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Estimating the dpm and ppm of the process from Cp and Cpk

O

oleg_v

#1
Hi
I am how can i calculate the PPM if CP is high = 1.6 and
cpk is low = 0.3

how can i estimate the dpm and ppm of the process?

thanks

Oleg
 
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D

Darius

#2
Your Cp high is because your low variation, your Cpk low is due to your process location, just center your process to your target and your Cpk will reach Cp value.

Just browse the site, you will find many posts about it.

http://elsmar.com/Forums/showthread.php?t=6326#2

If you still want it, interpolate across the table and you will obtain your dpm.
but remember, statistics are as good as their use.
 
D

debyang

#3
Hi
I am how can i calculate the PPM if CP is high = 1.6 and
cpk is low = 0.3

how can i estimate the dpm and ppm of the process?

thanks

Oleg
When Cp=1.6 and Cpk=0.3, it means your low Z value=3x0.3=0.9 or -0.3x3=-0.9, find the normal distribution probability for z=0.9 is 0.81594, so your estimated defect ratio is 1-0.81594=0.18406( or Z=-0.9 probability 0.18406), and in terms of ppm will be 0.18406x1,000,000=184060 ppm.
 
Last edited by a moderator:
D

DrM2u

#4
When Cp=1.6 and Cpk=0.3, it means your low Z value=3x0.3=0.9 or -0.3x3=-0.9, find the normal distribution probability for z=0.9 is 0.81594, so your estimated defect ratio is 1-0.81594=0.18406( or Z=-0.9 probability 0.18406), and in terms of ppm will be 0.18406x1,000,000=184060 ppm.
Thanks for the calculation, Deb. If you may, please post the formulas and explain what each number stands for so the OP and others understand the calculations and can aply as needed in the future. Thanks again!:agree1:
 
D

debyang

#5
I am not good at spread sheets, but I try to develop one as attached. Jut key in your Cp and Cpk values, and the defect ratio will be given automatically. The basic formula used in this spreadsheet is Cpk=(1-ABS(Ca))xCp. Besides, the Z values for defect calculation are equal to 3 times the corresponding Cp values.
 

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