Patent ID: 7260971

Claim:
An apparatus for locking a sheet of metal suitable to be shaped in a press having a first lower die part and a second die part, a base upper ram, comprising: a first sheet presser; a second presser; a circuit for regenerating and supplying working fluid; at least one fluid-operated actuator for actuating in vertical translational motion said first sheet presser, which is adapted to support, in an initial step of an operation for shaping by pressing or drawing, a sheet of metal to be shaped, the metal sheet being arranged above the press first lower die part, which is rigidly coupled to the base of the press, said first presser being adapted to cooperate with the second presser, which is rigidly coupled to the press second die part associated with the upper ram of the press, in locking a perimetric portion of the sheet of metal during said shaping operation, said at least one actuator being part of the circuit for regenerating and supplying the working fluid, that is provided with return means for delayed return of the at least one actuator, upon opening of the press, in order to protect integrity of the shaped sheet, said at least one actuator being a hydraulic cylinder and said working fluid being a hydraulic liquid.