Abstract: This paper focused on multi-stage flexible manufacturing systems working in variable loading conditions. Based on the proportional hazards model, a load-dependent degradation model is proposed for components operating in the variable loading condition. Besides, a modified machine-selecting and load-sharing model, considering the virtual age of components and capacity requirement，is proposed to quantify the load condition of components. Moreover, taking degradation of components into account, a hybrid imperfect maintenance model is developed, which is followed by the final objective to determine the best maintenance strategy to minimize the expected maintenance costs of system in the dynamic production planning phase. Furthermore, a greedy algorithm with constraint on preventive maintenance time of system is proposed to solve the problem. The illustrative example shows that this model can dynamically respond to variable system maintenance requirements under the flexible operation condition. It outperforms the full loading model and the expected loading model in cost rate.

Key words: multi-stage flexible manufacturing system, dynamic production planning, preventive maintenance, proportional hazards model, variable loading