I believe there's even a paper posted here somewhere which equates the two, if I remember correctly. I think Don Winton wrote it. Unfortunately I can't remember the name of it off hand. Maybe one of the others will remember the name of the paper Don wrote.
__________________
A Search is a terrible thing to waste! One Test is Worth 1000 Expert Opinions - The plural of anecdote is not data.
We can't solve problems by using the same kind of thinking we used when we created them. - Unknown
Assuming that you have verified the normality of the distribution before calculating the Cpk, you can determine the distance of the Upper and the lower spec from the distribution mean on the basis of the Cpk value.
Expressing these in multiples of the standard deviation will give you the Z values for Upper and Lower Spec positions on the distribution.
You can either refer to the Z tables or do normal distribution calculations to determine the fraction area under the Normal curve beyond each side of the specifications. This will give you an estimate of the ppm ( or DPM as you put it).
Cpk Vs DPM (Defects Per Million {aka PPM})
Cpk and PPM
Linear Mode
