Improving Changeover Time in 4 Simple Steps

Have you ever watched an auto race? If so, you probably noticed what happens when a car enters Pit Row and is tended to by a whole team of people trying to get it back on the track as fast as possible. If you wondered how they knew what to do and how they didn’t get in each other’s way, the answer is SMED.  

SMED stands for Single Minute Exchange of Die. It was developed by Dr. Shigeo Shingo in the 1960’s and 1970’s on behalf of Toyota. Dr. Shingo was interested in reducing the time and effort that it took to change a production line from one product to the next. By intense study and trial and error, he developed a 4-step method to drive all changeovers down to less than 10 minutes, thus coining the term single minute exchange of die. For auto racers, they use SMED to improve their auto changeover times and have achieved times below 15 seconds.

Changeover reduction is a team sport, just like in NASCAR, so picking the right team is critical. Bring people together who have had experience with the changeover being studied, use their differing opinions and techniques and encourage sharing and learning. By doing this and applying SMED, you should be able to reduce changeover time by more than 50%. You should also be able to improve the safety of the changeover for everyone.

STEP 1 – Identify All Elements of the Existing Changeover

The first step in SMED is to identify all elements of the existing changeover. This is done by observing the changeover as it occurs. Use a changeover that is typical for the process. Teams use tools such as a stop watch, video, and spaghetti diagram to truly understand everything that is happening during the changeover. Rather than just discussing things, they observe the changeover and then discuss it to better understand the current situation. It is also not unusual for team members to mimic the steps of the changeover so they can see the impact and difficulty of the changeover for themselves.

The spaghetti diagram is a paper exercise that shows everywhere a person travels during the changeover, whether it is to get tools, information, or do work on equipment. To use it, you should have a general layout of the area being worked on, then place a pen or pencil on the layout, moving it to the places that the worker moves during the changeover. Don’t lift the pen or pencil. If there is more than one worker performing the changeover, there should be more people creating the spaghetti diagram. At the end of that exercise, the lines on the page tend to look like spaghetti and people are amazed at the amount of travel required to complete the changeover.

STEP 2 – Separate All Elements into External and Internal

The next step in SMED is to identify what steps or elements can be performed while the line is running (External elements) and what steps must be performed while the line is down and waiting (Internal elements). Process Improvement Partners saw an example of this in one of our sessions. After a production run was completed, the press was shut off, a die was removed, the die was returned to storage, and the new die was brought back to the press from the storage area. At that point, every step was Internal, meaning that the line was not running while each step was completed. However, the team soon realized that the retrieving of the new die could have been done in advance of the changeover and the storage of the other die could be done after the line was back up and running. The team identified all of the elements that were external, and this step saved more than 25% of the changeover time.

STEP 3 – Convert Internal Elements to External Elements

The third step challenges the team’s creativity and they start to devise ways of doing some of the changeover steps that originally had to be done while the line is down and finding ways of completing them while the line is still running. A team we worked with created a fixture that allowed parts to be positioned for installation prior to the line stopping. This saved a significant amount of time and the fixture was built with existing materials, so no money was spent. Another example is to connect a tool to the equipment, so that it is immediately accessible to do the work once the line has been stopped. There are so many examples of this that teams can do research through the internet to get ideas, or they can visit other manufacturers to see the ideas in action.

STEP 4 – Streamline All Elements

In this step, the team thinks of ways of shortening time and effort required to do any remaining elements. They prioritize and work on the internal elements first, and then work on any of the external elements that have opportunity for improvement. This is a great time to look at the video and the spaghetti diagram again and see if the amount of travel can be reduced by the repositioning of tools, materials, and equipment, or if another sequence would be more efficient. Trial the new procedure, redraw the spaghetti diagram, and get the input of all team members to ensure that the new steps are truly better for them.

Once all steps of SMED have been completed, the team should observe the new changeover procedure and verify that it is truly an improvement. Time is one measurement, but effort, travel, and the anecdotal input of those performing the new changeover procedure are also important. People need to feel that the new way is better than what they had been doing personally. Because change is difficult, the team needs to develop methods to sustain the improvements that they created. Once they do so, they will realize the benefits of their efforts.