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A metal fabricator produces connecting rods with an outer diameter that has a 1 ± 0.02 inch specification. A machine operator takes several sample measurements over time and determines the sample mean outer diameter to be 1.004 inches with a standard deviation of 0.008 inch.
Calculate the process capability index for this example. (Round your answer to 3 decimal places.)
Process capability index ???
ANSWER:
Process capability index = 0.667
CALCULATION:
We have,
Mean, M = 1.004 inch
Upper specification limit, USL = 1 + 0.02 = 1.02 inch
Lower specification limit, LSL = 1 - 0.02 = 0.98 inch
Standard Deviation,
= 0.008 inch
The formula to work out the process capability index is as below
= Min{(1.004-0.98)/(3*0.008), (1.02-1.004)/(3*0.008)}
= Min (1, 0.67)
= 0.667
Therefore, the process capability index is 0.667