Scheduling of Rolling Ingots Production

We consider a real-world scheduling problem arising in the context of a rolling ingots production. We review the production process and discuss peculiarities that have to be observed when scheduling a given set of production orders on the production facilities. We then describe a model for this scheduling problem using prescribed time lags between operations, different kinds of resources, and sequence-dependent changeovers. The basic principle of the solution procedure is to relax the resource constraints by assuming infinite resource availability. Resulting resource conflicts are then stepwise resolved by introducing precedence relationships among operations compet ing for the same resources. The algorithm has been implemented as a beam search heuristic enumerating alternative sets of precedence relationships.