This article is a general overview of the use of Six Sigma and Lean Six Sigma to improve manufacturing processes. We begin with a discussion of the origins of Six Sigma, where we also introduce its core concepts. Next, we look at the development of Lean Six Sigma and compare Lean and Six Sigma to illustrate how the two fit together.

Introduction to Six Sigma


Six Sigma was conceived by Bill Smith in the late 1980s while working as a reliability engineer at Motorola. Two years after implementation, Motorola was awarded the highly prestigious Malcolm Baldrige Quality Award. Winners of the award agreed to share their methods upon request. Smith cited this fact as the driving force behind Six Sigma’s rise to prominence in the manufacturing industry.

Regardless of why it became so widely known, the ideas, tools, and techniques are today staples of all ‘world-class’ process improvement teams.

What is Six Sigma?

Over the years, Six Sigma has taken on a variety of forms in its application, and as such, there is no single consensus definition. As you will see, this isn’t as confusing as one might imagine as descriptions are more or less the same ideas, with variations in wording.

At Evocon, we define Six Sigma as a data-driven process improvement methodology that reduces variation to improve quality.

For context and to illustrate our point on similar definitions with different wording, the American Society of Quality (ASQ), defines Six Sigma as follows.

Six Sigma is a method that provides organizations with tools to improve the capability of their business processes. This increase in performance and decrease in process variation helps lead to defect reduction and improvement in profits, employee morale, and quality of products or services.

A central theme is the application of “statistical thinking” to improve business processes and the belief that all work is a series of processes that can be improved. As mentioned in both definitions, there is a focus on the reduction of process variability as a means of eliminating defects and thereby improving manufacturing quality.

Reduce process variation with DMAIC

The idea that variation is the enemy of quality is not, in and of itself, new thinking about how to improve production quality. What made Six Sigma novel was its application of scientific rigor and statistical tools in the fight to reduce variation.

The Six Sigma process for reducing variation uses a cross-functional team to analyze all potential causes of variability within the production process. The successful team must develop methods to minimize these sources of variation to deliver the project goals.

Fortunately, Six Sigma has a defined project methodology to guide process improvement teams known as DMAIC.

The acronym DMAIC stands for the five phases of a Six Sigma project: Define, Measure, Analyze, Improve, and Control.

Want to learn more? Here is a DMAIC project example that you can explore.

What results have been achieved?

In the first decade of using Six Sigma, Motorola delivered $15B in savings. As the tools of Six Sigma spread, many other organizations have used them to provide large amounts of bottom-line savings. Including the likes of Honeywell, who saved $1.4B and GE, who saved over $4B in the first two years alone.

Most would agree that these are remarkable results that inspired many to become Six Sigma practitioners. Further, there is little doubt that these early successes contributed to Six Sigma’s growing prominence and importance to the manufacturing industry. But it is Six Sigma’s reliance on statistics that often inspires fear in newcomers.

Let’s take a look at the statistical basis of Six Sigma next.

Sigma and Statistics

The term ‘Sigma’ has its roots in Statistics. It describes the amount of deviation from the mean, or average, in a given sample set (a group of numbers). Specifically, sigma is one standard deviation from the mean.

In manufacturing, a process may be said to be at “six sigma quality”. This means the process is capable of producing less than 3.4 defects per million opportunities.

Thus, “six Sigma” is six standard deviations from the mean, which is illustrated below.

six sigma curve illustration

Stated another way, if the desired result of a production process is the creation of a part that measures within a design’s dimensional tolerances (aka a ‘good’ part), then when you run the process 1,000,000 times, less than 4 of the parts that you manufactured will have any defect.

That is an incredibly well-designed process and would be extremely challenging, if not nearly impossible, to create the first time around. At first, the only way this was possible was through continuous improvement using the methods of six sigma.

Later, a spin-off discipline was created called Design for Six Sigma (DFSS). A complete explanation of DFSS is outside the scope of this article. Still, we can note that the main idea of DFSS is to design processes capable of six sigma quality during the new product introduction process.

