"TOOL FOR A PRESS BRAKE"

DESCRIPTION

The present invention concerns a tool for a press brake and in detail a tool formed partially or entirely of plastic material.

In the machine tool sector, press brakes configured to give certain bending angles to metal sheets, plates or the like, through cold deformation, are well known.

Press brakes generally consist of a bottom bed defining a fixed surface on which to place the metal sheet and carrying a bending die according to the profile of which said metal sheet is bent.

An upper beam is supported so that it can move towards and away from the bed, along a substantially vertical plane. The beam carries integral therewith a bending punch adapted to cooperate with the die to give the sheet the desired shape.

In the context of the present invention, and in the description below, the term tool relates generically to the aforesaid bending punch or bending die or to their assembly.

The majority of tools for press brakes are made of metal, typically of hardened steel. In fact, this structure allows the tools to withstand the high stresses that can be generated during bending of sheets of high thickness and at the same time guarantees limited wear of the working parts, ensuring a tool life of hundreds, or often thousands, of bends.

However, these metal tools have some drawbacks.

A first known drawback is the formation of scratches, scores or the like on the surfaces of the sheet. In fact, during bending, movement between the sheet and the tools, punch and die, causes scratches of various dimensions which, especially for some uses in which the sheet is not painted, are unacceptable.

To solve this phenomenon, the most widely used system is that of interposing a polymer film between the die and the lower surface of the sheet, i.e., the one most subject to degradation. The film is generally unwound from a reel located in proximity of the press.

Although this system is simple and inexpensive, it does not always guarantee optimal results, especially when the forces applied by the punch are considerably high. In fact, at times the film can tear or leave marks on the surface of the sheet, for example in the separation areas of side-by-side sectionalized punches.

Tools, dies and punches made of plastic materials such as polyurethane, nylon or polyethylene are also known on the market.

These tools, with which it is possible to obtain a high quality surface of the sheet, can however only be used for small samples of sheets of limited thickness.

In fact, the plastic materials used are subject to premature wear in the contact areas with the sheet; the most serious problem of wear consists of the fact that it causes unacceptable deviations from the machining dimensional tolerances. Moreover, the mechanical strength of these materials only allows limited forces, which are not suitable to bend thick sheets, to be applied.

Returning to hardened steel tools, another limit encountered are the long times and high costs required to produce special tools in a small number of pieces or even in only one sample.

In fact, it is often necessary for a special tool, i.e. with a non-standard shape, to be available in a few days, to produce samples of articles with only a few pieces.

On these occasions, the costs and times required to produce a steel tool, with a useful life unjustifiably much higher with respect to its effective use, are not compatible with market demands.

In this context, the object of the present invention is to propose a tool for a press brake consisting, as previously specified, of a punch, of a die, or of both, that overcomes the limits of the prior art cited above. It is therefore an object of the present invention to propose a tool for a press brake that allows a sheet to be bent without damaging its surfaces.

Another object of the present invention is to produce a tool for a press brake that has a longer useful life with respect to known tools made of plastic material.

Yet another object of the present invention is to provide a tool for a press brake that can bend sheets of greater thickness with respect to known tools made of plastic material.

A further object of the present invention is to provide a tool that with the same performance as a similar tool made of steel is less expensive and can be produced more rapidly.

These objects are achieved with a tool for a press brake, in the form of a punch or die, comprising a body connectable to a mobile or fixed part of the press brake, this body having a working part, intended to come into contact with a part to be bent, typically a sheet, said tool having, at least at the working part, at least the outer surface made of bisphenol A polycarbonate.

Therefore, according to this invention, at least the working part of said tool has an outer surface made of or covered with said bisphenol A polycarbonate.

The tool with the working part in this thermoplastic material ensures excellent protective properties of the surface of the sheet during bending and, at the same time, maintains the dimensional tolerances within the limits required for a number of bending cycles sufficient to complete samples or small production batches.

According to an embodiment of the invention, the working part is covered with a layer of said polycarbonate. Said layer preferably has a constant thickness comprised between 2 mm and 10 mm.

According to a preferred variant, said layer is comprised in an insert that can be movably attached to said working part. According to this variant, the remaining part of the body of the tool can be made of metal and said insert can be attached at the working part that contacts the surface of the sheet during bending.

For this purpose, advantageously, said insert can be provided with fixing means adapted to block it at least temporarily on the body of the tool. Said fixing means are preferably magnets. Alternatively, the fixing means are selected from interlocking profiles, adhesive material or the like.

According to another embodiment of the invention, the whole of the working part or the entire body is made of polycarbonate.

According to this variant, the tool is preferably obtained by means of 3D printing.

Especially when the whole body is made of polycarbonate, this tool thus obtained is particularly suitable for special applications in which it is necessary to construct only one or just a few examples of a tool with a given shape.

