Are Six Sigma and Lean Manufacturing Really Different? Are They Synergistic or In Conflict? - ASQ

Are Six Sigma and Lean Manufacturing Really Different? Are They Synergistic or In Conflict?


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By James Bossert
Vice president, Bank of America

I have found Six Sigma and lean enterprise methodologies synergistic, even though they evolved from separate paths.

Lean was developed by Toyota Motor Corp. as an extension of the Ford Motor Co. manufacturing system. Toyota took what it learned from Ford and advanced the concepts to a broader level. This helped improve productivity and profitability.

Six Sigma as developed by Motorola was an extension of many of the quality tools and techniques already around, but Motorola added the component of financial accountability. This resulted in process improvement gains at Motorola that improved productivity and profitability. Different approaches, similar results.

It was inevitable people would start to merge the approaches. The results depended on the circumstances. Results were complementary when the Champion and Six Sigma team worked to find the best combination of techniques to create a robust solution. GE Capital used this approach successfully time and time again.

Some companies treated each methodology as different and unique—a narrow-minded approach that tended to create other problems. Process teams were pulled in different directions and, with limited resources, were forced to decide which approach to take.

The end result was that the business and customer suffered. The business did not obtain the sustained gains in productivity, and the customer did not see an improved product. The customer does not really care which methodology is used, as long as results are seen.

Combination Works Best

I find a combination of the approaches tends to produce long lasting results. I have heard the argument that lean enterprise methodologies must be completed first to maximize the Six Sigma gains, the belief being that if the process is not lean, Six Sigma efforts will be suboptimized. But I think it really does not matter which approach you start with. Rather I see this as personal preference of the person leading the team.

If you start with Six Sigma, the team and the Champion should discuss what the next steps should be at the measure review. If it is determined some quick hit can be obtained using lean enterprise techniques, then they can be implemented. This usually results in some immediate buy-in by the team and process owners. Now they can focus on the discovery of the root causes of the problem. Then when the root cause is eliminated, lean techniques are used in conjunction with statistical process control to maximize the benefits.

In my experience, this is a successful approach in nonmanufacturing situations. If you survey nonmanufacturing companies, an overwhelming majority will show the success of the combined approach.

This synergy may surprise some because lean is traditionally seen as manufacturing oriented—a logical conclusion based on lean’s roots. But nonmanufacturing companies have recognized many of the techniques developed in manufacturing are also applicable in their areas. All companies are looking at having a number of techniques in their toolbox to help them attain their goals, and lean and Six Sigma techniques are just some of those tools.

By Kevin Grayson
Manufacturing specialist and Six Sigma program coordinator, North Carolina State University

This is a question I’m often asked. My short answer is “yes and no.”

Sure, there are differences. The two methodologies differ in the way they attack problems (or opportunities for improvements). Their subject experts are trained and deployed differently. Their approaches fit different types of problems. There are probably other differences.

But the two are the same—or at least very similar—in many ways, too. At least three strong similarities come to mind:

  • Both have the ability to make very significant positive financial impacts on an organization.
  • Both (like many other initiatives) need management support for success.
  • Both can be used in nonmanufacturing environments.

For most companies, Six Sigma and lean manufacturing attack problems in different ways. A Six Sigma project typically involves a well-defined problem statement and mission statement. An individual, often supported by a team of Green Belts (GBs), executes the project using data manipulated by software.

In a well-defined sequence, projects are defined, measurement systems addressed, analysis done, improvements made and controls implemented. These projects often take weeks or months to conclude successfully.

At many companies, lean projects often take the form of kaizens. In most organizations, kaizens are done in a brief period (perhaps three to five days). These projects also use team members, but differently. The team leader acts more as a facilitator—even though he or she may have extensive training and experience in lean tools. The team members are seen as the specialists and are expected to supply the ideas necessary to resolve the issue at hand. Compared with Six Sigma, the project path is much less defined, and the use of data is less common.

Another important difference is how subject experts are trained. Six Sigma training is formal. It has different levels of competencies (such as GB and Black Belt), with a relatively standard curriculum. Six Sigma usually includes a written assessment.

Learn As You Go

Lean training is more learn-as-you-go. With lean, the emphasis is on doing—training often is included as part of the kaizen. Some companies have developed lean aptitude levels, but you see these rarely, and there is great variation in the approach from company to company.

Six Sigma projects often attack problems in which there is variation that is not clearly understood. Six Sigma is also quite effective when it is necessary to optimize several inputs or independent variables to achieve a desired result. To arrive at effective solutions, data are necessary.

Lean manufacturing often addresses problems that are very visible (such as too much inventory, excessive motion or travel distance), and data are less important.

