Abstract
The electrically assisted forming of sheet metal holds a promising avenue in improving formability and green manufacturing. Manufacturers aim to enhance formability and reduce the load required for forming with fewer defects. In most sheet metal forming operations, a biaxial state of stress exists. In addition, it is challenging to align the current flow direction with the loading direction because of the complexity of processes. So, uniaxial testing with electric current is insufficient for the complete mechanical characterization of sheet metal. The current work aims to understand the effect of pulsed electric current in the complex phenomenon of the biaxial state of stress at different strain rates. The formability of Al 6061 in the presence of electric current is investigated using the Erichsen cupping test. The testing setup is fixed on the universal testing machine to control the loading rate precisely, and insulation is provided to prevent the current leakage into the machine. Short duration, high-frequency electric pulses with a peak current of 400 A and having square waveform are applied during the test. A comprehensive study is conducted by varying the punch speed from 10−3 to 20 mm/s. The blank holder force is maintained at 20 kN, and graphite powder is used as a lubricant because of its electrical conductivity. Experimental observation showed that the Erichsen Index (IE) is almost constant regardless of punch velocity when electric current is not applied. However, punch velocity affects the flow stress; the higher the punch speed, the more load is required for the same deformation in the sheet. Interestingly, a peculiar trend emerged when the electric current was applied at lower punch speeds. It is found that the fracture height (representing the IE) diminishes when the strain rate is reduced. When no electric current is used, the fracture starts in the transverse direction (TD) propagates concentric to the punch axis. Meanwhile, applying electric current changed the fracture behavior to a straight line along the rolling direction. Applying the pulsed electric current improved the Erichsen index by 15 to 20 %, and the load was reduced by 12.5 % compared to without electric current.
