Identification of parameters in the internal variable constitutive model and friction model for hot forming of steels

The inverse technique was used to evaluate the coefficients in the friction and theological models for metal fori-ning processes. Ring compression tests were used for the experimental data. A conventional flow stress equation and an internal variable model were considered as constitutive laws. The friction coefficient was investigated as a function of temperature and normal pressure, Identification was performed separately for each model and simultaneously for the two models. In the latter case, the objective function was defined as a distance between vectors containing the results of measurements and predictions of the compression loads and shapes of the free surfaces of rings after compression.