Research On Compiling Method Of Machining Center Load Spectrum Based On Parameter Extrapolation And Its Application

As the key core equipment of the basic manufacturing equipment industry,CNC machine tools represent the development level of the national advanced anufacturing industry.At the present stage,domestic CNC machine tools have made great progress in machining accuracy,speed,multi-axis linkage and compound machining,but the performance stability and reliability of domestic CNC machine tools are generally low.The inherent reliability of the product is first determined by the design,and the load spectrum is the objective basis for completing the reliability design of the CNC machine tool and key functional components.Therefore,scientifically and accurately compiling the load spectrum of CNC machine tools has great theoretical research significance and engineering application value.Taking domestic typical machining center products as the research object,this paper systematically explores the selection method of typical test conditions,the acquisition and preprocessing of cutting load data,load spectrum parameter extrapolation method and so on in the process of NC machine tool load spectrum compilation.The main research work is as follows:(1)According to the typical,authentic and comprehensive field data acquisition principles,the original process data of machine tool user enterprises are obtained.Under the condition of fully considering the economic cost and the requirements of laboratory cutting test,this paper proposes a method for selecting typical test conditions based on fuzzy cluster analysis,which fully considers the fuzziness and potential relationship between process parameters.The optimal threshold is determined to obtain the optimal number of classification clusters for fuzzy clustering.In order to obtain the load time history under typical test conditions,the laboratory load test system of the machining center was developed,and the load cutting test was carried out.(2)In order to reduce the influence of outlier points,trend items and random noise in the cutting load signal on the accuracy of the load spectrum compilation,the local characteristics of the cutting load data are fully considered,and the LOF algorithm is used to eliminate the local outlier of the data,and the trend term and random noise in the cutting load signal are processed by the fusion algorithm of EMD and KF.In order to further apply the machining center load spectrum to the reliability test of the spindle,the time-domain reconstruction of the radial force Ff in the cutting load provides a data basis for the compilation of the cutting load spectrum of the machining center.(3)In order to make the load time history under typical working conditions obtained by laboratory cutting test the same as that in actual working conditions,MCMC load time-domain expansion algorithm is used to reconstruct the original load timedomain signal.The multi-condition synthetic rainflow matrix of mean and amplitude of the machining center load is obtained by the rainflow counting method.According to the statistical distribution property of average and amplitude of load data,a mixed Weibull distribution model of load mean and amplitude is established.By introducing the grey relation degree as the objective function,the initial values of model parameters are obtained iteratively by PSO algorithm,and then the EM algorithm is used to identify the accurate parameters of hybrid Weibull distribution model.The complete priority relationship of multiple mixed Weibull distribution alternative models is obtained by using PROMETHEE theory,and the number of basic functions of mixed Weibull distribution is determined.A mixed Copula function is proposed to establish a joint distribution function of the mean and amplitude of the load,so as to realize the extrapolation of the cutting load.In order to guide the reliability test of CNC machine tools,an eight-level program loading spectrum of cutting load was compiled.(4)On the basis of compiling two-dimensional program loading spectrum,the reliability test scheme of machining center spindle based on load spectrum is formulated.The relevant precautions for the reliability test of the spindle of the machining center are put forward.The mathematical model of the sample size,confidence level and reliability test time is deduced,and the test period of the spindle reliability test is determined.The process of machining center spindle reliability test based on two-dimensional program loading spectrum is presented.