Capacitated Lot Sizing for Plastic Blanks in Automotive Manufacturing Integrating Real-World Requirements

Lot-sizing problems are of high relevance for many manufacturing companies, as they have a major impact on setup and inventory costs as well as various organizational implications. We discuss a practical capacitated lot-sizing problem, which arises in injection molding processes for plastic blanks at a large automotive manufacturer in Germany. 25 different product types have to be manufactured on 7 distinct machines, whereas each product type may be assigned to at least two of these machines. An additional challenge is that the following production processes use different shift models. Hence, the stages have to be decoupled by a buffer store, which has a limited capacity due to individual storage containers for each product type. For a successful application of the presented planning approach several real-world requirements have to be integrated, such as linked lot sizes, rejects as well as a given number of workers and a limited buffer capacity. A mixed integer programming model is proposed and tested for several instances from practice using CPLEX. It is proven of being able to find very good solutions within in few minutes and can serve as helpful decision support. In addition to a considerable reduction of costs, the previously mostly manual planning process can be simplified significantly.