Laser cutting copper and brass: practical constraints

The metal that reflects the beam back

Copper absorbs about 4% of a 1,064 nm fibre laser beam when the surface is clean and cold. Put 12 kW into it and the work sees roughly 480 W, which is a small fraction of what a 2 mm mild steel cut needs. The cut works anyway, because the moment the surface melts and a keyhole forms, absorptivity climbs to the order of 60% and the same 12 kW becomes 7,200 W. Between those two states sits the pierce, and on copper the pierce is where the cycle time goes.

That single fact organises everything else on this page. Laser cutting copper and brass is not a question of whether the machine can do it, because a modern fibre laser can. It is a question of thickness, pierce count and what the edge has to do afterwards.

Brass behaves better than copper at the beam because zinc in the alloy raises absorptivity and lowers the melting range, and worse in every other way because zinc boils before the alloy melts. The two metals share a shop, a machine and a drawing pack, and they need different callouts on all three.

Copper versus brass at the beam

Pure copper conducts heat at 385–401 W/mK, which is roughly eight times mild steel. Energy deposited at the cut is carried away into the surrounding sheet almost as fast as it arrives, so the cut needs high power density and a tight focus rather than raw power spread over a wide spot.

Brass, typically 63/37 copper-zinc, conducts at around 120 W/mK and melts in the 900–940 °C range against 1,085 °C for pure copper. It cuts faster and pierces faster. The trade is metallurgical: zinc boils at about 907 °C, close to the melting point of the alloy, so the cut face loses zinc as it forms.

The pierce arithmetic on copper

Take a 2 mm copper earthing strip, 40 mm × 600 mm, with eight Ø6 mm holes and two slots. The contour is 1,280 mm and the eight holes add 151 mm, so the cut length including the slots is about 1,560 mm: at 3 m/min that is 31 seconds.

The eleven pierces are the problem. On 2 mm copper a pierce takes about 2 seconds, which is 22 seconds for the part, and each one is a controlled ramp from 480 W of absorbed energy to the 7,200 W the keyhole can use. If the parameters ramp too fast the beam reflects off a cold surface and the pierce fails; too slow and the material oxidises around the entry.

There are three ways to reduce the pierce count on a copper part, and they are all design decisions. Move holes into a slot where the function allows. Put the pierce outside the part envelope and lead in from the scrap, so each contour costs one pierce rather than one per feature. Or accept a drilled hole where the batch is small enough that a drill is cheaper than the laser time.

Remnant value: the nest is money here

A 1,250 × 2,500 mm sheet of 2 mm copper weighs 56 kg at 8.96 kg/m² per millimetre. That is about 1.14 times the mass of the same sheet in 2 mm CRCA, 56 kg against 49 kg, and several times the value per kilogram.

The consequence is that a poor nest on copper is expensive in a way that a poor nest on steel is not. A 20% loss on that sheet is 11 kg of copper, which is a bigger number on the job card than the cutting time. Copper remnants also have to be controlled by grade: C11000 offcuts cannot go back into a brass job, and mixing the two in one scrap bin means the whole bin is priced as mixed.

The practical rules that follow: nest copper jobs on their own sheet rather than filling the gaps with steel parts, keep a remnant register by alloy and temper, and record which part carried the remnant on the quotation so the next release can use it. How nesting reduces sheet metal cutting cost works the yield arithmetic on a mild steel bracket; on copper the same percentage loss costs several times more per kilogram.

Dezincification and what it does to a brass part

The cut face on brass is zinc-depleted. In a dry indoor application with a painted or plated finish, that is cosmetic. In a wet or marine environment it is the start of dezincification, where zinc is leached out of the surface layer and the remaining copper turns porous, so the part loses section from the face inward.

Two design responses work. Keep brass out of standing water unless the grade is a dezincification-resistant alloy, and specify a coating that covers the cut edge rather than only the visible face. Where the part is a marine fitting, the alloy choice matters more than the cut: a 63/37 brass is not a substitute for a DZR grade simply because the drawing calls for "brass".

The laser's contribution to this problem is the same as its contribution to every other: it produces an as-cut edge. Whether that edge is acceptable is a decision for the drawing, and it should be written there rather than discovered at first article.

Lead, RoHS and the grades to avoid

RoHS, Directive 2011/65/EU, restricts lead to 0.1% by weight in a homogeneous material. Copper alloys carry an exemption permitting up to 4% lead, which is why free-machining grades such as CuZn39Pb3, at roughly 3% lead, are still traded and used. The exemption is not a licence to use them everywhere: parts in contact with potable water have their own limits, and swarf from a leaded grade is kept separate so it never contaminates a non-leaded job.

