CONWIP-based production lines with multiple bottlenecks: performance and design implications

Abstract

This research focuses on CONWIP, a closed production control system where all containers traverse a circuit incorporating the entire production line. We develop estimates, for an important level of work in process inventory, for four important performance measures: the means and variances of time between departures and flowtime. We develop our estimates through the concept of a “conceptual bottleneck machine”. This concept enables us to develop an analogy between deterministic and stochastic systems. This concept also allows us to handle migrating bottlenecks, an issue generally neglected. The model is widely applicable, assuming only finite means and variances of the processing time distributions. We test our model computationally, both against existing models and on a wide range of randomly generated problems. Finally we detail insights, obtained from our analytical model, into how CONWIP production systems operate. These insights enable us to explain the sources of the values of our performance measures, thus aiding system design and modification.