What is the formula I need to calculate Pp and Ppk?

[akiton]

Due to this our customer requesting us to come up with Pp, Ppk figures.
With the data given below can anyone help to figure out the pp,ppk value?

Spec: 107 ± 3 microns

Sample               1      2      3      4     5      6    
1) Part A    -      108    107    105    108    106    106 
2) Part B    -      106    107    105    105    104    106

I need to know the formula (not with those code) but the numerical formula using the example above so that in future I can calculate myself.

Please advice. Thanks

[Jim Wynne]

Have a look here: http://www.isixsigma.com/library/content/c010806a.asp

[akiton]

I've gone thru that site already and it doesn't have any numerical example shown there.

Anyone here please use the example posted to show me the formula. Thanks.

[Tim Folkerts]

Attached is the results of a Minitab analysis of the data - numbers & graphs pasted into a word document. Hopefully that points you in the right direction. If you have questions about specific numbers, I should be able to provide a little guidance.

Tim F

[akiton]

Originally Posted by Tim Folkerts

Attached is the results of a Minitab analysis of the data - numbers & graphs pasted into a word document. Hopefully that points you in the right direction. If you have questions about specific numbers, I should be able to provide a little guidance.

Tim F

Thanks for your reply. I need to know the numerical formula to get the result.

Please advice. Thanks

[Arvind]

You can calculate capability using a scientific calculator.

1) Find mean and standard deviation from the data.
2) Multiply std dev by 6.
3) In your case, tolerance band is +/- 3 or total 6
4) Divide 3) by 2) to get Pp

5) Find smaller of the two absolute values (UCL-Mean) and (LCL-Mean). Use only smaller value.
6) Multiply std dev by 3
7) Ratio of 5) by 6) will give Ppk.

Confidence band using such low sample size is unacceptably wide therefore your calculated values may not mean anything useful in real life. Even with 30 samples, capabilities have tolerance value of +/- 25 %.

[Marc]

Also see these related Cove threads:

Ppk vs Cpk - Good, clear explanation
Cpk vs. Ppk - Long Term vs. Short Term - Capability vs. Stability
Cp/Cpk vs Pp/Ppk (Short term using population sigma) - Formulas to use?

Some Process Capability visuals

[bobdoering]

Originally Posted by akiton

Due to this our customer requesting us to come up with Pp, Ppk figures.
With the data given below can anyone help to figure out the pp,ppk value?

Spec: 107 ± 3 microns

Sample               1      2      3      4     5      6    
1) Part A    -      108    107    105    108    106    106 
2) Part B    -      106    107    105    105    104    106

I need to know the formula (not with those code) but the numerical formula using the example above so that in future I can calculate myself.

Please advice. Thanks

There is not enough information here to calculate Pp or Ppk. What is the process. and what does the data represent? The capability analyses that have been provided from dumping this data into a number cruncher may only indicate that the variation you see is from measurement error and perhaps gage error (since a six micron tolerance should be measured with something with a resolution of 600 nanometers at a minimum - and more likely 100 nanometers - not 1 micron resolution), which tends to be normal, and tends to nicely mask the actual process variation. If this was a part from precision machining (the 6 micron tolerance makes me suspicious that it might be), and you both controlled and measured the part correctly, then the capability is (USL-LSL)/UCL-LCL) - not any of the citations listed previously.

See Statistical process control for precision machining for more information, if it applies.