Abstract
A multifactor reliability allocation method for CNC lathes is proposed in this paper based on the failure mode effects and criticality analysis (FMECA) modified criticality factor and objective information. Firstly, taking into consideration the cost of reducing subsystems’ failure rates, criticality in FMECA analysis is introduced into reliability allocation. By making severity value nonlinear and based on subsystems’ failure rate, mathematical model of the cost of reducing subsystems’ failure rates is established, and then computational formula for modified criticality is obtained. Secondly, according to the objective information in existence, failure frequency ratio, failure stopping time ratio, reliability influence degree and structure complexity are calculated respectively. The four sets of values above and modified criticality are combined together as allocation factors. Ratio matrix of each allocation factor is computed to get comprehensive allocation matrix and allocation vector. Finally, the method is applied to a case of reliability allocation of a certain type of CNC lathes, and practicability of the method is analyzed. According to the allocation results, reliability design can be improved to increase the mean time between failure (MTBF) of subsystems and the overall lathe. The proposed method together with the example serves appropriately to show the feedback effect of failure information on reliability design and role of cost reduction in the allocation process.
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