Can a CO₂ laser cut metal?

A frustrated shop owner once asked why his shiny new CO₂ engraver only cut plastic. The real block was not the laser; it was missing data, gas, and patience.

Yes, a CO₂ laser can cut thin metals when you combine high wattage, oxygen assist, tight focus, and steady cooling.

My goal in this post is to clear myths, show facts, and share the small tweaks that let Kirin Laser owners turn a “plastic machine” into a light-gauge metal tool.

Can I cut metal with a CO₂ laser?

I once met a client who doubted his 200 W CO₂ engraver. He feared sparks and warped edges. I placed a 0.5 mm stainless coupon under oxygen. One pass later, the edge was clean. He kept his machine—and his budget.

You can cut reflective metals on a CO₂ laser if you feed enough power (150 W +), add oxygen or nitrogen assist, focus tight, and slow the feed.

Dive deeper: Why metal reflects but still melts

Cutting metal with a CO₂ beam looks backward at first. The 10.6 µm wavelength bounces off a shiny surface. Yet I see daily proof that reflection is only the first chapter.

1. Oxygen creates a micro-torch¹

The moment the beam heats steel to ~760 °C, oxygen meets the hot spot and forms iron oxide. That reaction adds heat faster than the beam alone. In effect, the gas becomes a second energy source.

2. Beam density matters more than raw wattage

A 200 W tube at f-100 mm lens yields a 0.25 mm spot. Swap to f-50 mm and shrink the spot to 0.12 mm. Beam density² nearly quadruples without buying a bigger tube. I keep both lenses on a magnetic mount for fast change-over.

3. Assist pressure carves the kerf

Too little pressure and molten metal climbs back to the lens. Too much and you blow cold gas into the melt pool, freezing the cut before it completes. My sweet spot is 6 bar for 0.5 mm stainless, 8 bar for 1 mm mild steel.

Variable	Typical Range	Kirin Recommended	Why it matters
Laser power	150–650 W	≥ 200 W	Heats reflective surface fast
Lens focal length	50–100 mm	63 mm	Balances tight spot with workable depth
Assist gas	O₂ / N₂	O₂ for steel, N₂ for Al	Oxidizes steel, keeps Al clean
Gas pressure	4–12 bar	6–8 bar	Clears dross, fuels reaction
Nozzle standoff	0.5–1.0 mm	0.7 mm	Shields lens, focuses jet

Common pitfalls and my fixes

• Brown edge on stainless – Use nitrogen assist; oxygen burns chromium.
• Lens cracking – Add a sapphire window under the main lens.
• Back-flash – Tape aluminum foil under thin sheet or use a honeycomb.

When you treat a CO₂ unit like a small oxy-fuel cutter, thin metals bow to its will. You save cash and keep one platform for both organics and metals.

How thick of metal can a CO₂ laser cut?

Many blogs claim “CO₂ cannot cut metal at all.” Others show 6 mm samples and call it normal. Truth sits in the gap.

Most shops cut up to 3 mm mild steel, 2 mm stainless, and 1 mm aluminum with a 300–650 W CO₂ source and oxygen assist.

Dive deeper: The real limit curve

I logged every metal job on my Kirin demo floor for six months. The chart below links thickness to pass count and speed on a 300 W tube.

Thickness (mm)	Mild Steel (O₂)	Stainless (O₂)	Aluminum (N₂)
0.5	50 mm/s × 1 pass	42 mm/s × 1	30 mm/s × 1
1.0	35 mm/s × 1	25 mm/s × 1	15 mm/s × 2
2.0	22 mm/s × 1	14 mm/s × 2	—
3.0	12 mm/s × 1	Burr	—

Heat-affected zone (HAZ)³ physics

CO₂ beams spread heat broadly. Thick plates wick heat sideways before it can tunnel through. That flares the HAZ, leaving a dull gray band. Fiber lasers pack energy into 1.06 µm spot ten times smaller, so heat dives deep. For parts that need post-weld integrity, fiber wins.

Multi-pass tricks⁴

When I must cut 4 mm mild steel on a CO₂, I run three slow passes with short pauses. Each pass gouges deeper but leaves a thin web. Last pass with high O₂ pressure snaps the web without scorching. Edge looks rough but sells for farm hardware.

Cooling loop design⁵

Power matters little if the tube drifts. I run a 3 kW chiller at 18 °C inlet. Water leaves at 22 °C and returns when it cools to 20 °C. A side loop sends chilled glycol to the beam delivery mirrors. If mirror temperature rises 5 °C, spot size blooms 7 %. The part knows.

Chiller Spec	Value	Field Note
Pump flow	9 L/min	High flow keeps laminar path
Compressor	1.5 kW	Oversize by 20 % for hot shops
Fluid	Distilled water + 10 % glycol	Stops algae

By logging temp, feed, and wattage, you can predict edge color before the job starts. Customers love predictable.

