Page 116 - The Toyota Way Fieldbook

Chapter 5. Create Connected Process Flow 93

process is flawed. Learn to see operator deviation as a positive! Stop
and observe and find the real cause, which if corrected will yield a
stronger process.
If the cycle times were properly balanced and smooth flow achieved,
there is another less noticeable problem. Attempting single-piece flow
when the work cycle time is very short creates a high ratio of waste to
value-added. Here’s why: During any work process there is inherently
some amount of necessary waste, such as picking up the part and setting
the part down for the next operation. This waste can be minimized,
but in the best-case scenario will still require one-half to one second
for each motion (pick up, and put down). Assuming the best case, this
would require a total of one second per work cycle—a half second to
pick up, a half second to put down—of motion waste. If the work cycle
time is five seconds total, one second for handling amounts to 20
percent of the total time! This comes to over 30 percent on a three-
second operation. That is a huge amount of inevitable waste. Yet this
waste is often overlooked because of the assumption that if the material
is flowing and the operators are moving continuously, it is “lean.” As
we see here, that is simply not the case.
This operation would be improved by having two operators pick up
a part and complete it entirely, rather than breaking the operation
into multiple jobs in an attempt to create “flow.” The time would
be reduced by two seconds, and the result is 11 seconds to complete
(Figure 5-3). The net time per piece is 5.5 seconds (two people
working simultaneously produce two parts every 11 seconds and
11 seconds divided by 2 pieces = 5.5 seconds per piece), which is

Cycle balance chart: Fitting assembly

Takt time for 2 pieces = 10 seconds
12
10
Seconds 6
8
4
2
0
Operator 1 Operator 2

Figure 5-3. Cycle balance chart for improved fitting assembly