Joint determination of rotation cycle time and number of shipments for a multi-item EPQ model with random defective rate

- A multi-item EPQ model with random scrap rate and multi-delivery policy is studied.
- Mathematical modeling and the Hessian matrix equations are employed in this study.
- The optimal common cycle-shipment policy that minimizes the expected cost is derived.
- Effects of various scrap rates and operating policies on system cost are investigated.

This paper addresses the joint determination of a rotation cycle time and number of shipments for a multi-item economic production quantity (EPQ) model with random defective rate. The classic EPQ model considers production planning for a single product with a perfect production process and continuous inventory issuing policy for its finished goods. However, in real vendor-buyer integrated systems, the multi-delivery policy is often used in lieu of the continuous issuing policy, and due to various uncontrollable factors, the generation of defective items is inevitable. Furthermore, in order to maximize machine utilization, management often plans the production of m products in turn on a single machine, rather than a single product on one machine, as assumed by the EPQ model. Therefore, by assuming that all defective items produced are scrap, this study aims to jointly determine the optimal rotation cycle time and number of shipments that minimize the long-run average cost for such an imperfect quality multi-item EPQ model. We employ mathematical modeling with the renewal reward theorem and obtain closed-form optimal operating policies for the proposed model. Further, we demonstrate the practical use of the results by using a numerical example and sensitivity analysis.