August 1, 2019
By Darren Dolcemascolo
Continuous flow is a key principle of Lean
and the Toyota Production System. It means
that product or information is moved through
operations, from step-to-step, with no work in
progress (WIP) one piece at a time at the pace
of the customer demand downstream. It is a
True North principle that we work toward.
We want to get closer and closer to this
ideal. Whether we are performing a
service or building a product, the ideal
situation is to provide the next downstream
customer with what they need, when they need
it, and in the right quantity.
What are some of the benefits of
achieiving continuous flow? An
operation that has achieved continuous flow
- Eliminated WIP (Work-In-Progress)
inventory with the exception of a single
unit at each step in the operation.
- Minimized Lead Time Through the
process (or Turnaround Time). The
total time through the process should be
the number of operations X the cycle
time at each operation. There is
very little waiting.
- Increased the ability to detect a
defect. By moving one unit of work at a
time from one step to the next, defects
are discovered more quickly and fewer
overall defects are created.
(Consider that if product moves in large
batches with lots of waiting, many
defects can be created, and they may not
be detected for a long time.)
Continuous Flow is not easy to achieve.
In order to move toward continuous flow, we
need to work on the following:
- Achieving consistent quality and repeatability. We must minimize
variation and develop a high capability process.
- Improving equipment or systems reliability. If we are utilizing
equipment or other systems in the process, these systems must be reliable.
- Developing processes that can be scaled to takt time, the rate of customer
demand. For example, if we need to process one unit every minute, we need
to develop a process that can be scaled to 1 unit/minute at each operation.
Before we achieve these conditions, we must have some buffer of
inventory between operations (e.g. ,a FIFO
line/WIP queue or kanban system). As
we get closer to continuous flow, we reduce
the buffer incrementally until continuous
flow is possible.
Which types of operations can benefit
from continuous flow?
- Repeatable administrative processes such as claims processing, mail
processing, and order processing.
- Some healthcare processes.
- Assembly processes
- Other manufacturing processes
for which equipment can be
right-sized to achieve continuous
Continuous flow is one of the key concepts within lean manufacturing; in most cases, a piece of a value stream can be transformed into a
continuous flow operation. While
continuous flow is not always achievable for an entire door-to-door value stream,
lean organizations must continually improve their processes in an attempt to get closer and closer to true
continuous flow. This will reduce inventory levels, reduce lead time, and improve customer service levels.
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