If a process variable is normally distributed, in the long runvirtually all observed

Chapter 16, Problem 5

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If a process variable is normally distributed, in the long runvirtually all observed values should be between and, giving a process spread of 6s.a. With LSL and USL denoting the lower and upper specificationlimits, one commonly used process capabilityindex is C . The value Cp 5 1 "indicates a process that is only marginally capable ofmeeting specifications. Ideally, Cp should exceed 1.33(a very good process). Calculate the value of Cp for eachof the cork production processes described in the previousexercise, and comment.b. The Cp index described in (a) does not take into accountprocess location. A capability measure that does involvethe process mean isCalculate the value of Cpk for each of the cork-productionprocesses described in the previous exercise, and comment.[Note: In practice, m and s have to be estimatedfrom process data; we show how to do this in Section 16.2]c. How do Cp and Cpk compare, and when are they equal?"