Research On Modeling And Applications Of Life Circle Failure Process Of CNC Machine

In recent years, the gap between domestic CNC machine tools and advanced imported ones is narrowing in terms of functionality and performance, due to the spur of huge and potential market demands, and vigorous support of national policies. However, quality and reliability level of domestic CNC machine tools is not keeping pace with the development, so it is badly urgent to study on and improve the reliability of CNC machine. Failure process models are the basis to study on other reliability analysis, such as quantitative reliability assessment. At present, some misconceptions and misunderstandings exist when building reliability models of failure process, and the research of reliability models mainly focus on monotonic failure process. However, these models with monotonic characteristic cannot properly fit the complex life circle failure process occurred during operation of CNC machine. Therefore, based on production practices and the support of National Major Scientific and Technology Special Project, this paper will studies the models of life circle failure process from several aspects as follows:Firstly, the relevant theories of failure process models are analyzed and studied. The connections and differences in building reliability models between repairable products and non-repairable products are clearly explained. And it is more complex to analyze reliability of repairable products because of influences of maintenance after failure. A method is put forward to quantitatively analyze and evaluate the degree of repair, which is applied to a type of cooling & filtering system. It is concluded that for complex repairable products, repair actions are imperfect repair, but can be consider as minimal repair under approximation. So the nonhomogeneous possion process and imperfect repair process can be used to build models of failure process of CNC machine tools.Secondly, bounded and bathtub shaped intensity process is introduced to build the model of life circle failure process of CNC machine tools under the assumption of minimal repair. On the basis of analyzing characteristics of the model, a method is produced to determine two turning points of bathtub shaped model, and it is proved to be effective by applying it to a practical example. The parameters of the model are estimated through maximum likelihood method and numerical method. The model is applied to forecast failure process with Monte Carlo simulation.Finally, on the basis of the bounded and bathtub shaped intensity process, the imperfect virtual age model is established to describe the life circle failure process of CNC machine tools. It is explained that repair activities have a real effect on the reliability of CNC machine tools, so the imperfect repair model should be considered firstly to accurately describe the failure process. A new and more appropriate definition of reliable life for repairable products is put forward in consideration of actual production. And the proposed imperfect repair model is utilized to predict the reliable life of CNC machine, and then a case study is analyzed.