Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FLEXIBLE ROTARY CUTTING DIE
This application claims the benefit of United States Provisional
15
Patent Application Serial No. 60/159,270, entitled Flexible Rotary Cuttin
Die, filed October 13, 1999.
FIELD OF THE INVENTION
The invention generally relates to the field of rotary cutting dies
used in rotary cutting machines, and more particularly, to an improved
method and apparatus for making and using such dies.
BACKGROUND OF THE INVENTION
Rotary cutting machines are widely used in such industries as the
printing or converting industry to cut, score and perforate paper and other
web-products such as plastic, cardboard, non-wovens and the like. In
general, these rotary cutting machines have two cooperating cylinders,
one of which carries a rotary cutting die having a knife or cutting rule, and
the other cylinder that acts as an anvil against which the knife bears as the
paper is cut. The cutting edge of the knife and the surface of the anvil
cylinder normally rotate at the same speed and the paper is cut as the
cutting edge of the knife moves into and out of engagement with the anvil
surface.
Rotary cutting dies have been manufactured and used for
numerous years. Conventionally, rotary cutting dies are formed from a
rigid, epoxy-based material supporting a metallic cutting rule. The cutting
rule extends above the surface of the rigid die plate and defines a cutting
design. The design created by the metallic cutting rule is employed to cut,
score or perforate material, such as paper, cardboard or the like, through
the rotary cutting process.
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Conventional rotary cutting dies are mounted on discrete sections
of a rotary cutting machine die cylinder or along the entire surface thereof.
To accommodate either type of die, the die cylinder typically contains a
number of receiving holes spaced at predetermined intervals. The
receiving holes are positioned in an array along the die cylinder, and are
configured to receive screws or other fasteners that extend through or
along the side of the rigid die plate so as to affix the cutting die to the
die
cylinder. Mounting holes are bored into the die plate to align with the
receiving holes in the die cylinder. The rotary cutting die is thus aligned
and positioned on the die cylinder to reflect the predetermined pattern for
the cutting, scoring or perforating process.
Conventional rotary cutting dies must be sized to fit on the die
cylinder. In particular, each rotary cutting die must be manufactured with
a mounting radius that precisely matches the radius of the die cylinder on
which the cutting die is to be mounted. Precise matching of the rotary die
plate to the die cylinder is necessary to insure accurate cutting of the
material by the cutting rule. Precise matching of these components is also
necessary to eliminate excessive wear on the cutting rule. Imprecise or
inaccurate matching may lead to premature wear due to fretting corrosion,
and may even lead to breakage or failure of the rotary cutting die.
Manufacturing a rotary cutting die to precisely match the die
cylinder can be difficult. For example, it may be difficult to accurately
measure the radius of the die cylinder by conventional means. Moreover,
conventional rotary cutting dies are typically manufactured from a molding
process. Consequently, any deviance between the radius of the die
cylinder and the radius of the manufacturing mold will necessarily lead to
inaccuracies in the radius of the rotary cutting die.
Another reason for the difficulty in matching the rotary cutting die to
the die cylinder is because the die plate of a conventional rotary cutting
die is typically manufactured from a rigid; epoxy-based material. Epoxy-
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based materials tend to shrink during the curing process, thereby altering
the radius or distorting the shape of the rotary die plate. Moreover, the
amount and degree of shrinkage will very depending on the configuration
or layout of the cutting rule. It is therefore nearly impossible to predict
the
shrinkage of the die plate with any precision. Shrinkage of the die plate
material may also create internal stresses that may compromise the
integrity of the rotary cutting die.
The use of a rigid, epoxy based material for the die plates of
conventional rotary cutting dies results in a number of additional problems.
For example, if the radius of the rotary cutting die does not precisely
match the radius of the die cylinder, then the die plate must be "flexed" to
fit onto the die cylinder. In other words, the die plate must be "flexed" or
bent so as to eliminate any gaps between the die plate and the die
cylinder. The rigidity of the epoxy-based material, however, will prevent
any appreciable "flexing" of the die plate. If the die plate cannot be
"flexed" sufficiently to fit onto the die cylinder, then the rotary cutting
die is
typically discarded. On the other hand, even if the die plate can be
"flexed" sufficiently to fit onto the die cylinder, the rotary cutting die
will
tend to wear faster and have a shorter life span.
In the event that the rigid die plate is "flexed" to fit onto the die
cylinder, additional mounting fasteners or clamps will usually be required
to secure and hold the die plate tightly against the die cylinder. These
additional mounting fasteners will necessarily require the installation of
additional receiving holes in the die cylinder.
"Flexing" of the die plate to fit the die cylinder may also cause
adverse stresses in the die plate. These adverse stresses may lead to
premature wearing or failure of the rotary cutting die. Moreover, a failure
of the rotary cutting die can create a dangerous situation. This is because
the rigid die plate of a conventional rotary cutting die can shatter, thereby
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propelling shattered pieces of the die plate and the cutting rule outwardly
from the die cylinder.
