136 THETOYOTAWAYFIELDBOOK
Takt Time as a Design Parameter
Many people get confused about the difference between takt time and cycle time.
Takt time is not a tool. It is a concept that is used to design work, and it measures
the pace of customer demand. In terms of calculation, it is the available time to pro-
duce parts within a specified time interval divided by the number of parts
demanded in that time interval. The number you get tells you, for instance, that a
part needs to be produced every three minutes to satisfy customer demand. Seem
straightforward? Yet takt time is often misunderstood. And determining it for lines
that produce a variety of products with varying demands, becomes a tricky issue.
Here’s an example: If the available operation time for one shift is 400 minutes,
and the demand for the product is 400 per shift, the time allotted per piece (takt
time) is one minute for each part. The cycle time of each operation needs to be one
minute or less on average to meet the demand. If the cycle time (actual time to
complete the tasks in a single job) is greater than takt, the operation will be a
bottleneck and additional time will be necessary to meet the production schedule.
If the cycle time is less than takt, there will be overproduction or waiting time.
Amajor challenge that arises is determining the customer demand. In most
cases (unless you are a supplier to Toyota) the demand varies significantly. How
can takt time be determined when the demand varies? You must understand
that takt time is a “reference point” for designing the work, and consider what
the effect of an incorrect reference point will be.
The first thing to recognize is that cycle times—the time necessary to complete
the task—do not vary significantly if they are standardized. Using our example
above, the machine cycle time is 23 seconds and the operator work and walk
time is 56 seconds. The combined cycle time is 75 seconds and varies only to the
extent that the operator can load the robot faster now and then. This means that
the output from this process will be fairly consistent provided there are no losses
due to equipment downtime. If the demand varies significantly, what effect does
this have on the operation? None. The operation cycle time will not vary more
than a few seconds. If demand increases, how will the requirement be met? The
operation time can be increased (e.g., using overtime if the demand does not
increase too much). The utilization of takt time will not change this reality.
TIP
A New Standard Requires a Learning Period
It is not uncommon to see a slight drop in performance as people
adjust to the new method. Do not rush to “go back to the old way.”
Continue observing to ensure that the method is being followed as
planned and that any minor adjustments are made immediately.