Effect of the forming method on part shape quality in cold roll forming high strength Ti-6Al-4V sheet

Abstract

High strength titanium alloy sheet, in particular Ti-6Al-4V, is used for structural applications; roll forming has been found to be an appropriate cold forming process for the manufacture of long components in Ti-6Al-4V. Roll forming Ti-6Al-4V at room temperature requires extensive FEA-assisted process development and optimisation to keep springback and part shape defects to a minimum. Currently the material behaviour of Ti-6Al-4V in the roll forming process is not well understood. Two major roll forming approaches, the constant bend radius and the constant arc length method, are used in roll forming but the effect of each approach on springback or final part shape in high strength sheet materials such as Ti-6Al-4V is not well documented. A fundamental understanding of this will enable rapid and reliable process design for the cold roll forming of high strength titanium alloys.The primary aim of this study is to explore the potential use of different roll forming methods to reduce springback and part shape defects in the cold roll forming of Ti-6Al-4V sheet and to develop a deeper understanding of the material behaviour of Ti-6Al-4V in the process. For this, experimental roll forming trials and their simulation are performed and a novel constitutive material model based on the homogeneous anisotropic hardening (HAH) approach is used to represent the forming behaviour of Ti-6Al-4V under cold forming conditions. The experimental and numerical results indicate that the constant radius forming method leads to fewer shape defects in the process and reduced springback. A detailed discussion is provided explaining in part the observed trends.