Joint optimisation of quality-dependent production and economic-dependent maintenance for a degradation system under online and offline inspections

The relationship between quality-dependent production and economically dependent maintenance is generally ignored during the production process, especially for multi-unit degradation production systems. To bridge this gap, an improved Weibull distribution with two scale parameters and shape parameters is employed to depict the ‘bathtub curve’ characteristic of nonconforming product rates. Moreover, an acceleration factor related to product quality is considered to describe the effect of unqualified products on the degradation process of the downstream machine. New quality-based maintenance and condition-based opportunistic maintenance are proposed, and the opportunity originates from safety inventory capacity and the deterioration level of other machines. A comprehensive optimisation model of production, maintenance and inspection policy, is formulated under online and offline inspections, respectively. The aim is to minimise total costs that consist of falsely rejecting qualified products and accepting unqualified products under inspection errors by optimising the sampling proportion, the inventory capacity and the thresholds of maintenance. Furthermore, a Quadratic Particle Swarm Optimization with Local Search (QPSOL) algorithm is developed to effectively solve the optimisation problem. Finally, spiral grooves for air conditioning compressors are used to demonstrate the effectiveness of the proposed model, and we further prove that online inspection is more cost-effective than offline inspection.