| Zitatschlüssel |
Report-001-2009 |
| Autor |
Höhn, Wiebke and König, Felix G. and Lübbecke, Marco E. and Möhring, Rolf H. |
| Jahr |
2009 |
| Nummer |
001 |
| Notiz |
Published in Management Science 2011 |
| Institution |
Technische Universität Berlin, Institut für Mathematik |
| Zusammenfassung |
We consider a complex planning problem in integrated steel production. A sequence of coils of sheet m et al. needs to be color coated in consecutive stages. Different coil geometries and changes of coatings may necessitate time-consuming setup work. In most coating stages one can choose between two parallel color tanks in order to reduce setup times. As a complicating consequence, setup times for a coil may depend on the whole sequence of predecessors. A production plan comprises the sequencing of coils, and the scheduling of color tanks and setup work. The aim is to minimize the makespan for a given set of coils. We present an optimization model for this integrated sequencing and scheduling problem. A core component is a graph theoretical model for scheduling. It is instrumental for building a fast heuristic which is embedded into a genetic algorithm to solve the sequencing problem. The quality of our solutions is evaluated via an integer program based on a combinatorial relaxation, showing that our solutions are within $10$\% of the optimum. Our algorithm is implemented at Salzgitter Flachstahl GmbH, a major German steel producer. This has led to an average reduction in makespan by over $13$\% and has greatly exceeded expectations. |
