SMED (changeover reduction)
Single-Minute Exchange of Die
SMED reduces changeover time systematically by moving work from internal time (the machine is idle) to external time (the machine is running) — typically a 30-70% reduction without investment, through organisation and standardisation alone.
Use the method when
- →Changeovers limit capacity or force large batches
- →Changeover time varies strongly between people and shifts
- →As a prerequisite for smaller batches, shorter lead time and levelling (heijunka)
Don’t use it when
- →The machine is not the bottleneck, and changeovers don’t really cost output — prioritise elsewhere
- →The process is so unstable that the changeover drowns in breakdowns — stabilise first
Before you start
One specific changeover is chosen (machine + product switch) — the most frequent or most expensive
Permission to film, and the operators are on board with the purpose: we analyse the process, not the person
The baseline is measured: current changeover time from last good part to first good part
How to do it — step by step
Film a normal changeover
1 changeoverThe whole changeover is filmed — from the last good part of product A to the first good part of product B. A normal changeover, not a show: it is the variation and the small stops that carry the analysis.
Break it into individual activities
2-3 hoursReview the film with the operators and list each activity with its time: fetch tool, loosen bolts, adjust, search, wait. Typically 30-60 activities. Already here you see how large a share is searching, walking and waiting.
Separate internal from external time
2 hours + implementationEach activity is classified: MUST the machine be idle for it (internal), or can it be done before/after the stop (external)? Everything that can move to external time is moved: a preparation trolley, pre-fetched tools, a prepared recipe, the next tool set preheated. This step alone typically gives 30-50%.
Reduce the internal time
1-3 weeksFor the rest: can two work in parallel (choreographed, not improvised)? Can bolts be replaced by wedges, clamps and quarter-turns? Can adjustment be replaced by fixed stops and setting marks, so the first part sits right without a trial run?
Standardise the changeover
2-4 hours + trainingThe new method is documented as standard work: sequence, roles, a checklist for external preparation (a “ready for changeover” check BEFORE machine stop). All shifts are trained — the changeover time must be the same regardless of who does it.
Measure and follow up on the board
ongoingChangeover time per changeover is recorded and tracked on the team’s board. Overruns are treated as deviations with a cause. And the gain is HARVESTED deliberately: shorter changeovers must become smaller batches, not just more changeovers at the same batch size.
The classic mistakes
How it goes wrong in practice, and this is where most implementations part ways.
The analysis ends as a list, not as new practice
Moving to external time requires physical things: trolleys, boards, fixed places, checklists. Without them, everyone falls back to the old sequence within three weeks.
Only technician solutions
If the organising steps are skipped in favour of rebuilds, SMED becomes an investment project. The standard is clear: organisation first, technology afterwards — most of the gain is free.
The gain isn’t converted
Halved changeover time, same batch sizes: then the gain is only slack in the plan. Planning must be part of the follow-up, so batches are actually reduced.
Related standards
The standard is free. The anchoring is the craft.
The method only works when it becomes daily routines and leadership behaviour. The operations check shows in 4 minutes where your operations stand, and what should come first.