What does assist gas do in laser cutting?
The laser beam melts the metal; the assist gas, blown coaxially through the nozzle, ejects molten material from the kerf, shields the cut and protects the focusing optics from spatter. Three gases are used:
| Assist gas | How it cuts | Typical result | Typical use |
|---|---|---|---|
| Oxygen | Exothermic reaction adds heat | Oxidised edge, good on thick mild steel | Thicker carbon steel |
| Nitrogen | Inert; pure melt ejection at high pressure | Bright, oxide-free edge | Stainless, aluminium, quality-critical work |
| Compressed air | Mostly nitrogen with about 21% oxygen | Light oxide film, often acceptable for paint or powder coat | Thin to medium mild steel, galvanised, aluminium, some stainless |
Air cutting is attractive because it avoids buying bottled or bulk nitrogen and, on thin sheet, can cut quickly. The trade-offs are a slight edge oxidation, possible burr on some materials, and higher demands on the air system than most workshop compressors meet.
Is my laser approved for air cutting?
Start with the laser maker. Air assist is approved for a specific combination of source power, cutting head, nozzle, material, thickness and cutting parameters. Ask the maker for:
- Whether the machine and head are approved for compressed-air cutting
- Required pressure at the machine connection, and at what flow
- Required air quality: pressure dew point, particle size, oil content, often stated as ISO 8573-1 classes
- The material and thickness range covered
- Where the pressure must be measured and under what operating state
Without this, any compressor quotation is a guess. A machine approved only for nitrogen and oxygen should not be switched to air simply because a compressor is available.
Pressure and flow: why laser air is demanding
Fibre lasers cutting with air commonly need high pressure at the head, so many installations use a dedicated high-pressure package in the 16 bar (232.1 psig) class, or a standard screw compressor followed by a booster. Flow depends on nozzle diameter and pressure: a larger nozzle at high pressure consumes far more air than a small one, and nozzle wear increases it further. Use the laser maker’s consumption figures for your nozzles and pressures.
- List the cutting recipes you will run on air, with nozzle size and pressure.
- Take the flow for each from the laser maker’s data, at stated reference conditions.
- Build a cycle profile: cutting time, piercing, idle and rapid moves.
- Add any other air users on the same supply, such as clamps and machine pneumatics, which often need a separate lower-pressure feed.
- Choose a source whose free air delivery at the required pressure covers the governing recipe with margin, plus a receiver to cover peaks.
Remember the energy cost of pressure: every extra bar costs about 7% more compressor power, so do not generate higher than the laser actually needs at its connection.
Air quality protects the optics
Water droplets, oil aerosol or particles that reach the cutting head contaminate the protective window and lens, cause burning and poor cut quality, and can damage expensive optics. Air-cutting packages therefore use a full treatment train:
- Aftercooler and water separator at the compressor
- Refrigerated dryer, typically about +3 °C pressure dew point, or a desiccant dryer where the laser maker asks for a lower dew point
- Pre-filter, coalescing filter and often an activated-carbon filter for oil vapour
- A final fine filter close to the machine, after the last length of pipe
Oil-free compressors remove one source of risk but still need drying and filtration. With oil-injected compressors, coalescing and carbon filters must be sized for the flow at high pressure and changed on time. In Indian summers, compressor discharge and dryer inlet temperatures rise; check that the dryer is still within its rating at 45 °C ambient, or the dew point will drift up.
Dedicated supply or shared plant air?
Most plant air systems run at 7–8 bar (101.5–116 psig), which is too low for air cutting. The common options are:
| Option | Advantages | Watch points |
|---|---|---|
| Dedicated 16 bar class package with dryer and filters | Simple, matched to laser, independent of plant | Must be sized on the governing recipe |
| Plant air plus booster | Uses existing compressor capacity | Booster inlet must stay dry and stable; plant demand affects laser |
| Raising whole plant pressure | No extra machine | Wastes energy across all users; usually not recommended |
A receiver on the high-pressure side close to the laser helps cover piercing and peak flow. Pipework must be rated for the pressure, short, and sized for low pressure drop, with the final filter immediately before the machine.
