Research On Parameter Identification Of Machine Tool Bolted-joint Interface

Mechanical joints under the action of external load will show the characteristics of stiffness and damping.the dynamic characteristics of the joints has a significant impact on the overall dynamic characteristics of the machine tool.The study shows that the stiffness characteristic of the joints is an important part of the overall stiffness of the machine tool,and the damping of the joints is more than ninety percent in the whole damping of the machine tool.In the dynamic design of the machine tool,the accurate identification of the parameters of the joints is helpful to establish the dynamic model of the mechanical structure so as to accurately predict the overall dynamic characteristics of the machine tool.Generally speaking,we can study the macro and micro two aspects of the mechanical joints.The macro aspect is devoted to seeking the modeling method that can accurately simulate the joints,and the micro aspect mainly studies the dynamic characteristics of the joints from two aspects:the micro topography and the internal damping characteristics.On the basis of consulting a large number of relevant literatures,this paper mainly does the following research on the dynamic characteristics of the mechanical joints:(1)Taking the fixed joints of the machine tool as an example,this paper makes a stress analysis on the bolt connection structure and derives the approximate expression of the bolt preload torque and preload.Besides this paper analyzes the mechanism and influencing factors of damping and stiffness of the joints from the micro field and introduces three typical surface contact models.(2)The relevant parts of the bolt connection structure are processed,and the experimental modal analysis is made by using the dynamic signal testing equipment to obtain the modal parameters of all kinds of material—damping and natural frequency.We analyze the influence of the surface roughness,the bolt preload moment,and the material material on the modal parameters of the joint.In addition,the material damping of a single cast iron plate and joint damping of the bolt joint structure are compared and analyzed.(3)The stress analysis of bolt connection structure is carried out,and’ the dynamic model of the whole structure including the joints is established by the spring damping element.Based on the modal parameters of the test experiment,the combination of theoretical analysis and experimental testing is used to identify the stiffness parameters of the joints.(4)Based on the finite element software ANSYS,established three kinds of finite element model of the joints including the direct bonding finite element modal,the finite element model of spring damper unit,the finite element model of contact unit.Making the modal analysis of three kinds of finite element models,we compare the results with the experimental data to draw the relevant conclusion.