Pgbarranca's Blog

April 13, 2010


Filed under: Uncategorized — by pgbarranca @ 8:04 pm


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”). 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.

This is the SMED concept

History – Toyota

An increase in effective operating time caused by the change-over. SMED is the key to manufacturing flexibility.

Changeover time Lot size Process time per item Operation time Ratio
8 hours 100 1 min 5.8 min 480%
8 hours 1,000 1 min 1.48 min 48%
8 hours 10,000 1 min 1.048 min 5%

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) is a well-known, and heavily debated, 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.


Toyota found that the most difficult tools to change were the dies on the large transfer-stamping machines that produce car vehicle bodies. The dies – which must be changed for each model – weigh many tons, and must be assembled in the stamping machines with tolerances of less than a millimeter, otherwise the stamped metal will wrinkle, if not melt, under the intense heat and pressure.

When Toyota engineers examined the change-over, they discovered that the established procedure was to stop the line, let down the dies by an overhead crane, position the dies in the machine by human eyesight, and then adjust their position with crowbars while making individual test stampings. The existing process took from twelve hours to almost three days to complete.

Toyota’s first improvement was to place precision measurement devices on the transfer stamping machines, and record the necessary measurements for each model’s die. Installing the die against these measurements, rather than by human eyesight, immediately cut the change-over to a mere hour and a half.

Further observations led to further improvements – scheduling the die changes in a standard sequence (as part of FRS) as a new model moved through the factory, dedicating tools to the die-change process so that all needed tools were nearby, and scheduling use of the overhead cranes so that the new die would be waiting as the old die was removed. Using these processes, Toyota engineers cut the change-over time to less than 10 minutes per die, and thereby reduced the economic lot size below one vehicle.

The success of this program contributed directly to just-in-time manufacturing which is part of the Toyota Production System. SMED makes Load balancing much more achievable by reducing economic lot size and thus stock levels.

Effects of implementation

Shigeo Shingo, who created the SMED approach, claims that in his data from between 1975 and 1985 that average setup times he has dealt with have reduced to 2.5% of the time originally required; a 40 times improvement.

However, the power of SMED is that it has a lot of other effects which come from systematically looking at operations; these include:

  • Stockless production which drives capital turnover rates,
  • Reduction in footprint of processes with reduced inventory freeing floor space
  • Productivity increases or reduced production time
    • Increased machine work rates from reduced setup times even if number of changeovers increases
    • Elimination of setup errors and elimination of trial runs reduces defect rates
    • Improved quality from fully regulated operating conditions in advance
    • Increased safety from simpler setups
    • Simplified housekeeping from fewer tools and better organisation
    • Lower expense of setups
    • Operator preferred since easier to achieve
    • Lower skill requirements since changes are now designed into the process rather than a matter of skilled judgement
  • Elimination of unusable stock from model changeovers and demand estimate errors
  • Goods are not lost through deterioration
  • Ability to mix production gives flexibility and further inventory reductions as well as opening the door to revolutionised production methods (large orders ≠ large production lot sizes)
  • New attitudes on controlability of work process amongst staff

reference link

SMED Benefits

Now a day, SMED is offering a number of benefits to the manufacturing organizations. Commonly benefits obtained are as follows:

– Improved safety of systems and processes

– Reduction in lead time and hence improved and faster delivery

– Improved quality of product and service

– Almost zero inventory of work in process

– Reduction in working capital

– Lot size reduction

– Increase in profit margin, without any substantial investment.

– Improved equipment utilization.

SMED in Health Care

SMED is being utilized in various sectors of service organizations like health care, maintenance service, hotels and food industry etc. 
Its use in health care has proven good results and reduced many bottlenecks. It is being applied for acquisition of operation instrument, medications, setting of operation theaters, setting of private rooms for patients and doing paper work. All these activities are now being performed in very small considerable amount of time. SMED application in health care has given following benefits:

– Enhanced satisfaction level of Doctors, Surgeons, Physician and Nurses.

– Reduced inventories of medicines and consumable equipments

– Enhanced Satisfaction level of patient and their caretakers.

– Increase in operation and service productivity along with professional competitiveness

– Reduction in un-necessary wastes and non value-added activities

– Less time is required for treatment of patient and hence speedy operations

– Improved system capacity and enhanced volume of services

– Increased flexibility of systems and processes

– More profit and business due to higher productivity and less inventory and wastes.

– So by applying principles of SMED, so much productivity is increased that organization can – take care of more patients without hiring more doctors, surgeons and nurses. Also this does not require that you hire more space or extend your existing one.

I found this very short and illustrative video about SMED in Ferrari.

There´s also an interesting explanation, but it´s in spanish, sorry!!


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