Single-minute exchange of dies (SMED) is a process used to reduce the time it takes to complete equipment changeovers. The term “single-minute” is a bit misleading—it doesn’t mean every changeover should only take one minute, but that every changeover should take less than 10 minutes, or a single-digit minute.
What is changeover?
In most manufacturing environments, you’ll find machines that are designed to perform more than just one task. Perhaps there’s a drill press that is used to drill holes in the top of a part, and then is tilted in order to drill horizontal holes in the side.
The process of moving the drill from vertical to horizontal is called changeover. Depending on the size and complexity of the machine, the experience of the operator, and the process used during changeover, the time consumed during changeover is considered downtime—everything else is waiting on the machine to resume functioning.
Changeover can lead to waste.
To the Lean organization, waiting and downtime are wasteful and countermeasures need to be in place to keep waiting at a minimum during the changeover period. And in any business, one of the heaviest drains on profitability is waste.
Lean waste can come in the form of time, material, and labor. But it may also be related to the utilization of skill sets as well as poor planning. In lean manufacturing, waste is any expense or effort that is expended but which does not transform raw materials into an item the customer is willing to pay for.
By optimizing process steps and eliminating waste, only true value is added at each phase of production.
Why SMED was established.
Seventy years ago, Shigeo Shingo was at the end of his patience—and Shigeo was known as a patient man. Production at the Toyota plant where he worked was at a standstill. One of the 800-ton metal-stamping machines needed a changeover—and that required the current die to be taken off and a different one installed.
The entire line of stamping machines had to stop while an overhead crane lowered the old die and lifted the new one in place. The workers adjusted the position of the new die with crowbars and tested each adjustment by stamping a new sheet of metal and taking measurements.
A smooth changeover usually took twelve hours—a difficult one, three days of downtime. Downtime meant that every piece of machinery is waiting—and almost every employee is stalled while the changeover takes place.
To Shigeo, downtime and waiting is a form of waste—and Shigeo was on a mission to identify and eliminate all waste. Something had to be done to decrease or eliminate this downtime.
Crisis gave birth to new opportunity: SMED Quick Changeover
In order to decrease or eliminate waiting, Shigeo devised a process called Single-Minute Exchange of Die or SMED. The SMED system is a theory and set of techniques that make it possible to perform equipment setup and changeover operations in fewer than 10 minutes—in other words, in the single-minute range.
His pioneering work led to documented reductions in changeover times averaging 94% –for example, from 90 minutes to less than 5 minutes across a wide range of companies. Changeover times that improve by a factor of 20 may be hard to imagine, but consider the simple example of changing a tire:
- For many people, changing a single tire can easily take 15 minutes.
- For a Formula One pit crew, changing four tires takes less than 5 seconds.
Many techniques used by NASCAR and F1 pit crews (performing as many steps as possible before the pit stop begins; using a coordinated team to perform multiple steps in parallel; creating a standardized and highly optimized process) are also used in SMED. In fact, the journey from a 15-minute tire changeover to a 5-second tire changeover can be considered a SMED journey.
The Basics of SMED
In an SMED process, changeovers are comprised of steps or “elements.” There are two types of elements: internal and external.
- Internal elements must be completed when the equipment is stopped.
- External elements can be completed while the equipment is running.
The main goal of the SMED process is to have as many external elements as possible while streamlining and simplifying all other elements.
Identify a Test Area
One of the first things to consider before implementing SMED is the pilot or test area. Choose to work on only one machine or one area. In this step, it’s important to get everyone onboard with the SMED implementation—this includes all employees associated with the selection process and those who will work on the changeover.
After you’ve determined your pilot area, it’s time to work together with your SMED team to identify all the changeover elements—internal and external.
One of the most effective ways to visualize every step is by video recording an entire changeover as it is currently performed, and then sitting down with your team to record lists of each element, reordering as needed.
Include a detailed description of each task performed and how long each task takes to complete (cost in time). This video and outline can also serve as a baseline. Once step two is finished, you should have a complete list of all changeover elements with a description and cost in time for each.
Separate External Elements
Can this element be performed while the machine is running? This is the question your team needs to ask of each element you documented in the previous step. Any element in the changeover process that can be completed with little or no change while the machine is in operation must be identified and labeled as “external” to the process—in other words, the element can be done before or after the changeover.
In many cases, this step alone can cut changeover time in half. Once step three is completed, you should have an updated list of changeover elements divided into external elements (before changeover), internal elements (during changeover) and external elements (after changeover).
Convert Internal Elements to External Elements
Which internal elements can be converted to external elements? This question should be at the forefront of everyone’s mind as you go through the changeover process with a fine-tooth comb. Breaking down the question even further, your team might ask: If there is a way to make this element external, what would it be and how can we do it?
What’s left after this evaluation is a list of elements that require further action. Prioritize this list so the elements with the most promising results are dealt with first. In other words, perform a cost/benefit analysis on each element from the list.
Streamline Remaining Elements
How can this element be done in less time? Or, how can we simplify this element? Finally, your SMED team should review the remaining elements on your list. Focus on simplifying them so they can be done in less time. Since the goal is to reduce changeover time, give priority to internal elements before moving onto the external. Use a cost/benefit analysis to prioritize the remaining steps. Once step five is completed, update your standardized work instructions for the changeover.