Development of Pulsed Power Systems and Tooling Coils for Electromagnetic Manufacturing Applications

Abstract

Electromagnetic pulse manufacturing is an emerging non-conventional manufacturing technique used for the forming of workpieces at very high strain rates. The manufacturing assembly consists of the tooling coil (or actuator), the workpiece, a pulsed power source, and finally, a suitable die as per the required final shape that needs to be achieved. In this work, the author focuses on developing high voltage and high current pulsed power sources and the tooling coils required for the electromagnetic forming applications. The study encompasses theoretical simulations and practical experiments pertaining to electromagnetic forming applications involving workpieces made of sheet metal and tubular structures.

Electromagnetic forming is a complex multi-physics process that involves electromagnetic, thermal, and mechanical fields which are strongly coupled to each other. Initially, the author focused on understanding the interaction between various physical fields involved and development of fast analytical methods to predict the deformation in the workpiece due to their interaction. Impact velocity and the pressure applied to the workpiece are critical aspects that determine the workpiece’s deformation. Based on the developed coupled models, the author has proposed techniques to control the impact velocity and the applied pressure on the workpiece and designed the Pulsed Power Systems to achieve the same. The tooling systems are the most vital components in the electromagnetic forming process. This is because they generate the necessary pressure on the workpiece to achieve the final desired shape. The author has designed and developed various tooling coil assemblies for sheet metal forming and operations on tubular workpieces. The author has developed a novel clamp-on type electromagnetic tooling coil for agile manufacturing of tubular components. The designed actuator offers several advantages over conventional helical tooling systems, including a pressure distribution which does not produce any end effects as opposed to the pressure on the workpiece dropping to 58% of the peak in a conventional helical actuator. It is also marginally less sensitive to standoff distance, where the reduction in the peak pressure is only 13% as compared to the conventional actuator, which shows a drastic drop of 56% as the standoff distance varies from 2 mm to 5 mm. The proposed clamp-on tooling coil is also robust to failure as the stress on the proposed actuator is compressive and reinforces it against the toroidal former. In contrast, the stress on the conventional helical actuator coil is repulsive, requiring external reinforcements. The proposed actuator is openable and can be reused easily for repeated applications.

For sheet metal forming, the author optimized the uniform pressure actuator and proposed a high-efficiency dual-channel uniform pressure tooling coil (UPTC). The salient features of the designed dual-channel actuator are as follows. The designed tooling coil draws 6.2% more current and applies 24.9% more force than the conventional UPTC for the same pulsed power source parameters. The spatial distribution of the pressure is identical in both the tooling coils, but the magnitude of the pressure in the proposed dual-channel tooling coil is about 23% higher. In addition, the proposed tooling coil also has better capabilities for handling electromagnetic stress during the forming process. For the first time, the author has integrated attractive and repulsive sheet metal forming technology into a single assembly. The author introduces a novel design and analysis of a dual-mode universal uniform pressure tooling coil that integrates both forming techniques, simplifying the requirements for the pulsed power system.

Finally, the author has studied the effect of tooling coil designs on the efficiency of the forming process. The study aims to find the effect of coil design on the forming efficiency and compares the performance of multi-turn and multi-layer coils over the existing tooling coils. The study has been validated using the development of multi-layered uniform pressure tooling coils with experiments performed on free bulging of AA-6061-T6 sheets. The author found that the multi-layered tooling coils outperformed the single-layered wire-wound coils for all values of the system capacitances used.