SMED (Single-Minute Exchange of Die) is Shigeo Shingo's technique for dramatically reducing changeover time. The name comes from the goal of getting changeovers under 10 minutes (single-digit minutes), though the technique applies at any scale.
The core insight
Changeover activities split into two types: internal (must be done while the machine is stopped) and external (can be done while the machine is still running the previous batch). Most changeover time is external work being done as if it were internal.
The four steps
- Separate: identify which activities are truly internal and which could be external.
- Convert: move activities from internal to external where possible (pre-stage tools, pre-heat, pre-align).
- Streamline: reduce the time of the remaining internal work (quick-release fasteners, standardised heights, guided positioning).
- Eliminate: question whether the changeover needs to happen at all (product family cells, dedicated equipment).
Why it matters for flow
Long changeovers force large batch sizes, which drive up WIP, lead time, and inventory. Reducing changeover from 4 hours to 20 minutes doesn't just save 3.5 hours - it lets you halve batch size, which cuts lead time and inventory across the whole downstream process.