Integrated optimization model of economic manufacturing quantity and hybrid condition-based maintenance for continuous-production systems

Continuous production line degeneration is commonly observed in complex manufacturing systems, potentially leading to substantial financial losses and safety risks. In this paper, we propose a model that integrates Economic Manufacturing Quantity (EMQ) optimization with hybrid maintenance scheduling. This model leverages the health information of the production machine extracted through condition monitoring (CM) and employs stochastic processes to describe manufacturing deterioration. The maintenance strategy in this hybrid approach encompasses three components: (a) age-dependent preventive maintenance; (b) CM-dependent condition-based maintenance (CBM); and (c) reactive corrective maintenance. Preventive maintenance is scheduled at production halt points within each production lot, preceded by limited CMs. At each CM, the control limit for CBM is dynamically adjusted based on the amount of CM and defined by a reliability criterion. This study aims to jointly optimize the production lot size and reliability criteria to minimize the expected cost per production cycle. A case study on the converter system in a steel plant demonstrates the applicability of the proposed joint strategy.