Research on the selection principle of upper sheet in double-layer sheets hydroforming

Abstract

By combining the advantages of sheet hydroforming and multi-layer sheet deep drawing in wrinkling suppression, double-layer sheets hydroforming process was proposed. Different from the multi-layer sheet deep drawing, the two sheets are not bonded together, the upper sheet is introduced to eliminate the wrinkling defects occurred in the formed lower sheet. Therefore, how to determine the appropriate upper sheet is the key point in this process. Based on this, some investigations in selecting the appropriate upper sheet have been down, but the selection principle for the appropriate upper sheet is still ambiguous. To make clear this, in this paper, a semi-ellipsoid curved sheet part made of 2198 Al-Li alloy with an axial length ratio of 0.9 was chosen as the target part, by changing the thickness of the upper sheet (5A06-O aluminum alloy); the primary and secondary order of the anti-wrinkle ability and interfacial friction stress in suppressing the wrinkle defects were investigated and the selection principle for appropriate upper sheet is obtained.