Page 112 - Design for Six Sigma a Roadmap for Product Development

Product Development Process and Design for Six Sigma 87

problem solving such that the design entity can live up to its committed
potentials. Unfortunately, the latter mode consumes the largest portion
of the organization’s human and nonhuman resources. The design for Six
Sigma theory highlighted in this book is designed to target both modes
of operation.
The most recent trends in design research are featured by two streams
of development for enhancing the design process in order to create better
design solutions. The first stream is concerned with improving design
performance in the usage environment; the second is related to concep-
tual methods. The method of robust design as suggested by G. Taguchi
belongs in the first stream (Taguchi 1986, 1993, 1994). In this method, a
good design is the one that provides a robust solution for stated func-
tional objectives and can be accomplished through a design process
constituted from three phases: the concept (system) design, parameter
design, and tolerance design. For the second stream, a huge body of
research* in the design methodology arena has been published in
German on the design practice. Most of these efforts are listed in the
German Guidelines VDI (Varian Destscher Ingenieure), 2221 (Hubka
1980, Phal and Beitz 1988). The latest development in the second stream
is the scientifically based design as suggested by Suh (1990). A major
concern of the design principles is the design vulnerabilities that are
introduced in the design solution when certain principles are violated.
These vulnerabilities can be resolved or at least reduced by the efficient
deployment of basic design principles called the axioms. For example, the
functional coupling (lack of controllability) will be created in the design
solution when the independence axiom is not satisfied.
The theory of Design for Six Sigma (DFSS) is defined in this book as
a scientific theory comprising fundamental knowledge areas in the
form of perceptions and understandings of different fields, and the
relationships between these fundamental areas. These perceptions
and relations are combined to produce consequences in the design
entity, which can be, but are not necessarily, predictions of observa-
tions. DFSS fundamental knowledge areas include a mix of proposi-
tions and hypotheses, categorizations of phenomena or objects,
ideation, and conception methods such as axiomatic design (Chap. 8)
and TRIZ (Chap. 9) and a spectrum of empirical statistical and math-
ematical models. † Such knowledge and relations constitute our DFSS
theory. In the conception arena, this theory builds on the theoretical
system of other methods and can be one of two types: axioms or

* The reader is encouraged to visit the Appendix of this chapter for more literature on
design theory.
† Abstract of observations of real-world data.