When it comes to laser cutting, the choice of assist gas plays a crucial role in determining the quality and efficiency of the cut. Oxygen and nitrogen are two of the most commonly used gases, each offering distinct advantages depending on the material and application. In this article, we’ll explore why assist gases are necessary for laser cutting metals, how they impact the cutting process, and the differences between oxygen and nitrogen. Understanding how to choose oxygen and nitrogen for laser cutting will help you make informed decisions and achieve the best results in your laser cutting project.
Laser cutting offers significant advantages in terms of high precision and speed when processing metals such as aluminum, carbon steel, and stainless steel. The process works by generating a high-energy laser beam that is focused onto the material’s surface. This beam rapidly heats and either melts or evaporates the material, creating a cutting path. Oxygen or nitrogen for laser cutting help blow away molten material and maintain a clean cutting area. Oxygen is typically used to accelerate cutting of carbon steel, while nitrogen is often employed to reduce oxidation and provide a smoother cutting surface.
Why Choose Laser Cutting for Metal?
Laser cutting produces very narrow cut widths with high precision, and the heat-affected zone (HAZ) generated during the cutting process is relatively small. This makes laser cutting particularly suitable for applications that require high precision and high-quality cuts. The quality of the cut is directly influenced by factors such as the laser beam power, focus quality, gas flow rate, and material properties.
Compared to traditional mechanical cutting methods (such as shearing, sawing, etc.), laser cutting offers several advantages:
- High Precision and Quality
Laser cutting can achieve micron-level precision, making it ideal for cutting complex contours and intricate details with superior quality.
- Non-Contact Cutting
Laser cutting does not require physical contact with the material, eliminating tool wear and preventing material deformation.
- Fast Cutting Speed
Laser cutting is faster, particularly for thin materials, which significantly increases production efficiency.
- Versatility
Laser cutting can process a wide variety of materials (including metals, plastics, wood, ceramics, etc.) with minimal variation in cutting thickness and shape.
- Automation and Flexibility
Laser cutting can be integrated with computer numerical control (CNC) systems, enabling efficient, flexible automated operations, especially suitable for large-scale production.
Why Laser Cutting Need Nitrogen or Oxygen?
Laser cutting with nitrogen and oxygen is essential for achieving high-quality and efficient cutting results. Here’s why these gases are important:
- Chemical Reactions to Improve Cutting Efficiency and Quality
Oxygen and nitrogen can react with the material being cut, enhancing the cutting process. Oxygen, for example, can accelerate the cutting of carbon steel by promoting an exothermic reaction, while nitrogen helps prevent oxidation, leading to cleaner, smoother cuts.
- Blowing Away Molten Material and Keeping the Cut Path Clean
The auxiliary gases blow away molten material from the cutting area, ensuring that the cut path remains clean and clear. This prevents build-up of slag or debris, which could affect the quality of the cut and the precision of the process.
- Cooling the Area around the Cut to Reduce Heat-Affected Zone
Nitrogen and oxygen can also help cool the area surrounding the cut, reducing the heat-affected zone (HAZ). This is particularly important for materials sensitive to heat, as it minimizes thermal distortion or material degradation.
- Protecting the Focusing Lens and Optical Components from Contamination
The gases act as a protective shield for the laser focusing lens and other optical components. By preventing the accumulation of combustion byproducts, they help maintain the performance and longevity of the optical system.
What Are the Auxiliary Gases for Fiber Laser Cutting Machines?
Oxygen:
Gas purity (≥99.95 Vol.%).
Oxygen is commonly used in laser cutting, especially for cutting carbon steel. It accelerates the cutting process by chemically reacting with the material (e.g., oxidation reaction), providing additional heat to increase cutting speed.
Nitrogen:
Gas purity (≥99.999 Vol.%).
Nitrogen is mainly used for cutting stainless steel and other materials, particularly when high surface quality is required. It prevents oxidation, reduces surface burning, and provides a smoother cutting surface.
Air:
Air quality standard: GB/T 13277-1991.
Air is used as an auxiliary gas in some basic cutting processes, particularly when high cutting precision is not critical. It helps blow away molten material, keeping the cutting area clean.
Oxygen vs. Nitrogen Laser Cutting – Which is best?
The choice and role of assist gases in laser cutting mainly depend on the properties and requirements of the material being cut.
1. Compressed Air
Air: Air is one of the most commonly used assist gases in laser cutting. Due to the high oxygen content in air, which easily triggers oxidation reactions, pure nitrogen or argon is often required when high-quality edge finishes are necessary. Air has the broadest applicability, suitable for cutting various materials such as carbon steel, stainless steel, aluminum alloys, as well as non-metals like wood and acrylic.
