A comparison study on forming limit prediction methods for hot stamping of 7075 aluminum sheet

This paper provides an experimental and theoretical study of AA7075 hot forming limits. The limits were measured in a wide range of temperature and strain rates using Nakazima test. Elevated temperature tensile testing was performed to capture the constitutive behavior. Two flow models have been calibrated using the tensile data, the Misiolek model and a continuum damage mechanics (CDM) model. Two theoretical forming limit predictions methods have been investigated, the Marciniak-Kaczynski (M-K) method and a method based on CDM. In the MK model, the constitutive behavior was modeled by the von Mises yield with the Misiolek flow model. The strain rate sensitivity of the groove section was taken into consideration. The CDM forming limit prediction method utilized the corresponding flow model and a simplified plane stress CDM model. Parameters in the constitutive models and the forming limit prediction models were expressed as functions of temperature and strain rate. Both methods accurately predicted the AA7075 forming limits in the hot stamping temperature range and strain rate range.