Research On Solid Granule Medium Tube Outer And Inner Narrow Ring Forming By Inner High Pressure Bulging And Outer High Pressure Compressing

The tube part with narrow deformation zone presents particularity and complexityfrom that with wide deformation zone in the forming, which mainly includes: highforming pressure, hard fittability with the mould and substandard thickness distribution ofthe products in tube diameter increasing (bulging) forming, and the existence ofwrinkle-free forming range in tube diameter reducing (compressing) forming. Base on theforming characteristics of easy sealing, simple pressure providing, nonuniform innerpressure distribution, and beneficial friction action of Solid Granule Medium Forming(SGMF) technology, the forming problems of the tubes with narrow deformation zonecan be effectively solved, also the technology can be broadened to the tube outer pressurecompression forming area. Through theoretical method, numerical simulation andprocess experiment, the diameter increasing and reducing forming laws of the tube withnarrow deformation zone are explored, and a narrow convex tube of high-temperaturealloy which is used in the aero-engine and a circumferential diameter reduced tube withsmaller height-diameter ratio are successfully trial-produced.During the development of these two typical parts, aiming at the limitation and errorwhich are caused by using FEM to simulate the pressure-transfer and the flow of the solidgranule medium, the coupling approaches of finite element method (FEM) and discreteelement method (DEM) are proposed according to the laws of force balance, which cansolve the coupling problems of elastic-plastic mechanics in the contact between thecontinuum and discrete medium, and the breadth and depth of numerical analysisapplication are extended.As a discrete and friction-type material, the granular medium shows a quite differentmechanical behavior from other pressure transfer medium during the loading process.Through the performance experiments of granular materials, the macro and micromechanical characteristics of granular materials under confining pressure are studied andthe physical parameters of granular materials are obtained, therefore the material parameters in the numerical model of granular medium are established. In order to verifythe macroscopic mechanical performance in FEM and DEM numerical models of thegranular medium, the pressure transfer experiments are designed and carried out. The testresults agree with the simulation results well, which means that the necessary parametersfor simulating the solid granule medium forming can be obtained finally.Through the application of the thin shell theory, the deformation mechanism of tubebulging is analyzed, the long and short tube defomation modes which are related with thegeometrical dimensions are determined, and the particularity and complexity in theforming of tube with narrow deformation zone which belongs to short tube defomationmodes are explained. Based on the theoretical research, FEM is used to analyze theinfluence of the matching relationship between the feed force at the end of tube and theinner pressure on the forming performace of the tube, the device with the characteristicsof horizontal parting and axial elastic feeding structure for the solid granule medium tubebuldging process is designed, then the acting functions which include clamping, tubeends feeding and inner pressure loading on the single action stamping press are realized,and a high-temperature alloy GH3044thin-walled convex tube used in the aero-engine issuccessfully trial-produced.In order to extend the application range of solid granule medium forming process inthe tube forming, the new technology of solid granule medium tube outer pressurecompression is put forward. With the tube end fixed and the uniform external pressure,the expressions of the circumferential elastic instability critical loading and the wavenumber are deduced by using L.H.DONNELL linear buckling theory. Base on theassumption of linear-hardening material model, the critical loading and stress expressionsof circumferential plastic wrinkling instability are deduced with the tube end fixed in thetube outer pressure compression forming, and the critical geometrical condition forplastic instability is obtained. The influence laws of the geometrical parameters on theelastic-plastic wrinkling instability in the tube outer pressure compression forming areanalyzed. Circumferential wrinkling critical principal strain paths under different formingconditions are solved, which is certified by using FEM simulation, and the critical instability principal strain judging curve is founded finally. Base on the theoretical andnumerical analysis, the mould and process experiment of solid granule medium tubeouter pressure compression forming are designed. The process characteristics of solidgranule medium tube outer pressure compression forming are analyzed. The limitationsof using FEM to simulate granule medium forming are demonstrated.Using FEM to simulate the granule midum in the solid granule medium forming willbring a serious of problems, for example, the effect of particle medium mesoscopicparameter changing on forming cannot be considered, and the meshing fine degree oflocal medium has great influence on computational cost and accuracy. For these reasons,the FEM-DEM coupling method is put forward according to the equilibrium law ofboundary force and the FEM-DEM coupling simulation platform is developed throughVisual Basic, which can realize the interactive inheritance transfer of calculated databetween the finite element and discrete element, and solve the elastic-plastic mechanicalnumerical simulation problem of coupling deformation of the continuum tube and thediscrete medium. Solid granule medium tube outer pressure forming is taken as thecarrier to do the research of the coupling process, the pressure-transfer property andchanging rule of the mesoscopic structure on solid granules medium are achieved and theinfluence laws of process parameters, such as particle diameter, charging volume, contactfriction and particle stiffness, etc. on the tube blank plastic forming performace areanalyzed. Through the comparison between the experiments of solid granule midum tubeouter pressure compression forming and the simulation results, the correctness ofFEM-DEM coupling method is proved.