Kanban

KanBan is often seen as a central element of “Lean” manufacturing and is probably the most widely used type of “Pull” signaling system. Kanban stands for Kan- card, Ban- signal and as you probably guessed, is of Japanese origin.

Simply described a “pull” production system controls the flow of work through a factory by only releasing materials into production as the customer demands them i.e. only when they are needed. A “push” system on the other hand would release material into production as customer orders are processed and material becomes available, MRP (Material Requirement Planning / Manufacturing Resource Planning) systems are typically “push” systems. What must be made clear at this point is that Kanban is not a scheduling system but rather a production control system.

The concept of Kanban cards (or other indicators) have been around for many years, in fact the “two bin system” was used in the UK long before Japanese manufacturing methodologies started to be come popular in the 1970’s. Whatever the origins, or who the inventors, a Kanban system is generally easy to understand, simple to visualise and comparatively easy to set-up. Kanban systems are commonly used within the automotive industry where there is a stable demand and flow. Other such stable manufacturing environments will also likely benefit from a Kanban system.

Many companies we visit would not describe themselves as having a stable demand of any particular product, in fact the opposite is quite often the case, high product variety and low volumes. In these circumstances a Kanban system may not be suitable for the entire production process but there are probably sub areas where a Kanban system of one form or another will aid production planning and material control. Ideally the work carried out by the operations covered by the Kanban should also be as well balanced as possible.
There are a number of different Kanban flavours or variants, this article will concentrate on the simplest forms.

Product Kanban

Product Kanban is the most straightforward form of Kanban. It can take a number of forms but essentially does the same job. Production or materials ordering upstream is only carried out when a downstream operation signals it is needed i.e. a component is used downstream and it is simply replaced. The signal may be a painted square on the ground (when the square is empty of components then that is the signal to produce upstream), a card (when a component is used a card is passed upstream) or even so-called fax-ban or e-ban. Whatever the signal the effect is the same when a set number of components are used (1 – 10,000 depending on the component) then and only then will upstream operations receive the authority to begin production or order a specified number of that component to fill the requirement.

Emergency Kanban

An emergency Kanban allows for rush jobs to be carried out. If a job is to be rushed through production then it has to be given priority in some way or another. This can be achieved with different coloured Kanban cards say Red. If an operator has a stack of cards to produce to, then the red card would be carried out first allowing some orders to be carried out more quickly.

Kanban rules

1) A Kanban signal is only issued when the component it represents is used.
2) No Kanban no part (i.e. components are only made or issued when a Kanban exists).
3) Only good components are issued.
4) No over production
5) Components are only manufactured in the order the Kanban cards are received (unless emergency Kanban's are in use).
6) Components are only manufactured / issued in the number specified by the Kanban.
7) The number of Kanban cards should be reduced over time and the problems that are encountered by doing this should be tackled as they are exposed.
Calculating the number of cards
The number of Kanbans required can be calculated as follows.
Number of Kanbans = (Demand in period x Order Cycle time x Safety stock) ÷ Batch size (or container quantity)

Conclusion

This short article begins to explain the basic concept of a Kanban system. Kanban is a very simple and effective production control system that can be easily introduced in many production environments. Proper use of a “Pull” system is often seen as a large step towards achieving true JIT (Just In Time) production.

If you have further questions about Kanban or would like help in implementing a Kanban system in your factory then the SWMAS can help you. Please contact our help desk (0845 608 3838) and arrange a visit with one of our manufacturing specialists.