Sizing example: method, not a model
Suppose the laser maker states that the governing air recipe needs a given pressure at the machine inlet and a given flow in normal cubic metres per minute. Work back from the machine: add the pressure drop across the final filter, the coalescing and carbon filters at change-out condition, the dryer and the pipework. That sum, plus the regulator margin, sets the compressor discharge pressure. Convert the flow to free air delivery at that pressure and add any other users on the same package. Select a compressor whose rated free air delivery at that pressure covers the total, then size a receiver so that piercing and short peaks do not pull pressure below the requirement while the compressor responds. Finally, check the dryer and filter ratings at the actual pressure and at the hottest inlet temperature expected in summer.
Several lasers on one supply
When two or more lasers share one supply, combine their demand from their operating patterns, not by simply adding nameplate maximums or averaging. If all can cut thick material with large nozzles at the same time, size for that case or arrange the schedule. Install a pressure gauge or transmitter at each machine connection so that a pressure dip can be linked to a cut-quality problem.
Commissioning and troubleshooting
Before acceptance, confirm the source capacity, treatment and pipework, then measure pressure at the machine connection during the most demanding approved recipe, and check dew point and filter condition after a full shift. Utility acceptance and part acceptance are separate: the air may meet the specification while a recipe still needs adjustment by the laser supplier.
| Symptom | Possible air cause | Check |
|---|---|---|
| Dross or burr appears during long cuts | Pressure falling under sustained flow | Pressure at machine during the cut |
| Protective window contaminates quickly | Oil or water reaching head | Filters, drains, dew point |
| Problem only when another laser runs | Shared supply undersized | Log both machines together |
| Worse in afternoon in summer | Dryer overloaded by heat | Dryer inlet temperature and dew point |
If the air checks out, look at nozzle condition, focus, parameters and material batch with the laser supplier.
Cost per accepted part
Compare air cutting with nitrogen on cost per accepted part, not on gas cost alone. Include compressor energy in kWh, filter elements and dryer service, compressor maintenance, any extra edge preparation, scrap and rework, and the cutting speed achieved. On thin mild steel and aluminium air often wins; on thick stainless or where bright edges are required, nitrogen is usually still the right gas.
How Reddy Compressors helps
We supply new and used/refurbished high-pressure screw compressors, boosters, refrigerated and desiccant dryers, and filtration for laser cutting, from all major brands including ELGi, Atlas Copco, Ingersoll Rand, KAESER and Chicago Pneumatic, as an independent multi-brand specialist, not an authorised dealer. We have tie-ups with all major and reputed brands. Our engineers size the package from the laser maker’s requirements, measure pressure and dew point at the machine, and service and maintain the system through AMC or on call. Rental units are available from our own fleet while a permanent package is decided.
Fabrication shops across Hyderabad, Telangana and Andhra Pradesh are served by our 20+ service engineers and technicians from Tarnaka, Secunderabad, and we supply equipment and spares across India.
What to send us
- Laser make, model, source power and cutting head
- The maker’s air requirements: pressure, flow, dew point, particle and oil limits
- Materials, thicknesses and nozzle sizes you will cut with air
- Number of lasers and their working shifts
- Existing compressor, dryer and filter nameplates, if any
Frequently asked questions
Can any fibre laser cut with compressed air?
No. Air cutting must be approved by the laser maker for the specific machine, cutting head, nozzle and material range. Some machines are designed and set up for it; others are approved only for nitrogen and oxygen. Ask the maker for the required pressure, flow and air quality before buying a compressor, and confirm the approved materials and thicknesses for air assist.
What compressor pressure is needed for laser cutting with air?
Many fibre lasers cutting with air need high pressure at the head, so dedicated packages in the 16 bar (232.1 psig) class are common, or plant air is boosted. The exact pressure depends on the laser, nozzle and material, so take it from the laser maker’s data and measure it at the machine connection during cutting, allowing for losses in dryers, filters and pipework.
