Research On Static And Dynamic Model And Equivalent Method Of Machine Tool Bolt Joints

The bolt joint is one of the most common fixed joints in the machine tool structure,which directly affects the static and dynamic performance of the machine.The bolt joint is composed of the bolt head joint surface,the thread joint surface,the flange joint surface and the bolt itself.The interaction of these components is mutually coupled,resulting in the nonlinearity of the bolt joint,and the research is difficult,and it becomes a machine tool or even a mechanical structure.One of the hot spots in the research of the joint department in the system.Therefore.studying the variation law of bolt joint characteristics can not only provide scientific basis for the design of bolt joirnts,but also has important significance for improving the design,manufacture,assembly process level and machine performance of high-end CNC machine tools.Although domestic and foreign scholars have studied bolt joints fr-om different angles,they still do not compl,etely solve the problems in the analysis of the characteristics of the whole machine.For example,the bolt specifications,pre-tightening force and flange thickness in the bo lt joint should be followed in the actual design.The principle of this kind can meet the design requirements,and there is still no theoretical support.On th,e other hand,the current commercial finite element software analysis of bolt joints encounters two major problems.One is that commercial softwarre systems lack the support of an effective joint feature database,and the second is the complexity of bolt joints leading to finite element networks.The grid is difficult to divide,either it is computationally difficult or the model is too simplified and the calculation accuracy is too low.In vie,w of the problems existing in the current research on bolt joints,the main contents of this paper are as follows:(1)Starting from the main factors affecting the joint surface,the experimental acquisition method of the basic characteristic parameters of the joint surface was studied.Based on the experimental device for static characteristics of the joint surface,the normal and tangential static characteristic parameters of the joint surface pairing conditions related to the material of the bolt joint were obtained.The data mining of the joint surface by BP neural network was proposed to make up for the cause.The loading of uneven and missing data segments and the discovery of abnormal data points expand the high surface pressure data.The experimental model of the dynamic parameters of the joint surface was established.Based on the experimental equipment for the dynamic characteristics of the joint surface,the dynamic fundamental characteristics of the j oint surface were obtained.(2)The influence of flange thickness,pre-tightening force and bolt specification on the deformation of bolt joint surface is studied.The basic characteristic parameters of the joint surface are given to the joint surface in the form of two developments.The finite element analysis model of the unit bolt joint is established.The reasonable matching relationship between the pre-tightening force and the flange thickness under different bolt specifications is obtained,and the bolt head joint is established.The equivalent deformation model of the surface-to-thread interface is used to verify the reliability of the model.(3)An analytical model for the multi-bolt joint stiffness based on the characteristic parameters of the joint surface is established.Considering the coupling effect of the bolt head j oint surface,the thread j oint surface,the flange joint surface and the bolt,the bolt j oint can be obtained through analysis.Stiffness and stiffness of the unit bolt joint.The four-node and six-node equivalent spring model of the unit bolt joint is established.The validity of the equivalent model is verified by experiments,which provides a method for the effective treatment of the bolt joint in the finite element modeling analysis of the machine tool.(4)An anisotropic virtual material equivalent processing model of bolt joints considering stiffness and damping characteristics is established.The method for determining virtual material parameters is given.The beam structure model with multi-bolt joint is built.The feasibility of the model was verified.