Reliability Allocation Method Of Machine Center Based On Fuzzy Cost Function

As a manufacturer of machine,NC machine tools have an important position in the manufacturing industry. Machine Center has the characteristics of large consumption and wide range of application,so it is more representative of NC machine tools. With the fast development of Machine Center, many advanced technologies are applied,but the number of fault has been increased. So the reliability becomes the focus of the developers and users. Reliability design is a key technology to determine the reliability of Machine Center, and reliability allocation is a key technology for reliability design. This article mainly researchs on the reliability allocation method of Machine Center,the main contents are given as follows:1. According to a long term reliability test by our research group, we collected a large number of failure data. This paper firstly using traditional reliability model and analysis get the result that the time between failures of these products follows the two-paramter Weibull distribution with scale parameter 928.175 and shape parameter 1.1495, and their MTBF is 883.45. Whether or not considering load factors will directly affect the accuracy of the evaluation results. Based on power as the load of Machine Center,the acceleration model was built. And using this model complete data conversion and get the result that the time between failures of these products follows the two-paramter Weibull distribution with scale parameter 855.96 and shape parameter 1.18, and their MTBF is 809.42. The evaluation results,considering the load factor,are more accurately for the user and manufacture. Getting a accurate assessment result can prepare for reliability allocation and reliability prediction.2. Each enterprise pursues the smallest cost to produce eligible products,so the reliability allocation based on minimizing cost is of great significance. the cost function is established,and introduce a cost coefficient in this function. By combining with FMECA, influencing Machine Center’s design cost and maintenance cost are the severe degree, the difficulty of the improvement measures, fault detection method, the possibility of failure, compensation measures. And using fuzzy comprehensive evaluation determine the fuzzy cost coefficient of each subsystem. According to the cost function and the target, the reliability function allocation model is established. The reliability function allocation model regard the minimum fuzzy cost as the objective function and reliability as constraint conditions. The Lagrange multiplier method is applied to calculate this model to get the reliability allocation design program.3. Similar analogy based on the AHP that solving similar analogy without considering all the factors weight is applied to Machine Center reliability prediction. By the method to solve the comprehensive correction coefficient D, then The results of the reliability prediction solution will be come out, and using the results compare with the results of distribution to determine the rationality of the reliability allocation design program.In this paper, we research on the combination of FEMCA with fuzzy comprehensive evaluation of considering the cost factor of reliability allocation methods. In this process,we give full consideration to the enterprise efficiency of machine tool and the engineering actual situation, so this method has higher application value.