The present invention relates to a machine for working sheet metal parts and to a driving system for such a machine. More particularly, the invention refers to a flanging machine for connecting by flanging sheet metal panels, such as, for example, car body panels.
FIGS. 1A to 1C of the appended drawings schematically show the operation of flanging a pair of sheet metal panels 1 and 2, that is, an outer panel and an inner panel, respectively. The two panels 1, 2 are first arranged (FIG. 1A) with respective flat edge portions 3 and 4 in contact with each other on a workpiece-carrying structure (not shown), generally formed by a bed suitably shaped in accordance with the piece to be worked. The flat edge portion 3 of the outer panel 1 has an edge 3a which is initially bent at a given angle (typically 90 degrees) with respect to the plane of the portions 3 and 4 (FIG. 1A) and is intended to be further bent and pressed on the flat edge portion 4, thereby clamping the latter against the underlying portion 3. The flanging operation usually includes a first phase, known as “pre-flanging”, in which the edge 3a is bent to a given angle (typically 45 degrees) with respect to the plane of the edge portions 3 and 4 by applying a first force F1 preferably perpendicular to the said plane (FIG. 1B), and a subsequent phase, or “final flanging”, in which the edge 3a is further bent until it contacts the flat edge portion 4 and is then pressed against the latter by applying a second force F2, also preferably perpendicular to the plane of the portions 3 and 4 (FIG. 1C).
For the sake of simplicity, it will be assumed hereinafter that the two flat edge portions 3 and 4 of the panels to be flanged are arranged in a horizontal plane and therefore that the direction along which the flanging forces are applied is vertical. The terms “horizontal” and “vertical” are thus to be understood, in the description and the claims which follow, as parallel to the plane on which the edge portions of the panels to be flanged lie and as perpendicular to that plane.
The flanging operation described above is commonly performed with the use of a tool-carrying unit 10 of the same type as that schematically shown in FIG. 2. The tool-carrying unit 10 is mounted on the flanging machine (not shown) so that it can be moved vertically to perform the pre-flanging and the final-flanging operations, as well as moved substantially horizontally towards or away from the working area in order, for example, to allow the workpiece to be loaded or unloaded.
The unit 10 carries a first, pre-flanging tool 11 having a working surface 11a inclined at the pre-flanging angle (typically 45 degrees) with respect to the vertical direction, and a second, final-flanging tool 12 having a working surface 12a inclined at 90 degrees with respect to the vertical direction.
A flanging machine of the above-mentioned type is known, for example, from European patent application EP 0 924 005. According to this known solution, the vertical movement of the tool-carrying unit is driven by a screw mechanism controlled by an electric motor, whereas the movement towards and away from the working area (in this case, a tilting movement) is driven by a leverage controlled by a pneumatic cylinder.
The use of a screw mechanism for driving the vertical movement (working movement) of the flanging machine has first of all the disadvantage of a high cost, due both to the high precision required for the production of the screw and to the complexity of the electronic control system required to ensure the correct operation of the machine. Moreover, the precision of the machine, and hence the quality of the worked pieces, may tend to decrease with time as a result of the plays due to the wear of the screw mechanism.
German utility model DE 295 11 071 U discloses a driving sys-tem for driving a tool-carrying unit of a machine for the working of sheet metal parts, in particular a bending or punching machine, wherein the tool-carrying unit is slidably mounted along a vertical direction on a supporting structure of the machine. This known driving system comprises a driving shaft rotatably mounted on the supporting structure and carrying two cam discs engaging with two rollers mounted on the tool-carrying unit. The one cam disc and roller assembly controls the working stroke of the tool-carrying unit, while the other cam disc and roller assembly controls the return stroke of the tool-carrying unit.
A flanging machine for the working of sheet metal parts is known from European patent application EP-A-0 933 148. In this case, the vertical reciprocating motion of the tool-carrying unit is driven by an electric motor which is fixedly mounted on a supporting structure of the machine and operates a driving shaft rotatably mounted on the sup-porting structure and connected to the tool-carrying unit by means of a cam and lever mechanism.