In the next section, we look at the relationship of SS to lean manufacturing and OEE.

Introduction to Lean Six Sigma

Lean manufacturing is well known in the manufacturing community as one of the most effective management philosophies ever conceived. A chief tenant of lean is the relentless focus on reducing waste in all of its forms.

The gold standard for measuring waste, otherwise known as losses, is the OEE metric.

We have learned that Six Sigma is a data-driven process improvement methodology that has resulted in literally billions of dollars in bottom-line savings since its inception by Motorola in the late 1980s.  But this point by itself doesn’t readily explain why the Lean and Six Sigma have been combined. Let’s turn our attention to this point now.

Lean & Six Sigma – Better together

It didn’t take long for those in the manufacturing sector to realize the complementary nature of the two improvement methods. This awareness began a gradual and general blending process of the two disciplines into what is now known as Lean Six Sigma.

Below is a comparison to illustrate how the two disciplines complement each other.

LeanSix Sigma
PhilosophyReduce wasteReduce variation
FocusProcess flowProblem solving
Main resultReduce flow timeUniform process output
Secondary resultLess waste, improves efficiency, reduces costLess waste, improves quality, reduces cost

Lean thinking considers the use of resources a waste unless value creation for the end customer occurs in the process. It also defines value as anything that a customer would be willing to pay for. Six Sigma focuses on improving quality by removing the source of defects by minimizing process variation.

At Evocon, we define Lean Six Sigma as the blending of these two methods in recognition that both approaches are powerful improvement tools that actually complement each other and mitigate inherent weaknesses.

Lean Six Sigma embodies a vast array of tools and techniques for process improvement. It has proven to be highly effective in projects that seek to improve cycle times, limit process variation, and reduce waste. On the other hand, projects that aim to remove constraints or involve new automation may not be well suited for the use of Lean Six Sigma.

Six Sigma Certification

It can take quite a while to gain competency in the breadth of skills needed to realize the benefits of Six Sigma. This led to the development of a path of education defined by a series of “belts” that certify skill levels and knowledge.

Many organizations offer training, and just as many manufacturers have developed in house programs to accomplish the same. As such, the certification of belts has no defined standard, which can pose problems, though this is outside our scope.

Generally, there are four levels of certification for Six Sigma:

  1. The first is the yellow belt. These are people who gain basic knowledge in two days of training or less.
  2. The next level is the green belt. These are employees with around two weeks of training. They work on projects but continue to work on other activities.
  3. The next level is the black belt. The black belt leads projects full time and usually has 3-4 weeks of additional training to that of the green belt.
  4. Finally, there is the master black belt. They have a broader focus, typically on an entire business group or function. The master black belt may require an additional week of training following black belt certification. Either way, they will manage at a high-level to define quality goals and metrics and direct project portfolios.
six sigma certification system

Wrap Up

We should stress that Six Sigma is a broad topic with hundreds if not thousands of books devoted to the subject. Thus, this article is only the tip of the iceberg.

As always, if you have questions or comments on the article, or would like to connect with a process improvement expert, please feel free to contact our team.


  1. 1988. Malcolm Baldridge National Quality Award 1988 Recipient Motorola Inc.. [ebook] [Accessed 27 July 2020].
  2. Chandler, D., 2012. Explained: Sigma. [online] MIT News. [Accessed 27 July 2020].
  3. iSixSigma. 2020. Remembering Bill Smith, Father Of Six Sigma. [online] [Accessed 27 July 2020].
  4. Gygi, C., Covey, S., DeCarlo, N. and Williams, B., 2012. Six Sigma For Dummies (2Nd Edition). Wiley.
  5. Brue, G. and Howes, R., 2006. The Mcgraw-Hill 36-Hour Course Six Sigma. New York: McGraw-Hill.
  6. Sigma, S., n.d. Six Sigma – Lean Manufacturing And Six Sigma Definitions. [online] [Accessed 27 July 2020].

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