BENDING MACHINE FOR SHEET METAL PANELS HAVING A BLANK HOLDER WITH UNIFORM COMPRESSION

Abstract: The bending machine has a blank holder (4) with a support (16, 17, 18) hinged on a fixed base. The blank holder is operated by a plurality of hydraulic cylinders (20) which act from the bottom up, reacting on the fixed base (1). The machine has opposite blades (2 and 3) operated by horizontal (10) and vertical (15) cylinders, whose ends are hinged on the fixed base (1). Said opposite blades (2 and 3) are held by a common support (6, 7) through which pass the stems (21) of said hydraulic cylinders (20) operating the blank holder. Said hydraulic cylinders (20) are also equipped with a stoppage system for stopping the blank holder in a position above a sheet metal panel placed over a fixed counterblade (5).

Description: The present invention relates to a bending machine for sheet metal panels having a blank holder with uniform compression. Several bending machines are known which have a fixed counterblade on which a sheet metal panel is positioned for bending. The latter is held by a blank holder while a blade consisting of a pair of counterblades executes the required bend of the edge of said sheet metal panel. An example of such a bending machine is described in the AT-A- 372883 & EP-A- 0022 122 in the name or Voest Alpine Aktiengesellschaft, which document discloses the combination of features according to the pre-characterising part of claim 1. In such a bending machine a blank holder slides in lateral guides which are integral with the base of the machine to rise up and came down on a sheet metal panel positioned on a fixed counterblade. The blank holder is operated from above by hydraulic cylinders placed at its ends and is integral with arc-shaped supporting arms, on which actuators for moving the two blades are hinged. The fixed counterblade is in its turn integral with the fixed base of the machine, on which additional actuators for moving the blades are hinged. The greatest drawback which occurs in a bending machine of this type is that the forces which urge the blank holder upwards during the bending operation are not uniformly distributed in the direction of the line of bending but are concentrated more or less along the centre line of the machine according to the length of the bend to be executed and to the thickness of the sheet metal panel itself. It follows that the distance between the active edge of the blank holder and the underlying counterblade is greater in the centre than at the outer ends, so that, since the bending line follows the line of the blank holder's active edge, the bend is not straight. For the same reason it is not possible to make a so-called "safe hands" uncrushed U-shaped bend, because the distance between the superimposed edges would be less at the ends than at the centre. The problem is certainly not solved by the two cylinders which press the blank holder downwards. Since the two cylinders are at the ends of the blank holder, they are not in a position to generate uniformly distributed forces, except with a hypothetical infinitely rigid blank holder. In fact, if the sheet metal to be bent is short and of substantial thickness, such a drawback is heightened; the blank holder actually tends to bend inwards by pivoting on the edges of the sheet metal, so that the central part of the blank holder rises up and assumes a concave configuration. To overcome this drawback it is possible to exert pressure on the blank holder with a multiplicity of hydraulic cylinders uniformly distributed on the upper part of the machine, so as to counteract the force which tends to bend it, but this solution is of little advantage since it increases both cost and weight of the known bending machine and also makes its structure more complicated. US-A- 2552616 discloses a bending machine having a blank holder support moved downwards by hydraulic cylinders mounted on the fired base. The position of the hydraulic cylinders is however such as to require a rear extension of the blank holder support beyond its hinge point on the fixed base. In view of this state of the art, the object of the present invention is to accomplish a bending machine for sheet metal panels in which the blank holder is not bent inwards, more precisely it is required that said blank holder exerts on a sheet of metal to be bent in any required size a uniformly distributed pressure without increasing the weight of the bending machine or complicate its structure. According to the invention, such object is attained by a bending machine according to claim 1. This solution induces a movement of the blank holder that is accurately parallel, ensured by its being hinged on a rigid object such as the base of the machine, while the different cylinders distribute the closing force of the blank holder in the most appropriate manner without causing any complication in the machine's structure. In a preferred embodiment of the present invention the common support of the opposite blades is connected to vertical and horizontal operating cylinders, which react on the fixed base. In this way the inclination of the horizontal cylinders remains independent of the sheet metal's thickness. Working together with said horizontal cylinders are support levers which are connected by a torsion bar common to all the cylinders. A mechanically parallel movement of the blank holder support is thus ensured. Means are also provided to obtain the stoppage of the blank holder in a predetermined position so that so-called "safe hands" uncrushed U-shaped bends are produced on the edges of the sheet metal panels. Said means are preferably constituted by wedges which co-operate with said hydraulic cylinders which operate the blank holder so as to adjust the stoppage point of the downward stroke of the blank holder itself. An embodiment of the present invention is illustrated as a non-limiting example in the enclosed drawings, in which: Fig. 1 shows a bending machine for sheet metal panels according to a preferred embodiment of the invention, in a section along the line I-I in Fig. 2; Fig. 2 shows the above machine in a section along the line II-II in Fig. 1; Fig. 3 shows the above machine in a schematic section along the line III-III in Fig. 1. With reference to Figures 1 and 2, a bending machine is shown with a fixed base 1 comprising a counterblade 5 for supporting the sheet metal panel to be bent, a blank holder 4 and a pair of opposite blades 2 and 3. The two blades 2 and 3 are fixed to a C-shaped element 6 connected by means of an intermediate boxed support 7 to arms 8 rotating on pivots 9, which also connect one end of hydraulic cylinders 10 and of levers 11 fixed to a torsion bar 12. The hydraulic cylinders 10, which provide the horizontal translation of the blades 2 and 3, are supported by pivots 13 rotating in brackets 14 of the fixed base 1. The C-shaped element 6 is connected in the lower part to further vertical hydraulic cylinders 15 which produce the vertical translation of the blades 2 and 3 and which are hinged in the lower part of the base 1. As shown in Fig. 1, the blank holder 4 is integral with a plate 16 fixed by means of an intermediate boxed support 17 to arms 18 projecting inside the boxed element 17 fixed to the plate 16 and which are hinged in 19 to said brackets 14 of the base 1. The blank holder 4 is induced to rotate on the pivot 19 by means of hydraulic cylinders 20, whose stems 21 pass through the opening 28 of the boxed support 7 for the blades 2 and 3. Said stems 21 have their upper ends 29 connected to the arms 18 inside the boxed element 17 supporting the blank holder 4. Said hydraulic cylinders 20 are supported in a rotatable way in the lower part of the base 1 and exert a downward force on the blank holder 4, which is distributed along the longitudinal extension of the boxed element 17. The hydraulic cylinders 20 are connected to a stoppage system having stoppage means 22 of the stroke of the stems 21 so that the stop of the blank holder 4 is obtained in a position which is above the sheet metal panel positioned over the underlying counterblade 5. This stoppage condition is necessary for executing bends that are so-called "safe hands" uncrushed U-shaped bends on the edges of a sheet. Such stoppage means 22 are constituted by a pair of wedges 23 and 24 associated with each hydraulic cylinder 20, in which the upper wedge 23 is integral with the stem 21 of the corresponding hydraulic cylinder 20 and the lower wedge 24 is integral with all the other lower wedges 24 by means of successive portions of a rod 25 operated by a hydraulic cylinder 26. Each wedge 24 has a central aperture 27 (Fig. 3) for the passage of the stem 21 and such aperture 27 has an extension sufficient to permit a certain translation of the wedge in a longitudinal direction parallel to the blank holder 4 using as a sliding guide the upper end of the hydraulic cylinder 20. Given a preselected position of the lower wedges 24, a stoppage position of the stems 21 of the cylinders 20 is obtained, corresponding to a stoppage position of the blank holder 4. The operation of the bending machine described is as follows. Starting from the position shown in Fig. 1, since the edges of a sheet metal panel are to be bent, the blank holder 4 is raised through its rotation by means of the hydraulic cylinders 20 on the pivots 19 of the arms 18. A sheet metal panel is then positioned on the counterblade 5 so that the part of the panel to be bent protrudes from the edge of the counterblade, towards the inside of the machine, the blank holder 4 is then lowered onto the panel, pressing it in a uniform manner against the counterblade 5, if necessary modulating the pressure exerted by the hydraulic cylinders 20 in an appropriate manner. At this point, by means of the vertical 15 and horizontal 10 cylinders one of the two blades 2 and 3 is pushed up against the edge of the panel and the required bend is obtained. If a U-shaped bend is required, a so-called "safe hands" uncrushed U-shaped bend, it will be the lower blade 3 to operate first from the bottom up and thus produce a partial bend. The blank holder 4 is then raised again and the sheet metal panel will be positioned slightly further back on the counterblade; at the same time the downward stroke of the blank holder 4 is adjusted by moving the wedges 24 so that the stems 21 are stopped, by coupling with the corresponding upper wedges 23, so as to stop the downward movement of the blank holder in a position above the sheet metal panel. The hydraulic cylinders which lower the blank holder 4 are then operated again, the blank holder pushes against the previously-obtained partial bend, producing a so-called "safe hands" uncrushed U-shaped bend which is uniform along the entire side of the panel thanks to the wedged stoppage system and to the uniform distribution of the force along the entire edge of the sheet metal panel. If conventional-type bends are required, in which it is not necessary to stop the blank holder in a higher position, the wedges 24 are arranged in a rest position in which there is no connection with the wedges 23 when the blank holder is lowered onto the counterblade 5.

