In a recent conversation I again found myself between two smart blokes, one who was a black belt 6 sigma consultant who believed the problems of the world could be fixed by some aggressive, numerical focus on process improvement, and an exponent of Lean, who was of the “build the right culture and they will come” school.
To my mind, they are both right, and both wrong.
Six sigma means defects of less than 4/million. This requires rigorous emphasis on elimination of anything that creates variation in a process, or series of processes, ensuring that the output is exactly the same every time. Good six sigma implementations take great care to ensure that the output of the processes that are so exactly the same are adding value to the customer, but this can become lost in the welter of statistics and process control mechanisms.
Lean, by contrast starts with the macro question of “what customer value does this process add? What would the consumer prepared to pay for it?” Anything that does not add value to the customer, inventory, rework, excessive movement, and others, is deemed to be “waste” and is rigorously targeted for improvement using the old “Plan, Do, Check, Act” process, the ultimate objective of which is “flow” through a process.
The tools of lean and 6 sigma are widely interchangeable. I have seen 6 sigma implementations going through a 5S process, essentially a lean tool, and Lean implementations using SPC extensively to identify and manage out waste in a process.
It can be said, as my conversationalists did, that 6 sigma is an analytical, quantitative tool box, and Lean is a Cultural, management alignment toolbox, and they are both right, and both have their place, indeed elements of both are essential to competitive improvement.