Page 106 - Six Sigma for electronics design and manufacturing

Table 3.1 Control chart factors
Observations
Upper control
Lower control
R /
subgroup n
X chart
R limit D 4
R limit D 3
= d 2
0
1.88
3.27
0
1.02
2.57
1.693
0.73
2.28
2.059
0
2.11
0
0.58
2.326
0
0.48
2.534
2.00
1.92
0.08
0.42
2.704
0.37
2.847
0.14
1.86
9 2 3 4 5 6 7 8 A 2 Factor for Six Sigma and Manufacturing Control Systems 1.128 75
2.970
1.82
0.18
0.34
10 0.31 0.22 1.78 3.078
11 0.29 0.26 1.74 3.173
12 0.27 0.28 1.72 3.258
13 0.25 0.31 1.69 3.336
14 0.24 0.33 1.67 3.407
15 0.22 0.35 1.65 3.472
16 0.21 0.36 1.64 3.532
17 0.20 0.38 1.62 3.588
18 0.19 0.39 1.61 3.640
19 0.19 0.40 1.60 3.689
20 0.18 0.41 1.59 3.735
– – – –
Lower control limit (LCL X )= X – 3 s = X – A 2 · R (3.2)
R Control limits
Upper control limit (UCL R ) = D 4 · R (3.3)
Lower control limit (LCL R ) = D 3 · R (3.4)
where
X = average of n observation in a subgroup
– –
X = average of all X s
R = average of all R
R = range of n observation in a subgroup (highest to lowest value)
A 2 = factor for X chart
D 3 = lower control limit factor for R chart
D 4 = upper control limit factor for R chart
d 2 = estimator for based on range of samples
3.2.3 Control and specification limits
Control chart limits indicate a different set of conditions than the
specification limits. Control limits are based on the distribution of