Single-Minute Exchange of Die (SMED) is one of the many lean production methods for reducing waste in a manufacturing process. It provides a rapid and efficient way of converting a manufacturing process from running the current product to running the next product. This rapid changeover is key to reducing production lot sizes and thereby improving flow (Mura). The phrase “single minute” does not mean that all changeover and startups should take only one minute, but that they should take less than 10 minutes (in other words, “single-digit minute”). Closely associated is a yet more difficult concept, One-Touch Exchange of Die, (OTED), which says changeover can and should take less than 100 seconds. A Die is a tool used in manufacturing. However SMED’s utility of is not limited to manufacturing
The concept arose in the late 1950s and early 1960s, when Shigeo Shingo was consulting to a variety of companies including Toyota, and was contemplating their inability to eliminate bottlenecks at car body-moulding presses. The bottlenecks were caused by long tool changeover times which drove up production lot sizes. The economic lot size is calculated from the ratio of actual production time and the ‘change-over’ time; the time taken to stop production of a product and start production of the same, or another, product. If change-over takes a long time then the lost production due to change-overs drives up the cost of the actual production itself. This can be seen from the table below where the change-over and processing time per unit are held constant whilst the lot size is changed. The Operation time is the unit processing time with the overhead of the change-over included. The Ratio is the percentage increase in effective operating time caused by the change-over. SMED is the key to manufacturing flexibility.