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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 changeovers and startups should take only ''one'' minute, but that they should take less than 10 minutes (in other words, "single-digit minute").〔Study of Toyota Production System, Shigeo Shingo, 1981, p 70〕 Closely associated is a yet more difficult concept, One-Touch Exchange of Die, (OTED), which says changeovers 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 (see value stream mapping). ==History== 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-molding 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; which is 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. Toyota's additional problem was that land costs in Japan are very high and therefore it was very expensive to store its vehicles. The result was that its costs were higher than other producers because it had to produce vehicles in uneconomic lots. The "economic lot size" (or EOQ, Economic Order Quantity) is a well-known, and heavily debated,〔Theory of Constraints, Eliyahu Goldratt, North River Press, 1990, p 40〕 manufacturing concept. Historically, the overhead costs of retooling a process were minimized by maximizing the number of items that the process should construct before changing to another model. This makes the change-over overhead per manufactured unit low. According to some sources optimum lot size occurs when the interest costs of storing the lot size of items equals the value lost when the production line is shut down. The difference, for Toyota, was that the economic lot size calculation included high overhead costs to pay for the land to store the vehicles. Engineer Shingo could do nothing about the interest rate, but he had total control of the factory processes. If the change-over costs could be reduced, then the economic lot size could be reduced, directly reducing expenses. Indeed the whole debate over EOQ becomes restructured if still relevant. It should also be noted that large lot sizes require higher stock levels to be kept in the rest of the process and these, more hidden costs, are also reduced by the smaller lot sizes made possible by SMED. Over a period of several years, Toyota reworked factory fixtures and vehicle components to maximize their common parts, minimize and standardize assembly tools and steps, and utilize common tooling. These common parts or tooling reduced change-over time. Wherever the tooling could not be common, steps were taken to make the tooling quick to change. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Single-Minute Exchange of Die」の詳細全文を読む スポンサード リンク
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