The practical instruction for a drawing is simple. State the designation, not the word brass. A fabricator given "brass, 1.5 mm" will buy whichever grade is on the shelf, and the shelf grade may be leaded because it machines better even though the part is laser cut.

Beryllium copper is the other material to name explicitly. We do not cut it. Beryllium-bearing dust and fume carry a serious health risk, and the control measures are outside what a sheet metal shop should be improvising.

The three lines that decide a copper price

A copper part is priced from three things, and only one of them is the laser.

The metal is the first and largest. Copper is bought to grade and temper, and a half-hard C11000 strip is not interchangeable with an annealed sheet even where the drawing only says "copper". Ask which grade the quote is based on before comparing two prices, because the difference survives into the part.

The pierce count is the second. A copper part with fourteen holes is fourteen ramps from 480 W of absorbed energy to a stable keyhole, and that is where the machine time goes. A drawing that consolidates holes, or accepts one slot instead of four holes, can cut the cycle time by a third without changing the function.

The edge treatment is the third, and it is the line that is most often missing. As-cut copper has light dross at the exit face. If the edge feeds into a plating line or a lacquer, it needs deburring first, and that is a separate operation with its own handling risk on a soft metal.

Ask for those three lines separately and the quotation becomes comparable. Ask for a single price per part and the cheapest quote is usually the one that assumed an easier grade and no edge work.

Where the parts come from on a copper job

Most copper sheet metal parts are electrical. Busbar links, earthing strips, terminal plates, gaskets for RF enclosures, and the current-carrying parts inside a control panel. Brass is usually mechanical or decorative: hinges, nameplate blanks, marine fittings, instrument bezels, and trim.

That split decides the edge requirement. An earthing strip needs a clean, conductive edge and a hole pattern that matches the busbar it bolts to; a nameplate needs a cosmetic edge and a surface that will not be polished after cutting. Both are laser jobs at the thin end, and both are priced by different parts of the process.

Brass pressed components are a different route entirely. Where a brass part is a deep drawn or progressive-die item, the tool produces both the shape and the edge finish, and the laser only enters the process while the design is still moving. Copper and brass pressed components covers that route and the tooling economics.

What to put on the drawing

• The designation and temper: C11000 half hard, CuZn37, CuZn39Pb3, or the equivalent standard number.
• Thickness and its tolerance, stated with a unit; copper strip tolerances are not steel tolerances.
• The edge requirement: as-cut, deburred, or deburred and lacquered, with the faces named.
• Whether the cut edge will be plated, and if so which process, because the edge chemistry changes the pre-treatment.
• Hole callouts with the fit: clearance, tapped, or reamed after cutting.
• The RoHS or potable water statement if the part falls under either rule.
• Grain direction if the part is bent, because a half-hard copper strip cracks along a tight bend across the grain.
• Quantity and whether remnant stays with the customer or the supplier.

When the laser is the wrong tool for copper

Above roughly 3 mm on copper and 6 mm on brass, the cut slows enough that another process becomes the better buy. Thick copper busbar is often sawn, sheared or machined, and the resulting edge is better for a high-current joint anyway, because a laser-cut face is not a contact surface.

Mirror-finish and heavily polished decorative parts are the second case. Handling and the cut edge both spoil a polished face, and the part usually belongs to a polishing route rather than a cutting route.

The third is any part that needs a formed feature in the profile. A laser cuts a flat blank; it cannot press a louvre into a brass vent or coin a nameplate. Those are press jobs, and quoting them as laser jobs only moves the problem to first article.

Laser cutting copper and brass on our floor

Copper and brass run on the 12 kW fibre laser with the 40 ft × 16 ft bed, 12,192 × 4,877 mm, on the same floor as CRCA, mild steel, stainless and aluminium. Two 6 kW and two 3 kW machines take the smaller nests, and the 200 T, 5-axis press brake with a 4,450 mm bed handles forming where the part is bent after cutting.

The remnant is why the two materials are cut in one plant rather than split between suppliers. Running them in-house keeps the alloy separation in one register: a copper job does not share a scrap bin with a brass job, and the edge requirement for both stays on one drawing that the cutting and finishing teams read the same way.

Programmes run under ISO 9001:2015 and ISO 14001:2015, with first article inspection and PPAP documentation available. The copper, brass and aluminium fabrication page lists the materials and the handling rules. Where a job falls outside the thickness ranges above, we will say so at quotation rather than after the sheet is cut.

For the same reflectivity question in a softer metal, laser cutting aluminium sheet and plate covers the alloy and thermal expansion side. The laser cutting and fabrication hub collects the rest, and the laser cutting cost estimator gives a first-pass split of material and machine time for a copper part before you ask for a quotation.