Part allocation to nesting layouts under variable demand

The problem formulation presented here deals with the choice of parts for nesting layouts when cutting arbitrary sheet metal parts under variable demand. The parts are chosen based on their demand characteristics and size, but their actual positioning on a larger sheet is not discussed. Guidelines are created for a nesting strategy that minimizes the needs for part stocking and renesting while still meeting the production requirements. A new, practical and rubust method of determining the approximate numbers of parts of the different types to the nesting layouts is proposed. The performance measures used to compare the nesting strategies is the work in process, expressed as the average percentage of the required production. According to this method, at least the same number of nesting layouts is created as that of the different part types. The use of the method ensures that the work in process stays low, even if the demand differs considerably from the forecast on which the nesting was originally based. Numerical experiments were made with several random and deterministic parts, nesting layouts and production programmes. In the experiments, the nesting layout selection problem was solved for several successive planning periods and the effect of various nesting strategies, and the characteristics of the demand and the part types were studied.