Oxygen Compressor Selection for Fibre Laser Cutting: Pressure, Flow and Sizing Guide

Why Oxygen Assist Gas Matters in Fibre Laser Cutting

In fibre laser cutting of carbon steel, oxygen is not simply a stream of gas that blows molten metal out of the kerf. It participates in the cutting process directly: oxygen reacts exothermically with the iron in the steel, releasing additional heat that supplements the laser energy and dramatically increases the cutting speed and thick-plate capability. Without this exothermic contribution, cutting thick carbon steel with a fibre laser becomes significantly slower and more energy-intensive.

The quality and consistency of this exothermic reaction depends directly on two things: the purity of the oxygen assist gas and the stability of the delivery pressure at the cutting head. This is why compressor selection for a laser cutting installation is not simply a matter of picking a machine that “produces oxygen at the right pressure” — it requires understanding how pressure delivery behaviour and gas purity affect cut quality at the machine level.

Oxygen Assist Gas Pressure Requirements for Fibre Lasers

The oxygen assist gas pressure at the cutting head varies by application and material thickness. As a general guide:

The compressor outlet pressure must exceed the head pressure by enough to overcome distribution losses in the pipework between compressor and machine, and to allow for pressure regulator headroom at the machine. In practice, most laser cutting installations specify the compressor at 1.5 MPa (15 bar) to cover all thickness ranges and to provide sufficient regulator headroom. This is the standard specification for the ZW series machines we supply to this application.

⚠️ Always confirm the recommended assist gas pressure with your laser machine manufacturer. Different machine brands and cutting head designs have different requirements. The specification in their machine manual is the authoritative reference — not the general ranges above.

Gas Purity: What Fibre Laser Cutting Requires

The exothermic oxygen cutting reaction is sensitive to gas purity. Lower oxygen purity means a weaker and less consistent exothermic contribution, which manifests as:

• Increased dross on the cut edge, particularly on the bottom surface
• Slower cutting speeds on thick plate
• Inconsistent cut quality as purity varies (e.g., during PSA regeneration cycles)
• Oxidised discolouration extending further from the cut edge

Industrial laser cutting applications typically require oxygen purity of 99.5% or better. Standard PSA oxygen, which produces 93 ± 3% oxygen, is generally not suitable for high-quality fibre laser cutting — PSA oxygen is more appropriate for glass furnace combustion or water treatment where purity tolerance is wider.

Sources of 99.5% oxygen for laser cutting installations:

• Liquid oxygen vaporiser: Most common in larger operations. LOX is typically 99.5 – 99.9% purity. The vaporiser produces gas at approximately 0.1 – 0.4 MPa, which the booster compresses to 1.5 MPa.
• High-purity PSA or VPSA: Specialised PSA designs with additional purification steps can produce 99.5% oxygen — but at higher cost per Nm³ than standard PSA and at lower flow rates per unit size. Confirm purity specification with the PSA manufacturer.
• Cylinder supply: Suitable for small installations with few machine heads. As capacity grows, on-site generation with a booster becomes more economical.

Flow Rate Calculation for a Laser Cutting Installation

The oxygen consumption per laser machine head depends on the cutting head design, nozzle diameter, and the operating pressure. A typical fibre laser cutting head at 1.0 MPa consumes approximately 0.3 to 0.8 m³/min of oxygen at inlet conditions, depending on nozzle size and cutting mode.

For a multi-head installation, the required compressor flow is:

Total flow = (flow per head × number of heads) + 20% contingency

Example: 8 cutting heads, each consuming 0.5 m³/min

• Total peak demand: 8 × 0.5 = 4.0 m³/min
• With 20% contingency: 4.8 m³/min
• Specified compressor: ZW-5/15 (5.0 m³/min, 1.5 MPa) or LW-6/15 (6.0 m³/min, 1.5 MPa)

In practice, not all heads will run simultaneously at full demand. If your production schedule results in a maximum simultaneous demand of 60% of total heads, you can size more conservatively — but we recommend discussing your duty cycle with us before reducing from the peak demand calculation.

Why Moisture Control Is Critical for Laser Cutting Gas Supply

Moisture in the oxygen assist gas stream causes two problems in laser cutting:

• Spatter on the cut edge: Water vapour in the gas stream creates spatter deposits on the cut edge, particularly when the laser head is close to the workpiece surface. This requires post-cut cleaning and increases cycle time.
• Cutting head optic contamination: Water vapour that condenses on or near the cutting lens or protective window contributes to lens fouling and reduces lens life, increasing lens replacement costs and downtime.

The solution is an adsorption dryer between the oxygen source and the booster compressor inlet, reducing the dew point to −40°C or below before the gas enters the compression train. Our booster compressors have inter-stage coolers with moisture separators that remove condensed water at each stage — but they do not reduce the vapour content below the inter-stage temperature dew point. An upstream adsorption dryer is required to achieve the low dew points that laser cutting demands.

Specify the adsorption dryer for the maximum expected flow at the maximum expected inlet temperature — a dryer undersized for summer ambient temperatures will not deliver the required dew point during hot weather.

The Case for On-Site Compression vs Cylinder Supply

The economic break-even point between cylinder supply and on-site liquid oxygen with a booster depends on several variables: oxygen consumption per month, cylinder rental costs, delivery frequency, and the upfront capital cost of the booster system.

As a rough guide, installations consuming more than approximately 500 to 800 Nm³/month of 99.5% oxygen typically find that on-site liquid oxygen with a booster compressor is more economical than cylinder delivery over a 3 to 5 year horizon. The specific calculation depends on local liquid oxygen pricing and delivery costs.

We do not supply liquid oxygen or PSA generators, but we supply the booster compressors and can advise on the interface specification between any source gas system and our compressors. For a cutting centre considering the transition from cylinder supply to on-site generation, contact us with your current consumption and we can provide a compressor specification and indicative capital cost for comparison.

For full specifications on the ZW series range for laser cutting applications, visit our medium-pressure oxygen booster compressor page.