Theoretical Modeling And Experimental Study Of Precision CNC Machine Tools And Its Typical Interface

During the design phase to predict the machine products processing precisionperformance accurately is a hot research topic in recent years, but in most cases the resultsby means of theory analysis is different from that of experiment, which prolong the productdesign period and increase the cost of product. The main reason is that the machine toolshave complex structure, there are lots of interfaces. And how the interface influence theperformance of machine tools is still not very clear, so the model of interface become one ofthe bottleneck problems of NC machine tool design.In the early nineteen sixties, scholars have found that interface of the whole machinetool account for60%-80%machine tool rigidity, more than90%of the total damping,40%-60%total flexibility and85%-90%static deformation are derived from the interface.This article will focus on set up the static, dynamic and thermal model of interface, as wellas the finite element analysis of NC machine tools. According to the structure of NCmachine tool, the interfaces are further divided into five kinds of interface, they are bearinginterface, ball screw interface, rolling guide interface fixed interface and spindle toolsinterface. The main work of this paper is as follows.Aiming at the key problem in determining the parameters of FEAmodel of bearing jointinterfaces, a new scheme according to the experimental data of modal testing is proposed. A5-DOF dynamic equation following Lagrange theory is reported for the analysis to ballbearing vibrations, the stiffness and damping along normal of single ball is obtained by leastsquare method, then the stiffness and damping matrix of bearing joint interfaces areidentified. A new5-DOF dynamic equation by two pairs of springs instead of the ballbearings is established, where the of spring values are calculated by substituting the stiffnessand damping matrix into new equation to gain the FEA model of structure containing ballbearing. The results show that the first there modes by the FEA model coincide well with theexperiments, and the error of natural frequencies gets less than5%.Basing on the detailed analysis of the contacting deformation of ball screw, the staticand dynamic models of ball screw are established. And a performance parameter testingbench is designed and manufactured, which can test many kinds of ball screw. The ballscrew joint static characteristics parameters test principle and data analysis methods areillustrated elaborately, and both of static and dynamic characteristics parameter formula arededuced by means of fitting the experimental data. The spring damping element method andvirtual material method are adapted to establish the simulation model of ball screw interface,and the ball screw is analysis in the ANSYS13.0using the above method establishing theinterface. The results of the FEA analysis are compared with the experiment data, whichshows: the established finite element model has higher precision, the static characteristicparameters of the error in the5%less than, dynamic parameter simulation error is less than 10%, satisfy the need of engineering design.Statistical model and fractal model which are frequently used in analysis the contact ofrough surfaces are discussed detailed in this article. The lack of the two kind’s model ispointed out, and a new method is proposed here to advise the exiting model. The newmethod definite the radius of asperities vary with the fractal parameter D, and the relatedvalue such as real contact area, contact load could be calculated. According to the elasticplastic deformation limit theory proposed by GW model, a new elastic-plastic deformationlimit theory which relate with fractal dimension is propose here. The results which comparedwith experiment shows: compared to the previous model the new model has better accuracy.The surface fractal parameters of coarse surface processed by different methods are alsotested in our work, and relationship between fractal parameters and rough parameters areestablished.An FEA model containing five kinds of interface for Precision CNC machine tool isestablished to analysis the static, dynamic, thermal performance. According to the actualapplication situation of machine tool, the interface’s data could be acquired from database.Compared with the model without considering the influence of interface the new model hasbetter results compared with experiment data.