New Technique to Model the Effect of Intermediate Induction Heat Treatment (IIHT) in Pre-Strained Aluminium Sheets

Abstract

This paper presents a new technique to model the effect of intermediate induction heat treatment (IIHT) on pre-strained aluminium sheets, predominantly AA5182. IIHT is a heat treatment technique carried out between two conventional cold forming steps, which eventually lead to enhanced formability of aluminium alloys. The aim of IIHT is to alleviate the strain hardening of the material which is introduced in the first cold forming step and there by reducing the yield limit and increasing the hardening modulus for subsequent forming steps. As a result, a remarkable increase in formability can be achieved in the subsequent forming steps at room temperature. The scientific aspect of the IIHT process is demonstrated by defined pre-strained tensile test specimens at different object temperatures to establish a process window. To accurately model the effect of IHTT in simulations, it is necessary for the material model to consider the plastic recovery that the material undergoes during heat treatment. To this effect, material model Mat133 (Barlat_YLD2000) in LS-Dyna has been enhanced to account for the effect of intermediate heat treatment. The numerical simulation is carried out in four steps namely pre-forming, springback simulation to account for residual stresses, thermo-mechanical coupled simulation for heat treatment, and final forming with enhanced material model. To validate this model, experiments have been carried out on a simple cross-die deep drawn cup and compared with simulation results.