| EBH(Electromagnetic blank holder)is a novel blank holder control technique for deep drawing sheet metal,which has not been widely used in production practice.The reasonable loading of the BHF(blank holder force)is the key to the success of deep drawing in the drawing process of sheet metal cylindrical parts.It directly affects the quality of products.The flange wrinkling can’t be restrained well when the BHF is too small.The cylinder will be pulled out when the BHF is too large.Nowadays,mechanical blank holder,hydraulic blank holder and EBH are the three kinds of methods for blank holder.It is not easy to realize the continuous control of BHF by mechanical and hydraulic.And these two devices are large in size and high in cost.They belong to the traditional blank holder.EBH is a new blank holder Technology.The BHF is provided by the electromagnetic force.The continuous,flexible and precise control of the BHF can be realized by controlling the excitation current.The difficulty of EBH is the electromagnetic field design of drawing part geometry,the accurate control of electromagnetic force and BHF.With the increasing demand for high-precision and mass production of related products in this field,the research and application of EBH control technology have important application and promotion value.In this paper,the drawing process of thin metal tube is studied.The distribution of BHF and magnetic field is studied in the drawing process relying on the self-developed EBH device.The control strategy of EBH is proposed by studying the control technology of EBH.The design of EBH control system is given.The main research work is as follows.The control technology of electromagnetic force of EBH is studied.The range of BHF is deduced by analyzing the requirements of BHF in the process of deep drawing.The minimum BHF to restrain wrinkling and the maximum BHF to prevent fracture are determined.Aiming at the self-developed EBH,the principle of EBH for cylindrical parts is described,its mathematical model is established,and its electromagnetic force calculation formula is derived.The simulation model of EBH is established by using Maxwell software.The electromagnetic field intensity distribution and the stress distribution of the work-piece in the process of metal sheet deep drawing are analyzed.Control strategy of EBH control system is studied.According to the close relationship among the BHF,electromagnetic force and coil excitation current,the structure of the BHF closed-loop control system is determined.PWM DC power supply is adopted as the excitation power supply.The control strategy of charging and demagnetizing are determined.Because of the limitation of magnetic field and installation conditions,the computational model of BHF is used instead of pressure sensor detection.According to the measurable current,the mathematical model of BHF computational model is established.In this paper,the range of BHF is determined.The control of EBH with constant and variable BHF is discussed.The fuzzy control strategy of BHF is proposed.The relevant design is given.Simulation of EBH control system is studied.In order to make the simulation of the control system more accurate,Ansys/Maxwell,Ansys/Simplorer and Matlab/Simulink three kinds of software co-simulation methods are used.The simulation models of EBH device,PWM power supply and control system with fuzzy controller are established.The co-simulation of EBH control system with constant BHF and variable BHF loading mode is realized.The simulation results show the change of parameters in the process of EBH,response curve of BHF and response curve of current.The magnitude and distribution of magnetic induction intensity on EBH device are shown.Monitoring system of EBH is designed.Based on the experimental platform of EBH control system for deep drawing,the hardware and software of PLC monitoring system are designed.Some experimental studies are carried out to verify the feasibility of the proposed EBH control strategy. |
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