Adjustable current waveform via altering the damping coefficient: A new way to reduce Joule heating in electromagnetic forming coils

Abstract

The temperature rise of the working coil due to Joule heating is a very important issue in electromagnetic forming processes. A technically simple and cost-effective method was proposed to address this problem, which only needs to introduce an additional resistor in the discharge circuit. The core of this method is to alter the current waveform during the forming process by adjusting the damping coefficient of the discharge circuit. The effectiveness of the method was numerically analyzed in detail and verified by the experimental investigations. It has been demonstrated that the Joule heating in the coil can be significantly reduced when a resistor was applied, while ensuring the forming depth of workpiece unchanged. As an example, more than 50 % of the Joule heating in a bobbin coil can be decreased when a resistor of 400 mΩ is applied. Meanwhile, the versatility of the developed method was further verified through the analysis of an electromagnetic forming system with a spiral coil and a high-frequency discharge. Furthermore, this work found that the line resistance of discharge circuit should not be as small as possible. It has been proved that when the line resistance is already small, further reducing it has little effect on the improvement of forming efficiency, but it will greatly increase the Joule heating in the coil. The developed method of achieving adjustable current waveform and its application in reducing the Joule heating of coil could be of great significance to the development of electromagnetic forming.