There is an ongoing debate in the business world regarding the difference between Lean and Six Sigma, and whether they are mutually exclusive or actually compete with each other. These questions seem to revolve around three themes: “How do the Six Sigma and Lean approaches differ?,” “Which should I choose to apply?” and “Should Lean coexist with the application of Six Sigma?”
Toyota in particular is credited with making Lean a well-known word in manufacturing as embodied in the Toyota Production System (TPS). The results of applying these techniques are legend—though still poorly understood in many industries and government sectors in the United States and abroad. Lean is all about eliminating wastes, taking time out of processes and creating better flow. Asked about the essence Lean (or TPS),
Six Sigma has been defined in a variety of ways. Two popular definitions are as follows:
“Six Sigma provides companies with a series of interventions and statistical tools that lead to breakthrough improvements in profitability and quantum gains in quality, whether a company’s products are durable goods or services.” — Juran Institute Web site.
“Six Sigma is . . . a business strategy and philosophy built around the concept that companies can gain a competitive edge by reducing defects in their industrial and commercial processes. Classically speaking, a defect is anything that fails to meet the customer’s expectations or requirements . . . within the framework of Six Sigma, a defect is anything that blocks or inhibits a process or service.” — Six Sigma, by Mikel Harry and Richard Schroeder.
It is no surprise that the Six Sigma gurus and authors end up with different versions of the same thing. After years reading books on Six Sigma, working with and training Six Sigma Black Belts, and developing successful case studies, I have come to the conclusion that Six Sigma is an expansion on the approach pioneered by Taguchi and others (Deming and Juran included) and an “Americanizing” of the concepts.
Similarities and Differences
Though it is outside the scope of our purposes here to fully detail all the similarities and differences, let’s take a look at a short list of the key points of both approaches and see how they compare. For each point, there is a short explanation of how each of the two camps views the issue.
Focus on customer satisfaction. While both Six Sigma and Lean do focus heavily on satisfying customers, Six Sigma makes customers the primary driver for action. The premise is that without high levels of customer perceived “utility” and “value,” just reducing waste (a Lean focus) is not enough.
Endless war on waste-enterprise-wide
One of the appealing aspects of a Lean approach is focusing everyone on continuous elimination of wastes—indoctrinating “kaizen circles” as part of the culture. Six Sigma tends to focus only on those opportunities that are customer focused and promise a large (and immediate) financial reward.
Tools focused on common-sense improvements. Workplace organization and cleanliness (5S), Total productive maintenance (TPM), Kanban/Pull systems, Kaizen, setup reduction, teamwork, error proofing and problem solving, cellular manufacturing, and one-piece flow are the cornerstones of a Lean continuous improvement strategy. Lean tends to be more grassroots and centered on empowerment of people to create stability, repeatability and a culture of continuous improvement powered by natural and cross-functional teams.
On the other hand, one of the selling points that some Six Sigma gurus tout is that Six Sigma zeroes in better on “big bang” improvements. Black Belts are expected to target and drive six-figure, if not seven-figure, bottom-line savings projects every year.
While most Lean practices strongly suggest PDCA—a plan-do-check-act Deming wheel cycle of continuous improvement—Six Sigma drives a very rigorous and well-defined five-point process for working on improvement projects in the DMAIC (define, measure, analyze, improve, control) methodology.
5S and standardized visual work as a foundation for all processes
Six Sigma does not seem to have an overriding, common foundation implementation effort suggested. Lean teaches 5S—a five-point process for sort, straighten, sweep, schedule and sustain—and standard visual work is the one best method for work that builds safety, productivity and quality into processes. Both are considered part of a critical foundation in World class enterprises. In 5 Pillars of the Visual Work Place, Hiroyuki Hirano states, “World class facilities develop beginning with the 5S’s, and facilities that fail, fall apart beginning with the 5S’s.”
Problem identification and problem-solving techniques
These include brainstorming, fishbone/Ishakawa/cause-and-effect diagrams, five whys, Hoshin problem-solving, Pareto analysis, 8-D/7-step, failure mode effect analysis (FMEA) and others. Both Six Sigma and Lean methodologies have a heavy emphasis on careful evaluation and definition of problems, and both promote a rigorous, systematic process to find the true root cause(s) of the problem. Six Sigma is more data based and Lean tends to be more subjective—with a bias for immediate action versus a long period of data collection before action starts (Six Sigma). Common elements include a Pareto analysis of data and verification processes to ensure countermeasures are fully effective in the long term.
Value stream mapping
Also known as “information and material flow maps,” value stream mapping is credited to Toyota in its best-known form.
I have examined or practiced more than 20 methods of value stream mapping, and I believe the permutations are nearly unlimited. Value stream mapping is a scalable approach to create a visual representation of what is happening in a process and helps to identify where changes are needed to improve system performance.
On the other hand, process mapping is a tool favored by the Six Sigma community. Process mapping is used to identify the inputs and factors that can have an effect on the problem being pursued. Think “elegant”—more like what you would expect to see in a software process flow map. I have found process mapping effective for complex interrelated processes. For most people and business problems, I have found a variation on value stream mapping far more effective than process mapping because it is much easier to understand and has more visual features.
Team-based bias. Everyone must be involved to achieve excellence. This is an all-or-nothing deal for stakeholder involvement. Lean approaches ultimately mandate full involvement of all stakeholders. Six Sigma approaches suggest that full involvement is not possible or will take too long, and that fully engaging your best people to drive changes will get you where you want to go much faster.
Answering that Question
“Should Six Sigma and Lean coexist in my company?” I hope the answer to this question is self evident: Yes. Many of my Six Sigma Black Belt friends strongly contend that Lean approaches should precede and coexist with the application of Six Sigma methods. Why? Put simply, Lean provides stability and repeatability in basic processes. Once stability has taken hold, all the “noise” of variation due to human and easily controlled process variations goes away. The data and indicators collected to support Six Sigma activities thereby become much more reliable and accurate. This leads to a far more effective application of elegant studies of the causes of process variation and identification of the vital few factors that need to be controlled or changed to make quantum leap improvements. In this way, you can reap the best of both—by careful application of the right tool to fix the problem.
Remember: If the only tool in your bag is a hammer, all your problems start to look like a nail. It is best to fill your toolkit with a holistic set of tools, principles and ways of thinking. The rest is up to you.