In fact, bisphenol A polycarbonate is particularly suitable for use in 3D printing. The tool constructed by means of this process is therefore much faster and less expensive to produce with respect to a conventional steel tool.

According to an aspect of the invention, the material preferably has the following mechanical properties:

- tensile strength comprised between 45 MPa and 75 MPa and preferably between 60 MPa and 70 MPa, determined with the method ASTM D638;

- longitudinal modulus of elasticity (Young) comprised between 2100 and 2600 MPa and preferably between 2300 and 2500 MPa, determined with the method ASTM D638;

- elongation at break comprised between 2% and 12% and preferably between 4% and 10%, determined with the method ASTM D638.

The tool thus produced has a mechanical strength such as to allow bending of sheets of average thicknesses, for example up to 3 mm, even when the whole body is made entirely of polycarbonate. Moreover, the aforesaid mechanical properties give the tool a hardness and a stability of the shape of the outer surface of the working part such as to allow the tool to be used for a much higher number of bending cycles with respect to known tools made of other plastics or polymers.

The tool of the invention is therefore the deal solution when special tools destined for the production of small batches of articles to be bent required to be rapidly produced.

According to the invention, suitable polycarbonates, having the aforesaid mechanical properties, have a hardness, measured with the Rockwell method, standard ASTM D785, preferably comprised between R105 and R125.

Further characteristics and advantages of the present invention will become more apparent from the description of an example of a preferred, but not exclusive, embodiment of an adjustable die for a press brake, as illustrated in the accompanying figures, wherein:

- Fig. 1 is a lateral view of a die and of a punch according to a variant of the invention;

- Fig. 2 is a lateral view of a die and of a punch according to another variant of the invention.

The attached Fig. 1 schematically illustrates a punch 10 and a die 20 for a press brake , between which a sheet L to be bent is interposed.

The punch 10 comprises a body 11 provided with a coupling portion 12, for connection to the cross member of the press (not illustrated), and a working part 13 adapted to press the sheet L. The working part has one or more bending edges which, in collaboration with the die 20, give the shape of the sheet to be bent.

Similarly, the die 20 comprises a body 21 connectable to the bed of the press (not illustrated) by means of a coupling portion 22. The sheet L to be bent is placed at the working area 23 of the die 20 toward which the punch 10 is moved by means of the mobile cross member.

According to a first variant of the invention, the body 11, 21 of the tool, i.e., the punch 10 or the die 20, is made entirely of bisphenol A polycarbonate. As mentioned above, the tool is preferably obtained by means of 3D printing.

The presence of the aforesaid plastic material at the outer surface 13 a, 23 a of the working part 13, 23, makes it possible to almost totally eliminate the formation of scratches, scores or marks on the surface of the sheet L.

Moreover, said material provides the tool with a mechanical resistance sufficient to withstand the forces generated during bending of thin sheets, for example of around 0.5 mm, but also of thicker sheets, for example up to 3 mm.

According to another variant of the invention, illustrated in Fig. 2, the body 11, 21 of the tool, punch 10 or die 20, is made of metal, typically steel, optionally hardened.

At the working part 13, 23, the tool is covered with a layer 14, 24 of polycarbonate having the same mechanical properties listed above.

Advantageously, this variant of the tool is characterized by a greater strength, due to the body made mainly of metal, allowing bending of sheets of even greater thickness, while maintaining the ability not to damage the surface of the sheet.

According to a first embodiment, said layer 14, 24 is comprised in a removable insert 15, 25 which can be attached to the body 11, 21. According to this variant, said insert 15, 25 can thus be replaced when it becomes worn, while the same metal body is maintained.

Typically, the layer of polycarbonate of the insert has a constant thickness and covers only an area or all of the working part, i.e., those surfaces that come into contact with the sheet during bending.

The thickness of the layer is generally comprised between 2 mm and 10 mm and preferably between 4 mm and 8 mm. The insert can be simply placed on the working part of the tool, for example when it is attached to the body 21 of the die 20, or it can be provided with fixing means to block it on the body of the tool.

According to a preferred variant, said fixing means comprise magnets 16, 26, embedded in the polycarbonate layer and that, preferably, face the inner surface of the insert.

According to another variant, not illustrated, the fixing means can comprise interlocking profiles or adhesive strips or other equivalent means.

Also in these variants, the polycarbonate layer 14, 24, i.e., the insert 15, 25, is preferably produced by means of 3D printing.

According to another variant of the invention, the polycarbonate layer is applied directly to the body of the tool by means of the aforesaid 3D printing process.

The invention has been described purely for illustrative and non-limiting purposes, according to some preferred embodiments. Those skilled in the art may find numerous other embodiments and variants, all falling within the scope of protection of the claims below.