This article provides a practical explanation of SMED (Single Minute Exchange of Dies). After reading, you will understand the basics of this powerful and efficient manufacturing philosophy and quality management tool.
What is SMED (Single Minute Exchange of Dies)?
SMED (Single Minute Exchange of Dies) is a LEAN Manufacturing method that drastically reduces the time required to change equipment. The changeover time reduction ensures a more efficient and therefore usually cheaper process, leaving more focus and budget for the development of more important things. SMED can be applied both in process changeovers in machines and changes in processes involving people.
The essence of the SMED method is changing over as many sub-processes that were previously carried out simultaneously with the core process and carry them out externally. The other sub processes are then simplified and streamlined based on the core process to save time. The name Single Minute Exchange of Dies refers to the goal of the process to reduce the changeover times to single digits. Meaning less than 10 minutes. The correct use of SMED can lead to a 90% time reduction, as was documented by the inventor of the process.
SMED was developed by Shigeo Shingo in 1950. He was a Japanese industrial engineer with exceptional skills and success in helping companies drastically reduce their changeover times. This engineer is best known for his inventions and optimisation techniques within the Toyota Production System (TPS). He studied the exchanges of parts and tools on big 500-ton presses that were used to produce bodywork. He observed how this took hours, or even days. After the changes he made, the process’ time was reduced to several minutes.
Why SMED is necessary
Lean Manufacturing and Just in Time (JIT) strive to reduce waste and inefficiencies within a certain system. Waste is one of the three main areas as defined in Lean: the loss of Muda, Mura, and Muri. SMED addresses those three waste areas, but the main focus is on the elimination of Mura (unevenness). In order to achieve a smooth and predictable process flow, ever smaller batches need to be able to be processed in order to meet customer demands. The biggest hurdle to smaller batches is changing the equipment over time. These changes are time-consuming, expensive and need to be earned back through a more efficient process.
Because the changeover time for certain equipment can take many hours or even days, an attempt is made to maximise the output of these machines. This way, the biggest possible batch is used to make the process more economical. Efficiencies only become clear when the process has to be changed.
The only way to economically realise smaller batches is if the time every changeover requires is reduced. This is why the setup needs to be minimised to a point that the changeover time has little to no influence on the production process.
2 types of elements
Changeovers in SMED are built up of steps that are called elements. There are two types of elements:
1. Internal elements
These elements have to be applied or changed after the equipment is stopped. Examples of these are: removing old tools, placing new tools, change the material feed, or alter the programme settings. Think of it like a Formula 1 pit stop. The car enters the pit lane, stops, and the crew changes the tyres.
2. External elements
External elements can be applied or added when the equipment is in operation. Examples of these are: purchasing new material feeds, purchasing new tools, returning or storing old tools, and documenting the right procedures or requesting licences. During that same Formula 1 race, the crew is already getting the tyres ready, preparing tools, and positioning mechanics while the car is still on the track. As a result, the crew can carry out the entire process in mere seconds the moment the car comes in for a stop.
Follow the steps below to draw up a SMED action plan:
1. Separate internal and external setup processes
During this step, elements in the changeover process, which can be carried out with little or no change while the equipment is running, are identified and then carried out before or after the changeover. It’s not uncommon for this step to achieve a reduction of changeover times by half.
For each element, each sub-process, the team has to ask if the element can be carried out while the equipment is in use. If the answer is yes, it’s an external element.
2. Standardise external setup processes
With the aid of videos or flowcharts, all external phases can be identified and standardised during this phase. This means those activities can be carried out while the process is running. If this isn’t done carefully, there may be situations in which the tools still have to be gathered while the machines aren’t running. This makes the changeover time longer than it needs to be.
3. Convert internal to external setup processes
The current changeover process is carefully examined during this step with the goal of making as many of the internal elements as possible external. During this step, the team needs to consider: if there is a way to make internal elements external, what this method would be and how to go about it.
The result is a list of elements that are eligible for further action. This list with priorities is similar in some ways to a cost-benefit analysis.
4. Improve internal exchange processes
Shigeo Shingo once said, ‘Only the final turn of the bolt secures the part in its place.’ The rest is just movement and can be considered waste. The idea behind this is that the bolt can, for instance, be replaced by shorter, spring-loaded clamps that keep the part in place. The time that was previously spent on turning the bolt is then saved. Machines or tools can be changed to give it standard sizes and mounting points can be simplified so the job can be done with a minimal number of steps.
5. Improve external setup processes
During this step, the remaining external elements are evaluated. The goal is to streamline and simplify these and save more time. As with the previous steps, the team considers: How can this element be completed in less time? How can we simplify this element? A cost-benefit analysis can be used here as well in order to determine if it’s efficient enough.
6. Repeat SMED again and again
By closely examining the entire process again and again, it’s possible to achieve regular time savings. New technologies or other valuable insights offer opportunities to, for instance, optimise the process using video analysis.
- Reduction of the number of required tools
- Reducing the required inventory
- Reducing lead times
- Improved ability to produce small batches
- Quicker response time to customer wishes
- Increase capacity
- Increase quality
- Increase flexibility
- Reduce costs and grow profits
It’s Your Turn
What do you think? Are you familiar with this explanation of Single Minute Exchanges of Die by Sigeo Shingo? To what extent do you think changeover times in your company can be reduced using this tool? Do you have any tips for making manufacturing processes more efficient?
Share your experience and knowledge in the comments box below.
- Dillon, A. P., & Shingo, S. (1985). A revolution in manufacturing: the SMED system. CRC Press.
- McIntosh, R. I., Culley, S. J., Mileham, A. R., & Owen, G. W. (2000). A critical evaluation of Shingo’s’ SMED'(Single Minute Exchange of Die) methodology. International journal of production research, 38(11), 2377-2395.
- Dave, Y., & Sohani, N. (2012). Single Minute Exchange of Dies: Literature Review. International Journal of Lean Thinking, 3(2), 27-37.
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