Analysis of production control systems kanban and CONWIP

In this paper the authors describe and classify different pull production systems. The production control systems kanban and CONWIP are then analysed with respect to production rate and average WIP. They examine single product flow lines with exponential service time distributions and unlimited demand at the final buffer (saturated lines). The authors show that the distribution of cards (kanbans) has a significant effect on the performance of kanban systems. Different types of kanban control mechanisms show equivalent performance data, if the distribution pattern is adapted accordingly. The present research shows that the kanban system is more flexible with respect to a given objective than the CONWIP system, because in addition to the total card number the card distribution is a control parameter. Moreover for a given production rate the average WIP is lower in a kanban system than in a CONWIP system. The authors identify the average WIP in the interstage buffers as important parameter and describe the ‘WIP bowl phenomenon’ as result of optimum card distributions. Concluding remarks and directions for future research conclude the paper.