Which Stamping Jobs Still Belong on a Blanking Line?
A die shop in Ohio quoted two jobs in the same week: 900 brackets a month and 240,000 terminal lugs a year.
Both were progressive dies. One belonged on pre-cut blanks and one did not, and the difference was not the press tonnage.
The decision between a coil feeding line and a blanking operation comes down to four numbers, and three of them are usually estimated badly.
What follows is the comparison as it is actually run in a quoting meeting, including the jobs where blanks win outright.
The Four Numbers That Decide It
Run length, material yield, die type and scrap handling. Those four settle 90% of the cases before anyone opens a machine quotation.
Run length sets whether setup time can be amortised. A coil line takes 20-40 minutes to thread and set; blanks take 5-10 minutes to load a stack. At 500 parts a year, that gap is the whole cost difference.
Material yield sets the rest. A coil feeds one strip width and pays for the full width of the coil. Blanks can be nested, and nesting on a 0.8 mm stainless job routinely recovers 12-20% of the material.
Die type is the hard constraint. A die that needs the strip rotated 90° between stations, or that ejects parts upward into a hand-loaded fixture, will not run from coil at any speed.
Scrap handling is the quiet one. Coil produces skeleton scrap on a winder or chopper; blanks produce slugs and offcuts that somebody has to move.
In a shop with no scrap conveyor, that is a person, and a person is 45,000 USD a year.
Two Routes, Side by Side
| Job profile | Runs well from coil | Runs well from blanks | Where the wrong choice costs you |
|---|---|---|---|
| 20,000+ parts a year, one die | Yes, setup amortised in days | Feasible but stack handling dominates | Blank handling labour eats 8-12% of part cost |
| 800 parts a year, wide panel | No, threading exceeds run time | Yes, buy 2 t of sheet and run | Coil line capex never recovers at this volume |
| 0.8 mm stainless, 340 mm wide | Yes if nesting is not possible | Yes, 15% yield gain from nesting | Coil pays for 100% of a width it scraps |
| Die needing strip rotation | No, geometry forbids it | Yes, rotate the blank by hand or robot | A coil line bought for this die sits idle |
| Two-shift, 3 die changes a week | Yes with a quick-change head | Yes, no line setup at all | Changeover on coil can reach 50 minutes |
Read the table as a set of trade-offs, not a ranking. Every row has a case where the other column wins, and the row that matters most is whichever one your mix is heaviest in.
- Count the annual quantity per die, not per customer.
- Weigh the scrap value, not just the scrap percentage.
- Ask the die designer whether the strip can be fed in one direction.
- Measure the floor before the quotation, not after the order.
Run Length and the Setup You Pay For
Take a 6,000-piece order at 45 SPM. The press runs 2.2 hours. Setup on a coil line is 35 minutes, so setup is 21% of the order's time on the machine.
The same order from blanks: 6,000 blanks at 60 SPM runs 1.7 hours, and setup is 8 minutes. The press is free 30 minutes earlier, and the operator never touches a coil.
Now scale it. At 60,000 pieces the coil setup is 2% of the run and the blank premium per part is what decides it, not the setup.
That premium is real: cut blanks typically cost 8-15% more per kilogram than coil, because the service centre charges for shearing, packing and the yield it lost.
At 60,000 parts of 0.9 kg, the material premium is roughly 4,300-8,100 USD.
A coil line that saves 12% scrap on the same job recovers 3,000-6,000 USD, so the two effects nearly cancel and the labour difference decides.
This is why quoting on material price alone gets the answer wrong half the time. Run the three costs together: material, setup amortisation, and handling labour.
When the Die Itself Rules Out Coil
Some dies cannot be fed from coil, and no amount of line specification changes that. Recognise them at the quotation stage and the argument ends early.
Dies that rotate the strip between operations are the clearest case. A part with slots at 0° and 90° needs the material turned, and a coil line only feeds in one direction.
Compound and blank-through dies with upward ejection are the second case. The part leaves the die into the strip path, which is exactly where the next feed is trying to go.
Large panels are the third. A 1,400 x 900 mm body panel at 0.7 mm needs a coil wider than most standard lines carry, and the strip stiffness makes threading a two-person job with a risk of buckling.
