Changing market conditions often influence the way we manufacture.
At the same time, product life cycles can drive the transformation
from one manufacturing style to another.
In examining the life cycle of products, one often finds newly
introduced products are typically of a higher variety and lower
volume until acceptance, or maturity. As products mature and demand
increases, the variety may remain at the finished item level. But,
there is usually a commonality among lower level sub-assemblies
whose volume, but not varieties, will increase, creating the
opportunity to change the method of planning and producing these
Somewhere down this road we find ourselves facing situations where
we are attempting to manufacture in a mixed mode environment,
combining batch and repetitive production, and attempting to fit
our software to unfamiliar tasks. This evolution requires changes in
planning, organization, and systems. This presentation attempts to
point out what may or may not be known to those companies facing
Recognizing the Change to Mixed Mode
There are many companies, through evolution, rather than revolution,
who have changed over to mixed mode manufacturing and planning
strategies, and may not even be aware that this is what they are
This unmanaged evolution can create the misunderstanding that when
a customer order arrives at a company, we can pull all the BOM parts
needed to satisfy the order (including raw material parts) without
requiring any inventory "lying around" allowing this to happen.
This would mean that we can satisfy our customer because we are so
synchronized with our suppliers and various work centers that we can
respond immediately to demands in lot sizes as small as 1, without
anything in the pipeline.
In the real world, this cannot happen. The cumulative lead time
required to manufacture most products is longer than a customer will
accept for delivery time. With a completely demand driven, KANBAN,
JIT system, time is still a factor. Even without setup time to
contend with, the more operations required, the longer the lead
time will be. So, adopting KANBAN and JIT completely won't work
unless there is work in the pipeline (buffer inventory) through all
the operations until the final configuration has to be manufactured.
One way of accomplishingthis is to change the way we plan. We can
change to a pull system building end products to a signal and
backflushing labor and parts, while building subassemblies ahead to
a forecast with the historical knowledge that the products will be
required. In effect, what we have done is lower the level in the BOM
for what they forecast, while configuring end products strictly to
what the customer orders.
The Production and Inventory Management System
Fitting a production and inventory management system to meet the
unique demands of a mixed mode production environment requires a
reasonable understanding of software tools and implementation
strategies. While a variety of standardized or modular manufacturing
software applications exist, integrating them to create a mixed
mode solution poses a special challenge.
The Master Schedule
The Master Schedule is a plan of production to which a plant is
committed at any given time. Inputs to the Master Schedule usually
come from either forecasts or actual customer orders. In actual use,
a dual function occurs, first as an order launching plan (the Master
Schedule) and also as a reactive device (the Final Assembly
Raw materials and sub-assemblies require a master schedule to allow
for the variations in lead time required to purchase, fabricate, or
assemble. In addition, capacity constraints require us to plan
production based on real capabilities. Because of this, the master
schedule or forecast will never disappear. Attempting to get your
software to handle two levels of master scheduling has resulted in
some firms taking the final assembly off line and reverting to a
completely dis-attached system.
One method that will help is to use a "gross simulation" explosion
of the forecast and customer orders to report on what lower level
components are needed. These are then compared to pre-set reorder
levels for the various work cells which produce end items. In this
way we can build to plan and assemble to demand. Supply and demand
are brought into synch within the manufacturing environment through
the coordination of two ordinarily disconnected systems.
To be Continued
For balance of this article, click on the below link:
Lean Manufacturing Articles and go to Series 02
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