EP2159017A1

EP2159017A1 - Flat cutting die and method for setting it up

Info

Publication number: EP2159017A1
Application number: EP08425577A
Authority: EP
Inventors: Emanuele Antongini
Original assignee: Cartoproject Srl
Current assignee: Cartoproject Srl
Priority date: 2008-08-28
Filing date: 2008-08-28
Publication date: 2010-03-03

Abstract

The invention concerns a flat cutting die comprising one or more stripes and a flat support plate, provided with one or more seats in which said stripes are inserted in transversal position, partially projecting from its outer surface. Advantageously, the cutting die comprises at least one shim in a deformable material arranged between the stripes and the bottom surface of the corresponding seats. The differences in pressure exerted by the stripes of the cutting die on an abutment plane, and therefore also on the punched sheets, are automatically compensated allowing the elastic and/or plastic deformation of the deformable shim at the stripes.

Description

The present invention refers to a flat cutting die and to a method for setting it up.
Cutting dies are interchangeable components of machines defined as die-cutters, used in various industrial fields to cut, shape and bend materials of various types like, for example, paper, leather, rubber or plastic. The most common application of die-cutters is conventionally in the paper and cardboard industry for processing sheets of paper, card or similar materials.
Cutting dies divide into two main categories: flat cutting dies and rotary cutting dies.
Normally a flat cutting die comprises a support plate, typically made from wood or plywood, or else from metal, in which seats are formed for housing metallic strips that can be used for cutting (blades), for half-cutting, for creasing or for perforating the paper material to be blanked. The seats comprise slots that open onto the upper surface of the support plate and extend along a predetermined path. Usually, the slots are obtained by removing part of the material of the support plate, for example with a laser beam, so as to obtain the shape corresponding to the linear extension of the stripes. The cutting, half-cutting or creasing stripes (the latter being known as creasers), are bands, generally made from steel, bent and shaped so as to be inserted into the corresponding seats of the support plate.
When the cutting die is set up, a portion of the stripes projects perpendicularly from the upper surface of the support plate and interacts directly with the sheet to be blanked. The remaining portion of the stripes stays inserted in the corresponding seats of the support plate; in this way, the stripes are vertically stabilised.
Generally, the slots that form the seats of the stripes in the support plate are through slots, i.e. they cross the plate along its entire thickness. During the set-up of the cutting die, each stripe is strongly pushed through a slot until it is brought into abutment against a bottom surface of the seat that is substantially undeformable; the bottom surface acts as a stopper and prevents the stripe from coming out beyond the lower surface of the support plate. Generally, the bottom surface of the seats of the stripes is a substantially undeformable flat foil, for example made from hard steel, fixedly connected to the lower surface of the support plate. For the purposes of the present description the expression "substantially undeformable" refers to the mechanical characteristics of the material of the bottom of the seats; such a material does not undergo appreciable deformations when the stripes are subjected to the normal operating pressures typical for each application (paper and cardboard, leather processing, etc.).
Laterally to the stripes, on the front surface of the support plate intended to interact with the sheet to be blanked, there are usually rubber gaskets, for example glued to the plate. On the support plate there can also be elements for helping the gluing of the material to be blanked. The function of the rubber gaskets is well known in the paper and cardboard industry.
Generally, the flat cutting dies can be inserted into a frame of a die-cutter machine, opposite to an abutment plane. At least one sheet to be blanked is positioned between a cutting die and the relative abutment plane. When the die-cutter is operating, the cutting die moves relative to the abutment plane; in other words the distance between the cutting die and the abutment plane progressively decreases. When such a distance is low (but not zero), the stripes of the cutting die penetrate at least partially into the paper material of the sheet, producing cuts, partial cuts, creasing lines, etc., according to whether they are cutting, half-cutting stripes or creasers, according to the diagram of construction of the cutting die. Then the cutting die lifts with respect to the abutment plane, i.e. the distance between the two elements increases allowing the punched sheet to be ejected and a new sheet for blanking in a subsequent working cycle to be inserted.
Manufacturers of flat cutting dies know that the pressure exerted on the sheet being blanked by the different components of the cutting die is not uniform. For example, the pressure exerted on the sheet by a stripe arranged on a portion of the cutting die is generally different from the pressure exerted by another stripe arranged on another portion of the same cutting die. The differences are due mainly to the geometric imprecisions of the support plate, of the stripes or of the relative seats, as well as geometric or mechanical imprecisions of the die-cutter. The imprecisions of the cutting die or of the die-cutter are minimal, of the order of tenths of a millimetre, but in any case sufficient to influence the interaction between the stripes and the sheet being processed. Disadvantageously, the pressure differences have a negative impact upon the quality of the blanking; the cutting, half-cutting and creasing lines can be irregular or defective. In these circumstance, some stripes work correctly, whereas other stripes penetrate excessively into the material of the sheet being processed or do not penetrate sufficiently into the same material.
There are two solutions conventionally adopted to avoid the drawback described above.
The first solution is to increase the pressure exerted by the cutting die on the sheet or band being processed, reducing the minimum distance between the cutting die and the abutment plane with respect to an initial standard value. This solution involves a substantial disadvantage: the pressure of the stripes which initially work correctly is also excessively increased, actually causing a worsening in the quality of the processing carried out by these stripes. Moreover, the stripes biased at higher pressures than those initially provided are subject to rapid wear, deformations, or to the risk of yielding. Clearly, if a stripe is worn-out, the quality of the blanked sheet/band is reduced and it may be necessary to stop the die-cutter to carry out the replacement of the worn-out stripe with a new stripe. In the worst cases, the deformation of many stripes can involve a drastic reduction of the operating life of the cutting die.
