Three years ago a fabricator in Binh Duong asked me to quote an auto duct line. He had been running a shear, a folding machine, a lock former and a beader, all bought second-hand, in a shed with two overhead fans. His monthly output was around 1,800 square metres of galvanised rectangular duct, and he was doing it with eleven people across two shifts. I quoted a Line 3 with a plasma cutter and a coil feed. He said the number was more than his whole building was worth and stopped replying.
He called me fourteen months later. In between, he had lost a tender because he could not hold a delivery date, and his biggest customer had started auditing his dimensional consistency. Same machines, same shed, one more year of experience. He bought the line the second time without arguing about price. What changed was not the quote. What changed was that he had finally sat down and worked out what his existing process cost him per square metre, and the number embarrassed him.
That is the only ROI conversation worth having, and it does not start with the price of the machine.
Duct shops measure output in square metres of developed sheet, and every shop seems to measure it slightly differently. Before any payback calculation means anything, agree on what a square metre includes. Does it include the offcut? Does it include the fittings, or only straight duct? Is a 90 degree elbow counted at its developed area or at some nominal equivalent?
I use developed area of finished duct including fittings, excluding offcut and excluding scrap. It is the only figure that can be compared between two shops, and it is the figure that the customer is actually paying for. If a shop quotes you 3,000 square metres a month and it turns out they are counting the coil they consumed rather than the duct they shipped, the whole calculation is fiction.
You do not need a spreadsheet with forty tabs. Four numbers will get you a payback figure that is close enough to make a decision.
Labour hours per square metre on the current process. Get this from a timesheet, not from memory. Take last month's total production hours, subtract supervision and maintenance, divide by square metres shipped. A shop running shear, fold, lock and bead separately typically lands between 0.30 and 0.45 hours per square metre for straight duct, higher for fittings.
The loaded hourly labour cost. Not the wage. Wage plus social insurance, plus the cost of the space that worker occupies, plus the supervision overhead. In Vietnam or Indonesia this often works out at 1.4 to 1.6 times the wage. In the Gulf it is closer to 1.8. In Europe, 2.2 and upwards.
The material yield gap. Single machines with manual layout typically waste 8 to 12 percent of coil on offcut that is too small to use. A line with nesting software and a coil feed usually lands at 4 to 6 percent. On a shop consuming 22,000 USD of coil a month, three percentage points is 660 USD a month, and it is completely invisible in the accounts because it leaves the building as scrap.
The rework rate. Measure it for a month. Count the ducts that had to be remade or reworked because of a dimension error, a wrong seam, or a damaged edge. Most shops that have never measured this are shocked by it. Two to three percent is common on manual layout, under one percent on a line that cuts from a corrected drawing.
Take the shop above at 1,800 square metres a month, running 0.35 hours per square metre on manual equipment with a loaded labour cost of 7.50 USD per hour.
Labour cost per square metre today: 0.35 x 7.50 = 2.63 USD. Total monthly labour: 4,725 USD.
On a Line 3 running rectangular duct from coil with automatic notching and forming, the same work lands at about 0.11 hours per square metre, and the crew drops from eleven to seven because the cutting, notching and forming are one continuous pass instead of four separate handling steps. Labour cost per square metre: 0.11 x 7.50 = 0.83 USD. Total monthly labour: 1,485 USD.
Monthly labour saving: 3,240 USD.
Material saving at three percentage points on 22,000 USD of coil: 660 USD. Rework saving at 1.5 percent of production value, call it 400 USD. Add those: total monthly benefit 4,300 USD.
Line 3 with plasma cutting and coil feed, installed, in the region of 62,000 USD. Simple payback: 62,000 / 4,300 = 14.4 months.
Fourteen months is a good number and it is also a slightly optimistic one, because it ignores three things I will get to in a moment. Real payback on that project was closer to nineteen months. Still good, and still worth doing, but the difference between 14 and 19 is exactly where most buyers get burned.
The single biggest variable is not the machine price. It is how much duct you put through it. The table below holds the same assumptions and changes only monthly volume.
| Monthly output | Labour saving | Material + rework saving | Total monthly benefit | Payback on 62,000 USD line | Payback on 95,000 USD Line 5 |
|---|---|---|---|---|---|
| 900 m2 | 1,620 USD | 530 USD | 2,150 USD | 28.8 months | 44.2 months |
| 1,400 m2 | 2,520 USD | 820 USD | 3,340 USD | 18.6 months | 28.4 months |
| 1,800 m2 | 3,240 USD | 1,060 USD | 4,300 USD | 14.4 months | 22.1 months |
| 2,500 m2 | 4,500 USD | 1,470 USD | 5,970 USD | 10.4 months | 15.9 months |
| 3,500 m2 | 6,300 USD | 2,060 USD | 8,360 USD | 7.4 months | 11.4 months |
Read the top row carefully. At 900 square metres a month, a Line 5 takes almost four years to pay back on labour and material alone. That is a long time to be carrying debt against a machine that is running at a third of its capacity. It might still be the right machine if you have contracted volume coming, but if you are buying it in the hope that volume will appear, you are financing a hope.
