Is a Coil Line Worth Running at 300 Pieces a Month?

Three Routes to the Same Blank

Every press shop feeding a die at low volume chooses between three supply routes. They differ in who holds the inventory and who owns the scrap.

Route one is a coil line in-house: buy coil, decoil, straighten, feed, blank. Route two buys cut-to-length blanks from a service centre. Route three buys finished blanks cut on a laser or a turret.

The comparison is usually framed as machine price against blank price. That framing hides the two costs that actually decide it at 300 pieces a month.

Read the third column first. At 300 pieces a month, capital and idle months are the costs that dominate, and the material premium is smaller than most buyers assume.

The Number That Decides It: Kilos per Month

Work the arithmetic on a real part and the picture sharpens fast. Take a 400 mm by 250 mm blank in 1.2 mm cold-rolled steel, about 0.94 kg each.

Three hundred pieces a month is 282 kg of steel, or 30 m² of strip. A single one-tonne coil of 400 mm strip holds roughly 265 m, which is about 1,060 blanks.

That coil lasts three and a half months at this rate. The line runs for a few days and then sits, which is a very different operating pattern from a two-shift plant.

Now price the premium. A service centre typically charges 10% to 15% over coil price for cut-to-length blanks, which on $0.75/kg steel is $0.08 to $0.11 per kilo.

At 282 kg a month the premium is $23 to $31. That is not a rounding error in the machine decision. It is noise.

So the material argument for a coil line is dead at this volume, and pretending otherwise is how buyers end up with an underused asset.

The Money Comes From Lead Time, Not Steel

If material savings are $30 a month, the case has to rest on lead time, scrap and flexibility. Those three carry real money at low volume, and they are harder to put in a quote.

Lead time is the biggest one. Cut-to-length blanks arrive in two to four weeks; a coil in the rack is available the same afternoon when a customer calls with an urgent order.

Scrap is the second. Buying blanks means buying someone else's nesting decision, and a poorly nested blank can waste 8% to 12% of the strip.

Flexibility is the third. A coil line lets you change blank length by keystroke, which matters when a customer wants 280 mm instead of 250 mm on the next batch.

Put a number on each. If a single rush order per quarter is worth $2,000 in margin, that alone is $8,000 a year, which pays for a lot of idle machine time.

Be careful with that number, though. Rush-order value is margin on work you would otherwise decline, not margin on work you already have.

A shop that quotes a two-week lead time and never loses an order has no rush premium to capture. The flexibility is real and worth nothing.

Costs That Never Appear in the Quotation

Every low-volume coil line carries four costs that the quotation leaves out. Each one is small on its own and material at 300 pieces a month.

• Floor space. A 400 mm line with a coil car needs 6 m to 8 m of bay, occupied all year for three days of work.
• Skill. Somebody has to own the setup, the roll gap and the loop tuning, and that person is not free.
• Idle degradation. A machine that runs one week in twelve develops flat spots on rolls and stale grease in bearings.
• Coil inventory. One coil is three months of stock, so you tie up $700 to $1,200 and a rack position for a quarter.

Add those up honestly and a $55,000 line serving 300 pieces a month carries about $1,100 a month in ownership cost over five years. That is the number the material premium has to beat.

It does not. Which is why the decision at this volume turns on lead time, and why a shop that never has rush orders should not buy the line.

The Scrap Rate Nobody Measures

Every business case at this volume quotes a scrap rate. Almost none of them measures one, and the estimate is usually optimistic.

A service centre nests blanks to maximise its own yield from the master coil. That is a legitimate commercial decision, and it is not the same as maximising yours.

On a 400 mm strip a 250 mm blank leaves 150 mm of side trim. Whether that trim becomes scrap or a second part depends entirely on who does the nesting.

In-house, you can run two parts across the strip and change the split when the order book shifts. At low volume that is often worth more than the material premium.

Weigh the scrap skips for one month before arguing about percentages. The measured figure on a bought-blank process is frequently 10% to 14%, not the 5% in the spreadsheet.

Scale matters here. Fourteen percent of 282 kg is 39 kg, about $29 a month, which is trivial. The same percentage on a 3-tonne month is $315, and that changes the answer.

Where This Arithmetic Stops Working

The calculation above assumes one part, one die and a stable order book. Change any of those and the answer moves.

If the same coil feeds four different parts, the line earns its space in a way a single-part analysis never shows. Shared assets change the denominator.

If the material is high-strength steel or stainless, the service centre premium climbs to 25% or more, and the coil case strengthens quickly.

If the parts are large, a 300-piece month can be 3 tonnes of steel rather than 282 kg, which puts the shop well past the breakeven line.

The arithmetic also ignores quality. A blank with a burr from a worn service-centre shear can cost more in die wear than the entire material premium.

And it says nothing about the future. A line bought for 300 pieces a month is often bought because someone expects 900 within two years, which is a different question with a different answer.

How to Settle It in One Week

You do not need a consultant to run this test. You need one month of order history and two phone calls.

List every order from the last twelve months with its part number, quantity and the date the customer placed it. Mark the ones that arrived with less than two weeks of notice.

Then ask a service centre for a cut-to-length price on your three highest runners, delivered, in your quantity. Compare it against coil price plus your own scrap rate.

If the premium comes back under 15% and your rush-order count is zero, buy blanks and keep the capital. That is the honest answer at 300 pieces a month.

If the premium is 25% or the rush orders are frequent, the line is a service investment rather than a cost saving. Say so in the business case, because that is the argument that survives a finance review.

Whichever way it lands, the specification work is the same. The specification lines that actually earn their cost, and the ones buyers regret, are mapped in the coil line guide library.