Kanban Cards: Spitfire Parts Bins, Supermarket Shelves and Ohno's Rules

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Kanban, Japanese for signboard or visual signal, is the subject of this episode, which traces the system to two unlikely sources: the American supermarket and the British wartime factory. In the late 1940s Toyota engineers studied US grocery stores, where shelves were restocked only with what shoppers removed. In 1953 Taiichi Ohno applied that logic to the machine shop at Toyota's main plant, treating each upstream step as a store and each downstream step as a customer. The result replaced push manufacturing, which builds to a forecast, with pull manufacturing, where real demand travels backward up the line.

The physical card itself owes a debt to Britain. Factories racing to build Spitfire fighters during the Blitz used a two-bin system in which an empty bin was the signal to refill it. Ohno turned that into production kanban, which authorize making a fixed quantity, and transport kanban, which authorize moving it, often run through a three-bin loop linking the line, the factory store and the outside supplier. The episode closes on the digital era: barcode scans that feed ERP systems at companies such as Ford and Bombardier Aerospace, work-in-progress limits on Agile software boards, and Kanbrain, a just-in-time approach to employee training.

• Ohno set six strict rules, including that no item is made or moved without a request and that the card must stay attached to the item it represents.
• Rule six, limiting pending requests, is likened to lowering the water in a river to expose the rocks so problems must be fixed rather than buried in inventory.
• A heijunka box, a wall grid of slots by product and time interval, lets managers see bottlenecks forming at a glance.
• The middle bin in the three-bin loop is a calculated buffer against flat tires, jammed machines and supplier outages.
• Agile teams cap the in-progress column, for example at five tasks, so nobody pulls new work until something is finished.