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

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

0

2

4

6

8

10

12

Operator 1 Operator 2

Seconds

Takt time for 2 pieces = 10 seconds

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