Research On Pulsed High Magnetic Field Forming And Manufacturing Technology

The application of light alloys is one of the most important ways to achieve lightweight which can improve the carrying capacity of the aerospace vehicle and protect environment. Unfortunately, the light alloys have low formability at room temperature and the forming result of light alloys is bad with the traditional forming technology. Electromagnetic forming (EMF) is a novel technology for forming light alloys because it can significantly improve the metal formability. However, the electromagnetic force generated by the conventional EMF is not enough because of the strength of the driving coil. Hence, the pulsed high magnetic field forming technology is introduced in this thesis. And the distribution of the electromagnetic force, electromagnetic process of moving workpiece, dynamic electromagnetic-structural coupling analysis, system optimization, and experiments are studied.The deformational behavior and forming result of the workpiece is determined by the electromagnetic force distribution of the driving coil. The analysis of the magnetic field and the Lorenz force shows that the Lorenz force includes two components:Lorenz force by the driving coil and Lorenz force by workpiece itself. Based on this theory, the estimated formula of the average electromagnetic pressure is upgraded.In pulsed high magnetic field forming process, the eddy current in the workpiece is generated due to induced electromotive force (IEMF) and motional electromotive force. The IEMF is generated by the change of the magnetic field, while the motional electromotive force is generated by the motion of the workpiece. The Lorenz force and forming velocity of the workpiece is related to the eddy current. First, the effect of the motional electromotive force on the pulsed high magnetic field forming system is studied. It is found that the electrical energy transforms into the kinetic energy due to the motional electromotive force. Then, considering the workpiece acceleration process as the physical prototypes, the effect of the workpiece displacement and motional electromotive force on workpiece velocity is investigated. The workpiece displacement has little effect on the forming velocity when the velocity is less than100m/s. Both the workpiece displacement and motional electromotive force affect the forming velocity obviously when the velocity is larger than200m/s. The results show that the effect of the motional electromotive force on the forming velocity must be considered in the finite element model of the pulsed high magnetic field forming process.After the introduction of the electromagnetic-structural coupling physical process of pulsed high magnetic field driving forming, the deformational behavior of tube and sheet workpiece is analysed by loose coupling method and sequential coupling method. Because of the asymmetry of the constraint and the Lorenz force, the shape of the workpiece does not coincide with the die. Pulsed high magnetic field driving forming is introduced and the results show that it has a huge potential for forming technology.Based on the theory analysis, this thesis proposes a serial optimization of the pulsed high magnetic field forming system, including the size of the driving coil, the pulse width and the coil strength. First, coil capacity factor is introduced by considering both the workpiece’s Lorenz force and the coil’s mechanical strength to optimize the process capacity. Then, the number of coil turns and the reasonable pulse width is determined by the inductance design. Finally, the strength design of the driving coil is presented with respect to the reinforcement of the driving coil. A high strength driving coil has been designed and tested. The experimental results show that the processing capacity of pulsed high magnetic field forming is found to be improved as compared to the conventional EMF.A series of experiments have been carried out by using a25kV/200kJ pulsed power supply in Wuhan National High Magnetic Field Center. With pulsed high magnetic field forming and manufacturing technology, tube expansion, sheet forming, forming limit and plastic flow are studied. A plastic flow area with the height of20mm is achieved by the plastic flow experiment which provides the experimental basis for the future researches. With pulsed high magnetic field driving forming, deep drawing, flanging, and punching are established. The results show that pulsed high magnetic field driving forming has many advantages in sheet forming.All the theoretical and experimental results are summarized and the future developments of the EMF technology are discussed.