Single Minute Exchange of Dies (SMED)

One of the core principles to making a Lean system work is Single Minute Exchange of Dies (SMED). You may also hear it referred to as “Quick Changeover” especially in western companies.

Common Misconceptions

Contrary to what some think SMED is not just for the folks on the shop floor. I once heard an individual state, “We don’t use dies here so SMED is not relevant.” SMED is a concept and is just as relevant in the front office.   And no, huge dies are not required!

Another common misunderstanding stems around the term “single minute.” Some take this to mean that a changeover must happen in 60 seconds or less. This is not, and never was the idea around SMED.

Instead, our aim is to reduce the time it takes to switch from the last “good” part of product A to the next “good” part of product B in less than 10 minutes (generally).

7 steps to SMED

Depending on which book you read or consultant you talk to there are generally around 7 steps followed when improving changeovers.

1. Observe the current process.

An extremely valuable tool to help with this step is the video camera! Be careful though as in some countries video cameras can get you hot water with work unions, etc. So be sure to check all the local regulations. Also, be sure to ask the people you plan to video tape for their blessing. You can make friends and enemies at this stage of the game… I recommend you aim for the friendly side of things.

2. Categorize INTERNAL and EXTERNAL activities.

This is perhaps the most important concept behind SMED.

Internal activities are those that can only be completed when the machine or process in question is not running. You cannot, for example, change the bit on a running drill. At least I don’t recommend it!

External tasks are those things that can be done while the machine or process is running. For example, you may be able to knock out the paperwork required, gather tools and materials, and essentially get everything you need ready before the machine or process stops.

3. When possible convert Internal activities into External activities.

Are there things we can do while the machine is running so we don’t waste time once it has stopped? My Mom used to make me lay my clothes out for school the night before so I wasn’t searching for socks in the morning. She was teaching me SMED and I didn’t even know it. Bless her!

4. Make the remaining internal activities flow.

For tasks that cannot be moved externally our next focus is to do them as fast as possible. Think of the pit crew for your favorite racing team. They have mastered this step!

Also, if we need to screw things down how can we reduce the number of turns required (i.e. shorter bolts, wing nuts, etc.)?

And do we really need 28 bolts holding the fixture in place? Maybe. Maybe not. Of course do not jeopardize anyone’s safety. But often times no one has asked why there are 28 bolts!

5. Similar to step 4 we also need to optimize the external activities.

Again, think about making things flow as efficiently as possible with no stopping, waiting, or defects.

6. Document the new procedure so it is repeatable and reproducible.

Is it possible to video an excellent changeover so new employees can watch it and learn from it? Of course having things written down in words is important but seeing it on video may really accelerate the learning experience of a new associate.

7. Pursue Perfection.

As with all things Lean and Six Sigma… we must constantly work to make things better and faster. A good strategy is to attempt to halve the current changeover time. So if it takes you 2 hours today aim to get it down to 1 hour after the SMED Kaizen event! Our ultimate aim may be to change things over in less than 10 minutes but this probably won’t happen immediately.

Summary

In order to make things like level loading (heijunka) a reality we must be able to change our machines over quickly.

There are excellent books on this topic that go into much greater detail than I have here.  Also, Jon Miller has written on this topic here.  And the good men over at Evolving Excellence have some excellent food for thought here.

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Update: Here’s a good SMED article where I was interviewed.

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