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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. What are the upper and lower specification limits for this product? The process is known to operate at a mean thickness of 6.03 mm. What is the Cp and Cpk for this process? About what percent of all units of this liner will meet specifications?
On May 01, 2024
LSL = 5.9 mm, USL = 6.1 mm. Cp is (6.1 - 5.9)/6(.02) = 1.67. Cpk is the lesser of (6.1 - 6.03)/(3∗0.02) = 1.17 and (6.03 - 5.9)/(3∗0.02) = 2.17; therefore, 1.17. The upper specification limit lies about 3 standard deviations from the centerline, and the lower specification limit is further away, so practically all units will meet specifications.