58b of each pair of knives, in order to 
compensate for any misalignment in the indexing or conveying mechanisms. 
Such misalignment is often due to uneven stretching of the conveyor chains 
12, or of the sheet 14 of plastic itself. The feature of the diverging 
shape of the guiding portions 66 is assisted by the relatively lower upper 
operating position of the base plate 42, which enables the knives 58 to 
guide the articles into position. 
FIG. 4 illustrates the close tolerances between the adjacent knives 58a, 
58b and the thermoformed articles 20 which are achieved through the 
cutting apparatus 40 of the invention. In this manner, the score lines 70 
which are created by the cutting portions 64 of the knives are 
substantially flush with the sidewalls 30 of the articles 20. In some 
applications, the cutting apparatus 40 of the invention may provide cuts 
with a range of .+-.0" variability. 
Referring now to FIG. 3C, the sheet 14 is shown having been indexed another 
cycle in the direction 16, so that all four of the articles 20 in the 
portion 18 which were formed in one thermoforming cycle are directly 
between adjacent knives 58a, 58b. In order to fully accommodate groups of 
articles 20 of varying lengths, the knives 58 are preferably longer than 
any group of articles designed to be used with that particular set of 
knives. 
Upon the triggering of an automatic impact cycle by the pneumatic power 
system, the base plate 42 descends toward the sheet 14. The cutting 
portions 64 of the knives 58 create score lines 70 in the sheet which are 
substantially flush with the sidewalls 30 of the articles 20. A subsequent 
indexing cycle will bring the group of articles 20 to another die cutter 
(not shown), which will separate each article 20 from the sheet 14. 
Thus, the present cutting apparatus 40, including its floating knives 58 
each having a cutting portion with a separate diverging guiding portion, 
and having a relatively lowered upper operational position, is capable of 
accurately making cuts or score lines in thermoformed articles without 
damaging the articles. In this way the creation of thermoformed products 
is accomplished in less time with less waste. 
While a particular embodiment of the apparatus for making accurate cuts in 
thermoformed articles of the invention has been shown and described, it 
will be appreciated by those skilled in the art that changes and 
modifications may be made thereto without departing from the invention in 
its broader aspects and as set forth in the following claims.