Design And Research Of Split-Type Ultra-High Pressure Die

With the development of high pressure physics,geophysics,high pressure chemistry and the increasing demand for super-hard materials,the demand for high pressure equipment is also increasing.The ultra-high pressure die is the core component to produce ultra-high pressure in production practice.In addition to the ability to withstand ultra-high pressure,it is also necessary to ensure that the synthetic space is sufficiently large to meet the requirements of use.The main trend of the development of modern high pressure equipment is the large-scale high pressure die.The large high pressure die can not only improve the sample volume,but also improve the quality of the synthetic product.However,under the current technological conditions,the most important problem in the process of large scale high-pressure die is the difficulty in the production and processing of large cemented carbide part.The processing cost of large size parts is larger,and the quality could not be guaranteed,which limits the process of the large size of the die.In order to reduce the manufacturing difficulty of high pressure die cemented carbide cylinder,and reduce the difficulty of large scale of pressure die,a split type ultra-high pressure die is designed.This kind of die is a new type of ultra-high pressure die,which takes full consideration of the principle of massive support and lateral support,at the same time combines the characteristics of the thick wall cylinder.The structure mainly consists of three parts: the internal discrete hard alloy pressure cylinder,the middle high strength steel discrete block and the external high strength steel supporting rings.This type structure can effectively eliminate the circumferential stress of the cylinder,lower the cylinder stress level,and the ultimate bearing capacity of the die has been improved.The most important thing is to reduce the size of the parts,and it is easy to expand the volume of the cavity,and reduce the large-scale difficulty of the high pressure die.In this paper,a series of research and optimization of the split-type high pressure die is carried out by the finite element method.The stress states of the two types of cavity with the cambered and the plane surface inner wall are compared,and the stress of the pressure cylinder with different degrees of dispersion is analyzed.The stress characteristics of different discrete degrees of supporting ring are analyzed,and the high pressure die with discrete cylinder and discrete supporting ring are optimized,which provides a theoretical basis and reference for the design,manufacturing and application of the split type ultra-high pressure die.The main contents and conclusions of this paper are as follows:1.Design and structural analysis of split ultra-high pressure die.The split type high pressure die is designed to apply the principle of massive support and lateral support at the same time combined with the structure characteristics of the thick wall cylinder.It is a new idea to realize the large size of ultra-high pressure die.There are two forms inside the inner wall of the cylinder,one is the inner wall of the cambered surface and the stress level of the cylinder is greatly reduced compared with the belt-type cylinder,the other is the plane surface,which further reduces the stress level.The split type ultra-high pressure die is a new type of die structure.The related mechanical analysis is carried out,the characteristics of pressure transfer are derived,the calculation of the related parameters and the related design principles are introduced.2.The establishment of finite element model of split-type ultra-high pressure dieAccording to the structure characteristics of the high pressure die,the finite element analysis software Ansys/Workbench is used to establish the finite element model.The cell type,boundary condition,material parameter model and contact-friction condition in the model are discussed.The static implicit algorithm is used to analyze the stress distribution of the belt-type die and cambered surface split high pressure die under the pre-tightening state and the loading state.The inner wall of the cylinder of the belt-type die produces great stress.Circumferential stress is the main factor leading to the failure of the cylinder of belt-type die.However,the split cylinder with a cambered surface is low.In order to further reduce the stress level of the discrete cylinder,the cambered surface cylinder is optimized to a plane type cylinder.Through comparison and analysis,it is shown that the stress of the supporting ring has little influence on the cylinder of the split type die.3.Stress analysis of split-type cylinderThe stress distributions of the belt-type cylinder and split-type cylinder under the same loading condition are compared.The results of numerical simulation show that the stress of dissecting discrete cylinder with cambered surface is much smaller than that of the belt-type cylinder,and the split cylinder can efficiently eliminate the equivalent,maximum shear and circumferential stresses of the cylinder.Optimizing the cambered surface to plane surface can further eliminate the stress level of the cylinder,and under the action of pre-tightening of the supporting ring and internal loading on the inner wall,the cylinder is in a similar hydrostatic pressure environment,which greatly reduces the shear stress of the cylinder.The cemented carbide divided block squeezes another under the pre-tightening action of the supporting ring,and produces frictional effect,which enhances the effect of the lateral support,and improves the bearing capacity of the split cylinder.The simulation results show that the ultimate bearing capacities of the three kinds of dies are 5.0,5.9 and 7.6GPa,respectively.The ultimate bearing capacity tests results show that hydraulic oil pressures reach 7.5MPa,9.4MPa and 12.4MPa when the belt-type cylinder,split cylinder with cambered surface and split cylinder with plane surface breakup,respectively.4.The influence of cylinder discretization on the stress of the dieThe split number of the cylinder can be determined by the specific dimensions of the pressure die.The stress of the cylinder with plane surface increases gradually with the increase of the discrete degree,and at the same time the influence pre-tightening stress on the stress of cylinder is discussed.The ultimate bearing capacity of split cylinders with different degrees of dispersion is predicted.Finally,the simulation results are verified by the experiment.It is necessary to take full consideration of the pressure die's size and application when determining the divided number of cylinder.It is not fit to divide the cylinder too much when high pressure die with a small size.When the size of the cylinder is larger,it is appropriate to choose a large discrete cylinder to reduce the difficulty of the hard alloy processing and manufacturing.It is of great significance for the design and production of the high pressure die to select the suitable pressure cylinder with the degree of discretization.5.The influence of supporting ring dispersion on high pressure dieThe supporting ring of high strength steel is also discretized,which can make the mold larger and easier.The results of numerical simulation show that the stress change is very small when the dispersion degree supporting ring is relatively low.After comparison and analysis,it is found that the discrete degree of the supporting ring is not suitable for large.The stress changes of the supporting ring are discussed under different coefficient of friction.When making supporting ring parts,the manufacturing cost should be considered to reduce the surface roughness of the parts.In order to restrict the radial displacement of the discrete part,a method of transforming the die face from the plane to the inclined plane is put forward,which can effectively reduce the displacement of the discrete part.It is easy to realize the large cavity of the die by discretization of the supporting ring6.Optimization of the split type ultra-high pressure dieIn order to make the stress distribution of the split-type high pressure die more reasonable,the optimum design method of the target parameters is used to calculate the optimum size of the die.The influence of the height to diameter ratio,the height ratio,the outer diameter of the cylinder and the angle of the cylinder as well as the end angle of the pressure die on the stress of the structure are analyzed.The optimum value of each parameter under certain conditions is obtained,which provides a reference for the design of a split type ultra-high pressure die.