The purpose of the SMED method is to reduce the time required for a change of series and thus allow the minimum lot size to be reduced. This “quick tool change” method was developed by Shigeo Shingō on behalf of the Toyota company.

SMED is the abbreviation for the Japanese English single-minute exchange of die (s) , literally "change of die (s) in one minute". Being erroneous, the expression single-minute exchange was corrected in single-digit minute exchange , that is to say “change in minutes to a single digit”, that is to say “from 1 to 9 minutes” or even “in less ten minutes ”.

If the series change times become zero, then one can consider a unit production without increasing costs.

During a change in production, the set-up part (the start of production) can represent an important part in the production; and the part set in motion is not productive. The aim is to reduce this time spent on adjustment, in order to obtain quick tool changes or instantaneous adjustments.

There are two types of adjustment:

• internal settings / times: they correspond to operations which are carried out with the machine stopped, therefore outside production.
• external settings / times: they correspond to operations that are done (or can be done) with the machine running, therefore in production.