Sample size for Capability Analysis in PPAP

[AllenLee]

In PPAP manual, there are 2 times to mention the sample size for process capability/ performance study:
1. "25 subgroups with minimum 100 readings";
2. "100 samples"
(For the manual is not in my hand now, i can not remeber what exactly the sentences are.)

I am confused with it. I think "100 readings" is different from "100 samples", so how can I do to perform Ppk analysis?

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Allen Lee

 

[JRKH]

When Running a Capability Study, you need to have at least 100 sample parts. You select one feature and measure this on all 100 parts and you will have your 100 readings. These must be grouped in no fewer than 25 sub-groups, so the maximum subgroup size for 100 readings will be 4 readings.

Hope this helps

 

[AJLenarz]

When Running a Capability Study, you need to have at least 100 sample parts. You select one feature and measure this on all 100 parts and you will have your 100 readings.

Correct!

These must be grouped in no fewer than 25 sub-groups, so the maximum subgroup size for 100 readings will be 4 readings.

QS and the PPAP manual is not quite this rigid. Keep in mind that there are other types of control charts - ex. Xbar MR. But the PPAP and SPC manual does specify that there must be "at least 100 individual samples".