Research On Flow Mechanism Of Magnetic Pulse Shaping For5A02Aluminum Alloy Sheet

Recently, Aluminum, as an kind of important alternative materials inlightweight design, is becoming a hot topic. Electromagnetic forming, as a newmethod of forming, is gaining more and more attention because of the advantages inForming Limit, Control of Rebound and High Machining Accuracy. However, itsformability at room temperature condition is poor. Fortunately electromagneticforming has broad application prospects due to characteristics in aluminum alloysheet forming. In this thesis, the test material is5A02aluminum alloy. Flowbehavior of the electromagnetic forming, discharge parameters and processparameters on the deformation will be studied.At the outset, Split Hopkinson pressure tests and quasi-static tensile test areconducted to obtain stress-strain curves of5A02aluminum alloy at different strainrates. Johnson-Cook constitutive model is obtained by fitting method and used asthe material model. ANSYS Mechanical/LS-DYNA module is applied for thesimulation of the electromagnetic sheet free bulging. The results show that as theincrease of the discharge capacitors and the voltage conditions，the deformationspeed，the bulging height and the effective strain increases. At this condition, theheight of the free bulging is30.5mm and the bulging speed is136m/s respectively.The strain status of the blank’s surroundings is uniaxial tensile strain,。By studying of5A02aluminum alloy sheet free bulging, the effect of skindepth on the deformation is obtained. It is found that the results of the bulging arebetter when the discharge capacitors are768uF and1152uF. Material flow patternduring deformation is gained using high-speed cameras. The results show that thesheet locating at the above of half of the inductive circles are under a largerelectromagnetic force. This region deforms first and then induces other regionsdeform, the deformation speed tops at0.2ms, the highest speed is116m/s and thedeformation is finished at2.5ms. Compared with experimental results than theresults of numerical simulation is smaller.According to Aluminum alloy sheet electromagnetic bulging study atconditions of same discharge energy, different BHF and asymmetric constraints andprefabricated tensile stress. The forming local feature sheet plastic flow rule underthe action of pulsed magnetic field is obtained. When the nearby of the region ofblanket can flow, the deformation of the wide direction is homogenous. Theeffective strain is larger at the side of stronger constraint. The existence of theprefabricated tensile stress can make the sheet have elastic deformation to increasethe height of sheets. The prefabricated tensile stress is78.5MPa as the height of draw beads is7mm，the height of bulging has an increase of22%.