Maintenance policies and buffer sizing: an optimization model

In production, stops due to maintenance create imbalances within the system. Let's assume that you have a series of n machines and that the i stops. In this case the i+1 would be able to continue to work only as long as stocks were available on the machine, while the i-1 could continue to work only if there was the possibility that its production would be at least temporarily placed on the machine. Therefore it is normal in order to contain the system imbalances, due to maintenance stops, introduce some buffers. In this paper we propose a simulation model to define the optimal dimension of the buffer, with regards to the maintenance policy that is applied to the production system. The model can simulate a system of units that can have very different characteristics, such as productivity or reliability, and also we can simulate an inter-operational buffer between them. The model is based on the concept of thresholds which, when crossed by the parameter of wear, determine different maintenance interventions. The cost optimization consists in determining, by simulation, at what value the thresholds should be fixed to minimize the overall maintenance cost. We use the model to determine the buffer dimension trend depending on the cost of the buffer.