Extended economic production quantity models with preventive maintenance

This paper generalizes the standard economic production quantity (EPQ) model in process manufacturing industry by incorporating regular preventive maintenance (PM) activities into classic EPQ model. The PM program improves the condition of the production to an acceptable level, and avoids potential stoppages and disruptions, hence, it is a vital task in every production process. However, the standard EPQ model does not consider PM activities and then is not applicable to real-world situations. We consider manufacturer which produces a product under EPQ setting with a defective production process, in which every production cycle involves a number of sub-production cycles. Two models are proposed, based on the disposal time of defective items, to determine optimal number of sub-production cycles. In model I, the disposal of defective items is performed once per cycle at the end of each production cycle, while in model II, the disposal of defective items is performed multiple times per cycle, at the end of each sub-production cycle. The total cost functions are derived for each model separately, and then simple solution algorithms are designed. A numerical example is presented and discussed to evaluate proposed models. The results illustrate that model II is more cost effective than model I.