Air contains approximately 78% nitrogen and 21% oxygen, but its cutting efficiency is far inferior to oxygen and comparable to nitrogen. When air is used as the assist gas, a slight oxidation may occur on the cut surface, causing yellowing. The advantages of air are its low cost and easy availability; however, regular replacement of the air compressor filter is necessary to maintain cleanliness and avoid contamination of the optical components.
Best suited for: Applications where the material being cut is relatively thin, and the quality requirements for the cut edge are not very high. Commonly used in industries such as sheet metal enclosures, cabinets, and furniture.
2. Nitrogen
Nitrogen is the most commonly used laser cutting gas. It is mainly used for cutting materials such as stainless steel, aluminum alloys, and copper alloys. As an inert gas, nitrogen prevents oxidation reactions and blows away molten material, keeping the workpiece relatively cool and maintaining a clean, like-new cutting surface with superior quality.
Nitrogen requires high purity (especially for cutting stainless steel thicker than 8mm, where purity must reach 99.999%) and high pressure, typically around 1MPa. For stainless steel with a thickness exceeding 12mm or up to 25mm, the pressure needs to reach 2MPa or higher. Nitrogen is produced using industrial nitrogen generators, but it is less convenient to store than oxygen. Additionally, nitrogen consumption per unit time is typically higher than oxygen, making the overall cost of nitrogen cutting higher.
Best suited for: Applications requiring high-quality cut edges, effectively avoiding oxidation and ensuring the cutting surface remains clean and smooth.
3. Oxygen
Oxygen is primarily used as a combustion aid and is commonly applied to cutting thick plates of carbon steel and low-alloy steel or for high-speed cutting. Oxygen reacts with metals to form oxides, accelerating the cutting process and helping remove slag through high flow rates, thereby reducing slagging and blackening. It is suitable for processing thicker materials or situations with lower quality requirements. Among all assist gases, it provides the fastest cutting speeds.
Oxygen generally requires a purity of 99.5% or higher, with a pressure range of 0.3–0.8MPa. Using oxygen as an assist gas offers fast cutting speeds and relatively low costs; however, the cut edge tends to blacken or turn dark yellow.
Best suited for: Oxygen is used for cutting thicker materials, speeding up the cutting process, and improving efficiency.
4. Argon
Argon is mainly used for cutting materials like copper and aluminum, which have high thermal conductivity. It has excellent cooling properties, effectively reducing the heat-affected zone during the cutting process and improving cutting quality. Compared to nitrogen and oxygen, argon is more expensive.
Best suited for: Cutting metals that react with nitrogen, such as titanium and titanium alloys. Argon prevents oxidation and nitration during the laser cutting process, ensuring high-quality results.
Summary:
Choosing between oxygen and nitrogen for laser cutting metal depends on the material type and thickness:
When performing laser cutting, oxygen is ideal as an assist gas for cutting thick plates and high-speed cutting. Nitrogen, on the other hand, prevents oxidation in the cutting area, improving the cutting quality. Compressed air falls between the two, offering a balance between cost and performance.
For carbon steel, oxygen is recommended.
For stainless steel, nitrogen is preferred.
For materials prone to oxidation, like aluminum and aluminum alloys, argon may be considered.
When selecting the assist gas, it’s also important to consider both cost and cutting quality.
Which Assist Gas to Choose for Your Specific Project
Material: Choose the gas based on the material properties. For example, oxygen is suitable for cutting thick plates like carbon steel, while nitrogen is ideal for cutting non-ferrous metals such as stainless steel and aluminum.
Cutting Speed: Oxygen boosts cutting speed significantly, especially in thick plate processing, due to its combustion support. Nitrogen is better suited for more delicate cutting applications where precision is required.
Cutting Quality: If high-quality edges are required, nitrogen is recommended to avoid oxidation. If quality requirements are more general, oxygen can be used to enhance cutting speed.
Cost Considerations: Compressed air is the most cost-effective option, making it suitable for projects where budget is a priority. Nitrogen is more expensive but offers superior cutting quality, making it ideal for high-precision projects. Oxygen is a middle-ground option in terms of cost.
Post-processing Needs: If post-processing such as welding or painting is required, nitrogen is preferred as it reduces oxidation and impurities on the cut edges, helping to maintain quality during subsequent operations. If no post-processing is needed, oxygen can be used to speed up the cutting process and increase production efficiency.
Oxygen vs nitrogen laser cutting for metal depends on your project needs—whether you prioritize speed, cost, or edge quality.
In conclusion, choosing the right assist gas (whether oxygen or nitrogen) significantly impacts the efficiency, quality, and cost-effectiveness of the laser cutting process. Oxygen is the ideal choice for fast cutting of ferrous metals, providing cleaner edges and higher speeds, while nitrogen is better suited for non-ferrous metals, offering high-quality, burr-free cuts. By understanding the laser cutting with nitrogen and oxygen, you can enhance the cost-effectiveness of your laser cutting business.
