Page 223 - Design for Six Sigma a Roadmap for Product Development

DFSS Transfer Function and Scorecards 195

1. Obtain the high-level FRs from phase 2 QFD.
2. Define system boundaries from the project scope.
3. Conduct the zigzagging method to the lowest possible structure level
and identify the transfer functions in every level. The lowest level rep-
resents the very standard design parameters (DPs) or process vari-
ables (PVs) (Chap. 7). For example, in product DFSS projects,
dimensions, surface finish, and material properties are at the lowest
level. On the process side, machine speed and feed rate are the
corresponding-level PVs. On the service side, forms and fields are con-
sidered lowest levels. In many instances, the lowest hierarchical level
of the structure is owned by a vendor or a group of vendors due to
some outsourcing policy. A representation from the vendors should be
added to the team as necessary.
4. Define the respective hierarchical levels of design mappings.
5. Within a level, for each mapping, and for each FR, classify the
mapped-to DPs as
■ Signal M, and whether this is energy, information, or material
■ Other DPs and whether these are energy, information, or material
6. Plot the ideal function FR f(M) at a given constant DPs and
absence of noise factors.
7. Plot the P-diagram of every FR using step 5.
8. Add the noise factors to all P-diagrams. Noise factors are uncon-
trollable factors that inhibit or affect FR delivery and generate soft
and hard failure modes. The conceptual relation between score-
cards, structures, and FMEA is depicted in Fig. 6.7. The noise fac-
tors are generally categorized as piece-to-piece variation (e.g.,
manufacturing), changes in dimension or strength over time
(e.g., wear and fatigue), customer usage and duty cycle, external
environment (climate, road conditions, etc.), and coupling (e.g.,
interaction with neighboring subsystems).
9. Aggregate the chains of P-diagrams in every hierarchical level into
an overall structure using the precedence relationships in Sec. 6.3.2.

6.4 Design Scorecards and Transfer
Function Development

The transfer functions in the physical and process structures are usu-
ally captured in design scorecards, which document and assess quan-
titatively the DFSS project progress, store the learning process, and
show all critical elements of a design (CTSs, FRs, DPs, PVs) and their
performance. Their benefits include documenting transfer functions