Studies on a machine that molds plastic water pipe indicate that when it is injecting 25 mm diameter pipe,the process standard deviation is 0.50 mm.The 25 mm pipe has a specification of 25 mm plus or minus 1.0 mm.What is the process capability index (Cp)?
A)0.50
B)0.67
C)1.00
D)2.00

Question

Quizplus · Accepted Answer

The process capability index (Cp) is calculated by dividing the tolerance (the specification range) by six times the process standard deviation. In this case, the tolerance is 1.0 mm and the process standard deviation is 0.50 mm. Therefore, Cp = (1.0/6*0.50) = 0.67. A Cp value of 1.00 indicates a perfect process, so the answer cannot be C or D, and a Cp value of 0.50 indicates a poor process, so the answer cannot be A. Thus, the best choice is B, which represents an acceptable process capability.

Studies on a Machine That Molds Plastic Water Pipe Indicate