Research On Electro-Permanent Magnet Blank Holder Technique Based On Coupled Magnetic-Mechanical Analysis

As one of the basic stamping forming processes,the deep drawing process has the advantages of high material utilization and high productivity,and can form thin-walled parts.The electro-permanent magnet(EPM)blank holder technique applied to sheet drawing can realize independent loading and real-time control of blank holding force(BHF),which is of great significance for improving the existing deep drawing process.Compared with the conventional blank holder technique,the EPM blank holder technique uses the magnetic attraction force provided by permanent magnets as BHF,rather than hydraulic pressure or other external forces.Therefore,the EPM blank holder technique also has the advantages of high efficiency,low energy consumption and green manufacturing.In the deep drawing process of the EPM blank holder technique,the magnetic attraction force between the EPM cushion and the suction plate is mainly determined by the two parameters of the initial air gap and magnetic field level,and the magnitude of the magnetic attraction force is very important to the forming quality of parts.Through theoretical analysis and finite element method(FEM),the coupled magneticmechanical phenomenon involved in the EPM blank holder technique is analyzed.For drawing a sheet with certain material and dimensions,a specific combination of parameters of initial air gap and magnetic field level is given through coupled magnetic-mechanical field analysis,and the feasibility of the analysis is verified by EPM drawing experiments of cylindrical parts.Firstly,from the perspective of working principle,the deep drawing processes using conventional blank holder and EPM blank holder are compared.The structure of EPM cushion with double magnetic pole units and the working principles of magnetization and demagnetization,the EPM cushion with 46 magnetic pole units and the design of drawing mold integrated with EPM technology are introduced.The two main parameters that affect the coupled magnetic-mechanical field are screened out,namely initial air gap and magnetic field level,and the theoretical analysis of the interaction between cushion deformation and magnetic field is given.Secondly,for 08 AL cold-rolled steel sheet with a thickness of 0.98 mm and a diameter of 180 mm,the EPM drawing mold integrated with EPM cushion which includes 46 magnetic pole units is used to form it.Using finite element analysis(FEA),when the initial air gap is 0.4mm and magnetic field level is 4,the magnetic attraction force can reach the minimum BHF required by the sheet,which causes that the simulated drawn part has a better forming effect.The analysis result also shows that maximum displacement of EPM cushion along the thickness of sheet is 0.02 mm,and this degree of deformation has basically no effect on the normal operation of the cushion.When the drawing diameters of 08 AL sheet are 180 mm and 190 mm respectively,and the drawing height of the parts is 50 mm,theoretical calculations are used to give a comparison of energy consumption between EPM blank holder technique and conventional blank holder technique.The calculation results show that compared with conventional blank holder technique,the energy saving of EPM blank holder technique can be more than 50%.When the height of forming part is greater,the energy saving effect is more significant.Then,the non-ferromagnetic AA6061 aluminum alloy sheet and the ferromagnetic08 AL cold-rolled steel sheet with the same drawing dimensions are studied.By means of theoretical calculation and FEA,the EPM deep drawing technologies of these two kinds of sheets are compared from three aspects of mold structure,coupled magnetic-mechanical field analysis and energy consumption comparison.From the comparison of mold structure,it can be seen that compared to the ferromagnetic sheet,the overall dimension and weight of the cushion and drawing mold of the non-ferromagnetic sheet are significantly reduced,and weight reduction rate of the mold can reach 32.4%.According to the results of FEA,the forming effect of AA6061 parts is slightly better,indicating that the application of EPM technology to deep drawing process of non-ferromagnetic material is more practical.The theoretical calculation result of energy consumption shows that the EPM drawing mold of non-ferromagnetic sheets can save 24.3% energy compared with that of ferromagnetic sheets.Finally,a corresponding drawing experiment of cylindrical parts is designed to verify the previous research.The EPM deep drawing experiments are carried out on 08 AL coldrolled steel sheet with a thickness of 0.98 mm and a diameter of 180 mm.When the initial air gaps are 0.4mm,the forming qualities of drawn parts under different magnetic field levels are compared.When the magnetic field level is 4,the forming quality of drawn part is better,which is basically consistent with the finite element simulation result,and it verifies the feasibility of the coupled magnetic-mechanical field analysis.Using the same experimental method,non-ferromagnetic AA6061 aluminum alloy sheets with a thickness of 0.5mm and a diameter of 90 mm are selected for the drawing experiment.The results show that the coupled magnetic-mechanical field analysis is also applicable to the EPM deep drawing process of non-ferromagnetic parts.