Realistic modeling of economic design of (X‾) control chart and preventive maintenance in the presence of multiple independent assignable causes

Purpose This paper aims to address the limitations of Duncan's 1971 economic model for the X‾ control chart by resolving its internal contradictions and enhancing its applicability through integration with preventive maintenance strategies. Design/methodology/approach The research revisits Duncan's 1971 economic model, which assumes both independence and dependence among assignable causes – an inherent contradiction that undermines its realism. A new economic design framework is developed that accommodates multiple assignable causes and incorporates preventive maintenance strategies to improve process control. Findings The proposed model demonstrates improved reliability and extended production time under controlled conditions. It also significantly reduces unplanned downtime and overall operational costs compared to models based on Duncan's assumptions. Originality/value This paper challenges the foundational assumptions of a widely cited economic model and introduces a novel, more realistic approach that combines statistical process control with preventive maintenance. The model offers practical value for industries seeking to optimize quality and reliability in production and service systems.