Page 123 - Design for Six Sigma a Roadmap for Product Development

98 Chapter Three

CAs FRs PVs
• •
• (CTQs)CT •
• •

Physical mapping Process mapping
Figure 3.18 The design process according to Six Sigma.

(i.e., creative or incremental) is the deciding factor of whether to mod-
ify existing mappings of the datum design or develop new ones.
Many design practices, including DMAIC, drive for finding solutions
in the manufacturing environment, the last mapping, for a problematic
CTS. However, these practices don’t employ the sequential mappings,
design decomposition, and design principles in pursuing a solution that
is usually obtained with no regard to the coupling vulnerability, that is,
solving a design problem with process means by simply employing
*
the process variables, as the x variable. The conceptual framework
of current Six Sigma can be depicted as shown in Fig. 3.18, thus
ignoring the DPs. Additionally, we have the following remarks in the
context of Fig. 3.18:

■ The black belt may blindly overlook the need for design changes
(altering the DP array) when adjusting the PVs is not sufficient to
provide a satisfactory solution, that is, when the current process
reaches its entitlements. The risk in this scenario occurs when the
black belt may introduce a major manufacturing change, namely,
altering the PV array, when it is unnecessary.
■ Another disadvantage is concerned with ignorance of coupling which
may introduce new symptoms in CTSs other than the ones intended
when the solution to a problem is institutionalized.
■ On the other hand, taking the PVs as the x variable is usually
cheaper than taking the DPs as the x variable since the latter
involves design change and a process change while the former
calls only for process changes. The adjustment of process variables
may or may not solve the problem depending on the sensitivities
in the physical and process mapping.
Solutions to a design or process problem can be implemented
using alterations, changes, in independent variables, the x varible.

*Recall the y f(x) notation in DMAIC.