| Deep drawing forming can produce many kinds of parts,which is widely used in civil and military production.Blank holder force(BHF)and its control technique are an important method for improving the forming quality,and it is also one of the key technologies of advanced sheet metal forming technology and forming equipment.The electro-permanent magnet(EPM)technology is used for BHF control in the process of deep drawing to develop a blank holder technique using magnetic force applying BHF,which has the advantage of energy-saving control,safety,and reliability.According to the technical characteristics of the EPM technology and the requirements of the BHF load,the EPM technology is organically combined with the sheet deep drawing process,which can improve the appearance of the existing process,save energy and reduce consumption,develop new processes and new process equipment,improving sheet metal forming performance,and promoting automation and intelligent production have important theoretical significance and practical value.A method of controlling the BHF driven by magnetic force based on the EPM technology is proposed.A new BHF system is developed with the magnetic force provided by a controllable permanent magnet as the power source of the BHF,and the magnetic cushion as the driving device.To suppress wrinkling and improve forming quality,a new BHF control method combining electro-permanent magnet technology and segment blank holder is proposed.Utilizing theoretical derivation,numerical analysis,and experiment,the basic principle,parameter optimization,and related process theory of the new blank holding method are studied.The circuit structure and magnetic circuit structure applied to the magnetic field unit are designed,and then the structural form of the magnetic field unit is determined.Based on theoretical analysis and FE simulation,the process parameters affecting the performance of the magnetic field unit are determined.The raw materials and structural dimensions of the magnetic field unit are determined with the optimization goal of maximizing the magnetic field intensity and minimizing the demagnetization intensity.The tensile tests of the four magnetic field units are carried out on a tensile testing machine.The results show that the maximum magnetic force of the four magnetic field units using the designed magnetic circuit is more than 16000 N,about 160 N/cm2,which can meet the requirements of holding during deep drawing process.Also,the transient thermal analysis and temperature rise experiment of two magnetic field units is carried out to verify that there is no overheating problem in the electro-permanent magnet blank holder technique when the drawing operation is carried out continuously.It is easy to see that,even under the most heavy conditions,the maximum temperature of the magnetic field unit is less than 70 ? after 180 minutes of continuous deep drawing operation,which fully meets the requirements of deep drawing process.Based on the determined magnetic field elements,such as material,size,shape,and number,which affect the magnetization and demagnetization performance,the magnetic cushion is designed,which can be applied to both the forward drawing die and the flip drawing die.Through magnetic field analysis,it is determined that the average magnetic induction intensity and the magnetic force generated on the magnetic cushion are about1.36 T and 152598 N,respectively.In addition,the law of the magnetic force generated by the magnetic cushion varies with the width of the air gap is studied.According to the analysis results,it can be seen that the magnetic force decreases rapidly with the increase of the air gap width.Based on ANSYS software,the analysis method of the magnetic-force coupling problem of applying the BHF load with the EPM technology is given.Select a certain formed part,and according to the predetermined BHF load requirements,a specific method for determining the control parameters using the EPM blank holder method is given.First,on the basis of the magnetic-force coupling analysis,the initial distribution of the BHF acting on the sheet metal is determined.Then,the forming simulation method is used to compare and analyze the forming effect of the sheet under the action of the EPM blank holder method and the conventional blank holder method.The results show that the thickness strain of the sheet in three directions under the action of the two blank holder methods There is no obvious difference.This shows that the new blank holder method innovates the BHF loading method,has the advantages of energy saving and other advantages,and can achieve the forming effect of the traditional blank holder method.Using a 08 Al circular plate with a diameter of 190 mm,flip-chip drawing experiments were carried out when the magnetic field level of the magnetic cushion was 1,2,5,and 10,and the forming height was 45 mm.The results show that,based on the developed EPM deep drawing process,the new blank holder method can exert a large enough BHF,and the BHF is adjustable.In addition,in the formal assembly deep-drawing experiment,the BHF generated when the magnetic level is 4 and 12 was applied to the 08 Al sheet with a diameter of 180 mm.The experimental results further verified the feasibility of the EPM blank holder method and the front-loading deep drawing process.Combining the electro-permanent magnet blank holder method with the segment blank holder technology,a multi-ring segment blank holder technique for the axisymmetric cup is proposed.Theoretical analysis and formula derivation are used to determine the feasibility of the multi-ring segment blank holder method,and the magnetic cushion suitable for the multi-ring blank holder is designed.The initial BHF distribution and its linearization curve on the sheet metal obtained by static analysis show that the action range of the BHF exerted by the multi-ring BHF is larger along the radial direction,and the peak value of the BHF exerted by the multi-ring BHF is reduced effectively,which is conducive to the reasonable flow of the material.The deep drawing experiment of the galvanized sheet shows that the multi-ring segment blank holder can effectively suppress the wrinkling and improve the forming limit.A deep drawing experiment was carried out on a galvanized sheet with a diameter of 190 mm.The cup with the integral blank holder was wrinkled when the height was about 35 mm,while the forming height of the part with the multi-ring blank holder could reach 50 mm.The results show that the multi-ring partitioned blank holder can effectively suppress wrinkles and increase the forming limit.The circumferential and radial segment blank holder techniques are organically geometrically developed,and an electro-permanent magnet blank holder method composite segment blank holder method is developed for non-axisymmetric structures such as square boxes.The wrinkle model and energy consumption of the new composite segment blank holder method are deduced.Utilizing finite element analysis and experiment,it is verified that the composite segment blank holder method can improve the formability of square box shape more effectively with 08 Al sheet.The 08 Al sheet is used to verify that the composite segment blank holder method can more effectively improve the forming effect of the square box-shaped parts.The forming height of the integral blank holder is less than 38 mm,and the forming height of the cup under the new blank holder method can reach 50 mm.Besides,the energy consumption of the electro-permanent magnet blank holder method,electromagnetic blank holder method,and traditional mechanical blank holder method are analyzed and compared.The results show that the energy consumption of the electromagnetic blank holder is the highest,the traditional blank holder is the second,and the energy consumption of the electro-permanent magnet blank holder is much lower than the former two.Under the set parameters,the energy consumption of the electro-permanent magnet blank holder is only 32% of that of the traditional blank holder.Compared with the pulsed electromagnetic blank holder controlled by pulse current,the energy-saving effect of the electro-permanent magnet blank holder is more than 97%. |
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