Usually, the production schedule must deal with a complex
array of components numbering in the hundreds, thousands,
or even tens of thousands, and often a computer is brought
in to assist in the scheduling tasks.
The major drawback is that the information and materials
are not matched. The information is out anywhere between
three days and a week before the goods. In other words, the
required volume planning is completed several days before
the planned products are manufactured at the factory. It is
during these several days that the required goods are delivered
to the factory and operator instructions are issued.
Another problem is that each process operates according
to its own instructions, completely independent of other
processes. We call this type of production “independent
process production.”
Push Production
Pull Production
Required volume
planning
Production
planning
Subassembly
schedule
Processing
schedule
Materials
processing
schedule
Procurement
(outside vendor
schedule)
Production
Schedule
Main
assembly
stations
Subassembly
stations
Processing
stations
Materials
processing
stations
Buyer
(of outside
vendors’
products)
Buyer
(of outside
vendors’
products)
Main
assembly
stations
Subassembly
stations
Processing
stations
Materials
processing
stations
Flow of information Flow of materials
Figure 2.8 Flow of Information and Materials in Push and Pull
Production Systems.
54 ◾ JIT Implementation Manual: Volume 1
Independent process production suffers from inflexibility
in the face of scheduling changes. For various reasons,
the production schedule might undergo one revision after
another, but these changes cannot be easily carried over
to the individual production processes. As a result, the first
“official” delivery deadlines in the original production schedule
become firmly established as each independent process’s
delivery deadline and are thereafter very difficult to change.
The process station’s workers tend to regard such last-minute
changes as an intrusion and a hassle. This does not bode
well for these Japanese factories in today’s era of a high yen,
ongoing trade friction, and diversifying customer needs.
By contrast, the “pull” production method has, in principle,
no delivery schedule save for the final assembly schedule
(production schedule). The main assembly processes “pull”
just what they need from the subassembly processes. Since the
subassembly processes use processed parts, they in turn pull
just what they need from the processing line. In other words,
nothing happens upstream until something has happened
downstream. Since production at the previous (upstream)
processes depends on production at the next (downstream)
processes, we call this production method “previous processdependent
production.” This type of production emphasizes
the true importance of the next process as the customer.
In light of these two very different types of production,
we could argue that at most of the factories that display “The
Next Process Is Your Customer” signs, the real meaning of
the signs is “We pretend to use kanban.” Unless the factory is
actually using pull production instead of push production, its
kanban do not amount to anything more than a “theoretical”
or “decorative” improvement. Unless the factory realizes the
importance of matching information with the materials and
aggressively revamps its whole production system with a
“proactive improvement” attitude, the waste inherent in the
push production system will not be removable.
Destroying Factory Myths ◾ 55
Lesson 4. The Ocean Pulls the Flowing River
“Stop and Go” Production and
“Process and Go” Production
A factory where the company president is cautiously watching
over the machines and equipment is a tragedy. The main
character in this tragedy is not the president, but rather the
equipment operators who live under the president’s gaze.
Imagine a factory where the company president has just
had the latest, most sophisticated equipment brought in, and
now stands there telling the operators, “It’s your job to operate
these things. Get to it!”
Imagine, in this age of diverse models and small lots, a
company president having installed all sorts of machines
designed for mass production and then commanding the
workers, “Set the machines up for the whole range of
product models and start turning out products!” Imagine the
kind of agony those workers are going through in trying to
use machines that are fundamentally incompatible with the
factory’s needs.
No doubt the company president had thought that the latest
machines and equipment would readily solve his factory’s
various problems.
He may be proud to inform us, “This is great! This new
equipment will double our production capacity!” or, “This
brand new equipment will take care of our quality problems.
He might even go so far as to claim, “This new equipment
will enable us to meet our client’s delivery deadlines.”
Let us suppose that the factory has usually been incapable
of meeting its client’s short delivery deadlines, and that is one
big reason why the president bought the latest equipment,
which is supposed to cut processing time in half. The goal
here is to shorten the manufacturing lead-time.
Shortening lead-time by reducing processing time is a
mighty bold and eccentric way of doing things. We can spend
56 ◾ JIT Implementation Manual: Volume 1
a fortune on faster processing machines and still not shorten
the lead-time one bit. We might succeed, however, in shortening
the life of the company.
When we look at production as a flow of materials, we
can recognize four main categories of components in this
flow: retention, transfer, processing, and inspection. The first
thing this teaches us is that making things requires much
more than just processing.
As we go through the manufacturing process, imagine
that you are one of the parts that has been delivered to the
factory and is about to undergo the entire lead-time of the
manufacturing process. To start with, you are warehoused
along with the other purchased parts and materials. This falls
under the “retention” category. Now, it would be nice if the
processing machines could walk over to the parts warehouse,
pick out the things they need, and process them, but we have
not reached that day yet. So the factory needs to move you
and all the other goods from the warehouse to the processing
machines, a task that falls under the “transfer” category.
Next, you and the other materials that have just been
delivered to the processing machines sit in a pile until the
machines finish processing the previous lot of materials. This
sometimes takes a long time. At last, the machines start in
on the first of your lot of materials. You are the last in that
lot and are still waiting. All of this waiting is part of the
“retention” category.
Finally, you—the last of the lot—are picked up and, in a
few brief seconds, get processed. Those fleeting seconds are
in the “processing” category.
After being processed, you are plopped onto a pile of processed
units. Then you go through another round of retention,
transfer to the next group of process machines, more retention,
and processing.
To return to our music analogy, we can say that the four
parts of this manufacturing process—retention, processing,