Developments of methods for improving metal forming operations simulations: material hardening and friction characterization under process conditions

Abstract Metal forming operations are optimized by using finite element simulations. The numerical results are strongly dependent on the material data and the friction conditions. The present paper focuses on the tube hydroforming process and methods, developed by the authors, for the evaluation, the closest to the process conditions, of the hardening curve and the friction coefficient. For the hardening curve, an experimental set-up has been developed and instrumented, and an analytical model permits to translate the measures into stress-strain curve. Its capability to evaluate the best plastic criterion and its importance for a good prediction of forces during the tube hydroforming are illustrated. For the friction evaluation, the study of tube expansion in a square section die is proposed. By analyzing the thickness along the perimeter of the shaped tube, it is possible to evaluate the Coulomb’s friction coefficient, which can be different from the evaluation done with the classical pin-on-disk test.