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Control System Algorithm for the Prediction of Sprinback in Air Bending

The phenomenon of springback, which is ruled by strain recovery after removal of forming loads, is of remarkable interest in air bending of metal sheets. In this process, the final angle is affected by a number of parameters related to both process geometry (sheet thickness, die and punch radii) and material properties (elastoplastic stress-strain law); because of this, punch stroke has to be calculated in a nontrivial way and a number of input parameters should be taken into account. In this work the study of total load as a function of displacement is used to collect information about material stress-strain law; using this approach, load data may be exploited to fine tune the mathematical description of the material and, finally, to improve springback prediction. A customized press brake able to measure both displacement and force during bending was fabricated for this purpose. The press brake is equipped with a control system algorithm able to collect material information directly during the initial stage of the bending process. These collected data are used to feed a model based on a FEM simulation and the model output is the final punch displacement suitable to obtained a specific bending angle after unloading. The program utilized for the simulation is Deform 2D. Preliminary tests were executed on metal sheets having different thickness.