Experimental and numerical investigations of stamp hydroforming and ironing of wrinkling in sheet metal forming

The goal of this study was to verify, experimentally and numerically, that the stamp hydroforming process is a suitable alternative to conventional stamping as a means for producing defect-free sheet metal parts. The pressurized fluid used in stamp hydroforming is shown to have the effect of increasing the forming limits of materials; that is deeper drawing depths are achieved without rupture. Also, using a specific pressure profile, wrinkle-free parts with deeper draws could be produced. Stamp hydroforming involves supporting the sheet metal with a bed of pressurized viscous fluid during the entire forming process. The external support provides a through-thickness compressive stress that delays the onset of tearing and wrinkling. Stamp hydroforming experiments with a hemispherical punch were conducted using the Interlaken double-action stamping press. Numerical analysis was conducted using the explicit finite element code LS-Dyna3D. The accuracy of the numerical model was first established and fine-tuned using experimental data. The numerical model was then used to explore new forming ideas not currently possible with the present experimental setup. A new blank holder design is suggested from these numerical results.