Page 172 - Design for Six Sigma a Roadmap for Product Development

Design for Six Sigma Project Algorithm 145

requirements. Technology and structure choices are sometimes
closely interlinked via the physical and process mappings when con-
ducted following design axioms. New technologies (DPs) that can
enable new structures and different technologies may suggest
different mapping of functional requirements (FRs). The pursuit of
linked technology and structure options may reveal new opportuni-
ties for delighters. Conversely, because axiom-driven structures
often have very long lifespans, they need to be relatively insensitive
to technology choices. An axiom-driven structure should enable
reimplementation of new technologies without undue impact on
either the structure or other mapping (portions) of the design.
Therefore, to assure the insensitivity of the structure to future
unknown technology, they need to be derived using design axioms. It
is wise to examine the robustness of a structure against current,
known technology and design alternatives. Structures need to be
sturdy against customer use, misuse, and abuse; errors in require-
ments and specifications; unanticipated interactions with other por-
tions of the solution entity; or process variations. The functional
requirements should be verified over a range of operational parame-
ters which exceed known requirements and specifications. This may
require sensitivity studies in a form of a classical DOE (design of
experiment) or Taguchi’s parameter design. Determining sensitivity
of design element performance due to changes in operating condi-
tions (including local environment and solution entity interactions)
over the expected operating range is an essential task for transfer
function optimization within the DFSS algorithm (Sec. 5.10).
As preferred and optimized choices are made for physical struc-
ture including ideal and transfer functions (Chap. 6), the require-
ments cascade should be reverified to assure that the high-level
requirements and Six Sigma specifications are met. A powerful
approach to reverification of the requirements cascade is to compare
the top-down mapping specification cascade with a bottom-up capa-
bility of achievement. The approach seeks to synthesize the func-
tional requirements specifications established for the individual
solution entity elements (components and subsystems), into specifi-
cation for the next higher-level solution entity element. The synthe-
sized specification is assessed against cascaded requirements and
specifications for the higher-level solution entity element. The syn-
thesis is repeated for each hierarchical level of design; components
to subsystem, subsystem to system, and further specifications are
evaluated against higher-level requirements and specifications
established during the top-down mapping process, to identify spe-
cific regions which don’t meet the Six-Sigma-level specification
for further study.