| In the field of aerospace,a large number of lightweight high-strength aluminum alloys are used in lightweight design,therefore,the raw material of many parts on the aircraft body is aluminum alloy.In order to ensure the welding quality and strength between the aircraft fuel tank and the pipelines,the designer will firstly process a flanging component on the tank body.as for some fine structures in the pipeline,the small-sized circular holes need to be flanged which creates problems for processing.Flanging component need to be formed for small-sized circular holes.The traditional flanging process often causes cracking failure in the mouth area of the vertical wall,the process is usually complicated and the forming quality cannot be guaranteed.However,the energy utilization of the traditional electromagnetic forming(EMF)process is not high for small-sized circular hole-flanging and the coil working conditions are unstable.For small-size circular hole-flanging,the use of Lorentz-force-driven(LFD)hole-flanging process can improve the forming performance and can improve energy utilization.The research of LFD hole-flanging is very meaningful for the design of aerospace components.Firstly,With the help of FEA software LS-DYNA,an LFD hole-flanging model was established.A simplified version of the JC model was used to build a material model.Simulate pure structure field by inputting the speed curve photographed by DIC,the comparison between the process test and simulation test results verified the reliability of the simulation model.Similar to the traditional EMF,LFD hole-flanging had obvious inertial forming behavior characteristics,The difference was that EMF was the inertial forming of the sheet itself but LFD was the flanging of the sheet through the inertial action of the high-speed punch.The die-attaching results of the vertical wall was getting worse from the root to the mouth.As the size of the prefabricated hole was reduced,the thinning of the mouth area was severe,which led to die-attaching results of the mouth area was getting worse too.Secondly,the process comparison of quasi-static flanging,EMF hole-flanging and LFD hole-flanging was carried out,the unique advantage of the LFD hole-flanging process in small-size circular hole-flanging was verified.The limit coefficient(k=d/D)of LFD hole-flanging can reach 0.37,which had greatly improved the formability compared with the quasi-static flanging process(k=0.52).The micro-morphology analysis showed that the high-speed punch extruding the deformation of metal sheet can improve the flatness of the surface to a certain extent,which suppressed the formation of burrs to improve the forming performance of the flange.The DIC high-speed camera was used to record the punch speed curve under different working conditions,and the impact on the different working conditions was compared.The effects of energy and prefabricated hole sizes on circular hole-flanging were studied.The basic law of vertical walls were explored by combining microscopic analysis and hardness test.Based on the linear principle of the prefabricated hole formula,a new formula suitable for the process of LFD hole-flanging is derived.Finally,based on the verified LFD hole-flanging model obtained in chapter two to study the influence of mold parameters on the flanging results,The results showed that as the thickness of the sheet increased,the flanging height increased,the thinning rate of the mouth decreased,and die-attaching results of the mouth area was getting worse.The influence of the taper change of the punch on the vertical wall result was analyzed through simulation,which provided guidance for the design of the taper of the punch in the follow-up experiments.Using Design-Expert software,the interactive effect of three parameters(punch cone angle,die radius,and die inner diameter)on deformation results were analyzed. |
PDF Full Text Request