EP0715933A1 - Cutting rule - Google Patents

Abstract

The punch cutter (1) has a blade whose cutting edge (2) has a rounded area with radius (3) of 0.005 to 0.040 mm. The rounded edge is additionally hardened with a refined surface finish. The cutting angle (4) for the cutting edges is 30 to 60 deg. The cutting edge of the punch cutter may have straight edges. these taper toward a tip which can be rounded by laser melting.

Description

The invention relates to a punching knife for punching out parts of any shape from paper, cardboard, cardboard, plastic films, leather, rubber and the like.

Such punch knives, e.g. are known from DE-PS 33 17 777 C1 are preferably used in strip steel punching tools for punching out parts of any shape from flat materials, in particular folding box blanks. They are also increasingly used in rotary punching tools for the same purposes.

The punching knives have to meet three requirements: 1. that the material must be reliable and completely separated over the entire punching area, so that no production disruptions occur in the subsequent work stages, 2. that the cut is perfectly dust and fiber free with smooth cut edges and 3. that the cutting edge wear should be as low as possible, which is expressed in the number of good punchings. These three requirements can only be met inadequately with the current cutting edges.

The cutting edges of the known punching knives are generally produced by grinding, scraping partly by lapping, based on the idea that the cutting edge should be as sharp as possible. Cutting edges are clearly below 0.010 mm, but which have an uneven micro-saw-like contour and which, due to the manufacturing process, adhere to the smallest whiskers. These cutting edges must first level out in interaction with the material to be cut, smooth so that the best possible cutting quality can then be achieved. Depending on the material to be cut, several thousand punching strokes are required.

These very narrow cutting edges are extremely sensitive to mechanical loads, especially pressure. This is of particular importance because the usual way of working with this generic punching technique is that of steel against steel, i.e. the knife edges work against a hardened punching plate.

The production lines have height differences of +/- 0.02 mm. In addition, there are further height tolerances from the punching machines, tool manufacture and handling of the punching processes.

In unfavorable cases, all errors add up, so that height differences of up to 0.2 mm cannot be excluded.

In order to guarantee the secure cutting of the material to be cut, the height differences must be compensated so that the very sensitive cutting edges are not damaged by overloading.

In practice, the procedure is to press the punch until at least 50% of all interfaces have been cut. Then the remaining height differences are compensated for by gluing with suitable tapes of different thicknesses. Depending on the box cut, there are up to 100 meters of punching lines in a strip steel punching mold, from which it follows that the compensation of the height differences, in the technical language Called "dressing", requires a lot of care, experience and takes many hours while the punching machine is standing. In some cases, these preparation times are longer than the subsequent actual production time. These machine dead times cause unproductive additional costs. This often leads to the fact that the punch is brought together so far that most of the punching lines separate at the price that a large part of the cutting edges is damaged or destroyed. The cutting edge is deformed undefined under the excess pressure. This results in an unclean cut, in which dust and punch hair are increasingly formed, bursting cardboard covers and cardboard backs. The service life of such punch knives is significantly reduced, so that the tools have to be replaced prematurely, which means corresponding additional costs.

Many efforts have been made to simplify the dressing or to be able to replace it entirely. From DE 31 35 980 C1 a generic steel strip punching tool is known, in which punching lines with deformable knife backs are used for automatic height adjustment.

This solution fails due to the technological possibilities in the production of the target deformation points on these punching lines.

DE 39 28 916 C1 describes a method in which the cutting knives which are too high can move backwards against a soft metal plate. The plate is work hardened in the pressure area of the knife back, so that a stabilized state of equilibrium is established. This process fails due to the structural conditions of the punching machines dominating the market.

In a band steel punching tool known from DE 33 17 777 C1, the backs of the knives are designed as hardened cutting edges and sit on a softer metal plate, into which they can dodge under the influence of the punching pressure in accordance with the height difference. The production of these lines is costly and shows in use that the soft plates become prematurely unusable due to the digging in of the hardened back cutting edges due to fatigue fractures. They therefore have to be replaced relatively quickly, which means that the technical advantages are canceled out.

In recent times, the cutting edges can be coated to reduce wear and reduce friction. Such coatings have a generally ceramic character with extremely high hardness, but are correspondingly brittle. Our own investigations have shown that these wear-reducing layers are also destroyed by the cutting edge damage until they become ineffective.

A cutting knife for cutting a moving cardboard web is known from US Pat. No. 2,349,336, the cutting edge of which has a rounding with a radius of 0.05 to 0.1 mm and a cutting angle of 55 ° to 80 °. This shape of the cutting edge is intended to ensure that the cardboard web under tension is severed before the cutting edge has moved completely through the cardboard web. A punching stroke is not carried out with this cutting knife.

The invention has for its object to provide a punch knife whose cutting edge produces an optimal cut quality from the beginning.

This object is achieved by a punch knife that a cutting edge that has a radius with a radius of 0.005 to 0.060 mm.