Accordingly, it would be desirable to have a cutting die that
overcomes the disadvantages and limitations described above.
SUMMARY OF THE INVENTION
In view of the above, the present invention provides a unique rotary
cutting die that overcomes the disadvantages and limitations described
above. In particular, the rotary cutting die of the present invention
includes a durable, flexible rotary die plate having an inner surface and an
outer surface. The die plate supports a cutting rule that defines a cutting
design. The cutting rule includes a cutting edge, which extends above the
outer surface of the die plate, and a support edge disposed within the die
plate. The support edge includes a plurality of keyhole shaped notches.
Preferably, a plurality of S-shaped hooks are connected to the key-hole
notches, and serve to reinforce the rotary die plate and to support the
cutting rule in the rotary die plate.
The rotary die plate of the present invention is preferably formed
from a durable and flexible urethane-based material that exhibits a low
shrink factor during curing or hardening. The urethane-based material of
the preferred embodiment, when cured, is more flexible than the rigid
epoxy-based materials used for conventional rotary cutting dies. This
flexibility allows the die plate to be flexed or deformed as necessary to fit
onto the surface of the die cylinder, thereby eliminating the need to
manufacture the die plate with a radius precisely matching the radius of
the die cylinder. This flexibility likewise permits a single die plate to be
mounted onto die cylinders of different radiuses.
The urethane-based material of the preferred embodiment also
improves the distribution of adverse stresses that are often incurred by the
cutting rule during jam-ups. The flexibility of the die plate permits the
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cutting rule to flex slightly during such jam-ups, dissipating the adverse
stresses throughout the die plate. The flexible die plate is also less likely
to shatter during jam-ups.
The preferred embodiment of the invention includes features in
addition to those listed above. Moreover, the advantages over the current
art discussed above are directly applicable to the preferred embodiment,
but are not exclusive. The other features and advantages of the present
invention will be further understood and appreciated when considered in
relation to the detailed description of the preferred embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a rotary cutting die of the invention
having a cutting rule supported therein;
FIG. 2 is a side view of the rotary cutting die shown in FIG.1;
FIG. 3 is a side view of the cutting rule shown in FIGS. 1 and 2,
including an end view thereof;
FIG. 4 is a front plan view of a rotary cutting machine including the
rotary cutting die shown in FIGS. 1 and 2 mounted thereon;
FIG. 5 is a perspective view of the transfer plate
material disposed along a cutting cylinder;
FIG. 6 is a side view of the transfer plate showing the cutting rule
positioned therein;
FIG. 7 is an elevational view of a three-roll curver for curving the
cutting rule shown in FIGS. 1-3;
FIG. 8 is a partially exploded perspective view of a rotary cutting die
mold; and
FIG. 9 is a side view of the rotary cutting die and transfer plate after
being removed from the rotary cutting die mold shown in FIG. 8.
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DETAILED DESCRIPTION OF THE
PRESENTLY PREFERRED EMBODIMENTS
Referring now to the drawings, FIGS. 1 and 2 show the preferred
embodiment of the rotary cutting die 10 of the present invention. The
rotary cutting die 10 includes a cutting rule 12 supported in a flexible
rotary
die plate 14. The cutting rule 12 has a cutting edge 16, which extends
above the outer surface 18 of the rotary die plate 14, and a support edge
20 disposed within the rotary die plate 14. The cutting rule 12 forms a
predetermined cutting design 21 on the rotary cutting die 10.
The cutting edge 16 of the cutting rule 12 is preferably sharp to
enable it to cut, score or perforate the design 21 into a given cutting
material (not shown). Preferably, the cutting edge 16 extends
approximately 1/8 inch above the outer surface 18 of the rotary die plate
14. However, as those skilled in the art will appreciate, the cutting edge
16 can extend to any distance dictated by a specific application without
departing from the spirit and scope of the invention.
As best shown in FIG. 3, the support edge 20 preferably includes a
plurality of notches 22. As shown in FIGS. 1 and 2, the notches 22 are
connected to a plurality of interlocking connectors 24 disposed throughout
the rotary die plate 14. The interlocking connectors 24 serve both to
reinforce the rotary die plate 14 and to secure the cutting rule 12 in the
rotary die plate 14. Preferably, the notches 22 are keyhole shaped
notches and the interlocking connectors 24 are S-shaped hooks. As those
skilled in the art will appreciate, other shapes for the notches 22 and the
interlocking connectors 24 can be employed and are contemplated. For
example, the notches 22 can comprise circular holes through the cutting
rule 12, and the interlocking connectors 24 can comprise metal pins or
screws inserted through the circular holes.
