Laser cutting aluminium sheet and plate

The word aluminium is not a specification

A drawing that says "aluminium 2 mm" tells a supplier almost nothing. Between 1050-H14 and 6082-T6 there is a factor of four in strength, a difference in bend radius from one thickness to three, and a difference in how the cut edge anodises. Laser cutting aluminium is straightforward in the thin gauges and forgiving at the cut, and then the part reaches the press brake and the alloy becomes the problem.

Three physical facts explain most of what follows. Aluminium weighs 2.70 kg/m² per millimetre, roughly a third of steel, so handling changes before cutting does. It conducts heat about three to four times better than mild steel, which pulls energy out of the cut and softens the edge. And it reflects most of a near-infrared beam when cold, which is why the pierce, not the contour, is usually the slowest part of the program.

A 1,250 × 2,500 mm sheet of 2 mm aluminium weighs 16.9 kg against 49.1 kg for the same sheet in 2 mm CRCA. One operator moves three times as many parts an hour, which is the part of an aluminium quote that is genuinely cheaper than steel.

Why the cut behaves differently from steel

At 1,064 nm, a clean aluminium surface reflects roughly 94% of the incident beam. At 12 kW that leaves about 720 W in the work, which is less than a small steel-cutting job needs. The situation corrects itself: once the surface melts and a keyhole forms, absorptivity climbs to the order of 60–70%, and the same 12 kW delivers somewhere near 8 kW into the cut.

That asymmetry is the whole pierce problem. To start a cut you need power density high enough to break the oxide and melt the surface, and until you do, almost all the energy is going back up the beam path. On thin sheet the pierce is a fraction of a second. On 6 mm plate it is a second or more per pierce, so a plate part with 40 holes can spend most of its cycle starting cuts rather than making them.

The cut itself is fast and clean when the gas is right. Nitrogen gives a bright edge with minimal oxide at a slower speed; oxygen and compressed air are cheaper per hour and leave a darker, oxidised edge that has to be removed before welding or painting. On aluminium we default to nitrogen where the edge is functional or visible, and accept the slower cut because the downstream saving is larger.

Thermal expansion: the number that fails first articles

The arithmetic is worth doing once so it never surprises you again. Change in length equals length × coefficient × temperature change. For 2,000 mm of 5052 at 23.1 × 10⁻⁶ /K over 10 °C, that is 2,000 × 0.0000231 × 10 = 0.462 mm.

The same panel in mild steel at 12 × 10⁻⁶ /K moves 0.24 mm. So an aluminium part does not merely have a wider tolerance problem than a steel part; it has roughly double the problem, on top of a cut that is already less thermally stable.

The practical answers are cheap. Dimension long aluminium parts from a datum and let the far end float where the function allows. Inspect at the temperature the part will be used at, or record the temperature on the inspection sheet. And where a long part mates with a steel frame, put the slotted hole in the aluminium side, because the aluminium is the part that will move.

Nitrogen or air: the choice that changes the edge

The assist gas decides what the edge looks like before any deburring happens. Nitrogen is inert: it blows the melt out without reacting, so the edge stays bright and the oxide is thin. Compressed air and oxygen are cheaper and faster and leave a grey-to-black oxide that has to be removed before welding, anodising or powder coating.

Put numbers on the trade. On 3 mm 5052, a planning speed of 4 m/min with nitrogen becomes about 6 m/min with compressed air. Over 2,000 mm of cut, that is 30 seconds against 20 seconds, a 10-second saving. Over a program with 40 m of cut, it is 200 seconds, which is real money on a machine running two shifts.

Then add the downstream cost we do not quote at the cut. An oxidised edge that must be wire-brushed before welding is a manual operation at the weld station, and the operator has to reach both faces of every joint. Ten seconds saved at the laser can easily become a minute spent at the bench, which is why the gas choice belongs to the drawing's finish requirement rather than to the machine's hourly rate.

The exception is a part that will be shot blasted or phosphated before coating. There, an oxidised edge is an advantage rather than a problem, because the blast removes it and the pretreatment puts a controlled conversion coating over the whole surface.

Handling a sheet that dents when you look at it

Aluminium arrives with a protective film more often than steel does, and the film has to come off before cutting: a polyethylene film melts into the edge and leaves a residue that no deburr operation will remove cleanly. If the part needs protection after cutting, film it afterwards, on the finished part, and specify that in the packing.

Two more handling rules change the yield. Slats mark soft aluminium more than they mark CRCA, so a nest that drags a part across the bed will show a scratch line on the underside. And because the parts are light, they lift on the air assist and travel: micro-joints matter more on 1 mm aluminium than on 1 mm steel, and the eject sequence needs to be checked on the first sheet rather than the tenth.

