operations actually stop. It seems that nothing can be more uncomfortable in a
traditional manufacturing operation than stopping. Yet the alternative to stop-
ping is overproducing—producing more, sooner, or in greater quantity than the
next operation requires. Toyota considers overproduction to be the worst of the
seven types of waste because it leads to the other six types of waste (inventory,
movement, handling, hidden defects, etc.). This is the key to understanding how
less can be more (less means fewer parts produced in some individual steps in
the process, more means getting more value-added activity done from the overall
process). The case example below explains a typical situation of overproduction
that reduced the ability to meet the customer requirement.
Case Example: Control Overproduction to Improve
Operational Availability
While standing in the circle and observing a fabrication line, it was
clear that overproduction was rampant. The line was filled with product,
much of it stacked two and three layers deep. The workers were all busy,
but we could see that the operators overproducing were engaged in
“busy work” such as stacking and positioning the excess product.
Operators typically reached a point when no additional work would fit
on the line, and then excess time was spent care-tending the overpro-
duction (inventory). Cycle time comparisons to takt time revealed—
no surprise—that these operations were below the takt time and had
extra time available. Since they were not provided with additional value-
adding tasks, the operators filled their extra time by overproducing
and care tending.
Observation also showed that the process downstream of the over-
production (the customer) had to spend additional time moving and
unstacking the product that was poorly presented in large batches. The
cycle time of this operation was at takt time, but with the additional work
required to move and unstack product, the total time actually exceeded
the takt time. It could not achieve customer demand during scheduled
work hours. In this case, the supplier process created the excess waste,
but the negative effect was realized at the customer process.
We asked the operators at the initial operations to stop, and to stand
doingnothing, rather than to continue producing when the next process
had more than enough material to work with. It is, of course, very uncom-
fortable for operators to do nothing because they’ve been conditioned
by management to “keep busy.” Toyota stresses the importance of this
concept because it allows everyone to see and understand the amount
of opportunity available. Everyone can see the idle time because it is not
beingcloudedby busy work (overproduction).