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Mathematical Problems in Engineering
Volume 2016, Article ID 9842607, 11 pages
http://dx.doi.org/10.1155/2016/9842607
Research Article

Reliability Evaluation of NC Machine Tools considering Working Conditions

1College of Mechanical Science and Engineering, Jilin University, Changchun 130025, China
2College of Mechanical Engineering, Beihua University, Jilin 132013, China

Received 16 November 2015; Accepted 17 February 2016

Academic Editor: Yuming Qin

Copyright © 2016 Hongzhou Li et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Reliability evaluation is the basis for reliability design of NC machine tools. Since traditional reliability evaluation methods do not consider the working conditions’ effects on reliability, there is a great error of a result of a traditional method compared with an actual value. A new reliability evaluation model of NC machine tools is proposed based on the Cox proportional hazards model, which describes the mathematical relation between the working condition covariates and the reliability level of NC machine tools. Firstly, the coefficients of working condition covariates in the new reliability evaluation model are estimated by the partial likelihood estimation method; secondly, the working condition covariates which have no effects on the reliability of NC machine tools are eliminated by the likelihood ratio test; then parameters of the baseline failure rate function are estimated by the maximum likelihood estimation method. Thus, the reliability evaluation model of NC machine tool is obtained under different working conditions and the reliability level of NC machine tools is obtained. Case study shows that the proposed method could establish the relation between the working condition covariates and the reliability level of NC machine tools, and it would provide a new way for the reliability evaluation of NC machine tools.