ASSESSMENT OF A GEOMETRICAL FORMABILITY CRITERION FOR METAL SHEETS

This study aims at the development of a method for the prediction of the necking and wrinkling sensitivity just during the designing phase of sheet formed elements. The only information available from the CAD model, at this stage of project development, consists of the geometrical definition of the component. Neglecting material and machine effects, it is possible to roughly estimate the feasibility of the forming process which is of furthermost importance in order to guide the designer among different project alternatives. Information about process feasibility is therefore anticipated to the very early phases of component design according to the guidelines of Concurrent Engineering. The proposed method is based on the analysis of the main geometrical features of the die surface. The method attempts to reproduce on a computer program the inductive process used by expert technicians in evaluating the formability of a part just observing its shape. A set of curves is drawn along the surface. The knowledge of the values assumed by curvature and torsion along these curves allows making simplified assumptions on the metal sheet behavior during forming. A formability index can be built by means of weighted combination of curve constitutive parameters. It is therefore possible to induce the tendency of the material to exceed its forming limits, following to the insurgence of defects like necking, cracks or wrinkling. This study follows former researches. In the present one, authors give a more exhaustive mathematical model of the correlation between geometrical features and process parameters and propose a new formability index which requires a more reliable identification procedure.