Influence of Preforming on the Final Thickness Distribution of the Superplastically Deformed Domes

Abstract

This study reports the influence of preforming on the final thickness distribution of superplastically formed domes. It is very common to see about 50% thickness difference between apex and periphery of domes formed from initially uniform blanks. If the initial shape of the blank is modified properly by preforming, the stress-strain distribution of the test piece during bulge forming can be changed in order to reduce the non-uniformity of the final thickness distribution of dome. Ti-alloy sheets of thickness 0.83 mm of SP-700 containing 4.5%Al, 3%V, 2%Fe, 2%Mo were used as test material. The blank sheets were initially preformed to a torus type shape and then subjected to final hemispherical bulge forming. Both preforming and final bulge formings were conducted at 800 °C. Influences of shape parameters of preforming dies were examined and confirmed that optimized preforming would be effective to reduce the non-uniformity of the final thickness distribution of formed dome.