Why does Six Sigma need Lean?

There has been much written about both Lean and Six Sigma and many within the business improvement industry have promoted the use of both techniques combined as Lean Sigma, but just why do the experts say that you should use both techniques in tandem?


Process Improvement.


Six sigma seeks to reduce variation in a process through extensive study and analysis, often a six sigma specialist will spend 3 or 4 weeks collecting and analyzing data only to discover that there are significant differences in performance between personnel , different shifts or between different machines within the same process. These are all issues that would be addressed through some of the basic lean tools without the need for extensive analysis; most of these problems are expected and would be tackled by someone experienced within lean by implementing tools such as the 5S to implement standardized processes across shifts and personnel thus minimizing differences in performance.
An example of this could be seen in a six sigma project that I recently became involved in after it had been running for several weeks. The aim of the project was to minimize setup times on a group of machines; the specialist had measured many individual setups and graphed them all and quickly realized that he had multi-modal distributions for the data and needed to make more analysis to discover the reasons for this. The reason was pretty obvious and was down to each operator having slightly different methods for conducting their setups; this of course led to differences in times between each setup beyond normal variation. The lean approach would have just been to just jump into applying SMED or single minute exchange of die which would have standardized the method between shifts and operators removing the special causes of variation which were evident in the six sigma specialist’s data, thus saving the time spent on the initial data collection.


Strategic vision for business Improvement


Another problem that lean can address with six sigma is providing an overall aim for the business; at times you may spend time improving the efficiency of a process that is on the whole waste and adds no value for the customer. You get better at doing something that the customer does not even want and certainly does not want to pay for. This can be a problem for poorly implemented lean projects also, but lean provides tools such as value stream mapping that help you define an ideal state for the business. This ideal state then becomes the focus of defining what processes need to be improved, which can then be targeted with both lean and six sigma techniques, projects that look at processes throughout the whole value stream including office and service areas not just manufacturing.


Team Working


The greatest strength that lean adds to any six sigma project is involving the people, traditional six sigma is very much expert led and defined and is often implemented on the people in a working area; this can, and does, lead to resentment and resistance to any improvements. Lean’s team approach can better ensure that the people in an area understand the reasons for change as well as getting their enthusiastic support for change.
“Lean sigma” or “lean six sigma” is very much the way to move forward rather than either one in isolation; lean’s team working and simple tools to achieve standardization provide a firm foundation on which to use six sigma to reduce variation where standard lean tools fail to address the issues.

An example of a large company that uses both ideas together is General Cable which has factories in over 20 countries and is one of the world’s biggest consumers of copper. The companies CEO sang the praises of using the two techniques together at the 2012 Industry week best plants conference where he explained how his work force enabled the company to stay competitive within its global market place by using lean six sigma.

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