The Research Of Reliability Allocation Methods Of CNC Lathes Based On FMEA

Computerized numerical controlled(CNC)lathes are widely used in the manufacturing industry.The number and qualification of CNC lathes have become an important criterion to estimate the comprehensive strength of a country.At the stage of designing a CNC lathe,the reliability allocation results of its subsystems provide significant requirement and criterion of their design,which may affect the machining accuracy and costs of the CNC lathe.By applying appropriate allocation method can avoid high and unnecessary reliability requirement,which can then reduce the design and machining costs.Therefore,based on FMEA results,the present study investigate the reliability allocation method of CNC lathes.By introducing a new transform function and considering failure correlation,theoretical basis are provided to the CNC lathes' reliability allocation.Firstly,the present study reviews the related research works of CNC lathes' reliability allocation method,as well as the analysis method of failure correlation.The FMEA method and different reliability allocation methods of series system are introduced,and the methods of investigating failure correlation by using Copula function are summarized.In allusion to one kind of CNC lathe's structure,the combination of its system and subsystems are discussed.FMEA is employed in analyzing its structure and FMEA tables are designed.Secondly,considering the limitation of FMEA in reliability allocation,a new cubic transform function is designed.By comparing the new transform function with the traditional exponential transform function,it is proved that the cubic transform function can extend the applicable range of the exponential transform function without lose its advances.Moreover,the new cubic transform function can be designed according to the practical conditions,in order to adjust to distinguish degree of subsystems' reliability.By considering multiple factors'effects on the system's reliability,a comprehensive allocation matrix of series systems is obtained,and a new reliability allocation method is established.After that,based on the cubic transformed function of FMEA,failure correlation is considered.A reliability allocation method of series systems is established by introducing Copula function.Correlation matrix is calculated based on Copula function,and the correlated severities of subsystems are determined based on correlated coefficients.The correlated severity is regard as a criterion of reliability allocation.The allocation results indicate that the allocation method by considering failure correlation can decrease the allocation results of subsystems,which can well decrease the machining costs of the CNC lathe.Finally,a spindle system of the CNC lathe is taken as an example to validate the effectiveness of the new allocation method.The research conclusions are summarized and some expectations of the development of CNC lathes' reliability allocation method are presented.