How to Choosing Auxiliary Gases for Fiber Laser Cutting

During the laser cutting process, a laser is used as a heat source to melt or vaporize materials.
To cut the materials with a high-quality edge, an assist gas blows through a cutting nozzle on the laser cutting head. Then the molten material pushes out of the hot spot where the laser light is hitting the material. This area is known as the kerf.

The right assist gas can improve the edge quality and can increase the cutting speeds substantially for certain materials.
Additionally, the assist gas acts as a positive pressure within the head to protect the laser optics/lens from molten material spatter. This provides longer processing life with reduced maintenance.
There are several options for assist gas, and it is important to understand which to use for different applications and why.

Auxiliary Gases for Fiber Laser Cutting

Auxiliary gases used in fiber cutting machines are mainly including oxygen, nitrogen and air. Nitrogen is generally used to cut copper, aluminum, and stainless steel. The oxygen is generally used to cut carbon steel. When using air cutting, there a 10 kW air compressor is required, and a 7.5 KW dryer and a tertiary filter are required too.

1. Nitrogen (N₂)

Characteristics and Function:

• Nitrogen is an inert gas, meaning it does not react with the material being cut.
• It is commonly used for cutting stainless steel, aluminum, and non-ferrous metals.
• Nitrogen creates a clean, oxidation-free cutting environment, making it ideal for achieving smooth, high-quality cuts, particularly when surface finish is critical.

Advantages:

• Oxidation-Free Cuts: Nitrogen can blow away molten material while preventing oxidation reactions, resulting in clean, smooth finishes.
• Improved Cut Quality: Nitrogen produces fewer burrs and oxidation, which is crucial for applications where aesthetics and material properties are important.

Considerations:

• When using fiber laser cutters, nitrogen cutting tends to be more expensive than utilizing oxygen and compressed air, particularly in machines with power ranges from 1.5KW to 6KW. For illustration, in a 1.5KW fiber laser cutter, the operating cost for compressed air amounts to approximately 59 RMB per kWh, while for oxygen it is 50 RMB per kWh, and for nitrogen it skyrockets to 105.5 RMB per kWh—nearly double the cost of both oxygen and compressed air.
• Nitrogen is ideal for thinner sheets, but for thicker materials, the cost may become prohibitive.

2. Oxygen (O₂)

Characteristics and Function:

• Oxygen is an active gas that not only supports combustion but also blows away molten material, making it ideal for cutting carbon steel and mild steel.
• It accelerates the cutting process by providing an exothermic reaction that adds heat to the cutting zone.
• This results in faster cutting speeds, especially for thicker materials.

Advantages:

• Faster Cutting Speeds: Oxygen helps to speed up the cutting process by aiding the combustion of the material.
• Cost-Effective for Carbon Steel: Oxygen is often used for cutting carbon steel because it is more cost-effective compared to nitrogen.
• Improved Efficiency for Thick Materials: Oxygen is effective for cutting thicker materials (up to 20mm or more) because it provides additional heat.

Considerations:

• Oxidation: One of the main disadvantages of using oxygen is that it can lead to oxidation of the cut edges. While this is not an issue for all applications, it can be a concern for materials that require a clean, oxidation-free edge, such as stainless steel.
• Oxygen is also not recommended for non-ferrous metals (like aluminum and copper), as it can cause discoloration and affect the cut’s quality.

3. Compressed Air

Characteristics and Function:

• Compressed air is a readily available and inexpensive option for auxiliary gas during fiber laser cutting.
• It is typically used for cutting mild steel and non-ferrous metals.
• Compressed air is less reactive compared to oxygen but still helps remove molten material from the cut zone.

Advantages:

• Cost-Effective: Compressed air is much cheaper than both nitrogen and oxygen, making it a good choice for budget-conscious businesses.
• Ease of Use: Compressed air is readily available and does not require specialized equipment for storage or handling.
• Environmentally Friendly: Compressed air is a clean, non-toxic gas, making it an environmentally friendly choice.

Considerations:

• Lower Cut Quality: The cuts produced with compressed air tend to have more rough edges and can be less precise than those made with nitrogen or oxygen.
• Potential for Oxidation: Like oxygen, compressed air can cause oxidation, which may be undesirable in some applications.

Effect of gas and pressure on cutting quality

1) The cutting gas helps to dissipate heat and assist combustion, and blows off the melt to obtain a better quality cut section.

2) When the pressure of the cutting gas is insufficient, the following effects will be affected on the cutting quality: the melting will occur during cutting, and the cutting speed cannot meet the production efficiency.

3) When the pressure of the cutting gas is too high, the influence on the cutting quality: the cutting surface is rough, and the slit is wide; at the same time, the cut section is partially melted, and a good cutting section cannot be formed.

The effect of the pressure of the cutting gas on the perforation

1) When the gas pressure is too low, the laser does not easily penetrate the cut sheet, and the punching time increases, resulting in low productivity.

2) When the gas pressure is too high, the penetration point is melted to form a large melting point, which affects the quality of the cutting.

3) When laser drilling, a higher gas pressure is generally applied to the punching of the thin plate, and a specific punching method is adopted for the punching of the thick plate, thereby eliminating the disadvantage of the low air pressure to protect the lens.

4) When the laser cutting machine cuts ordinary carbon steel, the thicker the material, the lower the pressure of the cutting gas. When cutting stainless steel, the cutting gas pressure increases relatively with the thickness of the material.

In short, the choice of cutting gas and pressure during laser cutting must be adjusted according to the actual situation during cutting. In specific applications, different cutting parameters should be selected according to the specific conditions.

When oxygen is used to cut carbon steel plate, when the thickness of the thin plate is increased from 1 mm to 5 mm, the cutting pressure range is sequentially reduced to 0.1-0.3 MPa. , 0.1-0.2MPa, 0.08-0.16MPa, 0.08-0.12MPa, 0.06-0.12MPa;

And when the thickness of medium-thick carbon steel sheet is increased from 6mm to 10mm, the corresponding auxiliary gas pressure range is sequentially reduced to 0.06-0.12MPa, 0.05 -0.10 MPa, 0.05-0.10 MPa.

When a nitrogen (auxiliary gas) cut stainless steel plate (thickness increased from 1 mm to 6 mm), the cutting pressure was changed from 0.8-2.0 MPa to 1.0-2.0 MPa to 1.2-2.0 MPa, which was a high pressure cut.

Conclusion

Choosing the right auxiliary gas for fiber laser cutters is crucial for optimizing cutting efficiency, improving cut quality, and managing costs. While nitrogen provides clean, high-quality cuts, oxygen speeds up the process, and compressed air offers a cost-effective solution for less critical applications.

Different manufacturers might prefer different auxiliary gases. The best way to figure out the optimal setup is by gaining hands-on experience during actual processing.