Study On Forming Technology Of High Strength Stainless Steel Sheet Driven By Strong Pulsed Electromagnetic Force

As an important metal component to realize the light weight and improve the carrying performance of the vehicle,high-strength stainless steel sheet has been widely used in automobile,ship and other fields because of its good corrosion resistance and mechanical properties.However,under the traditional quasi-static stamping process,the forming performance of stainless steel is poor and the springback is large and easy to crack.Considered as one of the most effective way to solve the traditional stamping quality problems,electromagnetic forming technology is a high-speed forming method,which can significantly improve the metal forming limit.However,due to the poor electrical conductivity of the stainless steel sheet,the electromagnetic force generated by the internal eddy current in the conventional electromagnetic forming mode is small enough to cause the workpiece to be sufficiently deformed,and besides,the forming sheet does not coincide with the cavity of the die.In this paper,a high strength stainless steel sheet forming technology based on strong pulsed electromagnetic force is proposed,and the high strength forming coil is designed by pulse strong magnet technology so as to improve the mechanical strength of the coil remarkably.The stainless steel sheet is formed by driving the punch with a strong pulsed electromagnetic force generated in the copper sheet or aluminum sheet with high electrical conductivity.Combining the advantages of traditional stamping forming with electromagnetic forming,this technology can significantly improve the quality of the workpiece forming.On the basis of this,related forming scheme design,the multi-physical field analysis,the experimental system platform construction and the forming experiment are systematically carried out using the 316 L stainless steel material for the research.For the design of the program,by comparing the traditional electromagnetic forming technology of stainless steel sheet,forming technology driven by strong pulsed electromagnetic force not only can effectively improve the forming depth,but also can ensure the coincide the workpiece and the die.In addition,the method of using multiple discharge program is put forward.For the multi-physics analysis of the forming process,the multi-physics coupling process of electric field,magnetic field,temperature field and structure field in the driving process of stainless steel sheet driven by strong pulsed electromagnetic force is analyzed.The influences of the thermal resistance effect,the eddy current effect,the displacement of the driving sheet and the moving speed on the forming quality of the workpiece are analyzed by COMSOL simulation.The simulation results of COMSOL show that the thermal resistance of the coil has little effect on the final forming quality of the workpiece,which is almost negligible.The eddy current effect results in a reduction of coil current peak,a decrease in time constant but minor obstacles to the final forming quality of the workpiece.Compared with the eddy current effect,the displacement and speed of the driving sheet are more obvious for the coil discharge current and the final forming quality of the workpiece.For the construction of the experimental system platform,to make certain that the driving process can produce enough electromagnetic force,the power supply system and the forming coil are designed by combining the existing conditions of the laboratory with the design of the pulse strong magnet.The mold is also designed in accordance with the traditional mold design of stamping forming.They all meet the requirements of the drive forming system.For the experimental study of forming,a series of experimental studies are carried out on the basis of the forming platform system.The effect of blank holder force,discharge voltage,discharge capacitance,punch quality and thickness of driving sheet on the forming effect of workpiece is studied through single discharge experiment.It is found that there is an optimal value for the blank holder force as the workpiece is easy to wrinkle when the blank holder force was too small while the workpiece is not easy to form when the blank holder force is too large.The forming effect increases with the increase of the discharge voltage,but the discharge voltage is limited by the coil structure and the power supply system,therefore,it is best to adopt multiple discharge forming methods.When the thickness of the drive sheet is greater than the depth of the skin and the discharge voltage does not change,the discharge capacitance not only affects the amplitude of the discharge current and the electromagnetic force on the drive sheet,but also affects the pulse width.The larger the discharge capacitor is,the larger the amplitude and the width of the pulse are and the better the forming effect is.The discharge current and the electromagnetic force of the driving sheet increase with the increase of the mass of the punch,but the effect is not big,and the speed and kinetic energy of the driving sheet decrease with the increase of the quality of the punch,and the effect is obvious.When the drive sheet is thin or thick,the workpiece will not be well formed.It is thin because the drive sheet is less than the depth of the skin,the magnetic field penetrates the drive sheet and the field is not very efficient,and it is thick because the drive sheet increases,and its velocity and kinetic energy are reduced which will lead to a decline in speed and kinetic energy.