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A fully coupled semi-analytical model is proposed for a ring expansion test. In this model, we consider the electromagnetic, mechanical and thermal effects. During the development, an ideal case of electromagnetic ring expansion test is modelled using both semi-analytical and finite element methods. The analytical model also includes the changes in electrical resistance, mutual inductance and self-inductance as a function of radius during the ring expansion. The development procedure is divided into four separate calculation parts. Each individual part is validated before making the independent validation of the semi-analytical method to obtain a model with high accuracy and a robust calculation speed. The final prediction using this model closely resemble with the coupled finite element predictions, and it can be further extended to exploit for an inverse identification problem.

High speed forming methods become attractive in manufacturing and it significantl reduces the cost and energy requirements. Conventional manufacturing processes such as forging, forming, stamping and cutting of metals typically involve a strain rate of 10 2 – 10 4 s-1 which includes high energy rate fabrication (HERF) methods [1]. During advanced manufacturing methods such as high speed forming and high speed welding processes, certain local regions (e.g. interfaces) of materials could also experience significantly high strain rate (> 10 4 s-1). In order to understand the physical behaviours of materials and to design/control/optimise, such manufacturing processes that require an appropriate technique to capture the material’s viscoplastic property under the high strain rate deformation. Therein, the electromagnetic ring expansion test becomes a promising method to characterize the material behaviours under the high strain rate deformation. The ring expansion is caused by Lorentz force that is generated due to the magnetic induction on the ring. However, the realistic nature of the electromagnetic ring expansion test is quite complex because of the coupling physics between electromagnetic-thermal-mechanical components. Therefore, in this study we evaluate certain controlling parameters which govern the fundamental behaviour of the electromagnetic ring expansion test. Particularly the rotation and inhomogeneous deformation of the ring are noticeably observed and these phenomena require extra attention.

The Magnetic Pulse Welding (MPW) process involves a high speed collision between the flyer and inner rod. Conductivity of the inner rod may play a significant role in the collision speed and collision angle. The collision conditions were investigated with varying conductivity of the inner rod in this study. Coupled mechanical-electromagnetic 3D simulations were carried out using LS-DYNA package to investigate the effect of conductivity of the inner rod on the collision patterns during the MPW process. The simulation involves a welding process with a tube and a rod using a one turn coil with a separate field shaper. The electrical conductivity was varied to a wide range to investigate the influence on the collision condition. Moreover, in order to verify the independency of the collision condition with the mechanical properties of the inner rod, two cases including aluminum alloy AA2024-T351 and copper with appropriate Johnson-Cook parameters were used for the rod. In the entire simulations aluminum alloy was used as the tube material. It was identified that the impact velocity is almost consistent for each case and the impact angles vary between negative and positive values according to the angular measurement convention used in this study. Although, influence of the conductivity of the inner rod is not significant for the investigated current flow while it may sometime delay the incidence of collision at lower frequencies than the critical frequency (FCrit). Optimizing the collision conditions in the MPW process can help to identify the suitable materials for prescribed welding conditions.

Magnetic pulse forming (MPF) techniques work on the principle of Lorentz force induced by eddy current which can cause plastic deformation in a metal workpiece. Lorentz force depends on parameters such as frequency and amplitude of input current, electromagnetic properties of materials and distance between the work piece and coil. The development of vibration as a consequence of elastic strain recovery in a ring expansion process using a MPF technique has been identified and presented in this paper. Coupled mechanicalelectromagnetic 3D simulations were carried out to investigate the effect of various magnetic pulse currents in the development of reversal of motion during the MPF process using LS-DYNA package. Ring expansion using a multi-turn helix coil with an applied pulse current, with the rings made of aluminum alloy AA6061 –T6 is investigated for the effect of vibration during the process. The numerical results show good agreement with the experimental work for various currents. The underlying principle of vibration and formability has respectively been studied using force analysis and stress analysis. The results also show that the 5.6kJ energy already increased the formability by ~66 percent in comparison with the quasi-static formability value from the literature.