Page 396 - Design for Six Sigma a Roadmap for Product Development

Design for X 365

TABLE 10.4 Cost Differential Worksheet

Proposed design Redesign
Item Cost, $ Item Cost, $
Base (aluminum) 12.91 Base (nylon) 13.43
Bush (2) 2.40* Motor screw (2) 0.20*
Motor screw (2) 0.20 Set screw 0.10*
Setscrew 0.10* Plastic cover, including tooling 8.00
Standoff (2) 5.19
End plate 5.89
End-plate screw (2) 0.20*
Plastic bush 0.1*
Cover 8.05
Cover screw (4) 0.40*
Totals 35.44 21.73
*Purchased in quantity. Purchased motor and sensor subassemblies not included. Redesign:
tooling costs for plastic cover $5000.

7. Calculate the total savings in terms of both time (step 4) and parts reduc-
tion (step 6):
Total savings savings from assembly time reduction
savings from parts reduction

$0.95 $13.71
$14.66 (10.3)

The breakeven volume equals 342 total assemblies.

10.3 Design for Reliability (DFR)
Reliability is the probability that a physical entity delivers its functional
requirements (FRs) for an intended period under defined operating con-
ditions. The time can be measured in several ways. For example, time in
service and mileage are both acceptable for automobiles, while the num-
ber of open-close cycles in switches is suitable for circuit breakers. The
DFSS team should use DFR while limiting the life-cycle cost of the design.
The assessment of reliability usually involves testing and analysis of
stress strength and environmental factors and should always include
improper usage by the end user. A reliable design should anticipate all
that can go wrong. We view DFR as a means to maintain and sustain
Six Sigma capability over time. DFR adapts the law of probability to
predict failure and adopts:

1. Measures to reduce failure rates in the physical entity by employ-
ing design axioms and reliability science concurrently.