Six sigma certification or concept will be explained here. This is the basics of six sigma certifications such as six sigma green belt and six sigma black belt. It also gives the answer to the question why a project is called a six sigma project?.
An example to understand six sigma concept
A customer wants a shaft with a diameter with the specifications, the lower specification limit(LSL) and upper specification limit (USL) as 24.5 cm and 27.5 cm respectively. That means customer will not accept the shaft if the diameter goes beyond 27.5 or lower than than 24.5. He will reject the shaft if it’s not in the specification.
To understand the concept of Six Sigma projects we want to know the following basics also.
The bell curve
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Suppose we collected the dimensions of some samples of this shaft and made a graph with X axis as the diameter value and the Y axis as the frequency of the occurrence of the value. When we draw a curve including outer points of the graph, it will resemble like a bell curve, if it is a normal distribution. Here we will consider only normal distribution, because its best for understanding the basics. Also the centre portion of the curve will be the mean. Please refer the following graph.
Graph of Normal distribution
Let ‘d’ be the standard deviation of this data set. Standard deviation is the measure of how long the data is spread from the mean value. If the standard deviation is high the spread is also high. If the standard deviation is low the spread will also be low.
And one another property of this normal distribution curve is, 68.26% of the data will be accommodated within the one standard deviation from the either side of the mean, 95.46% of the data will be accommodated within the two standard deviation from the either side of the mean, 99.73% of the data will be accommodated within the three standard deviation from the either side of the mean, 99.9937% of the data will be accommodated within the four standard deviation from the either side of the mean, 99.99943% of the data will be accommodated within the five standard deviation from the either side of the mean and 99.9999998% of the data will be accommodated within the six standard deviation from the either side of the mean.
Six Sigma Concept Explained
Six Sigma Concept Explained
Please refer the picture above. If the LSL and USL of the operation in our previous example is at the sixth standard deviations from the mean to either side, we can say this operation is at the six sigma level. That means 99.9999998% of the shaft produced will be within the specification. In other words 0.0000002% of shaft will be out of specification. Or in other words 0.002 DPMO.
But in long run there will be a shift of mean by 1.5d either to the right or left of the starting mean. This will increase the rejection area which will be equal to 3.4 DPMO.
If the LSL and USL is not at the 6th standard deviation at the initial stage, here comes the role of six sigma project to reduce the standard deviation of the operation so that the customer requirement comes to the 6th standard deviation and make it to the six sigma level.
This is the basics of Six Sigma project.
What is a Six Sigma Project
A project which reduces the DPMO of a process to 3.4, by reducing the variation of the process is called a six sigma project.
But, it is not necessary if we do not achieve, the target, 3.4 DPMO, to call it as a six sigma project.
Six sigma project focus on DEMAIC method, to achieve the target of 3.4 DPMO.
This method will be taught in six sigma certification.
What is Six Sigma Certification
Six sigma certification is the process of training a candidate to handle six sigma project. Training will be including teaching of six sigma concepts, training on statistical concepts required for doing six sigma projects, on how to use minitab and also there will be practical examples and projects.
Six Sigma Certification Levels
According to the level of training the six sigma certification is categorized into the following from lowest level to highest level.
- Six Sigma White belt certification
- Six Sigma Yellow belt certification
- Six Sigma Green belt certification
- Six Sigma Black belt certification
- Six Sigma Master black belt certification
White belt and yellow belt are introductory level certification. After green belt certification you can participate in six sigma projects.
Black belt and master black belts certifications are advanced level certifications.
Thank you for reading.
You can also refer the article on DPMO
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Excellent sir, What if USL and LSL are within 3 or 4 standard deviation? Does it require to carry out six sigma project?
In the article, you said in the long run there will be a shift of mean by 1.5d? Why?