An MVA approximation for CONWIP priority modeling

Constant work-in-process control (CONWIP) by product type is a strategy for improving the cycle time in multiple product factories. For realistic sized systems, a mean-value analysis (MVA) approximation methodology yields quick and accurate results. A processing step modeling paradigm is developed for the MVA methodology and applied to multiple-product reentrant-flow sequences. A variety of sequencing rules have been proposed in an attempt to improve the mean cycle times while maintaining the product throughput rates. A general priority scheme is developed for the MVA modeling approach which allows many of the sequencing rules to be implemented and evaluated under multiple product CONWIP control. Four priority schemes (FIFO, shortest expected processing time, shortest remaining processing time, and Wein's work-balance) are illustrated for a data set from the literature. The best priority scheme, work-balance, obtained a 41% mean processing time improvement over FIFO under push control and 37% under CONWIP control.