SMED (Single-Minute Exchange of Die)

Shingo's SMED methodology follows three conceptual stages. Stage 1: Separate internal and external setup. Internal setup activities can only be performed while the machine is stopped (e.g., removing a die from a press). External setup activities can be done while the machine is still running the previous product (e.g., gathering tools, preheating a die, preparing materials). Simply identifying which activities are external and performing them before the machine stops typically reduces changeover time by 30–50%. Stage 2: Convert internal to external setup. Analyze each remaining internal activity and ask: 'Is there a way to do this while the machine is still running?' Techniques include using pre-heated dies, standardized mounting fixtures, and pre-assembled tool sets. Stage 3: Streamline all setup operations. Reduce the time of both internal and external activities through parallel operations (two people working simultaneously), quick-release fasteners (replacing bolts with clamps), elimination of adjustments (using pre-set fixed positions), and mechanization of heavy lifting. Each stage builds on the previous one, progressively compressing changeover time.

A practical SMED project starts by video-recording the current changeover process from the last good part of the old product to the first good part of the new product. The team reviews the video, listing every activity with its duration and classifying each as internal or external. This analysis alone is eye-opening: most teams discover that 30–50% of activities currently performed during machine stoppage could easily be done in advance. The team then redesigns the changeover process, reassigning external activities to a preparation checklist completed before the machine stops. For the remaining internal activities, the team applies conversion and streamlining techniques. Common wins include: pre-staging all tools and materials on a changeover cart, using color-coded fixtures for different products, replacing manual adjustments with positive stops or digital presets, and assigning parallel tasks to team members. After redesign, the team practices the new procedure, refines it, and documents it as the standard changeover method. Results of 50–90% changeover time reduction are typical even in first-round SMED projects.

SMED transforms production scheduling by making frequent changeovers economically viable. When changeover takes 4 hours, a planner is forced to schedule large batches to minimize the proportion of time lost to setup. If changeover drops to 20 minutes, the planner can schedule 12 times more changeovers in the same time, enabling much smaller batch sizes. Smaller batches mean shorter lead times, less WIP inventory, more frequent production of every product, and faster response to demand changes. For scheduling tools like LinePlanner, SMED success means planners gain flexibility — they can mix products across shifts rather than dedicating entire days to single products. SMED also makes heijunka (level scheduling) practical: leveling the product mix requires frequent changeovers, which are only feasible when each changeover is quick. The scheduling benefit compounds: shorter changeovers enable smaller batches, which reduce lead times, which improve delivery performance, which reduces the need for finished goods safety stock — a virtuous cycle that improves across multiple dimensions simultaneously.