What Is SMED?

Single-minute exchange of dies (SMED) is a process that reduces the time it takes to complete equipment changeovers. What originally took hours to complete can now be accomplished in less than ten minutes. 

Setup reduction techniques, such as SMED, were originally tested in 1915 by the Ford Motor Company and were popularized in the Toyota process by Taiichi Ohno in the 1950s, but it wasn’t until the 1990s that SMED became a widely adopted technique.

This is thanks to Shigeo Shingo, a former Toyota employee who moved to the United States as a lean manufacturing consultant and brought these techniques with him. Through his SMED process, Shingo was able to reduce changeover times by an average of 94% across a variety of industries, taking an average of fewer than five minutes to complete a successful changeover.  

Implementing an SMED program has multiple benefits that help facilities minimize waste and “go lean.” A successful SMED program can:

• Reduced manufacturing costs.
• Reduced equipment downtime.
• Improved schedule flexibility.
• Reduced inventory levels.
• Improved machine startups.
• Increased quality and consistency.

The Basics of SMED

In an SMED process, changeovers are comprised of steps or “elements.” There are two types of elements:

• Internal: Must be completed while the equipment is stopped.
• External: Can be completed while the equipment is running.

The main goal is to have as many external elements as possible while streamlining and simplifying all internal elements.  

Improving changeover rates by 94% may seem unrealistic, but consider some of the simple changes Toyota implemented to achieve these results with the dies on their larger transfer-stamping machines that manufactured vehicle body parts.

These dies weighed several tons, had to be changed with each new car model and had to be positioned with less than one millimeter of variation. Originally, these dies were removed and replaced using overhead cranes and eyeballing the position of the die while using crowbars to make smaller adjustments. This process took up to three days to complete.

To improve, Toyota placed precision measurement devices on the stamping machines to record measurements for each die. These standardized installation measurements immediately cut the changeover time to less than two hours. From there, they implemented other changes, such as scheduling die changes in a standard sequence, ensuring all tools were in their appropriate places, and properly scheduling the overhead cranes, which helped to lower the changeover rate even further.

Implementing SMED

When implementing an SMED program, there are five steps to consider.

Step 1 — Identify a Pilot Area

Before implementing SMED, you must select a pilot area. It might be tempting to pick a process with the longest changeover time, and while important, you’ll also want to make sure of a few things, such as:

• The changeover time is short enough to fully understand and long enough to show significant improvement.
• There are multiple variations in changeover times.
• This tells you there is a great chance for improvement.
• There are multiple chances to perform the changeover each week.
• This lets you quickly test improvements.
• Employees in the proposed pilot area are engaged and motivated.

In this step, it’s critical to get everyone on board with the SMED implementation; this includes all employees associated with the selection process and those who will work on the changeover.

Step 2 —  Identify Elements

After identifying a pilot area, work with your SMED team to identify all the internal and external changeover elements. This includes making a list of every step, detailing each task performed, and recording how long each task takes to complete (cost in time). This outline will serve as your baseline. Some things to keep in mind include:

• A typical changeover averages 30 to 50 individual elements.  
• Capture both human and equipment elements.
• Human elements can be easily optimized.
• When creating your baseline, have multiple team members create their own tasks list. Compare their notes with yours to ensure nothing was missed.

Step 3 —  Separate External Elements

After creating your tasks list, determine if each documented element can be performed while the machine is running. Elements that can be completed while the machine is in operation must be labeled as “external” to the process. In other words, the element can be performed before or after the changeover. Performing external elements helps significantly reduce the changeover time.

Elements considered external include:

• Retrieval and inspection of parts, tools and materials.
• Cleaning tasks that can be performed while the SMED process is running.
• Quality checks.

Once completed, you should have an updated list of changeover elements divided into three parts:

• External elements (before changeover)
• External elements (after changeover)
• Internal elements (during changeover)

Step 4 —  Convert Internal Elements to External Elements

After your elements have been categorized, evaluate which internal elements can be converted to external elements. Ask yourself: “Is there a way to make this element external?”

Perform a cost/benefit analysis to prioritize this list so that the elements with the most promising results are dealt with first. In this case, “cost” is the labor and materials needed to make the necessary changes, and “benefit” is the time that will be removed from the changeover once the element is converted.

Consider the following techniques to convert internal elements to external:

• Advance preparation: Preparing parts in advance and keeping them in a ready-to-go status can cut a significant amount of time.

• Make adjustments prior to the changeover: Consider using duplicate jigs for performing alignment and other adjustments before the changeover process begins.

• Equipment modification: Modify equipment to make it safer to perform tasks (like cleaning) while the machine is running.

