The Difference Between Lean and Six Sigma
Lean vs Six Sigma
While it may be desirable to use both lean and Six-Sigma, they are separate issues. An operation can be lean and still have an unacceptable level of variation in the output. It can also have the variation under control and not be lean. The two are complimentary, but neither is dependent on the other.
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While Lean encourages daily, general improvements, Six Sigma demands data-based, specific improvements for specific projects.
Lean doesn’t require a hierarchical structure of qualified “masters” to implement the changes. Every individual employee, regardless of their roles in the business is encouraged to participate in actively improving the manufacturing process.
Six sigma requires a hierarchical structure of various experts with various belts, signifying their level of experience and knowledge in the Six Sigma way.
With the Lean approach, you can walk into your factory today and instruct everyone on what to look for and give them methods for applying changes they see fit.
With Six Sigma, you’ll have to hire a certified expert who will assemble a team, identify a problem, and direct that team until the problem is solved.
In Lean, you let everyone test and experiment to see what works and what doesn’t – a bottom-up approach.
In Six Sigma, you let the qualified professional leading the team decide when you’ve completed the project – a top-down approach.
Which to do first? Lean or Six Sigma?
Undoubtedly in an ideal world you should do Six Sigma before lean.
If you do Six Sigma first, you’ll have a process that can reliably produce output that the client wants repeatedly. Then, use Lean to make that process very efficient and productive.
In other words, use Six Sigma when your process has a lot of variation or doesn’t always perform how the client wants it to. Use Lean when your process already delivers what the customer wants but the process itself needs to be more efficient or more productive.
Note that in the real world some management teams are more focused on efficiency and productivity than customer satisfaction, and in those cases Lean is the best choice. Also, it is sometimes helpful to do quick Lean activities so you can show improvements quickly (whether or not the customer cares about them) so you can build credibility to do the longer Six Sigma projects.
Tools Used by Both Six Sigma and Lean
In both cases process mapping and value stream mapping are essential. If you cannot define your process, how can you possibly know what is wasteful or what is variation? Once you have defined your process via a process map you can use value stream analysis to determine where the waste is.