Laser cutting CRCA sheet: thickness, tolerance and cost

CRCA is the cheapest sheet in the building per kilogram and the easiest to mis-specify. A drawing that calls for "2 mm CRCA, tolerance as per drawing" and carries a ±0.1 mm block on every dimension will be quoted at a price that has nothing to do with the metal: it has been priced as a machining job, because nothing on a laser-cut and folded panel holds that across a bend.

The material is not the problem. CRCA cuts predictably, takes a bend without the surface damage stainless shows, and holds a bright edge that accepts a conversion coating directly. Laser cutting CRCA sheet becomes expensive at the two ends of the range: below 1 mm, where handling dominates, and above 6 mm, where the cut slows and the edge needs preparation.

What follows is grade selection, cut time and kerf by thickness, the tolerance that actually survives the route, and where the money sits on a typical 1.2 mm panel. The other cutting guides are in the laser cutting and fabrication hub.

Which CRCA grade belongs on the drawing?

IS 513 grade D is the right default for a part that is cut and bent. It is a drawing-quality cold reduced sheet with enough ductility to take a 90° bend at a sensible radius and a consistent surface for coating. Grade DD is deep-drawing quality and costs more; it earns that premium only where the part is actually drawn, not where it is cut and folded.

The commercial grades are the trap. A flat panel with no bends can be cut from a cheaper commercial grade and nobody will know. The same sheet bent over a 1.0 mm inside radius at 2.0 mm thickness will crack at the outside of the bend, and the crack appears after coating, which turns a material saving into a warranty claim.

Surface condition is the second callout. CRCA arrives oiled to prevent rust, and the oil burns off at the pierce, leaving a small scorch ring on the top face. That is cosmetic on a hidden bracket and unacceptable on a visible panel, so either specify dry sheet or accept the mark on the non-visible side. Where the part is powder coated, the oil is removed in the first pretreatment tank anyway, so the callout is about appearance before coating rather than adhesion.

Thickness tolerance is the callout buyers forget. Coil is supplied to a mill tolerance that runs roughly ±0.05 to ±0.10 mm over the 0.8 to 2.0 mm range, and that variation passes straight into a formed height. A drawing that asks for ±0.1 mm on a 150 mm formed height is asking the press brake to correct the coil, which no brake can do consistently.

Laser cutting CRCA sheet: speed, kerf and cost by thickness

The numbers below are what we quote against on the 12 kW fibre laser. Speed is a production average including contour deceleration, not a peak figure from a parameter sheet. Kerf is measured at the top face, and the tolerance is what a cut feature holds in the flat with a competent nest and a clean sheet.

The last column is the one that changes a design. A 20 mm profile is at the edge of what the machine does, and the tolerance has moved to ±1.0 mm, which is ten times the tolerance quoted for 1.2 mm sheet. A part that needs ±0.2 mm at 12 mm thickness is not a laser job at any price we would quote.

Why a CRCA part costs more than the coil price suggests

Material is 55 to 70 percent of a coated CRCA part, and the rest is conversion, so a price that tracks the coil price alone will always be wrong. Cutting is 10 to 20 percent at 1.2 mm, bending 8 to 15, coating 8 to 15, and the remainder is welding where it exists, packing and inspection.

The balance reverses with thickness. At 1.2 mm, a 300 × 200 mm panel with six Ø8 mm holes has 1,151 mm of cut, which at 30 m/min is 2.3 seconds, plus seven pierces at roughly 0.3 seconds each. Call it 4.4 seconds of laser time. Three bends on the same part take 24 to 36 seconds including handling. The brake is five to eight times the constraint that the laser is.

Material sensitivity follows the blank mass, not the part mass. The 300 × 200 mm part carries 0.67 kg of sheet once the nest loss is included, so every ₹1 per kilogram move in coil price moves the piece price by ₹0.67 — comparable to the cost of the laser time on the same part. That is the arithmetic behind a metal clause: on a thin coated panel the coil price and the conversion cost are the same order of magnitude, and a fixed price that ignores one of them is a guess.

At 10 mm the same outline takes about 49 seconds of cut and 14 seconds of piercing, while the bends are slower but not five times slower. Past 6 mm, cut length is the price driver and nesting becomes a machining decision rather than a material decision. The guide to how thickness changes laser cutting price works through the same crossover from the quoting side.

Tolerance: what changes between the laser and the formed part

In the flat, the cut holds ±0.10 mm on thin sheet and ±0.20 mm at 3 mm. After bending, the formed dimension is a ±0.5 mm tolerance, because the bend allowance varies with the actual thickness, the actual yield strength and the tooling in the brake.

Three details decide whether the tighter number survives. The hole-to-bend distance must keep the hole outside the bend deformation zone, which is roughly the inside radius plus half the die opening plus the thickness; a hole inside that zone distorts into an oval. The bend radius must be at least the material's minimum, which for 2 mm grade D is about 2.0 mm inside. And the flat pattern must be developed with the fabricator's bend allowance rather than the CAD default, because a 0.3 mm error in the allowance shows up as a 0.3 mm error at the flange.

