All entries for Sunday 23 December 2012
December 23, 2012
To analyze the process in the company, it is essential to learn about process first, then to illustrate the process by charts and diagrams. Thus, after learning and describing the process, the individual and moving range charts were created to illustrate the process. Then to identify how process suits to customers’’ requirements the process capabilities were calculated. At this stage I face a problem – how to illustrate those calculations?
As I understood, this is a six-sigma logic, if you want, - first, to calculate and then illustrate results. Unfortunately, I didn’t know how to illustrate the process capabilities. I knew how picture should look like with Cp = 0,351 but couldn’t find the formula that helped me to build the graph. Luckily, I found an article where the application of Gaussian Bell Curve to six sigma project was described.
So what does, basically, Gaussian Bell Curve can show? The main aim of this function is to consider the distribution of the process. If the points of our process is distributed “Normally”, then around 68% of the points should lie within one standard deviation of the mean, 95% of the points should lie within two standard deviations of the mean, and 99.7% of the points should lie within three standard deviations of the mean.
Although the Gaussian Bell Curve is useful tool in six sigma analysis, its calculation is complicated, as was mentioned in the article. The Cp and Cpk calculations are much simpler and provide you the same results. Moreover, by calculating process capabilities you can also get picture of the process’s distribution. Maybe, it will be not as clear as using Gaussian Bell Curve but its calculation will be, definitely, less time-consuming.