Ans. Process capability (Cp) is a technique to find out the measurable property of a process to specification. Generally, final solution of process capability is specified either in the form of calculations or histograms.

Cp = [ (USL - LSL) / 6 x standard deviation) ]

USL: Upper specification limit

LSL: Lower specification limit

In above given case, USL = 2,400 hours

                              LSL = 1,600 hours

                              Standard deviation = 100 hours

                             Mean = 100 hours

Put all these in above formula, we get:

Cp = 2400 - 1600 / 6 x 100

    = 1.33

Cp is greater than one, then it means that the engineering tolerance is greater than process spread so the process has the potential to be capable.

Process capability index ( Cpk) is the measure of process capability. It shows how closely a process is able to produce the output of its overall specifications.

Cpk = min [ (USL - mean) / (3 x standard deviation) , (mean - LSL) / (3 x standard deviation) ]

      = min [ (2400 - 1800) / ( 3 x 100) , ( 100 - 1600) / (3 x 100) ]

      = 0.667

Larger the Cpk is better. The larger Cpk is, the less likely it is that any item will be outside the specification limits. It generally wants a Cpk of at least 1.33 or higher to satisfy most customers. In given case, it is 0.667.