Formability enhancement of DP600 steel sheets in electro-hydraulic die forming

The objectives of this paper are to quantify the increase in formability of DP600 steel sheets in electrohydraulic die forming (EHDF). The conventional (quasi-static) and high strain rate forming limits of this sheet material were experimentally obtained from specimens deformed using Marciniak tests and EHDF tests, respectively. A numerical model of EHDF was developed in order to determine the strain path of sheet metal experiencing large strains. Forming limits obtained from EHDF specimens formed in plane strain into a V-shaped die indicated that, locally near the top edge of the specimen, more than 120% formability improvement was achieved. Moreover, a formability enhancement of more than 60% was achieved in EHDF in biaxial tension using a conical die, provided sufficient discharge energy was applied. It was found that the significant increases in formability in EHDF are associated with the high-velocity impact against the die wall and the consequent high effective strain rate.