Machine dedication under product and process diversity

Increased product and process diversity in semiconductor manufacturing lines has confronted operations managers with the challenge of managing setups that usually accompany changes of processes or products at a machine. Under a flexible manufacturing regime, a setup is employed prior to processing in order to prepare the machine with the specific recipe required by the job at hand. Such a setup is performed only if the job last processed by the machine utilized a different recipe. One way to curtail setups is to divide like machines into groups and dedicate each group of machines to a small number of recipes. These machine-to-recipe dedications are aimed to eliminate (or reduce) the setups and hence improve productivity. However, these dedications also result in reduced flexibility at operation time, and hence serve as a detractor to productivity. To investigate this tradeoff and to evaluate the net effect on productivity, an analytical tool was developed. We first confined ourselves to those cases where the number of recipes was equal to the number of machines at the workstation under study. We found that the aforementioned tradeoff depends largely on two factors: the ratio of the setup duration to the processing duration, and the scheduling policy. This elucidated that the dedication decisions should be independent of the absolute values of the setup duration or process duration. Our experiments also indicated that the corresponding break-even points were fairly insensitive to the number of recipes (or machines). In this paper, we relax our assumption regarding recipe-to-machine equality