The Psychology of Quality and More

Further Kanban

Quality Tools > Tools of the Trade > 61: Further Kanban

In a previous article we looked at the basics of kanban. This month, we will explore a little further by discussing some of the different types of kanban that are used. In particular, the dual-card kanban system is shown in detail.

Dual card kanban

 The dual card kanban (also known as the Toyota system) employs two kanban cards, one for the supplier process, also known as the production kanban or P-kanban, and one for the customer process, also known as the conveyance kanban, or C-kanban. These are most useful in complex flexible systems. The sequence of actions is shown in the following diagrams.

Figure 1 shows how, at an assembly (or ‘customer process’) point, when the parts being used (often being assembled with other parts) go below a certain point that is defined by the Kanban card, the card is place out for the Materials Handler, who goes on a circular route from the stock point to the assembly point, replenishing parts as needed.

Fig. 1. Pull of parts

In Figure 2, the Assembler now can use the parts provided by the Materials Handler, who now takes the C-card to the stock point to get more parts. Note that at the stock point, there is a P-kanban card with the parts.

Fig. 2. Going to stock point

In Figure 3, the Materials Handler takes parts from the stock point to complete the requirement on the C-Kanban card. The P-Kanban card at the stock point is moved to a special rack to signal to the supplier cell that more of these parts are required.

An important point here is that the C-Kanban card has the same number of items on it as the matching P-Kanban card. If they did not match, the stock point would either run out of parts or a pile of inventory would build up. This the key aspect of the ‘dual card’ kanban.

Fig. 3. Taking parts from stock point

In Figure 4, the supplier cell takes the P-Kanban card from the stock point and uses this to trigger the manufacture or assembly of parts as defined on the kanban card. Another material handling loop may happen here, as needed. If the stock point is next to the supplier cell, then this is not necessary. This is a good reason for the stock point to be next to the supplier.

Fig. 4. Taking kanban to make new parts

Finally, Figure 5 shows how the supplier process, having completed the kanban order, puts the parts along with the matching P-Kanban card into the stock point, ready for the Materials Handler to pick it up in the next circular trip.

Fig. 5. Supplier completes Kanban order

The kanban square

 Kanbans do not need to be pieces of paper or card. One version is the kanban square, which is simply a rectangle or square painted on the factory floor. When it is empty, this is then the signal to re-fill it with parts. This is typically used for large items, for example that need to be moved with a fork-lift truck.

The kanban container

The kanban container is like the square, but is a moveable container. Kanban containers often are shaped to contain a fixed number of parts. For example, a kanban container for simple spindles may be a block of wood drilled with 12 holes, thus limiting it to contain a dozen parts. This may have a slot in it for the kanban card, or the kanban instructions may be attached to the side of the container.

Next time: Back to basics: Variation and the central limit theorem

This article first appeared in Quality World, the journal of the Chartered Quality Institute