The 4-Hour Changeover That Took 20 Minutes
A customer ran a stamping press that made 12 different part numbers. Every changeover took four hours — the die was unbolted, lifted out, the new die lifted in, bolted, and the press re-trialed. The production schedule lost two full shifts a week to changeovers. We did a SMED (Single-Minute Exchange of Die) study. We filmed the changeover, listed every step, and separated what could be done while the machine was running (external) from what required the machine stopped (internal). The result: the changeover dropped from four hours to 20 minutes. The machine did not change. The process did.
Changeover time is not a given. It is a process you can engineer. Here is how to attack it.
The SMED Idea: Internal vs External
Every changeover step is one of two types:
- Internal: Requires the machine to be stopped. You cannot do it while the press is running the previous part. Unbolting the die, lifting it out, setting the new die in place.
- External: Can be done while the machine is still running the last batch. Pre-staging the next die, warming it up, gathering the tools, pre-setting the settings.
The SMED principle is simple: move as many internal steps as possible to external. The four-hour changeover had three hours of internal work that was actually external (the next die was not pre-staged; the tools were not gathered; the settings were not pre-set). Once we moved those to “while the machine runs,” the stopped time collapsed.
The SMED rule: Film the changeover. For every step, ask: “Can this be done while the machine is running?” If yes, move it external. The goal is not a faster mechanic — it is a shorter stopped machine.
Quick Clamps Instead of Bolts
The slowest internal step is usually bolting the die down. Six bolts, each tightened to a torque, each requiring a wrench. Replace them with quick clamps (hydraulic, pneumatic, or mechanical toggle). The die drops in, the clamps close in 10 seconds, and the press runs. The capital cost of the clamps pays for itself in weeks of avoided downtime.
Standardize the Die Height
If every die has the same shut height, the press does not need to be re-set for the stroke. The die goes in at the same height every time. This is a design rule for the tooling: make all dies the same height. It is a small investment in tooling design that eliminates a 30-minute press-setting step.
Pre-Set the Offsets
Modern machines store recipe parameters (press force, speed, temperature, robot program). The operator calls up the recipe for the next part while the machine is still running the last batch. By the time the die is changed, the machine is already set. The recipe transfer is external — it costs zero stopped time.
The One-Touch Fixture
The ultimate SMED step is to design the die so it locates on a single datum (a taper, a pin) and clamps in one motion. The operator pushes it in, the clamp closes, the die is within tolerance. No shimming, no measuring, no trial-and-error. This is expensive tooling design, but on a high-changeover line, it is the highest-return investment you will make.
A Changeover Audit Checklist
- Film the full changeover (stopwatch, every step).
- List each step as internal or external.
- Move every possible step to external.
- Replace bolts with quick clamps.
- Standardize die height across the tooling.
- Store recipes by part number (call up while running).
- Pre-stage the next die, tools, and materials outside.
- Eliminate adjustment (shims, measurements) with one-touch fixtures.
- Time the new changeover; find the next bottleneck step.
- Train every operator on the new procedure (document it).
What a Good Changeover Looks Like
| Step | Before SMED | After SMED |
|---|---|---|
| Unbolt die | 25 min (6 bolts) | 1 min (quick clamps) |
| Lift out / lift in | 15 min | 10 min (pre-staged) |
| Set press height | 30 min (shimming) | 0 (standard height) |
| Set parameters | 45 min (manual) | 0 (recipe loaded) |
| Trial run / adjust | 60 min | 5 min (one-touch fixture) |
| Total | 175 min | 16 min |
The Bottom Line
The 4-hour changeover was not a slow operator. It was a process that did not separate internal from external. Film it, move what you can to “while the machine runs,” replace bolts with clamps, and standardize the tooling. The changeover that dropped to 20 minutes gave the customer two extra shifts a week — for the cost of a study and a few clamps.
