An investigation of the factors influencing the number of Kanbans required in the implementation of the JIT technique with Kanbans

Abstract

Japanese production environments exhibit a number of characteristics not present in many American firms that contribute to the success of the just-in-time (JIT) system with Kanbans. However, because of the advantages of a JIT system with Kanbans many firms have attempted implementation without the existence of the appropriate production environment to do so. The purpose of this paper is first to identify those factors that will influence the number of Kanbans required at a workcentre for the production manager implementing a JIT system in an uniquely American production environment. The factors that will be identified include the throughput velocity (i.e. the rate at which items flow through a workcentre machine), the coefficient of variation in processing times (i.e. the degree of variability of processing times), the machine utilization (i.e. the availability of slack time on a machine), and, autocorrelation of processing times (the degree to which successive processing times on a specific machine are related to each other). For example, considering just one of these factors, the coefficient of variation, it is demonstrated for a sample shop that reducing the coefficient of variation by a factor of three will reduce the number of Kanbans required by a factor of six. This type of analysis of these factors by the potential Kanban user can provide the user with some insight into the viability of a Kanban-tvpe system for a particular shop. The impact of these factors will be analysed via simulation. The second part of the paper will describe a methodology for determining the number of Kanbans to use at a workcentre given a dynamic production environment. This methodology will also be demonstrated via simulation.