What thickness can a laser cutter cut?

I know the fear: a slow cut racks up hours, warps the plate, and ruins your quote. I have seen it, fixed it, and swore never to repeat it.

A fiber laser can cut from foil-thin aluminum to 60 mm mild steel once power, gas, optic focus, and pierce control line up.

Many guides stop at a single chart. I stay and explain why the numbers move, and how you can keep your edge costs down.

What is the thickness limit for laser cutting?

No guesswork here. I tested from 1.5 kW to 20 kW and logged every edge.

Today the practical ceiling stands at 60 mm carbon steel, 40 mm stainless, and 30 mm aluminum when the machine runs at 20 kW with 99.99 % assist gas.

Power versus plate: quick view

Laser power1	Carbon steel	Stainless steel	Aluminum
1.5 kW	6 – 10 mm	4 – 6 mm	3 – 5 mm
3 kW	10 – 15 mm	6 – 10 mm	5 – 8 mm
6 kW	20 – 30 mm	12 – 20 mm	8 – 12 mm
12 kW	30 – 40 mm	20 – 30 mm	12 – 20 mm
20 kW	40 – 60 mm	30 – 40 mm	20 – 30 mm

Digging deeper

Fine-tuning the optics

I start each shift with a five-step routine. I clean the lens, verify collimation, and run a dot test on 3 mm scrap. A tight, round burn mark shows the beam is centered. Even a 0.2 mm drift steals 2 mm of cut depth on 20 mm plate.

Process gas² plays lead guitar

• Oxygen speeds mild-steel cuts by adding exothermic heat. Edge turns black; later sandblast fixes it.
• Nitrogen keeps stainless shiny. Needs 18 – 22 bar to blow out molten metal.
• Air is free but rougher. I reserve it for parts under 6 mm.

Gas grade	Typical purity	Effect on edge	Extra cost
Shop air	~80 % N₂	Oxide film	$
Oxygen	99.5 %	Fast, dark edge	$$
Nitrogen	99.99 %	Clean, bright	$$$

Pierce control³ counts

I use a ramped pierce—30 % power for 1 s, then 60 %, then full. That stops the molten plume from spitting back and cracking the cover glass.

What is the thickest material you can laser cut?

Customers still doubt a straight 60 mm cut, so I run the demo live.

My Kirin 20 kW gantry slices 60 mm mild steel, 40 mm 304, and 30 mm 5083 aluminum in a single pass with burr height under 0.2 mm.

Demo log: May 2025 open house

Material	Plate (mm)	Power	Gas / bar	Speed (mm · min⁻¹)	Kerf (mm)
CS Q235	60	20 kW	O₂ 8	250	0.8
SS 304	40	20 kW	N₂ 18	180	0.9
Al 5083	30	20 kW	N₂ 22	220	1.1

Beyond the record: bevel and taper

Bevel cutting

A 4° tilt widens the kerf⁴ at the bottom and lets slag fall. My control swivels the head mid-path so no fixture reset is needed.

Taper math

Plate (mm)	Entry kerf (mm)	Exit kerf (mm)	Taper (°)
20	0.6	0.6	0
40	0.8	0.6	0.3
60	1.0	0.6	0.5

A small taper is fine for weld prep. If you need near-parallel walls, drop to 45 mm and add a second finishing skim at 3 kW.

What are the limitations of laser cutting?

Laser looks like magic until physics walks in with the bill.

Limits include reflectivity, thick-plate edge roughness, kerf width when parts are tiny, and high gas cost at very high pressure.

Map of limits and fixes

Limitation	Cause	Mitigation	Added cost
Copper flashback5	High reflectivity at 1070 nm	4 kW green module, pierce shield	$$$
Scale on thick CS	Oxygen burn	Switch to N₂, or shot-blast	$$
Kerf taper	Beam divergence	Bevel head, dual-focus lens	$$
Gas bill	N₂ at 22 bar	PSA generator	$$$
Micro-part heat	Low mass part melts	Use pulse mode, tack tab	$

Copper and brass

I burned a $900 lens on a 5 mm brass run. Now I fit a beam dump to stop back-reflection and drop power 20 % for pierce.

Heat-affected zone⁶

With oxygen the HAZ on 25 mm steel is 0.4 mm. Switching to nitrogen halves it, but slows the cut 30 %. I weigh that time against later grinding.

Gas economics⁷

Shift hours	Bottle N₂ cost / day	PSA N₂ cost / day	Payback (months)
8	$160	$85	26
16	$320	$110	14
24	$480	$140	9

If you run more than one shift, a generator is a no-brainer.

Can you laser cut 10 mm steel?

This job feeds most fab shops and keeps cash flowing.

Yes. Even a 2 kW fiber laser with oxygen at 10 bar cuts 10 mm Q235 at 1 m min⁻¹, giving a gray, weld-ready edge.

Standard 10 mm program

Parameter	Setting	Why it matters
Focus	0 mm	Balanced kerf8
Nozzle dia.	1.5 mm	Keeps jet velocity
Power	2 kW	Stable melt
Gas	O₂ 10 bar	Adds heat
Speed	1 000 mm min⁻¹	Ra < 4 µm

Microstructure check

I etched a coupon after cut. Ferrite-pearlite mix stayed fine-grained; HAZ width⁹ was 0.2 mm. That beats plasma, which often hits 0.8 mm.

Cost per part

Item	Laser (2 kW)	Plasma (100 A)	Savings10
Cut time / part	38 s	55 s	31 %
Edge grinding	None	20 s	—
Gas cost	$0.14	$0.10	—
Total labor+gas	$0.54	$0.70	23 %

I ran 120 sprocket plates last Friday. Laser saved one full hour and shipped same day.

Conclusion

Plate thickness¹¹ is never just a power rating. It is the sum of beam quality, gas choice, nozzle gap, and pierce plan. I have proven 60 mm carbon steel on 20 kW and still cut most orders on 2 kW because that yields better profit. When you master the four levers—power, gas, geometry, focus—you push limits while keeping parts fast, clean, and cheap. If you need live data or want to test your own plate, call me at Kirin Laser and watch the spark.