100% Efficiency is Not the Goal

As we do in each of our trips to benchmark the best lean companies in Japan, on our latest trip in March we visited Toyota. One of the surprising things to come out of this visit and later on our Q&A time with them was that Toyota doesn’t want their line to operate at 100%.
To Toyota, 100% efficiency means that the employees are not stopping the line. They are not finding opportunities for kaizen. The manager there told us that they think a good goal is 97% or 15 minutes of downtime in 8 hours. This efficiency number indicates to the management that the workers are hungry to find defects and problems. They have the mindset and eyes for kaizen.
A little background information. In a Lean Manufacturing facility, the idea is to stop the production whenever a defect is found. This is called Jidoka, and it is how people ensure built-in quality. This is often done by pulling on a cord or pushing a button to stop the production line. The defect or problem is fixed and then the line gets moving again. Workers are told that besides their normal job of value-added work, another part of their job is to “stop the line” when something is not right.
There is a healthy tug of war between workers and managers. Workers are told “stop the line!” Managers who are told “don’t let the workers stop the line” This means not that workers are scolded by managers when the line stops, but that managers should actively find ways to error proof and make it harder to find problems because there are fewer problems.
To have daily, persistent kaizen, 100% efficiency (or line uptime) is not the goal. This is yet another counterintuitive lesson from Toyota, the masters of Lean.