P. N. Comley, The Boeing Company, Seattle, WA
Superplastic Forming of Ti-6Al-4V alloy has traditionally been performed at 1650 degrees F. Although SPF equipment and dies have been developed to withstand this high temperature, their life is limited and maintenance is high. In addition the formed sheets need chemical milling after processing to remove a significant layer of alpha case, and parts require hand polishing due to a rough die surface caused by the high temperature. The recent development of Ti-6Al-4V titanium alloy with a grain size of around 1 micron has led to the possibility of superplastic forming at a much lower temperature than the regular Ti-6Al-4V alloy. In addition, the forming speed could be increased. This paper looks at some of the SPF attributes of fine grain titanium, in particular the optimum forming temperature, the thinning characteristics compared to regular Ti-6Al-4V, the formation of alpha case during processing, and forming speeds. Some prototype and pre-production aircraft parts on Boeing airplanes are presented. The results show that this material could significantly lower the cost of SPF titanium part production for the Aerospace Industry.