What air quality does a laser cutter need?
Laser assist air must be dry, oil-free and particle-free to protect the lens and protective window. A typical treatment train is an aftercooler and separator, a refrigerated or desiccant dryer, pre-filter, coalescing filter, activated-carbon filter and a final fine filter close to the machine. The laser maker usually states the required ISO 8573-1 classes.
Is air cutting cheaper than nitrogen cutting?
Often, for thin to medium mild steel, galvanised sheet and aluminium, because it avoids buying nitrogen and can cut fast. But it costs compressor energy, filter and dryer maintenance, and may leave an oxide film that needs attention on some jobs. Compare cost per accepted part, including speed, energy in kWh, maintenance and rework, against nitrogen for your actual mix of jobs.
Why is my laser lens getting dirty with air assist?
Usually oil aerosol or water is reaching the head because a coalescing or carbon filter is saturated, a drain has failed, or the dryer has lost dew point, often in hot weather. Check the filters, drains and dew point, and fit a final fine filter right at the machine. Spatter and wrong nozzle or focus settings can also contaminate the window.
Can I use my existing plant compressor for laser air cutting?
Only if it can deliver the required pressure, flow and quality at the machine. Most plant systems run at 7–8 bar, which is too low, so either a booster or a dedicated high-pressure package is needed. Raising the whole plant pressure wastes energy across every user. A survey of your existing compressor, dryer and demand will show which option fits.
Related pages
Calculators and worked examples
These tools give indicative figures for screening, comparison and for preparing an enquiry. They run in your browser and send nothing. No prices or tariffs are assumed: enter your own to see costs. Efficiencies and other figures shown are example values: replace them with your own. Results are not a performance guarantee or a design certificate; final selection is confirmed by a service engineer against the machine data sheet and the site.
Pressure budget and the cost of excess pressure
Add up the pressure that is lost between the compressor and the point of use, and see what a lower set-point would be worth.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Pressure needed at the point of use (bar g): 6
- Dryer and filter loss (bar): 0.5
- Piping loss (bar): 0.3
- Hose, fittings and regulator loss (bar): 0.3
- Control band and safety margin (bar): 0.3
- Current compressor set-point (bar g): 8
- Compressor input power (kW): 75
- Saving per bar reduced (%): 7
- Running hours per year: 6000
Result
- Total pressure losses: 1.1 bar
- Control band and safety margin: 0.3 bar
- Compressor pressure needed: 7.4 bar g (point of use + losses + band and margin)
- Possible reduction from current set-point: 0.6 bar
- Indicative energy saving: 18,900 kWh per year
- Indicative cost saving: Enter your electricity tariff (cost per kWh) above
Method. Required compressor pressure = point-of-use pressure + sum of losses. Savings = power × (reduction in bar) × saving per bar. A saving of roughly 6–8% of compressor power per bar of pressure is commonly quoted; it is indicative and varies with machine type and control, so edit it to suit.
What to take from it. The saving is real only if the farthest and most demanding point still works at the lower set-point. Prove it before you change the setting.
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 17 October 2026. How our engineering content is reviewed.
Flow and reference-condition conversion
Convert a flow quoted at one set of conditions to another, and between units. Different suppliers quote at different reference conditions, so always compare like with like.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Flow as quoted: 10
- Unit: m³/min
- Quoted at pressure (bar a): 1.013
- Quoted at temperature (°C): 20
- Convert to pressure (bar a): 1.013
- Convert to temperature (°C): 0
Result
- Converted flow: 9.32 m³/min
- 155.3 L/s
- 559.1 m³/h
- 329.1 cfm
Method. Q₂ = Q₁ × (P₁ / P₂) × (T₂ / T₁), with absolute pressure and absolute temperature. Dry-air basis; humidity is ignored. Unit factors: 1 m³/min = 16.667 L/s = 60 m³/h = 35.31 cfm.
What to take from it. A flow quoted at 20 °C and the same air quoted at 0 °C differ by about 7%. Check the reference conditions before comparing two machines.