Single-piece continuous flow is the most effective and cost-efficient way to produce or process anything. It is what lean is all about. However, we also realize this is not always possible. There are steps within the process that run at dissimilar speeds. If the process steps or equipment speeds cannot be synchronized or changed, we need to inject a buffer inventory into the systems so as to simulate single piece continuous flow.

Kanbans are signals which automate the replenishment of repetitively used materials and supplies from internal or external suppliers to the buffer inventories. Kanbans reduce outages and shortages of materials and supplies, which improves customer service levels. Kanbans support “pull production” and continuous flow, since material is not produced at the supplier until a signal to replenish material is received from the customer. Using this approach, kanbans will reduce overall inventory levels (30 percent reduction on average).

Kanbans can be used anywhere in the organization where there is repetitive usage including: maintenance supplies, janitorial supplies, raw materials, office supplies, etc.
The type of signal used in a kanban is only limited by your imagination, but there must be agreement on the type of signal and the information it contains between the supplier and the customer. (In general, all kanban development is accomplished by negotiation, at least for the first few kanbans, between the supplier and customer.)

Note that kanbans are the most efficient at eliminating waste when the signals are returned from the point of use (customer) to the supplier. Sending the signal back through purchasing so they can cut another purchase order to the suppler is not a kanban system.   

All signals must contain the information that the supplier needs to replenish the material. The following information is typical.

Figure 1.

Note the above “number of containers” also means the “number of kanban signals.”   

Other information that might be included:

  • Previous operation
  • Time/date of delivery
  • Where used (in what model number)
  • Storage area (the goal is to have suppliers deliver to the point of use) 

Examples of other kanban signals include:

Figure 2. Container Kanban

The empty container is sent back to the supplier for refilling.

Figure 3. Faxable Kanban 

On the way to delivering this material to the production line, the material handler stops at a conveniently placed fax machine and faxes the kanban card back to the supplier.

Figure 4. Office Engineering Plotter Kanbans

As plotter supplies are used (ink cartridges and paper), the faxable sheets are sent to the supplier (the engineers send the signals).

Figure 5. Internet Kanban

The internet kanban allows an external supplier to monitor in real time the inventory levels of a raw material that is stored in a bulk storage tank. The weight of the material is converted by a load cell into a fill level. The supplier then decides when to give themselves an order to produce more material, and when to ship it so the customer does not run out.

Figure 6. Shipping Trailer Kanban 

When material usage is very high, the material is only unloaded from the trailer as it is used. In this case the supplier has two full trailers on site. When the first trailer is emptied, the signal is sent, and the second trailer is backed up to the dock.

When kanbans are developed through negotiation with both your internal and external suppliers, the outcome will be a win-win.

About the author:
Larry Rubrich is the president of WCM Associates LLC. For more information, visit www.wcmfg.com or call 260-637-8064.