Page 397 - Design for Six Sigma a Roadmap for Product Development

366 Chapter Ten

2. Techniques to calculate reliability of key parts and design ways to
reduce or eliminate coupling and other design weaknesses.
3. Derating—using parts below their specified nominal values.
4. Design failure mode–effect analysis (DFEMA), which is used to
search for alternative ways to correct failures. A “failure” is the
unplanned occurrence that prevents the system or component from
meeting its functional requirements under the specified operating
conditions.
5. Robustness practices by making the design insensitive to all uncon-
trollable sources of variation (noise factors).
6. Redundancy, where necessary, which calls for a parallel system to
back up an important part or subsystem in case it fails.

Reliability pertains to a wide spectrum of issues that include human
errors, technical malfunctions, environmental factors, inadequate design
practices, and material variability. The DFSS team can improve the reli-
ability of the design by

■ Minimizing damage from shipping, service, and repair
■ Counteracting the environmental and degradation factors
■ Reducing design complexity. (See El-Haik and Young 1999.)
■ Maximizing the use of standard components
■ Determining all root causes of defects, not symptoms, using DFMEA
■ Controlling the significant and critical factors using SPC (statistical
process control) where applicable
■ Tracking all yield and defect rates from both in-house and external
suppliers and developing strategies to address them

To minimize the probability of failure, it is first necessary to identify
all possible modes of failure and the mechanism by which these fail-
ures occur. Detailed examination of DFR is developed after physical
and process structure development, followed by prototyping; however,
considerations regarding reliability should be taken into account in
the conceptual phase when axiom 1 is employed. The team should take
advantage of existing knowledge and experience of similar entities and
any advanced modeling techniques that are available.
Failure avoidance, in particular when related to safety, is key. Various
hazard analysis approaches are available. In general, these approaches
start by highlighting hazardous elements and then proceed to identify
all events that may transform these elements into hazardous condi-
tions and their symptoms. The team then has to identify the corrective