Page 124 - The Toyota Way Fieldbook

Chapter 5. Create Connected Process Flow 101

Schedule

1 PC 1 PC

Model 2
Model 1 Operation Operation 1 Operation
Model 2 A B C
Model 3 3 2 2
In Process In Process In Process

Figure 5-9. Sequenced flow for high product variety production

workstation. In effect, Operation B still dictates what to do (build the next item
on the schedule) and when to do it (when the space is empty). If Operation B
completes the part before the signal space for Operation C is empty, the operator
will hold it in the workstation and wait for a signal from Operation C to replenish
the space.
In a high model-mix environment, the level of flexibility is limited by the
lead time from the point-of-schedule introduction to the completion of the prod-
uct. This is dictated by the number of operations that must be “flowed through.”
Instant changes to the schedule will not yield instant changes in the output
because of the flow-through time delay.
For this type of flow to work well, each operator must have the capability to
produce any model that comes at any time. Often the greatest challenge in
establishing sequenced flow in a custom environment is achieving a balance of
operation times. Refer to the case study in the previous chapter for an example
of reducing the high degree of variation often found in a custom production
facility, and how better balance is achieved by defining the time requirements
more narrowly.
What if there is not a perfect balance in cycle times across Operations A,
B, and C? First, ask: “Can each operation consistently perform the task in less
than the customer requirement time—the takt?” Second, if on average the
answer is yes but because of variability, the takt time is often missed, we need
to put in some buffer. The buffer does not have to be an unmanaged push sys-
tem. It can be defined with a specific visual arrangement showing the num-
ber of pieces allowed, e.g., three between stations. And the principle of first
in-first out (FIFO) should be used to prevent a particular part from “cutting
in line.”