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Integrating Lean Six Sigma and TOC Part 6

Integrating Lean Six Sigma and TOC Part 6

By Bob Sproull

The Answer

At the end of my last post, I asked  for the reason why you think so many LSS improvement initiatives have failed/been abandoned.  There isn’t any one right answer, but based upon my experiences in a variety of organizations and industries, the disappointing results coming from Lean and Six Sigma are directly linked to failing to adequately answer the question, “What to change?” or, worse yet, failing to ask it at all. In failing to ask and answer this question, the improvement initiatives I have witnessed have very little structure.  This is one of the reasons I have merged these two methodologies with the Theory of Constraints (TOC).  In short, TOC provides the improvement-focusing mechanism missing from both Lean and Six Sigma.

Short Review

In my last post I introduced you to the Ultimate Improvement Cycle and, in general terms, the step-by-step process.  I did so by including two distinct figures which included TOC, Lean and Six Sigma.  In today’s post I will begin the “nuts and bolts” of how this integrated methodology is intended to work.  Just to refresh your memory on these two figures, here are both of them again, with their alpha-numeric steps listed.

So let’s work our way around the Ultimate Improvement Cycle (UIC) and dig into how it is supposed to work.


The UIC Steps 1a, 1b and 1c

So just what is it that we are attempting to do when we combine these three improvement methodologies?  Let’s take a more in-depth look at Step 1. In the first step of the Ultimate Improvement Cycle, I have combined identification of the value stream from the Lean cycle, identification of performance metrics from Six Sigma, identification of the current scheduling system used to schedule the plant, and identification of the current and next constraint from the TOC cycle.

In some respects, this first step is the single most important one of all because it forces us to view and evaluate the entire value stream in order to locate the area, policy or process step that is preventing us from reaching our full financial potential. This is the system constraint. This first step focuses resources where they will do the most good and is the basis for continuous improvement. In addition, we need to not only measure our progress toward improvement, but also to reinforce our efforts. To this end we need to select performance metrics that drive the right behaviors. However, if we aren’t careful the metrics we choose can actually motivate behaviors that are counter to what we are trying to accomplish.

Taiichi Ohno, one of the founding fathers of Lean, used a technique known as “standing in the circle” [1] which emphasized going to the process to observe and understand. It was not uncommon for a person to have been left standing for eight solid hours or more before Ohno was satisfied that they had seen the waste in the process and the reasons why the waste exists. During this “standing in the circle exercise” I believe it is best to simply acknowledge that the waste exists without trying to eliminate it just yet.

By the same token, we are also looking for sources of variation within the process. What are the things we see that are preventing our process from being consistent and stable? Keep in mind that the next phase deals with stabilizing the process by reducing both waste and variation in the constraining operation so it’s important, for now, to remember that we are simply trying understand what is happening in our current process and, more specifically, our constraint operation.

Although we will focus our attention primarily on the operation that is limiting our throughput, since the upstream and downstream process steps could be contributing to this limitation they must be observed as well. For example, if an upstream process consistently stops the flow of product to the constraint, then we can’t ignore it. Conversely, if a downstream operation is consistently losing constraint output to scrap or rework, then it can’t be ignored eitherIn both cases the result would be less than optimal throughput.


A Question to Ponder

You will notice in this first step, Step 1a, that I am recommending that you identify not only the current constraint, but also what you believe could or would be the next constraint, once the first constraint is broken. Why do I recommend identifying the next constraint in this first step?


Next Time

In my next post we will continue our discussion of how best to implement the UIC within your company and we will do so by describing more of the alpha-numeric steps outlined in the two figures.   As always, if you have any questions or comments about any of my posts, just leave a message and I will respond. 


Until next time.

Bob Sproull



[1]  James P. Womack and Daniel T. Jones, Lean Thinking, Free Press – A division of Simon & Schuster, NY, NY, 1996



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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