Toyota Way Fieldbook : A Practical Guide for Implementing Toyota's 4Ps

138 THETOYOTAWAYFIELDBOOK

much of a change would be needed to meet a hypothetical takt of 90 seconds
per part. We see that two operations are currently over that estimated takt time.
If these two operations were improved, how much improvement would
be necessary before the next balance “plateau” is reached? Figure 6-9 shows the
next plateau. Several other jobs have a cycle time of approximately 60 seconds.
Reducing the two jobs to 60 seconds would allow the entire value stream to flow
at a rate of one part every 60 seconds. Does that mean we should immediately
pursue this goal? In fact if we do this and the takt time based on actual demand
is greater than 60 second we will be over producing—the fundamental waste.
After reducing the time it took for the two operations, it was determined that
the actual takt rate necessary to meet the demand was 80 seconds. This allowed
for “rebalancing” the operations and reducing their total number. In this case, after
reducing the time it took to grind and buff, the total amount of work across all
operations added to 645 seconds. If we divide 645 seconds of work by the takt
of 80 seconds, we get a total of 8 operations at the takt time, compared to the
original 12. Thus, we could reduce one-third of the operations by rebalancing to
the 80-second takt. If this were manual processes, it would equate to 4 fewer
operators (note: these “extra” operators could be used to develop a team leader
structure as outlined in Chapter 10). It is interesting to note that if we balanced
to the faster takt of 60 seconds, 11 operators would be needed (645/60
10 .75).
Thus, going faster can cost more (provided it was not necessary to go faster).
Use takt time to help make decisions about how the work will be designed
and which improvements need to be made to meet the need. If you select a takt
time that is too high, you will not meet the production need, which is worse
than choosing a number that’s too low and exceeding the need (provided you did
not add resources to meet the false need). It is always easier to stop production

Line 1 Cycle Times

0

20

40

60

80

100

120

NOTCH/PIERCE

FORM 1FORM 2

SPOT WELDSTUD WELDSEAM WELD

GRIND BUFF

SPOT WELDFOOT WELD

ATTACH COVER

LOAD

Takt Time = 90 seconds

Next Plateau

Figure 6-9. Cycle balance chart showing next level plateau