The Psychology of Quality and More

Kanban

Kanban means 'display card' or 'instruction card' in Japanese. Kanban cards and systems are used to synchronize the flow of parts in systems (often manufacturing and assembly) where many different parts come together at various points in a long and often complex process. Cards can, of course, be replaced with electronic system can be used to inform the upstream process in real time of parts usage.

 Imagine a supermarket, where there are cards attached to all items on shelves. At the checkout, the cashier takes the cards off the items and sends them to the warehouse, who send replacement items. The warehouse also uses the same system, and when a carton is picked off the shelves, the card attached to it is sent further back upstream. This is a pull system, where consumption of an item leads to the kanban card associated with it being used to 'pull' replacements from upstream in the process.

Consider the alternative. Every Friday, the warehouse sends three cartons of frozen peas to each supermarket. The number of cartons delivered is based on a calculation, done at some time in the past, on average usage. This means that some supermarkets will run out, whilst others will have peas coming out of their ears! This is a push system.

Kanban thus leads to less stock-outs and stock-overflows, with the attendant cost savings and more reliable system. But (and it is a big but) synchronizing an entire system, as the use of kanban does, only works if you can predict demand and manage the changes in it. High stock levels may have masked seasonal swings from upstream producers, but in a synchronized system, they now will have to cope with this effect. Reliability becomes increasingly important as

Move cards ( also called C-card, Conveyance or Withdrawal kanban cards) signify that a part has moved, but has not been consumed: this may trigger movements upstream, but not production of a new part. A Production Card (or P-card) indicates that the part has been consumed and will trigger production of a replacement part. There are also sub-categories of these types. Thus a Signal (or Material) card is a type of Production Card that can be used to flag low stock levels and thus trigger purchases. A Supplier card is one that goes directly to a supplier and enters their kanban system.

Kanban cards may include instructions to the person upstream, so when they receive the card, they simply move or produce items as instructed. A production operator, when receiving a kanban card, will make only as many parts as are in the kanban lot size. Any more would simply create a bigger pile of parts than is needed, with the accompanying material and storage costs.

One card may be attached to a single item or to a number of items, where the number of items in the batch will depend on the variation within the system, the time taken to product items, and other factors. An improvement objectives is to reduce the number of parts in the kanban batch or lot size. Reducing this size exposes variation and other problems, and so must be linked to process improvement. 

A Kanban Post is a place where kanban cards are placed (sometimes in a 'post-box').

See also:

Kanban, Basic, Kanban, Advanced