Kanban is a key tool used in operational excellence, and more specifically in Lean and Lean Six Sigma systems. In the 1950s, when Taiichi Ohno observed the pull system established in American supermarkets, he adapted the term to describe a signal that triggers production from one process to another, based on what has been consumed. Today, the term Kanban can be translated to mean “visual signal,” and is typically implemented in pull systems, where a process is executed based on actual demand rather than predictions or forecasting.
Kanbans can be used in every business environment, from assembly lines to doctors’ offices. Manufacturing facilities use a variety of Kanbans to keep production lines moving. The visual signals alert employees to dwindling stocks or to perform the next step in the process. The purpose of Kanbans in a manufacturing environment is to regulate the pace of work that moves through assembly or production. Materials are not pushed to stations; rather, they are requested when needed. Signals in the form of lights, cards, tape and empty bins all signal the need for products or information.
Doctors’ offices use a simple Kanban system that often goes unnoticed by patients. When you check-in, your chart is placed in a special box to indicate your arrival. This signals the nurse to take you to an exam room and to perform certain preliminary activities. Your chart is then placed in a bin outside the room. This signals the doctor that you are ready to be seen. The doctor does not come looking for you until signaled to do so.
There are three types of Kanbans.
- Kanban Square is a marked area designed to hold items. In a work cell with continuous flow, Kanban squares are located between each process and can only hold one piece of product, assembly, or information based on the consumption of the previous process. The X’s are the signal to work. As work is completed at each station, the X’s signal the need for more work. The work being held in the Kanban square delivered from the preceding station moves into the work station and the cycle continues. Workflows one way, while information, or the signal to work, flows the opposite direction. In this way, work is delivered as it is needed.
- The Signal Kanban is a triangular Kanban used to signal production at the previous workstation. It is typically used between processes that cannot afford the changeover time associated with producing parts in the order that they were withdrawn. Signal Kanbans are calculated and placed within inventories so that they come to the workstation with enough materials to cover production time. As inventory is removed, the triangles are revealed. The triangles are moved to the signal board to alert the previous workstation that inventory is needed. When inventory is replenished, the triangles are replaced. The order of the triangles must not be changed unless production schedules are altered. If the order of the signals is altered customer demand may not be met.
- The Material Kanban is used to order material in advance of a process. There are three types of material Kanbans. A “Production” Kanban triggers the production of parts. A “Withdrawal” Kanban is a shopping list that instructs the material handler to get the transfer parts. “Supplier” Kanbans signal the supplier for more raw material.
The benefits that Kanbans create for companies translate into savings for customers. Companies that implement Kanbans have increased on-time deliveries. Because they are triggered before the parts or services would be needed, Kanbans eliminate the delay workers would spend waiting for those parts or services. Fewer delays in the production process result in a higher likelihood of delivering on time.
Because Kanbans have reduced unnecessary inventories, they decrease lead times in processes. Parts and information can move smoothly through the process, reducing delays and eliminating bottlenecks.
Improved quality is another benefit of Kanbans. Because Kanbans help to smooth the flow of the process, quality problems produced by overburdening and unevenness are reduced. Reducing inventories and creating more streamlined operations also allows companies to reduce their operating costs. This results in lower costs for customers.\
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