Origins, evolution and thoughts about Kanban
1. The need, the Just-In-Time attitude
The resolute and clear Toyoda Kiichiro’s message stated at the end of WW II “catch up with America in three years, otherwise the Japan’s automobile industry won’t survive”, surrounded his team by enthusiasm and faith. This was the environment where Taiichi Ohno and his collaborators started to innovate and make more Japanese the occidental mass production system.
“catch up with America in three years”
The enormous success of Ford’s Model T, was the result of economic wealth of the American society at the beginning of the Twentieth Century, where the market could assimilate almost every product proposed by the industry, especially products with identical features, typical of the mass production system. The whole process of production of large batches of Model T, a car which was sold as fast as it was built (push system), was hiding big amounts of waste, typically called overproduction.
Forty years later, in Japan, the economy was stagnant; still the Japanese people needed to own cars. All this encouraged Toyoda to create an innovative production system, in order to be able to manufacture a wide range of car in small batches, while being economically profitable: this goal (the variety of models) was challenging hard the Ford’s Model T production system.
Small batches, greater responsiveness of customer’s demand
In order to avoid manufacturing and stocking unsold cars, Toyota manufacturing policy changed and set to meet exclusively the actual demand/sales (pull system). Offering more than one model with different customizations, pushed the Japanese car manufacturer to start producing in small batches by enhancing his flexibility and managing fast changeovers, in order to keep the production efficiency level unchanged. As said, the variety of the offer triggered a positive response and the reduced reaction time to customers’ demands allowed to manufacture only what was requested at the exact time, or as Toyota called, the Just-In-Time.
2. The tool, the Kanban
One of the Just-In-Time weapons was the innovative concept of Kanban, literally a tag which lead the production in a direction opposite to the traditional system (pull), an idea borrowed ”from the analysis of a supermarket customer who gets the commodities when and in the exact amount s/he desires. The later process (customer) moves to earlier process (supermarket) then buys the products (commodities) which activates the process of production (shelf replenishment)”.
The supermarket/customer process was brought to the shop floor by using a visual tool as Kanban, a data tag which allowed every operator (assigned to each subprocess), to get the right information at the right time; reading the car’s feature reported on Kanban (later process), the operator picks up the right items (earlier process) to complete the assembly procedure (earlier process) so the partially assembled car can move to the next step.
Only a perfect and detailed daily production plan can support the Kanban: an unexpected and little change of the planned schedule can nullify the whole process. Let’s imagine one step of a process, e.g. the bumper installation, which might not be completed because the previous car (with the changed Kanban) used one extra rivet contrary to the initial production plan, leaving the rivet basket empty. Without stabilization and accurate planning the workflow might be interrupted making the Kanban useless.
Another important feature of Kanban, is its capacity to keep high quality standards, stopping the production (by andon) whenever a defective item is discovered, both preventing the use of another unconformable item, and turning on an analysis on what is wrong.
Toyota took almost 10 years to fully integrate the use of Kanban within its processes
I’d like to emphasise the fact that Toyota took almost 10 years to fully integrate the use of Kanban within its processes; behind a simple tag, and its impressive goal of avoiding overproduction, there are several hours of work and tests, to make such an innovative tool efficient and effective.
In my work experiences I saw Kanban used inappropriately during multiple occasions, but the most dangerous one is the recurring (and undisciplined) use of it as a tool to get an unplanned item by bypass the production plan.
In this manner the Kanban loses its precious ability to arrange the workflow as Taiichi Ohno said: “the kanban method is the means by which the Toyota production system moves smoothly”.
“the kanban method is the means by which the Toyota production system moves smoothly”
More discipline during the planning phase and the standardization of all processes are the minimum required steps to achieve the real meaning of Kanban. This is the only way to improve the manufacturing process, and to finally justify the (common) assertion “Yes, we are certainly using the Toyota model”.