A two-phase model for planning the production of aluminum ingot

This paper addresses an important scheduling problem associated with the electromagnetic ingot casting process which is used in the production of a variety metal alloys. The casting procedure begins when molten metal is poured into casting facilities which house a fixed number of ingot molds each of a specified width. The casting process requires that all ingots produced in a given batch be of the same alloy and length. The resulting ingots can differ only in width as determined by the particular mold configuration in a casting pit. In general, mold width changes occur infrequently since they are both costly and time consuming. Given the nature of the process, it is difficult to produce a mix of ingots that exactly matches demand. When required ingots are not available, they must be either imported from outside sources or longer, wider ingots must be trimmed (‘misapplied’), generating excess scrap. The objective of this paper is the development of an effective solution procedure for scheduling the ingot casting process which reduces ingot misapplication/import and maintains low inventory levels. A two-phase model is designed to address this problem. Application of the model at the ingot production facility of a leading US aluminum manufacturer resulted in lower average inventory levels and a decrease in ingot misapplication/import from 20.4% to 0.4% of corresponding production.