Alloy and temper limits at a glance

The table carries the decision rule. If the part is bent and the bend is tight, the alloy is 5052 or 3003, and the temper is H32 or H14 rather than T6. If the part is structural and needs T6 strength, the bend has to be designed around a 3 × thickness radius, or the part has to be formed in T4 and aged afterwards. Either way, the alloy goes on the drawing before the price is agreed, because a switch from 5052 to 6082-T6 after first article changes the tooling, the radius, the price and sometimes the whole design.

Edge quality, anodising and welding

ISO 9013:2017 classifies thermal cuts, including laser cuts from 0.5 mm to 32 mm, and it separates the cut face into measurable features: perpendicularity, drag, dross and roughness. On aluminium the class matters less than it does on stainless because the edge is usually painted over or hidden inside an assembly, but two cases need attention.

Anodising is the first. A laser-cut edge carries a recast layer a few micrometres thick and a fine oxide, and both anodise differently from the rolled face. On a decorative part this shows as a dark band along every cut edge, and it cannot be polished out without changing the edge geometry. Specify a deburred or machined edge before anodising, or accept the band.

Welding is the second. Aluminium oxide melts at about 2,072 °C against 660 °C for the metal, so the oxide film has to be removed mechanically at the joint faces. Wire-brush or machine the edge within a few hours of welding, because the film regrows in air and a 24-hour-old edge is already harder to weld cleanly. On 5083 and 6061 the same oxide is where hydrogen porosity starts.

Deburring is the third and the cheapest to get right. Aluminium burrs are soft and lift less than steel burrs, but they smear rather than break, so a tumbled edge can look rolled over under a low-angle light. Where the edge is visible after powder coating, specify a linished edge and check it on the first article under the same lighting the customer will use.

What laser cutting aluminium on a 12 kW bed gives you

The 12 kW fibre laser with a 40 ft × 16 ft bed, 12,192 × 4,877 mm, cuts aluminium sheet and plate for canopy panels, rack parts, coach components and brackets, with two 6 kW and two 3 kW machines taking the smaller nests. Mild steel, CRCA, stainless, aluminium, brass and copper all run on the same floor, which means an assembly that mixes steel and aluminium can be cut in one release rather than two.

Forming is on the 200 T, 5-axis press brake with a 4,450 mm bed, to 10 mm, with Delem control. Cutting and forming the same aluminium part in one plant removes the argument about which operation made the part 0.4 mm short, because both operations record their own measurements against the same datum. The copper, brass and aluminium fabrication page covers the material handling and the tooling used on the softer alloys, and the custom parts route covers the one-off and low-volume end.

The plate limit is honest: the laser cuts to 20 mm on steel, and on aluminium the practical ceiling is lower, roughly 10–12 mm, before speed and edge quality make another process the better buy. We would rather quote a saw-and-machine route than sell a 16 mm aluminium contour that arrives with a ragged lower edge.

What to put on the drawing

• Alloy and temper, not the word "aluminium": 5052-H32, 3003-H14, 6082-T6.
• Thickness with the tolerance: 2.0 mm ±0.10 mm, or the standard for the grade.
• The bend radius as an inside radius, and whether it is a minimum or a nominal.
• Which face is cosmetic, and whether the cut edge will be anodised, painted or left bare.
• The weld prep on any edge that will be joined, and whether the oxide removal is the fabricator's scope.
• The measurement temperature or a tolerance that survives 10 °C of shop floor variation on long parts.
• Quantity, nesting expectation if the customer supplies material, and the finish specification.

How material thickness changes laser cutting price works through the thickness effect on the same geometry, and it applies to aluminium with the correction that reflectivity and conductivity make each step steeper.

When aluminium on the laser is the wrong choice

Thick plate is the first case. Above roughly 12 mm, a saw or a waterjet gives a squarer edge with no recast layer, and the laser's advantage disappears into a slow cut and a second finishing operation.

The second case is a tight bend in a high-strength temper. If the drawing calls for 6082-T6 with a 1 × thickness inside radius, no cutting route will save it; the alloy will crack. The fix belongs in the design, which is why aluminium sheet metal bending guidelines is the companion to this page.

The third is a decorative anodised part with a visible cut edge and an A-class finish requirement. We can cut it, but the edge will anodise differently and we will say so before the order rather than after the first batch. Where a project cannot accept that, the edge has to be machined, and the route changes.

For stainless parts on the same machine, laser cutting stainless steel for industrial parts covers the nitrogen and oxide questions; for copper and brass, laser cutting copper and brass covers why the reflectivity problem is worse there. The laser cutting and fabrication hub collects the rest, and the laser cutting cost estimator gives a first-pass material and machine split for an aluminium part before you ask for a quotation.