A Line 5 does more in one pass: it coils, levels, notches, beads, forms the lock and the flange, and cuts, all in one continuous flow at up to 20 metres a minute on thin gauge. Its labour per square metre is lower than a Line 3 and its floor space is roughly double. But its fixed costs are also higher, and the payback arithmetic only rewards it above roughly 2,000 square metres a month of rectangular work.
If you are comparing the two formats, the Line 3 page and the Line 5 page set out the pass sequences, which matters more than the headline speed. A pass sequence that does not match your product mix will cost you more in changeover than you gain in throughput.
A Line 3 with plasma draws around 18 to 22 kW in production and a Line 5 with hydraulic notching around 28 to 35 kW. At 160 hours a month that is 3,500 to 5,600 kWh, and in most of Southeast Asia that is 400 to 800 USD a month. Plasma also consumes consumables: electrodes and nozzles typically every 300 to 600 pierces depending on thickness and air quality, which on a busy line is a real monthly line item rather than a rounding error.
Compressed air is the one people forget. A line with pneumatic clamping and a plasma torch needs 6 to 8 bar at 300 to 500 litres a minute, and if the shop compressor is sized for hand tools it will cycle constantly and deliver wet air, which destroys plasma consumables. Budget for a refrigerated dryer. It is cheaper than the consumables it saves.
Plan on 3 to 5 percent of the capital cost per year, averaged over five years. That covers forming rolls, shear blades, plasma consumables, hydraulic oil and filter changes, and the occasional bearing. The first year will be lower than average and the fourth year higher. Shops that budget zero and then get a 4,000 USD roll regrinding bill in year three tend to conclude the machine was a bad purchase, when in fact they simply did not budget.
A Line 5 needs 22 to 28 metres of length with coil loading at one end and offload at the other, plus clearance. In a rented building that is real money per month. The coil handling also needs either a crane or a forklift with a boom, and coil at 2 to 3 tonnes is not something two men move with a bar.
The first month on a new line is slower than the old process. Not slightly slower. Materially slower, because the operator is learning the nesting software, the changeover sequence, and the machine's tolerances at the same time. Plan for 60 to 70 percent of expected output in month one, 85 percent in month two, and full output in month three. Any payback calculation that starts at full output on day one is wrong by roughly one month of benefit.
I have talked more than one buyer out of a line, and I will do it again. Three situations where separate machines win.
The first is a shop whose product is mostly fittings. Elbows, tees, transitions and offsets do not benefit from a coil line the way straight duct does, because each fitting is a separate nested shape and the handling is the cost. A shear, a notcher, a lock former and a set of cheek benders will beat a line on fitting-heavy work.
The second is a shop under about 700 square metres a month. Below that, the labour saving does not cover the fixed costs of the line, and the flexibility of separate machines is worth more than the speed.
The third is a shop making a lot of one-off and non-standard work: stainless, aluminium, heavy gauge, unusual dimensions. A line optimised for 0.5 to 1.2 mm galvanised rectangular duct is a poor tool for 3 mm stainless transition pieces, and forcing that work onto it damages both the machine and the schedule.
Ask for a trial on your own material. Not a demonstration on the supplier's galvanised coil, on your coil, cut to your widths, making a duct from your order book. Time it. Count the operators. Then take the finished duct and measure it against your drawing, because a machine that hits cycle time but misses dimension is not saving you anything.
Ask what the changeover is from 0.6 to 1.0 mm and from 500 to 900 mm width, and insist on watching both. Ask which parts are consumable, what they cost, and how long they last in hours rather than in months. A supplier who cannot answer the consumable question in hours has not spent time in a shop.
And ask for two references at your volume, not at ten times your volume. A shop running 8,000 square metres a month will tell you the line is wonderful and will not tell you anything about whether it pays back at 1,500.
If you want to see how the different formats lay out against a floor plan, the duct machinery section covers the full range including the single-machine options, and it is worth looking at those before assuming a line is the answer.
For equipment in this category, most of our customers target 18 to 30 months. Under 18 months is excellent and usually means the shop was already losing money on the old process. Over 36 months, look hard at whether the volume assumption is real or aspirational. And remember that the machine will still be running in year ten, so a 30 month payback on a machine with a fifteen year life is a good investment, provided the volume is there.
It changes the cash flow, not the payback. If you finance at 8 percent over three years, the monthly payment on a 62,000 USD line is roughly 1,940 USD. Against a monthly benefit of 4,300 USD, the line is cash positive from month one even before the payback period ends. That is the argument to make to a bank, and it is a stronger one than the payback figure itself.
Sometimes. The frame, the coil car and the control platform are the expensive parts, and a line bought with a smaller cutter or without a beader can often be extended. What cannot be extended cheaply is the frame length. If you think you will want a Line 5 within three years, buy the longer frame now even if you populate it partially. Ask the supplier specifically which upgrades are field-retrofittable and which are not, and get it in writing.
Typically 4 to 8 percent of the machine price, covering foundation work, power and air connection, rigging, and three to five days of commissioning with a technician on site. Add travel and accommodation for the technician, and add the cost of your own people standing around watching, which is real even if it never appears on an invoice.