Research On Reliability Modeling And Control Technology For The Assembly Process Of CNC Machine Tools

Aiming at the problems of reliability control for CNC machine tools, this paper analyzed the relation between the machine reliability and the assembly process, confirmed that the machine reliability is formed by the connection function reliability and basic function reliability of components. Besides, decomposition methods of CNC machine tools functions including decomposition of the whole equipment function, joint function and unit function. The whole equipment function is decomposed for joint function and unit function; joint function are decomposed for connection parts and connection mode; unit function is decomposed for movement and meta-action. Then, decomposition model is established. On account of the decomposition process, exclusive signs are defined for the events in the decomposition model and the success trees of different decomposition models are built respectively. The mathematical expressions of relations among different events and in events themselves are given out.Facing with the unquantifiablility of reliability of CNC machine during assembly, after analyzing the connection relation between assembly process and function formed process, it is confirmed that on the basis of guaranteeing design and machining reliability. CNC machine assembly reliability impacts directly on machine function formed process reliability. Analyzing assembly reliability directly needs to analyze the assembly process, which makes it difficult to quantify the assembly reliability. Above all, the paper aims at the relation between assembly reliability and function formed process reliability, turns quantification analysis of assembly reliability into quantification analysis of function formed process reliability which leads to the solutions. The GO-diagram model guided by Success is built by success tree according to the logical relation among events. The reliability of CNC machine assembly process is calculated by GO method.To put the control technology of assembly process reliability into effect, the failure performances of connection mode and the meta-action which are called reliability defects are analyzed. Aiming at some problems, such as the large amount of sources of reliability defects and uneasily-control, Entropy Method is utilized to give the conception of Entropy Weight of reliability defects during assembly. The Entropy Weight and the value of Entropy are calculated combining with the Experts Weight, the main defects patterns which may occur during the assembly process are confirmed and the main defects sources are analyzed.On the basis of confirming main defects and sources, the assembly reliability control measures are established. Moreover, utilizing the polychromatic sets theory, matrixes between main defects and main defects sources, main defects sources and control measures are related. Boolean Control forms are built respectively and the relevant information of control technology of assembly process reliability is integrated, which contributes to the clearness of assembly reliability.To evaluate a set of reliability modeling during assembly process of CNC ma-chine and the effectiveness of control technology studied in this paper, Grey System Theory is utilized to build a model of the relation of historical data of whole machine assembly process reliability, assembly process reliability of joint function and reliability of unit function. In addition, the analogue value of historical data of assembly process reliability is worked out. On condition that the simulation precision is effective, the historical data controlled by reliability control technology is simulated uncontrolled. Using GO-method, the corresponding historical data is actual-valued calculated and the analogue values which are not controlled by control technology are compared and analyzed. It proves that it is effective for control technology of assembly process reliability to guarantee the reliability of CNC machine tool.The study results above are all able to use in the reliability study of assembly process of machining centre which has been proved by instance.