Effect Of Lubrication Of Rarefaction On Aerostatic Guide Way

With the continuous improvement of China’s manufacturing level,it is a continue increasing for China’s demand for precision and ultra precision machining equipment.Aerostatic guideway is a kind of guide mobile device that commonly used in ultra pre-cision machine tools.When the air film thickness of aerostatic guide way reaches sev-eral microns under conventional gas supply condition,the gas flow pattern has changed in the gas film,and the bearing capacity,stiffness and stability of aerostatic guide way also has changed.At this point,it is necessary to study the gas flow in the film based on molecular dynamics.According to the molecular dynamics,supporting area in the film of aerostatic guide way is studied in this paper.At first,according to the flow,the distribution law of gas density and slip velocity,the gas stratification theory is put forward preliminary along the direction of the film height.According to the gas molecular activity law in the gas film,gas in the film was divided into near wall layer,thin layer,continuous flow layer,and physical model and the corresponding mathematical equations were given.Gas velocity,pressure distribu-tion in the film was calculated by LAMMPS,and molecular motion was also simulated,which was verified the rationality of gas stratification.Secondly,according to the characteristics of the pressure gradient in the gas film,the theory of the gas film partition is proposed preliminary along the direction of gas flow.There’s a trend of decreasing first and then slowly decreasing for the pressure gradient along the flow direction of the film,which is a base for gas partition theory.Gas in the film was divided into pressure driven area and Newton friction area alone the radial direction in the film.And the corresponding mathematical expression were given in this paper.The gas pressure and velocity in the film were calculated by Fluent and LAMMPS numerical simulation to verify the rationality of the stratification model.In addition,by combining the velocity slip phenomenon,slip velocity in near wall,thin layer,continuous flow layer under pressure driven area and Newton friction area was analyzed.In third,velocity slip domain model based on stratification model was established,which is according to the sliding law of gas molecules in each layer and gas stratifica-tion model.And the corresponding mathematical expression were given in this paper.Besides,the gas viscosity in the gas film is corrected.The viscosity,velocity and pres-sure in gas film were analyzed by LAMMPS,COMSOL and 2DMD,to verify the model.Finally,devices of partition experimental and stratification model experimental based on density variation were built in this paper as the last part.Because of the ina-bility to measure directly on the micrometer scale at home and abroad currently,a de-vice based on density variation and gas film characteristics was designed to prove the validity of the film stratification theory by indirect method in this paper.In order to verify gas film partition theory,a set of accurate measurement of the pressure distribu-tion within the device was designed and manufactured,the experimental results were compared with the numerical calculation.the accuracy of the partition model was veri-fied furtherly.In addition,by measuring the variation of the flow rate under different film thickness,the paper also proved the conclusion of the boundary velocity slip.