1. Online Cpk Calculator

It's easy to calculate Cp Cpk and analyze process capability using the QI Macros Cp Cpk template.Just enter your target value,spec tolerances and measurements in the yellow shaded areas. The worksheet will automatically calculate Cp, Cpk, Pp, and Ppk.

Dear Sirs,i would like to define a future process, but i am stucked with Cpk values and Yield. I am not able to calculate them, in order they fit together.Moreover, i am not able to recalculate Cpk to Yield. I found several conversion tables, but the results differ.In the process, following needs to be checked:Parameter 1: Cpk should be 1 - continuousParameter 2: Cpk should be 1 - continuousParameter 3: Cpk should be 0,85 - continuousParameter 4: Cpk should be 0,85 - continuousParameter 5: 95% - variableHow do i calculate an Yield?In my case would be the Yield also the Rolled Throughput Yield.Many thanks. Here is what i calculated:-Cpk = Sigma (Z) / 3Cpk=1 = 3 Sigma = 66807,2 ppm = error rate 6,68% or Yield 93,32%Cpk=0.85 = ca. 2,5 Sigma = Yield 85.25%The whole YIELD:Parameter1 x Parameter2 x Parameter3 x Parameter4 x Parameter50.9332. 0.9332. 0.8525.

0.8525. 0.95 = 60%It seems to too creepy.-In the Minitab i found that to the sigma level 3 correspond Cpk=1 and the failure rate 96.75% and to Cpk=0.85 the failure rate 93.06%.Then: 0.9675. 0.9675.

0.9306. 0.9306. 0.95 = 77%This seems to me okay.What do you think? Thank you for your replies.I have found out already, that the relationship in Minitab between a Cpk and a defect rate differs.In any of quality guidelines for suppliers are listed Cpk and / or Ppk values - requirements for a minimal capability of the process.This is why i wanted to how, how these requirements could be translated into yield.But back to the origin question:I have no data. It is a new product that is currently in the development phase. My task is to define requirements under which the process could be taken over from the development to the production.How to set the Cpk values, which could be later recalculated into Yield?I mean something like:Feature 1: Cpk must be more than 1Feature 2: Cpk must be more than 1Feature 3: Cpk must be more than 1,33Yield needs to be more than 85%.How could be the required Cpk values recalculated into Yield? If with such Cpk values is possible to achieve for example Yield of 85 percent.

There are some very good articles talking about Cpk and Ppk in the Resources Section. You can learn a lot. Boot camp 3 0 rapidshare downloads. Hope it will help you.And how to calculate or predict the future Yield with Cpk? As I mentioned before, you need the actual Sample data, USL and LSL.First, use minitab/Excel to find your process`s average and standard variance. (A big 'IF' here is your process is a normal distribution.)Second, calculate the defect rate at the your process left tail and right tail.right tail defect rate = 1- norm.dist(USL, average, standard variance, 1)left tail defect rate = norm.dist(LSL, average, standard variance, 1)NOTE: I am using the function from Excel.Then, get the yield. Yield = 1- (left tail defect rate + right tail defect rate)NOTE: I don`t take into consideration the process drift here. Oh for Pete's sake.

Online Cpk Calculator

The calculation of mathematical formulas is no substitute for thinking. Nor are theoretical models any good at predicting actual yields.

The whole Cp/Cpk thing went totally off the rails when we conflated the capability index with defect rate. I understand the power of seduction of the mathematical approach but our parts are built on real manufacturing lines by real human beings and not by a theoretical distributional model.

Compounding this is the fact that most processes are simply not homogenous and the sampling used for the Cpk calculation is too small and too constrained to give us a real picture of total variation of the process.all this work for a theoretical answer that doesn't match reality.I get that some Customers ask for this calculation (which frequently drives the under sampling and further manipulations to get an acceptable answer). Many thanks for your replies. I really appreciate that.Ncwalker: I tried today some Minitab simulations again, but the results were rather confusing. Now it seems to me that the Cp value is the key. Thank you.Bev D: There is necessary to have in any development goals or boundaries. Such words, to do something and see what happens seem off-date to me.

We are able to do one product in a day, therefore we need to have process / Yield / Cpk - whatever specifications to do not spend much time when samples are ready and and somebody needs to judge them.