• Modularize equipment: Equipment portability and customization can reduce the number of interfaces or interactions, resulting in significantly faster changeover times. For example, designing equipment on skids can make each piece highly mobile.

Once this step is completed, you should be left with a new list of changeover elements that includes fewer internal elements and more external elements.

Step 5 —  Streamline Remaining Elements

Finally, your SMED team should simplify the elements so they can be done in less time. Give priority to internal elements before moving on to external, which can be prioritized using cost/benefit analysis.

Some of the quickest ways to streamline elements include things such as:

• Replacing bolts with quick-releases or other functional clamps.
• Eliminating adjustments by standardizing numerical settings.
• Using centerlines and shims to standardize die sizes.
• Cutting out motion by adjusting the layout of workspaces.
• Standardizing hardware to use fewer tools.
• Reducing wait times.
• Create simultaneous operations.

Once step five is completed, update your standardized work instructions for the changeover.

Factors to Consider While Implementing SMED

While nearly every company with changeovers can benefit from SMED, it’s important to determine where productivity time is being lost to decide if SMED should be your top priority. This is done by analyzing hard data, such as overall equipment effectiveness (OEE), specifically the OEE loss categories, as they pertain to the six big losses.

Collect this data for a couple of weeks to get a snapshot of where time is being lost. If you notice that changeovers comprise at least 20% of this time, SMED might be a good process to implement. If not, you might want to focus on total productive maintenance processes.

• Capture a baseline. Consistently measuring changeover time is critical, so you need to define how you’ll measure it. According to lean manufacturing publisher Vorne, “Changeover time is measured from the last good part of the previous job at normal production speed to the first good part of the next job at normal production speed.” Once you’ve defined how to measure changeover time, create a baseline by measuring a normal changeover.

• Ask questions. Having an inquisitive mindset and asking how every element can be made external is the best way for SMED teams to approach the process. The following questions can help your SMED team achieve this mentality. 
• • Separate: Can this element be done with little to no change while the machine is running?
  • Convert: How can we convert this internal element into an external one?
  • Streamline: How can this element be simplified, streamlined and completed in less time? 

• Standardize best practices. With the implementation of SMED comes a concern that machine operators will tend to rush through the changeover process, putting quality and safety at risk. The most effective SMED programs standardize processes and procedures for continuity in quality and safety. Treat instructions as living documents by having a process in place to continuously update them as needed.

• Focus on human improvements. Human improvements are faster and less expensive to implement and are made during setup as opposed to implementation. Human improvements can be made by:

• Defining roles, metrics and accountability.
• Offering training, coaching and brainstorming sessions on immediate improvement ideas.
• Creating standardized work instructions.

SMED Pitfalls to Avoid

For a successful implementation of an SMED program, teams should avoid a few common pitfalls, such as:

• Failure to organize: At least half of reducing changeover times revolves around better organization. Your SMED team should address who will perform the external elements. Should it be an operator? A dedicated setup person? A combination of the two? The answer most likely depends on the types of processes and external activities. If you have more traditional machines, multiple people may be needed to complete the required duties.

Organization also means effectively rearranging the areas around the equipment so it’s optimized for minimal motion. This involves setting up storage areas to make tools and material more easily accessible and applying point-of-use storage concepts wherever possible.

• Not standardizing new processes: Failure to standardize the new-and-improved changeover processes results in highly variable outcomes that are dependent on the individual doing the changeover. One person might be able to perform a setup quickly, while another might take much longer, needing multiple tries to complete the setup.

Everyone should know the best sequence of events for each process. Standardizing a changeover process should be a team activity where everyone involved in the setup is fully engaged. Standardized procedures are particularly important when more than one person is working on a changeover at the same time.

• Failure to maintain equipment: Studies have shown a strong correlation between changeover times and equipment conditions. Setting up a poorly maintained piece of equipment is more difficult than the alternative, as more experienced or highly skilled employees will be needed, and achieving the required accuracy will be challenging.

In some cases, the desire to keep equipment running has trumped preventive maintenance from being performed. This can result in a run-to-failure maintenance practice, which can have serious ramifications on equipment conditions and lead to longer changeover times.

• Making unnecessary equipment investments: Companies frequently try to gain more flexibility by purchasing new equipment or technology. While worth considering, it is crucial to ask whether it’s necessary.

If you are investing in new equipment or software, be sure to consider the different skill sets required to operate the assets. If insufficient training is provided or there is a lack of manpower to operate the equipment, you probably won’t be reaping the full benefits of your investment.

Also, keep in mind that not all equipment manufacturers take SMED into account when designing assets. This leads to a more complicated changeover, particularly with highly automated operations where multiple processes are combined into one line.

 

This article was originally featured on reliableplant.com and has been revitalized for the purposes of Reliable Plant Digital Magazine.