Electro-hydraulic forming of sheet metals: Free-forming vs. conical-die forming

This work builds upon our recent advances in quantifying high-rate deformation behavior of sheet metals, during electro-hydraulic forming (EHF), using high-speed imaging and digital image correlation techniques. Aluminum alloy AA5182-O and DP600 steel sheets (1 mm thick, ∼152 mm diameter) were EHF deformed by high-energy (up to ∼34 kJ) pressure-pulse in an open die (free-forming) and inside a conical die. The deformation history (velocity, strain, strain-rate, and strain-path) at the apex of the formed domes was quantified and analyzed. The data shows that the use of a die in the EHF process resulted in an amplification, relative to free-forming conditions, of the out-of-plane normal velocity and in-plane strain-rate at the dome apex. This amplification is attributed to the focusing action of the die on account of its conical geometry. Further, while the strain-path at the dome apex was generally linear and proportional, the use of a die resulted in greater strain at the apex relative to the strain during free-forming. The sheet deformation profile in the EHF process was found to be different from that previously observed in electromagnetic forming (EMF) and, thus, the two processes are expected to result in different strain-paths and formability. It is anticipated that quantitative information of the sheet deformation history, made possible by the experimental technique developed in this work, will improve our understanding of the roles of strain-rate and sheet–die interactions in enhancing the sheet metal formability during high-rate forming.