Scheduling of a Large-scale Industrial Make-and-Pack Process with Finite Intermediate Buffer using Discrete-time and Precedence-based Models

摘要

We address the short-term scheduling of a two-stage continuous make-and-pack process with finite intermediate buffer and sequence-dependent changeovers from the consumer goods industry.In the current layout of the plant under consideration,the two stages,product formulation and packing,are directly coupled,i.e.the products of the formulation stage go directly to the packing stage.As for different products either one of both stages can be the bottleneck,a gain in productivity can be obtained if the two stages are decoupled by a buffer so that the formulation lines and the packing lines can both run at full capacity.The disadvantage of this setup is an increased complexity of the scheduling problem,so that support for the schedulers must to be provided.We employ a mixed-integer programming problem formulation for this purpose.The problem at hand is characterized by a large number of products in several product families,product specific order quantities and deadlines,product dependent production times,sequence-dependent changeover times,and a finite intermediate buffer.As the problem turned out to be intractable for the planning horizons of interest,a solution approach that employs a discrete-time scheduling model,a precedence-based presorting model and a decomposition strategy that is enhanced by several heuristics was developed.