Developing an EPQ Model with Considering Preventive Maintenance, Imperfect Product, Shortage and Work in Process Inventory

The determination of optimal production lot size has been always noticed by the researchers and various models have been proposed in this area. Among the issues under less consideration in these models is the issue of machine failure. Obviously، the machine may be encountered during the work with random failures and stop working; this makes clear the need for applying an appropriate maintenance policy for the machinery. In this paper by the consideration of some assumptions as authorized shortage، taking into account the work in process inventory and the possibility of producing imperfect products with and without the ability to re-work، EPQ model were investigated to select preventive maintenance policy for the machinery. Also by minimization of the system total cost over a period of time، a formula for determining the optimal production lot size is presented and by the presentation of various numerical examples، its applications is shown.