The second solution is to carry out the interlaying of the cutting die. A test blanking is carried out and the quality of the blanked piece is observed. In particular, information relative to the stripes that have penetrated insufficiently or have not penetrated at all into the blanked sheet, for example card, is acquired. In other words, the test blanking allows to detect the stripes on which it is necessary to act to compensate for the pressures. An operator arranges one or more thicknesses of paper between these stripes and the bottom of the respective seats. By suitably positioning the thicknesses of paper, which are compressed and thus substantially undeformable, a precise adjustment of the pressure that the stripes exert on the sheet to be blanked is obtained, i.e. it is possible to compensate for the pressure differences encountered between different portions of a cutting die. The interlaying allows the useful life of the cutting dies to be maximised, without changing the other operating conditions. Disadvantageously, the time taken by a specialised operator to carry out the interlaying of a cutting die can even be 3 - 4 hours, i.e. very long compared to typical production time in the paper and cardboard industry. The operator's experience may not be sufficient to understand what thickness must be positioned between a stripe and the relative seat; sometimes a trial and error approach is necessary, with clear negative consequences in terms of set-up time and productivity.
The technical problem forming the basis of the present invention is therefore to provide a flat cutting die that is simple to set up quickly and that has minimal problems of compensation of the pressures exerted by the stripes on the sheet being processed.
Therefore the present invention refers, in a first aspect thereof, to a flat cutting die comprising one or more stripes and a flat support plate provided with one or more seats in which said stripes can be inserted, partially projecting from the surface of the support plate, characterised in that it comprises at least one shim made from deformable material arranged between at least one stripe and the bottom surface of the corresponding seat.
Advantageously, the deformable layer arranged between at least one stripe and the bottom of the relative seat acts as a damper or as a deformable cushion that allows the stripe to penetrate further into the support plate when the thrust applied onto it is excessive or in any case greater than a threshold value. This characteristic allows the pressures to be balanced in the set-up step of the cutting die without it being necessary to carry out the interlaying manually. In other words, it is not necessary to arrange shims of paper between the stripes and the bottom of the seats in the support plate.
The bottom of the seats of the stripes is substantially undeformable, i.e. in normal conditions of use of the cutting die it does not undergo appreciable deformations with respect to the deformable material.
The material from which the shim is made is elastically and/or plastically deformable, locally in the contact area with a stripe, when a thrust is acting on the same stripe and the pressure exerted on the shim is greater than a threshold value. In particular, the material of the deformable shim is characterised by a threshold value for elastic deformation and by a threshold value for plastic deformation.
When a stripe is pushed in its seat and the pressure generated on the deformable shim exceeds the threshold value for elastic deformation, but not the threshold value for plastic deformation, the shim deforms elastically, squashing and going back into its initial configuration when the pressure exerted decreases with respect to the threshold value for elastic deformation. In this circumstance the deformable material acts as a damper of the vertical movements of the stripes. The elastic deformation of the deformable material is only provided for rare applications of the cutting die that do not require great thrusts, like in the case of graphical incisions or punching of low-thickness paper, or decorative paper.
Most applications in the field of blanking, on the other hand, provide for great thrusts on the cutting die, i.e. high pressures exerted on the stripes. For this reason, for the most common applications, like for example those in the paper and cardboard industry, it is foreseen for there to be plastic deformation of the deformable layer, as described hereafter.
When a stripe is pushed in its seat and the pressure generated on the deformable shim exceeds the threshold value for plastic deformation, the shim deforms plastically, squashing permanently and at least partially receiving the stripe.
Preferably for applications in the paper and cardboard industry, the deformable shim is a band, or a foil, made from metallic material, more preferably a band of aluminium or of aluminium alloy. These materials are characterised by a low threshold value for plastic deformation.
The deformable shim is arranged between at least one stripe of the cutting die and the bottom of the corresponding seat in the support plate. Preferably, the deformable shim is arranged between all of the stripes of the cutting die and the base of the corresponding seats, i.e. all of the stripes of the cutting die are in abutment against the deformable shim.
The bottom of the seats of the stripes can be a wall of the support plate, or else a wall of an element fixedly connected to the support plate at its lower surface, i.e. at the face of the plate opposite the upper surface from which the stripes project. Preferably, the bottom of the seats of the stripes is substantially undeformable, i.e. it does not undergo appreciable deformations during punching, especially if compared with the deformations undergone by the deformable material.
The setting up of the cutting die according to the present invention provides that the pressures applied by the stripes to the sheet being processed be balanced, i.e. made substantially the same for all of the stripes, by ensuring that the shim on which the stripes abut deforms to comply with the thrust exerted on the stripes themselves during blanking.
In a second aspect thereof, the invention concerns, indeed, a method for setting up a cutting die according to claim 8.
In particular, the present invention concerns a method for setting up a cutting die, comprising the steps of:

arranging a support plate provided with seats for housing at least one portion of stripes;
inserting one or more stripes into the corresponding seats, partially projecting from the surface of said support plate, and

The set-up comprises the further step of applying a thrust onto one or more stripes to elastically and/or plastically deform the deformable shim, locally at the contact area with a stripe, when the pressure exerted by the stripe exceeds a threshold value, respectively for elastic or plastic deformation, which is characteristic of the material of the shim.
Preferably, such a thrust is applied by bringing the stripes into abutment against an abutment plane of the cutting die, for example the abutment plane associated with the cutting die in a punching machine.
Once the threshold value for plastic deformation has been exceeded, the stripe at least partially penetrates in the material of the deformable shim. When the pressure applied by a stripe to the material of the deformable shim is between the threshold value for elastic deformation and the threshold value for plastic deformation, once the thrust applied to the stripe has ceased, the material of the deformable shim goes back into its initial undeformed configuration.
The differences in pressure exerted by the stripes of the cutting die on the abutment plane, and therefore also on the sheets punched subsequently, are automatically compensated, without the manual intervention of the operator, allowing the deformation of the deformable shim at the stripes. In most applications the deformation undergone by the deformable layer is of the plastic type, i.e. it is provided for there to be at least partial penetration of some stripes.
In practice, the deformable layer undergoes an initial deformation during the set-up of the cutting die. The pressures acting on the stripes are balanced and the cutting die is ready to be installed on a punching machine, i.e. it is ready to carry out the punching cycles. This procedure effectively replaces the conventional interlaying carried out manually by the operator.
The maximum deformation undergone by the deformable layer, at a stripe, is preferably less than 0.5 mm. In other words, the shim of the deformable layer is reduced to the maximum of 5 tenths of a millimetre to aid the vertical movement of a stripe. This value of the deformation allows the pressures to be balanced in the most common applications in the paper and cardboard industry, i.e. to blank paper, card, cardboard or similar materials.
The cutting die according to the present invention makes it possible to blank different materials effectively and with the precision needed by current requirements, and it does not require interlaying, with clear advantages in terms of reducing set-up times.
Another advantage of the cutting die according to the present invention compared to conventional solutions is given by the fact that the balancing of the pressures acting on the stripes allows the wear of the stripes to be minimised and, therefore, allows the useful life of the cutting die and/or the production speed to be maximised.
Further characteristics and advantages of the present invention shall become clearer from the following detailed description of a preferred embodiment, made with reference to the attached drawings. In such drawings:

figures 1-6 are schematic section views of a flat cutting die according to the present invention in different configurations during its set-up;

