Chapter 5. Create Connected Process Flow 97second is to look for additional problems that the operators feel compelled to
“work around.”
The primary causes of deviation by operators are:
- Imbalanced work cycle times that may be due to normal variation in work
content, operator skill, or machine cycle times. Ty pically, the person with
extra time will deviate. - Intermittent work stoppages due to lack of parts or (the fear of) operators
leaving the work area to perform additional tasks—such as retrieving
parts or performing quality checks—machine failures, or correction of
defects. - Intermittent work delays due to struggles with machines or fixtures, or
overly difficult or complex tasks. - Miscellaneous issues such as “building ahead” to “buy time” for change-
over, an operator leaving the line for some reason, or to stagger break or
lunchtimes, or such.
In some situations the correct course of action would be to adjust the defined
quantity of WIP between operations. Single-piece flow requires perfectoperation
time balance, which is extremely difficult to achieve. Consider an operation that
will incur natural variations in the work cycle time, such as deflashing an injection-
molded part.
The cycle time will vary slightly each time because this is largely a manual
task, and no one can complete work cycles with exact precision (Olympic athletes,
after all, do not run every race in the exact time every race). These minor variations
may cause intermittent interruption in the flow. Operators do not like to wait with
nothing to do, so they will naturally add buffer to compensate. The addition of
buffer is the logical choice to compensate for minortime variation; however, the
quantity to add needs to be defined as the standard. Perhaps the defined buffer to
allow for the minor time variations should be two or at most three pieces.
TIP
The Value of Outside Eyes
The problem with communication is that it is hard to understand
why others misunderstand what we clearly understand. The point
of an agreement on a standard is for everyone to have the same
understanding. One simple way to test this is to find someone who
is not familiar with the work area, show her the standard, and ask
her to explain the agreement. You may be surprised to discover
how challenging it is to clearly communicate agreements visually!