Question

Product specifications call for a part at Vaidy​ Jayaraman's Metalworks to have a length of 1.100"±.060" Currently, the process is performing at a grand average of

1.1​00" with a standard deviation of 0.017​". Calculate the capability index of this process.

a. The Cpk of this process is? (round to two decimas)

b. Is the process​ "capable"?

Answer 1

To calculate capability index we require USL and LSL which we can decide from 1.1 +/- .06

Upper specification limit which is = 1.1 + .06= 1.16

Lower specification limit = 1.1 - .06 =1.04

Mean = 1.1

Standard deviation () = .017

C_{PK =} Minimum [ ( USL - Mean) / 3 , (Mean - LSL)/ 3 ]

= Minimum [ (1.16 - 1.1)/ 3* .017 , ( 1.1 - 1.04) / 3*.017 ]

= Minimum [ .06/.051 , .06/ .051 ]

= Minimum [ 1.18 , 1.18 ]

C_PK = 1.18

At C_PK value > 1 production process is said to be just capable but tight controls are required. If Production process C_PK is < 1 sproduction process cannot said to be capable . The C_PK is 1.18 which means it is capable under tight control that value should not be below 1.