The CORRECT steps to implement an SPC chart
Posted 17th November 2010 at 11:46 AM by bobdoering
Updated 22nd November 2010 at 05:27 PM by bobdoering
Updated 22nd November 2010 at 05:27 PM by bobdoering
Some Related Topic Tags spc standard deviation variance charting
You might have had some SPC training in the past, but it probably skipped over the correct steps to implement charting on the shop floor. Check it out, here they are:
1. Develop the total variance equation (Yes! This is the very first step!)
2. Determine which variance factors are adjustable, which are noise, and which can be set as a constant.
3. Minimize the variation of each of the participating variables  get the process in a steady state and capable. This includes eliminating your "special causes".
4. Accurately determine the correct distribution of each of the remaining variances
5. Determine which of the remaining variance factors you are going to chart
6. Pick the correct chart to evaluate that variance factor (variable)
Did anyone share that with you in your SPC training? If not...you missed out on the important stuff...
Don't feel bad, it's common.
1. Develop the total variance equation (Yes! This is the very first step!)
2. Determine which variance factors are adjustable, which are noise, and which can be set as a constant.
3. Minimize the variation of each of the participating variables  get the process in a steady state and capable. This includes eliminating your "special causes".
4. Accurately determine the correct distribution of each of the remaining variances
5. Determine which of the remaining variance factors you are going to chart
6. Pick the correct chart to evaluate that variance factor (variable)
Did anyone share that with you in your SPC training? If not...you missed out on the important stuff...
Don't feel bad, it's common.
Total Comments 16
Comments

Bob;
I have to hand it to you, you always get me to think! Thanks! A terrific addition to the steps you stepped out was the additional questions asked by Dorian Shainin: Is the primary variance within part, parttopart, or lottolot! Thanks again for the post!Posted 18th November 2010 at 04:20 PM by Sturmkind 
One of the points I have made elsewhere in the cove that shows the importance of the Total Variance Equation is that it is the true origin of 6 Sigma. Sigma  the standard deviation  is the square root of the variance. So, therefore, the square root of the sum of all of the variances shows the critical importance of knowing what the factors of variance are to the proper implementation of the 6 Sigma tools. I bet you rarely see that in 6 Sigma training!
Whats more, it shows that virtually all processes are multimodal  unless you can eliminate or make statistically significant ALL (or all but one) of the total variance factors! Unfortunately, the ones usually not minimized (and therefore masking all others)  is measurement and gage errors. They are typically normal, giving the false facade that the underlying process is, too  and that all of the normal statistics apply.Posted 18th November 2010 at 06:31 PM by bobdoering 
Posted 25th February 2011 at 09:47 PM by selena15 
Hi Bob,
Can you share one particular example? To enlighten me more.. Hope you can...thanks!Posted 20th July 2011 at 04:33 AM by Erick Mirabel 
Posted 20th July 2011 at 11:36 AM by bobdoering 
what is the difference between ISO 90012008 and TS 16949?
Posted 2nd December 2011 at 01:45 AM by bukee 
Posted 2nd December 2011 at 10:38 AM by bobdoering 
The move from ISO9001 to TS 16949 is very significant, with much more documentation overhead, and many more customer specific requirements no even listed in the requirements. It is extremely comprehensive, and will take much more resources to implement and maintain. Only do it if you are required to. You may want to get a gap analysis before deciding to dive in.
Posted 5th December 2011 at 03:54 PM by bobdoering