The Reliability Test Technology Of CNC Turrets

With the development of modern manufacturing, the use of CNC machine tools has been increasingly common. The CNC equipment manufacturing industry has bright prospects, but also it faces enormous challenges. The reliability of China-made CNC machine tools compared with the reliability of imported CNC machine tools is in disadvantage. Especially the high-end China-made CNC equipment, the reliability index was significantly lower than the index of the CNC machine tools made in Europe, the United States and Japan. Therefore, our country is developing the CNC equipment manufacturing, and inputs a lot of money and manpower to support the reliability research of CNC machine tools. The turnery takes large part in machine processing, so the reliability of CNC lathes are acquired particular attention. According to the research of the existing reliability data which were acquired previously, it can be seen that the reliability of CNC turrets has a great impact on the reliability of CNC lathe. At present, the reliability test specifications of CNC turrets are even more important. In this paper, based on the national major projects, the reliability test methods of CNC turrets are specially researched.In this paper, the previous failure data of CNC turrets were processed, forming a reliability database of CNC turrets. According to the failure data of the reliability database, the CNC turret is divided into some failure position by the functional module, in order to accurately discover weaknesses of the CNC turret. Failure modes table and failure causes table of the CNC turrets are established, as comprehensively as possible, including possible failure modes and causes of CNC turrets. Failure mode, effect and criticality analysis (FMECA) of CNC turrets'failure can discover the fault-prone modules and the failure positions that have high criticality to the entire CNC turret.The reliability test program can be established for exposing fully weaknesses of CNC turrets which were acquired by FMECA, and its goal is that faults of CNC turrets are exposed as quickly as possible in the process of reliability test. There are environmental test, functional test, static stiffness test, cutting test and so on to be included in the reliability test program of CNC turrets. In this paper, the relevant provisions of failure definition, criterion and classification of CNC turrets, the establishment of failure data acquisition and processing method of CNC turrets, monitoring of the sample in the process of reliability test, processing and record of failure data and relevant operation of faults, ensure the smooth progress of reliability test and failure data continuous collection.The reliability test of CNC turrets belongs to the fixed time test. The reliability level of CNC turrets should be evaluated on the evaluation index after the test. Currently CNC machine tools and parts are evaluated comprehensively on mean time between failures (MTBF), mean time to repair (MTTR), inherent availability (Ai) and time to maintain accuracy (Tk). Because of the special nature of CNC turrets, in this paper, mean time to first failure (MTTFF) and so on are added, and the reliability of CNC turrets can be evaluated more comprehensively. The evaluation indexes on time is used as traditional evaluation indexes, meanwhile, the evaluation indexes which are the combination of the evaluation indexes on time and transposition times are improved to specifically aim at the CNC turrets. Because the development of CNC turret" s faults and its transposition have great connections, and the turret has not always been on the status of transposition in the actual work process of CNC machine tools, the reliability evaluation on transposition times is necessary to CNC turrets. In this paper, the evaluation indexes on transposition times are raised, and the transposition times of CNC turrets need to be counted in the reliability test process. The reliability evaluation indexes on transposition times can evaluate accurately the reliability of CNC turrets, and it is of great significance to the reliability evaluation of CNC turrets.The reliability test of CNC turrets just is to make the sample to accelerate failure, and to discover the failure mechanism and causes and to propose the solutions to improve, and to carry through the test again, until the reliability level of CNC turrets reaches to the required level, which the reliability level of turrets can be improved.