CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a National Stage under 35 U.S.C. § 371 of International Application No. PCT/EP2018/025173, filed Jun. 25, 2018, which claims priority to German Patent Application No. 102017115167.2, filed Jul. 6, 2017, the contents of all of which are incorporated by reference in their entirety.

The invention relates to a punching tool comprising a punch and a die, in particular for deforming sheet metal so as to create local projections which can be used as creasing projections for generating creases in sheet materials.

Creasing machines are used for generating one or more creases in a sheet from which blanks are cut which are folded. Each of the creases forms kind of a “hinge” which allows the later formed blanks to be folded at a well defined place.

The creasing machine can be formed as a device or system which is either a standalone unit or is integrated into a larger machine or system such as a printing machine or a finishing machine.

The sheets can be made from cardboard, carton or a foil, and they can be provided to the creasing machine separately or in a continuous manner as part of a web.

The creases are formed by locally applying a pressure onto the sheet. To this end, creasing knives are known which are pressed onto the surface of the sheet so as to generate the crease. It is also known to provide local projections on the creasing tool, for example by etching away those portions of the creasing tool which shall not project, or by locally applying a plastic material in a liquid condition, which is then cured.

The creasing tool can either be generally flat and be moved back and forth in a direction which is generally perpendicular with respect to the plane in which the sheet extends, or it can be generally cylindrical and be rotated so as to engage at the sheet when it is being transferred through the creasing area.

The problem with all creasing machines is that they can hardly be quickly adapted to a specific pattern of creases to be applied to a sheet. This has become more of a problem since digital printing allows changing very quickly from one printing job to a different one.

Assuming that the creasing tool is to be manufactured by means of an etching process, it may take several hours until a new creasing tool is available. Assuming that the creasing projections are formed by applying a plastic material to a carrier, the manufacturing times might be shorter, depending on the time which is necessary for curing the plastic material. However, the lifetime of such a creasing tool is significantly shorter than the lifetime of a creasing tool comprising an etched steel plate. In any case, the step of adapting the creasing machine to a new creasing job is the bottleneck when the creasing machine is used in connection with a digital printing machine.

The object of the invention is to provide a punching tool with which a creasing plate can be quickly manufactured so that it is available in a flexible manner for working on a new creasing job.

In order to achieve this object, the invention provides a punching tool comprising a punch and a die, in particular for manufacturing a creasing plate, the die having a straight recess for accommodating material deformed by the punch, characterized in that the die has an outer contour which extends, adjacent the open end of the recess, at an angle of less than 90° with respect to the longitudinal direction of the recess. Owing to the special contour of the die, it is possible to generate creasing projections in a creasing plate, which terminate at a small distance from each other. This is particularly advantageous as it allows generating creases in a sheet to be folded, between which only a very small portion of uncreased material is present so that the folds are very precise.

Preferably, the angle is in the order of 45°. The advantage of this geometry is that merging creasing projections can be generated which extend at an angle of 45° with respect to each other.

According to a preferred embodiment, the punch has a projection with rounded end portions. The rounded end portions help in ensuring a smooth transition between the individually deformed areas so as to create a continuous creasing projection.

Depending on the geometry of the creasing projection, the rounded end portions have at least one of a large and a small radius. A large radius is advantageous for achieving a smooth transition between the separately deformed areas which form the creasing projection. A small radius is advantageous for creating a creasing projection which either terminates in a very small distance from an adjacent creasing projection, or which even intersects with the adjacent creasing projection.

Regarding the large radius provided at a forward or rearward end of the projecting portion of the punch, values in the order of 2 to 15 mm have shown to be beneficial in that they ensure a smooth transition from the deformed material of the creasing projection towards the undeformed material.

Regarding the small radius provided at a forward or rearward end of the projecting portion of the punch, values in the order of 0.2 to 2 mm have shown to allow the desired small distance between adjacent creasing projections while at the same time ensuring that there is no damage to the deformed material of the creasing plate.

According to an embodiment, the punch extends along a straight line and has a length, measured along the straight line, in the order of 5 to 50 mm. The longer the punch, the less individual strokes are necessary for generating a creasing projection. However, shorter punches increase the flexibility and decrease the force which is necessary for deforming the creasing plate.

According to a preferred embodiment of the invention, an elastic ejector is associated with the die. The ejector helps pushing the plastically deformed material out of the die. Further, it prevents that the creasing plate be scratched by touching the die.

The elastic ejector can have the form of a plate made from rubber or an elastomer. Such plate can be cut in a very precise manner by waterjet cutting.

Preferably, the ejector surrounds the die. This allows mounting the elastic ejector to the die by simply forming the elastic ejector with a suitable inner contour adapted to the outer contour of the die.

In view of the aim of generating creasing projection, it has been found out that a height of the projecting portion of the punch in the order of 1.0 to 2.0 is advantageous, in particular in the order of 1.6 mm.

Further, the projecting portion can have at its apex a radius, when viewed in a cross section perpendicularly to the longitudinal direction of the projection portion, which is in the order of 0.1 to 0.5 mm.

Still further, the projecting portion has, when viewed in a cross section perpendicularly to the longitudinal direction of the projection portion, a width in the order of 0.5 to 4 mm.

