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mass production perspective, any lost production time is bad. From an overall
lean system perspective, making smaller batches is good. The choice to level
will leave no option but to reduce the time it takes to change over, which means
having a controlled and standardized changeover process.
Some people do not like the fact that when you put this level of requirement
on the process there is pressure to perform. And there’s some risk of missing
production numbers. Our minds are designed to naturally protect us from risks,
and the purposeful creation of risk is not a natural act. This is the rub of the
Toyota Way. We must put ourselves in harm’s way, but not haphazardly. It
requires a carefully crafted system, and diligent effort and management of the
process, to minimize the risk. You must realize that when you sign up for the cre-
ation of a lean process, you sign up for life. If you want it to work, it’s a permanent
commitment.
So, why would you do this to yourself? If we look at any typical operation,
we hear terms like “bubble” and “wave,” which refer to the change in demand
and the amount of work that flows through the value stream. Many managers
spend time managing the waves—attempting to adjust the balance of resources
and constantly fighting the fires that erupt as a result of the crashing waves.
These managers are always looking for the day when they catch the wave and
get things back to “normal.” Unfortunately, like in the ocean, the next wave is
not far behind. This continuous riding of the waves diverts efforts from the
process of improvement. Management is devoting much of their time to the
containment effort rather than the strengthening activity.
Smoothing Demand for Upstream Processes
What if your demand were consistent? How would that affect your process? The
introduction into the value stream of consistent “customer” demand signals (the
quotes signify that heijunka is not the “true” customer demand) will provide a
smoothing effect for all of the processes. This smoothing allows for the stan-
dardization of resources, which greatly simplifies planning and control.
Let’s revisit our value stream model introduced in Chapter 3 and depicted in
Figure 7-2, below. We see that the future state value stream has a heijunka “board”
or “box.” This is a common approach to visually displaying the leveled schedule.
Each slot in the box represents a specific time period (such as 8: 00 A.M. to 8: 15 A.M.)
in which the material handler might pick up a production kanban, deliver it to the
pacesetter as the next order, and pick up what was produced based on the previ-
ous order. In reality there are many ways to do this; for example, sometimes the
orders are posted on a white board by the hour. There are several variations on the
theme, but all serve the same purpose—to show the “pitch” time increment
between when orders are delivered and picked up, and the quantity to produce