| With the continuous development of the key components of China’s aerospace vehicles towards integration,lightweight and high precision,how to achieve high-performance integral forming of large lightweight components has become one of the core issues that urgently need to be solved in many major projects in the field of advanced manufacturing in China.However,lightweight components represented by aluminum alloys have poor forming performance under traditional stamping/hydraulic quasi-static processes,and are prone to some problems such as wrinkles,cracks,and serious spring-back.Meanwhile,the existing forming process is limited by pressure equipment table and tonnage.For the forming and processing of large-size shell parts,the method of split forming and tailored welding is mainly adopted,which has the disadvantages of complicated process,long cycle,high cost,and low forming accuracy.As a high-speed forming process,electromagnetic forming can significantly improve the forming limit of materials,inhibit the wrinkling and spring-back of workpiece,and reducing the cost of equipment manufacturing.It provides a new technical way to break through the integral forming and manufacturing problems of large-scale aluminum alloy shell parts.However,how to achieve the effective loading and control of electromagnetic force for forming in a large-scale area is extremely challenging,and the existing electromagnetic forming technologies are mainly applied to the forming of small-size shell parts,which cannot provide the relevant theoretical and experimental data support for the integral forming of large-size shell parts.Aiming at the above problems,the goal of this work is to realize the high-quality electromagnetic integral forming of the 1000 mm shell part which is in proportion to the bottom of the actual rocket fuel tank.The numerical analysis model of the forming system,the control method of the forming force and the analysis of the deformation behavior of workpiece,as well as the development of the forming device and experiments have been carried out.The related results have important academic value and practical significance for realizing the breakthrough of electromagnetic integral forming of large-size shell parts and expanding its industrial application.In the research of numerical analysis model of electromagnetic forming system,the coupling relationship between electromagnetic and structural physical parameters in the electromagnetic integral forming process of large-size shell parts was analyzed.The influence of the increase of the distance between the coil and sheet metal caused by the operation of the vacuum system on the electromagnetic coupling between them,and the electromagnetic interference caused by the blank holder and the counterweight for inertial restraint on the forming system were clarified.On this basis,a two-dimensional full coupling numerical model of the circuit-electromagnetic field-structure field of the electromagnetic integral forming system for large-size aluminum alloy shell parts was established,and its solution accuracy is verified by experiments,which provides an effective analysis method for accurate prediction of the shell deformation behavior and optimization design of the forming system.In the research of forming force regulation and workpiece deformation behavior,firstly,combined with numerical simulation and experimental methods,the effects of coil structure parameters,circuit parameters,workpiece flange constraints,and the residual air in the die on the electromagnetic integral forming of the shell part was investigated,and the design points of high-performance shell forming were clarified.On this basis,to solve the problem that the force generated by the traditional single-coil and single-power forming system is difficult to control,a multi-coil and multi-power electromagnetic forming method for shell parts with controllable axial force was proposed.A dual-coil and dual-power electromagnetic forming experimental platform was built to form the aluminum alloy sheet with a diameter of 398 mm,a thickness of2 mm and the material of 2219-O state.Then the regulation law of axial force distribution characteristics on the contour size accuracy and the maximum thinning rate of shell parts was systematically explored,the coil voltage matching process window with high forming accuracy and minimum thinning rate was obtained,and the feasibility and effectiveness of the controllable axial force-based forming technology in further improving the formability of shell parts has been demonstrated.These results lay a foundation for realizing high-quality electromagnetic integral forming of large-size shell partsIn the development of large-scale electromagnetic forming setup and experimental studies,in order to achieve the electromagnetic integral forming of a 1000 mm shell part with the same proportion to the bottom of the rocket fuel tank,the electromagnetic forming experimental platform integrating controllable axial force forming system,electromagnetic blank holder system,power and control system as well as inertial restraint system was built.In the aspect of forming system,the multi-coil and multi-power controllable axial force-based forming scheme is adopted,and a hierarchical forming coil system(four-stage)based on the outer layer reinforcement technology of pulse magnet is proposed and developed,which can maintain the structural stability and thermal stability(the single temperature rise is less than 6 K).In the aspect of blank holder system,the repulsive electromagnetic blank holder system based on modular coil is adopted,which effectively improves the amplitude of blank holder force and ensures the stable loading of blank holder force in the forming process of large-size shell parts.On this basis,the numerical analysis and experimental research on the electromagnetic integral forming of the shell parts were carried out on the aluminum alloy sheet metal with a diameter of 1378 mm,a thickness of 4 mm and the material of 2219-O state.The variation characteristics of shell deformation behavior under different coil discharge parameters and matching modes were explored.Finally,the high-quality integral forming of this kind of shell part was realized by single discharge,and the forming depth is more than 310 mm,the maximum dimension deviation between the formed part and the die contour is less than 10 mm,and the maximum thinning rate is less than 15%. |
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