Two metaheuristic methods for the common cycle economic lot sizing and scheduling in flexible flow shops with limited intermediate buffers: The finite horizon case

This paper addresses the common cycle multi-product lot sizing and scheduling problem in deterministic flexible flow shops where the planning horizon is finite and fixed by management and the production stages are in series, while separated by finite intermediate buffers. The limited intermediate buffers between the stages result in a blocking scheduling problem, where a completed part may remain on a machine and block it until a downstream machine becomes available. This prevents another part from being processed on the blocked machine. We propose a new mixed integer nonlinear program and due to difficulty of obtaining the optimal solution in medium and large-scaled problems, we use both genetic algorithm and tabu search methods to find an optimal or near-optimal solution for the problem. The two proposed solution methods are compared with optimal enumeration method (OEM) on randomly generated problems. Computational results show that the performance of both GA and TS are very promising.