Lean teams use SMED because long changeovers force big batches. Faster changeovers allow smaller lots, more frequent production of every product and less inventory.
Where it comes from
Shigeo Shingo developed SMED through work with Toyota and other Japanese manufacturers. It became one of the methods that made small-lot, just-in-time production practical.
At a glance
Changeover before and after SMED
Swipe sideways to see the whole diagram.
How to apply SMED
- 1
Observe and record the changeover
Video a full changeover and list every task with its duration. Include searching, walking and adjustments.
- 2
Separate internal and external work
Internal work can only happen while the machine is stopped. External work can be done while it runs.
- 3
Convert internal to external
Prepare tools, dies and materials before the stop. Preheat, preassemble and stage everything at the machine.
- 4
Streamline internal work
Use quick-release clamps, standard heights and locating pins. Eliminate adjustments by setting positions in advance.
- 5
Streamline external work
Organize tool storage and carts with 5S. Cut walking and searching during preparation.
- 6
Standardize the new method
Write the changeover as standard work and train every crew. Track changeover time to hold the gain.
Worked example
A molding press stops while operators fetch the next mold and its fittings. The team stages the mold and a fitting kit on a cart before the stop and adds locating pins. The press now runs smaller batches because changeovers no longer eat a large share of the shift.
Common mistakes
- Buying faster equipment before separating internal and external work.
- Improving one crew's changeover without writing standard work for all shifts.
- Using the time saved to run even bigger batches instead of smaller, more frequent ones.
When SMED is not the right tool
SMED pays back where changeovers are frequent or long. A machine that rarely changes over gains little.
It also needs a measured baseline. Without timing the current changeover, you cannot see which steps to move or remove.
SMED meaning
SMED stands for single minute exchange of die. The goal is a changeover of under ten minutes, a single-digit number of minutes.
Shigeo Shingo developed the method with Toyota and other Japanese manufacturers. He set it out in his 1985 English book A Revolution in Manufacturing: The SMED System.
SMED steps
First, film or observe a full changeover and list every task. Second, mark each task as internal, done while the machine is stopped, or external, done while it runs.
Third, move external tasks out of the downtime, such as fetching tools and preheating dies. Fourth, convert internal tasks to external where possible, for example with standard heights.
Fifth, streamline what remains with quick clamps, parallel work and fewer adjustments. Finally, write the new method into standard work.
Quick changeover example
Say a press changeover takes 60 minutes, and the video shows 20 minutes spent finding tools and the next die. Staging them before the stop removes that time from the downtime.
Standard shims and quick-release clamps then cut adjustment time. Each change is small, but together they make smaller batches practical.
Measuring a changeover
Changeover time runs from the last good part of one run to the first good part of the next, at full speed. Adjustment and trial runs count.
Video of a real changeover makes it easy to list each element, time it and sort it into internal and external steps.
Beyond presses
The same idea applies to any switch between jobs, such as line clearance in packaging or turning around an operating room.
Shigeo Shingo set out the method in his book on the SMED system. The time study category covers tools for timing the steps.