The impact of sequencing decisions on multi-item lot sizing and scheduling in flow shops

The problem of sequencing, lot sizing and scheduling a number of products in flow shops has been studied by several authors. It has been reported by some of them that the sequence to be used has a negligible impact on total cost. Consequently, little attention was given to the sequencing sub-problem. The purpose of this paper is to study the impact of sequencing decisions and to suggest some methods to determine the sequence to be used. We propose a mathematical programming based heuristic as well as some construction and local search heuristics. The proposed heuristics are compared and computational results for 360 test problems are reported. These results reveal that sequencing decisions may have a non-negligible impact on total cost and may allow us to identify the best among the heuristics tested.