Kanban, a Japanese word meaning signboard or billboard, is a method used to control production sequences, usually in just-in-time production. Personnel use cards to communicate with other work benches about parts that are to be produced, usually in regard to placing an order with upstream stations. This "pull" principle cuts the volume of warehouse stock needed for series production and boosts flexibility for dealing with fluctuations in requirements volumes.
Kanban in concrete terms
Fundamentally, Kanban cards depict three types of information that vary within all companies – withdrawal, transport and production information. This information helps ensure that parts and materials are ordered, produced and moved precisely in accordance with requirements. Once a workstation has used up all its parts, a new order is sent as a Kanban card to the upstream production station, which then produces more parts in line with the information on the card. In a narrow sense, the term Kanban therefore describes a production order system – separate production planning is unnecessary. The Kanban system prevents overproduction and capital-consuming buffer warehousing and ensures that faulty products are not passed on downstream. As a result, all end-products are free from faults and do not lead to repairs and returns.
Establishing Kanban is just half the battle when striving to achieve lean production. Indeed, the actual objective of Kanban is to eliminate itself. In other words, by carefully and consciously removing cards from a functioning circuit, stock levels are reduced until problems surface. These problems are then dealt with and the production process improves as a result. Once there are no cards left to initiate a production flow, the company has achieved a one-piece flow (OPF). In an OPF, all the personnel involved in a production process control all the work that takes place and accompany the workpiece throughout the entire sequence from one workstep to the next, right up to completion – without interruption.
Cards vs. containers
Sometimes the flow of information in a Kanban system also uses mobile containers, particularly when it is always the same containers that are involved. On the arrival of a specific container, each source knows what is to be produced. To prevent mix-ups, the size of the container should match the size of the material. Both systems – Kanban cards and Kanban containers – are subject to the same basic requirements: handling, safety and differentiation all need to be safeguarded.
The Kanban system was developed in 1947 by Taiichi Ohno at Toyota. The initial ideas of the inventor have been quoted as follows: "It simply must be possible to organise the flow of materials in production according to the principles that apply in a supermarket – a consumer picks an item with a certain specification and quantity from the shelf, the gap is noticed and the item is restocked."