Where a hole pattern must hold ±0.2 mm after bending, the answer is a fixture or a post-bend operation, not a tighter laser tolerance. That is a cost decision worth taking early: a checking fixture costs less than a rejected batch, and it removes an argument at first article.

Coil set and flatness before the first bend

CRCA arrives as a coil, and a coil remembers its diameter. Sheet cut from the outer wrap of a tight coil has a longitudinal bow that a laser will faithfully cut into a curved blank, and a blank that is 2 mm out of flat over a metre will not sit down on the brake die. The first bend then closes at the wrong angle and every subsequent dimension follows it.

Two controls deal with it. Ask for sheet that has been levelled or cut from a slack coil, and check the blank on a surface plate before it goes to the brake. A 2 mm bow over 1,000 mm is common on thin coil and is worth flagging on the drawing as a flatness requirement of 1 mm over 1,000 mm if the assembly depends on it.

The bend sequence is the second control. Bending the two long edges first and the cross bends last leaves the part free to straighten between operations; bending a cross bend into a bowed blank locks the bow in. A brake operator who knows the sequence produces a flat part from mediocre sheet, and one who does not produces a twisted part from good sheet.

Nesting arithmetic on a 1.2 mm sheet

A 1,250 × 2,500 mm sheet of 1.2 mm CRCA weighs 29.4 kg at 9.42 kg/m². The 300 × 200 mm panel weighs 0.565 kg net, so the sheet carries 3.125 m² of material against 0.060 m² per part.

With the 200 mm side across the sheet width and a 10 mm web, five columns and eight rows fit inside a 5 mm edge margin: 40 parts. Rotate the part so the 300 mm side runs across the width and the same sheet takes four columns and eleven rows: 44 parts. The gain is 10 percent, or 2.4 kg of sheet per nest, and it costs one decision at the quotation stage.

The scrap that remains is 4.5 kg per sheet, and some of it can be recovered. A remnant register lets the next job use the tail of the sheet rather than starting a new one, and a nest that leaves a straight 300 mm band at the end is worth more than one that leaves a ragged edge. How nesting reduces sheet metal cutting cost covers the remnant discipline; on CRCA the gain is smaller per kilogram than on copper but the volume is higher.

The 12 kW bed and what it changes for long parts

The 12 kW fibre laser runs on a 40 ft × 16 ft bed, which is 12.2 m × 4.9 m. A 6 m canopy panel or a 3 m enclosure side is cut in one piece with no splice, no butt weld and no accumulated tolerance stack from joining two shorter panels.

The two 6 kW and two 3 kW support machines take the thinner and smaller work, so a mixed release of 1.2 mm panels and 6 mm brackets can run in parallel rather than queueing behind the large bed. Plate work up to 30–40 mm is done on the iron worker, which shears and punches but does not cut profiles.

We cut CRCA, mild steel, stainless, aluminium, brass and copper on the same line, which matters where a subassembly mixes materials and the fit between them is toleranced. Parts are inspected in process, and first article inspection and PPAP documentation are available where the programme requires them. Ganesh holds ISO 9001:2015 and ISO 14001:2015 certification.

What to put on the drawing

• Grade and standard: IS 513 grade D, with the surface condition (oiled or dry) stated.
• Thickness with tolerance, and whether the mill tolerance is acceptable.
• Tolerance block: ISO 2768-1 class m is realistic for a laser-cut and bent part; class f is not, unless the tight dimensions are individually toleranced.
• Critical features only, toleranced individually, with the datum scheme named.
• Bend radius and bend allowance, or a note that the fabricator's allowance applies.
• Hole-to-bend clearance where holes sit near a bend line.
• Edge requirement: burr limit, deburr, and whether the edge will be visible after coating.
• Coating specification, including the film thickness range and the pretreatment expectation.
• Quantity and release pattern, because the nest and the remnant plan depend on it.

DXF layer conventions matter more than most drawings admit: cut contours, bend lines and etch marks on separate layers, with the bend line as a centre line rather than a cut. The DXF preparation checklist lists the layer and unit rules we work to.

When laser cutting CRCA is the wrong purchase

Above roughly 10,000 to 30,000 parts a year for a bracket of this size, stamping usually wins once tooling is amortised. The laser cutting versus stamping comparison sets out the crossover, and the deciding factor is usually the number of operations rather than the part size.

A simple rectangular blank with no features is cheaper sheared than cut, and a part that needs 30 mm of thickness is cheaper flame cut or plasma cut and machined. We do not offer either process for profiled parts, and saying so early saves a week of quotation.

A part with a powder coat over an oxygen-cut edge above 6 mm should be blasted first, which adds a handling step. If the edge is visible and unprotected, the specification should say so, because a coated oxide edge fails by lifting a flake of coating with the oxide attached.

Send the DXF with the grade, thickness and bend drawing, and the quotation will show how thickness and cut length move the price. Blank weight follows from the sheet mass, 9.42 kg/m² at 1.2 mm, and custom cutting work is described under laser cutting.