Page 386 - Design for Six Sigma a Roadmap for Product Development

356 Chapter Ten

1. Use DFX as early as possible in the DFSS algorithm.
2. Start with DFA and Design for Variety for product projects and
Design for Service for transactional projects.
3. From the findings of step 2, determine which DFX to use next. This
is a function of DFSS team competence. Time and resources need to
be provided to carry out the “design for” activities. The major chal-
lenge is implementation.
A danger lurks in the DFX methodologies that can curtail or limit
the pursuit of excellence. Time and resource constraints can tempt
DFSS teams to accept the unacceptable on the premise that the short-
fall can be corrected in one of the subsequent steps—the second-chance
syndrome. Just as wrong concepts cannot be recovered by brilliant
detail design, bad first-instance detail designs cannot be recovered
through failure-mode analysis, optimization, or tolerance.

10.2 Design for Manufacture
and Assembly (DFMA)

DFM and DFA are systematic approaches within the DFX family that
the DFSS team can use to carefully analyze each design parameter
(DP) that can be defined as part or subassembly for manual or auto-
mated manufacture and assembly to gradually reduce waste. Waste, or
muda, the Japanese term, may mean any of several things. It may
mean products or features that have no function (do not add value) and
those that should have been trimmed (reduced, streamlined) using the
zigzagging method in the physical mapping. It may also mean prolif-
eration of parts that can be eliminated using the zigzagging method in
the process mapping as well. But the most leverage of DFX in the
DFSS algorithm, beyond the design axioms, is attacking the following
muda sources: (1) assembly directions that need several additional
operations and (2) DPs with unnecessarily tight tolerances.
As a golden rule, the DFSS team should minimize the number of
setups and stages through which a high-level DP (e.g., a part or sub-
assembly) must pass through before it becomes a physical entity. This
objective is now feasible and affordable because of the significant
development in computer numerically controlled (CNC) machines with
single-setup machining and multiaxis capabilities. The employment of
CNC machines will reduce lead times, tooling, and setup costs while
responding to customer demands with added flexibility. Single-setup
machines are usually equipped with touch trigger probe measuring
part position and orientation. By reducing expensive fixtures and
setup times, CNC machines gradually become very attractive with