Coupling Modeling And Influence Analysis For Availability Of Numerical Control Machine Tools

Numerical control(NC) machine tool is the key equipment on the mechanical manufacturing industry, and its yield and technology level stands for manufacturing level and competitiveness of a country in some extent. The development of NC machine tools technology is related to national industrial strategic status and the comprehensive national strength level. The market demand of NC machine tool increases continuously in china in recent years. Facing the strong demand of Chinese market, foreign-capital enterprise are subordinate to the Chinese market for expanding market in China in succession, and begin to increase investment. Even so, there is still a certain gap compared with developed countries on the performance and availability level of NC machine tool because of the lag of China's technical level and industrial base. Brutal competition imposes very great impact on NC machine tool market of China, and makes enormous pressure and severe challenge on domestic market. In the face of pressure and challenge, the only way to make homemade NC machine tool industry invincible is to improve the quality and availability of NC machine tool. Therefore, the most critical problem of the domestic NC machine tool manufacturer that should be solved at present is to improve the quality and availability of NC machine tool.Availability is the product quality from view of the user, and the core of products competitiveness. To improve the availability level of NC machine tool, basic technology research is prerequisite and guarantee. This article relies on the National Natural Science Foundation of China "The coupling model of availability influence and analysis techniques for NC machine tools based on life cycle ", studies on China-made NC machine tool to research on the theory of " the coupling modeling and influence of availability ", and opens up new ways and new methods for availability work state to promote NC machine tool tend to be "to use when you can use ".The research of availability bases on a large number of field data, and only has true and reliable data that can analyze coupling modeling and influence for availability perfectly. Combining with the subject, the availability experiment program was made through the coordination among operators of NC machine tool consumer, maintenance personnel, equipment management department, and manufacturer service personnel. In this program, large number fault information from the field of NC lathe was gathered using the data collection and information exchange technologies platform developed in this subject. In order to dig the reliability and maintainability which impact on the internal relations and coupling rules of availability better, the analysis of coupling and influence combining with field data should find out two aspects of availability-the status of reliability and maintenance.According to analyze the coupling and influencing factors of availability and seek the status of reliability and maintenance, the reliability and maintenance model for whole machine and subsystem were established. When whole machine reliability model was making based on censored data obtained, the reliability estimation, model primary and parameter estimation from the incomplete data were conducted. The method combing with Graphical method and correlation coefficient, using the result of graphical method as initial value of the correlation coefficient iteration was brought in the parameter estimation. This method also integrate the point that graphical method simply but low precision, the correlation coefficient iteration precise but iterating complexity, and the initial value of whole machine influencing on the result. The fault time distribution model of NC lathe selected for check was made according to the method of k-s inspection, which includes the fault time distribution function F (t), fault time probability density function /(t). According to judge the model of repair time date for whole machine modeling, using the method of maximum likelihood method parameter estimation and hypothesis testing, the functions were established such as maintenance function M (t), maintenance probability density function m (t) and the repair rate functionμ(t). When conducting subsystem reliability modeling, the subsystem was reclassified combining with laboratory research experience of many years, and the gray small sample GM (1,1) model was referred in order to improve accuracy first time at the same time. Finally, each maintenance model of subsystem was established according to the assumptions of subsystem repair time distribution type, parameter estimation and fitting inspection. The coupling analysis of availability settles the foundation for identifying the key subsystem quickly, analyzing the coupling and influence of availability further.When making the availability coupling of NC machine tool, the characteristics of structure and dynamics running of NC lathe should be analyzed firstly, and the coupling relations framework and dynamic running process model that was based on stochastic Petri net theory was built. The dynamic model of stochastic Petri net combined with Monte Carlo simulation for numerical analysis on NC lathe availability was used. The coupling model of subsystem which put turret cutter as an example synthesized with the change of fault rate and repair rate, and mainly analyzed the change rule of availability and non availability. The analysis of coupled process made the availability as the core, and put the reliability and maintainability coupled to solving process. The result of analysis provided the basis for making the improvement measures and maintenance decisions. It is practical significance for the loss of reduced maintenance, downtime costs and improving the use efficiency for NC machine tool since developing improvement measures and best maintenance period for availability.The analysis of availability influence is to study and evaluate each subsystems that influence the size of the whole machine in the desired interval time, measure proportion sequence of each subsystem that effects the whole system, identify a few key sub-systems and weak links. First of all, this article divided the life cycle of NC machine tools into part combining with the coupling modeling results of the availability, and analyzed the character that runs in different life time and fault mechanism. The segmentation research method was adopted in the period of early fault and occasional fault to study the availability influence of NC machine tool selected according to the analysis result of influence factors and coupling process. Then, the hierarchy structure of availability features was analyzed, using the method of the goodness evaluation principles of extension to determine the index weight and multi-index model,and this reflected the real situation of characteristic elements exist in running of NC machine tools objectively. The influence degree which early fault and occasional fault of subsystem impacted on whole system was analyzed qualitatively and quantitatively, after that, the critical subsystems that effected on availability during different fault time was obtained. All these point out the direction of improvement for this series of NC machine tool. Finally, specific improvement measures of availability influence such as early fault tested, early fault eliminated, and critical subsystems fault corrected and availability growth was proposed after compared the analyzed result of influence between the early faults and occasional faults and aimed at a small number of critical subsystems and availability weak links. All these provided the basis for improvement availability of new products.The interactive platform that combined with task research content was built between the school and factory from different place for information collection, and was used for research on data collection and information exchange technology for NC equipments base on network. Architecture framework was first putted forward on data collection and information exchange of availability. This system was consisted of three function module as follows:the institute of NC equipment, NC machine tool users, and NC machine tool manufacturers. Based on key technology and implementation pattern such as database and network, the data collection and information exchange technology platform was developed that can be used commonly for NC lathes, machining centers, etc. This platform include:information recorded for some type of NC machine tool like NC lathes, NC milling machines and machining centers; equipment center like information query, data export, data analysis, results published, information viewed; the content of user knowledge base, machine information and training courses, virtual labs, fault case database and so on. The development of availability information collection and information exchange technology platform makes NC machine tool availability information collection more efficient, make availability analysis more convenient and shortcut, make different machine manufacturers, research institutes and users share resources information of availability, and make resources of availability play a greater role fully in different NC machine tool companies.