Research On Electromagnetic Calibration Of The Sheet Metal Based On The Field Shaper

Electromagnetic forming can improve the forming properties of the aluminum alloy materials significantly,and is one of the most effective ways to form the aluminum alloy.The traditional electromagnetic forming was devoted to the forming process of the sheet or the tube,and did not pay enough attention to the forming accuracy,which slowed down the process of industrial application.Therefore,the electromagnetic forming process of the plate was analyzed in this paper.The inherent problems of the cavity wall area in the deep forming process were difficult to form.The main reasons were as follows: The forming coil structure was limited by the mold and the sheet,and could not generate effective radial electromagnetic force in the sidewall region of the cavity.The sheet of the sidewall region mainly relied on the inertia of the central region to drive downward deformation.To solve this problem,it was proposed to use a solenoid bulging field shaper in the deep drawing system,to change the magnetic field distribution and improve the stress state of the sheet metal in the side wall region,so as to realize the radial calibration.In order to achieve the above objectives,this paper intended to carry out the two aspects of the force forming field analysis and experimental verification,trying to optimize the magnetic field distribution,improve the electromagnetic force distribution state,and realize the radial correction of the plate.This paper mainly studied from the following three aspects:Firstly,this paper analyzed the principle and characteristics of the field shape from theory and simulation.Then,combined with the forming process of the sheet metal,the reasons for the low forming accuracy of electromagnetic forming were analyzed.Therefore,it was proposed to use the field shaper to achieve radial calibration.Secondly,the mathematical model of the circuit,electromagnetic field and structure field were analyzed.Then,it used COMSOL to simulate the finite element model with or without the field shaper,and a series of simulations based on AA 1060 were finished.The results showed that the current density on the field shaper realized the transfer of coil energy successfully at 10 k V discharge voltage.The magnetic field has been changed effectively,the stress state was changed obviously,and the radial electromagnetic force was enhanced greatly in the side wall of the sheet metal.Further,the simulation of the structural field showed that the sheet metal had been formed in the region of side wall.So the method proposed in this paper was feasible in theory.Besides,the influence of the thickness of the field shaper and the pulse width of the discharge current were studied.The result showed that(1)the greater the thickness of the field shaper,the closer the distance between the field shaper and the sheet metal,so the higher the coupling coefficient and the better the forming effect;(2)When the discharge current peak was the same,the shorter the pulse width,and the higher the forming efficiency.However,the higher the voltage applied to the system,the higher the insulation requirement of the actual system.Finally,to verify the results of theoretical analysis and the feasibility of the method,this paper also carried out an experimental study.A set of flexible and controllable forming system was designed.Based on Wuhan National High Magnetic Field Center and State Key Laboratory of Advanced Electromagnetic Engineering and Technology,the experiment of AA1060-H with diameter of 210 mm was carried out under two different conditions.(1)Under the condition of semi-ellipsoidal die,the 1mm-thick sheet metal was discharged for 3 times under the discharge voltage of 9 k V,in which the field shaper was added at the third discharge.The results showed that the deformation of the side wall increased by 1.2 mm after adding the field shaper.(2)Under the condition of the straight die,the 2 mm-thick sheet metal was discharged for 5 times under the discharge voltage of 10 k V,in which the field shaper was added at the fifth discharge in the case where the fourth time had reached the bottom.The results showed that the deformation of the sheet metal was increased significantly in the side wall after the field shaper was added,and the maximum deformation was increased by 2.3mm.The above experimental results showed that the field shaper could control the magnetic field distribution effectively,improve the local stress state of the workpiece,enhance the radial deformation of the sheet metal,and finally achieve calibration effect.This method is helpful to improve the forming accuracy of electromagnetic forming and provide a potential optimization scheme for large-scale industrial application of electromagnetic forming technology.