Beating the delivery deadline is what “in time” means. Just-InTime
means something quite different.
Let us suppose next Friday is our delivery deadline date.
The In Time concept interprets this as meaning we need to
deliver our products by next Friday. We could deliver them
next Thursday if we wish. We could even deliver them on
Monday. Or, if they are ready now, we could send them over
immediately and not even wait for next week.
The same principle can be seen at work within factories.
For instance, next to the press machine there might be a
large pile of workpieces that has been sent down from the
previous process. The In Time concept says that is OK. In
fact, though, the workpieces are a little too much in time.
Compare that with an example in which the press operator
calls out “Ready!” and immediately receives a single workpiece
from the previous process. He presses it, then calls
out “Ready!” again and receives another workpiece. Here we
have a manifestation of the Just-In-Time concept.
But even when we add the term “just” to “in time,” we still
are not saying half of what Just-In-Time really means.
This is because the JIT production system is more than
just a new production method and production system for
maintaining delivery deadlines, building things in small production
runs, and so on. It is also a technique for thoroughly
eradicating waste by rooting out deep-seated waste wherever
it exists in the company—in both factories and offices—and
using JIT improvements to eliminate the waste.
Let us consider for a moment just how thorough this eradication
of waste under the “Just” concept really is.
For example, if we interpret the “just” in Just-In-Time as
meaning “about one month,” that means the factory is allowed
to operate with one month of inventory-related waste.
If we take the “just” to mean “about one day,” then we will
have a day’s waste. We can go on to even smaller time increments,
such as an hour, minute, or second, and in all of these
cases we are managing the factory based on a waste measure.