Page 79 - The Toyota Way Fieldbook

Chapter 4

Create Initial

Process Stability

First Get to Basic Stability

If you have not already been using lean methods and improving processes, in
all likelihood your individual processes are unstable. Stability is defined as the
capability to produce consistent results over time. Instability is the result of
variability in your process. It could be that equipment is not well maintained
and so breaks down regularly. It could be that for any number of reasons defects
are regularly produced. Or perhaps there is no standard work, and the amount
of time it takes to perform a given process varies tremendously from person to
person, across shifts, or over time.
The first step in creating lean processes is to achieve a basic level of process
stability. The primary objective in developing stable processes is to reach a con-
sistent level of capability. Based on the spiral model of continuous improvement
presented in the last chapter, there are increasing degrees of stability. The initial
level of stability is generally defined as the capability to produce consistent results
some minimum percentage of the time. This is measured based on the outcome
and is related to producing the same quantity of products, with the same amount
of resource time (people and equipment), with a high degree of reliability (the
exact level may vary according to the process and conditions, but a reasonable
rule of thumb is 80 percent or better). A simpler indicator would be the ability to
meet the customer requirements with quality products the first time through on
time (again, 80 percent or better). In many cases the “customer requirement” is
not clearly defined and becomes one of the first tasks of the stability phase.

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