Question

A key joint in a precision machining process has a lower specification limit of a width of 0.99 mm and an upper specification limit of 1.01 mm. The standard deviation is 0.005 mm and the mean is 1 mm. The company wants to reduce its defect probability and operate a "Six Sigma process." To what level would this company have to reduce the standard deviation in the process to meet this target?

Answer 1

Answer:

To meet this target, the standard deviation has to be reduced to 0.0033 mm.

Explanation:

The objective of a six-sigma process is to ensure that the results outside the specifications are limited to the results corresponding to 3 sigma above the average or 3 sigma below the average, comprising a range of 6 sigma between the maximum and minimum values of the specifications for that process.

It implies that 99.7% of the outcomes of the process will be satisfactory and only 0.3% will fall out of the specifications.

If the actual specifications are 0.99 and 1.01, the standard deviation for the process to achieve the sig sigma level has to be

$US-LS=1.01-0.99=6\sigma\\\\6\sigma=0.02\\\\\sigma=0.02/6=0.0033$

To meet this target, the standard deviation has to be reduced to 0.0033 mm.