Single Minute Exchange of Dies (SMED)
As we all know, there are five Lean implementation steps:
- Specify what does and does not create value from the customer’s perspective and not from the perspective of individual firms, functions and departments.
- Identify and map all the steps necessary to design, order and produce the product across the whole value stream to highlight non-value adding activity (muda).
- Make those actions that create value flow without interruption, detours, backflows, waiting or scrap.
- Only make what is pulled by the customer.
- Strive for perfection by continually removing successive layers of waste as they are uncovered.
Single Minute Exchange of Dies, commonly known as SMED, helps with step three.
Origin of SMED
Dr. Shigeo Shingo is known as the father of SMED (developed in the late 1950s) and Poka-Yoke, and is also known for developing the Just-in-Time (JIT) concept. He used SMED to reduce the lot size of Toyota cars and the set-up time of hull assembly on a 65,000 ton super tanker, setting a record in shipbuilding in 1956.
What is SMED?
SMED is a concept to reduce changeover time (i.e., minimize the time lost in changing over from one size to another, or one product to another, or one service type to another, etc).
Does SMED mean changing the die in less than a minute?
There is a common misconception that SMED means changing the die in 1 minute. Actually, SMED means changing the die in less than 10 minutes. It is single (digit) minute exchange of dies.
Running large batches is good….right?
We always want to run large batches of a product and not have to deal with changing over from one product to another, or from one size to another. What we don’t realize is that it causes other problems, as illustrated in the figure below. (Click on image to enlarge.)
Figure 1: Why running large batches is harmful
As a result of running large batches and producing more than what is required at the right time, we pay more in terms of downtime (the eight wastes of Lean, namely defects, overproduction, waiting, non-utilized talent, transport, inventory, motion, and excessive processing; but these costs are not easily visible).
SMED increases the flexibility of a line or company to respond to customer requirements. Instead of producing AAAAAAABBBBBBCCCCCCDDDDDD, it gives us the flexibility to produce AAABBBCCCDDDAAABBBCCCDDD. Therefore, satisfying our customers by giving them what they want on-time and at the same time reduces our company costs as well.
SMED should not be used to run even larger batches as a result of cutting down on the set-up time. It is a total abuse of the tool.
SMED implementation steps
There are eight steps to implementing SMED.
1. Develop and complete the external set-up checklist.
- Create a list of molds/dies, tools, fixtures, materials and gauges.
- Process information and storage locations.
|Single Minute Exchange of Dies (SMED)|
|External Set-Up Checklist|
|Line 1||Size Change 1||Size Change 2||Size Change 3|
|Tools required||Tool # 1; Tool # 3; Tool # 45||Tool # 4; Tool # 3; Tool # 46||Tool # 1; Tool # 3; Tool # 90|
|Dies required||Die # 320; Die # 420; Die # 100||Die # 30; Die # 40; Die # 100||Die # 3; Die # 2; Die # 10|
|Gauges required||Gauge # 32; Gauge # 6||Gauge # 32; Gauge # 6||Gauge # 12; Gauge # 16|
|Molds required||Mold # 1; Mold # 4||Mold # 7; Mold # 10||Mold # 7|
|Storage location||Storage # 4; Storage Rack # 8||Storage # 8; Storage Rack # 5||Storage # 21; Storage Rack # 51|
|Change part carts|
|Line 2||Size Change 1||Size Change 2||Size Change 3|
|Tools required||Tool # 4; Tool # 3; Tool # 46||Tool # 4; Tool # 3; Tool # 46|
|Dies required||Die # 30; Die # 40; Die # 100||Die # 30; Die #40; Die # 100|
|Gauges required||Gauge # 32; Gauge # 6||Gauge #32; Gauge # 6|
|Molds required||Mold # 7; Mold # 10||Mold # 7; Mold # 10|
|Storage location||Storage # 8; Storage Rack # 5||Storage # 8; Storage Rack # 5|
2. Develop and complete set-up reduction observation forms.
- Observe the whole process (videotape if necessary).
- Identify and list each step.
- Time each step (from last good part to first good part).
- Classify into P, R , L or A activity.
- Classify into internal or external activity.
