Reliability Modeling and Evaluation of Electric Spindle Without Sudden Failure
Author:Zheng Yu Bin
Supervisor:shen gui xiang
Reliability evaluation is one of the important contents of reliability research.Based on the major national science and technology project of "High-grade CNC machine tools and basic manufacturing equipment" and Jilin Province’s science and technology development plan project,under the industry’s demand for high-power motorized spindle of CNC machine tools,this paper studies the accelerated reliability test design,reliability test,reliability modeling and evaluation technology of motorized spindle.The main work of this paper are as follows:(1)Failure analysis of motorized spindle integrated with FMECA/DEMATEL/FMMESAFirstly,based on the structure and functional principle of motorized spindle unit,the subsystem of motorized spindle unit are divided,and then the fault information of field reliability test of motorized spindle is sorted out and analyzed.Aiming at the problem that a single fault analysis method cannot clarify the fault mechanism,a fault analysis technology integrating FMECA,DEMATEL and FMMESA was proposed.Based on FMECA analysis,the proportion distribution of failure modes of each component is determined.DEMATEL is applied to define the formation mechanism of key failure modes through failure correlation analysis and "four-degree" calculation.Finally,FMMESA method is introduced to conduct failure-environmental impact qualitative analysis to the root of failure modes,so as to realize critical component modes,key failure causes and environmental stress assessment,and to make up for the bias and deficiency of traditional single fault analysis method.It provides a reference basis for the subsequent design of measuring points,sensor selection and reliability growth of motorized spindle reliability tests.(2)Reliability test time design of motorized spindle based on Weibull distributionMotorized spindle is a product with high reliability and long life.In order to quickly evaluate the reliability level of motorized spindle,bench tests are conducted to simulate the design of accelerated reliability test time of motorized spindle under actual working conditions.In order to eliminate the deviation caused by load switching in current stepping load test,the reliability model parameter estimation is proposed using the survival analysis and likelihood function principle based on the field reliability information of the electric spindle,then the model inspection is carried out using Hollander inspection criterion.Combined with load information,load spectrum compilation and load spectrum research are carried out.According to this,combined with the modified Miner fatigue damage accumulation theory,the acceleration factor of motorized spindle life test is determined under the Weibull distribution model with known shape parameters.Combined with the average life level of the newly developed product,the accelerated life test time design under constant loading is carried out,which lays a foundation for laboratory reliability test.(3)Timing Truncated Reliability test and Test Information Collection of Motorized SpindleIn order to control the test parameters effectively and to shorten the test time,the reliability test of the electric spindle is carried out on the reliability test table of the motorized spindle.Therefore,the structure of the reliability test bed of the motorized spindle is described from the aspects of the mechanical structure and the control system.The selection of measuring points directly affects the accuracy of test information.In order to reduce the error,the test signal is determined based on fault analysis,the primary selection of load test points is carried out,and the grey theory is used to select the measuring points and sensors,and the test scheme is formed.On the premise of simulating the actual working conditions of the motorized spindle,combining with the engineering practice,the test program is formulated,the reliability test of the motorized spindle is carried out,the test signal information is collected,and then the information is preliminarily analyzed to determine degradation characteristic parameters.(4)Reliability Evaluation of Motorized Spindle without Sudden Failure InformationThere is often no sudden failure phenomenon when carring out the accelerated reliability test of motorized spindle under simulated actual working conditions on the motorized spindle reliability test bench.At this time,the traditional reliability modeling based on statistical principle and the small sample theory based on Bayes method are not effective.Based on the reliability model of motorized spindle in field tests and experimental test information,a partial distributed competitive risk modeling and life assessment method from the perspective of competitive failure is proposed,in where modelling the basic failure rate by one-sided confidence limit method and taking performance degradation data as covariates.Finally,the partial distributed competitive risk model and Wiener process model are compared with the target motorized spindle reliability model of the enterprise to verify the rationality of the proposed method.It is compared with the degradation process modeling method to verify its rationality,enrich and improve the reliability technical system of motorized spindle.The method proposed in this paper solves the problem that it is difficult to evaluate the reliability of high-reliability and long-life products without failure data.It can provide reference for reliability modeling and life evaluation without sudden failure information.