So we see that flow and pull work hand in hand. Establishing the three ele-
ments necessary for pull then creates defined connections between operations.
These connections are important to surface and highlight problems. They create
a singular process in which all operations are interdependent. This step will sig-
nificantly increase the level of urgency to resolve any interruptions to flow. If a
problem occurs in any operation, it will quickly affect all other operations.
Wo r king around the problem by shifting manpower or machinery, or changing
the schedule, will cause additional problems throughout the entire system
because all operations are linked.
Creating Pull Between Separate Operations
From this understanding of the basics of pull it is possible to design a system
that will be effective in any situation. The single-piece flow model above is
specifically for line- or cell-type operations where the workers pass the product
down the line.
How are the basics applied in operations that are separated physically, or
for operations that produce parts in batches? First of all, it is important to
understand the inherent nature of an operation. Someone well trained in TPS
will understand that at the current time some operations are not conducive to
single-piece flow for some reason. It may be the size of the part (very large or
small), a resource that is shared (has multiple suppliers and/or customers), or has
a limitation in the process, such as changeover times.
For example, the stamping operations at Toyota are not currently capable of
producing one fender, then changing to a hood, and then back to a fender one
piece at a time. The stamping operation has multiple constraints preventing
single-piece flow, and the parts are produced in “lot size” quantities. First, the
size of the equipment prohibits placement next to the customer operation (the
body welding department). Second, the machine (“shared resource”) produces
multiple part models that are required by different customers (the fender is
installed at a different location than the hood), so it is not possible to place the
equipment in proximity to all customers. Also the changeover time, while it is
very good, still limits the ability to make one piece, change over, make another,
and change over again.
How do the basic concepts of define, dedicate, and control apply in this sit-
uation? Start with an understanding of the agreement between the supplier and
the customers. Supply the correct material when requested. All operations must
adhere to the basic rule: “Always satisfy the customer,” or put another way,
“Never short the customer.” This is Rule 1. Always follow Rule 1! (Note the
paradox of this statement. While it is the goal to always satisfy the customer we