The application of air as an auxiliary gas in laser cutting.
In the daily production of laser cutting, the choice of assist gas is rarely a simple single-answer question. Oxygen combustion releases heat, significantly enhancing cutting performance with strong capability for thick plate cutting—particularly suitable for medium-thick carbon steel exceeding 6 mm thickness. It is the mainstream process for medium-to-low-power laser cutting of thick carbon steel. The cutting speed is moderate and stable, exceeding that of nitrogen-based cutting in this power range, while maintaining controllable heat-affected zones. Oxygen cutting is not recommended for thin carbon steel plates, stainless steel, aluminum alloys, workpieces requiring direct spraying/welding/electroplating, or precision components.
Pure nitrogen produces a bright, silver-white finish, yet the gas bill alone can make the financial controller frown. Compressed air - the gas least regarded as a "gas" - is quietly becoming the cost-saving weapon of choice in more and more sheet metal shops. Its cost is almost zero. Used correctly, it translates directly into profit; used poorly, it brings scrap and downtime.
The Working Principle of Compressed Air-Assisted Cutting
The cutting logic of compressed air is fundamentally different from that of oxygen or nitrogen. Oxygen cutting relies on the additional heat supplied by the iron-oxygen combustion reaction. Nitrogen cutting is purely physical melt ejection combined with inert gas shielding. Compressed air, in essence, is a high-pressure, clean airflow ejected at supersonic speed from the nozzle, accomplishing three tasks: blowing away molten metal, cooling the kerf, and-since it contains roughly 21% oxygen-providing a very mild oxidation reaction as an auxiliary boost.
There is a physical nuance here that is easily overlooked: the density and heat capacity of air differ from pure nitrogen. At the same pressure, the cooling effect of air is slightly weaker than that of nitrogen, because the presence of oxygen subtly shifts the thermodynamic properties of the gas stream. This results in a slightly larger heat-affected zone with air cutting. However, the benefit is that for thin sheets, the airflow is powerful enough to eject the molten slag cleanly without needing any extra chemical reaction.
Therefore, the fundamental nature of air cutting is purely physical removal + mild oxidation. It does not rely on oxygen combustion for speed, nor does it completely isolate the cut edge from oxygen as nitrogen does. This determines its kerf characteristics and its application boundaries.
Applicable Scenarios and the Cost Disruption
Air cutting is not a one-size-fits-all solution, but at the right price point, it can handle a large share of the work.
Using carbon steel as an example, the maximum plate thickness achievable by air cutting is directly proportional to laser power. Under identical unit conditions (in kW and mm), the values are nearly identical: a 6 kW system achieves a maximum air-cut thickness of 6 mm, while a 20 kW system reaches 20 mm.
For parts requiring subsequent welding, painting, or use as structural components, this oxide film fully meets the requirements. When the thickness exceeds 50% of the maximum thickness for carbon steel, air cutting remains feasible with superior speed compared to oxy-cutting; however, the oxide layer on the cutting edge becomes thicker, and noticeable burrs readily form along the cutting contour—the higher the plate thickness, the greater the burr height. Consequently, air cutting offers distinct advantages in quality, efficiency, and cost-effectiveness for thin carbon steel plates. For thick plates such as internal supports, base frames, or reinforcement ribs (which require no post-processing), air cutting is the most economical option.
Then there are stainless steel and aluminum alloys. On stainless steel, air cutting produces a blackened cut edge and is only suitable for applications with no surface finish requirement.
Laser cutting of aluminum alloys using air as the auxiliary gas produces fewer burrs and less slag adhesion compared to nitrogen, though it does not achieve "zero burrs." To attain near-zero burrs and eliminate oxidation, a nitrogen-oxygen mixture (a small proportion of oxygen combined with nitrogen) is recommended, which balances the "minimal burrs from air" with the "oxidation-free effect of nitrogen," resulting in extremely fine burrs suitable for direct welding.
The cost advantage of air cutting is undeniable. For a typical high-power laser cutting system operating continuously, the use of pure nitrogen as an assist gas can result in significant gas consumption — a single high-pressure cylinder may last only minutes under full load, and the monthly gas expense can easily reach a substantial portion of operating costs. Switching to liquid nitrogen improves the unit cost but still involves logistics and storage losses.
In contrast, the cost of compressed air includes only the electricity used to operate the compressor and maintenance expenses. When selecting a screw compressor with appropriate power output (not necessarily the larger one), the hourly electricity costs remain highly economical.
Three Critical Parameters Determining Air Cutting Quality
When using compressed air, the biggest fear on the shop floor is not slow speed but inconsistency. Yesterday's cuts were perfect; today, they are covered in burrs and black stains. Where is the root cause? Four parameters not being controlled.
