FC Series
Copper · brass · aluminum
Buyer
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Copper, brass and polished aluminum are hard for a fiber laser because of two properties acting together: a large share of the ~1 µm beam reflects off instead of being absorbed, and these metals are excellent thermal conductors, so whatever energy does get in is pulled away from the cut zone fast. The ranking, stated once: copper is the hardest, brass is next, aluminum is easier than both — and all three are harder than stainless. The energy that bounces back up the optical path is back-reflection, which older machines genuinely feared; modern fiber systems include protection for it, which is why cutting copper is now ordinary work rather than a stunt. It remains strongly power- and machine-dependent.
1 · Why reflective metals fight you.
Two independent problems that happen to coincide in the same metals:
| Problem | What happens | Consequence |
|---|---|---|
| High reflectivity at ~1 µm | Much of the beam bounces off the surface rather than being absorbed | Less energy available to cut — and the reflected portion has to go somewhere |
| High thermal conductivity | Heat spreads out of the cut zone almost as fast as it arrives | Harder to reach and hold melting temperature where you need it |
It’s worth being clear about what is not the reason. Melting point is not the driver — copper melts at a substantially lower temperature than steel does, and steel is the easy metal here. Any explanation that rests on melting point has the physics wrong.
2 · The ranking — once, clearly.
From hardest to easiest, among the metals a shop actually handles:
| Metal | Reflectivity | Thermal conductivity | Verdict |
|---|---|---|---|
| Copper | Highest of the common metals | Very high | The hard case. Most demanding on power and machine |
| Brass | High | High | Easier than copper, still demanding — alloy composition matters |
| Aluminum | Moderate-to-high; worse when polished | Very high | Routine, but noticeably harder than stainless |
| Stainless | Low | Comparatively low | The easy, well-behaved reference point |
Surface finish matters within a metal, not just between metals: a mirror-polished sheet reflects substantially more than the same alloy with a mill or brushed finish.
3 · Back-reflection — what it actually threatens.
The energy that doesn’t enter the metal travels back up the path it came down: through the nozzle, through the focusing optics, toward the source. That’s back-reflection, and it is a real engineering problem rather than a marketing worry.
The history matters for reading old advice. On earlier fiber systems, back-reflection could damage the source, which is why plenty of documentation from that era simply prohibits cutting copper. Modern industrial fiber lasers are built with back-reflection protection and optical isolation, and that engineering is precisely why copper and brass moved from “don’t” to “routine.”
The nuance that matters when you’re buying
“Fiber lasers can cut copper” is true as a class statement and not automatically true of every machine or every power level. Protection is a designed-in feature, and capability on reflective material is specified per configuration. If reflective metal is part of your actual work, make it an explicit question about that machine at that power — not an assumption inherited from the category.
4 · What’s realistic — and why we’re not printing numbers.
Copper and brass are cut commercially every day. What’s fair to say:
- Thinner is much easier. Difficulty rises steeply with thickness on these metals — faster than it does on steel.
- Power matters more than it does elsewhere. The gap between a low-power and a high-power machine is far wider on copper than on stainless.
- Nitrogen is the normal choice, for a clean edge without oxidation.
- Expect a slower, more parameter-sensitive process than the same thickness in steel.
We hold published thickness figures for both metals and are deliberately not printing them: the brass data is single-source at the lower power classes and the copper data is single-source across every power class. That’s not a strong enough basis for a number someone might buy a machine against. Boss can give you a validated figure for a specific FC configuration — and on this material, that’s the only kind of number worth having.
5 · Silver and gold — briefly, because you’ll see them listed.
Articles about “reflective materials for laser cutting” routinely lead with silver and gold. Physically they belong on the list — both are highly reflective and highly conductive, and silver is the extreme case on both counts. Practically, essentially nobody is running sheet silver or gold on a fabrication laser: the material cost makes the kerf itself expensive, and precious-metal work is dominated by other processes entirely.
If you find a buying guide that spends equal space on gold as on stainless, it was written for search engines rather than for a shop.
6 · The alternatives, honestly.
If reflective metal is a small part of your work, a fiber laser is still the right machine and you’ll cut it. If reflective metal is your work, it’s worth knowing the alternatives exist: waterjet is entirely indifferent to reflectivity and conductivity, and mechanical processes like punching or shearing remain perfectly good for simple geometry in thin copper.
Choosing the laser anyway is a legitimate decision — the flexibility and the no-tooling advantage are real. It should just be a decision, not a surprise.
Ready to actually cut it?
Knowing why it’s hard is half of it. The other half is the four settings that decide whether the cut works — and the order to approach them in. How to cut reflective metal →
7 · FAQs
Frequently asked
Reflective Metals: the Honest StoryQWhy are reflective metals hard to laser cut?
Two properties together: much of the beam reflects off instead of being absorbed, and these metals conduct heat away from the cut zone very quickly. Copper is the hardest common case, brass next, then polished aluminum.
QWhat is back-reflection?
Beam energy reflected off a shiny workpiece travelling back up the optical path toward the head and source. It was a genuine risk on older machines — hence old advice prohibiting copper — and modern fiber systems include protection and isolation for it.
QCan a fiber laser cut copper?
Yes, routinely, on suitably equipped machines. It’s the most demanding common metal because it’s both the most reflective at fiber wavelengths and an excellent conductor. Capability is strongly power- and machine-dependent — confirm for the specific configuration.
QCopper or brass — which is harder?
Copper. More reflective and a better conductor, so it needs more power for a given thickness. Brass is easier than copper but harder than aluminum, which is harder than stainless.
QDoes a low melting point make metal easier to cut?
Not meaningfully. Copper melts well below steel and is far harder to cut. Reflectivity and thermal conductivity dominate; melting point is close to irrelevant by comparison.
8 · Related in this series.
Part of Fiber & Metal Cutting:
- How to cut reflective metal — the four settings that matter
- Which metals cut well — the full ladder with thicknesses
- Fiber vs. CO2 — why wavelength decides absorption
- Beam quality and M² — power density at the cut
Keep exploring
One idea leads to the next.
Metal cutting rewards getting the details right. Follow the rest of the series, or talk it through with someone who runs these systems.