SMED means ‘single minute exchange of dies’. It is one of the great enablers of Lean manufacturing for the simple reason that it reduces batch sizes.
Simply put, when changeover takes a long time, a machine that makes many parts needs to run big batches all at once to be able to provide enough product to the downstream processes. This drives up inventory and reduces flexibility of the production system.
SMED uses setup reduction to lower the time it takes to shift from part A to part B. This rapid changeover comes from basic process improvement (waste reduction) and from turning internal setup (when the machine is shut down) to external setup (done when the machine is running to prepare for the next changeover).
Common changes with SMED include using clamps instead of bolts, making shims and spaces to reduce the distance machine components need to move, and making standard-height installation fixtures to reduce the use of hoists and cranes to lift heavy objects.
The term SMED is commonly accepted to mean single digit exchange of dies—effectively getting changeover under ten minutes. In most cases, this is sufficient to get products flowing through a production facility.