Due to the rounding of the cutting edge according to the invention, the punching knife produces an optimal cutting quality right from the start. In addition, the punching knife can be subjected to high loads during dressing and punching without deforming plastically under the punching pressure when it hits the steel punching plate. In addition, the preparation time is short. Finally, a wear-reducing cutting edge coating can be provided to increase the service life.

The rounded cutting edge is preferably additionally hardened or surface-finished.

In a preferred embodiment, the cutting edge angle of the rounded cutting edge is 30 to 60 °.

The cutting edge meets the punching plate during the punching process. With this line contact, a mutual flattening takes place in the plane of contact, which can be estimated using Hertz's equations and thus the resulting stresses in the cutting edge. When punching, the punching knife is subject to a swelling continuous pressure load and has a limit load capacity of approx. 1160 N / mm² for a typical steel strip, eg Ck 55. Ideal cutting conditions, for example with a folding boxboard of 300 g / m², stress the steel in the cutting edge with a cutting edge radius of 0.010 mm with only approx. 350 N / mm². This value is higher for commercially available cutting edges, since there is neither a defined radius nor a sufficiently precise, uniform cutting edge width of 0.010 mm. As the cutting radius increases, the cutting load on the steel decreases and is, for example with a cutting edge radius of 0.030 mm arithmetically approx. 180 N / mm². The calculation further shows that a rounding of the cutting edge with 0.010 mm by punching can withstand an overload until the critical tension of 1160 N / mm² of approx. 100 N / cm punching line length is reached, a cutting radius of 0.030 mm is approx. 330 N / cm.

If one overloads a commercially available new cutting edge corresponding to a height difference of 0.035 mm, the cutting edge widens to at least 0.015 mm and with an overload of 0.200 mm, the cutting edge becomes 0.050 to 0.060 mm wide and is flattened unevenly over the cutting length, i.e. not rounded. The cut quality is severely affected.

A rounded cutting edge according to the invention with a radius of 0.030 mm shows no cutting edge change under the same conditions and produces flawless cutting edges in the material to be cut. Extensive tests show that the cut quality e.g. on cardboard boxes with undamaged cutting tips up to 0.040 mm edge radii perfect and indistinguishable from edge radii 0.010 mm.

An embodiment of the invention is explained in more detail with reference to the accompanying figure, which shows the cross section of the cutting area of a punching knife.

The punch knife 1 shown in the figure essentially corresponds to a punch knife as shown for example in DE 39 28 916 C1. A number of such punching knives are usually attached together with creasing lines to the underside of a carrier plate of a punching tool of a punching machine. The punching knives are used, for example, for punching out folding boxes from one lying on a counter-punching plate Carton. During the punching process, the carrier plate is pressurized and moved in the direction of the counter-punching plate until the punching knives touch the counter-punching plate and the cardboard is severed. The carrier plate is then moved away from the counter-punching plate.

The punch knife 1 according to the invention is elongated and has a symmetrical cutting edge 2 running in its longitudinal direction at its end facing the counter-punching plate (not shown).

The cutting edge 2 has two inclined flanks 5, 6 which run symmetrically to the longitudinal center plane 10 of the punch knife 1, which run at an angle of preferably 30 to 60 ° to one another and merge into the side flanks 7, 8 of the punch knife 1. At the outer end of the punch knife 1, the inclined flanks 5, 6 merge into a rounding 9 connecting them, which is also symmetrical to the longitudinal center plane 10 of the punch knife 1. The fillet 9 has a radius of 0.005 to 0.04 mm.

The rounded cutting edge 2 can additionally be hardened or surface-finished.

The rounded punch knives with the increased surface area reduce the fact that the cutting edge does not dig into the punch plate so deeply during punching, so that the impression is not so large. This is gentle on sensitive surfaces to be cut. The reduced impression due to the increased contact area between the cutting edge and the stamping plate reduces the notch stresses in the area of the burial and thus the premature occurrence of fatigue fractures in the stamping plate.

The punch knives lose height in connection with wear. A compromise can therefore be made between increased resilience of the cutting edge and wear. A cutting radius of 0.020 mm is considered to be particularly favorable for this.

The rounding of the cutting edge can be created mechanically, e.g. by remelting by means of lasers with appropriate heat management on normal and cutting-hardened punching knives, which are produced as steel strip lines or from fully machined punching lines as flat flat tools or as curved ones for rotary tools.

Claims (4)

Punching knife for punching out parts of any shape from paper, cardboard, cardboard, plastic films, leather, rubber and the like, characterized by a cutting edge (2) which has a rounding (9) with a radius (3) of 0.005 to 0.060 mm . Punching knife according to claim 1, characterized in that the rounded cutting edge (2) is additionally hardened. Punching knife according to claim 1, characterized in that the rounded cutting edge (2) is surface-finished. Punching knife according to claim 1, characterized in that the cutting angle (4) of the rounded cutting edge (2) is 30 to 60 °.

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