Integrated hydrobulging of prolate ellipsoids from preforms with multiple thicknesses

Abstract

The integrated hydrobulging of stainless-steel prolate ellipsoids from preforms with two thicknesses was investigated. The produced ellipsoids were closed with two 16-mm-thick closures and had nominal semiminor and semimajor axes of 89 and 125 mm, respectively. The ellipsoidal preforms comprised eight conical segments inscribed inside the target perfect ellipsoid.The four end and middle segments of the preforms had nominal thicknesses of 0.67 and 0.83 mm, respectively. The hydrobulging of these preforms was explored analytically and numerically and was compared with that of prolate ellipsoids with constant thickness. Two nominally identical ellipsoidal preforms were fabricated, measured, and hydrobulged to confirm the theoretical predictions. The results indicated that varying the preform thicknesses is an efficient method of overcoming insufficient hydrobulging of the ends of prolate ellipsoids in other methods.Moreover, hydrobulging instability can be effectively monitored by measuring geometric dimensions, such as axial height.

Internal Hydroforming of Large Stainless-Steel Eggshells from Stepped Preforms

“…Non-uniform wall thickness could ensure the excellent hydroforming of an eggshell by achieving a uniform stress distribution. This approach was favorably validated through theoretical, numerical, and experimental analyses for the hydroforming of prolate ellipsoids from preforms with multiple thicknesses [62].…”

“…Wall thickness was assumed uniform; the average tested value of 1.9 mm was obtained by measuring the parent stainless-steel sheet prior to hydroforming because the variations in the wall thickness of parent stainless-steel sheet were very small. Such an average assumption has been widely utilized in the previous works of Błachut et al and Zhang et al [15,16,62]. The thickness of the shell was defined as the symmetrical offset from its mid-surface, and finite shell elements were generated accordingly.…”