Dies designed around a hand-loaded second operation belong on blanks as well, at least until the second op is automated.
Feeding coil into a die that expects a flat, deburred blank produces burr direction problems that show up in the finished assembly.
Material Yield: Where Blanks Win on Alloy
On mild steel at 0.6 USD/kg the yield difference is noise. On 5182 aluminium or C110 copper it is the whole business case.
A coil-fed die consumes one strip width. If the part is 180 mm wide and the coil is 300 mm, you scrap 120 mm on every stroke unless the die is laid out two-up, which needs a coil of 360 mm and a wider press.
Nested blanks from sheet can share that 120 mm with a mirrored part. On a 340 mm part from 400 mm sheet, proper nesting recovers 15-22% of the material.
At 1,800 USD per tonne for aluminium and 300 t a year, 18% is 97,000 USD. That buys a blanking cell and leaves change.
The same logic applies to thin gauge where strip camber matters. A 0.3 mm strip with 3 mm of camber per metre cannot be fed straight, and blanks sidestep the problem entirely.
| Material and gauge | Coil-fed yield | Nested blank yield | Where the gap pays for itself |
|---|---|---|---|
| SPCC 1.2 mm, 400 mm part | 72-78% | 76-82% | Rarely, because mild steel scrap is low value |
| 5182 aluminium 1.0 mm | 64-70% | 80-86% | At 150 t a year the gap pays for a destacker |
| C110 copper 0.8 mm | 60-68% | 78-84% | Immediately, on both scrap and purchase price |
| SUS304 0.6 mm | 66-72% | 74-80% | Inside two years if the part nests in pairs |
Two caveats on those figures. They assume the part can be nested at all, which a 180 mm part on 300 mm coil often cannot without a mirrored pair in the die.
They also ignore what the skeleton scrap is worth. Copper and stainless skeleton returns 60-75% of the purchase price at a scrap dealer, so the yield loss is smaller than the percentage suggests.
On mild steel the same skeleton returns 15-25%, which is why a 4% yield gap on SPCC never justifies a second process on its own.
Cases the Comparison Cannot Settle
The four-number test assumes the shop already owns a press and has floor space for whichever route it picks. Neither assumption is safe.
A coil line needs 6-9 m of floor in front of the press plus a coil storage bay. A shop in a 900 m² building often has the press and not the length, and a tight-bay layout costs more than the line.
Capex is the second break. A line sized for 800 mm strip runs 90,000-180,000 USD against 15,000-30,000 for a blank destacker.
Below roughly 15,000 parts a year the line does not pay back inside five years on labour alone.
Blank quality is the third. Cut blanks carry a shear burr and a flatness tolerance of their own, and a die that was set up on coil will show a different burr direction on the finished part.
Then there is the case the comparison ignores: a job that is growing.
If the 800-piece order is a prototype for a 200,000-piece programme, buying blanks today and a line in eighteen months is the correct sequence, and buying the line now is capital sitting still.
Does 15,000 parts a year justify a coil feeding line?
Typically 15,000-20,000 parts a year on a single die, on two shifts. Below that the setup and capex do not amortise, above it the handling labour dominates.
How much more do cut blanks cost per kilogram than coil?
8-15% for mild steel from a service centre, and 10-20% on aluminium where the centre carries the nesting loss. The gap narrows above 20 t per order.
Can a 1,400 mm panel be run from coil?
Yes, but it needs a line rated above 1,500 mm and a threading procedure with two operators. Most shops under 400 t press capacity keep panels on blanks.
Is 6 m of floor enough for a coil feeding line?
A coil line needs 6-9 m in front of the press plus a coil bay. A blank destacker needs 3-4 m and a stack of blanks delivered on a pallet.
The choice also changes what the line can do later. A coil line bought for one die can be re-set for another in 30-50 minutes, which is why the route decision and the line layout are usually made together.
The layout options for a single coil feeding two presses are worked through in our coil line knowledge base.
Where to go next
The four-number test sits underneath a wider question: what a coil line replaces, and what it cannot replace. That overview, from decoiler to die, is the entry point to this cluster.
The Coil Line Guide Library
