| Numerical control(NC) machine tool is the mainstream equipment of modern manufacturing industry in the 21st century, its quality and availability level is directly related to the national strategic status of a country.Recent years, with development of relevant technique such as information technique, electronic technique and precision machinery technique, many performances of NC machine tool have been improved. However, availability is one of primary problems puzzling the development of domestic NC machine tool. The NC machine tool occur faults frequently, which is unavailable when it is needed, thus loses its advanced capability.Today machine tool market compete drastically, the user prefer those NC machine tool which have high availability. Availability level has become the important criterion for consumer to choose machine tool. Enhancing availability of NC machine tool has become the key factor for survival and development of machine tool manufacturer. If the domestic product NC machine tool manufacturer wants to occupy the market steadily, enhances the product market share and the market competitive strength, they must carry on the quality enhancement and the innovation, enhances the product availability. Therefore, it is necessary to perform the availability research on the NC machine tool.Combining with several national projects, and taking domestic NC machine tools as the research object, the availability experiment plan of NC machine tools was worked out and the availability appraisal system was determined. Through processing of the NC machine tool availability information, the NC machine tool reliability mathematical model was established. The correlation coefficient optimization method based on the particle swarm algorithm was first applied to perform the parameter estimation of Weibull distribution. The hypothesis test showed that the 3-parameter Weibull distribution is better than other distribution for the reliability model. The maximum likelihood method was used to carry on the parameter estimation and to use the d-s method was used to carry on the examination, the check result demonstrated that the maintainability model of the investigated NC machine tools obey log-normal distribution. The point estimation and interval estimation were carried out on NC machine tool availability indices, which include the parameters of reliability and maintainability distribution models, MTBF, MTTR, steady-state availability, etc..While the NC machine tool in actual use, faults caused by the factor such as design, manufacture, operation and so on occur unceasingly. Therefore, it is very necessary to perform the fault analysis for the NC machine tool. And failure prediction technology enables the NC machine tool maintenance personnel to predict the occurrence of fault so as to take a series of maintenance or preventive measures, thereby reduce the failure rate of NC machine tool. To perform the fault analysis and forecasting technology is not only an important basis for working out the maintenance strategy, but also has positive promotion effect on improving the availability, security of NC machine tool and reducing the entire lifetime cycle cost.The major & minor chart method and criticaility analysis method were used to carry on the fault analysis of the numerical control machine tool. The fault mode analysis, the fault reason and the reason classification analysis were carried on the entire NC machine tool, and the fault mode, effect, the reason classification and the criticality analysis were carried on the subsystems. It was found that the mold was the weak link for the numerical control machine tool, which had indicated the availability improvement direction for the numerical control machine tool.The improved grey model G(1,1,P) based on the particle swarm algorithm was first applied to perform fault predication for numerical control machine tool. On the basis of the collected fault time, the metabolism model was established to forecast the fault occurrence time in the future. This would provide theoretical foundation for further target-oriented preparation of preventive maintenance strategy.During the course of the NC machine tool availability testing, availability estimation, fault analysis, operation and maintenance, it can not be separated from the availability information. The data collection and analysis of the availability is a basic work for availability work, which always plays an important role. Only on the basis of true and reliable data, the complete fault analysis and scientific assessment can be made, and the reasonable proposal can be put forward for the availability improvement of the NC machine tool. The accumulation of data availability is a long-term and arduous work. The information must be organized and managed effectively in this work, which is difficult to complete by hand and should be complete by means of computer database technology.The availability information management system for numerical control machine tool was developed by using object-oriented database technique. This system is commonly applied to evaluation and analysis of availability for NC machine tool such as (heavy-duty) NC lathe, machining center, NC puncher etc. This database system can make fault statistics and classification, Fault Mode, Effect and Criticality Analysis, the primary selection, parameter estimation, hypothesis test of reliability model and maintenance model and, ultimately, determine the model of the distribution function, as well as the availability indices such as the mean time between failure (MTBF), the mean time to repair (MTTR), the inherent availability (AI), and make the availability verification test.Through assessing the availability of NC machine tools in the initial course of the project research, we can see that the availability of Chinese-made NC machine tool is low, which influences their social reputation and market competitive strength. To this end, it is necessary to perform the study on the availability growth technology of domestic NC machine tool.The NC machine tool is always accompanied by the availability work in the various stages of its lifetime cycle. According to those availability influence factors exposed during the initial project research period, a series of availability guarantee measures, which were based on the life cycle, were implemented systematically and comprehensively for the first time on the studied NC machine tools. Established reliability design criteria and maintainability design criteria were prepared for the NC machine tool. The improved design study was performed on the basis of the fault analysis. For a large number of faults were caused by the quality of the bought-in and purchased parts, the availability growth and quality optimization measures were put forward for them. The improvement advice was put forward for the manufacturing and assembly process of the NC machine tools. For the key working procedure, the quality control points were established. The availability growth measures for the operation and maintenance phase were proposed.It is shown that the availability indices have gotten a big rise through check the second batch of NC punchers on which after implementing the availability guarantee measures were implemented. The MTBF of NC machine tool has been enhanced from no more than 300 hours to 500 hours above. The MTTR was reduced from 0.98 hours to 2.05 hours, the inherent availability was raised from 0.9905 to 0.9981, the operation availability was increased from 0.9786 to 0.9983. The time between failure distribution of the NC machine tool also had fundamental change, which changed from obeying the Weibull distribution to obeying an exponential distribution, while the failure rate reduced from the original type curve into a constant value,which shows that most original phase faults of the NC machine tools have been eliminated, and the NC machine tools step into a stable period of the occasional failure directly. All these can fully prove that the availability growth technology adopted to the NC machine tool is effective.
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