Effects of dispatching and down time on the performance of wafer fabs operating under theory of constraints

A number of companies have reported significant improvements in manufacturing performance through implementing the concepts of the Theory of Constraints suggested by Goldratt (1986). However, the implementation of these concepts in wafer fabs is not straightforward due to the presence of reentrant product flows. In this paper we examine the effects of downtime at non-bottleneck machines and different dispatching rules on the performance of a wafer fab operating under the Drum-Buffer-Rope release policy (Goldratt and Fox 1986). Our results show that downtime at non-bottleneck machines has significant detrimental effects on fab performance, and that the Critical Ratio dispatching rule performs well in terms of the tradeoff between cycle time and throughput