Initial Process Studies - Number of samples - 100 for Individuals Chart?

[Stuart Andrews]

Hi folks!
A simple question! When performing Initial Process Studies for QS-9000 should the number of samples be at least 100 for Individuals Charts?

And should the Ppk be above 1.33 or is there a specific reason why using this type of chart should give you low Ppk values.

Your help is appreciated.

 

[AJLenarz]

Yes, according to QS standards, 100 is the general rule of thumb.

Reference: PPAP manual – Rev 3, pg. 6&7, section I.2.2.9.2 Quality Indices
Reference: SPC Manual, pg. 31, section A.1.c.

Should the Ppk be above 1.33? Well, if we just go by the standard, a Quality Index of <1.33 doesn’t cut it. 1.33 to 1.67 acceptable but may require some improvement. > 1.67 – rock on. But ultimately it is what you and your customer agree upon.

 

[Stuart Andrews]

Thanks AJLenarz

It's just that I've never dealt with individuals charts before and a supplier to us submitted a PPAP with a sample size of 68 and a Ppk of 0.74.

I just wanted to make sure that there wasn't a special rule with these charts that differed from xbar and rbar charts.