Assist gas is a critical part of metal laser cutting, alongside the laser source and optical system. Different gases have different chemical and physical behavior, so their operating pressures must be optimized for the material and cutting process.
· Oxygen (O₂): Supports an exothermic oxidation reaction and helps eject molten metal.
· Nitrogen (N₂): Provides a largely nonreactive cutting environment and ejects melt primarily through gas flow.
· Compressed air: Contains approximately 78% nitrogen and 21% oxygen; it combines aspects of both processes and can offer lower gas cost.
Choose the assist gas according to the material, required cut-edge quality, equipment configuration, and operating cost.
Once the laser melts the metal, high-velocity assist gas enters the kerf and drives molten material out through its lower opening. Sufficient gas momentum is required to overcome melt viscosity and surface tension, limiting the amount of material that resolidifies on the lower cut edge.
Assist gas exits the nozzle around the laser beam and helps keep splatter and fumes away from the cutting optics. It also affects local cooling and heat transfer, which can help limit undesirable heat accumulation and distortion under suitable conditions.
Nitrogen typically acts as a protective, non-oxidizing assist gas and relies on mechanical melt ejection. Oxygen, by contrast, reacts with iron during carbon-steel cutting and releases additional heat. Depending on the material thickness and process settings, this can increase achievable cutting speed; the source text cites a possible 40–50% improvement, which should not be treated as a universal value.
Property | Oxygen (O₂) | Nitrogen (N₂) | Compressed Air |
Cutting mechanism | Exothermic oxidation + melt removal | Melt removal + protective atmosphere | Partial oxidation + melt removal |
Typical cut-edge appearance | Black / dark gray oxide layer | Bright metallic finish under suitable conditions | Possible yellow or gray oxidation |
Cutting speed | Can be faster for some carbon-steel conditions | Depends on laser power and melt ejection | Intermediate; application-dependent |
Gas cost | Moderate | Relatively high | Often lowest supply cost, excluding equipment and energy |
Typical pressure range | 0.08–0.3 MPa | 0.8–2.0 MPa | 0.8–1.5 MPa |
Typical materials | Carbon steel, low-alloy steel | Stainless steel, aluminum alloys, brass | Carbon steel, aluminum, copper; cost-sensitive work |
Note: The ranges above are reference values from the source article, not universal machine specifications. Confirm the approved pressure range for the cutting head, gas circuit, nozzle, and specific process recipe.
More pressure does not automatically mean better cutting. Pressure that is either too low or too high can reduce cut quality.
Insufficient gas momentum may fail to expel molten metal fully. Material can resolidify on the lower cut edge and form dross or slag.
· Continuous or intermittent dross on the lower edge
· Rough cut surfaces with prominent striations
· In severe cases, resolidified melt bridging the kerf
· Longer piercing time or reduced process reliability
Excessive pressure may disturb gas flow and melt ejection. Depending on the nozzle and cutting conditions, it can also increase gas consumption without improving quality.
· Rougher surfaces or excessive kerf width
· Poorly formed edges or localized melting
· With oxygen, greater oxidation or darker cut surfaces in some conditions
· Higher gas consumption and operating cost
· Possible thin-sheet movement or deformation
Pressure trends depend strongly on the gas and material:
· Carbon steel cut with oxygen: Thicker sections may use lower oxygen pressure to control the oxidation reaction, depending on the process.
· Stainless steel cut with nitrogen: Thicker sheets often require greater gas flow or pressure to eject more molten material, within the machine’s limits.
These are useful starting tendencies, not strict rules. Final settings depend on thickness, available laser power, nozzle geometry, focus position, and delivered gas flow.
Optimize assist gas pressure together with power, speed, focal position, nozzle configuration, and actual gas delivery. Change one variable at a time during controlled test cuts.
1. Start with a pressure appropriate to sheet thickness (source examples: thin 0.20 MPa, medium 0.15 MPa, thick 0.10 MPa).
2. Reduce pressure in approximately 0.02 MPa increments and inspect dross formation.
3. If dross or incomplete cutting appears, restore the most recent satisfactory setting.
4. Check the edge for excess oxidation or burning. Do not assume pressure alone is responsible; also assess speed, focus, and power.
5. Verify quality at corners and small holes. Use corner-specific compensation only if supported and validated.
1. Start from the approved process recipe (source examples: thin 0.7 MPa, medium 1.0 MPa, thick 1.4 MPa).
2. Increase pressure in 0.1–0.2 MPa increments while checking lower-edge dross.
3. Continue only while quality improves; observe whether surface ripples or striations worsen.
4. Return to the best tested setting rather than automatically selecting the highest pressure.
5. Identify the point where additional pressure no longer improves quality and avoid unnecessary gas use.
1. Use an approved initial pressure within the source reference range of 0.6–1.2 MPa.
2. Increase pressure gradually while monitoring dross and through-cutting.
3. Check oxidation color and cut-face roughness against the required finish.
4. Prefer the lowest verified pressure that meets quality and production-stability requirements.
Symptom | Oxygen | Nitrogen | Air |
Dross at lower edge | Check pressure, purity, speed and focus; increase if deficient | Consider more pressure/flow or suitable nozzle | Check pressure and reduce speed if needed |
Excessive burning / dark edge | Check oxygen pressure and cutting speed | Check heat input and gas purity; not necessarily pressure-driven | Check oxidation and heat input |
Rough / rippled edge | Test lower pressure; verify focus | Test lower pressure and adjust focus | Test lower pressure |
Excessive kerf width | Review pressure and focus | Review pressure and focus | Review pressure and focus |
Incomplete cutting | Check power, speed, focus, gas delivery; pressure may help | Check gas delivery and cutting speed | Check gas delivery, speed and power |
Upward spatter | Review piercing/focus and nozzle selection | Check pressure, focus and nozzle | Check pressure, focus and nozzle |
Poor corner quality | Validate corner power/speed and pressure control | Validate corner settings; pressure direction depends on recipe | Validate corner settings; pressure direction depends on recipe |
Adjustment directions in this table are diagnostic starting points. Observe the actual cutting result before changing pressure; a single visible defect can have several causes.
Assist gas pressure is one of the most effective process variables for controlling dross and edge finish, but its optimal value lies within a material- and process-specific operating window.
1. Too little pressure may leave dross; excessive pressure can disrupt melt ejection and waste gas.
2. Source reference ranges: carbon steel 0.1–0.3 MPa; stainless steel 0.8–1.6 MPa; aluminum alloys 1.0–1.8 MPa; and brass 1.2–1.6 MPa (subject to the selected assist gas and equipment).
3. Pressure must be optimized together with laser power, cutting speed, focus offset, and nozzle geometry.
For repeatable production, build a pressure library for each material and thickness combination. A practical procedure is to start from a validated baseline, make incremental test cuts, inspect dross and surface finish, and return to the setting that provides the best stable results.