Research On The Electromagnetic-Electrohydraulic Hybrid Forming Technology For Integral Manufacturing Of Large-Scale Aluminum Alloy Shell Part

Large-scale aluminum alloy shell parts are the core components of aerospace vehicles.Their high-performance integral manufacturing brings a great challenge to the present manufacturing industry.On the one hand,the key specifications,such as size,tonnage,cost,etc.,of the traditional forming equipment sharply increase with the size of shell parts,hardly meeting the economical requirements of small-batch customized manufacturing for largescale parts.On the other hand,high-strength aluminum alloys used in the aerospace industry are hard to form.The forming issues such as wrinkling,springback and fracture,etc.are easy to arise.Quality control in large-scale parts forming faces severe challenges.The high-velocity forming process is a kind of plastic forming method based on impact loadings(such as pulsed electromagnetic forces,underwater shock waves,etc.),which has advantages of light-weight equipment,flexibility,etc.,and can significantly improve the formability of materials like aluminum alloys,providing a potential technical means for the forming of large-scale thin-wall aluminum alloy shell parts.At present,relevant attempts have been made,and remarkable progresses have been attained in the manufacturing methods and equipment of large-scale parts in high-velocity forming.However,existing studies are focused on processes based on a single type of impact loadings,which are restricted by their inherent loading modes.Thus,there are numerous shortcomings of existing high-velocity forming processes in equipment and forming performance.Aiming at the problems above,an electromagnetic-electrohydraulic hybrid forming method based on a two-step process is proposed in this dissertation.The forming mechanism,the influencing law of parameters,and the manufacturing of forming equipment,etc.are systematically investigated,combing numerical models and experimental research.Finally,the integral forming with millimeter-class precision for 1 m-scale fuel tank bottoms of carrier rockets is manufactured.The main contents of this dissertation are summarized as follows:An electromagnetic-electrohydraulic hybrid forming method is proposed.Electromagnetic-mechanical coupling analyzing models for electromagnetic forming are built based on the finite element-boundary element method,and fluid-solid coupling analyzing models for electrohydraulic forming are built based on the Arbitrary LagrangeEulerian algorithm,and the reliability of which are estimated.Based on that,the coupling of electromagnetic forming models and electrohydraulic forming models are realized through restarting modeling and numerical analyzing models for the whole electromagneticelectrohydraulic multi-step process are built,which provides an efficient analyzing means for researching the electromagnetic-electrohydraulic hybrid forming process.Aiming at the problem that the energy of underwater electrical wire explosion is hard to quantify accurately,a calibration method for underwater electrical wire explosion energy based on intermediate quantity(impulse)equivalence is proposed.The quantified calibration device for underwater electrical wire explosion is built and experimental investigations on underwater electrical wire explosion equivalent energy are systematically conducted.The influencing law and influencing mechanism of initial energy storage in the capacitor and metal wire diameter on underwater electrical wire explosion equivalent energy are revealed,and a fitted empirical formula of equivalent energy with electrical wire explosion parameters is obtained based on regression analysis,which provides a theoretical guidance for experimental investigation and numerical modeling of the electromagneticelectrohydraulic hybrid forming process.An experiment platform of electromagnetic-electrohydraulic hybrid forming for semiellipsoid shell parts with a diameter of 300 mm is built.Combing the numerical simulations and experimental validations,the die-fitting process of the workpiece and the influencing law of discharge energy on wall thinning of formed parts in the hybrid process are systematically analyzed and the important role of continuous water pressure in the diefitting process of the workpiece is clarified.Aiming at the springback of the workpiece in the electrohydraulic calibration step with small energy,the key role of the impact velocity of the workpiece onto the die in the die-fitting process of the workpiece is revealed,and a method of restraining springback is proposed.Based on this,an optimum forming strategy of electromagnetic-electrohydraulic hybrid forming is presented,which provided a theoretical foundation for electromagnetic-electrohydraulic hybrid forming of large-scale aluminum alloy shell parts.Aiming at the integral forming of the rocket fuel tank bottoms,a modular prototype of the electromagnetic-electrohydraulic hybrid forming process for 1000 mm-class scaleddown parts of rocket fuel tank bottoms is developed.Based on the prototype platform,the integral forming for rocket fuel tank bottoms of two typical aluminum alloy materials used in the aerospace industry(AA2219 and AA5A06)is attained,in which the forming accuracy is within 1 mm and the wall thinning ratio is lower than 15%.In addition,the mechanical performance of AA5A06 formed parts is systematically estimated,among which the tensile strength increased by 12.9% in comparison to the base material,and the residual stress on the formed part is less than 23% of the yield strength of the workpiece.The mechanical performance of the formed parts meets the service standard.Relevant studies provided data support for the equipment and processes of larger-scale aluminum alloy shell parts forming.