In this chapter, the concepts needed to define six sigma quality in design 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 manufacturing line performance are also developed for use in the six sigma concept. The following topics are discussed in this chapter: 1 2 3 4
1. The quality measurement techniques: SQC, six sigma, Cp and Cpk. This section is a review of the different methods used to design 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 reduces some of the ambiguities of the 1.5 a shift of the process average used in the traditional Six Sigma calculations. Cpk calculations, 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, defect 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 distribution is an important part of calculation defects, yields, and performing other statistical analyses of six sigma. In this section, the requirements for assuming normal distribution of manufacturing process are examined, as well as tests that can be made to review normality of data. In addition, methods for handling normal distribution of data for six sigma analysis are also shown.