Research On Quality Control Technology For The Assembly Process Of Numerical Control Machine Tool

Assembly is a process of assembling a variety of different parts into a whole function.The quality control of the assembly process is an important link to ensure the quality of the product.Poor assembly is an important factor in product failure.Therefore,to ensure the quality control of the product in the assembly process is of great importance to the improvement of the quality of the product.In view of the problems existing in the reliability control of CNC machine tools,the relationship between the assembly process and the reliability control is analyzed.This paper makes a systematic study on the assembly quality control technology in different assembly stages,and puts forward a scheme to improve the quality of the assembly link of the CNC machine tools.The paper mainly includes the following aspects:(1)According to the existing literature,the purpose and significance of reliability control in the assembly process of mechanical and electrical products were analyzed.Then the basic concepts was introduced.The research status of reliability control in assembly process at home and abroad was discussed,and the source,main contents and overall structure frame of the paper were expounded.(2)Assembly sequence optimization method based on multi objective fuzzy comprehensive evaluation.In order to solve the problem that the optimal assembly sequence of mechanical products was difficult to determine,an assembly sequence optimization method for multi objective fuzzy comprehensive evaluation was proposed.On the basis of research and expert opinion,the evaluation index set of assembly sequence scheme was defined,and the quantitative calculation method of each evaluation index was given.Then the fuzzy analytic hierarchy process method was used to evaluate the relative relation among the indexes so as to obtain more accurate weight of each evaluation index of the assembly sequence.Finally,according to the quantized attribute value and fuzzy weight of each index,the method of elimination and selection conversion was used to evaluate the assembly sequence synthetically.As a result,the best assembly sequence was selected from several feasible assembly schemes.(3)Assembly reliability control technology based on motion unit fault modeling.The status of quality control in assembly process was analyzed,and the idea of assembly reliability control was given.The structural decomposition mentality of “function-motive-action” based on basic motor function was proposed,the motive units likely occurring failures were determined through analysis on failures data of products,and the fault tree of motive unit likely occurring failures was established.The binary decision diagrams was used to transform the fault tree for enhancing efficiency of analysis.The importance of basic events was calculated according to the occurrence probability of basic events.The events with higher importance were identified as reliability control points.The fault source of the reliability control point was analyzed,and the reliability control measures of the assembly process was proposed.In order to improve the reliability of the assembly process,the reliability control table of the fault source and the control measures was set up by using the polychromatic set theory.(4)Fuzzy evaluation of assembly quality of whole machine based on combination weight by least squares method.Based on the prediction of the whole machine assembly quality of the existing CNC machine tools,the evaluation indexes of the assembly quality of the whole machine are sorted out.Then we can use expert knowledge to screen the evaluation index system by use the Delphi theory,and a complete and reasonable evaluation index system was established.According to the statistical data and relevant weights of each evaluation index,the objective weight and subjective weight of the evaluation index were calculated by Information Entropy and Fuzzy sets,and the weight of the index was obtained by least square method.The comprehensive evaluation of the feasible assembly design scheme was realized by using technique for order preference by similarity to ideal solution.