Preventive maintenance policies for a deteriorating manufacturing system with product quality improvement and random working time

In this paper, two novel preventive maintenance (PM) policies are proposed for a deteriorating manufacturing system in consideration of product quality improvement and random working time. First, the degradation process of quality-related components (QRCs) is analyzed. Based on the proportional hazards model (PHM), a hybrid failure rate function is established to combine manufacturing system age and the degradation process of QRCs. A linear regression model is used to describe the quantitative relationship between the degradation QRCs and product quality. Then, considering that the manufacturing system processes jobs with random working time, the system is maintained before failure at age T or at random working time Y, whichever occurs first/last. The optimal maintenance scheduling is achieved by minimizing the long-run expected cost rate that includes the maintenance cost and the quality loss cost. Furthermore, the existence and uniqueness of the optimal solution for the two maintenance models are analyzed in detail. The conditions for selecting an appropriate policy under specific production conditions are obtained analytically. Finally, two case studies are presented to demonstrate the effectiveness and applicability of the proposed maintenance policies.