金属薄壁管件液压胀形过程的数值模拟研究

金属薄壁管液压胀形过程的数值模拟研究AbstractAlong with the development of science and acceleration and industrial production,themetallic tube (tube for short)has been widely used in the sectors of mechanical engineering,aerospace industry,petrochemical industry,transportation industry and light industry.Thetechnology of tube plastic forming becomes more important.As a new special technology,thetube hydro-forming process is developed in recent years.It uses the liquid pressure to formthe work piece.The process is a kind of complex plastic forming process with the charactersof large disturbance and large deforming,which involves the plastic flow of metal tube underthe complex stress state.There can be many defects in the practical production such aswrinkling,cracking,buckling,etc.Just by virtue of the experience,it is difficult to predictaccurately the performance of tube bulging and assess the correctness of mold design.Based on the metal elastic-plastic theory,this paper carries out a series of simulations onthe platform of ETA/DYNAFORM which is a type of software for finite element analysis.The simulations include modeling and meshing the metal tube,exerting boundary conditions,power loads,and controlling the loading paths.We use the LS-DYNA solver for numericalanalysis and solving.And the powerful post-processor shows the whole bulging simulationand the result data.We observe the results such as the simulation animation of the bulgingprocess,the figure of the wall thickness distribution,the figure of the thinning rate of wallthickness over time and the figure of the stress-strain behaviors at different time.Then weconclude the influence of some factors (e.g.the internal pressure,wall thickness,loadingpaths and friction situation)on the hydro-forming bulging process.Thus various defectswhich may appear in the hydraulic bulging process can be further predicted.The conclusions in this paper are as follows.Under the same initial wall thickness andthe same boundary conditions,increasing the internal pressure helps to improve the height ofthe branch tube.But it affects the uniformity of the wall thickness during the tube bulging andmakes the wall thickness of the bulging zone excessively thin.Linear load path leads to thewrinkle instability due to the insufficient internal pressure at the initial stage,while thestaircase load path can significantly eliminate such defect and achieve a better bulging effect.Under the same internal pressure and the same boundary conditions,increasing the initial wallthickness of the tube embryo can slow down the thinning rate.But it decreases the height ofthe branch tube after the tube bulging.Finally,overmuch friction causes a thin wall thicknessof the bulging zone.Meanwhile,it affects the smooth feeding of the main tube and results inthe instability of the end of the main tube and the insufficient height of the branch tube.Andovermuch friction makes the tube surface with scratches and impacts the quality of the tubesurface.Thus reducing part of friction is good for the tube hydraulic bulging.-Ⅱ-