Single Minute Exchange of Die (SMED)

The origin of SMED (Single-Minute Exchange of Die) dates back to 1950 when Shigeo Shingo of the JMA was asked to perform an efficiency improvement survey at Toyo Kogyo’s Mazda plant in Hiroshima.  Toyo was interested in eliminating the bottlenecks caused by their large body-molding presses that were not performing up to capacity.  Shingo asked the section manager if he could perform a week-long analysis of the presses. The section manager felt that it would be a waste of time, but Shingo was able to convince him by saying that he would recommend to management to buy more machines if he found that there was no other way to eliminate the bottlenecks.

During Shingo’s study, he witnessed a die change on an 800-ton press.  He observed several workers removing the old die and then searching around the press for something. Shingo asked one of the workers was what going on and he replied that “one of the mounting bolts for the new die was missing”.  The worker continued searching and after more than hour returned with what appeared to be the missing bolt. It ended up that the worker had borrowed the bolt from another die and that this problem had previously caused them problems when performing changeovers. Shingo realized that setup operations were composed of two different types: internal setup (IED) and external setup (OED).

From his analysis, Shingo found that the 800-ton press was utilized in the main operation for less than 3% of an entire day. He decided that a more organized system needed to be creating during changeover. The operation of organizing and preparing the bolts could be done while the machine was still running, an external operation. In addition to solving the bolt problem, the entire changeover procedure was improved by shifting as many aspects of the setup externally. This activity resulted in a 50% improvement in efficiency and reduction in the bottleneck.

Seven years later Shingo made an advance in his SMED concept.  He had been requested to perform a study at the Mitsubishi Heavy Industries shipyard in Hiroshima.  The plant manager explained that a large, open-sided planer that was used to machine diesel engine beds was not performing to capacity and that he would like to improve this operation. Shingo observed that the marking-off procedure for dimensioning and centering the engine bed was being performed on the planer table itself.  Shingo proposed utilizing a second planar table.  The marking-off procedure would be done on this table for the next lot and then when the changeover occurred it would be swapped with the existing table.  This activity resulted in a 40% improvement in productivity.

The concept of SMED has continued to develop and spread throughout the years. SMED has become an integral part of the Toyota Production System.  It has allowed companies to dramatically reduce changeover times, from hours to only a few minutes, leading to improved production flexibility.