Priority Scheduling for a Flexible Manufacturing System with Multiple Loading/unloading Stations and Multi-fixturing Pallets

Abstract

This thesis addresses a scheduling problem for a flexible manufacturing system with multiple loading/unloading stations that load/unload parts on/from multi-fixturing pallets that can load multiple parts at the same time and release/take the pallets into/out of the system. The problem consists of three sub-problem: palletizing that selects the parts to be loaded on each multi-fixturing pallet; pallet routing that determines the routes of each pallet to process all its loaded parts through loading/unloading stations and machines; and pallet process sequencing that determines the sequence of pallets to process their loaded parts on each machine. Practical constraints, such as re-palletizing of identical parts, central buffer capacity, limited number of pallets and pallet setup worker availability, are also considered. Due to the complexity of the problem, a fast heuristic approach is proposed that uses priority rule combinations in an integrated fashion. Simulation experiments were done on a number of test instances, and the best rule combinations are reported for each of the two objectives, minimizing makespan and total tardiness. Effects of the number of loading/unloading stations on the two objectives are also reported to support decisions on the appropriate number of loading/unloading stations.