SMED Meaning: Single-Minute Exchange of Die in Manufacturing and How it Reduces Changeover Times
Time is money, and in manufacturing, every minute of downtime comes at a cost. Unproductive time when changing or replacing tools is especially expensive, because you have the continuing costs of labor and equipment while production of parts is on pause.
When there are considerable production losses because of time-intensive or frequent changeovers, manufacturers need to pay attention to the changeover process itself. That’s because it can significantly impact downtime, overall equipment effectiveness (OEE), productivity, and even scrap costs.
A lean concept that can help is single minute exchange of die (SMED), a group of tools focused on the goal of reducing setup and changeover time by examining the steps, tools, and responsibilities during the setup.
We’ve helped many customers apply the SMED system in their plants. In some cases, that has delivered millions of dollars in savings over the course of a year. Here, we tackle the SMED meaning, taking a closer look at this process and the considerations for implementing it in your plant, as developed by Shigeo Shingo.
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Basics of SMED
SMED is a group of lean tools for eliminating waste in setups and standardizing work to reduce machine setup and changeover times, ideally to single digits (under 10 minutes).
One of the key ways it does so is to convert as many internal elements as possible—tasks that previously required the machine to be stopped—into external ones that can be completed while it’s still running.
Reducing Changeover Time: SMED Metrics
To understand how the SMED system drives manufacturing efficiency and productivity, let’s look at two key KPIs that come into play when launching a SMED workshop or project.
The first is what’s often called “hit to hit,” or the time it takes to complete a full production cycle, from when a machine produces the last good part to when it produces the next good one. This represents the total time the machine was unproductive. For example, if the last good part is made at 12:00, the line shuts down for a tool change, and the first acceptable part passes quality control (QC) at 12:28, the actual changeover process took 28 minutes. That’s 28 minutes of lost production.
The second KPI is average hits per hour, which is strongly affected by setup activities and downtime. Applying SMED tools and principles helps minimize these interruptions. When the transition between runs is faster, productivity rises, with more parts produced per hour and fewer delays.
To illustrate the impact, imagine a plant performing five changeovers per day. If each setup takes an hour, that’s five hours of non-productive time — leaving a maximum of 19 hours for production, which could be reduced by converting internal processes. Halving setup time to 30 minutes recovers 2.5 additional hours of output daily, amounting to hundreds of hours gained over a year.
Benefits of SMED: How Single-Minute Exchange of Dies Helps You
Reducing the time to changeover with SMED has a number of downstream effects on manufacturing KPIs, including:
- Productivity: Less downtime means more time that machines are producing parts and higher profitability overall.
- Overall equipment effectiveness (OEE): Shorter changeovers increase availability rate, one of the three parameters that go into calculating OEE.
- Scrap: Extended changeover times can allow for machines to change in other ways (which we discuss below), leading to downstream scrap and customer complaints.
While reducing scrap isn’t the first thing people think about in this context, it is an important benefit of SMED.
One customer we worked with had a plastic molding process where the plastic would cool and absorb moisture when the machine shut down. By reducing changeover time from an hour to less than 20 minutes, the plant was able to reduce startup scrap and the likelihood of shipping defective products. Scrap can also be reduced by simplifying work instructions and standardizing many elements of the process so operators spend less time troubleshooting and more time producing.
Implementing SMED: Key Steps to Reduce Changeover Time
A SMED event is a type of Kaizen event, which is typically defined as focused, short-term continuous improvement projects aimed at improving a specific process within the plant.
A typical SMED event takes place over a series of a few days, bringing together a cross-functional team to analyze the process, identify inefficiencies, and implement improvements. The goal: to drive significant change quickly while building a culture of collaborative problem-solving.
With that in mind, let’s take a look at how the SMED process breaks down in five steps.
1. Observe the Process
The first thing we do in any SMED project is to videotape the process from multiple angles to help quantify every movement and delay. This provides a clear visual template for improvement. Here, we might take one video from the front of the machine, one from the back of the machine or at the control panel, and one from the top down, depending on what you can see.
From there, we sync the videos together to get a full view of the process.
2. Cross-Functional Review
Since the goal here is to help identify waste, especially unnecessary movement or waiting, across many changeover steps, the next step is to sit down with the changeover team and review the video, including:
- Maintenance and toolroom employees
- Die setters or mold setters
- Any operators involved
- Quality management employees responsible for checking parts and approving the setup
The goal at this step is to get agreement on what the process is right now, which is harder than it seems. Teams may think they are doing a specific set of steps, but when they see it on video, it’s actually something different.
