Cp / Cpk Calculations

TOLERANCE= HSL – LSL

C_pk1 = ((HSL - X_av) / 3 б)

C_pk2 = ((LSL - X_av) / 3 б)

Ideally C_{pk1 ≈}C_pk2

However Practically, it is never so. Hence one of the two C_pk , whichever is lower is taken as the actual C_pk.

If C_{pk1 < >}C_pk2(if both the values are not very close), please repeat the process.

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(B)Range Method:

Terminology:

R_av = Average value of all the groups

d₂=It is a Constant & it’s value is 2.326 if we select a group

of 5 readings. For other group size, I have no data. I will

furnish it as soon as I get it.

R₁, R₂,…R_n = Average of a Group of 5 readings.

For Example, we take 30 readings of a diamension as follows:

X₁, X₂, X₃, X₄, X_{5-----------------} Average is R₁

X₆, X₇, X₈, X₉, X_{10-----------------} Average is R₂

………………….

………………….

X₂₁, X₂₂, X2₃, X2₄, X2_{5-----------------} Average is R₅

X₂₆, X₂₇, X₂₈, X₂₉, X_{30-----------------} Average is R₆

R_av = ((R₁+R₂+R_n-1+R_n) / n)

In our Case:

R_av = ((R₁+R₂+R₃+R₄+R₅+R₆) / 6)

б = (R_av / d₂)

C_pk1 = ((HSL - X_av) / 3 б)

C_pk2 = ((LSL - X_av) / 3 б)

Ideally C_{pk1 ≈}C_pk2

However practically, it is never so. Hence one of the two C_pk , whichever is lower is taken as the actual C_pk.