Changeover Time

Accurate changeover measurement requires a clear definition of start and end points. The standard definition measures from last good part off (the last unit of the outgoing product that meets quality standards) to first good part off (the first unit of the incoming product that meets quality standards). This definition captures the full impact of the changeover, including trial runs and quality verification. Many factories underestimate changeover time by measuring only the physical tooling swap and ignoring the setup verification, trial run, and quality adjustment time — which can equal or exceed the physical swap time. To measure accurately, observe and time several changeovers of the same type, noting the start and end times by the standard definition. Record the component activities and their durations. Calculate both the average changeover time and the variability (standard deviation), because high variability is itself a problem that makes scheduling unpredictable. Compare changeover times across operators, shifts, and product transitions to identify best practices and training opportunities.

The SMED (Single-Minute Exchange of Die) methodology is the gold standard for changeover reduction, targeting changeovers under 10 minutes. The approach works in three stages: First, separate internal activities (which require the machine to be stopped) from external activities (which can be done while the machine is still running) — simply moving preparation activities before the machine stops typically achieves 30–50% reduction. Second, convert internal activities to external where possible — for example, preheating a mold before installation eliminates the in-machine heating time. Third, streamline remaining activities through parallel operations (two people working simultaneously), quick-release mechanisms (replacing bolts with clamps), elimination of adjustments (using pre-set fixed positions), and standardization (using the same tools and procedures for all products). Beyond SMED, product design changes can reduce changeover — designing product families to share common tooling and fixtures reduces the scope of changeover activities between family members.

Changeover time directly shapes scheduling strategy. When changeovers are long, schedulers batch similar products together to minimize the number of changeovers (campaign scheduling) — for example, scheduling all blue products before all red products to avoid color changeovers. When changeovers are short, schedulers can sequence products more freely based on delivery priorities rather than setup constraints. The production sequence itself affects total changeover time: in many processes, transitioning from Product A to Product B takes a different amount of time than from Product B to Product A (sequence-dependent setup). For example, in injection molding, switching from a light-colored to a dark-colored material is faster than the reverse because the dark material purges quickly. Smart sequencing — scheduling the changeover path that minimizes total setup time — can recover significant capacity. LinePlanner enables planners to visualize product sequences across shifts and experiment with different orderings to find the most changeover-efficient plan.