Research On Mechanism And Rule Of Electromagnetic Forming For Aluminum Alloy Grid-rib Integral Panel

Electromagnetic forming is an advanced method for forming integral panel,an important component of high-end equipment in aviation and aerospace.However,the multi parameters coupling during this process makes the forming mechanism and rule complex and it is difficult to control the forming precision.To this end,this paper takes a high-strength aluminum alloy grid-rib integral panel as the research object,and uses numerical simulation,experimental research and theoretical analysis to systematically and deep study the electromagnetic forming mechanism,parameter influence rule and forming defects of the panel.The main research contents and results are as follows:The stress-strain evolutions data of 2A12-T4 aluminum alloy at high strain rates were obtained by Hopkinson bar test.The constitutive model of 2A12-T4 aluminum alloy suitable for electromagnetic forming process was established.Based on the ANSYS/LS-DYNA platform,a finite element model of the whole process of the electromagnetic forming-springback of the grid-rib integral panel with the two-way coupling between the electromagnetic field and the structure field is established.The dual-restart technology of electromagnetic field and structural field and the distortion control based on ALE algorithm are used to solve the key techniques affecting the prediction accuracy of the model.Experimental verification shows that the established model is reliable.Using the established finite element model,the electromagnetic forming mechanism of the grid-rib integral panel is revealed.The results show that the eddy currents mainly gather on the top of the rib;the magnetic forces are distributed on the rib and the web at the same time;the ribs exacerbate the uneven distribution of the magnetic forces on the web;the ribs weaken the effective area of the magnetic forces on the web;the magnetic forces on the web play a major role in the forming of the panel.During the electromagnetic forming of the panel,the stress mainly concentrates on the ribs and web at the fillet corner of the die,where the ribs are subjected to tensile stress,and the upper and the lower surface of the web are subjected to tensile stress and compressive stress,respectively;the ribs along the longitudinal direction of the panel are subjected to compressive stress.Compared with press bend forming,the elastic strain during electromagnetic forming is very small,and there occurs plastic deformation on the web of the forming region.The influence rules of process parameters and geometric parameters on the electromagnetic forming of the grid-rib integral panel are obtained.The results show that both the process parameters and the geometric parameters significantly affect the attaching capability to the die along the width-center path.If the discharging voltage is small,the forming is insufficient,while it is easy to cause collision rebound and free edge tilting as the voltage increases.Increasing the discharging gap is beneficial to reduce the collision rebound;when the discharging gap increases to a certain value,the collision rebound does not change obviously,but the free edge tilting can be reduced.Increasing the turns of the coil,the gap between the two discharging positions,the width of the ribs,and decreasing the height of the ribs are all conductive to increase the forming height.The parameters discharging voltage,discharging gap,blank holder force,width of the ribs have no significant effect on final forming height of the panel along the length-center path.The formation mechanism of typical defects during electromagnetic forming of grid-rib integral panel is revealed.The results show that the lack of the normal force constraint is the main reason for the wrinkling of the free edge;excessive kinetic energy causes the collision rebound,which in turn causes the wrinkling and tilting in the free edge;the tensile stress on the upper surface and compressive stress on the lower surface results in the reverse bending of the web at the fillet corner of the die;the ribs along the width direction of the panel produce side bends under the effect of horizontal magnetic forces,and the ribs along the length direction are unstable due to compressive stress.Based on these mechanisms,a new method for electromagnetic forming of the grid-rib integral panel is proposed,that is,the auxiliary forming is realized by filling metal or rubber between the ribs.Simulation and experimental studies have shown that the metal filler is beneficial to increase the effective area of magnetic forces on the web,suppress wrinkling,rib side bend and instability,and the rubber filler is beneficial to weaken the collision rebound phenomenon.