Kanban Scheduling System for Lean and Just in Time
The ideal lot size is one - how many can we work on at one time? - usually one. Even in batch production, only one item in the batch is being processed while the remainder of the batch is idle in the queue. To achieve one at a time production, we must close couple operations, without excess inventory in between to take up the variances in the processing speed. To achieve right first time production with close coupled operations producing zero deviation from the schedule, requires a method - material flow synchronisation. The method adopted is one which 'pulls' rather than 'pushes' inventory, is called Kanban, which literally translates into visible plate. Kanban can refer to the philosophy or to the card or token that is used on the shop floor. To pull material from the assembly area, we must assume stable demand. (The possibility of stable demand will be discussed later.) The Kanban cards themselves are attached to special containers. These containers are usually custom made for the parts. The container might hold a number of parts. Usually, a convenient quantity is used, either in the ratio needed for assembly, i.e. 10 items for each assembly or a convenient number for the process. When production commences, there are more Kanbans and hence totes (bins) containing material than are needed. As production becomes more synchronised, the extra Kanbans can be gradually withdrawn. (Kanbans may be viewed as a simple two-bin method of inventory replenishment).