Cost minimizing scheduling of work and rework processes on a single facility under deterioration of reworkables

The problem of scheduling the production of new and recovering defective items of the same product manufactured on the same facility is studied. The items are produced in batches. The processing of a batch includes two stages. In the first stage, all items of a batch are manufactured and good-quality items go to the inventory to satisfy given demands. In the second stage, defective items of the same batch are reworked. After rework each item has the required good-quality. During waiting for rework defective items are assumed to deteriorate. This results in an increase in time and cost for performing rework processes. It is assumed that the percentage of defective items is the same in each batch, and that they are uniformly distributed in each batch. A setup time as well as a setup cost is required to start batch processing and to switch from production to rework. The objective is to find batch sizes such that all demands are satisfied and total setup, rework and inventory holding cost is minimized. Polynomial time algorithms are presented to solve two realistic special cases of this problem. A generalization to a multiple product case is discussed.