Optimal maintenance policy for degrading manufacturing systems using long-term average cost criterion

Most established maintenance policies are focused on the downtime or the performance loss of each tool. The impact of the tool-degraded state on the product quality has not been well addressed. The degradation of a certain tool from its preset nominal state may considerably deteriorate the product quality, which may incur a huge quality loss later. The degraded states of a tool are set back to its nominal value through preventive readjustment, minimal repairing or merely through corrective replacement. In this research, the maintenance cost, the related quality loss and tool obsolescence cost are formalised in a quantifiable manner, which allows one to examine how these cost constraints play fundamental roles in selecting various maintenance policies, and to determine associated optimal parameters. An illustrative example is used to demonstrate the effectiveness and applicability of the proposed approach. The results presented a comparative analysis of specified maintenance policies with respect to the total maintenance cost with consideration of the product quality loss and the obsolescence cost.