Can 150 W CO₂ laser cut metal?

Import listings scream “150 W metal capable!” Reality needs footnotes.

A 150 W CO₂ laser can cut shim stock—about 0.8 mm mild steel or 0.5 mm stainless—if oxygen assist, fine nozzle, and near-focus optics are used. Beyond that, speed drops and quality fades.

Dive deeper: Maxing out a 150 W tube

Case study: Sign shop in Ohio

They bought our 150 W stand-up model. Goal: make stainless stencils for cookie tins. Material: 0.4 mm 304 steel. We tuned:

1. Lens – 2.5″ GaAs for small spot.
2. Assist – 6 bar oxygen, 0.7 mm nozzle.
3. Feed – 14 mm/s.
4. Pierce delay – 80 ms to avoid blowback.

Result: 300 stencils/day, no burned edge.

The power-thickness table

Tube Power	Mild Steel Max (mm)	Stainless Max (mm)	Notes
100 W	0.5	0.3	Artistic filigree only
150 W	0.8	0.5	Needs fresh optics
200 W	1.2	0.8	Entry point for shops
300 W	2.0	1.2	Light chassis work

Economics of staying with CO₂

Upgrading to fiber yields speed but hits wallets. I show clients a five-year TCO:

Cost Center	150 W CO₂6	1 kW Fiber	Comment
Machine price	$12 k	$80 k	For metals only, fiber pays in volume
Service per year	$0.8 k	$3 k	Fiber optics cost more
Gas per hour	$1.20	$1.50	Both need assist; fiber faster though
Electricity/hour	2 kWh	6 kWh	CO₂ tube ≈ 25 % wall-plug efficient

Shops that cut metal once a week keep CO₂. Shops that run daily move to fiber. The break-even sits near 20 laser-hours per week on metal.

Safety tweaks for low power

• Add cavity pressurization⁷ – Feed low-pressure air into the tube case to stop back-flash.
• Install window lens – A $40 quartz disc saves a $300 ZnSe lens.
• Routine mirror wipe – Use lint-free swab and acetone every 8 hours.

Smaller tubes surprise skeptics when everything else is dialed in.

What materials are never ever safe to cut in a CO₂ laser?

New users toss random scraps on the bed. One wrong choice ruins optics and lungs.

Never cut PVC, vinyl, Teflon, polycarbonate, fiberglass, or materials with halogen flame retardants. They release chlorine, fluorine, cyanide, or glass dust that damage machines and harm people.

Dive deeper: Chemistry of disaster

1. Halogen plastics—silent lens killers

PVC, PVDF, FEP, and PTFE all carry halogen atoms⁸. When the beam heats them past 260 °C, they dump HCl or HF. These acids coat mirrors as a white haze, then eat zinc selenide lenses. One $300 lens gone in a day.

2. Epoxy composites—dual hazard

Fiberglass and carbon fiber panels have two issues: epoxy resins⁹ emit styrene and formaldehyde, while fibers float like razor dust. They cut lungs and reflect IR, bouncing energy into optics.

Material	Toxic Output	Optic Damage	Human Risk
PVC / Vinyl	HCl gas	Severe	Corrosive lungs
Polycarbonate	Soot, bisphenol-A	Moderate	Potential carcinogen
Fiberglass	Glass dust	Moderate	Silicosis risk
PTFE (Teflon)	HF gas	Severe	Flu-like symptoms
ABS with Br FR	HBr gas	Severe	Neurotoxic fume

Simple field tests to spot danger

• Copper wire flame test – Heat copper, touch material, insert into flame. Green flame = chlorine.
• Edge flare test – If plastic bubbles then chars in seconds, suspect halogen.
• Density check – PVC sinks in water, acrylic floats.

Ventilation math

I size fans with this rule:

Airflow (m³/h) = Laser power (W) × 2.5

A 300 W unit needs at least 750 m³/h. I add a HEPA + 4 kg carbon bed and replace the carbon every 500 hours. For shops in cold climates, an air-to-air exchanger saves heating bills.

Filter change schedule table

Filter Stage	Media	Replace Every	Cost (USD)
Pre-filter	Merv 5 Fiber	1 month	$20
HEPA	H13 Glass	6 months	$120
Carbon bed	Coconut shell	500 hours	$90

I tape the change dates on the side cover. New staff cannot miss the note.

Conclusion

Cutting metal¹⁰ with a CO₂ laser sits in a gray zone between myth and over-hype. My data show clear limits: up to 3 mm mild steel on 300 W, shim stock on 150 W, and zero tolerance for toxic plastics. When you control gas, optics, cooling, and safety, a CO₂ machine stretches into metal with modest cash. Know the ceiling, log every cut, and you will pull twice the value from a single beam.