Dimensional Analysis of Semi-spherical Structure Forming for Ti-6Al-4V Alloy to Hydrostatic-Superplastic Method

Experimental tests on superplastic forming of alloy Ti-6Al-4V with large dimensions can be quite difficult and expensive. In order to avoid the expense of manufacturing alloy sections، numerical modelling is used to simulate the alloy’s superplastic behaviour. However the results obtained from the numerical modelling need to be verified against experimental tests. In order to reduce the expense of the experiments، tests are conducted on smaller samples first and then alloy forming is simulated with larger dimensions numerically. In this article، for superplastic hydrostatic forming purposes، design procedures of Ti-6Al-4V plates as well as their experimental parameters have been studied. Superplastic constitutive equation of Ti-6Al-4V alloy at 970 C has been determined and implemented in the finite element software Abaqus. The results obtained from the numerical simulations show an excellent agreement with the existing experimental results indicating that the new equation reliably predicts the alloy’s grain growth، stress، strain and the strain rate. Investigation on the effective parameters in the superplastic forming process of the alloy provided the possibility of varying these parameters and their ratios accordingly. Thereafter the superplastic forming process was conducted for both sub and full scale alloy sections with scaling ratio of 1:20 and the effective parameters obtained from these two numerical simulations were compared. Results comparisons of experimental and numerical tests demonstrated that the conducted tests on the proposed design of alloy sections is able to overcome the difficulties associated with superplastic behaviour of Ti-6Al-4V alloy after forming.