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Mixed Model
Production--What Is It?
Mixed Model
Production is the practice of assembling several distinct
models of a product on the same assembly line without changeovers
and then sequencing those models in a way that smoothes the demand
for upstream components.
The objective is to
smooth demand on
upstream workcenters, manufacturing cells or suppliers and thereby reduce inventory,
eliminate changeovers, improve kanban operation. It also eliminates difficult assembly line changeovers.
Toyota developed the concept in the
1960's in response to the problems created by line changeovers. It
originally applied to
long assembly lines such as
those used in automotive.
However, Mixed Model Production is
adaptable to other situations.
There are also alternatives, such as
assembly cells, that accomplish the same purpose,
often with better results. This topic also relates to
Focused Factories in because it
addresses the same issues at a more detailed level.
The Underlying Principle
Henry Ford demonstrated that
steady,
repetitive production dramatically reduces cost. This is true for
both assembly operations and for upstream fabrication. However, when
final assembly models proliferate and the issue is addressed by
changeovers and long runs on the assembly line, it creates highly
variable demand in upstream fabrication and subassembly.
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Ideal Workflow
The ideal production system would be
like a smoothly flowing stream with many tributaries and no pools,
dams or other accumulations.
Or...
...like a marching
band with everyone in step, spaced at a fixed distance,
all in time to the music beat and smoothly flowing from one figure
to another throughout the performance. This is the origin of "Takt
Time."
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