Claims: Bending machine for sheet metal panels consisting of a fixed base (1) with a counterblade (5), a superimposed movable blank holder (4), a pair of opposite blades (2 and 3) which are integral with a common support (6, 7) and means (10 and 15) for operating said pair of blades to bend said sheet metal panels, characterized in that said blank holder (4) has a support (16, 17, 18) hinged on the fixed base (1) and operated by a plurality of hydraulic cylinders (20) mounted on the fixed base (1) along a line parallel to the longitudinal direction of the blank holder (4) and acting downwards on said support (16, 17, 18), said opposite blades (2, 3) are movably mounted on the fixed base (1) under said blank holder support (16, 17, 18) and are provided with openings (28) for the passage of stems (21) of said hydraulic cylinders (20). Machine according to claim 1, characterized in that said means (10, 15) for operating said blades (2, 3) are constituted by vertical and horizontal cylinders (15, 10) reacting between said base (1) and said blades (2, 3). Bending machine according to claim 2, characterized in that said horizontal cylinders (10) are connected to said blades (2, 3) by means of pivots (9) which are also connected with levers (11) rigidly connected to a torsion bar (12). Machine according to claim 1, characterized in that said hydraulic cylinders (20) are equipped with a stoppage system (22) for stopping the downwards strokes of the blank holder (4) in a prefixed position above a sheet metal panel positioned on the counterblade (5). Bending machine according to claim 4, characterized in that said stoppage system (22) comprises a plurality of wedges (23 and 24) associated with said hydraulic cylinders (20) so as to vary the extension of the downward stroke of the blank holder (4). Machine according to claim 5, characterized in that said wedges (23, 24) comprise movable elements (24) connected to one another and to the stem (25) of a further hydraulic cylinder (26) operating in a horizontal direction.

Inventors: SALVAGNINI, GUIDO
Applicants: SALVAGNINI S.P.A.
Application year: 1988
Main classification: B21D5
IPC codes: B21D5