稀薄效应对空气静压导轨润滑特性的影响

发布时间：2018-04-21 08:10

本文选题：稀薄效应 + 分层理论　；参考：《昆明理工大学》2017年硕士论文

【摘要】：随着我国制造水平的不断提升,我国对精密及超精密的加工设备需求不断增加,空气静压导轨是超精密加工机床中常用的引导移动装置。常规供气条件下,当空气静压导轨工作气膜厚度达到几微米时,气膜内气体流态发生变化,气浮导轨的承载性、刚度、稳定性随之发生变化,此时,需要充分考虑尺度效应对气膜内润滑规律的影响。本文根据分子动力学和薄膜润滑理论对气浮导轨支撑区润滑气膜开展了深入研究,主要研究内容如下。首先,根据空气静压导轨气膜内气体流态及气体密度和滑移速度分布规律,沿气膜高度方向初步提出气体分层理论。根据气膜内气体分子运动规律,将气膜内气体沿高度方向分为近壁层、稀薄层、连续流层,建立相关物理模型并给出相应的数学控制方程。通过LAMMPS数值模拟计算出气膜内沿高度方向速度、压力分布,并且模拟出气膜内气体分子运动,验证膜内气体分层理论的合理性。其次,根据气膜内部压力梯度的变化特征,沿气体流动方向初步提出气膜分区理论。空气静压导轨气膜内沿气体流动方向压力梯度变化呈现先骤降再缓慢递减的趋势,本文根据膜内径向压力变化规律,提出了气体分区理论,沿气膜径向方向分为压力驱动区和牛顿摩擦区,并建立相应的数学描述和控制方程。通过Fluent、LAMMPS数值模拟计算膜内气体压力、速度等,验证分区模型的合理性。此外,通过结合速度滑移现象,分析了近壁层、稀薄层、连续流层在压力驱动区、牛顿摩擦区的速度滑移规律。再次,建立基于分层模型的全域速度滑移模型。根据气体分子在近壁层、稀薄层、连续流层的滑移规律,结合气膜内气体分层模型,建立气膜内气体分子速度滑移模型,并给出相应的数学表达式。此外,对气膜内气体黏度进行修正。通过LAMMPS、COMSOL、2DMD分析计算了气膜内的黏度、速度、压力等,对速度滑移全域模型进行了验证。最后,分别搭建基于密度变化的分层模型实验装置和分区理论实验装置。由于现阶段国内外就微米级气膜测量还无法实现直接测试,本文设计搭建一种基于密度变化和气膜特性的测试装置,通过间接方法验证气膜分层理论的有效性。对于气膜分区结论的验证,本文专门设计加工制造了一套准确测量膜内压力分布的装置,实验结果与数值计算进行了比较,进一步验证分区模型的准确性。此外,通过测量不同气膜厚度下,流量的变化规律,也论证了前期得到的边界速度滑移结论。
[Abstract]:With the continuous improvement of manufacturing level in China, the demand for precision and ultra-precision machining equipment is increasing in our country. Air static pressure guideway is a commonly used guiding and moving device in ultra-precision machining machine tools. Under the condition of conventional air supply, when the working film thickness of the air static pressure guideway reaches several microns, the gas flow state in the film changes, and the bearing capacity, stiffness and stability of the air floating guide rail change accordingly. The influence of the scale effect on the lubrication law in the film should be fully considered. Based on the theory of molecular dynamics and film lubrication, the lubrication film in the support region of air bearing guideway has been studied in this paper. The main contents are as follows. Firstly, according to the gas flow state, gas density and slip velocity distribution in the gas film of the air static guide rail, the theory of gas stratification is put forward along the direction of the film height. According to the motion law of gas molecules in the film, the gas in the film is divided into the near wall layer, the rarefied layer and the continuous flow layer along the direction of the height. The relevant physical model is established and the corresponding mathematical control equation is given. The velocity and pressure distribution along the height of the film are calculated by LAMMPS numerical simulation, and the molecular movement of gas in the film is simulated, which verifies the rationality of the theory of gas stratification in the film. Secondly, according to the variation characteristics of internal pressure gradient of the film, the theory of gas film zoning is put forward along the gas flow direction. The variation of pressure gradient along the gas flow direction in the air static guideway shows a tendency of first plummeting and then decreasing slowly. According to the variation law of radial pressure in the film, the theory of gas partition is put forward in this paper. Along the radial direction of the film, it is divided into pressure driving region and Newtonian friction region, and the corresponding mathematical description and governing equation are established. The rationality of the zonal model is verified by calculating the pressure and velocity of gas in the film by numerical simulation of fluentum lamps. In addition, the velocity-slip law of near wall layer, rarefied layer and continuous flow layer in the pressure driven region and Newton friction region is analyzed by combining the velocity slip phenomenon. Thirdly, a global velocity-slip model based on layered model is established. According to the slip law of gas molecules in the near wall layer, thin layer and continuous flow layer, combined with the gas stratification model in the film, the velocity slip model of the gas molecule in the film is established, and the corresponding mathematical expression is given. In addition, the gas viscosity in the film is modified. The viscosity, velocity and pressure in the gas film are calculated by Lamps ComSol 2DMD, and the global model of velocity slip is verified. Finally, the layered model experimental device and the partition theoretical experimental device are built based on the density variation. Since the direct measurement of micrometer film can not be realized at present at home and abroad, a testing device based on density variation and film characteristics is designed and built, and the effectiveness of the theory of film stratification is verified by indirect method. For the verification of gas film partition conclusion, this paper specially designed and manufactured a set of equipment to measure accurately the pressure distribution in the film. The experimental results were compared with the numerical calculation, and the accuracy of the partition model was further verified. In addition, the boundary velocity-slip conclusions obtained in the previous period are also demonstrated by measuring the flow rate variation law under different film thickness.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG502.39

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