Optimizing opportunistic preventive maintenance strategy for multi-unit system of CNC lathe

Due to the many components in the multi-unit system (i.e., CNC machine tools), the existing preventive maintenance (PM) strategies conducting independent PM for every component are time-consuming and waste unnecessary maintenance and downtime costs. Hence, this paper introduces the idea of opportunistic maintenance into the PM and proposes an opportunistic imperfect PM approach, which is a more realistic PM policy for a multi-unit system. In this approach, the effect of PM is assumed to be imperfect to correct the failure rate of each unit. According to the corrected failure rate function, the imperfect PM strategy of a single unit is optimized by minimizing the proposed unit maintenance cost rate under the limitation of minimum reliability. Then, these independent imperfect PM strategies for units are rescheduled by the proposed opportunistic PM strategy under the condition of judging the reliability OM threshold of units. We further optimize the opportunistic PM strategy by minimizing the total maintenance cost. Finally, the advantage of our approach is verified by the case study of 18 CNC lathes.