Investigation of dynamic deformation behaviour of large-size sheet metal parts under local Lorentz force

Abstract

Electromagnetic incremental forming (EMIF) is an effective manufacture method for large-size sheet parts of aluminium alloy due to the advantages of improving material formability and increasing the part dimensions. However, the dynamic deformation behaviour of sheets under local Lorentz force is so complex that it is difficult to achieve precise forming control of large-size sheet parts of aluminium alloy in the EMIF process. To address this challenge, a numerical simulation model was established and validated by experiments in this study. Then the forming height, plastic strain, and velocity propagation of a sheet were analysed. In addition, the Lorentz force action stage and inertia effect stage were distinguished quantitatively, and on this basis, the effects of Lorentz force and the inertia effect on deformation were analysed. Finally, the effects of discharge voltage and discharge position on the deformation were revealed. The results showed that there are differences between the distribution rules of forming height and plastic strain. The velocity peak first appears at the sheet area corresponding to the radius centre of coil, then the accelerating downward velocity peak propagates to the sheet centre, while the downward velocity spreads outside. The Lorentz force is the leading factor of the forming peak height, while the inertia effect is decisive on the forming area. The forming peak height and forming area, especially at the inertia effect stage, can be effectively controlled by changing the discharge voltage and the discharge position, thus guiding the adoption of the process parameters according to the requirement of the deformation.