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Small Batches and Frequent Changeovers: The Hidden Cost of Packaging
A model linking batch size, changeover time and run time to good packs and cost per good pack, with a worked shift example and a simple changeover log.
A plant that moves from a few long runs to many short ones rarely sees the full cost on any single report. Wages are paid, the machine is “on”, and packs still come out. The decision question is how much good output and how much money each extra changeover takes, and whether to cut the number of changeovers, shorten them, or accept them.
The short answer: every changeover removes minutes of run time and a quantity of setup material, and both fall on the same fixed shift cost. Doubling the changeovers on a shift can raise the cost of each good pack by several percent or more, as the example below shows. Fixing this does not always mean larger batches.
What a changeover is
Define a changeover from the last good pack of product A to the first good pack of product B at target speed. That definition matters. If you stop the clock when the machine restarts, you miss the slow minutes that follow.
A changeover has five parts:
- Stopping and clearing: ending the run, emptying product, cleaning the filling and sealing areas.
- Swapping parts and materials: format parts, film or pouches, labels, date coding.
- Adjustments: sealing temperature, weight settings, registration, guides.
- Trial packs and rejects: packs made to check seals, weights and print, most of which are scrapped.
- Ramp back to speed: running below target while settings settle.
The hidden part is the last three. Stopped time is easy to see on a clock. Setup material and the slow first minutes are often absorbed into the next batch’s reject and speed figures, so they are never tied to the changeover that caused them.
The model
Set out the variables on a per-shift basis. Rate here means the effective running rate in good packs per minute, taken while the line is running and already net of micro-stops, speed loss and rejects, as built up in Why Faster Machines Do Not Always Increase Line Output. Changeover losses are counted separately, so they are not counted twice.
changeovers per shift ~ packs demanded per shift / batch size
(or the number of product changes actually scheduled)
changeover time = changeovers x minutes per changeover
run time = planned time - changeover time - other downtime
good packs = run time x effective running rate
setup waste = changeovers x packs (or film meters) lost per changeover
share of shift lost = changeover time / planned time
Cost per good pack uses the definition in Cost per Good Pack: cash operating cost for the period divided by good packs in the same period. Here is the convention used below. The setup waste is made during the changeover minutes, so it does not reduce the good-pack count a second time. Its cost is the material it consumed, so it enters through material spend. If your material spend is taken from purchases or issues to the line, it already includes the waste, and you must not add a separate scrap line on top.
Worked example: one shift, three batch patterns
Illustrative numbers, not a quote, benchmark or customer result.
Assumptions for one 8-hour shift (480 minutes):
- Effective running rate: 35 good packs per minute (the 35.64 from the throughput article, rounded down).
- Changeover: 25 minutes each, including trial packs and ramp back to target speed.
- Setup waste: 60 packs per changeover.
- Other downtime (breaks, planned cleaning): 30 minutes, the same in every pattern.
- Shift labor and overhead: $1,200, fixed regardless of the pattern.
- Material: $0.08 per pack, applied to good packs and to setup waste alike.
| Changeovers | Changeover minutes | Run minutes | Good packs | Setup waste (packs) | Share of shift lost |
|---|---|---|---|---|---|
| 2 | 50 | 400 | 14,000 | 120 | 10.4% |
| 4 | 100 | 350 | 12,250 | 240 | 20.8% |
| 8 | 200 | 250 | 8,750 | 480 | 41.7% |
The arithmetic for the 4-changeover row: 4 x 25 = 100 minutes; 480 - 100 - 30 = 350 run minutes; 350 x 35 = 12,250 good packs; 4 x 60 = 240 packs of waste; 100 / 480 = 20.8%. The other rows follow the same steps: 2 x 25 = 50, 480 - 50 - 30 = 400, 400 x 35 = 14,000; 8 x 25 = 200, 480 - 200 - 30 = 250, 250 x 35 = 8,750.
Now the cost line. Material covers good packs plus setup waste, and the $1,200 of labor and overhead is added.
| Changeovers | Material cost | Shift cost | Cost per good pack | Cost per 1,000 good packs |
|---|---|---|---|---|
| 2 | (14,000 + 120) x $0.08 = $1,129.60 | $2,329.60 | $0.1664 | $166.40 |
| 4 | (12,250 + 240) x $0.08 = $999.20 | $2,199.20 | $0.1795 | $179.53 |
| 8 | (8,750 + 480) x $0.08 = $738.40 | $1,938.40 | $0.2215 | $221.53 |
Dividing by thousands of good packs gives the last column: $2,329.60 / 14.00 = $166.40; $2,199.20 / 12.25 = $179.53; $1,938.40 / 8.75 = $221.53.
