Page 187 - The Toyota Way Fieldbook

Chapter 7. Leveling: Be More Like the Tortoise Than the Hare 163

the volume of the first group; and a third group, one-half again lower than the
second group (the volumes in the leveling example above represent a typical
example). Generally, the first group is relatively small in terms of the quantity
of part numbers but large as a percentage of total volume. (If you are thinking
that this is the Pareto principle in action, you’re exactly right. This method allows
you to isolate the “significant few” from the “trivial many.”)
We began with 25,000 part numbers. The top 100 part numbers in terms of vol-
ume accounted for 35 percent of the total sales volume for the company! That is a
significant reduction. An additional slice revealed that the volume for the number
one item was 10 times greater than the fiftieth item. It was decided to focus on lev-
eling production for the top 50 part numbers (out of 25,000). While looping
through the continuous improvement spiral, we work on specific segments or lay-
ers (slices), and each successive pass through the cycle brings the addition of sub-
sequent layers. After the first 50 parts are successfully leveled and the value stream
is performing consistently, the next 50 parts (or more) will be initiated.
With the focus quantity reduced to 50, the magnitude of the effort is mini-
mized and the benefit is maximized. Many people incorrectly assume that if it’s
not possible to level everything, it’s not possible to implement heijunka. In reality,
the question is a matter of simple math. Is it better to be stabilized zero percent
of the time on 100 percent of the items, or to be stabilized 100 percent of the time
on 25 percent of the items? This is not an all or nothing proposition.
As your operations develop greater capabilities, it becomes possible to con-
sider leveling smaller and smaller quantities. It may never make sense to level
all items. Consider the slice and dice: If 75 percent of all items are leveled—and
therefore 75 percent of the total resource needs are leveled—the remaining 25
percent of the resource time (people and equipment) can be devoted to the “as
needed” items. The raw materials may be shared between the leveled and non-
leveled items, and the additional need can easily be factored into the material
replenishment calculations.

Case Example: Leveling Workload in a
Custom Cabinet Shop
The workload required at various operations in this company fluctuated
greatly, depending on the product, which caused many problems,
including poor quality (workers were frequently rushed), line stoppage,
and unpredictable production schedules. Because of the custom nature
of the product, it was assumed that standardized work for the processes
was not possible.
When dealing with a situation of this nature, the apparent complexity
can be overwhelming. There were many interconnected and interrelated
issues resulting from the ripple effect of the workload (imagine the snake