Melt scheduling to trade off material waste and shipping performance

The ingot formation or "melt" process is the first step in many steel-makin g operations. This process involves melting steel and alloys in the desired chemical composition, then pouring it into a variety of ingot molds. Compl ex technological and resource constraints can make the planning and schedul ing of such processes extremely challenging. In this paper, we report our e xperience in developing solution methods for this "melt scheduling" problem at BethForge, a division of the Bethlehem Steel Corporation, and a manufac turer of custom-made heavy steel forgings. We describe the main issues asso ciated with generic melt-scheduling problems as well as constraints that ar e specific to BethForge. The problem at BethForge is particularly challengi ng, because of the need to keep the ingot at a high temperature before forg ing, their large product variety, and the need to consider trade-offs betwe en two conflicting objectives. We first formulate the base melt-scheduling problem as a mixed-integer program. We then decouple the scheduling decisio ns into two levels and develop a local search algorithm based on Storer and Wu's problem space neighborhood. Our aim is to generate a family of effici ent schedules that allow decision makers to balance the trade-off between t wo criteria. Computational experiments are performed using data from BethFo rge. The melt-scheduling procedure developed here has been implemented and installed at BethForge. It has made fundamental improvement in their melt-s cheduling process.