A comparative study of pull control mechanisms for unreliable homogenous transfer lines

The problem of tandem production lines composed of multiple unreliable workstations producing a single part type with holding (inventory and storage space) and shortage costs is considered. Given the numerous control mechanisms introduced in recent years, it is a difficult task to evaluate which mechanism is best suited for a specific application. Using simulation, design of experiments and response surface methodology, various homogenous lines controlled by Kanban, CONWIP and the hybrid Kanban/CONWIP control mechanisms are optimized and then compared. It is observed that the hybrid mechanism always outperforms CONWIP and Kanban when storage space and inventory costs are considered explicitly. However, hybrid is equivalent to CONWIP when storage space costs are not considered explicitly but rather aggregated with the inventory costs in the holding costs as usually found in the literature. Furthermore, with the increase of storage space cost and the number of workstations, Kanban outperforms CONWIP.