Influence of the inclination angle of stiffeners on folding during superplastic forming of corrugated core panels

Abstract

Superplastic forming of thin sheet corrugated structures is of special interest in developing aircraft technologies of new generation. The manufacture of such structures includes pressure welding of a package of three sheet blanks, consisting of two outer skin sheets and one inner core blank. The stop-off coating is applied to the inner surfaces of the skin sheets before welding. During superplastic forming of the package, the skin sheets take the form of a die cavity, while the core sheet stretches between the skins to form stiffeners. One of the main problems in manufacturing three-layer structures is known to be the formation of folds on the outer surface of the skins. The paper reports on studies of the influence of the inclination angle of stiffeners on folding. The choice of skin sheets with a thickness exceeding the thickness of the core sheet by 2 -3 times may prevent the formation of folds. However, when manufacturing the corrugated structures of variable cross-section, such as hollow fan blades of an aircraft engine, the recommended ratio may not always be implemented. Moreover, its performance is limited by the permissible weight of the blade. In the present study, finite element modeling of the process of superplastic forming of three-layer structures made of titanium sheet alloy VT6 (analog of Ti-6Al-4V) is done using ANSYS software. According to the simulation results, it was found that with an increase in the inclination angle of the ribs, the holding time under pressure should be increased.