Driving coils in a multistage induction coilgun are stacked end to end forming a barrel. During launching, the pulsed current flows through the driving coil, and the electromagnetic force propels the projectile ahead. The driving coil endures not only the radial expansionary force because of the magnetic flux compression, but also the axial force due to the compressive force and counterforce of the projectile. In the process of coil design, both the mechanical strength and the electrical insulation must be considered. Due to the nonlinearity of insulation materials, the theoretical calculation cannot reflect the true state for the driving coil. The conventional static-state test method is analyzed and verified through experiments. The experimental results show that this method is ineffective for the multistage launching, because it neglects the axial counterforce and does not reflect the true state of launching. An improved method for evaluating the coil strength is proposed based on the analysis of the basic principle. The projectile is accelerated by the former stages, and the testing coil accelerates the projectile with an initial speed. Equipment for testing single coil is designed and installed in the muzzle of the existing multistage coilgun. The experimental results show that this method can test the coil's mechanical strength and electrical insulation more effectively than the conventional method. The dynamic-state method can be used to approximately evaluate the performance of different types of the coil. The structure of the driving coil can be improved through testing and evaluating, which provides experimental reference for the multistage induction coilgun design.
Based on understanding the characteristics of the impulse force generated by pulsed current of the armature, it is valuable to explore effective ways to improve the armature structure in order to enhance the stability and prevent from the transition and erosion during launching. This paper firstly lists a series of conversional armature and analyzes the advantages and disadvantages. A C-shape armature is simulated based on the electrical-magnetic-mechanical coupled analysis method. The simulation shows that the stress is mainly distributed in the area between the cross member and arm. A novel concave armature is proposed and the simulation results indicate that the stress is mainly distributed near the front of armature. It is beneficial to push heavy load and avoid deformation and fracture. A device is built to validate the feasibility of armature. The armature is staying still to simulate pushing the infinite heavy load. The experimental results show that the concave armature endures higher current and has the stronger capability of pushing load compared with the Cshaped armature. This type of armature provides a valuable reference for future armature design.
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