Product Stock Maintenance in PHP

This paper investigates integrated models joining Non Quality effect and preventive maintenance (PM) policy. We consider a single machine subject to random failure rate and producing progressive deteriorating products. A preventive maintenance (PM) strategy with minimal repair is applied with non negligible durations of maintenance tasks. This study consists in developing analytical models in order to determine the optimal integrated maintenance plan taking into account the impact of non-conforming products. Two strategies are developed. The first strategy consists on selling products at a discount price due to the loss of quality caused by the machine degradation. The aim of this strategy is to determine the optimal number of batches produced N* before applying each preventive maintenance action maximizing the total profit (PT) per time unit. For the second strategy, we propose a rework activity for deteriorated products in order to improve their quality condition to be sold at the best price Pmax. For this second approach, our objective is to determine the number of batches sold after a reworking task N1 and the number of batches sold at a discount price N2. A mathematical model is developed to find simultaneously the optimal value of the two decision variables N1* and N2* which maximize the total net profit (PNT) per time unit for a finite horizon H taking into account rework and setup costs. The preventive maintenance action will be undertaking after each N1+N2 batches. Numerical examples are presented in order to illustrate proposed models and a sensitivity study is used to evaluate the influence of model parameters.