Scheduling High-Grade Steelmaking

The paper describes a scheduling system for a high-grade steel making plant. Because very specialized steel grades are produced the variety of the chemical analysis of the heats is very high and the lot sizes are small. One of the most constraining factors in the production is the infiltration of chemical elements between consecutive heats in the electric arc furnace. To find a schedule that violates no compatibility constraints is theoretically in the worst case an NP-hard problem. An earlier attempt to solve the problem with conventional software failed due to this complexity. Some difficult to schedule jobs remained unscheduled. The expert system solves the problem because it first determines the criticality of jobs and applies then a heuristic based on the criticality values to guide the search for a feasible schedule. Important is further the system’s capability to use and relax constraints locally. The expert system was fielded successfully in 1992 at Böhler Uddeholm in Kapfenberg.