The SMED (Single Minute Exchange of Die) is a method to optimize the time of serial change.
- According to the terms of the standard AFNOR NF X50-310, the “SMED is an organisational method which seeks to systematically reduce the time of change of series, with a quantified objective” with the Takt time.
- Isolated processes are to be avoided : The operations of the same line are grouped.
This methodology was created in the years 1950-1960 by Mr. Shigeo Shingo. Working as a consultant for many companies including Toyota, He observed that there were many bottlenecks in bottlenecks. Even as the context evolved towards the leveling, we were still working on the basis of Economic batch size Because the change of tooling times were very long.
From this observation, Shigeo Shingo developed a methodology to reduce production downtime due to the time of series change. The acronym SMED begins to be used from 1969. He himself explained that he had put in more than 20 years to theorize the methodology, by observations and trial and error.
By definition, the time of Change of series is:
Time that happens between the last good Part of a series produced at the nominal cadence and the first good Part of the next series at nominal cadence.
The SMED responds to the principle of just in time. Above all, it allows you to adapt to an increasingly moving market where customers are increasingly demanding diversity and responsiveness. In this it goes:
- Increase the degree of flexibility to better adapt to customer demand (Takt Time).
- Reduce stocks.
- Reduce The Lead Time of the line.
- Improve the settings to produce without faults the first time.
- Increase the rate of use of the equipment.
The ultimate goal of the SMED is to reach the OTED (One Touch Exchange of Die), the cancellation of the serial change times.
We also use the acronym OTC (One Touch Changeover), or noted, (no Touch Exchange of Die-i.e. a change of automated tool, without any human intervention in the decision or the execution of the change of tools.).
Before being able to completely remove the time of change of series, one considers:
- A series change time must be maximum duration 10 to 20% of the production time.
- The cost of storing the parts must be maximum equal to the cost of the production downtime.
A Japanese economist, Eiji Ogawa, was the first to study the impact of batch size on costs in the years 70-80. Previously, the size of the economic batch was only considered according to the volume of production (via the formula of Wilson).
The diagram below shows that in reality, the economic batch size can be even better through the reduction of the series change times.
Source: E. Ogawa (1982)-Modern production management, a Japanese experience
The increase in batch size is often chosen to compensate for important adjustment times. This is one of the characteristics of mass production. If the batch size increases, the ratio of setting time to production time can be greatly reduced. We generate productivity gains but in some sort of leak forward.
Step 1: Measure and observe total time
This first step makes it possible to make an inventory of all the operations that takes place during a change of series. To do this, we need to gather a whole set of information:
- Machine data: Design, maintenance, implementation, hourly capacity…
- Production data: Parts Reference, details of operations and times, Takt time, number of change of series per week/month…
- Actual production data: Average serial change time, OEE, stock level in-progress, upstream and downstream stock.
- Operator data: measure distances using a Spaghetti diagram (the best one is a video), measure the time and purpose of each operation, identify the tools/ Products used…
- Meeting opportunities for Progress : Quality, working conditions, cleanliness…
- Identify the Muda : In a series change usually only 4 of the 7 types of Muda are found: Transport Muda (moving a mould from stock to machine…), Muda (hoist not available…), Muda of movement (search for a tool, X key laps…), Process Muda (many times and adjustments to position a tool).
The challenge of this stage is to reap the ” real ” facts: The operational must not change their method but do as usual.
It is also at this stage that the operator must trace all the ideas of progress that they wish. This may concern tools that are too heavy, poorly adapted or worn, problems of non-quality…
Step 2: determine internal and external operations
Once the observation is made, the second step is to classify the operations by:
- Internal operation: Any action that requires the machine or process to be stopped.
- External operation: Any action that does not require the machine or process to be stopped.
Example of internal and external operations:
Cleaning the Machine
Setting up the new tools
Connecting Power Supplies
Set to 0
Step 3: Convert internal operations into external operations
It is about transforming internal operations into external operations to keep only the bare necessities. the preparation, cleaning or packing of the finished products can be done off machine. While disassembling the tool can only be done during machine shutdown. Therefore, all of these actions can be considered external operations and make them outside of the time series change.
Step 4: Reduce the time of internal operations
It is a matter of reducing the time of internal operations. You have to take one to one operations and find solutions to optimize them. Different lines of Reflections :
- Synchronize tasks to gain time by paralleling internal tasks to promote simultaneous work. This solution is particularly suitable if the movements around the machine are important or if interventions on independent equipment are necessary. We will use a Simogramme to do this study. you should not hesitate to ask several operators at the same time. The goal is to secure the equipment as little as possible.
- Standardize and optimize functions and operations: Use a single screw size, unify the ribs of adjustments, set up Poka-Yoké…
- Setp-up 5S and Visual Management on all équipement and tools.
- Simplify as much as possible: U-washers, snaps, quick tightening, cams, quick-tightening pliers…) …
- Remove unnecessary tasks If possible: displacement, series of tests…
Step 5 : Reduce time of external operations
Step 6 : Standardize
We will create the standard detailing all the steps of the tool change and train the staff on this new standard.
Example of Formula One
The example of tyre changes at pit stops in a Formula 1 race is a good example of SMED. Changing 4 tires in a few seconds seems unfeasible and yet. Here are some elements of response to this performance:
- Each individual function is clearly defined, the material is preset.
- The operating procedures are standardized, known and mastered.
- The locations are planned and clean.
- The tasks are simultaneous: 1 wheel for 1 person for screwing and 1 person per wheel for positioning.
- People and equipment are ready.
- A person is responsible for the team.
- The pilot is not leaving until the security signal is secured.
- The equipment is adapted to the staff: Trained, qualified, trained, motivated.
- The stops are planned.
- The tests and controls are removed.
The SMED in the services
Who has never been bothered by changing an ink cartridge from a desktop printer? Find the cartridge, how to use it… So many non-standardized tasks to which the staff are not trained, requiring to use the service “utility“, or to lose their morning on the subject.
The SMED applies to any process that requires a production stoppage, a change and then a re-route :
- A coffee maker to change the filter.
- A mess to change the kneading tool or dough.
S. Shingo (1985)-A Revolution in manufacturing: The SMED System
T. Leconte (2011) – The practice of SMED
K. Arai, K. Sekine (1987)-Kaizen for quick changeover
J. R. Henry (2013)-Achieving Lean changeover: putting SMED to work
F. Birmingham, J. Jelinek (2007)-Quick changeover Simplified
G. Bleach (2004) -production organization and management
M. Nakla (2006)-The bulk of industrial management