Question

What would be the Cpk for the process if it were centered between the specification limits (assume the process standard deviation is the same)?

Short answer

The method capability index, or Cpk, assesses a process's capacity to produce an item within specified parameters.

Step-by-step solution

Cpk process

Theprocessing average = (2.4 + 1.4) / 2 = 1.9 MM, where the upper standard limit is 2.4, and the lower standard limit is 1.4. If the activity is balanced between top and bottom specified tolerance, the process variance stays at 0.2096.

The revised Cpk

The formula is given below:

Minimum ((upper standard limit - revised process mean)/ (3 x sample standard variation)), (revised process mean - minimum specification limit) / (3 x sample standard variation)).

Upper standard limit = 2.4

Samples mean = 1.9

Sample standard variation = 0.2096

Lower Specification limit = 1

Minimum ((2.4 - 1.9) / (3 x 0.2096), (1.9 - 1.4) / (3 x 0.2096))

= The Absolute Minimum (0.7951, 0.7951)

= 0.7951

Hence, 0.7951 is theCpk for the process.