what is kanban?.How does the kanban system work?

Kanban

The literal definition of kanban is composed of two words in Japanese which: kan means "visual," and ban means "card" or "board".
So Kanban was to become Visual Board or visual card, but its use goes beyond a simple visual management, also called "card system" and its implementation is regularly accompanied by cards that are attached to the materials and serve as a signal to produce a part or batch of parts.

Kanban does not have to be a card, another definition of kanban is "signal", kanban is a sign that tells us we have to perform a certain task (like a traffic light). An empty space inside a supermarket its (kanban) the signal that may indicate that it is time to produce a part, a space in the production line may be the signal for placing new parts if we talk about supplying material .

Where the Kanban system born?

Toyota is famous for its Toyota Production System (TPS). Toyota builds its vehicles with more than 25 000 parts that come from suppliers around the world, imagine the chaos that takes to try to manage inventories generated by all these parts, excluding different styles and models of vehicles made, talking about a very large number of parts.

As we know inventory generate cost associated with space, plus associated costs required to maintain and manage these inventories, a very large inventory of parts can hide defects, imagine that there is a part with an inventory of 100 000 pieces having a defect  that due to the large inventory has barely begun processing on the line and the customer has noticed that the part do not join properly, the cost to repair or convert to scrap the parts is greater because they are too many pieces and could have been avoided or minimized by maintaining a lower inventory of parts, it is not the intended of kanban but allow to describe that inventories are hidden costs and increase the lead time of a product and finally Lean looks for minimize the Lead time.

Imagine also the amount of surplus and / or missing parts that could have, lack of flexibility in the assembly line and the incredible management that would be required to supply the parts to the line without a sign, without a kanban to give us the exact  point in space and time and the exact number of parts required in the assembly line.
Kanban as a Just in Time subsystem (JIT) is then used to transport the parts to the customer (in this case Toyota) to ensure that the exact number of pieces is produced by the supplier with the same rate that marks the assembly line , helping to eliminate waste MUDA

How does the kanban system work? 

There are several types of Kanban but can be classified into two: Parts Retrieval Kanban  and the Production Instruction Kanban, both have the part number and quantity of parts needed.

Kanban as a Signal:

An empty space may be the kanban signal indicating that a part is required and must be provided.