SMED: what is it ?

SMED (Single Minute Exchange of Die) is a method used in the industrial world in a continuous improvement process. This method was developed by the Japanese engineer Shigeo Shingō for the car manufacturer Toyota. Noticing some slowness of tool changes on the presses of a mechanical workshop, Shingō imposed a significant reduction in presses downtime. The goal was to spend less time changing these tools and therefore more time producing.

The implementation of the SMED method must allows to optimize the changeover times. This method has proven itself in the industrial sector. Indeed, it is estimated that savings ranging from 30 to 70% on the time required for a tool change can be achieved. Shigeo Shingō has succeeded in reducing changeover times by an average of 94% in the companies he has worked for.

The objective of the SMED method is to reduce the possible batch size and thus increase the flexibility of production. Tool change is defined as the time between the production of the last good part of the batch that is ending and the first good part of the new batch, when the machine is at its nominal speed.

To illustrate this method, we often take the case of tire changes in Formula 1 cars. During the 1950s, teams used to take an average of more than a minute to change the wheels. Today, with SMED solutions, this kind of intervention is done in less than 2 seconds.

Although this example is not about reducing batch sizes, it does reflect the principles of SMED. The method proposes a formalized approach to reduce the change time to the most appropriate time.

In the traditional industry, the tool change includes the removal of the tool itself, the cleaning of the machine, the installation of the new tool and the adjustments. Overall, there are two types of times:

• Internal time: these are the proper times, the period during which operations necessarily require a production downtime.
• External time: this is the production period during which operations can take place (e.g. preparation of tools and equipment, pre-setting or pre-heating, storage of equipment, etc.).

Of course, it is necessary to switch a maximum of “internal time” tasks to “external time”.

What about implementation ?

During a SMED workshop, a group of people (from production, maintenance, methods) observes the change process in a situation of use. This same group identifies several changes and notes all the operations performed during this period. In this way, we can identify all the time wasted. All the operations carried out are evaluated using different filters, so we distinguish four stages:

1. Identify internal and external adjustments.
   
   List all the operations done internally that can be done externally. Look for these same operations that can be done in hidden time: for example, fetching a tool, preparing the raw material for the next production run, etc… This first step is above all organizational.
2. Separate internal and external adjustments.
   
   During this stage, it will be necessary to distinguish the proper times from the external times and thus to separate them.
3. Transform internal adjustments into external adjustments.
   
   The objective is to outsource as many internal operations as possible. Each operation is analyzed to see if it can be performed while the machine is still running. In this way, the teams will be able to identify the internal adjustments that can be transformed into external adjustments. For example, the use of templates or production standards. During this step, some operations can even be eliminated in order to reduce downtime.
4. Streamline all aspects of the operation change.
   
   Once the internal adjustments are transformed into external adjustments, the remaining internal operations will need to be streamlined. A connected factory makes it easy to optimize these internal adjustments to increase productivity rates and thus reduce inefficiencies.

The cases of application in the industry are numerous: change of mould on a press, change of format on a packaging line, etc…

From a global point of view, the objective of the SMED method is to improve the performance of a production system by reducing the execution time of external operations.

The SMED method and Astn’go

By implementing the SMED method, producers try to optimize tool change procedures and achieve even faster restart times.

The target is to minimise change times in order to be able to reduce series and thus be more flexible and agile.

With Astn’go, the manager defines the target of the SMED. Astn’go measures the time and place teams in real time in relation to the target. A dedicated analysis is available for the manager.

The SMED is measured between the last good part of a series and the first good part of the next series.