Indicators of Instability
There is a wide belief that stability is indicated mainly by equipment performance.
As a result, the pursuit of certain lean tools—like “quick changeover”—and
attacking equipment failures through preventative maintenance become pri-
mary activities. Developing process stability is not an end onto itself. In fact, it’s
more about creating a foundation for further aspects of a lean process. Through
direct observation, an unstable process is indicated by the following conditions:
◆ A high degree of variation in performance measures—either pieces pro-
duced or pieces per labor hour.
◆ Changing the “plan” often when a problem occurs. This includes relocating
labor or leaving a position vacant when an absence occurs, moving product
to another machine when a breakdown occurs (and thus not producing
the planned product), and stopping work in the middle of an order to
change to another order.
◆ It is not possible to observe a consistent pattern or method to the work.
◆ Batches or piles of work in process (WIP) that are random—sometimes
more, sometimes less.
◆ Sequential operations that operate independently (island processes).
◆ Inconsistent or nonexistent flow (also indicated by random WIP piles).
◆ Frequent use of the words usually, basically, normally, typically, generally, most
of the time, when describing the operation, followed by except when,as in:
“Normally we do this... except when... happens, then we do this... .”
(By its very nature, an unstable operation does not often experience “nor-
mal” in terms of consistent method. In fact, the abnormal becomes the
normal.)
◆ Statements such as, “We trust the operators to make decisions about
how the work is done” (part of a misguided application of employee
empowerment).
It’s important to realize that no operation will ever achieve a perfect level
of stability, and thus to some degree these conditions will always exist. In
fact, stability is not only a requirement for flow, but developing flow helps
motivate disciplined approaches to stability—they go hand in hand. The
main consideration is how unstable the process is, and how stable it needs to
become in order to move into the next phase of achieving some degree of
flow. Based on the spiral model of continuous improvement, during the
incremental leveling phase the operation will be “squeezed” and a higher
level of stability will be necessary to meet the tighter requirements. This, in
turn, will force a refinement in the methods, beginning a new turn around the
spiral in ever tightening cycles.
Chapter 4. Create Initial Process Stability 57