a foundation for creating flow and establishing standardization. In essence, this
isolation of variation is a basic application of heijunka,or leveling. By grouping
similar products, we were able to level the workload for the majority of the
process. The highly variable work is still difficult to standardize, but in this case
80 percent of the total is possible. This is an important aspect of creating stability.
Some basic applications of leveling can be done in the stability phase, and there
are advanced applications of heijunka as well, that will incrementally tighten the
timing and pressure on the system in later phases. (We will discuss this in detail
in Chapter 7.)
One common mistake is to attempt to establish flow or standardization too
soon. As we will go into in the next chapter, creating flow between operations
is designed to surface any issues quickly and to make them critical in nature
(ignoring them would be disastrous). If this step is taken before eliminating
major obstacles, the result will be too many problems and a consequent retreat
to the “old way.” Likewise, an attempt to standardize a chaotic process with a
high level of variability will most certainly cause frustration, since it is not pos-
sible to standardize variation.
If we liken the creation of lean processes to building a house, we understand
that in order to support the roof, we will need walls and trusses. Foundations and
subfloors, in turn, support the walls. This is easy to see and understand because a
house is a real, visible, tangible object with common elements (they all have roofs
of some type). A lean system, on the other hand, is not so clear. If you focus your
effort on developing an understanding of the intentof each phase, rather than the
application of lean tools, this process will be more successful. Understand the what
before trying to apply the how. The lean tools are applied to address specific needs,
and should not be applied simply because they are in the toolbox.
78 THETOYOTAWAYFIELDBOOK
Figure 4-9. Process stability after variation of welding time is isolated
Throughput Time (Days)
0510152025Nov-02Dec-02Jan-03Feb-03Mar-03A pr-03May-03Jun-03Jul-03Aug-03Sep-03Oct-03Nov-03Dec-03Jan-04Feb-04Mar-04A pr-04May-04Jun-04Jul-04Days