Research On Reliability Evaluating Indicator Expansion And Evaluating Methods For Machining Centers

一,Introduction The technique of manufacture is the foundation stone of national economic development. Machine tool is the basic means of production of the manufacturing industry. In order to improve quality of the numerical control lathe, we must to improve reliability level of the numerical control lathe and it is the key that the numerical control lathe manufacturing company survives and develops by oneself . As the mainstream equip of mechanical manufacturing industry , the numerical control lathe is hot goods on the market . Its developing level reflect the level of a national manufacture level to a certain extent and is an important sign of weighing a national industry's modernized degree and economic strength.. This thesis is just put forward under this kind of background .it is a part of development plan of national high-tech research(863 Program)-key technical development and application of reliability of NC equipment and its system. Regard machining centre as project background, to reliability evaluation and relevant methods carry on research. 二,Reliability evaluation of the first falure time of machining center Appraising the reliability of the numerical control lathe accurately, scientifically is the goal which we pursue. MTTFF influence the consumer's confidence to the products and have the important connection with the economic benefits of enterprises directly. The reliability evaluation of first falure time means to check-up the quality of numerical control lathe. Based on the falure datas obtained from the test, we can judge the type of falure time and experimental informations of every unit. Utilizing probability statistical method,we can assess out the characteristic value of reliability of the lathe.This paper has analyzed the reliability index of machining center MTTFF. Through using Weibull distribution with three parameters and estimating-parameters methods, to set up the distributed model of MTTFF , calculate other corresponding formula and draw out relevant function figures. With the grouping of the failure data, the paper analyzes and gives out the reliability eigenvalue and model of the first falure time of machining center reliability evaluation system. The author analyzes and gives out four pieces of mathematics models of basic function: reliable degree of this serial machining centre (R (t)), accumulate failure probability (F (t)), accumulate failure probability density (f (t)), instantaneous crash rate(λ(t)), and its mean time to first failures (MTTFF). According to the dot graph of the test data,the distribution pattern of the mean time between failure is initially sized up. Compared with all kinds of general distribution pattern, it is relatively distributed to theWeibull distribution curve, Based on the correlative method ,we can calculate the parameters of the Weibull distribution. We also have worked out the measured value and point estimation of the first falure time.