Flexible preventative maintenance for serial production lines with multi-stage degrading machines and finite buffers

In production systems, machines are typically subject to degradation, which is a gradual and accumulating process that can influence the performance of the production systems. In this work, we focus on the flexible preventative maintenance problem on serial production lines with multi-stage degrading machines and finite buffers. Condition-based maintenance decisions are first investigated for a two-machine-one-buffer system, considering machine degradation stages and the buffer level. The optimal maintenance policy is obtained using Markov decision models. For longer lines, approximation methods are developed based on the results from the two machine case. Specifically, an iterative state and machine aggregation approach is developed to find the optimal preventative maintenance policy for each machine in large systems. Numerical experiments show that the proposed method outperforms the state-of-the-art.