Lean Manufacturing vs. Lean Six Sigma

February 1, 2011
By Darren Dolcemascolo

There are two major competing initiatives in the marketplace today for continuous improvement: Lean Manufacturing (e.g., the Toyota Way/Toyota Production System) and Lean Six Sigma. In this article, we will compare and contrast the two approaches. I have been involved in implementing both methods and continue to teach both methods.

Let's consider the Lean Manufacturing or Toyota Way Approach. This system is an approach to eliminating waste or non-value-added activities in an effort to provide a high-quality product/service to the customer at the lowest cost and in the shortest lead-time possible. When undergoing a lean transformation, we utilize tools like value stream mapping to systematically identify opportunities for improvement (or kaizen, change for the better). We then use the time-tested PDCA (Plan Do Check Act) approach to implementing and sustaining solutions. The solutions might include tools like one-piece flow, kanban, 5S, and other tools, and we might use a kaizen event approach for rapid implementation (though this is NOT required). Lean becomes part of the culture when employees at all levels are utilizing the concepts of problem solving and eliminating waste on a regular basis (as part of their regular jobs).

A Lean Six Sigma program is based on the Six Sigma DMAIC (Define Measure Analyze Improve Control) approach to solving problems. It is also based on the concept of eliminating defects, which are defined as failures to meet customer requirements. Projects are typically selected based on the best return on investment/financial benefit; very often but not always, Value Stream Mapping is used to identify opportunities. Each project is assigned to a team typically consisting of a Black Belt (Lean Six Sigma trained expert) or Green Belt as a leader plus several team members. Using the DMAIC approach, the team solves the problem at hand, implements solutions, and puts controls in place to sustain the improvement. The team will typically use six sigma tools such as process mapping, data collection, process capability analysis, hypothesis testing, cause and effect analysis, graphical analysis, Design of Experiments (DOE), FMEA, and many others to solve the problem; if the problem lends itself to the lean tools, very often they will be utilized. Typically, it takes longer for a lean six sigma program to drive to all levels of employees; however, the program itself tends to be more structured on average than a lean program.

Below is a chart comparing lean manufacturing and lean six sigma, which may aid in understanding the two approaches.

System Lean / TPS Lean Six Sigma
Philosophy Eliminate Waste Eliminate Variation / Defects
Improvement Process / Cycle PDCA DMAIC
Tools VSM, 5S, Standard Work, Leveling, SMED, Flow and Pull, Poka Yoke, Problem Solving plus other Quality Tools Process Mapping, SIPOC, statistical methods, DOE, Control Charts, plus lean tools

Some companies view Six Sigma as their prevailing, culture-changing program and add lean tools to their Six Sigma toolbox. These will typically embrace a Lean Six Sigma program. Others have lean as their program of emphasis while integrated necessary quality tools into their program just as they are a major piece of Toyota's system. Either approach can work. In general, the toolsets necessary to make improvements will be the same. The approaches to improvement are different (Six Sigma projects versus Lean kaizen events, day-to-day kaizen activities, and problem solving teams).

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