Page 445 - Design for Six Sigma a Roadmap for Product Development

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cross-multiply the rate of the effect by the RPN to total each row
(cause). These totals are then used to analyze and prioritize where to
focus the effort when creating the DFMEA. By grouping the causes
according to their classification (coupling, environment, manufactur-
ing, wear, etc.), the team will firm up several hypotheses about the
strength of these types of causes to devise their attack strategy.

11.4 Process FMEA (PFMEA)
The activities in the PFMEA are similar to those of the DFMEA but
with focus on process failures. The fundamental steps in the PFMEA
to be taken by the DFSS team are
1. Constructing the project processes boundary (scope) as bounded by
the process structure. The team can maximize its design quality
by preventing all manufacturing, assembly, and production failures.
Starting with the DFMEA at the lowest hierarchical level, the
component level, the team should utilize the component process
structure to map all the relevant processes. The team then proceeds
to the next higher hierarchical, subsystem, level, finishes all sub-
system PFMEAs, and proceeds upward.
2. Constructing the corresponding PFMEA process mapping as formed
from step 1 above that fully describes coupling and interfaces at that
level of the hierarchy within the process structure and scope. Inter-
faces will include controlled inputs (the PVs) and uncontrolled
input noise such as manufacturing and assembly errors and varia-
tions. The team may start with macrolevel process mapping, but
the maximum leverage is obtained at the micro mapping.
Micromappings exhibit detailed operations, transportation,
inspection stations, cycle times, and so on. The relative information
from the lower levels is inputted to the next higher hierarchical
PFMEA level, where appropriate, in the respective columns.
3. Revisiting the process structure at all hierarchical levels where
the respective DPs are defined. The task here is to make sure that
all PVs in the process structure end up being hosted by some
process. The set of mutually exclusive processes constitute the
production or manufacturing line of the project.
4. Identifying the potential failures for each hierarchical level in the
process structure. Having gone through the corresponding hierar-
chical level DFMEA, the team needs to identify all potential ways
in which the design may fail as a result of all process failures. For
each design parameter in the structure, the team will brainstorm
the process failure modes. Failure modes describe how each hier-
archical entity in the structure may initially fail prior to the end