Note: Descriptions are shown in the official language in which they were submitted.
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Method for adjusting cutting dies, compensating sheet
used to this end and die cutting machine equipped with
such a compensating sheet.
The present invention concerns a method for adjusting
cutting dies, in particular in a die cutting machine
equipped with several simultaneously operated cutting
dies, a compensating sheet used to this end, as well as
a die cutting machine equipped with such a compensating
sheet.
I~ the first place, the invention is designed to be
applied for the die cutting of paper and/or boxboard, for
example to form cartons, such as folding cartons and
such, out of a sheet or roll of cardboard or corrugated
board, or for the die- cutting of any other material
which can be processed on bending/die cutting machines
and similar cutting machines.
It is known that for the die cutting of cardboard, use is
made of a cutting forme in which several cutting dies
and/or bending, scoring or embossing formes are provided,
as well as a metal cutting plate provided against the
backsides of the cutting dies and the cutting forme and
which can be moved by means of a press-on system. During
the die cutting, the cutting dies go through the
cardboard, after which they make contact with a typically
hard, usually metal base. It is hereby of primary
importance that all the cutting edges of the cutting dies
make contact with the base at the end of the die- cutting
movement. Otherwise, a number of cuts will be
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incomplete.
Due to inaccuracies and/or wear and tear of the cutting
dies and due to tolerances, deviations and/or wear of the
parts of the die cutting machine concerned, the above-
mentioned demand will in fact be hardly or never met
right away, at least when no compensation is provided
for.
According to a known method, of which a number of
embodiments are described in the documents US 4.955.855,
EP 0 125 667, EP 0 297 324, EP 0 655 303 and WO 91/03358,
the differences in height of the cutting dies are offset
by means of a compensating sheet made of a compressible
material working in conjunction with the cutting dies.
By using such a compensating sheet, those cutting dies
which stick out the most can be easily set back, so that
all the cutting dies make contact with the above-
mentioned base with their cutting edges.
According to the known method, use is made of
compensating sheets or compensating foils made of
polyurethane, metal, tetrafluoroethylene, paper or a
combination thereof.
It has been revealed in practice that the use of
compensating sheets made of these materials do not meet
the required demands in many cases, especially when die
cutting boxboard. In many cases, the use of the existing
compensating sheets either results in an insufficient
compensation or in a too heavy load on the cutting edges
of the cutting dies. In both cases, this leads to an
incomplete cut, in the first case because certain cutting
dies do not go entirely through the material to be cut,
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and in the second case because a number of the cutting
edges become blunt.
The invention aims among others to remedy this problem.
To this end, the invention concerns a method for
adjusting cutting dies, in particular in a die cutting
machine equipped with several simultaneously operated
cutting dies, which preferably work in conjunction with
a base during the die cutting, whereby the differences in
height of the cutting dies are offset by means of a
compensating sheet made of a compressible material
working in conjunction with the backsides of the cutting
dies, characterized in that a sheet made of polycarbonate
or a material on the basis of polycarbonate is used as a
compensating sheet.
By applying a compensating sheet made of polycarbonate
according to the invention, particularly good adjusting
qualities are obtained. In particular, a perfect
compensation is obtained without any damage to the
cutting dies.
Moreover, the invention also concerns a compensating
sheet to realize the above-mentioned method with, as well
as a die cutting machine whose characteristics will
become clear from the following description.
In order to better explain the characteristics of the
invention, the following preferred embodiment of the
invention is described as an example only without being
limitative in any way, with reference to the accompanying
drawings, in which:
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figures 1, 2 and 3 schematically represent three
steps of the method.
As represented in figure 1, it is known that when die
cutting a material 1, in particular paper and cardboard,
as well as corrugated board, use can be made of a
cutting forme 2 in which several cutting dies 3A-3B are
provided, as well as a metal cutting plate 4 working in
conjunction therewith, provided against the backsides 5
of the cutting dies 3A-3B and the backside of the cutting
forme 2, for example by means of fixing means such as
bolts 6, and which can be moved by means of press-on
means 7, with for example what is called a top platen 8
and a makeready 9.
The material 1 to be die cut is provided under the
cutting dies 3A-3B on a usually very hard base 10 which
is supported either directly or indirectly by the machine
frame or the lower platen 11. A supporting plate, for
example made of steel or plastic, can be either or not
provided between the base 10 and the lower platen 11.
As described in the introduction, the cutting edges 12 of
the cutting dies 3A-3B are initially not all situated at
the same distance from the base 9. AS represented in
figure 1, for example the cutting edges 12 of a number of
cutting dies 3B may be situated at a larger distance from
the base 10 than the cutting edges 12 of the other
cutting dies 3A, due to tolerance differences in the
cutting dies or due to wear and tear. Similar
differences may occur due to deviations in the machine
parts, such as for example the base 10 or other machine
parts nat being flat. In fact, we are speaking of
differences of some one hundredths to tenths of a
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millimetre.
