The Relationship of Lean and Six Sigma

I was recently asked how lean manufacturing and six sigma are related. The great discussion also wondered which one was better and if one would overtake the other. The context of the conversation was "the next big initiative in quality".

Well, if you have traveled along the path to lean, you know that one of the key pillars of success is having perfect quality. Lean is about being quicker. Shortening the distance between your products and/or services and your customers. If your process flow abounds with high scrap rates and your machines can't stay operative for extended periods of time, lean will only be a dream.

So, quality must be perfect. Easy to wish for but hard to accomplish. Not impossible though. With the right tools and old fashioned perseverance, you'll get there.

Right tool.... That's where six sigma comes in to the picture. It is, among other things, a tool to improve quality. To optimize processes. To target and reach a goal of perfect quality. That's what six sigma means.

Traditionally, when we discuss process capability, we say that plus/minus 3 sigma (or six sigma) must fit within the customer's tolerances. Six sigma means that plus/minus six sigma (or twelve sigma) must fit within the tolerances. In other words, the standard deviation really needs to drop.