Page 191 - Six Sigma for electronics design and manufacturing

Six Sigma for Electronics Design and Manufacturing
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GR&R data by multiplying the range of part averages as measured
by the operators by the constant K 3 . K 3 is calculated from d * in
2
Table 5.6, depending on the number of parts examined in the
GR&R measurements, as follows:
PV = R p · K 3
K 3 = 5.15/d *
(5.17)
2
The values for K 3 are for number of parts examined in the GR&R:
K 3 = 3.65 2.70 2.30 2.08 1.93 1.82 1.74 1.67 1.62 (5.16)
n p = 2 3 4 5 6 7 8 9 10
TV = G R & R + P V 2 (5.18)
2
3. If the process variation is known through process capability stud-
ies and is based on six sigma, then P can be derived independent-
ly from the GR&R study and used for PV and TV calculations, with
PV = 5.15 · P .
The GR&R% of total variation can be used to determine if the meas-
urement system is acceptable for its intended applications. General
guidelines for the value of GR&R% are:
If GR&R% < 10%, then the measurement system is acceptable
If 10% < GR&R% < 30%, then the system may be acceptable, based
on whether the part characteristic classification is not critical or
from customer input
If GR&R%0 > 30%, then the system is not acceptable. It is then de-
sirable to seek resolution through the use of quality tools, better
operator training, or the purchase of new inspection equipment.
5.3.4 GR&R examples
Example 5.15
Table 5.7 is a complete GR&R example of three operators and two tri-
– –
als, measuring parts with specifications ±0.500. R is obtained from
the average R of the three operators and is equal to 0.0383. X diff is ob-
tained from the difference between the highest average operator and
the lowest and is equal to 0.0600.
X
EV = X diff · K 1 = 0.03833 · 4.56 = 0.1748
2
2
2
AV= [( 0 .0 6 · 2 .7 0 ) – ( E V / n r) ] = [0 .0 2 6 2 4 4 – ( 0 .1 7 4 8 / 2 0 )] = 0.1572
2
2
GR&R = 0 .1 7 4 8 + 0 .1 5 7 2 = 0.2351