External Setup Time
Definition
External setup time is the portion of a changeover that can be performed while the machine is still running the previous job — such as staging tools, fixtures, and materials — so it consumes no production capacity.
In Practice
The internal/external split comes from SMED (single-minute exchange of die), the lean setup-reduction method. The core move is converting internal setup — work that requires the machine stopped — into external setup done in parallel with the current run.
For example, if a press changeover takes 60 minutes of downtime and the team learns to pre-heat the die, stage bolts, and kit the next coil while the press runs, 35 of those minutes become external and downtime drops to 25 minutes. Shorter internal setups make smaller batches economical, which reduces inventory and improves flow.
Frequently Asked Questions
What is the difference between internal and external setup time?
Internal setup time requires the machine to be stopped — swapping the die, adjusting guides, first-piece inspection. External setup time happens while the machine still runs the previous job — staging tools, kitting materials, pre-heating. SMED programs work by converting internal steps to external ones.
Why does external setup time matter for lot sizing?
Only internal setup consumes capacity, so moving work to external setup shrinks effective changeover time. Cheaper changeovers lower the economic batch size, letting planners run smaller lots more frequently — less inventory, shorter lead times, and a schedule that follows demand more closely.
Related Terms
Internal setup time is the portion of a changeover that can only be done while the machine is stopped — such as removing and mounting dies, making adjustments, and running first-piece inspection — so it directly consumes production capacity.
Idle TimeIdle time is time during which a worker or machine is available but not producing — waiting for materials, instructions, setups, repairs, or upstream work — representing paid capacity that generates no output.
Lean ManufacturingLean manufacturing is a management philosophy focused on maximizing customer value while systematically eliminating waste, such as excess inventory, waiting, overproduction, and defects.
Level ScheduleA level schedule (production leveling or heijunka) is a production plan that distributes volume and product mix evenly across time periods, so the line builds a stable, repeating pattern instead of large batches that follow demand spikes.