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 (illustrative)
A molding press stops for 90 minutes per changeover while operators fetch the next mold and its fittings, so it changes product only once a shift. The team stages the mold and a fitting kit on a cart before the stop, preheats the mold and adds locating pins. Changeover falls to about 20 minutes, so the press can change product 4 times a shift and each batch is a quarter of the size, with less stock waiting.
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
Shingo described the method in three main stages. Separate: sort each task into internal, done while the machine is stopped, or external, done while it runs, and move the external ones out of the downtime.
Convert: turn internal tasks into external ones where you can, such as preheating a mold or presetting a fixture. Streamline: shorten what remains with quick clamps, parallel work and fewer adjustments, then write the new method into standard work.
Quick changeover example
Take the illustrative press from the worked example above. The changeover takes 90 minutes, and the video shows about 35 minutes spent fetching the mold, fittings and tools. Staging them on a cart before the stop removes that time from the downtime.
Preheating the mold moves another 15 minutes outside the stop. Locating pins and quick couplings then cut alignment and connection time, leaving about 20 minutes. 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.
Guides on this topic
- How to measure OEE: start tracking without a big IT projectHow to measure OEE with a paper tracking sheet before buying software: what to record, how to calculate it and when OEE tracking is worth automating.Read the guide
- Kaizen event: meaning, steps and a 3-5 day agendaA kaizen event is a focused workshop that improves one process in 3-5 days. Learn the meaning, roles, agenda, steps, measures and common mistakes.Read the guide
- Lean vs Six Sigma: differences, history and when to use eachLean vs Six Sigma compared: what each method targets, where they came from, how they differ in manufacturing and how Lean Six Sigma combines them.Read the guide
- Lean manufacturing examples from shop floor to officePractical examples of lean in action: what the problem looked like, which lean tool was used and what changed, in factories and beyond.Read the guide
Sources
Books and papers show their publication year. Web pages show the month we last checked them.
- 1.Shigeo Shingo, A Revolution in Manufacturing: The SMED System (Productivity Press, 1985)