Research On Reliability Assessment For Heavy-duty CNC Machine Tools Considering Maintenance Degree

Reliability is an important index to evaluate the performance of NC machine tools.The existing reliability evaluation methods based on Bayes are often carried out under the assumption of "complete maintenance",which is obviously not in accordance with the state of the machine tool after actual maintenance.Therefore,there are insufficient considerations for the influence of the maintenance degree existing in the reliability evaluation of heavy CNC machine tools.This paper focuses on the establishment of reliability model and the construction of prior distribution of model parameters.In this paper,the reliability evaluation method of heavy-duty CNC machine tools considering the degree of maintenance is studied.It is of theoretical significance and practical value to improve the reliability evaluation level of heavy NC machine tools.The specific contents of the study are as follows:Firstly,a hybrid model based on the ordinary renewal process and the non-homogeneous Poisson process is established theoretically,and the parameters in the mixed model are characterized by the Bayesian model averaging method(Bayesian Model Averaging,BMA).Furthermore,the calculation of posterior probability is realized by programming with OpenBUGS software,and the mathematical expression of mean interval time of reliability evaluation index under mixed model is obtained,which is verified by time trend test and repair efficacy test.The veracity of the model is given.Then,the flow of expert scoring and reliability determination is designed,and the prior distribution of similar machine tool parameters is constructed by using Bootstrap method,and a reasonable prior distribution of machine tool parameters is obtained.An engineering example shows that the method is simple and accurate.Finally,based on the reliability evaluation method of heavy-duty NC machine tool considering the degree of maintenance,the reliability evaluation of a heavy-duty turn-milling machining center is completed,and the average failure interval time of reliability index is obtained.By comparing the evaluation results of the turn-milling machining center under the hypothesis of "complete maintenance" and combining with the demonstration of the validity of the model,it is shown that the method is more practical.