Economic production quantity models for imperfect product and service   with rework
  When imperfect quality products are produced in a production process, rework may be performed to make them become serviceable. In an inventory system, items may deteriorate. Selling deteriorated items to customers will create negative impact on corporate image. In this paper, two economic production quantity (EPQ) models are proposed for deteriorating items with rework process. A single production-rework plant system and a system consists of $n$ production plants and one rework plant are considered. Approximated analytic results are obtained and numerical examples are provided to illustrate the solution procedure. 
Allen H. Tai
math.OC