Page 409 - Design for Six Sigma a Roadmap for Product Development

376 Chapter Ten

a. All parts necessary for the service are placed within easy reach
with no tools “ideally” required.
1
b. Following DFMA, the “ DFS ideal design” rule of thumb is
3
used, which states that in ideal design for assembly, approximately
one in every three parts will need to be unsecured and later rese-
cured by efficient methods such as snap-fit and release fastening.
Using these assumptions, the ideal service time for the parts that need
no additional removal or insertion can be given by

3T 1 T 2

2T 3 T 4
5
t min T T 6 (10.4)
3 3
where T 1 unsecured item removal time ( 2.4 s from database)
T 2 snap-fit item removal time ( 3.6 s from database)
T 3 unsecured item insertion time ( 3.8 s from database)
T 4 snap-fit item insertion time ( 2.2 s from database)
T 5 item acquisition time ( 4 s from database)
T 6 item set-aside time ( 1.4 s from database)

Therefore

3
2.4 3.6 2
3.8 2.2
t min 1.4 1.4
3 3
9 s (10.5)

and with N m 1, the time-based efficiency is given by

t min
N m
time
100%
T s
9
1

100%
235.2
3.8% (10.6)

The efficiency value is very low, leading us to conclude that the service
procedure needs to be simplified using efficient disassembly methods
and the assembly reconfigured so that the items requiring frequent
service are conveniently accessed. In our example, considering PCB as
a primary service structure, the assembly is reconfigured so that the
board is on the outermost layer (Fig. 10.8). Using the same database
values, the estimated time for both disassembly and reassembly T s ,
equals 16.5 s. Hence, the new efficiency is