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| Influence and Mechanism of Field Shaper on Heating of Electromagnetic Forming Drive Coil |
| Xiong Qi1,2, Li Qingshan1,3, Li Zhe1,3, Zhao Xiang1,3, Li Yanxin1,3 |
1. College of Electrical Engineering & New Energy China Three Gorges University Yichang 443002 China;
2. National Pulsed High Magnetic Field Science Center ; Huazhong University of Science and Technology Wuhan 4430074 China;
3. Hubei Provincial Engineering Technology Research Center for Power Transmission Line China Three Gorges University Yichang 443002 China |
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Abstract As an emerging metal processing and forming technology, electromagnetic forming (EMF) has been widely studied by domestic and foreign experts because of its unique technical advantages. The electromagnetic environment in the process of EMF is very harsh. Existing studies have confirmed that the electromagnetic heat loss of the drive coil is caused by the accumulation of Joule heat, and the electromagnetic heat in the EMF process will affect the structural strength of the drive coil, which in turn reduces the service life and frequency of the coil. The coil performance will be improved by reducing the electromagnetic heat loss of the coil. The integral area of the coil current will be reduced, as the electromagnetic heat loss of the drive coil is due to the accumulation of Joule heat. Based on this, this paper proposes an optimization method for solenoid coil heating.
Firstly, by analyzing the temperature field in the EMF system, it is proposed to use a filed shaper to assist the forming to reduce the coupling mutual inductance of the system, the reduction of time constant results in the decrease of the integral area of the coil current and finally achieving the purpose of reducing the electromagnetic heat generated by the coil. At the same time, the inductance matrix of the solenoid coil, the forming workpiece, and the field shaper is calculated to support this. Through the finite element method, the temperature field is introduced on the basis of the electromagnetic-structural field coupling model, and a fully coupled electromagnetic-structural-temperature field model considering the change of the resistivity of the materials used in each component of the EMF device with temperature is established to verify the feasibility of the forming scheme.
The simulation results show that the electromagnetic expansion of pipe fittings is carried out by using a drive coil with an inner diameter of 49.6mm, an outer diameter of 68mm, and a turn count of 4×10 turns, with the help of introducing a filed shaper when the discharge voltage is 10.5kV, the maximum temperature of the coil is reduced by 12.35%, which is 3.42℃. The Joule heat generated by the coil decreased by 12.3%, a reduction of 0.7kJ. The filed shaper reaches a maximum temperature of 45℃ at 0.2ms, but drops to 31.7℃ at 10ms (when the coil current decays to 0); The magnetic flux density in the workpiece is increased by 21.2% and the induced eddy current density is improved by 3.94%, resulting in a 5.72% enhancement in the Lorentz force on the workpiece. The final forming volume has grown 176%, from 2.52mm to 6.96mm.
The results show that: ① The heat loss of the coil is the result of the gradual accumulation of coil current, and the integral region of the current is proportional to the Joule heat generated by the coil. After the introduction of the field shaper, the coupling mutual inductance in the system is reduced, thereby reducing the equivalent inductance value in the original dynamic circuit and accelerating the attenuation rate of the current in the coil. It alsobrings a reverse voltage, so that the equivalent voltage decreases, resulting in a decrease in the peak value of the current; The combination of the two reduces the additional current losses. ② The induced eddy current in the field shaper has a very short acting time, and compared with the coil, the surrounding air circulation is better, which is easy to do the cooling treatment. ③ Under the same deformation conditions, the introduction of magnetizer assistance can reduce the initial discharge energy and reduce the temperature rise of the coil, which is a simple and effective way to improve the service life and efficiency of the coil.
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Received: 30 September 2021
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2023, Vol. 38 
