Quality bottleneck transitions in flexible manufacturing systems

In this paper, we introduce a Markov chain model to evaluate the quality performance in flexible manufacturing systems with batch productions. In such a model, the product quality is a function of the transition probabilities characterizing the changes among good and defective states (where good quality or defective parts are produced during a cycle, respectively). A transition that has the largest impact on quality, i.e., whose improvement will lead to the largest improvement in quality, is defined as the quality bottleneck transition (BN-t). Analytical expressions of sensitivity of quality with respect to transition probabilities are derived. Indicators to identify bottleneck transitions based on the data collected on the factory floor are developed. Numerical experiments show that such indicators have high accuracy in identifying the correct bottlenecks and can be used as an effective tool for quality improvement effort. Finally, a case study at an automotive paint shop to improve quality through quality bottleneck transition identification is introduced.