Page 438 - Design for Six Sigma a Roadmap for Product Development

400 Chapter Eleven

Before embarking on any FMEA exercise, we advise the black belt to
book the FMEA series of meetings in advance, circulate all relevant
information ahead of the FMEA meetings, clearly define objectives at
the start of each meeting, adhere to effective roles, and communicate
effectively.
The fundamental steps in the DFMEA to be taken by the DFSS
team are
1. Constructing the project boundary (scope) as bounded by the phys-
ical structure. Components, subsystems, and systems are different
hierarchical levels. The team will start at the lowest hierarchical
level, the component level, and proceed upward. The relative infor-
mation from the lower levels is inputted to the next higher level
where appropriate in the respective columns.
2. Constructing the block diagram that fully describes coupling and
interfaces at all levels of the hierarchy within the scope. Interfaces
will include controlled inputs (the DPs) and uncontrolled input
such as environmental factors, deterioration, manufacturing, and
DFX methods.
3. Revisiting the physical structure at all hierarchical levels where
the respective FRs are defined. The task here is to make sure that
all DPs in the physical structure end up being hosted by some com-
ponent or subsystem. The set of components constitute the bill of
material of the project.
4. Identifying the potential failures for each hierarchical level in the
structure. The team needs to identify all potential ways in which
the design may fail. For each FR in the structure, the team will
brainstorm the design failure modes. Failure modes describe how
each hierarchical entity in the structure may initially fail prior to
the end of its intended life. The potential design failure mode is the
way in which a physical entity in the structure may fail to deliver
its array of FRs.
5. Studying the failure causes and effects. The causes are generally
categorized as weaknesses due to
a. Design weakness because of axiom violation. In this type of
failure causes, a component is manufactured and assembled to
design specifications. Nevertheless, it still fails.
b. Noise factors mean effects and their interaction with the DPs:
(1) Unit-to-unit manufacturing and assembly vulnerabilities
and deficiencies, such as a component not within specifica-
tions. Assembly errors, such as components manufactured
to specifications but with attached assembly process error
at the higher levels in the structure. In addition, material
variation is fitted under this type.