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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:
In an SMED process, changeovers are comprised of steps or “elements.” There are two types of elements:
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.
When implementing an SMED program, there are five steps to consider.
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:
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.
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:
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:
Once completed, you should have an updated list of changeover elements divided into three parts:
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:
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.
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:
Once step five is completed, update your standardized work instructions for the changeover.
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.
For a successful implementation of an SMED program, teams should avoid a few common pitfalls, such as:
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.
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.
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.
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.