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 C p and C pk for this process? About what percent of all units of this liner will meet specifications?

Question

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 C p  and C pk  for this process? About what percent of all units of this liner will meet specifications?

Megan Trainor · Accepted Answer

Final Answer : LSL = 5.9 mm, USL = 6.1 mm. C p  is (6.1 - 5.9)/6(.02) = 1.67. C pk  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.

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