In order to compensate for these differences, it is known
to provide a compensating sheet 13 between the cutting
forme 2 and the cutting plate 4.
In order to offer an optimal compensation, use is made of
a compensating sheet 13 according to the invention which
consists of polycarbonate or a material on the basis of
polycarbonate.
Other components may be added to the polycarbonate, such
as colorants, additives which promote the processability
and the shaping of the sheets, or even other base
components. Preferably, however, the material of the
compensating sheet 13 predominantly consists of
polycarbonate in this case as well.
Better still, pure or almost pure polycarbonate will be
used.
The thickness D of the compensating sheet, which is
exaggerated in the figures for clarity~s sake, preferably
amounts to 0.1 to 1 mm, and better still to 0.4 to 0.6
mm, and according to the most preferred embodiment to 0.5
mm.
This relatively reduced thickness offers the advantage,
apart from optimal compensating qualities, that such a
compensating sheet 13 can be used in any existing die
cutting machine, since the parts of such die cutting
machines are usually made such that this thickness is
acceptable, even when said die cutting machine was
originally not designed to be equipped with a
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compensating sheet.
The compensating sheet 13 is preferably put directly into
contact with the backsides 5 of the cutting dies 3A-3B,
i.e. without any other compensating layers being
included, as differences in height can be set off
immediately there.
Preferably, cutting dies 3A-3B with blunt, flat backsides
5 are used, as this offers optimal compensation qualities
in combination with the typical toughness and hardness of
polycarbonate.
If required for the fixing of the cutting formes 2 by
means of bolts in the manner shown, pre-formed openings
14 can be provided for the bolts 6 or for any other
penetrating elements.
During the die cutting movement, the situations as
represented in figures 1 to 3 successively occur.
After a compensating sheet 13 has been applied, and as
the movement begins, the situation as represented in
figure 1 occurs.
As represented in figure 2, the cutting dies 3A which
stick out the most will go first through the material 1.
By applying a suitable die cutting pressure, also all the
other cutting dies 3B will be subsequently pressed
entirely through the material 1, as is represented in
figure 5, which is possible because the backsides 5 of
the cutting dies which previously stuck out further, in
this case 3A, are pressed in the compensating sheet 13.
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By making use of a compensating sheet made of
polycarbonate according to the invention, it is obtained
that the differences in height of the cutting dies, plane
parallelism deviations, machine distortions and/or
inaccuracies are perfectly compensated for, so that very
precise cuts are finally obtained.
According to the invention, the die cutting pressure is
preferably systematically increased at the transition
from the situation in figure 2 to that in figure 3 until
all the cutting dies 3A-3B go through the material 1.
Thanks to such a temporary, systematic increase of
pressure, a pressure can be applied which is just
sufficient, which may possibly be maintained for the
following cycles, and it can be excluded that a pressure
which is bigger than necessary is applied for the cutting
and that the cutting edges are loaded more heavily than
necessary. Thus is also avoided that cutting dies are
pressed into pieces.
The use of polycarbonate is advantageous in that, in
particular when die cutting boxboard products, the
cutting dies 3A-3B can go through the material 1 to be
die cut without any or hardly any compression of said
material. Such a polycarbonate sheet offers just enough
resistance to let the cutting dies 3A-3B cut through the
boxboard material, but it is still sufficiently soft so
as not to damage the cutting edges 12 on the base 10 when
the pressure is increased.
To sum up, it may be said that polycarbonate provides the
best results, especially when die cutting paper or
boxboard, both solid cardboard and corrugated board.
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It is clear that the invention concerns the above-
described method and the compensating sheet 13 used
thereby, as well as die cutting machines equipped with
such a compensating sheet 13 and which are possibly
equipped to this end with special features for the
application of such a compensating sheet 13.
Although the invention was described above on the basis
of what is called a flat-bed die cutting machine, it is
not excluded to apply it in rotary die cutting machines.
The cutting dies 3A-3B must not necessarily have a sharp
cutting edge 12. They can also be impress knives, for
example to realize folding lines or embossing formes.
The term "compensating sheet~ is to be interpreted in a
broad sense according to the invention. The compensating
sheet according to the invention may also consist of a
polycarbonate coating provided on a base sheet or of a
layer in the form of a foil.
The present invention is by no means restricted to the
embodiments described as an example and represented in
the accompanying drawings; on the contrary, such a method
and such a compensating sheet can be made in all sorts of
variants while still r~m~'n'ng within the scope of the
invention.
