METHOD FOR CONTROLLING THE BENDING ANGLE IN A SHEET-METAL BENDING PRESS

DESCRIPTION

The present invention relates to presses, and in particular relates to bending presses for sheet metal or the like.

Bending presses normally comprise a bench on which the counter-die or bending die is positioned, and a movable member, otherwise called "pestle", which has a bending blade mounted on the side directed towards said bench; the pestle is supported suspended above the bench by a gantry structure and is operated with an alternating movement along two vertical guides by means of suitable hydraulic or mechanical operating means.

Bending is performed by means of co-operation of the blade with the die; the metal sheet is positioned on the bench above the die and the bending blade is lowered with force onto the metal sheet, thus producing the bend. The reaction force arising from the deformation of the metal sheet, which is uniformly distributed along the entire length of the workpiece, is the cause of elastic deformations which affect both the bench and the pestle and the "shoulders" of the press. Consequently, the article has a more marked fold which generally corresponds more to the desired fold, in the end zones, and is more "open" in the central portion, where there are the greater elastic deformations. Obviously, the longer the workpiece to be machined, the greater are the defects which are encountered, since the greater is the force applied to the fold.

According to a patent in the name of the same applicant, in order to overcome the abovementioned problem, a bending press provided with a hydraulic compensation device has been developed, said compensation device consisting of a plurality of hydraulic units interconnected in a closed circuit and operationally arranged in the machine so as to support, directly or indirectly, the pestle and/or the bench. In particular the compensation device is positioned inside the bench underneath the die.

With this type of bending press significant results are achieved for sheet-metal bending operations which are performed by exerting a compressive force with the bending blade until the metal sheet comes into contact with the bottom of the cavity formed by the die; this operation is normally called "hollow bottom bending" or

"coining". This, however, is not the sole machining operation possible in machines of this type, and so-called "air bending" is equally important, namely bending performed by adjusting the stroke of the pestle so that the blade stops before the blade has reached the bottom of the die cavity.

The object of the present invention is to provide a system which is able to control the uniformity of the profile acted on by the tools in a bending press, namely allows adjustment of the bending angle in a machine where the pestle, the bench supporting the die, or both the parts, are provided with a compensation device, irrespective of the type of bending operation performed.

The present invention therefore relates to a method for controlling the bending angle of a bending press and for use thereof with any type of bending operation, said press comprising a movable member carrying the bending blade, a bench supporting the die, a device for compensating for the load deformations of the bench and the movable member, and a control unit, said method comprising the following steps: entering the characteristic data of the metal sheet, the characteristic data of the bending blade and the die, and the data for calculating the force to be applied; performing a complete idle stroke of the movable member with application of the previously calculated force until the bottom of the die cavity is reached; fixing the compensation device in the configuration thus obtained; recording the configuration obtained by means of optical readers and sending the corresponding data to the control unit which will regard it as zeroed and an initial condition for setting the desired angle; subsequent positioning of the metal sheet on the bench and consequent bending in accordance with the settings determined.

Further advantages and characteristic features will become clear from the following detailed description of an embodiment of the method according to the present invention, provided by way of a non-limiting example with reference to the accompanying sets of drawings in which:

Figure 1 shows a schematic diagram of a bending press of the type used in the method according to the present invention;

Figure 2 is a side elevation view of the machine according to Fig. 1 ; and

Figure 3 shows the flow diagram for the method according to the present invention.

Figure 1 shows schematically a press which operates in accordance with the method according to the invention; 1 denotes the load-bearing frame of the press, which has in its top portion a movable member 2 connected at its ends, via two hydraulic jacks 101 , to the frame 1 of the press. On its bottom side directed towards the bottom portion of the frame 1 the movable member 2 carries a bending blade 3 intended to co-operate with the die 104 situated on the bench 4 of the frame 1. The bottom portion of the frame, which is supported by the support feet 201 , contains a bench 4 having, arranged thereon, the die 104 intended to co-operate with the bending blade 3 for bending the metal sheets intended for machining in the press. A device 5 for compensating for the load imparted by the movable member 2 is positioned underneath the bench; in this specific case the compensation device comprises a plurality of hydraulic actuators 105, each of which controls a section of the length of the bench 4. Each actuator 105 is connected, by means of a respective line 205, to a regulating unit 305 which in turn connects the actuator to a fluid supply manifold (not shown in the figures) which supplies in a manner known per se the hydraulic circuit of the actuators 105; the compensation device 5 is also connected to the control unit 10.

With reference to Fig. 2 of the accompanying drawings, the bending machine comprises two optical sighting units 6 which are situated on the sides of the machine and are connected to the control unit 10 visible in Fig. 1. The hydraulic jacks 101 which are visible in Fig. 1 are also connected to this control unit 10. Each of these optical sights 6 comprises two parts 106 and 206 which are fixed respectively to the movable member 2 of the machine and to the frame 1 thereof. These parts 106 and 206 are therefore mounted slidably with respect to each other, in particular the part 106 is mounted slidably with respect to the part 206. The part 206 is connected to the frame 1 by means of a link piece 216 which allows a certain adjustment of the heightwise position thereof with respect to the frame 1.

The operating principle of the method according to the present invention will become clear from the description below, with particular reference to the flow diagram in Figure 3. The first step in the method, which is indicated by 20 in Figure 3, envisages entering in the processor of the control unit the characteristic parameters of the metal sheet to be machined, namely its length, which is used to determine the position thereof on the bench and therefore any exclusion of the end zones of the compensation device, the thickness, the type of material and the bending angle, which is required only when the bending operation in question is performed using the so-called "air" method described above. Moreover, the dimensional characteristics of the bending blade, as well as the characteristics of the die, with particular reference to the opening of its cavity, which also represents a necessary piece of data for performing "air" bending operations, must be introduced into the processor.

On the basis of the data entered, the control unit 10 distinguishes (step 22) the type of bending operation which must be performed, making a distinction on the basis of the data introduced into its memory; if, in fact, the data for the bending angle and the data for the opening of the die cavity have been entered, the bending operation to be performed will be an "air" bending operation, otherwise it will consist of cavity bottom bending or coining.

In the latter case, the successive steps will be: blocking the actuators (30) which are situated beyond the lengthwise limits of the metal sheet to be machined and which therefore must not be active during compensation, positioning the workpiece (31 ), and executing bending (32). The bending force, suitably regulated on the basis of the data introduced into the control unit, will result in the reaction of the compensation device, and bending will therefore be free from the defects which are commonly encountered during machining using presses which do not have this device.

In the case where instead the control unit detects that the bending operation for which the machine is being prepared is of the "air" type, an idle stroke of the movable member 2 will be performed (23), namely without any metal sheet, until the bending blade 3 reaches the bottom of the cavity of the die 104. In this way, the bench, or more specifically the compensation device 5, will react to the impression force applied; the configuration of the bench resulting from this idle stroke of the movable member is then fixed (24) by means of the regulating units 305. At this point, the optical sights 6 will record the real configuration assumed by the ends of the bending blade (25) and will send the data to the control unit 10 which will regard said data as an initial condition for calculating the penetration of the bending blade, thus obtaining the required bending profile. The workpiece will at this point be inserted into the machine (27) and bending will be performed (28).

This thus overcomes the drawbacks of the known machines described above, which, during air bending, were unable to achieve the same advantages as those associated with a bending operation of the coining type.