Minimizing makespan with multiple-orders-per-job in a two-machine flowshop

New semiconductor wafer fabrication facilities use Front Opening Unified Pods (FOUPs) as a common unit of wafer transfer. Since the number of pods is limited due to high costs, and the increase in wafer size to 300-mm reduces the number of wafers required for a customer order, combining multiple orders into a single job is a necessity for efficient production. We investigate the multiple orders per job scheduling problem in the context of a 2-machine flowshop. A lower bound for the makespan performance measure is provided. An optimization model is presented that addresses both job formation and job sequencing.