The rotary die plate 14, as best shown in FIGS. 1 and 2, may be
formed of any suitable material and to any suitable thickness to obtain the
desired flexibility and durability. Preferably, the rotary die plate 14 is
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formed of a urethane-based material that exhibits a low shrink factor upon
hardening. The low shrink factor is desired to ensure that the design 21
formed by the cutting rule 12 is not skewed when the die plate 14 is
formed, and to ensure that the required shape of the die plate 14 is
retained. The rotary die plate 14 preferably has a thickness of between
1/4 to 7/16 inches, although other thicknesses dictated by particular uses
for the rotary cutting die 10 are contemplated. For example, rotary die
plates 14 having a thickness in the range of 3/16 to 5/8 inches have been
used with satisfactory results. A preferred urethane-based material is
distributed by Ciba Geigy Corp., located in East Lansing, Michigan, and is
referred to as RP 6444R/TDT 178-87H Polyurea Elastomer. This
particular material is a wear resistant, semi-rigid, black, two component
polyurea elastomer having a hardness of approximately 60 t 5 (Shore D).
An alternative urethane-based material that can be used for the rotary die
plate 14 is referred to as TDT 178-88R/RP 6444H Polyurea Elastomer.
This alternative material has properties similar to the preferred material,
but is red in color. Of course, any material, and particularly urethane-
based materials, having the required properties can be used for the rotary
die plate 1 4.
The urethane-based material of the preferred embodiment can also
be altered with additives, dyes or color pastes to change the color of the
rotary die plate 14. Changing the color of the material may be
advantageous for a number of reasons, such as increasing the visibility of
the rotary cutting die 10 on the die cylinder 26, or of the cutting rule 12 on
the die plate 14. Since the die cylinder 26 is typically rotated at a high
rate
of speed, increasing the visibility of these components could enhance the
safety to the operator. For example, manufacturing the rotary die plate 14
from a urethane-based material that has been dyed a light color such as
white, yellow or red would improve the operators ability to see the
contrasting dark colored cutting rule 12, even when the die cylinder 26 is
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rotating. Different colorings could likewise improve the operator's ability to
inspect the rotary cutting die 10 for wear or damage.
The urethane-based material of the preferred embodiment, when
cured, is more flexible than the rigid epoxy-based materials used for
conventional rotary cutting dies. The flexibility of the urethane-based
material allows the die plate 14 to be flexed or deformed as necessary to
fit onto the surface of the die cylinder 26. This eliminates the need to
manufacture the die plate 14 with a radius precisely matching the radius of
the die cylinder 26, thereby reducing manufacturing costs. Moreover, a
single die plate 14 can be flexed to fit onto die cylinders 26 of different
radiuses. This eliminates the need to manufacture individual rotary cutting
dies 10 for each individual die cylinder 26.
The urethane-based material of the preferred embodiment permits
the manufacture of a thinner rotary die plate 14 than the conventional
epoxy-based die plate. The urethane-based material therefore allows a
more free flowing injection molding process with fewer, if any, air voids in
the finished product.
The rotary cutting die 10 of the present invention is also a more
durable and safer product. In particular, a die plate 14 manufactured from
the urethane-based material of the preferred embodiment will distribute
any adverse stresses that may be incurred by the cutting rule 12. Such
adverse stresses often occur during a jam-up, which typically places
transverse loads on the cutting rule 12. With a conventional rotary cutting
die, these loads are transferred directly to the die plate, occasionally
causing the die plate to shatter. The die plate 14 of the preferred
embodiment, however, has sufficient flexibility to permit the cutting rule 12
to flex slightly, thereby alleviating most of the adverse stresses.
Moreover, the flexibility of die plate 14 of the preferred embodiment makes
the die plate 14 unlikely to shatter during such a jam-up, thereby reducing
or eliminating potentially dangerous situations. Of course, the urethane-
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based material of the preferred embodiment must have sufficient stiffness
so that the cutting rule 12 is supported and securely held in position by the
die plate 14.
Referring now to FIG. 4, the rotary cutting die 10 is preferably sized
for use on a discrete section of a die cylinder 26 of a rotary cutting
machine 28. Alternately, however, the rotary cutting die 10 may be sized
to cover all, or a substantial portion, of the die cylinder 26, and numerous
individual rotary cutting dies may be mounted on the die cylinder 26. To
properly fit on the die cylinder 26, the radius of curvature of the rotary
cutting die 10 should approximate that of the die cylinder 26. However,
and as discussed above, the urethane-based material of the preferred
embodiment permits some disparity between the radius of the rotary
cutting die 10 and the die cylinder 26.
