Scheduling of the optimal tool replacement times in a flexible manufacturing system

In Flexible Manufacturing Systems (FMSs), a cutting tool is frequently used for different operations and on different part types to minimize tool chan ge-overs and the number of tools required, and to increase part-routing fle xibility. In such situations, the tools become shared resources and work in job-dependent, changeable and nonhomogeneous conditions. It is well known that the tool failure rate depends on both age and machining conditions and that tool reliability is a function of the duration, machining conditions, and the sequence of the operations in FMS. The objective of this paper is to obtain a schedule of the optimal preventive replacement times for the cu tting tools over a finite time horizon in a flexible manufacturing system. We assume that the tool will be replaced either upon failure during an oper ation or preventively after the completion of each operation, incurring dif ferent replacement costs. A standard stochastic dynamic programming approac h is taken to obtain the optimal tool replacement times. The optimal schedu le is obtained by minimizing the total expected cost over a finite time hor izon for a given sequence of operations. A computational algorithm is devel oped and a numerical example is given to demonstrate the procedure.