Page 183 - The Toyota Way Fieldbook

Chapter 7. Leveling: Be More Like the Tortoise Than the Hare 159

TRAP
Use Inventory Reduction as a Yardstick for Success,
Not a Goal
Many people pursue inventory reduction as a primary goal of lean
activities. There are numerous ways to achieve this goal, including
manipulation of the inventory. It is better to establish a goal to
create connected flow and to use inventory as a measure of success.
Kanban are used to control inventory, and it’s simple to measure
the effectiveness of the process by regulating the kanban. Inventory
control via kanban is standardized, and the possibility of false
manipulation is reduced.

These reductions should be done systematically, either as improvements are
made to the process or to force the need for improvements. The quantity of
inventory needed to support a process can be used as a yardstick for your
improvement efforts. Sustainable inventory reductions are an indication of a
capable process.
Inventory turns can also be influenced by the kanban. If the part quantity
per kanban (also the container quantity) is reduced, the kanban will “cycle” more
frequently, moving inventory through the process at a faster rate. Reducing the
quantity per kanban also provides a greater degree of flexibility in the replenish-
ment process, and reduces the size of the work area and waste. Strange as it
seems, having more kanban “in the system” is an advantage. For example, if the
total inventory level of an item is 2,000 pieces, it’s better to have 20 kanban of 100
pieces each than two kanbans of 1,000 pieces each. It’s difficult seeing the
demand with only two kanban in the system, and each time a kanban is
returned, it must be filled immediately.

A Leveled Schedule Dictates Replenishment

In addition to the smoothing effect for all processes, heijunka establishes a
“pitch” time. Because materials are being consumed at a standard rate during
a defined pitch time, it’s possible to establish a defined process for material
replenishment. Material replenishment is subordinate to the primary value
adding operation; therefore, establishment of material replenishment “routes”
or methods should not be attempted before creating a standardized “core” in the
primary process.
The following example illustrates how a leveled schedule dictates the mate-
rial replenishment needs and establishes a consistent requirement. This allows