Quantitative Modeling & Application Study Of Failure Rate Bathtub Curve Of Machine Tool

Under the specified conditions and within a specified time interval, Reliability is to describe the product's ability that complete the specified function.As an essential attribute of products, reliability is an important index for evaluating product quality and reliability has gradually become the focus of market competition for the machine tool industry.Compared with imported machine, the mainly gap of the domestic tool is embodied in the poor reliability, Poor reliability has become the weak link that occupy the market in China, especially for high-grade machining center. Therefore, improving the reliability of the domestic machining center has the important practical influence on improving market competitiveness and international market share. Based on the national major special project, A series of horizontal machining center were researched as object, the failure curves of bathtub were researched quantitatively, at the same time the mathematical model was established and the model was applied to practice.Anciently, research on failure data of the machining center mostly concentrated on using of a single distribution model for its analysis, but, from the perspective of the life cycle, for machining center such complex products, using a single distribution model is not fit for modeling its reliability model, because of its different failure periods have different failure mechanism; Therefore, firstly, this paper adopt a single weibull distribution model and two weibull sectional model are used to establish the life cycle distribution laws of earlier failure period and the random failure period and their relationship of the whole machine; and the turning point of the fitting model that is the demarcation point between the earlier failure period and the random failure period is determined. Finally the use of goodness of fit test of the model selection and ultimately determine the optimal model.On the basis of the study, the failure data collected during the different failure periods is analyzed with FMEA based on the above mentioned model to determine the main failure location,failure model in the failure period and the main cause of these failures and their respective frequencies; then some improvement measures of the reliability and security are put forward. Finally, the optimal warranty period series of machining center and preventive maintenance strategy of different fault period was studied, Based on the two weibull failure piecewise model and the failure curves of bathtub fitting map, the failure distribution as theory model was used to guide the series of machining center best warranty period and preventive maintenance cycle formulated, Respectively introduces the best warranty period of this series machining center was determined using the method of the total economic benefit and equal economic benefit and different fault periods preventive maintenance strategy was studied by the availability of maximum and minimum total cost of principle.