Joint optimization of inspection, maintenance, and spare ordering policy considering defective products loss

Abstract

This paper proposes a joint inspection-based maintenance and spare ordering optimization policy that considers the problem of integrated inspection, preventive maintenance, spare ordering, and quality control for a four-state single-unit manufacturing system. When an inspection detects a minor defect, a second phase inspection is initiated and a regular order is placed. Product quality begins to deteriorate when the system undergoes a severe defect. To counter this, an advanced replacement of the minor defective system is carried out at the 7th second phase inspection. If a severe defect is recognized prior to the Jth inspection, or if system failure occurs, preventive or corrective replacement is executed. The timeliness of replacement depends on the availability of spare. We adopt two modes of ordering: a regular order and an emergency order. Meanwhile, a threshold level is introduced to determine whether an emergency order is preferred even when the regular order is already ordered but has not yet arrived. The optimal joint inspection-based maintenance and spare ordering policy is formulated by minimizing the expected cost per unit time. A simulation algorithm is proposed to obtain the optimal two-phase inspection interval, threshold level and advanced replacement interval. Results from several numerical examples demonstrate that, in terms of the expected cost per unit time, our proposed model is superior to some existing models.