Page 64 - Six Sigma for electronics design and manufacturing

Chapter
2
The Elements of Six Sigma
and Their Determination

In this chapter, the concepts needed to define six sigma quality in de-
sign and manufacturing are differentiated from each other. Several
techniques are developed for analyzing individual parts, as well as
higher orders of complexity such as assemblies, modules, systems,
and product designs. In addition, techniques for measuring manufac-
turing line performance are also developed for use in the six sigma
concept. The following topics are discussed in this chapter:
1. The quality measurement techniques: SQC, six sigma, Cp and
Cpk. This section is a review of the different methods used to de-
sign for quality as well as to control quality. Several techniques are
outlined and the differences between the methods are contrasted.
2. The Cpk approach versus six sigma. In this section, the concept of
Cpk is analyzed and compared to six sigma. The Cpk approach re-
duces some of the ambiguities of the 1.5 shift of the process aver-
age used in the traditional Six Sigma calculations. Cpk calcula-
tions, including negative Cpk, are analyzed, and the effects of
average shifts on Cpk are also shown.
3. Calculating defects using normal distribution. In this section, de-
fect calculations are shown for variable and attribute processes
and designs. Many examples are shown for different conditions of
average shift and process variability.
4. Are manufacturing processes and supply parts always normally
distributed? Assuming normality of manufacturing process distri-

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