Research On Electromagnetic Forming Law Of Attracting Sheet Metal Based On Dual-coil

Electromagnetic forming(EMF)technology is a kind of high speed,non-contact,and high energy rate forming method which can drive metal materials to plastic deformation by the action of eddy current and magnetic field in the coil which produces pulse strong magnetic field.The technology has the advantages of significantly increasing the forming limit of a light alloy such as aluminum-magnesium at room temperature,restraining wrinkling,and reducing spring-back.Therefore,its technical characteristics perfectly meet the processing requirements of the lightweight electric vehicle body and the policy requirements of energy-saving and emission reduction.Attraction electromagnetic forming is one of its unique applications.It uses two currents with different pulse widths to drive one coil to generate an attractive electromagnetic force,which is suitable for plate dent repairment and micro-tube forming.However,the single-coil structure requires very strict parameter matching of the two currents,and the energy utilization efficiency is extremely low.To solve this problem,this paper puts forward two kinds of current respectively drive a coil of double coil structure attraction electromagnetic forming process,and the eddy current competition regulation mechanism,the attraction generation method and the feasibility of attraction sheet forming under the dual-coil structure have been studied.Firstly,starting with the equivalent circuit model of the repulsive electromagnetic force sheet forming,the current in the coil and the electromagnetic force distribution on the plate under a single pulse current are analyzed in detail.The simulation results show that: when the current is in the falling edge stage,the plate will produce a small attraction,so that the realization of electromagnetic attraction is clear.Therefore,based on this,and then effective competition of eddy current on the dual-coil and plate is realized,to realize attraction forming of the dual-coil and plate.Secondly,based on the above analysis,a horizontal coaxial distribution and a vertical coaxial distribution double coil-plate fully coupled simulation model were established respectively.The discharge parameters of the long pulse width current and the inner diameter of the coils L and S in the "Scheme 1" were analyzed respectively,and the attractive forming of the plate(the plate was dented)was realized.In addition,by increasing the inner diameter of the coils L and S,the maximum axial displacement of the dented area on the plate can be effectively reduced to 0.01 mm,which is only 1% of the thickness of the plate.Then,based on "Scheme 1",the structural parameters of coil L and S in "Scheme 2" are analyzed by adjusting them(without changing the discharge parameters of the external circuit),and the simulation results show that: increasing the number of turns of the coil L,which can effectively increase the magnetic flux density on the plate,thereby increasing the axial displacement of the plate,effectively avoiding the appearance of the dented area on the plate.Besides,the axial layer number of coil L must be greater than that of coil S,or the current of coil L should be increased,so that the flux density on the plate can meet the requirements of attractive forming;and the number of radial layers of the coil L is slightly larger than that of the coil S,which is better optimize the uniformity of the attractive forming of the plate.Moreover,in this scheme,the discharge energy of the coil is significantly reduced on the premise of satisfying the forming quality.Finally,by designing the corresponding coil,and launching the discharge experiment on it,and the discharge current waveform results show that the designed forming device can meet the forming requirements of the attraction plate.The relevant research results can deepen the understanding of the attractive EMF process and have important significance for expanding the application of EMF technology in plate processing.