The influence of spare parts provisioning on buffer size in a production system

We consider a discrete-part production line consisting of two machines with random processing and failure times. One option that can mitigate the effect of these uncertainties is the installation of a buffer between the two machines to avoid starving and blocking of the machines. In this article, we additionally allow the keeping of spare parts in stock to enable a fast repair and reduce machine downtime. We introduce a new model to support the optimization of the buffer size and the spare parts inventory level simultaneously. The model is based on a continuous-time Markov chain and our aim is to minimize the average costs, which are composed of costs for work in process and the stock-keeping of spare parts, subject to a minimum target throughput. Our numerical analysis reveals that the availability of spare parts can increase throughput enormously or reduce the required buffer size for a given target throughput. Using our approach, as opposed to a sequential approach, we can quantify the cost savings, which can be obtained by a joint optimization of the buffer size and the inventory level. Large cost savings can be obtained by the application of our new approach.