Methods Of Imperfect Repair And Health Assessment For CNC Machining Centers Based On Hybrid-uncertainty Information Processing

As the technology-intensive modern machine tools, CNC machine centers play an important role in the fundamental equipment of digital enterprises. They are typical the degradation devices which are also repairable. Considering the uncertain factors inherent in the long-time running and maintenance process of CNC machine centers, health assessment of such equipment provides more evidences for the decision-making in the usage and maintenance replacement for CNC machine centers. Thus it is of great importance in improving economic benefits for the enterprise productions. Taking on CNC machine centers as the complex systems whose maintenances behaviours are mostly imperfect maintenances, this thesis investigates the GMC2000 A machining center by analyzing its structure, functions and requirements in order to comprehend the uncertain factors affecting the machining quality. After that, the methods of imperfect maintenance under hybrid-uncertainty handling can also be addressed.The main contributions of this thesis could be shown as follows:(1) The structural properties and functional requirements of the GMC2000 A machining centers are illustrated, especially concerning with the operating principles, technical parameters and structural constituent so as to grasp, the main influencing factors due to uncertainties during operation and maintenance.(2) The uncertainty factors and their principles rules which affect the processing quality(including the machining precision and surface quality) of the GMC2000 A machining centers are studied, contributing to control rules of the operating precision and running stability of this machine centers.(3) With respect to each subsystems’ contribution to the whole machining center system, functional partitioning and quality evaluation of the GMC2000 A machining centers are carried out so as to perform a hierarchical analysis for the health status assessment of whole systems. For that, the fuzzy comprehensive evaluation and Monte Carlo simulation are adopted to address the availability modeling and importance ranking.(4) Based on the above models, failure mode and effects analysis(FMEA) for the hydraulic system of GMC2000 A machining centers are carried out by means of FMEA tables and description of the Quasi-Renewal process based on maintenance environment, and then a model of steady-state availability is established. What’s more, the rate of maintenance costs of the system is defined, and then a model for the system replacement policy is constructed so as to obtain the maximum expected profit within a time unit.In view of practical application and development, the proposed methods in this thesis are applied to the hydraulic system of GMC2000 A machining centers, including data handling of running and maintenance, sensitivity analysis between the lapse factors for running time and increment factors for maintenance time, decision-making of the maintenance replacement strategies for the key factors. The results provide the basis for prediction of equipments’ states according to equipment cell usage, as well costs of maintenances and maintenances replace decisions.