Slab scheduling at parallel continuous casters

Continuous casting is the central process of steel shaping in the steel industry. Here, liquid steel is transformed into solid cuboid shape using a continuous casting process. In most companies, there are parallel continuous casters, which need to be balanced and scheduled. The production process is order driven. Orders in terms of slabs to be casted are not assigned to a specific caster per se. As a result, production planning has to decide about the assignment of slabs to casters as well as the sequence of slabs on individual casters. Scheduling a single caster has to take four specific requirements into account. These are a material supply in batches, flexible slab specifications, a continuous adjustable casting width and different types of setup. While scheduling of a single caster has been studied recently, approaches taking the assignment of slabs to casters as well as its impact on the individual scheduling task into account are missing. In our contribution we present a planning framework for the problem. The framework consists of a MIP-model formulation and a two stage heuristic solution procedure for given problem instances. the framework is applied to a numerical case study and compared to a lower bound as well as to an industry benchmark. The numerical case study shows, that the framework is always able to obtain feasible solutions of the problem with a better quality than the discussed industry benchmark.