In such figures, reference numeral 1 indicates a cutting die according to the present invention intended for the paper and cardboard industry, i.e. suitable for blanking sheets of paper, card or cardboard. In general, however, the present invention is also applicable to other fields.
The cutting die 1 shown in figures 1-6 comprises a support plate 11, preferably made from wood, provided with one or more seats in which several stripes 15 - 20 are inserted. The seats comprise grooves formed directly in the support plate 11. The stripes 15 - 20 are inserted in such grooves, projecting for a certain portion from the upper surface 11A of the plate 11, in the vertical direction in the attached drawings, i.e. transversally to the plate 11.
The stripes 15 - 20 can be intended for cutting, half-cutting, creasing or perforation of sheet.
Each seat opens on the upper surface 11A of the support plate 11 and has a bottom surface 11B in the opposite direction, i.e. the seats are blind grooves. The bottom surface 11B of the seat can be a wall of the same support plate 11, but preferably, as shown in the attached figures, the bottom surface 11B belongs to a wall 13 fixed stably to the support plate 11. The bottom surface 11B is substantially undeformable, for example it is made from carbon steel characterised by high mechanical strength.
Advantageously, between at least one stripe 15 - 20 and the bottom surface 11B of the relative seat, but preferably between all of the stripes 15 - 20 and the bottom surface 11B, there is a layer 14 made from deformable material, for example a foil or a band made from deformable material. For the purposes of the present invention the term "deformable" identifies a characteristic of the material of the layer 14: the material is elastically and/or plastically deformable, locally in the contact area with the stripes 15-20, according to the pressure exerted by the same stripes 15 - 20. In particular, the material of the layer 14 has an elastic deformation threshold and a plastic deformation threshold. When the pressure exerted by a stripe 15 - 20 is less than a threshold value for elastic deformation, the layer 14 does not deform; when the pressure exerted by a stripe 15 - 20 is greater than the threshold value for elastic deformation, but less than the threshold value for plastic deformation, the layer 14 deforms locally in an elastic manner, going back into its undeformed configuration once the pressure ceases; when the pressure exerted by a stripe 15 - 20 is greater than the threshold value for plastic deformation, the layer 14 deforms plastically, staying deformed even when the pressure has ceased.
In the most common applications in the paper and cardboard industry, the pressures at which the stripes 15 - 20 of the cutting die 1 operate, interacting with the sheets to be blanked, are high. Preferably, the layer 14 is made from a material intended to be plastically deformed during the initial set-up of the cutting die 1, and such as to withstand the pressures involved during blanking.
A material suitable for the purpose is aluminium. Alternatively, it is possible to use aluminium alloys, like ergal, or else magnesium. In the embodiment shown in figures 1-6, the layer 14 is an aluminium foil arranged between the support plate 11 and the steel foil 13.
The cutting die 1 preferably also comprises a plurality of rubber elements 12 fixed to the upper surface 11A of the plate 11, on the side of the stripes 15 - 20. The use of the rubber elements is known in the field, in particular for blanking sheets made from paper material, and it shall not be described any further.
As shall be described hereafter, during the set-up of the cutting die 1, i.e. before its use to blank sheets of paper, card or similar materials, the aluminium foil 14 is deformed to at least partially receive one or more stripes and ensure the better distribution of pressures.
