How Lean and Six Sigma Co-exist

by Enrique Bekerman

Lean Six Sigma has grown out of the realization that the two systems, Lean Manufacturing and Six Sigma, can not only co-exist, but actually complement each other.

There are many ways of approaching this "merger".   If the problem is complex and requires careful definition and analysis, the DMAIC approach and the Six Sigma statistical tools should be used.  Depending on the problem, and the process, a VSM (a Lean tool) along with SIPOC and VOC (6 Sigma tools) can be used during the Define phase to fully understand the problem.

As waste is identified, the type and complexity of the problem will dictate whether to continue to follow a DMAIC approach for a specific problem or whether a Lean Tool is more appropriate such as a Kaizen Event, 5S implementation, production cell, etc. In general, if the problem involves organization, lack of flow or speed of delivery, most likely a Lean tool would be used.  Lean solutions are meant to be low cost solutions; Six Sigma evaluates solutions based on cost/benefit analysis.

There is a difference in problem solving attitude.  Lean has a "Just do it" approach. An "imperfect Lean Solution is better than no solution".  Six Sigma is more methodical and is best used for the more complex projects requiring careful analysis. The "low hanging fruit" are often dealt with a  Lean approach . It never makes sense to take a DMAIC approach when the ideal solution is evident.

 Although both are methods for Continuous Improvement, Lean tends to be incremental in nature with small gains adding up over time to great gains, whereas, Six Sigma is a breakthrough method looking to make significant changes to the underlying process, resulting in major quantifiable impacts.

While Six Sigma’s main focus is defect reduction by reduction in process variation, Lean focuses on waste elimination and flow.  However, Lean also uses "Poke Yoke" or mistake proofing to prevent defects. So you can see how they complement each other.

In some companies, quotas are given to Belted employees to produce a number of Six Sigma projects and projects that can be easily handled by other means are called “Six Sigma” to comply with the expectation.  I have also seen some large companies that have a Lean Department and a Six Sigma Department. That separation does not make sense and conflicts can arise. A good Lean Transformation involves all employees, whereas, Six Sigma is often limited to technical and management people.

The combination of Lean and Six Sigma is very powerful. Any conflicts between the methodologies should be easily resolved once their unique characteristics are understood.