Prediction of superplastic forming of 7475 aluminium alloy sheets

Abstract

Superplastic forming is mainly used in the aeronautic and astronautic domains and to fabricate the complex shape parts with the materials hard to process. The numerical simulation is used to predict the superplastic forming process due to the difficulty to predict a forming pressure by a traditional trial and error method. In the article, the superplastic behaviour of a 7475 aluminium alloy has been investigated. Uniaxial tensile tests over a wide range of temperatures and strain rates have been performed. An Arrhenius-type model using strain compensation has been identified. A failure criterion based on the evolution of fracture work is also proposed. This material model has been implemented by user subroutine in numerical simulations (ABAQUS) to predict the ability of the material to form a complex revolution part by superplastic forming. A pressure control algorithm has been developed to minimize the pressure instability and decrease the simulation CPU time. The numerical results, in terms of thickness evolution in the formed component and location of damage-risk zones, have finally been compared to experimental results after the realization of some bulging experiments using the generated pressure cycle.