SMED: How to Cut Changeovers from 2 Hours to 15 Minutes

What Is SMED? #

Single-Minute Exchange of Die = changing tooling in single-digit minutes (under 10 minutes).

Developed by Shigeo Shingo at Toyota, it's the method that makes small batches profitable. Without SMED there's no Just-in-Time, no Lean and no agility.

The Big-Batch Trap #

Traditionally, if changing a mold takes 4 hours, the logic says: "Run a lot to amortize the changeover."

The only way to break this cycle is to drastically cut changeover (setup) time.

The 4 Steps of SMED #

Step 0: Measure (Baseline)

Video a complete changeover. Don't trust what people say it takes. Time it from the last good part of batch A to the first good part of batch B at rated speed.

Step 1: Separate Internal from External

• Internal activities (IED): Can only be done with the machine STOPPED (e.g., mounting the mold).
• External activities (OED): Can be done with the machine RUNNING (e.g., fetching tools, preheating the mold, bringing material).

Step 2: Convert Internal to External

Look for ways to do internal activities BEFORE or AFTER the stop.

• Preheat: Don't heat the mold in the machine. Do it outside.
• Pre-assembly: Build subassemblies on a separate bench.
• Pre-setting: Use jigs to set guides to the exact dimension before installing them.

Step 3: Streamline Internal Operations

Whatever must be done with the machine stopped, do it at Formula 1 pit-stop speed.

• Eliminate bolts: Use clamps, levers or quick-release fixtures. A long bolt takes 40 seconds. A clamp takes 2 seconds.
• Eliminate adjustments: Use fixed stops and visual marks. No tape measures allowed during the changeover.
• Parallel work: Two people working in coordination (the "SMED dance") can do one person's work in a third of the time.

Step 4: Streamline External Operations

Organize everything so the next changeover is even smoother: dedicated changeover carts, checklists, tool kits.

Example: Plastic Injection Molding #

Illustrative results for a Tier 2 automotive plant after 3 months of SMED:

Metric	Before	After
Changeover time	2 h 15 min	18 min
Batch size	5,000 pcs (weekly)	500 pcs (daily)
WIP inventory	High (weekly batches)	About one fifth of before

By cutting setup time, the plant could run every product every day (Heijunka), eliminating the need for huge warehouses.