Question

4) The specification for a plastic liner for concrete highway projects calls for a thickness of 6.0 mm 0.1 mm. The standard deviation of the process is estimated to be 0.02 mm. The process is known to operate at a mean thickness of 6.03 mm. Your manager has requested the process produce no more than 3.4 defects per 1 million produced. Calculate Cpk and then determine if the process is capable.

Answer 1

Cpk = minimum of Upper specification limit - X X - Lower specification limit 30

[6.1 - 6.03 6.03 - 5.9 Cpk = minimum of 3 x 0.02' 3 x 0.02

Cpk  = minimum of [ 1.17 , 2.17)

Cpk  = 1.17

A Cpk value of 1.17 suggests that the process is capable of producing no more than 6200  defects per million. Hence the process is not capable of producing no more than 3.4 defects per million produced.