Sheet metal — steel, stainless, aluminum
Melt-and-blow / fusion cutting
Concept → operator
Oxy-fuel torch cutting
Melt-and-blow cutting — also called fusion cutting — is how a laser cuts metal. The beam melts a small spot of metal, and a stream of high-pressure assist gas through the nozzle physically blows the molten metal out of the cut. The gas isn’t cleanup here; it’s part of the cut. The big decision is which gas: oxygen reacts with the hot metal and adds heat, cutting faster and thicker but leaving an oxidized edge; nitrogen is inert and just ejects the melt, giving a clean, oxide-free edge but needing more laser power. This is not oxy-fuel torch cutting — there’s no fuel-gas flame, just the laser and the assist gas.
1 · What melt-and-blow cutting is
Most metal cutting on a laser works this way. The focused beam heats a spot on the metal to its melting point; the metal turns liquid; and a coaxial jet of assist gas — flowing through the same nozzle as the beam — blows that liquid down and out of the kerf. Move the beam along the path and the molten front travels with it, leaving a cut.
Two things make this different from vaporization: the material melts rather than boiling straight to gas, and the assist gas does mechanical work — without enough pressure, the melt just re-solidifies in the kerf as dross and the cut fails.
2 · Oxygen or nitrogen — the choice that sets your edge
The single most consequential setting in metal cutting is which assist gas you run, because it changes the physics of the cut, not just the cleanup:
| Oxygen (reactive) | Nitrogen (inert) | |
|---|---|---|
| What the gas does | Burns the hot metal — an exothermic reaction that adds energy to the cut | Only ejects the melt — no chemical reaction |
| Speed / thickness | Faster, cuts thicker for a given power (the reaction helps) | Slower, needs more laser power for the same thickness |
| Edge result | Oxidized edge (an oxide layer); fine for many parts | Clean, oxide-free edge — weld- and paint-ready |
| Typical use | Mild/carbon steel, speed-driven work | Stainless, aluminum, edge-quality work |
The trade in one line
Oxygen buys you speed and pays in a scaled edge. Nitrogen buys you a clean edge and pays in laser power. Match the gas to what the finished edge has to do next. More on assist gas & metal cutting
3 · The cut, step by step
- Focus. Optics bring the beam to a tight focal spot at the right depth for the material.
- Pierce. The beam first melts through the sheet at the start point to open the kerf.
- Melt. The beam heats the leading edge of the cut to a molten front.
- Blow. High-pressure assist gas ejects the melt down and out of the kerf.
- Travel. The head follows the path; the molten front and gas jet move with it, leaving a finished cut.
Cut quality is the balance of four dials — power, focus, speed, and gas pressure — against the material and thickness. These are typical starting points for a mid-power fiber cutter; you tune from there:
| Material | Assist gas | Thickness | Starting cut speed† | Gas pressure |
|---|---|---|---|---|
| Mild steel — for speed | Oxygen | 3 mm | ~3 m/min | ~0.4–0.6 bar |
| Mild steel — clean, thin | Nitrogen / air | 1 mm | ~20–25 m/min | ~10–12 bar |
| Stainless | Nitrogen | 3 mm | ~6 m/min | ~12 bar |
| Aluminum | Nitrogen | 3 mm | ~4 m/min | ~12–14 bar |
† Reference starting points for a ~2 kW-class fiber cutter, compiled from published fiber-laser cutting data (IPG-class laser-source charts and industry cut charts). Note how oxygen runs at low pressure and nitrogen at high pressure — that’s the mechanism, not a typo. Real numbers shift with power, material grade, optics, and nozzle; Boss sets the exact parameters for your machine and job.
See laser cutting parameters
4 · Clearing up a common mix-up: this is not torch cutting
Laser melt-and-blow ≠ oxy-fuel torch cutting
You’ll see “oxidation cutting” explained with a list of fuel gases — acetylene, MAPP, propane. That’s oxy-fuel torch cutting: a burning fuel-gas flame heats the metal and an oxygen jet cuts it, with no laser involved. It’s a different process, different machine, far coarser than a laser. In laser melt-and-blow, the laser beam is the heat source and the assist gas (oxygen or nitrogen) only ejects the melt. They both use oxidation, which is where the names blur — but don’t confuse the two. Everything on this page is about the laser process.
5 · What it cuts well
Melt-and-blow is the workhorse of metal cutting: mild and carbon steel, stainless, aluminum, and more, across a wide thickness range. Higher power reaches thicker material — a rough guide by fiber power class†:
| Material | Assist gas | 1.5 kW | 2 kW | 3 kW |
|---|---|---|---|---|
| Mild steel | Oxygen | ~12–15 mm | ~16–20 mm | ~20 mm |
| Stainless | Nitrogen | ~6 mm | ~8 mm | ~10 mm |
| Aluminum | Nitrogen | ~4 mm | ~6 mm | ~8 mm |
† Maximum clean-cut thickness, compiled from published fiber-laser cutting references. These are cut limits, not pierce limits, and the deepest cuts run slowest. Reflective metals (brass, copper) cut thinner and depend heavily on the machine; Boss confirms capability for your specific material.
As a rule, mild steel is cut with oxygen for speed and stainless/aluminum with nitrogen for a clean edge — but the right call depends on your parts. See metals for fiber cutting
Which mechanism cuts metal?
Metal melt-and-blow cutting is a fiber cutter job. (For very thick steel above about an inch, high-power CO2 can also cut — a different discussion.) Next in this series: see the full cutting process →
6 · FAQs
QWhat is oxidation or melt-and-blow cutting?
It’s how a laser cuts metal: the beam melts a spot and high-pressure assist gas blows the molten metal out of the cut. It’s also called fusion cutting. With oxygen the process is reactive (the gas burns the metal and adds heat); with nitrogen it’s inert (just ejecting the melt). This is how fiber lasers cut steel, stainless, and aluminum.
QOxygen vs nitrogen — what’s the difference?
Oxygen reacts with the hot metal, adding energy, so it cuts faster and thicker but leaves an oxidized edge. Nitrogen is inert and only ejects the melt, so it needs more laser power but leaves a clean, oxide-free edge for welding or paint. Choose by the metal and what the edge is for.
QIs this the same as oxy-fuel torch cutting?
No. Oxy-fuel torch cutting uses a fuel-gas flame plus oxygen, with no laser. Laser melt-and-blow uses the focused beam as the heat source and assist gas only to eject the melt — a different, far more precise process.
QWhat metals can it cut?
Steel, stainless, aluminum, and more across a wide thickness range. Mild steel is often cut with oxygen for speed; stainless and aluminum with nitrogen for a clean edge. Practical thickness depends on the laser’s power.
7 · Related in this series
Part of How Laser Cutting Works:
- Vaporization cutting — when material boils to gas instead of melting
- Controlled-fracture cutting — cutting brittle materials by cracking them
- Laser cutting, start to finish — the full process this fits into
- Fiber vs CO2 — which laser for metal
Keep learning
Understand the machine before you spec it.
Melt-and-blow is one piece of how laser cutting works. Browse the rest of the Learn library, or tell a specialist what you cut and we’ll help you find the right system.