Changeover — also called setup — is the time between the last good part of one production run and the first good part of the next. It includes removing the previous job's tooling and fixtures, installing new tooling, adjusting machine parameters, loading the correct program, running test pieces, and verifying the first article. During changeover, the machine is not producing saleable output.
Changeover time directly impacts scheduling flexibility and batch size decisions. Long changeovers force large batch sizes to amortize setup cost — which increases WIP, lead time, and inventory. Short changeovers enable smaller batches, more frequent product changes, and faster response to customer demand. This is the core insight behind SMED (Single-Minute Exchange of Die), which aims to reduce changeovers to under ten minutes.
SMED categorizes changeover activities as internal (must be done while the machine is stopped) or external (can be done while the machine is still running the previous job). Converting internal to external activities — pre-staging tools, pre-heating molds, pre-loading programs — is the primary lever for reducing changeover time without capital investment.