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SMED calculator: what a shorter changeover is worth

Enter today’s setup time, the target, how many changeovers the line makes and what an hour of stopped line costs. See the machine hours and money the reduction frees, and how much smaller your lots can be.

Setup and changeovers

min
From the last good part of the previous product to the first good part of the next, machine stopped.
min
days
$/h
Not sure? Work it out with the downtime cost calculator. Leave it empty to see hours only.
units/h

Result

33machine hours freed per month

66 changeovers a month: from 49.5 h to 16.5 h of machine time lost to setup.

Setup per month today49.5 h
Setup per month after16.5 h
Saved per changeover
30 min (67%)
Hours per year
396 h
Savings per month
$4,950
Savings per year
$59,400
Extra capacity per month
3,960 units
Extra capacity per year
47,520 units

Smaller lots: in the same 49.5 h of setup a month, 198 changeovers fit instead of 66. That means lots 3 times smaller, with less inventory waiting between one changeover and the next.

How SMED works

Shigeo Shingo developed SMED through the 1950s and 1960s at plants such as Mazda and Toyota, and wrote it up in A Revolution in Manufacturing: The SMED System (1985). The method has four steps:

  1. Watch the changeover as it is. Film and time every step, from the last good part to the first good part.
  2. Separate internal and external setup. Internal needs the machine stopped. External can happen while it runs.
  3. Convert internal to external. Stage the tools, preheat the dies, preset the fixtures before the machine stops.
  4. Streamline both. Quick clamps instead of bolts, standard heights that need no adjustment, two people working in parallel, no trial parts.

Steps 2 and 3 alone, with no spending on equipment, often cut setup by 30% to 50%.

The math

Hours freed per month = (current setup − new setup) × changeovers per month

Savings per month = hours freed × cost of an hour of stopped line

Extra capacity = hours freed × output per hour

If you do not know the hourly cost of a stopped line yet, work it out with the downtime cost calculator.

Worked example

The calculator starts with an injection molding machine: setup of 45 min, target 15 min, 3 changeovers a day, 22 days a month, a stopped hour costing $150 and 120 units per hour.

  1. Changeovers per month: 3 × 22 = 66
  2. Saved per changeover: 45 − 15 = 30 min (a 67% reduction)
  3. Hours freed: 66 × 0.5 h = 33 h per month, or 396 h per year
  4. Money: 33 × $150 = $4,950 per month, or $59,400 per year
  5. Extra capacity: 33 × 120 = 3,960 units per month, or 47,520 per year

Smaller lots in the same setup time

The biggest SMED gain is often not the freed hour. Today the machine spends 66 × 45 min = 49.5 h a month on setup. At 15 minutes a changeover, those same 49.5 h fit 198 changeovers instead of 66: three times as many, with lots three times smaller. Smaller lots mean less inventory sitting around, faster response to customers and shorter lead time, and Little’s law shows why.

Common mistakes

  • Timing only the tool swap. Setup runs until the first good part, adjustments and trials included.
  • Counting money on a machine with spare capacity. If it is not the bottleneck, a freed hour does not become a sale. The gain is in smaller lots and less inventory.
  • Buying equipment before separating internal and external. Most of the gain comes from organization.
  • Not standardizing. Without a written procedure for the new changeover, the time creeps back within weeks.

Freed hours on a bottleneck raise availability and OEE. To see what the line can make with the time you gain, use the production capacity calculator.

Frequently asked questions

How do you measure changeover time?

From the last good part of the previous run to the first good part of the next, at normal speed. Adjustments, trial parts and waiting for tools all count, because the machine is not producing. Film the changeover so you can break it into steps later.

What is SMED?

Single Minute Exchange of Die: Shigeo Shingo’s method to cut setup time below 10 minutes, a single digit of minutes. The core idea is to do everything that does not need a stopped machine while it is still running.

What is the difference between internal and external setup?

Internal setup can only be done with the machine stopped, like swapping the die. External setup can be done while it runs, like fetching the die, preheating it and laying out the tools. The first SMED gains come from moving work from internal to external.

How do you calculate SMED savings?

Multiply the time saved per changeover by the changeovers per period: (current setup − new setup) × changeovers per month = hours freed per month. Times the hourly cost of the stopped line gives the money, times the output per hour gives the extra capacity.

Does setup reduction always save money?

Only if the freed hours get used. On a bottleneck, every hour becomes output you can sell. On a machine with spare capacity, the real gain is running more changeovers with smaller lots, which cuts inventory and lead time. That is why the calculator shows both.

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