SMED: Single-Minute Exchange of Die

The SMED method is a framework for reducing the time associated with completing an equipment changeover.

Understanding the SMED method

The SMED (single minute exchange of die) method is a lean production framework to reduce waste and increase production efficiency. The “single-minute” aspect of the method refers to the goal of reducing equipment changeover time by any number in the single digits. That is, in any time under ten minutes.

Like similar lean process improvement strategies, the SMED method originated at Toyota in the 1950s after inefficiencies were identified in the process of molding body parts. When different parts of the car body needed to be molded, it took between two and eight hours to load the necessary tools into the equipment. This laborious process combined with the fact that Toyota had to purchase extra land to store the vehicles caused a lot of waste. 

To speed up the process, Toyota made modifications to the machinery and vehicle components and also re-ordered the steps in the molding process. By the 1970s, the equipment changeover time was occurring in a matter of minutes.

Today, the SMED method can be used in any industry or situation requiring a changeover of product or equipment. The most commonly mentioned examples are in software development and motor racing where pit crews need to change tires and drivers as quickly as possible.

The two principles of the SMED method

Generally speaking, the SMED method incorporates both internal and external setup components.

1 – External 

External components are process steps or parts that can be replaced while a product or piece of equipment is still in operation. 

For external components, the primary focus is preparation. This means the tools, materials, or other important resources are available before the changeover takes place. A Formula 1 pit crew, for example, does not search for new tires once the driver has pulled into the pit lane. Instead, they are pre-arranged on the tarmac at precisely the point where the driver will stop. 

2 – Internal 

Internal components require the product or piece of equipment to be non-operational before the changeover can take place. One example of an internal component is the molding equipment Toyota made more efficient in the 1970s.

Note that the goal for any team using the SMED method is to transform internal components into external components wherever possible.

Where is the SMED method most effective?

The SMED method is most effective in the following situations:

  • The process is performed frequently.
  • The process is a bottleneck whose resolution will have immediate and significant benefits.
  • Employees involved in the changeover are adequately trained and have bought into the change itself.
  • The duration of the changeover is long enough that an appreciable improvement is possible, and
  • There has been historical variance in past changeover times. For example, if one year the change over time was 7 hours and the next it had reduced to 45 minutes.

Key takeaways:

  • The SMED method is a framework for reducing the time associated with completing an equipment changeover.
  • The SMED method incorporates internal or external setup components. External components are process steps that can be altered while the process itself is still running, while internal components are those where the process must be halted. The goal for any team is to have more external components and fewer internal components.
  • The SMED method is effective in situations where processes are performed repeatedly or for bottlenecks whose resolution will result in process efficiency gains. The method is also useful when there has been significant variance in changeover time.
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