In many businesses, machine changeover times can have a significant unfavorable impact on productivity. It is not unusual to find machines that can take up to a full 8-hour shift to change from producing one product to producing the next product. Long changeover times lead to several of the wastes listed in Volume 16 of this series, A Primer on Lean. Specifically, these long times contribute to excess inventory, waiting, overproduction, and defects.

The SMED (Single-Minute Exchange of Dies) process is designed to reduce changeover time. The focus is to move internal set-up (set-up that occurs while the machine is stopped) to external set-up (set-up that can occur while the machine is running) and eliminate transportation, motion, waiting, and defects.

Changeover time is defined as the time it takes to go from the last good part produced prior to changeover to the first good part after the changeover is completed.