Kanban in Lean manufacturing distilled

You’ll find a lot of terminology in Lean software development comes from Japan and from the Toyota Production System in particular. Kanban translated literally: “Kan” means visual, and “ban” means card or board.

Picture yourself on a Toyota production line. You put doors on Priuses. You have a stack of 10 or so doors. As you keep bolting them on, your stack of doors gets shorter. When you get down to 5 doors, sitting on top of the 5th door in the stack is a card — a Kanban card — that says “build 10 doors.” Well it may not say exactly that — but it is a request to build exactly 10 more Prius doors.

You pick the Kanban card up, and run it over to the guy who builds doors. He’s been waiting for you. He’s been doing other things to keep busy while waiting. The important thing here is that he’s NOT been building Prius doors. He takes your Kanban card and begins to build doors.

You go back to your workstation, and just a bit before your stack of doors is gone, the door guy comes back with a stack of 10 doors. You know that Kanban card is slid in between doors 5 & 6. You got the doors just in time. The whole thing sorta works like magic. Only you wish you had the door-building job. That guys seems to have a lotta free time on his hands.

Kanban cards are used to limit the amount of inventory the factory builds. It doesn’t do the Toyota factory any good to build doors faster then they can assemble cars. It just wastes money on excess doors, and parts of doors. Excess work in progress is considered to be waste in Lean manufacturing. (It’s probably waste in non-Lean manufacturing too.) In the above completely made up example, you’ll never have more than 15 finished doors hanging around. (Mudha is Japanese for waste. Learn it to impress your Lean friends.)

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