Research For The Radial-segment Blank Holder Method Based On Electro-Permanent Magnet Technique In Deep Drawing Process

As the key of advanced forming process,the technology of blank holder force control plays an important part in improving sheet metal forming limit and quality.Combining the radial-segment blank holder method with the electro-permanent magnet technique,taking into account the advantages of safety,efficiency,energy saving and environmental protection of the electro-permanent-magnet technique,as well as the good restraint effect on wrinkling and fracture in deep drawing process of the radial-segment-blank-holder method,it provides new ideas of further study in forming process,and also advances the intelligent and automatic development of advanced equipment.In this paper,the principle of electro-permanent magnet chuck and radial blank holder technology of cylindrical parts are studied by theoretical analysis and finite element simulation.Finally,the new method is verified by experiments.Firstly,the principle of magnetization and demagnetization of electro-permanent magnet chuck is studied,and the first and second equations of magnetic circuit and the calculation formula of magnetic force are given by Maxwell equation.Secondly,using ANSYS finite element software,taking the magnetic force of chuck in magnetization and demagnetization states as the research object,the simulation model of chuck with two magnetic field components is established,and several main parameters affecting the performance of electro-permanent magnet chuck are analyzed.The results show that with the increase of the gap between the chuck and plate,the length of magnetic circuit increases,the magnetic flux density B and the magnetic force of the chuck in magnetization state decrease gradually.The magnetic force per unit area can reach165N/cm~2 while the gap is 0.1mm.With the increase of the cross-sectional area of AlNiCo,the magnetic flux and magnetic force of the chuck in magnetization state increase,but there is an optimum value to minimize the magnetic force of the chuck in demagnetization state.The magnetic force of chuck in demagnetization state is only 0.05N,while the length and width of AlNiCo is 40mm.The height of AlNiCo material has little effect on the magnetic force of chuck,but the magnetic leakage in magnetization state increases if the height is too small.Based on the design principle of maximum magnetic force of chuck in magnetization state and minimum magnetic force of chuck in demagnetization state,the electro-permanent magnet chuck with two magnetic field components is designed and achieves good results in magnetization and demagnetization states under the conditions of 20A exciting current and 200 turns.Then,the stress-strain analysis is carried out in each area of the sheet metal,and the stress balance equation and the stress calculation formula of the sheet metal in the flange area are given.Using DYNAFORM finite element software,the simulation model of radial-segment blank holder is established.The optimum radial-segment blank holder scheme is determined by orthogonal test method,and compared with the overall blank holder method.By comparing sheet metal forming limit diagram,stress and thickness distribution,the effect of radial-segment blank holder method on restraining wrinkling and fracture and improving sheet metal forming quality is verified.Finally,a deep drawing die set based on electro-permanent magnet technique is designed,and the experiments of overall blank holder and radial-segment blank holder are carried out.Experiments show that under the same conditions,the maximum forming height of the formed parts obtained by radial-segment blank holder method is larger.under the condition of magnetizing grade 4 and certain drawing depth,the formed parts with overall blank holder method have obvious wrinkling,while the quality on flange area of the parts with radial-segment blank holder method is pretty good,without obvious wrinkling;under the condition of magnetizing grade 12 and certain drawing depth,the formed parts with overall blank holder method rupture,while the parts with radial-segment blank holder method have better forming effect.The results of experiments are in good agreement with the finite element simulation results.