Six Sigma Vs Lean Six Sigma

When you think of Six Sigma, you may think of organizations striving to improve quality. The technical term for Six Sigma is a process and methodology for eliminating defects through the development of a disciplined and data-driven approach. The methodology is designed to reduce any defects to 3.4 per million events.

The basic idea of Six Sigma is the development and implementation of improving processes and reducing defects through a series of measurement-based strategies. The two applications most used to do this are the DMAIC and DMADV. DMAIC is an acronym for defining, measuring, analyzing, improving and controlling. This application is used to improve systems and processes that fall below specifications. The DMADV application is also an acronym meaning: defining; measuring; analyzing; designing; and verifying systems in order to improve processes or products that have already gone through the initial Six Sigma quality improvements.

Regardless of where your organization is at, Six Sigma stands to reduce or save companies a substantial amount of money each project, provided that there is a certified Black Belt heading up the projects.

Lean Six Sigma, on the other hand, takes the principles of lean and Six Sigma, and marries the two concepts to produce an even better system—producing speed and quality by improving and streamlining the processes, creating excellent customer service and products. While speed has a negative connotation that working fast creates hastily put-together work, Lean Six Sigma focuses on streamlining the core processes in order to make them flow smoothers and produce on time.

It is important to understand when you are looking at Lean Six Sigma principles that when we’re talking about “speed” it does not equate to the same thing as schedule. More specifically, speed is how quickly something gets done, and schedule is when it is due to be finished. Again, speed is not how hastily a project can be done, but how to streamline the core processes, by breaking down the processes into smaller more efficient cycles, in order to get a project done swiftly, yet producing quality work with little or no defects.

In essence, Six Sigma and Lean Six Sigma are both great improvement process exercises. However, in the describing the differences between the two, it seems that to get to Lean Six Sigma, your organization should incorporate Six Sigma into your process improvement and then engage in Lean Six Sigma to speed up the processes after you have broken down the systems into smaller components.

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Introduction to Six Sigma

Six Sigma is a process improvement tool used to measure quality in order to reduce or eliminate defects. The thought behind Six Sigma is that it is a way of approaching a process that is disciplined, using data to eliminate defects and reduce the variation of these processes. How can your organization benefit from it? In many ways, but Six Sigma is a commitment to improving your whole organization, not just a few things here and there.

More specifically, while the above explanation of Six Sigma may seem simple, Six Sigma is actually fairly complicated because the process is entrenched in mathematics and statistical methodology. For example, the goal of Six Sigma is to produce a process where there are no more than 3.4 defects per million opportunities.

What is a defect and how would you define opportunities within Six Sigma? A defect is anything that is outside of the customer’s specification, while an opportunity is the chances for a defect to occur during the process. Let’s take a look at a simple calculation. Suppose you produce 100,000 gadgets in a week, and it is discovered that the defect rate is 15 defects per 100,000. When using a Sigma calculator, your results are:

DPMO: 150
Defects (%): 0.02
Yield (%): 99.99
Process Sigma: 5.12

What exactly do these numbers mean? Let’s break it down ever further so you can see what exactly you’re looking at. DPMO is “defects per million opportunities”. Since the goal of true Six Sigma is to only have 3.4 defects per million opportunities, looking at 150 defects doesn’t seem like that is too good.

However, there is more that goes into determining the amount of defects in order to have truly implemented Six Sigma, such as knowing if there is one specification limit or two. This affects the Upper and Lower standard deviations between the customer specifications and the process. The Process Sigma is 5.12, which as it increases from zero to six, the variation in the process around the mean value decreases. As the value of the process sigma increases, the variation decreases creating a process with zero defects.

Six Sigma literally means the number of standard deviations away from the mean, or the average, as indicated on a bell curve. This is also known as the normal distribution. Thus when calculating the mean, Six Sigma allows for 3.4 defects per million. In essence, if you are making one million widgets, then you should only have 3.4 defects per that million widgets produced. The rest of the widgets fall under the “normal distribution” as indicated on the bell curve. Below is an example of what the bell curve looks like—indicating the deviation from the mean, which is Zero, or the target.

six sigma curve

When looking at the graph above, LSL is the Lower specification limit, and the USL is the upper specification limit. Again, Six Sigma allows for six process standard deviations between the mean in the process and what the customer’s specification limit. As your value process stigma increases from zero to six, then the variation in your process around the mean will decrease. This indicates that if your value of process sigma is high enough then when the process reaches zero variation you have reached zero defects.

Six Sigma quality is not easy to achieve, particularly when you roll throughput yield into the mix, resulting in yields of each process is multiplied together to obtain the final yield. In short, this is the percentage of good widgets that are produced in a given process. For instance, if there are four different processes, each having a four percent (4%) yield the total throughput yield is calculated as: .99 x .99 x .99 x .99 = 96%. This is a great example of how Six Sigma can work and how when the proper check points are established within each process, no defects are passed onto the next process or stage within production.

This is a lot to process at this basic level, but in essence, Six Sigma and the role of the professional is to quantify the process performance, which is the short and long term capability, taking the process entitlement and process shift, to create the right strategy in order to reach the determined performance objective. One thing to remember when determining what your short term and long term capability is, that when you decrease your process variation, your process sigma increases, resulting in greater customer satisfaction and lower costs.

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