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Lean Manufacturing and Six Sigma are two of the most popular improvement initiatives utilized by major corporations. Many companies employ both methodologies combined under the name Lean Six Sigma.

Many companies are struggling to determine which initiative will bring the most impact for their organization.

It is critical for those individuals tasked with making the decision to understand the differences between lean manufacturing and six sigma.

First of all, they are both improvement initiatives. However, they are very different. Both are a collection of various 'tools'. For example, lean utilizes the tools of 5S, SMED, value stream mapping, takt time, standardized operations, error proofing, kaizen, line balancing, cellular manufacturing, and many others. Six sigma utilizes the tools of process mapping, FMEA, Cause and Effects Analysis, statistical analysis and process controls, regression analysis, design of experiments, and many others.

Lean manufacturing is a much less structured and is often viewed as the low hanging fruit of opportunities. Lean manufacturing initiatives often employ the Plan-Do-Check-Act (PDCA) model, while Six Sigma utilizes the Define-Measure-Analyze-Improve-Control (DMAIC) model.

When companies combine the methodologies into a 'Lean Six Sigma' initiative, most will utilize the DMAIC model and utilize lean tools where applicable. For example, when the six sigma project is at the Improve phase, a line balancing exercise could be used.

The PDCA model utilized with lean is often a quick process compared to the DMAIC model. Lean projects are often completed in hours or days, whereas most six sigma projects will take weeks or months to complete.

The lean manufacturing method is more of a 'just do it' approach. The project might be planned, conducted, checked, and acted upon in the same day. For example, a manufacturing line might be changed to a U shaped cell in the morning, and fine tuned in the afternoon.

Maximum improvements are obtained when the tools are not forced into use. The business problem, challenge, or opportunities should point to which tools should be used.

For example, if a business wants to cut cycle time, it could be a six sigma, lean manufacturing, or combined project, depending on the complexity of the issues. If the setup time is the majority of the cycle time, a SMED project or simple kaizen event may obtain the improvement. If the entire supply chain is complex and the problems (opportunities) are not obvious, a six sigma project might be necessary.

The key is to determine the business problem first, and then decide which tools are necessary to solve it.

Most companies employing six sigma conduct the DMAIC phase model. Most of these projects range from a few weeks to several months. However, there is an emerging trend of utilizing the DMAIC model even if the project will only entail the use of lean tools. Proponents of this method believe the DMAIC model adds structure to lean projects, even when used in a quick manner.

Regardless of which methodology a company chooses to use, lean tools should be part of it. Utilizing six sigma tools without lean tools would limit the improvement potential of many projects. Also, lean tools alone will not solve all business problems, and six sigma increases the probability of success.

The bottom line is a company will benefit most to have both lean manufacturing and six sigma expertise. Although it may be difficult to have people with expertise in both disciplines, any expert in lean or six sigma should have a good understanding of the other

If possible, individuals should continue training until expertise is gained in both methods. When there is no bias toward one discipline, it is easier to keep an open mind as well as an understanding of which tools are best to solve a problem.

In summary, let the business problem determine the tools to use, rather than try to fit a tool to a problem.