Page 447 - Design for Six Sigma a Roadmap for Product Development

408 Chapter Eleven

7. Classifying any special PVs as “special” characteristics that will
require controls such as “operator safety” characteristics as related
to process parameters that do not affect the product but may
impact safety or government regulations applicable to process oper-
ation. Another category of process “special” characteristics are the
high-impact characteristics, which occur when out-of-specification
tolerances severely affect operation or subsequent operations of the
process itself but do not affect the component(s) or subsystem being
processed. Both types of classification are inputted to the PFMEA
and are called “special” characteristics.
8. Deciding on “process controls” as the methods to detect failure modes
or the causes. There are two types of controls: (a) those designed to
prevent the cause or failure mechanism or failure mode and its
effect from occurring and (b) those addressing the detection of
causes, or mechanisms, for corrective actions.
9. Identifying and managing of corrective actions. According to the
RPN numbers, the team moves to decide on the corrective actions,
as follows
a. Transferring the risk of failure to other systems outside the
project scope
b. Preventing failure altogether [e.g., process poka-yoke (error-
proofing)]
c. Mitigating risk of failure by
(1) Reducing “severity” (altering or changing the DPs)
(2) Reducing “occurrence”
(3) Increasing the “detection” capability (e.g., brainstorming
sessions, concurrently using top-down failure analysis such
as FTA)
PFMEA should be conducted according to the process structure. It
is useful to add the PFMEA and DFMEA processes to the design
project management charts. The PERT or CPM approach is advis-
able. The black belt should schedule short meetings (less than 2 h)
with clearly defined objectives. Intermittent objectives of an
FMEA may include task time measurement system evaluation,
process capability verifications, and conducting exploratory DOEs.
These activities are resource- and time-consuming, introducing
sources of variability to the DFSS project closure cycle time.
10. Review analysis, document, and update the PFMEA. The PFMEA
is a living document and should be reviewed and managed on an
ongoing basis. Steps 1 to 9 should be documented in the appropri-
ate media.
An example of the time delivery distribution process PFMEA is
depicted in Fig. 11.7.