The figures 1 - 6 show a sequence of configurations of the cutting die 1 during set-up, i.e. before actual use. The cutting die 1 is opposite an abutment plane 2, for example the cutting plate used during the blanking steps. In figures 1-6 the abutment plate 2 has a stepped upper surface. In reality the plate 2 is flat and the steps have been designed only for the purpose of schematising the different pressures that the stripes 15-20 exert on a sheet of paper to be blanked, before the balancing of the pressures. In other words, the plate 2 is flat on top and the steps are shown in figures 1-6 solely for didactic purposes to explain how set-up occurs.
Figure 1 shows a first initial configuration. The stripes 15 - 20 are distant from the surface of the cutting plate 2 and the aluminium band 14 has not yet undergone any localised deformation.
In the second configuration shown in figure 2, the distance D between the upper surface of the cutting die 1 and the upper surface of the cutting plate 2 is reduced compared to the first configuration. The stripes 15 and 19 are in abutment against the upper surface of the cutting plate 2. The aluminium band 14 has not undergone alterations with respect to the initial undeformed configuration.
Figure 3 shows a third configuration of the cutting die 1. The distance D has been further reduced compared to the second configuration, bringing the cutting die 1 closer to the cutting plate 2. Correspondingly, the stripes 15 and 19 have been pushed against the bottom of the relative seat, i.e. against the steel plate 13. The vertical movement of the stripes 15 and 19 is aided by the aluminium band 14, which deforms locally to receive a base portion of the stripes 15 and 19. The deformation can be elastic, but preferably it is of the plastic type, i.e. the band 14 stays deformed even when the pressure exerted by the stripes 15 and 19 has ceased. The extent of the deformation is a few tenths of a millimetre and in the figures it has been amplified for reasons of clarity. In particular, the deformation undergone by the band 14, indicated with letter d, is a compression that brings about a reduction in thickness of the band 14 localised at the stripe 15, 19.
The rubber elements 12 have no influence upon the movements of the stripes 15 - 20.
Figure 4 shows the cutting die 1 in a fourth configuration during its set-up. The distance D has been further reduced compared to the third configuration. The hollow punches 15 and 19 penetrate more into the aluminium band 14, i.e. the deformation d at each of these stripes increases with respect to what is shown in figure 3. Moreover, the stripe 17 also starts to penetrate into the aluminium of the layer 14 through the effect of the thrust exerted by the upper surface of the cutting plate 2.
Figure 5 schematically shows the cutting die 1 in a fifth configuration, closer again to the cutting plate 2. The stripe 20 is also partially inserted into the plastically deformed layer 14 to receive it.
Figure 6 shows the cutting die 1 brought completely up to the cutting plate 2. This configuration simulates the moment when, during the operation of the die-cutter machine, the cutting die 1 carries out the blanking of a sheet. In the example shown, all of the stripes 15 - 20 are at least partially inserted into the layer of aluminium 14. In general, however, the cutting die 1 can provide for the insertion of just some of the stripes 15 - 20 into the layer 14.
In the sixth configuration shown in figure 6 the pressures exerted by the stripes 15 - 20 on the cutting plate 2 have been balanced. Consequently, during the use of the cutting die 1 the pressures acting on the sheets being processed, arranged between the cutting die 1 and the flat plate 2, shall also be balanced.
The cutting die 1 is now ready to be used. The deformation of the layer 14, plastic and permanent, has made it possible to quickly set up the cutting die 1 and to balance the pressures, without it becoming necessary to carry out interlaying manually.
The punching takes place by pressing the cutting die 1 against the cutting plate 2 at lower pressures that those corresponding to the sixth configuration shown in figure 6 , or the same. In this way the stripes 15 - 20 are prevented from penetrating into the layer 14 more than they should.

