Production and Maintenance Policies for an EPQ Model With Perfect Repair, Rework, Free-Repair Warranty, and Preventive Maintenance

Manufacturers increasingly emphasize improving product reliability and ensuring product uniformity; these two factors have become critical aspects of industrial activities. This paper describes an economic production quantity model with maintenance, production, and free-repair warranty (FRW) programs for an imperfect process. When defective parts are produced, perfect repair, inspection, and rework are conducted after the production run period. For a deteriorating production system, this paper defines an inferior item as satisfying specifications on each inspection but being likely to incur post-sale servicing costs when sold under FRW. Preventive maintenance (PM) is performed after the "in-control" production run period and can be classified as one of two types: 1) imperfect or 2) perfect. The probability of a perfect PM is calculated based on the number of imperfect PMs from the last renewal cycle. An optimal production runtime is determined by minimizing the total cost. Several special cases are discussed, including the case of maintenance learning effect. Finally, a numerical example and sensitivity analysis are reported to illustrate the model.