SMED stands for “Single Minute Exchange of Die.” It is a team problem solving process that significantly reduces equipment set up time, to under 10 minutes.
SMED methodology, developed by Shigeo Shingo, divides all setup tasks into two categories: “internal” and “external”. Internal activities must be performed when the machine is stopped. In contrast, External tasks can be completed only while the machine is running.
To reduce changeover time, use four strategies:
- Eliminate external tasks. Perform them before or after the setup.
- Reduce duration of external tasks: change mounting system, use better tools, and so on.
- Reduce adjustment time by applying standards.
- Convert internal tasks into external, i.e. enable accomplishing a task before a machine stops. Example of this could be heating a die before mounting on an extrusion machine.
A typical result of SMED is 50% reduction in setup time, each time you conduct the activity.
Case Study - Automatic Weaving Loom
A manufacturer of textile products operates a number of large automatic weaving looms. The machines are set up on the production floor in such a way that three people can operate two machines. The majority of looms are “12 color machines,” each making products from 12 different types of color thread. For each color there are 840 thread spools, making a total of 10,080 spools for each loom. Given that each full spool weights about 7 pounds, it’s quite a hefty weight to replace during a changeover. Production planning tries to minimize the number of colors that need to be changed each time a new carpet is produced, nevertheless, usually 3 to 4 out of 12 colors need replacing. A typical changeover lasts about 750 minutes.
After a loom is stopped, a material handler begins to deliver pallets with new spools to a storage area near a loom. When all of the spools are delivered, the two people assigned to the machine start carrying spools into the alleys between the spool frames. Because of a lot of demanding physical labor involved (factory employees are mostly women) a team leader then tries to find other people who can help out. Since an ideal crew size is 8 people it takes the team leader an hour or more before he can assemble enough helpers.
To accomplish a changeover, new spools need to be carried into the alleys between frames on which spools are mounted, an old thread needs to be cut, an old spool needs to be replaced with a new spool and an old and new thread need to be tied together using a special knot. Before a loom can be turned back on, the floor inside the alleys and around the machine needs to be swept clean and old spools need to be removed from the alleys.
During the adjustment phase of the changeover, tied knots travel through the entire length of the loom so that only a new color of thread is used in the production of a carpet. Typically, this process alone takes up to 1,5 hours as knots often jam or break and cause the loom to stop.
A multifunctional team that took part in a 3-day workshop comprised of production workers, supervisors, quality people, material handlers, as well as representatives from marketing and top management. After initial training on Lean Manufacturing techniques, the team observed the changeover process recorded on videotape a few days earlier. Process steps were then analyzed using a Fishbone Diagram and divided into external tasks, or steps than can be accomplished before loom is stopped, and internal tasks, or steps that can be done in the current configuration only after loom is stopped.
Next, the team divided into two groups that separately brainstormed improvement ideas to move external functions out of the set up process and reduce internal tasks. Groups also immediately tested out some of the ideas on the production floor. The team then got together to finalize the suggestions and composed an action plan to implement proposed improvements within one month.
The workshop ended with the presentation of the results to management.
All new spools are prepared while machine is still working and some of them are transported very close to the alleys between the spool frames – time savings of 60 minutes.
Every set up is now planned in order to maximize the number of people working on a changeover team at the beginning of the process. Selected workers are notified in advance about the time and place and a team leader divides roles among team members. When majority of the physical labor is done, people that are no longer needed are discharged to return to their other duties – time savings of 80 minutes.
Factory installed carts to transport spools into the alleys were redesigned to allow for easier loading and unloading. Previously these carts, each with a capacity of around 60 spools, were not used because it was uncomfortable to reach inside to retrieve material. With a slightly modified design they are now transporting a majority of all the spools – time savings of 80 minutes.
Standardizing knot types significantly reduced jamming and breaking of knots. A study showed that each type of thread required a slightly different knot type. A visual standard showing required knots and additional training allowed to significantly reduce the amount of jamming – time savings of 30 minutes
Improvements allowed shortening the changeover time on one automatic loom from 750 to 500 minutes – an improvement of 33%. After similar ideas were implemented on all other machines, the total production time gained was equal to about the annual output of one new automatic loom.