Page 36 - Six Sigma for electronics design and manufacturing

The Nature of Six Sigma and Its Connectivity to Other Quality Tools
Several industries, especially the auto industry, have worked to
standardize their relationship with their suppliers. They created the
Advance Product Quality Planning (APQP) Task Force. Its purpose
was to standardize the manuals, procedures, reporting format, and
technical nomenclature used by Daimler-Chrysler, Ford, and General
Motors in their respective supplier quality systems for their design
and manufacturing. The APQP also issued a reference manual devel-
oped by the Measurement Systems Analysis (MSA) Group for insur-
ing supplier compliance with their standards, especially QS9000.
These standards contain many of the principles of six sigma and asso- 7
ciated quality tools, such as Cpk requirements. These manuals were
published in the mid-1990s and are available from the Automotive In-
dustry Action Group (AIAG) in Southfield Michigan.
Six sigma can be used as a standard for design and manufacturing,
as well as a communication method between design and manufactur-
ing groups, especially when part of the design or manufacturing is
outsourced. This is important for companies in meeting shorter prod-
uct lifecycles and speeding up product development through faster ac-
cess to design and manufacturing information and the use of global
supply chains.
1.3 Defending Six Sigma
Six sigma, like many new trends or initiatives, is not without its crit-
ics and detractors. The author has run into several issues brought up
by engineers and managers struggling with six sigma concepts, and
has attempted to address these concerns by writing this book. Some of
the most frequent critiques of six sigma, and the author’s approach to
addressing these problems are listed below.
1. The goal of six sigma defects, at 3.4 PPM, and some of its princi-
ples, such as the ±1.5 sigma shift of the average manufactured part
from specification nominal, sound arbitrary. In addition, there is no
solid evidence as to why these numbers have been chosen.
These are reasonable assumptions that were made to implement six
sigma. There are other comparable systems, such as Cpk targets used
in the auto industry, that could substitute for some of these assump-
tions. Discussions of these concepts are in Chapters 2 and 3.
2. The cost of achieving six sigma might result in a negative return
on investment. Conventional wisdom once held that higher quality
costs more, or that there is an optimum point at which cost and quali-
ty balance each other, and any further investment in quality will re-
sult in negative returns (see the discussion of the quality loss function
in Chapter 6).
These beliefs are based on the misconceptions that more tests and