Going from 2 to 4 changeovers raises the cost per 1,000 good packs by $13.13, or 7.9%. Going from 2 to 8 raises it by $55.13, or 33.1%. Total spending falls as the line makes less, yet each good pack costs more, because the $1,200 shift cost is spread over fewer of them. Setup waste is a small part of that rise. Most of it comes from lost run time.
Two levers
There are two ways to reduce the loss. Fewer changeovers means larger batches and smarter sequencing: light colors before dark, small formats before large, and products grouped by film width or pouch size so adjacent runs need fewer part swaps. Faster changeovers means shortening the 25 minutes itself.
For faster changeovers, start by sorting the work into two groups. One group is work that can be done while the line is still running, such as staging the next film roll, pre-assembling format parts, printing labels and preparing the cleaning kit. The other group needs the line stopped, such as removing the old parts and fitting the new. Moving tasks from the second group to the first shortens the stop without changing what gets done. Quick-release format parts and recorded standard settings, so no one hunts for the right seal temperature, shorten the remaining stop.
Larger batches carry costs of their own. They build inventory, tie up warehouse space, use up shelf life on finished goods, and lengthen the lead time for customers who order small quantities. If a product sells slowly, a long run produces stock that sits. The answer is not “always run big batches”. It is to count what a changeover costs, count what extra stock costs, and compare them.
How to record changeovers
You cannot manage what you only estimate. A short log, filled in by the operator at each change, is enough to start.
| Date | From product | To product | Stop time | First good pack | Back at target speed | Packs or film wasted | Reason for delays |
|---|---|---|---|---|---|---|---|
| (date) | (product A) | (product B) | (hh:mm) | (hh:mm) | (hh:mm) | (count or meters) | (short note) |
Three timestamps matter. The gap from stop to first good pack shows the setup and trial work. The gap from first good pack to target speed shows the ramp, which is the part most often left out. The waste count gives the setup material. Add a few words on reasons, such as “waited for film” or “seal temperature adjusted twice”, and patterns appear within a few weeks. Use the average for your model, and keep the range, because a changeover that sometimes takes 40 minutes costs more than the average suggests.
Where it changes an automation decision
A faster rated machine is not automatically the better buy on a high-mix schedule. Compare two machines on the same shift as above, with 30 minutes of other downtime and setup waste left out for clarity.
Machine X has an effective running rate of 42 good packs per minute and a 45-minute changeover. Machine Y runs at 35 and changes over in 15 minutes.
| Changeovers per shift | Machine X good packs | Machine Y good packs |
|---|---|---|
| 2 | (480 - 90 - 30) x 42 = 15,120 | (480 - 30 - 30) x 35 = 14,700 |
| 4 | (480 - 180 - 30) x 42 = 11,340 | (480 - 60 - 30) x 35 = 13,650 |
At two changeovers X leads by 420 packs. At four, Y leads by 2,310. The crossover sits where (450 - 45N) x 42 = (450 - 15N) x 35, which gives 18,900 - 1,890N = 15,750 - 525N, so N = 3,150 / 1,365 = about 2.3 changeovers per shift. Above that, the slower machine delivers more good packs. This is the same bottleneck logic as before, applied to changeover loss. For the wider choice between manual, semi-automatic and automatic setups, see Manual, Semi-Automatic or Fully Automatic Packaging? A Cost Model.
Equipment that runs few hours changes this again, because idle time dilutes any speed advantage. That effect is covered in How Equipment Utilization Changes Automation Payback.
When the conclusion changes
The model matters most for mixed schedules. If the line makes one product for weeks, changeovers are rare and this article barely applies. If demand is for many small orders, the question becomes how to shorten changeovers, not how to avoid them.
It also changes when the line is not the constraint. If an upstream stage or the case packer limits output, lost minutes on a faster stage may cost nothing. Check which stage is the bottleneck before spending on quick-change parts. Other articles on this theme are collected under Production Economics.
Keep reading
- Cost per Good Pack: A More Useful Measure Than Nameplate Speed: defines the cost measure and the no-double-counting rule used above.
- Why Faster Machines Do Not Always Increase Line Output: shows how the bottleneck stage sets the effective rate used in the model.
- Manual, Semi-Automatic or Fully Automatic Packaging? A Cost Model: compares setups at different volumes and product mixes.
Assumptions and limits
- All figures are illustrative. Your changeover length, waste and shift cost will differ by product pair and crew.
- Every changeover is treated as 25 minutes and 60 packs. Real changeovers vary with the product pair, and a log will show the spread.
- Inventory, shelf life, storage space and customer lead times are not priced, though they matter when choosing batch size.
- Shift labor and overhead are held fixed. Overtime, extra cleaning labor and wear from more frequent changes could raise them.
- The machine comparison ignores setup waste, purchase price, financing, taxes and ramp-up, and assumes the machine is the bottleneck of the line.
- This is a comparison tool and does not replace financial, legal, safety or engineering review.