Effect of Blank Curvature and Thinning on Shell Stresses at Superplastic Forming

Abstract

The paper studies the relationship between principal stresses, curvature radii and shell thinning during superplastic forming of sphere-shaped domes from sheet blanks of several Al-Mg alloys and Sn-38% Pb alloy, which is the basis for refining the calculations of the power characteristics of the process. When using the Lame’s superellipse to describe the curvature of the shells, it was established that the principal stresses, especially the tangential stress, depend on the principal curvature radii. It is shown that the intensity of stresses also depends on the thinning of the shells during superplastic forming. It is revealed that the higher the level of superplastic properties of the material of the blank, the less the principal stresses and effective stresses depend on the difference between the principal radii of curvature. It has been established that when calculating the power mode of superplastic forming of shells, it is unacceptable the assumption of uniform thinning of the blank during forming, since the calculation error can reach 130%.