Studies On Modeling Dynamic Characteristics Of Bolted Joints

With the continuous development of manufacturing,the proportion of accuracy heavy duty machine tool in the production is more and more large,the requirement of machining efficiency and machining precision is also more and more high,the dynamic performance of the machine tool affects the development and progress of the manufacturing industry.Bolted joint is one of the most typical forms of machine tool,and its parameters and precision directly affect the accuracy and performance of the machine tool.Therefore,the study on the dynamic characteristics of the joints can not only provide theoretical and method support for the research of the overall dynamic characteristics of the machine tool,but also can be used to improve the precision and efficiency of the domestic machine tool,There is great theoretical significance to improve the quality of domestic machine tools and the development of manufacturing industry.From the microscopic point of view to study,the joint surface topography,micro contact mechanism and the existing classical contact models are analyzed,combined with the Hertz contact model,a new normal stiffness model of rough surface contact which has different materials in the surface and lower layer,the accuracy of the new model is verified by the results of finite element analysis simulation.Specific research contents are as follows:Firstly,according to the particularity of the bolted joint surface in the machine tool,this paper expounds the important significance of the research on the dynamic performance of the machine tool,the characteristics of the joint surface micro topography and the surface contact mechanism are introduced briefly,and a new model is proposed based on the classical rough surface contact model: based on the study of single asperity contact,the global stiffness of the joint surface is obtained by using the probability distribution function of the surface roughness.Next,Based on the Hertz contact theory,the deformation of the asperity and bulk substrate during is analyzed which surface has different materials,The relationship between the deformation of the asperity,the bulk substrate and the applied displacement is deduced,a new normal stiffness model considering the influence of the deformation of bulk substrate is presented by coupling method.Then,according to the real contact surface,a large number of finite element simulation models are established by using the finite element software ABAQUS,the validity and the range of validity of the new model are verified by comparing with the relationship between applied displacement and maximum contact force of new model,the Hertz model and the Finite element simulation results.The results show that the when ?=0.6-0.9,the new model is more effective than the Hertz model to reflect the real situation;when ?>1.25,the new model and the finite element simulation results is very close,the new model is more effective and more accurate than Hertz model.Finally,the distribution of asperity distribution in rough surface is assumed to be exponential distribution according to the statistical method of GW model,and the normal stiffness model of the joint surface is derived by the new normal contact model of single asperity.Compared with the existing experimental data,it is proved that the new normal stiffness model is closer to the experimental results,the new model is accurate and effective.