There are different ways to integrate Lean and Six Sigma. It is difficult however to see the two systems at the same level. We see Lean much more as a philosophy, a way of thinking, a way of looking at the business world. Within that philosophy Six Sigma is a very powerful tool to address problems that prevent the application of the Lean philosophy.

Not all methods of integration see it in this way. Very often Six Sigma is used as the base and Lean tools are added. There is nothing wrong with that but it limits the possibilities created by using Lean as the business philosophy.

Lean as philosophy and apply Six Sigma when needed

Anyone who has been involved with Lean knows the word “Muda” meaning "Waste" or "Loss". Lean is often and wrongly reduced to the slogan “Eliminate Waste”. But even within this very narrow definition integration with Six Sigma is possible because part of the waste can be caused by excessive variation.

Within Lean this is known as “Mura” and it means variation (generally of an input) that leads to “Muda”.

In addition to this, there is also something called “Muri” that can be translated as “frustration”. This is an ideal way to discover opportunities for improvement, especially in service industries when there are no data available. Frustration generally is the result of a systematic problem.

Add Lean tools to the Six Sigma toolbox

The base for this integration is the problem solving capacity of the Six Sigma DMAIC cycle. The focus is no longer on the Lean philosophy but on the practical use of some of the Lean tools.

In part this is related to the fact that projects that address througput time reduction, on time delivery, better service, … are not always suited to apply a lot of statistics. Moreover, some of the Lean tools are very powerful to show the weak points in a supply chain.