Scheduling Manufacturing Systems of Re{entrant Lines

Re{entrant lines are manufacturing systems where parts may return more than once to the same machine, for repeated stages of processing. Examples of such systems are semiconductor manufacturing plants. We consider the problems of scheduling such systems to reduce manufacturing lead times, variations in the manufacturing lead times, or holding costs. We assume a deterministic model, which allows for bursty arrivals. We show how one may design scheduling policies to help in meeting these objectives. To reduce the mean or variance of manufacturing lead time, we design a class of scheduling policies called Fluctuation Smoothing policies. To reduce the holding costs in systems with set{up times, we introduce the class of Clear{A{Fraction scheduling policies. We study the stability and performance of these scheduling policies. We illustrate how scheduling policies can be unstable in that the levels of the bu ers become unbounded. However, we show that all Least Slack policies, including the well known Earliest Due Date policy and all the Fluctuation Smoothing policies, are stable. 1.