A New Method For Compiling A Program Loading Spectrum Of Reliability Test Of Machining Center's Spindle

With the continuous improvement of processing precision requirements and the introduction of personalized customization concept,machining centers are widely used in the field of mechanical manufacturing.However,the market share of domestic medium and high-grade machining centers has always been lower than that of foreign brands due to many factors,such as low precision retention and low reliability.One of the important reasons for low reliability is that there is no reference basis for loading during reliability growth tests and reliability verification tests,so that the inherent reliability of the whole machine and its functional components is not high.The main spindle is one of the key functional components that significantly affect the reliability level of the whole machine.Therefore,it is of theoretical significance and engineering value to study a scientific and reasonable method for compiling the program load spectrum of machining center's spindle.Combined with the National Natural Science Foundation of China,"Research on Fundamental Problems of Accelerated Reliability Testing of Spindle of CNC Machine Tool",the paper takes the main spindle of machining centers as the research object,sets the real working conditions as the main objective,and carries out the research on the method of compiling milling,drilling and boring load spectra of the spindle.Finally,three eight-level program loading spectra are compiled into one,which is the loading spectrum for the reliability test bench of spindles.The main contents of the paper are as follows:1.In order to accurately obtain the load data of the spindle,the machining process is firstly classified,and the process data table is determined according to the cutting parameters.To reduce the calculation amount of the subsequent processing,a pretreatment technique is proposed for the collected process data.At the same time,different methods for pre-processing the measured cutting force signals are adopted and compared.2.In order to clarify the correlation among different loads,a milling force model is introduced to fit the measured cutting force signal,and a calculation method based on the milling force model is proposed.At the same time,the instantaneous dynamic torque can be solved by the model.The milling load spectrum was compiled with the thought of “grasping the main load,summarizing and integrating other loads”.Firstly,according to the statistical analysis of the fault data,it is found that the main load of the spindle is the radial force's amplitude.And then the eight-stage program loading spectrum of the amplitude of radial force is compiled.Afterward,the other loads corresponding to each stage of the spectrum are integrated.Finally,the eight-stage program spectrum is added to the milling load spectrum containing the three-way force,torque,rotation speed,and loading frequency.3.Setting a tool rotation cycle as a load cycle and selecting the axial force as the main load,a drilling loading spectrum based on the characteristics of the drilling force was developed.At the same time,the revised coefficients in the empirical formula of drilling force are corrected through fitting the measured load data,so that the calculated values of axial force and torque are more reasonable.4.Setting the process from drilling in to drilling out as a load cycle and selecting the total radial force as the main load,a boring load spectrum based on the characteristics of boring force is developed.At the same time,different boring load spectra are compiled for two different loading mechanisms.5.The milling,drilling and boring load spectra are directly synthesized into the total loading spectrum,which can be used as the loading basis of the reliability test bench of spindles.During the synthesis process,the time occupied by the loading spectrum at all levels is allocated proportionally,and the acceleration factor of the total loading spectrum relative to the actual working conditions is calculated.In summary,a new method for compiling the program loading spectrum of the spindle of machining centers is proposed,which provides a loading basis for a series of tests in the reliability growth stage.At the same time,a set of auxiliary spectrum-compiling software is compiled,which helps to quickly compile loading spectra for different spindles.