Method for free bending

A bending machine for free bending of a workpiece at a prescribed bending angle, comprising:

• a control device for controlling a trajectory of a bending punching tool relative to a bending edge of a lower die, and
• a measuring device for:
• (i) determining a trajectory of the bending punching tool and for determining a plurality of forces applied to the workpiece by the bending punching tool during the trajectory such that the plurality of forces are used to form a measuring curve relative to the trajectory;
• and
• (ii). calculating a correcting parameter, relative to the prescribed bending angle and a determined angle deviation therefrom, the created measuring curve and a model calculation representing the free bending process, with which bending forces for achieving the prescribed bending angle are determined, wherein:
• the model calculation includes a simulation of the free bending process based upon an iterative calculation according to a finite element method.

A free bending process, comprising:

• prescribing a bending angle about which a workpiece is to be bent;
• bringing the workpiece into contact with a bending edge of a lower die about which the bending angle is to be formed, the workpiece arranged as a sheet metal plate relative to the lower die;
• executing a first bending process step including bending the sheet metal plate across the bending edge by moving a bending punching tool relative to the lower die for generating a current bending angle of the sheet metal plate;
• measuring the generated current bending angle at least after executing the first bending process step;
• executing further bending process steps each corresponding to the first bending process step;
• determining during the further bending process steps a plurality of bending forces to be applied by the bending punching tool for achieving the prescribed bending angle relative to a trajectory of the bending punching tool;
• creating a measuring curve including the determined bending forces related to the trajectory;
• determining an angle deviation from the current bending angle and the prescribed bending angle;
• calculating a correcting parameter based on the determined angle deviation, the created measuring curve and a model calculation representing the free bending process, wherein the correcting parameter includes at least one bending parameter having an influence on bending characteristics of the workpiece, the at least one bending parameter included in and acquired from a material property database, wherein new values for the database are generated based upon a precise analysis of the bending result of the implemented bending process, such that the stored data of the database continuously increases;
• and
• executing at least one final bending process step corresponding to the first bending process step based upon the calculated correcting parameter.