Both claim to improve processes through eliminating waste. However, Lean and Six Sigma define and reduce waste in a very different way.
Below a very short but accurate description between the core differences and the consequences for applicability.
Lean's approach is basically: eliminate Non-Added-Value-Activities (NAVA), improve Added-Value-Activities (AVA). Or in plain English, do and only do the right things.
Six Sigma is all about eliminating variation in the process. Or in plain English, do and only do the things right.
On first glance Lean and Six Sigma are born to be married: doing the right things AND doing the things right.
There is however one small requirement for Six Sigma to work that is way too often overlooked. Six Sigma is about reducing variation. Reducing variation is only possible when you can measure it. And in order to measure it you need the same process doing the same things. The more frequent and in the larger volume the same things are produced, the better Six Sigma can be applied. Equally true is the opposite: the lower the frequency and/or the volume, the less useful (and too often the more destructive) Six Sigma is.
Six Sigma brings standardization, uniformization, discipline to the procedure. Anything else adds variation and must therefore be eliminated. There is no room for thinking while executing the process. Hence the fact that Six Sigma works very nicely in highly automated high volume production streets.
Lean on the other hand is very different. It thrives when people are thinking, experimenting and trying alternative approaches to see what works and what doesn't work. All in the pursuit to boost AVA and remove NAVA. And the truth of yesterday, might be the problem of tomorrow; what was wrong yesterday, might be the thing to do tomorrow.
- Highly volume, high frequency, AND preferably no 'individual creativity'
- Do 6 Sigma
- Lean thinking/practise only 'outside' the regular production process
(mind you: doing the wrong things right = serious problem!)
- Low volume, infrequent OR rapid adjustment required to new (unpredictable) changes
- Lean thinking & practise in the regular production process
- Use the 6 Sigma books for wobly tables
(don't be afraid to 'reduce' the size of the book)
This is what 3M, one of the earlier adoptors of Six Sigma, has to say about it: