A two-bin system is a kanban method used to simplify replenishment on a production line.
Click the image to see how kanban cards work.
The process is simple. An operator pulls from one bin until it is empty, and then, depending on how the kanban card is attached, either turns in the kanban card (if fastened by hook and pile), or turns in the whole bin (if the card is permanently fixed).
The operator then pulls from the second bin while the order is placed for materials to fill the first bin. If all goes well, the first bin is filled and replaced when there are a few items left in the second bin.
The two-bin system is generally designed with a bit of safety stock, hence those extra parts. If things don’t go well, the safety stock is used while the delays are resolved. The bigger the potential for problems, the larger the safety stock.
A two-bin system is the most common form of kanban you will likely see. Parts using more than two kanbans are possible, but are generally used for local replenishment or for special situations.