Study On Stiffness Modeling And Equivalent Clearance Model Of Lubrication Guide Joint Surfaces

The surface of machine parts isn't absolutely smooth but a bit rough.and actually the contact of two surfaces is the contact of higher asperity.The joint surface of smooth guide is the coexistence of fluid lubrication and asperities in micro scale.The study of the joint surface asperity is mainly based on the sphere or periodicity assumption,and some relative research results have been gained.However,there is little research about grinded and chipped cylindrical asperities,and most research is still in the elastic contact stage.The existence of lubricant in the joint surface can effectively improve its stability.The influence of fluid film shouldn't be neglected during contact analysis.Therefore,based on the elastic-plastic contact deformation of cylindrical asperities and lubrication factors,establish more consummate contact dynamics models and study of the contact of joint surface and the characteristics of fluid film stiffiness.It has theoretical sicgnificance and engineering value not only to the analysis of dynamic and static characteristics of machine tool but also to the optimum structural design of machine tool.The thesis takes sliding guide joint surface of machine tool as the object of the research,analyzing and comparing the contact characteristics of joint surface through theoretical model derivation,numerical analysis,finite element analysis and experimental analysis,which are as follows:First of all,on the basis of the contact characteristics during elastic,elastic-plastic and plastic deformation stages and Tresca yielding criterion of cylindrical asperity,the normal and tangential contact stiffness fractal models are derived,which can be applied to wider ransge.And then adopting MATLAB software to analyze the models'numerical simulation,the thesis systematically studies the influence of fractal parameter of joint surface,scale parameter and loading to normal stiffness and tangential stiffness.Secondly,comprehensively considering the influence of lubrication factor,using elastohydrodynamic lubrication theory,the generalized Reynolds equation of the average flow and partial film lubrication equation,comprehensive stiffness model of inlet oil film stiffness,oil film stiffness and normal stiffness of contact zone is established,which is on the basis of the serial and parallel structure.Thirdly,based on the similar characteristics of surface micro topography,the fractal dimension and fractal amplitude parameter of sliding guide rail joint surface are calculated by adopting TR200 handheld roughness meter,which can provide truthful data about how surface micro topography influences component natural frequency.According to measured fractal parameters,numerical solution of stiffness model is reached.Fourthly,the stiffness model of joint surface is verified through modal experiment of slide guide rail experiment platform.On the basis of unit equi,valent stiffness identification method of single degree system joint surface,equivalent stiffness in per unit area is got and the mathematical model of rail joint is verified.Single factor method is adopted by dynamic stiffness experiment,analyzing the influence of sliding joint surface dynamic stiffness to sliding line velocity,press surface and lubricant oil.The thesis compares dry friction with lubrication condition,analyzing contributions which lubricant film makes in the joint stiffness.Fifthly,combining the macro perspective and micro perspective,the experiment reconstructs the joint surface of "solid-synthetic equivalent layer-solid" model,and the joint surface is equivalent to a sort of virtual material.On the basis of stiffness formula and modal strain energy equivalent method,equivalent clearance layer material parameters are gained,and finite element modal analysis is carried out.Finally combining with the experiment,the verification of equivalent clearance model of rail joint is completed.