1. Air Pressure Stability
During cutting, if the gas pressure fluctuates by more than 0.5 bar, the kerf will immediately show striations and attached dross. This isn't a nozzle problem-it's a gas supply problem. In factories, it's common to see pressure plunge when multiple machines simultaneously pierce. The solution is not to crank the compressor's output pressure to the maximum, but to install a sufficiently sized air receiver tank (typically sized at 20%-30% of the compressor's output in m³) and ensure piping pressure losses are under control.
2. Flow Rate Matching
The gas consumption for air cutting depends on the nozzle diameter and cutting gas pressure. A rough estimate shows that using a nozzle with a diameter of 3.0 mm and a pressure of 10 bar results in a consumption rate of 40 m³/h per unit; when three units operate simultaneously, the total gas consumption reaches 120 m³/h—exactly matching the full-load operating capacity of the PAB30 model (120 m³/h). Equipping multiple units with compressors that are too small will actually limit the nozzle's gas delivery capability, leading to substandard cutting quality.
3. Dew Point Control
This is where most failures occur. The compressed air coming out of the compressor is hot, wet, and oily. If it enters the cutting head directly, water vapor will condense on the protective lens. Hit by the laser beam, the lens fogs instantly and burns. Therefore, the pressure dew point must be kept at 3°C or below, ideally -20°C or even lower. This means that an air compressor must be followed by a refrigerated dryer and precision filters, and in high-humidity regions, a desiccant dryer is mandatory. Therefore, the pressure dew point must be kept at 3°C or below, ideally -20°C or even lower.
This requires connecting a refrigerated dryer and precision filter after the air compressor; in high-humidity areas, a refrigerated dryer with higher flow capacity must be installed to maintain stable dew point levels.
4. Control of oil content
The lubricating oil in screw compressors participates in the compression process, resulting in an oil content of 1–5 ppm in the exhaust gas. Higher oil levels impair laser cutting performance, increase the risk of lens burn, and elevate safety hazards; laser cutting requires an oil content ≤0.01–0.03 mg/m³ (≈0.01–0.03 ppm), ideally ≤0.001 ppm or direct use of oil-free equipment. To ensure economic efficiency and stability when employing screw compressors for laser cutting, a four-stage precision filtration system must be installed: C/T/A activated carbon to progressively remove water, particles, and oil mist. A refrigerated dryer with a pressure dew point ≤−20°C should be employed to minimize oil emulsification.
Drain daily, replace the filter element every 3 months, and clean the pipelines annually.
Long-term stable (recommended) oil-free air compressor: Oil content = 0, addressing the issue at its source; suitable for high-power units (6 kW+) mass production, such as the PAP series of fully oil-free air compressor from Raysoar.
Typical Kerf Characteristics and Acceptability
The carbon steel cut edge produced by air cutting exhibits a pale golden-yellow or light brown color. It feels smooth to the touch but, on close inspection, has a thin, dense oxide film. It is not the rough black scale of pure oxygen cutting, nor is it the bright white of pure nitrogen.
Can it be used directly? It depends on the downstream process. If the part is to be powder-coated, painted, or welded, this oxide film provides good adhesion and pre-weld grinding can be avoided. But if the customer drawing states "exposed surface, no post-treatment," then do not use air cutting-switch to mixed gas or pure nitrogen. Thus, the value of air cutting lies not in "looking good" but in "being good enough and cheap."
The Supporting Logic of Air Compressor and Post-Treatment System
At this point, a key conclusion emerges: Air cutting is not simply plugging a pipe into an air compressor; it's a system. This system must at least include:
screw air compressor → air receiver tank → refrigerated dryer → three-stage precision filters → piping → cutting head.
A refrigerated dryer plus precision filtration is a mandatory requirement, not an option. Without them, the oil-water mixture enters the beam path, burning the protective lens first, then the focusing lens. The cost of one such repair could fund the purchase of a dryer for many years. If the ambient humidity consistently exceeds 70%, a refrigerated dryer alone cannot pull the dew point down to -20°C. An adsorption dryer (desiccant dryer) must be added to push the dew point to -40°C or even lower.
The support that Raysoar provides starts right here: not just selling an air compressor, but based on your laser power, plate material, workshop humidity, and the number of machines running simultaneously, we specify the complete package-the compressor model, the receiver tank volume, the drying solution, and the filtration configuration-complete with a full set of parameter templates. You install according to the plan, you set the parameters, and the variables of the gas circuit are locked down.
One-sentence summary: Air cutting is the most underrated cost-saving process in laser processing, but its requirements for gas circuit cleanliness and stability are no less stringent than nitrogen cutting. Control the four parameters of pressure, flow, and dew point，oil content, and air becomes profit. Lose control, and air means trouble.
