Simulation of hot forming processes: Using cost effective micro-structural constitutive models

• Constitutive models are proposed for hot forming.
• Three dimensional constitutive equations are proposed for grain boundary mechanisms.
• Visco-plastic models are proposed to decrease computational costs.
• The models consider affecting parameters such as grain size, strain and strain rate.
• The models predictions are compared with hot forming experiments.

Constitutive models for dominant mechanisms in hot forming are proposed. These models consider inter-granular deformation, grain boundary sliding, grain boundary diffusion and grain growth. New stress–strain rate relationships are proposed to predict deformation due to grain boundary sliding and grain boundary diffusion. Besides a Taylor type polycrystalline constitutive model, a visco-plastic relation in conjunction with two different yield functions is used to predict inter-granular deformation. Step strain rate tests and bulge forming test are simulated with the proposed models. Results are compared with experimental data to verify the constitutive models. It is concluded that the visco-plastic models can predict material behavior in hot deformations as accurately as the polycrystalline model but with much less computational costs. To examine the hardening effects, the model is calibrated with tensile test data of AA5083 at 550 °C, where hardening is remarkable. Then, as an example, it is used to simulate a tray forming experiment. Dome heights and tray thicknesses at various positions during forming process are very close to experimental observations.