Once you establish the baseline process, you start looking for different areas of waste, particularly movement. For example, let’s say employees move the old material somewhere, and then they have to move it again to make room for the new material. That is essentially wasted movement that increases the time to changeover, where streamlining movements can have an impact.
3. Externalize Changeover Steps
Remember that, as soon as you turn the machinery off, the clock starts ticking in terms of time between hits, making whatever you do during that time especially critical.
The key idea here is to start as many possible changeover steps as possible before shutting the machine down, while it’s still making good parts.
One classic example would be a stamp within the machine marking parts with the date. Many companies put the die or mold in the machine, then open it up and increment the date in the machine. Rather than doing it during changeover, however, you can look to have the date set correctly before the setup even begins.
Another example would be to look at whether you can get all of your molds or dies to a single shut height. This may mean installing a backplate onto a mold to get it to a specific height, but the advantage is that it’s something you can do while the press is running. If you have to put the mold in and inch the press down, that’s time you could be using to continue making parts.
4. Streamline Remaining Internal Changeover Steps
Next up, you want to look at all remaining internal changeover steps and find ways to make them as efficient as possible. If someone is using a hand wrench, for instance, could they use a pneumatic driver instead?
Another example would be if you have a person who has to tighten bolts in the front of the press and then walk around to work on the back of the press, which could be streamlined by an industrial engineer. If you instead have two people working simultaneously, one in front and one in back of the press, you’ve just saved valuable time in the changeover process.
Ultimately, externalizing all steps possible and improving the efficiency of what’s left is what will get you closer to a true SMED changeover.
5. Create Your Pre-Flight Checklist
Every good SMED changeover requires a good pre-flight checklist to make sure all the right elements are in place.
As an example, let’s say a changeover process requires fastening a mold with eight fresh bolts rather than using potentially damaged or dirty ones. Your pre-flight checklist would then ask questions like:
- Are the eight bolts there?
- Are the bolts cleaned?
- Are the threads good?
- Is the socket head cap screw still solid?
- Is the half-inch driver used to fasten the bolts there?
The focus at this step is turning your standardized process into a list of items that people must follow to ensure conformance.
Is SMED Process Automation Necessary?
Notice that in all the examples above, automation wasn’t necessary to drive improvement, which is true in the vast majority of changeovers. Externalizing changeover steps and streamlining remaining internal steps represent the low-hanging fruit for reducing the time it takes for the process.
That’s not to say automation can’t help; however, it tends to be very expensive and often requires changes to how molds and dies are designed. A better strategy is to optimize and standardize your process and make it more efficient. This approach delivers substantial savings with minimal investment.
Successful SMED Implementation Factors
If you’re looking to conduct a SMED project in your plant, it’s important to know a few things up front.
First, the event requires a lot of support, commitment, and involvement from management.
That’s because any die change team can do a great die changeover once. The question is, how do you do it on a consistent basis? That’s where management comes in, providing support and regular feedback to keep the process on track.
Changeovers are a process, and one way to make sure the new SMED activity is maintained over time is to verify it with layered process audits (LPAs). Someone from management can attend changeovers and look for key elements using an LPA checklist or even the pre-flight checklist.
Second, SMED is an ongoing activity, not a one-and-done event. Once our team helps manufacturers establish a baseline changeover, we then establish a six-month plan that moves you incrementally toward your goal and more and more sources of variation are identified and eliminated.
In other words, you’re not going to go from a 30-minute changeover to a 13-minute changeover in a day. Rather, it’s a long-term process where you continually shave down the process over time. Management commitment, tracking progress, sustaining the gains—all of this is a process, not an event.
After all of this, you may be wondering—can you really get changeovers down to less than 10 minutes? In many cases, the practical answer is no, unless the process is very simple or you invest in expensive automation.
At the same time, reducing an hour-long changeover to 17 minutes has huge cost savings and efficiency implications, making SMED a worthwhile investment for those willing to go the distance. Standardize your process, externalize all changeover steps possible, and streamline the rest: These, plus consistent tracking and feedback, are the ingredients needed to reach the finish line, which is reducing costs.
