Page 126 - The Toyota Way Fieldbook

Chapter 5. Create Connected Process Flow 103

have stated previously that a process that never stops a customer operation is
likely to have excessive waste built in.)
Is the agreement defined? The first step is to establish the correct amount of
WIP between supplier and customer to buffer the time requirement of the sup-
plier to changeover and also to supply the second customer. Many operations
currently have loosely defined (not visual and controlled) agreements that are a
good starting point for the quantity needed.
Are the locations for the storage of WIP defined? Are they dedicated, and
are they clearly marked? This should include information defining the maximum
allowable amount, and the minimum. The maximum serves as a visual indica-
tion that overproduction has occurred, and the minimum serves as an “early
warning indicator” that a problem with supply may occur and should be inves-
tigated (find the potential problem early, before it becomes a problem). Are the
containers used to transport material dedicated? In our stamping example the
containers are specifically designed to hold a certain part. A fender will not fit
in a hood container.
The final piece is visual awareness of the needs of the customer. If the cus-
tomer process is not within visual sight distance, a mechanism must be used to
provide visual awareness of the customer needs and status. The visual mechanism
used to provide a signal from customer to supplier is the kanban. Traditionally
when dealing with suppliers that are physically separated but close enough to
send truckloads throughout the day, Toyota used a physical card as the kan-
ban. A kanban that has been returned from the customer represents the con-
sumption of material, and as kanbans are accumulated at the supplier, they
are a visual representation of the WIP agreement. The kanbans represent an
inverse of the WIP quantity. More kanbans at the supplier equals less WIP at
the customer.
We do not intend to completely explain the workings of kanban here, but
the principles are easily understood. The kanban is a control mechanism. It can
be a space on the floor if two operations are near each other. If customer and
supplier are separated by line of sight, it can be a card, or return of an empty
rack, or an electronic signal. The kanban must contain information relevant to
the agreement, such as the supplier and customer locations, machinery utilized,
material, and of course quantity and model.
Refer back to the single-piece flow example above. How did Operation B
know that Operation C needed another Model 1? Operation C removed the
part, and the empty space signaled Operation B of the need to replace it. The
space serves as a kanban, with the pertinent information regarding quantity
and model specified by visual indicators. Any kanban system is simply a deriv-
ative of this basic concept.