Kanban systems are used to signal when a material needs to be produced or ordered and how much is needed. It is a type of pull system which is based on customer demand and in which materials are only made when they are needed. A kanban system is a type of lean manufacturing, and it strives to have no more material on hand than is necessary.
The first kanban systems were developed by Taiichi Ohno for use by Toyota® manufacturing. In the mid 1900s, Ohno studied inventory strategies used in supermarkets. Many supermarkets actually function like a kanban system and have cards for every type of item sold. Ohno took what he learned from supermarkets and applied it to manufacturing.
Later, Toyota issued six rules to guide its kanban system. Most of these rules deal with ordering only what is needed to keep the rate of production as steady as possible. Whenever a defect is noted, it must be immediately fixed or discarded. If a defective product is allowed to go down an assembly line, it wastes both time and money.
Visual aids are used in kanban systems to show when a specific part is needed. These visual aids are usually kanban cards that feature the part’s name, picture, code, and the quantity needed. Kanban cards are often attached to a container where they become visible as soon as the quantity reaches a point where more should be ordered.
A stable level of demand is almost a requirement for kanban systems. Companies that produce seasonal items, such as snowsuits or beach toys, must adjust their numbers with the season. Otherwise, there will be too much stock in the off-season and too little stock when it is needed.
Kanban systems are also a tool for achieving just-in-time manufacturing (JIT). JIT manufacturing occurs when a facility has a stable rate of production. In an assembly line, every station must finish at exactly the right time in order to keep the line moving. Kanban systems make sure that no one ever runs completely out of a material, so the line never stops moving.
Although the kanban system was originally created to use kanban cards for each item, some production facilities now use other items. Other signals, such as kanban squares or golf balls, can be used to signal the need for more material at a workstation. Some production facilities have even implemented electronic kanban systems.