Let’s now see what P, R, L and A activities are for:
P – Preparation activities: This is the preparation stage for changeover (or set-up).
- Actions performed to support the changeover process
- Ensures all parts, tools and dies are located in their proper locations before and after a changeover has occurred
- Includes both transportation and storage of these items
The quality of the materials and tooling being utilized must be verified.
R – Replacement activities: Refer to Figure 2.
- Includes mounting, replacing, securing and removing of dies, tooling, blades, etc. after completion of the process
- The attachment of parts and tools needed to perform the next job
- Refers to the measurements, settings and calibrations that must be performed to successfully complete a process
Performing the following activities places items in their proper position:
- Adjusting temperature and pressure
A - Adjusting activities
- Actions repeated in order to attain the correct machine setting to produce an acceptable part
- Most difficult aspect of the changeover process
- Frequency depends on the pre-planning and accuracy of previous steps (P, R and L)
- Elements that can only be performed while the machine is shut down.
- Elements that can be performed while the machine is running.
3. Convert internal to external set-up: The third step is the most important step. Here we involve subject matter experts (those who do the changeover or set-up) and brainstorm on the following:
- Re-examine operations to see if any steps were mistakenly assumed to be internal.
- Analyze ways to convert internal steps to external steps.
- Move required materials and tools to the workstation prior to the start of the changeover.
- Remove previous tools and materials after the changeover is completed, or, use separate material handlers for the task.
Separating internal and external operations can reduce internal set-up time by 30 to 50 percent.
4. Standardize: In this step, the size changeover tools are examined and replaced with standard sizes. What we find usually is that as machines age, their maintenance deteriorates, as they are often fitted with non-standard parts (sometimes due to non-availability of the original parts). In this step, we remedy the situation.
- Standardize sizes and dimensions of machine parts and tools.
- Standardize functional elements of tooling, fixtures, molds/dies, etc.
Standardization requires uniformity necessary for set-up operations.
- Removing (expelling)
5. Use clamps and "one-touch" fasteners.
- Use one touch functional methods such as wedges, cams, clamps or springs.
- Use interlocking methods that simply fit and join parts together.
- Analyze the direction and magnitude of the force required in clamping methods.
In one of the companies, we implemented a one touch automatic changeover. We programmed the points of changeover (after several trials), and the computer remembers the set-points for different sizes (of bottles) on the conveyor line. So instead of 3 hours of changeover, it took under 30 minutes.
6. Use intermediate jigs.
- Intermediate jigs reduce external and internal set-up time.
- Can be used on large machines with multiple dies/guides/molds to reduce clamping and positioning time
7. Adopt parallel operations
- Two people performing operations simultaneously reduce the muda of movement.
- Increases the operating rate of the machine
- Parallel operations can reduce set-up times by more than 50 percent.
We should clearly define each and every person’s role and responsibility during the changeover/set-up operation. It should be synchronized such that not even a second is wasted.
8. Eliminate adjustments
Settings vs. adjustments: We should clearly differentiate between the two.
- Settings occur when the position of a limit switch is changed.
- Adjustment occurs when the limit switch is tested and repeatedly adjusted at a new position.
Adjustments can be eliminated if a gauge is used to precisely determine the correct position of the limit switch.
- Use dial gauge or numerical control device for greater precision.
- Use visual controls (calibration markings) on the machine.
9. Mechanization: This should be used as the last resort.
- We should ALWAYS promote creativity before capital.
- Mechanization (automation) is an expensive technique for reducing changeover times.
- Use mechanization ONLY after all techniques have been implemented.
Benefits of SMED
- Increased availability/uptime of machines/lines
- Increased throughput with NO capital investment
- Standardized changeover
- Short changeover times help in having more frequent product (or flavor or size or alloy) changes and smaller batch quantities.
- By increasing the number of changeovers, we can carry less inventory of raw materials, supplies and finished goods.
- Become more efficient and identify opportunities for continuous improvement
SMED is an ideal tool which can be used to reduce the changeover time/set-up time in many industries (including manufacturing, logistics, and service). It increases the flexibility of the company to produce the right number of products (hence less inventory, carrying costs, etc.) at the right time and eliminates or minimizes bottlenecks to increase flow.