Studies on a machine that molds plastic water pipe indicate that when it is injecting 1-inch diameter pipe, the process standard deviation is 0.05 inches.The one-inch pipe has a specification of 1-inch plus or minus 0.10 inch.What is the process capability index (Cpk) if the long-run process mean is 1 inch?
A)0.50
B)0.67
C)1.00
D)2.00
E)none of the above

Question

Quizplus · Accepted Answer

Cpk = minimum((USL-mean)/(3*sigma), (mean-LSL)/(3*sigma))

USL = 1.10
LSL = 0.90
mean = 1.00
sigma = 0.05

Cpk = minimum((1.10-1.00)/(3*0.05), (1.00-0.90)/(3*0.05)) = minimum(0.67, 0.67) = 0.67

Therefore, the process capability index (Cpk) is 0.67. The best choice is B.

Studies on a Machine That Molds Plastic Water Pipe Indicate