A model for lot sizing and sequencing in process industries

Abstract

Scheduling in process industries is exceedingly challenging, due to the high capital intensity, relatively long and sequence-dependent setup times, and extremely limited capacity resources that are found in these industries. As a result, it is important to simultaneously consider lot sizing and sequencing factors in the development of a production schedule. This paper presents a mixed integer linear programming model for scheduling production in process industries that embodies the economic trade-offs encompassed in three avenues of research: capacitated lot sizing, flowshop scheduling and sequencing with sequence-dependent setup times. The model is used to schedule production Tor a problem representative of those found in the food processing industry. The corresponding schedule is then compared with approaches that consider lot sizing and sequencing as independent decisions and it is shown that decomposing the scheduling problem into smaller subproblems can result in the generation of infeasible production schedules.