An Innovative Deep Drawing Process of Thin Curved Shells with Positive Local Bulging

Thin-walled shells with curved surfaces are widely used in the aerospace field. As the thickness to diameter ratio decreases, it becomes increasingly challenging to control inner wrinkling during the conventional deep drawing process. In this paper, a novel deep drawing process with positive local bulging was proposed to suppress inner wrinkles in the deep drawing of a semi-ellipsoidal part. The effects of loading paths, rigid ring numbers, and thickness to diameter ratio of blank on forming defects were analyzed by experiments. The results indicated that the defects-free parts with a small ratio of thickness to diameter were formed by the novel process, which cannot be formed by the conventional deep drawing process. Both inner wrinkling and splitting were suppressed by the optimized loading path of the reverse bulging force. Although the local thickness of the curved surface part was decreased by the reverse bulging tools, the minimum thickness was improved by the increased rigid rings. In addition, a larger reverse bulging force was required to prevent the inner wrinkles for a smaller thickness to diameter ratio. This research provides valuable experimental guidance for the development of a novel deep drawing process for curved surface parts.