Claims

Flat cutting die (1) comprising one or more stripes (15-20) and a flat support plate (11), provided with one or more seats in which said stripes can be inserted, partially projecting from the surface (11A) of the support plate (11), characterised in that it comprises at least one shim (14) made from deformable material arranged between at least one stripe (15 - 20) and the bottom surface (11B) of the corresponding seat.
Cutting die (1) according to claim 1, characterised in that said deformable shim (14) is deformed elastically and/or plastically by a portion of a stripe (15-20) when a thrust is acting on the same stripe and the pressure exerted on the deformable shim (14) is greater than a threshold value for the elastic, or plastic, deformation characteristic of the material of said deformable shim (14).
Cutting die (1) according to one of claims 1-2, characterised in that said shim (14) is deformed plastically to receive at least one part of a stripe (15-20).
Cutting die (1) according to one of claims 1-3, characterised in that said deformable shim (14) is a band, or a foil, made from metallic material.
Cutting die (1) according to claim 4, characterised in that said band (14) is made from aluminium or aluminium alloy.
Cutting die (1) according to claim 5, characterised in that the maximum deformation of said band (14) at a stripe (15-20) is less than 0.5 mm.
Cutting die (1) according to any one of the previous claims 1-6, characterised in that it also comprises a substantially undeformable wall (13) fixedly connected to the support plate (11), at its lower surface, and in that the bottom surface (11B) of said seats belongs to said wall (13).
Method for setting up a cutting die (1), comprising the steps of:
- arranging a support plate (11) provided with seats for housing at least one portion of stripes (15-20);

- inserting one or more stripes (15-20) in the corresponding seats, partially projecting from the surface of said support plate (11), and
characterised by the further step of arranging at least one shim (14) made from deformable material between at least one stripe (15-20) and a bottom surface (11B) of the corresponding seat.
Method according to claim 8, characterised in that said deformable shim (14) is a band, or a foil, made from aluminium or aluminium alloy.
Method according to claim 8 or claim 9, characterised by the further step of applying a thrust onto one or more stripes (15-20) to elastically and/or plastically deform said deformable shim (14), locally at the contact area with a stripe (15-20), when the pressure exerted by the stripe (15-20) exceeds a threshold value for the elastic, or plastic, deformation characteristic of the material of said deformable shim (14).
Method according to claim 10, characterised in that said thrust is applied by bringing said stripes (15-20) into abutment against an abutment plane (2) of the cutting die (1).
Method according to claim 11, characterised by the further step of compensating for the pressure differences exerted by two or more stripes (15-20) of the cutting die (1) on said abutment plane (2) allowing the at least partial penetration of at least one of said two or more stripes (15-20) in said deformable shim (14).
Method according to claim 10 or claim 11, characterised in that said at least one stripe (15-20) at least partially penetrates into the material of said deformable shim (14) when the pressure exerted exceeds said threshold value for plastic deformation.
Method according to claim 12, characterised in that when the pressure applied by a stripe (15-20) to the material of the deformable shim (14) is between the threshold value for elastic deformation and the threshold value for plastic deformation, when the thrust applied to the stripe (15-20) has ceased, the material of said deformable shim (14) goes back into its initial undeformed configuration.