Reliability Evaluation Method Of NC Machine Tools Considering The Influence Of Working Load

High-efficiency,high-performance,high-stability,high-reliability domestic NC(numerical control)machine tools are of great strategic significance to enhance China's advanced basic manufacturing capabilities and the added value of Chinesemade products.Accurate reliability assessment method is the premise for health maintenance management,reliability growth design,reliability level identification and verification of NC machine tools.During the actual use of NC machine tools,the working conditions and the environment are constantly changing,and the working load is diverse.As a result,the reliability of the same batch of NC machine tools under different working conditions is also quite different.However,there are few research literatures and application reports on reliability evaluation methods of NC machine tools considering the influence of working load.Most of the reliability evaluation methods of related NC machine tools are statistical evaluation based on the historical fault data and time history data of machine tools,The influence of working load factors is not considered in the process of reliability modeling and evaluation.Therefore,this paper takes NC machine tools as the research object to focus on its accurate reliability evaluation method considering the influence of working load.The specific research content is as follows:1)The ability of NC machine tool load to affect its reliability level is analyzed.The AHP-fuzzy comprehensive evaluation method is used to evaluate the working load.First,a hierarchical structure model for the importance evaluation of the working load of NC machine tool is established.Second,a discriminant matrix is constructed and the discriminant matrix is checked for consistency.Finally,the evaluation result matrix of fuzzy comprehensive evaluation is established to realize the quantitative analysis of the working load of NC machine tools.2)A mixed variable parameter model based on multi-dimensional exponential distribution is proposed,and the model parameters are estimated to use maximum likelihood estimation method and partial likelihood estimation method.The working conditions are grouped,and the hybrid distribution model is established to accurately evaluate the reliability level of NC machine tools.In the case,K-S goodness-of-fit test was performed on the model to verify the feasibility of the model.3)The method of estimating the reliability feature quantity considering the influence of working load is as follows: the method of estimating the scale parameter interval and the shape parameter of the reliability model considering the influence of working load,and the MTBF interval estimation method in the reliability evaluation index of machine tools.In the case,the interval parameters of the scale parameters,shape parameters,and MTBF of the reliability feature of the NC machine tool under different confidence levels are estimated.4)A set of reliability evaluation software for numerically controlled machine tools considering the influence of working conditions has been developed.The implementation technology of load data collection,reliability data recording,reliability data sorting and reliability evaluation software for working conditions of numerically controlled machine tools has been studied.Basic data,practical tools and technical support for the reliability evaluation of NC machine tools are provided.