中文摘要：

基于故障模式、影响及危害性分析理论,以数控车床关键子系统修正危害度的取值大小作为子系统可靠性指标分配值的衡量标准,指导可靠性分配。将严重度取值非线性化,考虑降低失效率成本问题,将两者结合起来得到修正危害度的表达式,更好地反映了可靠性设计过程中失效模式影响程度的重要性。介绍了危害度分析的相关理论,分别论述了基于传统危害度及修正危害度的可靠性分配方法。最后,将可靠性分配方法应用到数控车床关键子系统可靠性分配的实例中,并加以比较。结果表明,基于修正危害度的可靠性分配方法充分考虑了严重度水平较高子系统的影响以及降低子系统失效率的难易程度,其能够有效地通过可靠性分配结果指导可靠性设计,对于危害度较高、可靠度不达标的子系统在外购、设计、加工、装配等环节应予以足够重视,从而保证整机的平均无故障间隔时间（MTBF）达到要求。

英文摘要：

Based on FMECA theory,taking the modified criticality values of key subsystems of CNC lathes as allocation criteria,the reliability allocation was conducted.By making severity nonlinear,considering the cost of reducing failure rate,an expression of modified criticality was obtained through combining them,and the importance of failure mode effect level through design process could be vividly reflected.Criticality analysis theory was explained,and then reliability allocation methods were pointed out based on traditional and modified criticality respectively.Finally,a real case of reliability allocation of key subsystems of a CNC lathe was presented applying the methods illustrated before and the comparison between traditional method and modified criticality method was conducted.Results show that the reliability allocation method based on modified criticality herein gives full consideration to effects of subsystems with high severity and difficulty level of reducing failure rates,which can guide reliability design based on results of reliability allocation effectively.More attention must be paid to subsystems with high criticality values and low reliability in aspects such as outsourcing,design,processing and assembling so as to ensure that mean time between failures（MTBF）of CNC lathes can meet the requirements.