A couple of days ago, I got in a great discussion with my colleague and fellow lean thinker Gene. Our discussion was about lean versus six sigma and its unique applications. In industry, companies seem to focus on one or the other – recently, the balance has been on the lean side because of the success of the Japanese automotive industry. The company that we work for has focused predominantly on lean and the creation of flow. Gene mentioned that he was doing a value stream map at another site and noticed that one kaizen burst was a clear candidate for a six sigma project. The problem was that with a focus mainly on lean, the site lacked the six sigma bench strength. There aren’t really tools in the lean toolkit to solve highly advanced multivariable problems. Lean focuses on eliminating waste and creating flow but does it really have the ability to reduce inherent process variation? Standard work to an extent can reduce variation, but doesn’t address those complex situations where you have many interacting and confounding inputs affecting a key output. Many argue that lean has the element of practical problem solving but really there’s only so far you can get with a fishbone and a 5-why.
Opportunities for six sigma projects can be identified during value stream maps when rework loops or yield problems are prevalent. The power of six sigma is in reducing process variation through creating controls of primary input variables. This is accomplished through the use of the DMAIC process and a rigid set of statistical tools. Hypothesis testing to determine if differences/changes are actually significant is so critical when trying to solve problems but this tool isn’t taught in many practical problem solving systems. Hypothesis testing is a fundamental tool in the six sigma package.
Lean and six sigma really have to go hand in hand. If the company focus is on lean, then there needs to be some six sigma bench strength it can draw on when the need arises – and vice versa. You can’t create flow until you create stability and the six sigma statistical toolkit helps you create stability.