Single Minute Exchange of Die. SMED.

Single-minute exchange of die (SMED) belongs to one of the many lean manufacturing techniques that aim to reduce waste in production processes. This tool provides a way of analysing the changeover from one reference to a different one and gives a solution in which time and non-added value operations are reduced. The quick changeover is very important in order to reduce production batch quantities and to reduce production loss and output variability.“Single minute” doesn’t mean that the changeovers should take only one minute, but that they should take less than 10 minutes.

A die is a tool used in production processes which is unique for each format and that needs to be changed anytime a new or different product is manufactured.

Some examples

Plastic extrusion machines are large, very complex and need between 6 to 12 h to change from one type of plastic to another (PET –> PP, PP –> PET, for example), as they need a thorough clean so as to eliminate all the impurities from the previous plastic.

One of the most time-consuming operations is the heat-up of the die, as it needs to be between 250ºC to 300ºC depending on the plastic extruded. This operation could last for several hours and can be done separately before the changeover. The die can be brought to the extrusion machine at the working temperature, thus, we will avoid heating it up on the machine.

Another example where SMED should be applied could be the changeover of a stamping mould to manufacture interior automobile parts (such as headliners). Let us suppose that the mould is heat up when it is set up on the machine from room temperature to working conditions. Now, let us suppose that we heat the mould up separately and when it is at working conditions we set it up on the machine. Just by doing the previous mentioned, we could save about two hours in the preparation of the new format.

The aforementioned are very simple examples to illustrate the need of analysing changeovers to reduce time and wast and SMED is a very useful tool which will allow us to do it efficiently.

The key process of SMED is to separate between internal and external operations so that those internal can be converted to external.

Internal changeover operations: those procedures which need to be performed during the changeover.

External changeover operations: those procedures which can be done while the last batch is being produced.

Consequences of its implementation

Shigeo Shingo (the Industrial Engineer who created the SMED technique) states that the reduction achieved, according to his data, is over a 70 %, which is admirable.

Some of the effects that will be achieved, apart from reducing changeover time, are the following:

  1. Stock tends to be reduced as the flexibility for manufacturing different formats increases.
  2. Increase of free floor space as a consequence of the inventory reduction.
  3. Increase of productivity by:
    • Increased machine productivity from reduced setup times.
    • Elimination of setup errors.
    • Improved product quality from Standardised Operating Conditions in advance.
    • Increased safety.
    • Better housekeeping as a result of  better organisation.
    • Reduced energy consumption.
    • Boosts operator motivation as the process is easier to start.
    • Lower skill requirements as changes are pre-designed by using SOPs (Standard Operating Procedures).
  4. Elimination of stock from format changeovers.

How to implement it?

Shigeo Shingo (the father of SMED) states the following eight sequential steps:

  1. Separate internal from external setup operations (explained before).
  2. Convert internal to external operations. The more operations we are able to undertake out of the changeover time, the less time we will need for the changeover.
  3. Create a SOP (Standard Operating Procedure).
  4. Use functional clamps or eliminate fasteners altogether
  5. Use intermediate jigs
  6. Adopt parallel operations.
  7. Eliminate adjustments.
  8. Mechanisation.

Shigeo suggests that in SMED improvement we should take into account the following conceptual stages:

a) Make sure that the external actions are performed while the machine is running.

b) Separate external and internal setup actions.

c) Convert internal actions to external.

d) Improve all setup actions. As continuous improvement philosophy aims, once we have our operations standardised, then we are able to improve them.

Methodology

  1. Observe the current methodology (workforce, internal movement, machine shut down and start up, inventory, etcetera). It can be useful recording a video of the changeover and watch it together with the team to detect points of improvement.
  2. Separate the internal and the external operations.
  3. Convert as much as it is possible, the internal operations into external ones.
  4. Coordinate and simplify the internal activities or operations.
  5. Coordinate and simplify the external activities or operations.
  6. Document the new changeover procedure.
  7. Iterate and continuously improve the new procedure for several times until a 45 % of reduction is achieved (approximately).
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