| It is easy to produce wrinkling or fracture during the drawing process of cylindrical part.Blank holding is one of the key technologies for eliminating drawing defects of sheet metal.Traditional blank holding methods are mechanical type and hydraulic type.Mechanical Blank Holder Force(BHF)usually can not be flexibly adjusted.Hydraulic BHF produced by hydraulic force is always with low responding speed and high cost.To overcome the disadvantages,a novel electromagnetic blank holding technology is raised in this paper.Further,an Electromagnetic Blank Holding Device(EBHD)is developed to realize flexible,accurate and rapid adjustment of BHF for increasing drawing quality.Main study content and conclusions are summarized as follows.(1)The development of EBHD for cylindrical part drawing.To effectively overcome wrinkling and fracture,technical requirements of EBHD is proposed and the scope of BHF is given.Developed EBHD consists of cylindrical part drawing system,blank holding system and the fixtures.Based on the size of cylindrical part,the size of blank,the scope of BHF,the BHF parameters are acquired.To the design of the winding type,simulation is conducted to compare the produced BHF by the single winding type and the trail winding type.It is found that the single winding type is more beneficial to increase BHF.(2)The establishment of EBHD.Based on the structure of EBHD,magnetic circuit is established.MAXWELL magnetic theoretical formulas are used to deduce the formula about Electromagnetic Force(EMF)and input voltage.To verify the correctness of deducted formula,EMF testing system is designed and corresponding testing experiments are conducted.From the testing results,the factual value and the theoretical value of EMF match well with each other.The established EMF formula reveals the effectiveness law of the physical parameters relative to EMF,which provides theoretical instructions to the accurate adjustment of BHF in latter experimental research.(3)The simulation of electromagnetic field based on EBHD.Simulation is made use of ANSYS/Multiphysics.The finite element model of EBHD is established.By simulation,the distributions of electromagnetic field and EMF are obtained.According to the simulation results,the maximum magnetic intensity occurs in the fringe of sheet metal,and the produced maximum EMF can satisfy the requirement of blank holding.Simulation also analyzes the distributions of electromagnetic field at different displacements of punch.It is found that the displacement of punch has poor impact on electromagnetic distribution,which can provide instructions to simplify the simulation process of drawing process.(4)The simulation of cylindrical part drawing process based on EBHD.Simulation is with the use of LS/DYNA.The real Stress-Strain curve of SPCC is obtained by tensile experiment.The deformation process of the sheet metal of ?90mm is studied.It is found that the drawing defects will occur in the radius of the punch and the die.It also found that reasonable BHF can restrain wrinkling.Additionally,the study on thinning rate is conducted.It is found that the smaller sheet metal and the larger BHF are helpful to restrain wrinkling.(5)The cylindrical part drawing experiments based on EBHD.Drawing experiments are implemented based on the sheet metal of ?80mm,?85mm and ?90mm.It is found that the EBHD can produce enough BHF to restrain wrinkling and fracture,which can prove the feasibility of the EBHD.Through carrying out the orthogonal testings,it is found that the effectiveness of BHF is larger than that of the size of sheet metal.Besides,neither of the two parameters has great impact on the thinning rate of cup wall.It can be also found that the larger BHF will cause larger thinning rate of cup wall,and the maximum thinning rate will always occur in the radius of the punch during drawing process.Additionally,it is concluded that it will occur thickening in the fringe of sheet metal,and the larger size of sheet metal will cause the decreasing of the maximum thinning rate of cup wall.(6)The optimization of BHF during cylindrical part drawing process.The optimization is made use of BPNN-GA algorithm.The BPNN model is established with the input parameter “BHF” and the output parameter “the maximum thinning rate”.Genetic algorithm is used to search for the most optimum BHF of the sheet metal of ?80mm,?85mm and ?90mm.The feasibility of the optimized BHF are verified by numerical simulations and experiments.According to the study results,making use of BPNN-GA algorithm is effective in increasing the drawing quality of cylindrical part. |
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