"Single-minute" doesn't mean 60 seconds — it means single-digit minutes, under 10. The internal-vs-external setup distinction that's the entire method, and why changeover time is often what makes small-batch flexibility economically viable.
“Single-minute” doesn’t mean 60 seconds — it means single-digit
minutes, under 10. That distinction trips up almost everyone hearing
about SMED for the first time, and it matters, because chasing a
literal one-minute changeover on the wrong process wastes effort a
realistic single-digit target wouldn’t.
Single-Minute Exchange of Die (SMED) was formalized by Shigeo Shingo
in the late 1970s, building directly on die-change methods Toyota had
been refining since the 1950s and 60s. The original problem was
brutally concrete: large stamping presses that took hours to change
dies between part numbers, sitting idle the entire time generating zero
output. Shingo’s core insight wasn’t a specific tool — it was a way of
categorizing setup work that made the time visible and attackable.
| Internal setup | External setup | |
|---|---|---|
| Definition | Steps that require the machine to be stopped | Steps that can be done while the machine is still running |
| Example | Removing the old die, mounting the new one | Staging tools, pre-heating the next die, gathering fasteners |
| SMED goal | Minimize what’s left here | Convert as much internal work into this category as possible |
The method is deceptively simple to state: separate internal work
from external work, convert as much internal work to external as
physically possible, then streamline whatever internal work is left.
Most of the real gain in a typical SMED project comes from that
conversion step, not from making the internal work itself faster — a
changeover where someone is hunting for a wrench while the machine sits
idle is a conversion problem, not a speed problem.
A more aggressive extension of the same idea, One-Touch Exchange of
Die (OTED), targets changeovers completed in under 100 seconds —
usually through mechanical design changes like standardized die heights,
quick-clamp fixtures, and locating pins that eliminate adjustment
entirely rather than just speeding it up. OTED is a design investment,
not just a procedural one, which is why most plants pursue SMED first
and treat OTED as a longer-term target for their highest-changeover-volume
equipment.
Long changeovers push plants toward large batch sizes, since the
changeover cost has to be amortized over more parts to stay economical
— which is exactly the opposite of the small-batch, high-mix flexibility
most manufacturers actually need to compete today. Cutting changeover
time isn’t just an efficiency win on its own; it’s often the thing that
makes smaller batch sizes and faster response to demand changes
economically viable in the first place.
SMED itself isn’t a standalone course in SCMEP’s current catalog —
it’s part of the changeover and flow concepts covered inside our
Lean 101 Overview. As a
NIST Manufacturing Extension Partnership affiliate
serving South Carolina manufacturers since 1989, our focus is
connecting SMED’s internal/external framework to your specific
changeover bottlenecks, not abstract lean theory.
If your plant is looking to reduce changeover time, you can
browse the Lean and Continuous
Improvement training catalog or email the training team.
Faster changeovers and pull-based replenishment are complementary lean tools. See our related guide on kanban pull systems for how two-bin replenishment keeps production tied to actual consumption.
Fast changeovers are what make mixed small-batch production possible in the first place. See our related guide on heijunka production leveling for how volume and mix leveling depend on the changeover speed SMED delivers.
Single-Minute Exchange of Die — a lean manufacturing method for reducing equipment changeover time, formalized by Shigeo Shingo in the late 1970s based on Toyota’s die-change practices.
No — it means single-digit minutes, under 10 minutes total, not literally 60 seconds. A more aggressive extension called OTED (One-Touch Exchange of Die) targets sub-100-second changeovers.
Internal setup requires the machine to be stopped, like removing an old die. External setup can be done while the machine is still running, like staging tools or pre-heating the next die. SMED’s core method is converting as much internal work into external work as possible.
Long changeovers push plants toward large batch sizes to amortize the changeover cost over more parts. Reducing changeover time makes smaller batch sizes and faster response to demand changes economically viable.
