Page 398 - Design for Six Sigma a Roadmap for Product Development

Design for X 367

actions to eliminate or reduce these conditions. One of these approaches
is called fault-tree analysis (FTA). FTA uses deductive logic gates to
combine events that can produce the failure or the fault of interest
(Sec. 11.3). Other tools that can be used in conjunction with FTA
include DFMEA and PFMEA as well as the fishbone diagram.

10.4 Design for Maintainability
The objective of Design for Maintainability is to assure that the design
will perform satisfactorily throughout its intended life with a minimum
expenditure of budget and effort. Design for maintainability (DFM),
Design for Serviceability (DFS), and Design for Reliability (DFR)
are related because minimizing maintenance and facilitating service
can be achieved by improving reliability. An effective DFM minimizes:
(1) the downtime for maintenance, (2) user and technician maintenance
time, (3) personnel injury resulting from maintenance tasks, (4) cost
resulting from maintainability features, and (5) logistics requirements
for replacement parts, backup units, and personnel. Maintenance
actions can be preventive, corrective, or recycle and overhaul.
Design for Maintainability encompasses access and control, displays,
fasteners, handles, labels, positioning and mounting, and testing. The
DFSS team needs to follow these guidelines:
■ Minimize the number of serviceable design parameters (DPs) with
simple procedures and skills.
■ Provide easy access to the serviceable DPs by placing them in ser-
viceable locations. This will also enhance the visual inspection
process for failure identification.
■ Use common fasteners and attachment methods.
■ Design for minimum hand tools.
■ Provide for safety devices (guards, covers, switches, etc.).
■ Design for minimum adjustment and make adjustable DPs accessible.

The DFSS team should devise the criteria for repair or discard deci-
sions within the context of life-cycle costing. The major maintainability
cost factors to consider include transportation, shipping, and handling;
training of maintenance people; and repair logistics, which encom-
passes the design of service, production, distribution, and installation
of repairable DPs (components and subassemblies).
The “repair” procedure should target
■ Enhancing the field repair capability to react to emergency situations
■ Improving current repair facilities to reflect the design changes