A two-stage solution approach for scheduling flexible manufacturing systems with multi-fixturing pallets

This study addresses a scheduling problem for flexible manufacturing systems with multi-fixturing pallets that can load multiple parts under the practical constraints of central buffer capacity, limited number of pallets and pallet setup worker availability. The problem consists of four dependent sub-problems that determines: (a) the parts to be loaded onto each pallet, i.e. palletizing; (b) the sequence of pallets to be initially released into the system, i.e. pallet input sequencing; (c) the route of each pallet over machines to process its loaded parts, i.e. pallet routing; and (d) the sequence of pallets to process the corresponding parts on each machine, i.e. pallet process sequencing. After showing that pallet routing and process sequencing is an open shop scheduling problem, a two-stage solution approach is proposed for the objective of minimizing makespan. In the two-stage solution approach, an initial solution is obtained by a greedy randomized adaptive search procedure (GRASP) based construction method for the parts released into the system using a palletizing/pallet input sequencing rule, and then it is improved by an extended disjunctive graph based local search method. Computational results show that the two-stage solution approach outperforms the existing one significantly.