Compiling Load Spectrum Of Machining Center Spindle By The Diffusion-based Kernel Method

With the increasing market demand for mechanical products in China,machining centers are more and more widely used in automobile,aerospace,rail vehicles,ships and other fields.Load spectrum is the statistical law description of the load borne by NC machine tools.It is the basis of reliability design and reliability test of NC machine tools.At present,the domestic machine tool industry lacks a scientific and reasonable load spectrum of CNC machine tools,which leads to the failure of predicting the performance index and reliability level of machine tools in the design stage,and can not effectively guide the reliability loading test of key functional components of CNC machine tools,which is the main reason for the low reliability and accuracy retention of domestic CNC machine tools.Therefore,this paper takes the spindle of machining center as the research object,compiles its load spectrum,and applies the load spectrum to the reliability loading test of spindle of machining center.The main research contents of this paper are as follows:1.Determination of cutting force test process parameters.Based on the field process data collected by the predecessors of the research group in the engine production enterprise,the characteristic cutting force and cutting torque are calculated by using the empirical formula,the distribution model of relative characteristic main cutting force under various machining methods is established,and the number of cutting force test groups and process parameters under various machining methods are determined.2.Calculation of radial force time history and axial force time history of spindle of machining center.The cutting force signals of various machining methods are obtained through the cutting force test.In order to improve the analysis accuracy,the cutting force signal is preprocessed by removing singular points and filtering.In order to ensure that the time length of each group of cutting force signals is equal,the cutting force signals with insufficient time length are extrapolated in time domain.Finally,the time history of radial force and axial force under each cutting force test are obtained.3.Compilation of two-dimensional spectrum of average amplitude of cutting force and torque spectrum.The mean value and amplitude distribution model of cutting force and cutting torque distribution model under various machining modes are established by using maximum likelihood estimation method,kernel density estimation method and diffusion kernel density estimation method respectively.The effectiveness of the model is tested by K-S test method to prove the effectiveness of the mean value and amplitude of cutting force and cutting torque distribution model established by diffusion kernel density estimation.The mean value and amplitude of cutting force and the maximum value of cutting torque are extrapolated,and the cycle frequency of cutting force is extrapolated.The independence of the amplitude and amplitude of the cutting force is verified.The two-dimensional torque spectrum and the final cutting force spectrum of the spindle are compiled.4.The reliability loading test loading scheme of the spindle of the machining center is formulated,and the parameters of each loading block in the program load for loading are determined based on the load spectrum.Using the load spectrum,the loading time,load value and loading frequency of each loading block in the program load are preliminarily determined.Considering the limitation of loading frequency of electro-hydraulic servo loading system,the loading time and loading frequency of each load block in the program load are corrected to obtain the program load suitable for the spindle reliability test-bed of machining center.