Reliability Design For Double Power Servo Turret Based On The Failure Correlation Analysis

CNC machine tools are the basic equipment to realize modernization of manufacturing, CNC lathes and turning centers occupy absolute number of CNC machine tool applications. Nowadays, domestic CNC lathes and turning centers have significant increase in accuracy, speed, multi-axis, but there still is a large gap with foreign products, the most important reason is that the reliability of domestic CNC lathes and turning centers is low. The reseach shows that domestic CNC lathes and turning centers are mainly limited by its key function components. So, in order to improve the reliability of the domestic products, it is necessary to reseach the reliability of key function components of domestic CNC lathes and turning centers.For CNC lathes and turning centers, power turret is the key function component. The area, which is also faults frequently, so the power turret is important factor to increase CNC lathes’ and turning centers’ reliability. The research experience of reliability in home and abroad show that: the reliability designing of products is the key factor to improve the reliability of the products. Reliability designing is composed of reliability modeling and analysis, reliability allocation. The paper combining with National Science and Technology Major Project "Reliability Improving Engineering of Thousands of CNC Lathes", chooses a typical domestic power turret-Double Power Turret for reliability designing, finally, improving the reliability of domestic CNC lathes and turning centers.The paper contents about Double Power Turret include the following aspects:1) Considering the characteristics of the reliability research, and referencing the structure of AK33100 D Double Power Turret, the Double Power Turret is divided into several subsystems. FMECA analysis of the Double Power Turret, and the criticality of each subsystem is obtained, the most criticality subsystems are signaling device and seal cutter fastening device, so we should focuse on how to reduce criticality of these two subsystems, when designing new product development. At the same times, FMECA analysis also lay the foundation for reliability modeling and analysis, reliability allocation.2) On the basis of detailed analysis of the reliability data, using DEMATEL method, judging out the fault correlation and the degree of correlation between the subsystems of Double Power Turret; Then, we establish two-paramter Weibull distribution of Double Power Turret subsystems respectively; After that, obtaining Double Power Turret subsystems’ mathematical model by considering failure correlation of and applying Copula function as the link function. Finally, obtaining MTBF = 4293.9h of Double Power Turret. This method make reliability assessment more accurately.3) Because traditional reliability distribution ignores subsystems failure correlation, leading to the distribution index unreasonable. According to this case, proposing a reliability allocation method for Double Power Turret, which based on failure correlation. This method uses the reliability house as base tool. Firstly, the matrix obtained by DEMETEL method as ‘house roof’ of the reliability house, showning correlation degree between the Double Power Turret subsystems; Then, the sub-severity index values as reliability ‘house room’, the Risk Priority Number is directly used to analyze Double Power Turret subsystems in this part; Then, through the reliability house’ matrix operation, the comprehensive criticality of every subsystem is obtained, and optimizing degree of score distribution method, obtaining each subsystem reliability allocation indicators of Double Power Turret. The distribution compared with the assessment results of the fourth chapter: the most criticality subsystems are signaling device and seal cutter fastening device, which fit the results of FMECA of the third chapter.