How about the similarities? The most important similarity may be that both Six Sigma and lean can produce large return on investments. Both methods identify the enemy with different terms (cost of poor quality and waste), but the results are measured in the same units—real dollars. Results from both efforts often deliver paybacks that are measured in terms of months or even weeks.

Like most initiatives we have seen through the years, Six Sigma and lean need the visible support of top level management. In fact, top level backing is probably the single most reason for success or failure.

The second part of the question is easy. Six Sigma and lean are completely synergistic. Both seek to improve the health of an organization—just as your heart and lungs support your body’s health. To only adopt and consider one method may limit a company’s ability to make adequate progress. As a colleague of mine once asked, “Why wouldn’t I want to have both a healthy heart and healthy lungs?”

Regardless of the terminology, more and more nonmanufacturing companies are using both concepts to improve their business processes, such as order entry, customer services and material procurement.

I’m also seeing more and more companies adopt strategies that include both methodologies, but they are calling their initiative something else. They are giving it a name that means something to the company’s business but does not tie them to one or even two methods. These are the companies I see having the best chance for success in the next few years.

By Jane Heyward
Process improvement program manager, Invensys Powerware

Six Sigma and lean are the same in that they are both structured tool kits used to help solve problems and improve performance in one way or another. However, the tools and the circumstances under which they are used are different.

When you want to reduce waste and improve the efficiency of a process, you use the lean tools. When your goal is to reduce variance and improve performance, you should be using Six Sigma tools.

Lean manufacturing tools are great for reducing process time and improving such things as safety, floor space usage and cleanliness, but they can’t help you if your product keeps failing your final test sequence. For that, you need to do in-depth root cause analysis, which is where the Six Sigma tools come into play.

Conversely, making your product as consistent as possible without any defects or quality issues does not mean you are making optimal use of your floor space or assembling as efficiently as possible. So, lean tools are used to reduce waste, and Six Sigma to reduce variation.

Six Sigma and lean tools are definitely synergistic. If you truly want a continuous improvement culture in your organization, then you need to be able to use both tool kits together or you’ll hit a brick wall.

A kaizen conducted on removing waste from a process may uncover a step that constantly requires rework of some kind. That should be a red flag alert to begin using Six Sigma tools to go after a root cause for that rework.

Once those tools collect the data, determine the root cause and develop a solution, another kaizen may be used to actually implement the solution.

For example, you may want to reduce the overall cycle time of one of your product lines. After running a kaizen, creating a process map and balancing the line to takt time (total available time/customer demand time), you may find you have a bottleneck at test because the unit will not pass.

Using your Six Sigma statistical tools, you then determine one of the main causes of failures is worn out cabling on test fixtures. As a result, you need to do a total process management kaizen on the test equipment to create a program for swapping out test cables after four weeks’ usage.

Or, to give you a transactional example, you may hold a kaizen to streamline the order entry process and find there is a significant amount of rework going on. You learn employees are constantly having to deal with issues that bog down the process, such as incorrect addresses, customer numbers and taxes on orders. Your process may be efficient but have a lot of variation.

To determine the root cause of the variation, you take data at different points in the process and summarize that data in a Pareto chart to determine the main causes. You then may use a failure mode effect analysis/error mode effects analysis or other analysis and idea generation tools to come up with a poka yoke (mistake proofing) solution of some kind, and then use another kaizen to get the department together to implement it.

These examples illustrate a kaizen rolling into a Black Belt project, which uses another kaizen to implement or integrate the solution into the process. This is a common scenario if you use both sets of tools in conjunction because they work together and are enablers of each other. Using just one of the tool kits will cheat you of a total solution.

Having employees who understand both sets of tool kits and when to use what is critical. If you are trying to use a lean tool to determine why you are having so much rework, you will be spinning your wheels. If you try to use a Six Sigma tool to figure out why the cycle time is so long, you will get nowhere.

The key is understanding what parts of your process can be affected by waste and what parts can be effected by variation. Once you understand that, you can apply the right tools to the right problem.

By Randy Kesterson
Senior vice president operations, Curtiss-Wright Flight Systems

Lean and Six Sigma can be synergistic, but I believe you need a recipe to ensure success. Let’s talk baseball for a minute.

Consider the second baseman and shortstop. Each may cover his correct part of the infield, but if they don’t work together, they won’t turn many double plays. If both go after the same ground ball or pop-up, they may even collide and hamper their combined performance. But, if they work together, they can cover most of the infield and even turn an occasional double play.

