A dynamic dial-a-ride model for optimal vehicle routing in a wafer fab

We consider the problem of moving production lots within the clean room of LFoundry, an important Italian manufacturer of micro-electronic devices. The problem is modeled as dial-a-ride in a dynamic environment with the objective of makespan minimization. This general objective is achieved by minimizing, at each optimization cycle, the largest completion time among the vehicles, so as to locally balance their workloads. A cluster-first route-second heuristic is devised for on-line use and compared to the actual practice through a computational experience based on real plant data.