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SMED: What It Is, and How Internal and External Setup Differ
SMED, single minute exchange of die, is a lean method for slashing changeover time from hours to single-digit minutes. Its key move is separating internal setup, which can only happen with the machine stopped, from external setup, which can be prepared while it’s still running. Shift work from internal to external and the stopped time collapses.
Why is SMED important?
SMED matters because long changeovers eat available production time and push plants toward large, wasteful batches. Cutting changeover time from hours to minutes frees capacity, makes small-batch and pull production practical, and improves overall equipment effectiveness. For many lines, faster setups are the single biggest lever on output without buying new machines.
How does SMED cut changeover time?
The method works in a clear sequence:
- Record the whole changeover and list every step.
- Sort each step into internal (machine stopped) or external (machine running).
- Move as much as possible from internal to external, so it’s prepped in advance.
- Simplify what’s left internal: quick clamps, standard tools, no hunting for parts.
- Standardize the new changeover and keep shaving time off it.
What’s the difference between internal and external setup?
When the work can happen. Internal setup can only be done with the machine stopped, so it directly adds to changeover downtime. External setup can be done while the machine still runs the previous job, so it costs no stopped time at all. The whole point of SMED is to convert internal into external, which frees capacity that lean production and small-batch pull production depend on.
Internal vs external setup at a glance
Where changeover time hides, and where it doesn’t.
| Aspect | Internal Setup | External Setup |
|---|---|---|
| Machine state | Stopped | Running |
| Adds to downtime | Yes | No |
| Examples | Swapping the die | Staging tools and materials |
| SMED goal | Minimize it | Move work here |
Free SMED Changeover Worksheet
It lists each changeover step, tags it internal or external, and tracks the time you move off the stopped machine, so the saving is measured not claimed. Download the checklist (PDF). You can also complete the checklist digitally in flowdit on your phone, tablet or PC.
Related Terms
- Downtime – changeover is planned downtime.
- Overall Equipment Effectiveness – changeover hits availability.
- Batch Size 1
- Changeover Time
