SMED: how to carry out a quick changeover
In one sentence
Gain in a quick changeover is measured at the same last-good to first-good boundary with mandatory checks kept; external preparation and parallel work need separate resources.
By the end of this lesson
- Classify eighteen setup activities as safe internal work, external work and verification.
- Calculate elapsed time and per-person workload separately for sequential and parallel work.
- Find the real reduction in changeover time while keeping the last-good to first-good boundary.
- Separate annual machine hours gained from the economic value that can actually be realized.
Why it matters
During a product changeover, it is not only a connection that is removed and fitted. Finding the new tooling, verifying the material, safe stopping, adjustment, trial and acceptance of the first part are all in the same flow. Single-minute exchange of die, abbreviated SMED, aims to reduce the part of this flow that holds up production. Measurement runs from the last good part of the previous product to the first good part of the new product. Counting the moment the tooling is fitted as the end removes the trial and verification from the record. What a first good part means is defined in advance; the first part that physically comes out is not enough. When the product acceptance condition is not kept, a time that looks shorter is not a real improvement.
Internal setup is work for which the equipment must be safely stopped. External setup is work that can be completed safely while the previous production continues. That an activity is done during downtime today does not make it mandatory internal work. Searching for tools or checking the new material can be moved outside if a suitable layout is set up. However, declaring as external work a removal task that requires reaching into the danger zone of a running machine is not a safe conversion. Moving from internal to external requires a concrete design that changes the working conditions. It is verified that the required space, person and tool really exist. Writing the work earlier in the schedule does not by itself prove that external preparation can be done while production runs.
Work moved outside is not considered to have disappeared. While the production interruption may fall, the total per-person workload may stay the same or increase. In work done simultaneously by two workers, the elapsed time under suitable conditions is set by the longer arm, while the person times are added. A shared tool, a shared hazard area or a precedence relationship can prevent parallel work. For this reason, the changeover schedule shows the worker, the equipment and the person responsible for checks together. The shortest schedule is not a workable option if the resource conditions are not met. Removing a worker's need for rest or forgetting that they have another task at the same time is not accepted as a quick changeover design.
The machine minutes gained can help set up production more flexibly. Smaller batches, earlier order completion or less need for overtime may be possible; which outcome will occur is tested separately. Multiplying the minutes by an hourly value gives only a conditional economic calculation. If there is no demand and costs do not fall, the freed time is not direct cash gain. The cost of the new fixture, the extra setup labor and the maintenance need are also considered. In this lesson, the technical and safe time of the changeover is verified first. The economic interpretation does not replace the time measurement; it explains which planning decision will use the verified time. Data notice for this lesson's figures, examples, counterexamples and three short quiz questions: This dataset was generated synthetically for training; it does not represent a real business, employee or customer study.
Formula
Changeover time (min) = Time of first good new product − Time of last good old product
Sequential work (min) = Sum of durations
Independent parallel arms with a common start (min) = Longest arm duration
Reduction (%) = Time gained (min) ÷ Old time (min) × 100
Annual time gained (hours/year) = Gain (min/changeover) × Changeover frequency (changeovers/day) × Working (days/year) ÷ 60 (min/hour)
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- Step-by-step instructions
- Worked example with real numbers
- Where the method misleads
- Common mistakes
Lab instructions: Sample fixture changeover
- Measure 1 cycles at every station.
- Enter the elements with the names below and in this order. Each element starts at its start point and ends at its end point.
- Enter the operator's elements and waits on the Operator track and the machine's running on the Machine track; a machine row runs from the moment the machine starts until it stops.
- Enter a wait or a machine run as a row of its own every time you see it. Assign every row to its station.
1.Open the door
Starts: right hand reaches for the door handle · Ends: door is fully open
2.Take the last 1/2" part out of the chuck
Starts: right hand reaches for the chuck · Ends: part comes out of the chuck
3.Measure the last part, put it in the crate
Starts: operator turns to the side table · Ends: part is put down in the crate
4.Walk to the tool cabinet
Starts: operator leaves the side table · Ends: operator stands at the tool cabinet
5.Take the box with the 3/4" jaws and tool holder
Starts: both hands reach for the box · Ends: box is lifted out of the cabinet
6.Go back to the machine
Starts: operator leaves the cabinet · Ends: box is put down on the side table
7.Loosen the jaw screws
Starts: right hand reaches for the hex key · Ends: third screw is loose
8.Remove the 1/2" jaws
Starts: left hand reaches for the jaws in the chuck · Ends: jaws are put down in the box
9.Fit the 3/4" jaws
Starts: left hand reaches for the 3/4" jaws in the box · Ends: jaws sit in the chuck, hand lets go
10.Tighten the jaw screws
Starts: right hand reaches for the first screw with the hex key · Ends: third screw is tight
11.Change the tool holder
Starts: left hand reaches for the holder on the turret · Ends: 3/4" holder sits on the turret, hand lets go
12.Select the program
Starts: operator turns to the panel · Ends: program opens on the screen
13.Clamp the trial part
Starts: operator walks to the side table · Ends: part is clamped in the chuck, hand lets go
14.Close the door, start the trial cycle
Starts: left hand reaches for the door handle · Ends: start button is pressed
15.Machine runsMachine track
16.Wait for the trial cycleWait
Starts: lathe starts cutting · Ends: lathe stops
17.Take out and measure the trial part (out of tolerance)
Starts: right hand reaches for the door handle · Ends: part is put down at the scrap place
18.Correct the tool offset
Starts: operator turns to the panel · Ends: offset is entered, hand leaves the panel
19.Machine and measure the first good part
Starts: operator walks to the side table · Ends: good part is put down in the crate