Numerical Simulation And Experimental Study On Electrohydraulic Forming Of 6061 Aluminum Alloy Sheet

Aluminum alloy is one of the most commonly used light alloy due to its low density,high strength and good corrosion resistance.However,the forming performance of aluminum alloy sheet is poor and prone to fracture at room temperature.The high rate forming process can significantly improve the above problems,so it has been widely concerned in the forming of aluminum alloy sheet.Pulse electric hydraulic forming is a kind of common high velocity forming process,compared with the traditional way of forming,electric hydraulic pulse forming technology only half mold,forming of high precision and small plate rebound,but the current domestic electric hydraulic forming technology for pulse related theory,experiment and numerical simulation study are limited,need for systematic study of this process,in order to improve the application in the field of aluminum alloy in advanced manufacturing.In this paper,the pulse electrohydraulic forming technology of 6061 aluminum alloy sheet was studied at room temperature.The main research contents are as follows:Firstly,the mechanical properties of 6061 aluminum alloy sheet under quasi-static conditions and high strain rates were obtained through quasi-static uniaxial tension and Hopkinson tie bar experiments.Based on the obtained stress-strain curves,the Johnson-Cook flow stress model under high strain rates was established,which laid a foundation for the constitutive relationship of the material in the subsequent finite element simulation.Secondly,the forming limit curve of 6061 aluminum alloy sheet was predicted based on M-K theory,Barlat89 yield criterion under quasi-static condition and Johnson-Cook hardening model,and the reliability of the predicted curve was verified by Nakazima experiment.At the same time,the pulse electrohydraulic forming experiment of 6061 aluminum alloy sheet printed with grid circle was carried out,and compared with the quasi-static FLC,it was verified that the process can effectively improve the forming limit of 6061 aluminum alloy sheet.Thirdly,the finite element simulation of the pulsed electro-hydraulic forming process is carried out based on the fluid-structure coupling method.The results show that in the swelling process,the medium water first contacts with the middle position of the sheet metal,and the plastic deformation can occur within microseconds when the material exceeds the yield strength.At the same time,the simulation results show that due to the reflection between the shock wave and the wall of the forming chamber,the material can still maintain a certain pressure after forming the mold,and the rebound of the material is reduced.Finally,the experimental study of pulsed electrohydraulic forming under different process parameters was carried out.The results show that the higher the discharge voltage is,the better the mold sticking effect is.There is an optimum value of lifting height and electrode spacing,which can make the mold sticking effect of plate reach the best.The existence of metal explosive wire can effectively improve the mold sticking effect of plate;The forming effect can be improved by an average of 20% per loading.