The preferred die cylinder 26 contains a plurality of receiving holes
30 positioned in a uniform matrix or array about its outer surface, as
shown in FIG. 4. The rotary die 10 is mounted on the die cylinder 26 by
means of a plurality of fasteners 32 disposed through mounting holes 34
located in the rotary die plate 14 of the die 10. The fasteners 32 are
secured within the receiving holes 30 in the die cylinder 26 to mount the
rotary die plate 14 of the rotary die 10 to the die cylinder 26. Any suitable
form of fastener may be utilized to secure the rotary die 10 on the die
cylinder 26. In one preferred embodiment of the invention, the fasteners
32 comprise screws, or the like, that turn into the preferably threaded
receiving holes 30 in the die cylinder 26.
As shown in FIG. 4, the rotary cutting machine 28 also includes an
opposing cylinder 36 positioned parallel to and in opposite rotary
relationship with the die cylinder 26. When the rotary cutting machine 28
is in operation, the opposing cylinder 36 rotates counter to the die cylinder
26. During operation of the rotary cutting machine 28, cutting material,
such as paper, cardboard, plastic, polyethylene, non-wovens or
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paperboard, is fed between the die cylinder 26 and the opposing cylinder
36. The cutting rule 12 in the rotary die plate 14, which is mounted on the
die cylinder 26, and the opposing cylinder 36 cooperate to cut, score or
perforate the cutting material in the pattern of the cutting design 21.
A method for forming the rotary cutting die 10 of the present
invention is described below. As shown in FIGS. 5 and 6, a curved cutting
rule transfer plate 38, preferably formed of phenolic material 56 and
having an inner surface 40 and an outer surface 42, is provided. The
phenolic material56 from which the transfer plate 38 is formed is fixedly
secured to a cutting cylinder 54 having approximately the same radius of
curvature as the die cylinder 26 on the rotary cutting machine 28.
Preferably, the phenolic material 56 is fastened to the cutting cylinder 54
by screws 58 or the like. Alternately, the phenolic material 56 may be
adhered to the cutting cylinder 54 by the use of glue or spray mount.
A Computer Numeric Controlled (CNC) machine (not shown), which
is operatively associated with the cutting cylinder 54 supporting the
phenolic transfer plate material 56, cuts the phenolic material 56 to form
the transfer plate 38, in a manner generally known in the art. In addition,
the CNC machine forms a cutting rule channel 44 in the transfer plate 38
in the pattern of the cutting design 21.
As shown in FIG. 7, a three-roll curver 46 is use to bend and shape
the cutting rule 12 into the cutting design 21 cut into the transfer plate 38.
Because the transfer plate 38, and the resulting rotary die plate 14, are
curved, the cutting rule 12 must be curved to the same radius of curvature.
Referring back to FIGS. 5 and 6, after the cutting rule 12 is curved
in the three-roll curver 46, the cutting edge 16 of the cutting rule 12 is
inserted into the inner surface 40 of the transfer plate 38, through the
cutting rule channel 44, until the cutting edge 16 is substantially flush with
the outer surface 42 of the transfer plate 38. At this point, the support
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edge 20 of the cutting rule 12 is exposed and extends beyond the inner
surface 40 of the transfer plate 38.
As shown in FIG. 8, the curved transfer plate 38 is placed in the
rotary cutting die mold 50 with its inner surface 40, and the support edge
20 of the cutting rule 12, exposed. The interlocking connectors 24 are
connected to or through the notches 22 present in the support edge 20, as
described above. Consequently, the interlocking connectors 24 are also
exposed, as shown in FIG. 8.
After the mold cylinder 52 is lowered onto the inner surface 40 of
the transfer plate 38 and the mold 50 is sealed, a urethane-based die
plate material (preferably having a low shrink factor) is injected into the
mold 50 at ambient temperature. The urethane-based material is cured at
an elevated temperature until the urethane hardens and forms the
durable, flexible rotary die plate 14 on the inner surface 40 of the transfer
plate 38. Preferably, the die plate material is cured at 180°F,
although it is
contemplated that various other curing temperatures could be used
depending on the particular urethane-based material and the specific
application.
As shown in FIGS. 8 and 9, subsequent to the rotary die plate 14
being formed, the mold cylinder 52 is raised, and the rotary die plate 14
and the transfer plate 38 are removed from the mold 50. The transfer
plate 38 is then physically removed from the rotary die plate 14, and the
resultant rotary cutting die 10 is formed. The rotary cutting die 10 may
now be mounted to the die cylinder 26 for use on the rotary cutting
machine 28. As can be readily seen, it is contemplated that numerous
individual rotary cutting dies may be mounted on a single die cylinder.
It should be appreciated that the present invention may be
performed or configured as appropriate for the application. The
embodiments described above are to be considered in all respects only as
illustrative and not restrictive. The scope of the invention is indicated by
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the claims rather than by the foregoing description. All changes, which
come within the meaning and range of equivalency of the claims, are to be
embraced within their scope.
