Reliability Evaluation And Failure Analysis For CNC Belt-grinding Machine

In recent years, NC machine tools developed rapidly in China. However, thereliability of the machine is still far away from the foreign NC machine tools. In orderto improve the reliability level of domestic NC machine tools combined with theMajor National Science and Technology Program’s sub-topic:“study on the six-axisCNC belt-grinding machine’s reliability. Taking domestic CNC belt-grinding machineas the research object, design a machine fault management system, evaluate thereliability level of the belt-grinding machine, and make necessary failure analysis,then provide the reliability assurance techniques for CNC belt-Grinding Machine.In order to solve the data records onerous and difficulty to deal issues in CNCBelt-grinding machine’s reliability test, a machine fault management system isdesigned to managing the machine fault data. The system is developed by the VisualC++and based on the Microsoft Access database. According to the characteristics ofthe machine tools’ reliability analysis, the database’s conceptual structure and logicalstructure are designed with E-R diagram, and design a database table. According tothe functional requirements analysis of the system, each module of the system isdetailed designed. The system can not only achieve the basic management of faultinformation, such as add, delete, modify, query the information, but also can makefault statistics according to the fault type; it will help the reliability analysis ofmachine tools.In order to understand the reliability level of domestic CNC belt-grindingmachine, the CNC machine tools’ reliability is evaluated. First establish a distributionmodel of time between failures for the machine with failure time data that collected.Then Select the Weibull distribution as the CNC Belt-Grinding machine’s time between failures distribution model. Secondly, using regression analysis to estimatethe unknown parameters, and test the model with the d test method, obtain the specificmachine tool’s time between failures distribution model. Finally, select MTBF, MTTR,and Aias the CNC belt-grinding machine’s reliability evaluation indexes according tothe relevant standards. Results show that the machine’s reliability level is low, so inorder to improve the reliability of the machine, the necessary reliability design shouldcarry on this series of belt-grinding machine.In order to find out why the CNC belt-grinding machine’s reliability level is low,make the failure analysis for this Series CNC belt-grinding machine with FMECA.First, make the fault location analysis, failure mode analysis and cause analysis for themachine tool, then master the failures of the machine in overall. Secondly, abrasivebelt grinding device and CNC systems which are the machine’s subsystem were madefailure mode analysis and the cause of the fault classification analysis, clarified thefault conditions of the subsystem. Finally, the criticality analysis is made on thebelt-grinding machine and the results show that the abrasive belt grinding device andthe CNC system are the weak links of the whole machine. Then propose improvementmeasures and reliability assurance techniques according to the comprehensiveanalysis of the results.In order to improve the reliability of machine, the further failure analysis of theweak links with fuzzy fault tree analysis is making. Important failure mode is selectedas the top event of the fault tree, then finds fault tree minimal cut sets and makes aqualitative analysis. In order to solve the problem of reliability analysis datainsufficient, combining the fuzzy theory and AHP method to make a comprehensiveevaluation of bottom events, and then calculate the fuzzy failure rate of the bottomevents and the top event as well as the importance of bottom events. The results of theanalysis have major significance for machine improve design and fault diagnosis.