Page 165 - Six Sigma for electronics design and manufacturing

Six Sigma for Electronics Design and Manufacturing
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The data volume is important in increasing the accuracy and the
amount of effort necessary to correct the design or the manufactur-
ing process to meet the process capability goals. This section will
also examine moving range control charts as a means of controlling
quality in low-volume production.
3. Determining gauge capability. The use of gauge repeatability and
reproducibility (GR&R) to quantify measurement variability will
be presented in Section 5.3. In addition, The relationship of GR&R
to six sigma concepts and calculations will be examined.
4. Determining short- and long-term process capability. Section 5.4
will discuss the issues of determining process capability during the
different stages of the product lifecycle, beginning with multiple
specifications of the product and prototype quantities manufac-
tured, and continuing with production volume. The strategies of
setting different quality expectations during prototype versus vol-
ume production will also be examined.
5.1 Process Average and Standard Deviation
Calculations for Samples and Populations
The knowledge of certain properties of a subset (sample), can be used
to draw conclusions about the properties of the whole set (popula-
tions). Properties can be of two types, as discussed in earlier chapters:
1. Quantitative (variable). These properties can be observed and
recorded in units of measure such as the diameter of shafts. The
units are all produced under replicating conditions in production.
2. Qualitative (attribute). These properties can be observed when
units are being tested with the same set of gauges or test equip-
ment; for example, the set of all shafts produced under the same
conditions, either fitting or not fitting into a tester consisting of a
dual set of collars. A shaft with a diameter within specifications
should fit into one of the collars whose diameter is equal to the
shaft upper specification limit, and the shaft should not fit into the
other collars whose diameter is equal to the lower specification lim-
it.

The sample size (n) is the random choice of n objects from a popula-
tion, each independent of each other. As n approaches , the sample
distribution values of average and standard deviation become equal to
that of the population.
It has been shown in Chapter 3 that variable control charts consti-
tute a distribution of sample averages, with constant sample size n.