WIP-Oriented Dispatching in Complex Manufacturing Facilities

Abstract

Most of the current dispatching approaches for complex manufacturing facilities like semiconductor fabs are related to due dates. They are variants of classical dispatching rules such as Critical Ratio (CR), Apparent Tardiness Cost (ATC), or Operation Due Date (ODD). Besides that there are a number of operational control policies which target the control of the inventory level of the work centers such as Kanban, Starvation Avoidance, or Minimum Inventory Variability Scheduler (MIVS). While the first set of dispatching rules does not primarily lead to low inventory levels, the latter ones do not always lead to good on-time delivery performance. We are currently developing an approach which combines both ideas, i.e., keeping a low WIP level, avoiding bottleneck starvation, and meeting the due dates. While due dates are usually given by the planning department, adequate WIP levels usually have to be set appropriately by means of pilot studies or educated guessing. As a consequence, an adaptive procedure to determine the adequate inventory levels should be implemented. In our contribution, we provide an overview of current dispatching approaches of both types and discuss their pros and cons. Then, we present our approach in detail and compare its performance with the classical approaches from the literature. Recently, we were able to outperform ODD with respect to WIP levels while having the same on-time delivery performance. The disadvantage is that the optimal target WIP levels (minimum and maximum workload level for the work centers) had to be set experimentally. In our future study, we intend to develop a back-propagation neural network for adaptive parameter setting.