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Integrating Lean Six Sigma and TOC Part 2

Integrating Lean Six Sigma and TOC Part 2

By Bob Sproull

The Integrated Improvement

In my last post we began discussing the TLS improvement methodology’s first component, the Lean Improvement Cycle.  And while I am an avid supporter of the Lean improvement methodology, my concern is that using Lean in isolation from TOC and Six Sigma will not deliver the most optimal results. In today’s post, we will discuss the second component of TLS, the Six Sigma Improvement Cycle. 


As we have discussed in previous posts and videos, TLS is the acronym for our integrated Theory of Constraints, Lean and Six Sigma improvement methodology.  Like the Lean Improvement Cycle, I absolutely believe in everything that the Six Sigma Improvement Cycle brings to the table, but like Lean, if it is used in isolation from TOC and Lean, the results obtained will be much less than they could be.

It’s important to remember Six Sigma was originally developed as a problem solving method, but has since evolved into a management approach.  Six Sigma as we know it today was originally developed by Motorola circa 1986 and is a set of tools and techniques used for both problem solving and process improvement.  In 1995 Jack Welch took Six Sigma to a new level by making it the centerpiece of his business strategy at General Electric.  In fact, if you worked at GE and wanted to grow within the company, one of the prerequisites was to become a Green or Black Belt.

Whereas Lean focuses on reducing waste and improving flow, Six Sigma focuses on reducing variation and defects, both of which are key ingredients for optimized flow within a process.  My only problem with using the Six Sigma Improvement Cycle is the length of time required to see quantifiable results.  It’s not unusual for a Six Sigma project to take three to six months to realize any benefits.  Six Sigma is top-heavy with data analysis and many times there is a “failure to launch” because data collection and analysis are the driving forces.

The Six Sigma Improvement Cycle

The acronym, DMAIC represent the five steps of the Six Sigma Improvement Cycle. So let’s take a look at each of these steps in a bit more detail. In the graphic below, we see the Six Sigma Improvement Cycle which starts by defining problems and requirements and then establishing goals for each one.  The purpose of this step is to clearly state the business problem, the goal, potentially required resources, the scope and the timeline for the project. Because Six Sigma is based upon the scientific method, it’s important that you clarify and validate the “facts” of the problem and then clearly articulate the objectives of the Six Sigma project.

Six Sigma Improvment Cycle

The next step in the Six Sigma Improvement Cycle is measure with the purpose being to objectively establish performance metric baselines. These baselines will be compared to the performance metric at the conclusion of the project to determine if improvement has been achieved. It’s important that the Six Sigma team takes the time to objectively decide what should be measured as well as the measurement method.  Because “good data” lies at the heart of the DMAIC process, much time is spent on things like assessing the measurement system for acceptable levels of gage accuracy and precision.

The purpose of the next step in the Six Sigma Improvement Cycle is to analyze the collected data to develop and validate causal hypotheses.  It is possible that the team will have developed a large number of potential root causes of the project’s problem.  At this point, the team will use tools like a Pareto Analysis to identify the top three or four potential root causes for further validation. A data collection plan is then created and data are collected to establish the relative contribution of each root cause to the project metric. This time-consuming data collection and analysis process is repeated until "valid" root causes can be identified which leads us to the next step in this process, improve.

The purpose of the improvement step is to identify, test and implement creative solutions to eliminate the key root causes to both fix and prevent a recurrence of the project problem.

The final step in the Six Sigma Improvement Cycle is to establish some sort of control mechanism to sustain the gains. It’s important to monitor the improvements and create a control plan to ensure continued and sustainable success. One of the most common tools to achieve this sustainability is the process control chart.

While I believe in and support the Six Sigma Improvement Cycle, my single biggest problem with this approach is the length of time required to achieve a quantifiable success.  Most companies cannot afford to wait three to six months for the results to materialize.  

Next Time

In my next post we will discuss the final component of TLS, the Theory of Constraints Improvement Cycle.  As always, if you have any questions or comments about any of my posts, leave me a message and I will respond. 

Until next time.

Bob Sproull

Bob Sproull

About the author

Bob Sproull has helped businesses across the manufacturing spectrum improve their operations for more than 40 years.

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