If lean and Six Sigma tools are used separately, they can produce good results. If management permits an environment where lean and Six Sigma teams fight for the same projects or resources, the results can be counterproductive. But if the tools are used together in a coordinated manner, the users can turn a business double play.

Based on my experiences at Curtiss-Wright, I believe the recipe for success is “Lotsa lean, then some POCS (see following) and a dab of Six Sigma.”

  • Lotsa lean. Most business processes can benefit from the application of lean tools. The difficulty comes when trying to identify the problem process that will yield the biggest bang for the buck. Deciding where to apply lean is key. Senior management must be involved in project selection.
  • Then some POCS. Not another business acronym, you shout! Don’t fret. Consultants won’t be able to charge you for plain old common sense—POCS—which should come before Six Sigma. Once the process has been “leaned out,” you should examine it for quality problems. If quality variation is a problem, you should try to apply commonsense solutions first. Don’t yield to the temptation to apply Six Sigma tools to every process quality problem. People with colored belts want to use them.
  • And a dab of Six Sigma. Compared to lean, Six Sigma tools tend to require more data gathering and number crunching. Lean tools are typically more intuitive and team based. Six Sigma can become ivory towerlike, with knowledge of the tools possessed by only a few technical experts. Most people understand lean tools (5S or process mapping, for example) before they grasp Six Sigma tools (regression analysis, for example). Six Sigma involves powerful tools that can be expensive to use. My recommendation: Use Six Sigma tools selectively.

There are at least two exceptions to the recipe. One I’ll call “Six Sigma triage.” In this situation, the patient (key business process) is bleeding to death and there’s no time for fine-tuning. Swift, bold measures are needed to save the patient (process). Commonsense solutions have failed, and Six Sigma tools must be employed right away. The process can be “leaned” another day.

Another exception is at a company that has eliminated all low hanging lean opportunities. Such a company might then reverse the recipe to “Lotsa Six Sigma and a dab of lean.”

Lean and Six Sigma work best when used together, with one person responsible for coordinating both tools. Try the recipe when starting out. Turn some business double plays. Win the game.

By Sam Windsor
Change program manager, Filtronic Comtek

n the surface, Six Sigma and lean manufacturing appear to be two completely different approaches to the common goal of satisfying the customer while making a profit. On closer examination, both similarities and differences begin to appear.

Lean thinks in terms of constraints, and the focus is on eliminating barriers to a smooth continuous process flow. In Six Sigma, the focus is on eliminating variation to reduce cost and cycle time and improve quality.

Lean looks at how the individual process steps relate to the overall process, while Six Sigma examines the relationship of variation in process steps to the variation in the process output. Some comparison is required to answer the question of whether they are really different, synergistic or in conflict.

Same Tool, Different Name

In lean, we speak of value stream mapping, and in Six Sigma we call it process mapping. We’re using two similar tools to achieve slightly different goals. Value stream mapping focuses on how the individual process steps contribute to the overall process as it relates to optimizing product lead time and takt. Six Sigma process mapping looks at process steps as operations requiring certain critical inputs, then producing a desired outcome.

While the focus in lean is on eliminating muda (waste), the Six Sigma focus is on reducing the variation of process inputs and creating a robust process, thereby producing very predicable outputs.

Total productive maintenance (TPM), a tool used in lean, is designed to ensure equipment is operational and available when required. TPM can be compared with the Six Sigma tool of gage repeatability and reproducibility. Both are intended to ensure manufacturing or measuring equipment performs as expected when required.

Many techniques used in both do not have direct parallels. Single minute exchange of dies (SMED) from lean and design of experiments (DOE) from Six Sigma are an example, but this may not mean they are different. The goal of TPM and SMED is to reduce waste from equipment downtime either from malfunction or tool changeover. DOE is used to evaluate variation and determine relationships between process inputs and outputs with the goal of optimization through variation reduction, which in turn reduces waste.

Both lean and Six Sigma boast of breakthrough improvement levels in quality, cost and cycle time. These improvements in lean are centered on optimizing process though removing waste such as distance traveled and nonvalue added activities and managing processes based on takt time. Six Sigma cycle time reduction typically results from reducing variation in process inputs and controls, thus producing a consistent process output.

Attempting to separate lean and Six Sigma into programs is really a mistake. This would be like saying a wrench and a ruler could not exist in the same toolbox.

There are cases in which lean and Six Sigma actually compete for the greatest dollar savings, which can lead to the failure of both. While there are differences in specific tools and the focus of specific tasks in the two approaches, both seek to eliminate waste, satisfy customers and return profits. Optimizing the synergy between Six Sigma and lean will help ensure tomorrow by satisfying customers today.


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