Numerical Simulation Of Some Topics In Hydrostatic Extrusion Process

Hydrostatic extrusion is the forming process that transfer the pressure through highpressure medium,and thus force the material to deform.During the process,the pressure medium can ensure the material under the hydrostatic compressive state,so the materials' formability is improved.Meanwhile,the medium also generates good lubricant conditions between the billet and the die.Thereby,it is one of the most effective methods to fabricate the difficult-to-form materials.By means of finite element analysis,the stress strain distributions and the materials' flow behavior can be observed.The purpose of this study is to do some research about the hydrostatic extrusion through the finite element simulation method.Further,some guidance for the design of the hydrostatic extrusion experiment can be provided.Firstly,a finite element model with hydrostatic pressure load was designed,which conforms to the physical loading process of hydrostatic extrusion.Meanwhile,another most co mmonly used displacement load model was also established for comparision.Through the stress and strain distribution and the extrusion pressure statistics under different working conditions,the two models were compared and then analyzed by the theories of hydrostatic extrusion.The superiority of the pressure load model in the reflection of the general laws of hydrostatic extrusion was finally proved.Secondly,the hydrostatic extrusion processes of pure tungsten under different temperature(T),extrusion ratio(R)and die angle(2?)were simulated by pressure load model.Through the investigation of the extrusion pressure,stress strain distributions and other information under different working coditions,the hot hydrothermal extrusion of pure tungsten was optimized,and the suitable parameters were determined.Then,with the parameters given by the simulation,the corresponding experiment was carried out.Through the comparision of the product quality,microstructure and mechanical properties before and after the extrusion.The guidance effect of the pressure load model for the design of the hydrostatic extrusion experiment was proved.Meanwhile,it was also proved that the hydrostatic extrusion process can greatly improve the properties of the sintered pure tungsten.Finally,the hydrostatic extrusion processes with different die contour(C,E,H and T)and different back pressure modes(by punch,pressure medium and shell)were investigated.The influence of the die contour on the stress and strain distributions and extrusion pressure was then compared.It was proved that the H shape die contour could guarantee uniform material flow and meantime reduce the axial tensile stress.Then,the influences of the back pressure value and back pressure mode were respectively compared by the materials' flow behavior and the stress and strain distributions.It was proved that the punch back pressure mode only provided the most significant inhibitive effect on the axial tensile stress,the inhibitive effect provided by the shell back pressure modes to the axial tensile stress in the center of the billet is non-significant,and the hydrostatic back pressurecould inhibite the growth of the tensile stress of three dimensions.