Optimization of the Attractive Electromagnetic Bulging of Small Tubes Based on Non-Uniform Solenoid Coils

Abstract

The attractive electromagnetic bulging is a novel technology which has unique advantages in the formation of small tube fittings. To generate the attractive electromagnetic force, a dual-frequency current method has been proposed in the existing research on the attraction bulging of the small tube fittings. This method, however, has a flaw that the tube fittings are subjected to a large repulsion electromagnetic force before the attraction, which will lead to a negligible effect on the final forming results. To solve this problem, a non-uniform solenoid coil structure is proposed in this paper to suppress the repulsion to improve the attraction. On this basis, a finite element model is built to analyze the process of an aluminum tube with an inner diameter of 20 mm and an outer diameter of 22 mm and the thickness of 1 mm. The influences of the coil structure on the magnetic induction intensity B, eddy current density Je and the stress of the coil have been studied. The results show that the expansion of the tube can be improved when the non-uniform solenoid coil is used. The maximum expansion in this dissertation is achieved with a 28 turns non-uniform solenoid, and its expansion uniformity standard deviation is only 0.156. These simulations have a significant outcome to the design of the coils and the application of electromagnetic bulging in small tube fittings. INDEX TERMS Electromagnetic forming, numerical simulation, metal tube, bulging, solenoid coil.