In short: Use oxygen for thick carbon steel when an oxidised edge is acceptable, nitrogen when you need an oxide-free edge on stainless, aluminium or parts that will be welded or painted, and clean, dry compressed air for thin-to-medium material when edge colour is less critical and gas cost matters.
How each gas works
- Oxygen reacts with hot iron and adds energy to the cut, which is why it is used for thick carbon steel at relatively low pressure (source 4). The cut edge carries an oxide layer (source 3).
- Nitrogen is inert. It blows molten metal out of the kerf at high pressure and leaves an oxide-free edge. Atlas Copco gives roughly 8–14 bar for stainless steel; gas flow depends on laser power, nozzle diameter, cutting speed and thickness (source 1).
- Compressed air is mostly nitrogen with some oxygen. It can be produced on site with a compressor and dryer instead of buying nitrogen, but the edge is not as bright as a nitrogen-cut edge and the air must be clean and dry (sources 5, 6).
Comparison
| Oxygen (O₂) | Nitrogen (N₂) | Compressed air | |
|---|---|---|---|
| Typical materials | Carbon steel, especially thick plate | Stainless steel, aluminium, carbon steel needing clean edges | Thin-to-medium carbon and stainless steel, aluminium |
| Edge | Oxide layer (source 3) | Oxide-free, bright (source 3 notes dross can occur on mild steel) | Not as bright as nitrogen; may need prep before coating |
| Pressure | Low (source 4) | High; ~8–14 bar for stainless (source 1) | On request |
| Gas supply | Cylinders, bundles or bulk tank | Bundles, liquid tank or on-site generator | Compressor + dryer + filtration |
Choose by what happens to the part next
If the part will be welded, painted or powder coated, the oxide layer from oxygen cutting usually has to be removed first (source 3). Nitrogen edges go straight to the next process. Air sits in between: acceptable for many painted parts, but check with your coating supplier.
Assist gas cost: keep nitrogen consumption under control
Nitrogen consumption rises steeply with nozzle diameter and pressure. A 2022 study on stainless steel found that the best results came from the lowest workable pressure, and that quality cuts were still possible after reducing pressure by 2–3 bar without changing other parameters (source 2). Ask your supplier for a gas table per nozzle and pressure, and use it in the calculator.
Nitrogen generator for a laser, or bulk gas?
An on-site nitrogen generator replaces deliveries with electricity and maintenance; bulk liquid or bundles avoid the investment. The break-even depends on your annual consumption, required purity and pressure, and local gas prices — calculate it from your gas table and cutting hours.
Air cutting with a fiber laser needs clean, dry air
Moisture, particles or oil in the air damage cutting-head optics. ISO 8573-1 purity classes are the usual reference for specifying compressed-air quality (source 5); the exact class, dew point and pressure should come from the cutting head and machine manufacturer.
Frequently asked questions
Nitrogen, oxygen or air: which assist gas, and what does each cost per hour?
Oxygen for thick carbon steel where an oxide edge is acceptable; nitrogen for oxide-free edges on stainless, aluminium and parts to be welded or painted; clean, dry air for thin-to-medium material when gas cost matters. Cost per hour = gas consumption (from the supplier gas table for your nozzle and pressure) × your gas price.
Can I cut stainless steel with compressed air?
Yes, in the thin-to-medium range with enough laser power. The edge is slightly darker than a nitrogen-cut edge, which matters mainly on visible stainless parts.
Why does oxygen cut thick carbon steel well?
Oxygen reacts with the hot steel and adds energy to the cut, so thick plate can be cut at low gas pressure. The trade-off is an oxide layer on the edge.
Should I buy a nitrogen generator?
It depends on your nitrogen consumption and local gas prices. Calculate annual consumption from your supplier's gas table and your cutting hours, then compare bulk supply with a generator quote.
Sources
- Atlas Copco, compressors and nitrogen for laser cutting — nitrogen pressure for stainless, factors that drive gas flow — www.atlascopco.com (accessed 2026-10-20)
- FME Transactions (2022), “Optimization of nitrogen use efficiency in cutting of austenitic stainless steel by a fiber laser” — machinery.mas.bg.ac.rs (accessed 2026-10-20)
- University of Nottingham, “Investigations into fibre laser cutting” (thesis) — oxide layer on oxygen-cut mild steel, dross on nitrogen-cut edges — eprints.nottingham.ac.uk (accessed 2026-10-20)
- STYLECNC, “Laser cutting assist gas” — oxygen adds reaction energy; low-pressure oxygen cutting — www.stylecnc.com (accessed 2026-10-20)
- The Fabricator, “Purging the plenum for better laser cutting” — ISO 8573-1 as the reference for compressed-air purity — www.thefabricator.com (accessed 2026-10-20)
- Cormak, air compressors for fiber laser cutting — dry, oil-free air to protect optics — www.cormak.pl (accessed 2026-10-20)