Page 270 - Design for Six Sigma a Roadmap for Product Development

240 Chapter Eight

After satisfying axiom 1, design simplicity is pursued by minimizing
the information contents per axiom 2. In this context, information content
is defined as a measure of complexity and is related to the probability
of successfully manufacturing (producing) the design as intended.

8.4 The Independence Axiom (Axiom 1)

The design process involves three mappings between four domains
(Fig. 8.1). The first mapping involves the mapping between critical-to-
satisfaction (CTS) customer attributes and the functional require-
ments (FRs). A functional requirement is a solution-neutral, that is,
design-parameter-independent, statement of what a system does and
usually is expressed as a (verb, noun) pair or an active (verb, noun,
phrase) triplet (e.g., carry load, conduct heat). In this mapping, in all
elements of the physical structure there should be a team member
responsible for the structure’s life through the design algorithm
stages. Functional specifications are established and propagated up
regardless of the array of DPs used. The physical mapping is very crit-
ical as it yields the definition of the high-level minimum set of func-
tional requirements needed to accomplish the design objective from
the customer perspective. It can be performed by means of quality
function deployment (QFD) (Chap. 7). Once the minimum set of FRs or
CTSs are defined, the physical mapping may be started. This mapping
involves the FR domain and the design parameter (DP) codomain. It
represents the preliminary and detail design phases in the develop-
ment cycle and can be represented by design matrices, hence the term
“mapping” is used, as the high-level set of FRs are cascaded down to
the lowest level of decomposition. The set of design matrices forms the
conceptual physical structure that reveals coupling vulnerability and
provides a means to track the chain of effects for design changes as
they propagate across the structure.
The process mapping is the last mapping and involves the DP
domain and the process variables (PV) codomain. This mapping can be

Y=f(x)
Matrix A
CAs FRs DPs PVs
• • • •
• • • •
• • • •
Y=f(x) Matrix B

Physical Mapping Process Mapping
Figure 8.1 The design process mappings.