Page 115 - Design for Six Sigma a Roadmap for Product Development

90 Chapter Three

research is at the heart of operational vulnerabilities as it deals with
the assignment of tolerances in the design parameters and process
variables, the assessment and control of manufacturing processes, the
metrological issues, as well as the geometric and cost models.
On the contrary, the conceptual vulnerabilities are usually over-
looked because of the lack of a compatible systemic approach to find
ideal solutions, ignorance of the designer, the pressure of schedule
deadlines, and budget limitations. This can be attributed partly to the
fact that traditional quality methods can be characterized as after-the-
fact practices since they use lagging information to developmental
activities such as bench tests and field data. Unfortunately, this prac-
tice drives design toward endless cycles of design-test-fix-retest, creat-
ing what is broadly known as the “firefighting” mode of operation, that
is, the creation of design hidden factories. Companies who follow these
practices usually suffer from high development costs, longer time to
market, lower quality levels, and marginal competitive edge. In addi-
tion, corrective actions to improve the conceptual vulnerabilities via
operational vulnerability improvement means are only marginally
effective if at all useful. In addition, these corrective actions are costly
and hard to implement as design entity progresses in the development
process. Therefore, implementing DFSS in the conceptual phase is a
goal and can be achieved when systematic design methods are inte-
grated with quality concepts and methods upfront. Specifically, in this
book, we developed a DFSS theory by borrowing from the following fun-
damental knowledge arenas: quality engineering (Taguchi 1986), TRIZ
(Altshuller 1988), axiomatic design principles (Suh 1990), and theory of
probability and statistical modeling. The DFSS objective is to attack
the design vulnerabilities, both conceptual and operational, by deriving
and integrating tools and methods for their elimination and reduction.
In general, most of the current design methods are empirical in
nature. They represent the best thinking of the design community
that, unfortunately, lacks the design scientific base while relying on
subjective judgment. When a company suffers as a result of detrimen-
tal behavior in customer satisfaction, judgment and experience may
not be sufficient to obtain an optimal Six Sigma solution. This is
another motivation to devise a DFSS method to address such needs.
Attention begins to shift from improving the performance during
the later phases of the design life cycle to the front-end phases
where product development takes place at a higher level of abstrac-
tion, namely, prevention versus solving. This shift is also motivated
by the fact that the design decisions made during the early stages of
the design life cycle have the greatest impact on total cost and qual-
ity of the system. It is often claimed that up to 80 percent of the total
cost is committed in the concept development phase (Fredriksson