Optimization of Thickness Variation of Cone Formed by Superplastic Forming of Ti-6Al-4V Alloy

Abstract

Superplastic forming is a valuable tool for the fabrication of complex parts used in aircraft and automobile
industries. A number of techniques are applied to form components in these industries. In common method called blow
forming, a sheet of super plastic material is clamped in rigid die and formed into the desired shape through pressure applied by
an inert gas. This process usually leads to rather non-uniform thickness distribution with greatest thinning occurring in regions
where stresses are higher such as centre of the sheet. In order to obtain uniform thickness distribution, the suggested method is
to pre-form the sheet in such a way that the thickness of the initial sheet before the blow forming at the center is high so that
after the blow forming the component will have uniform thickness throughout. For this in a 3mm thick Ti-6Al-4V sheet
superplasticity was induced by “quench- roll-recrystallise” method was used to form a cone by blowing argon gas over the
sheet in a die. A second blank was pre-formed so that the thickness at the centre of the blank was 3 mm and that at the ends
(periphery) was 1.5 mm. After blowing the cone, the variation in the thickness from the apex to base of the cone was reduced to
0.3mm. In order to obtain further uniformity in the cone formed, another blank was pre-formed, to make that central thickness
as 2.5mm, which tapers down over periphery to 1.5mm. This time variation of thickness from the apex to base of the cone is 0.2
mm, which is nearly 10%, which is acceptable in most of the cases.