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How to choose auxiliary gas in the laser cutting process?

It seems that I have tried various plates, matched with various gases, various pressures, different powers, etc…, and then, it seems that there is still no accurate answer.

How to choose auxiliary gas?

What aspects of cutting quality will be affected by different gases?

Which auxiliary gas to choose for different plates?

How to control the pressure of auxiliary gas?

What is the purity requirement?

First of all, do you know the role of auxiliary gas, what exactly is it?

Laser cutting machines use different auxiliary gases to cut different materials. 
With the difference in the thickness of the cutting material, the pressure and required flow rate of the auxiliary gas are different, and the pressure of the auxiliary gas has a direct influence on the result of laser cutting. 
The main auxiliary gases that can be used by laser cutting machines are oxygen, nitrogen, air, and argon. The following describes their uses and characteristics for different auxiliary gases.

If you don’t know how to choose the auxiliary gas of the laser cutting machine, we have to understand the use of auxiliary gas and the role of auxiliary gas in advance.

1. Use auxiliary gas to blow away the slag in the coaxial slot

2. Cool the surface of the processed object to reduce the heat-affected zone

3. Cool the protective lens to prevent contamination of the lens and overheating of the protective lens

4. Some cutting gases can also protect the base material.

The choice of gas pressure and type has a great influence on the cutting process, and the choice of auxiliary gas type will have an impact on cutting performance, including cutting speed, cutting quality and many other aspects.

Air typeAdvantageWeakness
O21. An oxide film can be formed to improve the laser absorption capacity of high-reflective materials2. Cutting some oxidizable materials can improve the quality of the cut section (such as making the carbon steel section black and shiny)Combustion-supporting gas, easy to burn and return to slag
N21. Suppress the combustion gas, not easy to burn and not easy to return to slag2. After cutting, there will be corrosion resistance and other characteristics3. The maximum air pressure is relatively large, which can increase the cutting speed to a certain extentexpensive! ! !High purity requirements, large amount of cutting process
Air1. Low cost2. Micro oxide film will be formed on the cut surfaceCan also support combustion, easy to burn and return to slag, less than oxygen(It is not recommended to use when the product cutting requirements are relatively high)

Auxiliary gas suitable for cutting materials

Since the auxiliary gas has its own characteristics, the materials suitable for cutting are not the same.

Air typeSuitable Materials 
O2Carbon steel, high tension plate, tool plate, stainless steel, electroplated steel plate, copper, copper alloy, etc.
N2Stainless steel, electroplated steel plate, brass, copper, aluminum, aluminum alloy, etc.
AIRCarbon steel, aluminum, stainless copper, brass, electroplated steel plate, non-metal, etc.

O2:

  • Mainly used for laser cutting carbon steel. While the oxygen reaction heat is used to increase the cutting efficiency in a large format, the generated oxide film will increase the beam spectrum absorption factor of the reflective material. The cut end is black or dark yellow.
  • Mainly suitable for rolled steel, rolled steel for welding structure, carbon steel for mechanical structure, high tension plate, tool plate, stainless steel, electroplated steel plate, copper, copper alloy, etc.
  • The purity requirements are generally 99.95% or higher. The main function is to support combustion and blow off the cut melt. The pressure and flow are different, which is inseparable from the size of the nozzle model and the thickness of the cutting material. Generally, the pressure is required to be 0.3-1Mpa, and the flow rate is different according to the thickness of the cutting material. For example, when cutting 22mm carbon steel, the flow rate must reach 10m³/h (including the protective oxygen of the double-layer nozzle).

N2:

  • Some metals use oxygen to form an oxide film on the cutting surface when cutting, and nitrogen can be used to prevent oxidation film from appearing in oxidation-free cutting. Therefore, it has the characteristics of direct welding and painting, and strong corrosion resistance. The end face of the incision is whitish.
  • The main applicable plates are stainless steel, electroplated steel plate, brass, aluminum, aluminum alloy, etc. The role is to prevent oxidation reaction and blow off the melt.
  • There are very high requirements for the purity of nitrogen (especially stainless steel above 8mm, which generally requires a purity of 99.999%), and the pressure requirement is also relatively large, generally about 1.5Mpa, if you want to cut more than 12mm, or thicker to 25mm For stainless steel, the pressure must be 2Mpa or higher. The flow varies according to the nozzle model, but they are all very large. For example, cutting 12mm stainless steel requires 150m³/h, while cutting 3mm only needs a flow below 50m³/h.

AIR:

  • Air can be provided directly by an air compressor, so the price is very cheap compared with other gases. Although the air contains about 20% oxygen, the cutting efficiency is far less than that of oxygen, and the cutting ability is similar to that of nitrogen. A small amount of oxide film will appear on the cut surface, but it can be used as a measure to prevent the coating layer from falling off. The end face of the incision is yellowed.
  • The main applicable materials are aluminum, stainless copper, brass, electroplated steel plate, non-metal and so on.
  • However, when the quality of the cutting product is high, aluminum, aluminum alloy, stainless steel, etc. are not suitable for air, because air will oxidize the base material.

Purity standard of auxiliary gas

The laser processing process of different materials needs to use matching auxiliary gas. The impurities in the auxiliary gas will damage the lens and cause fluctuations in the cutting power. At the same time, it will also lead to inconsistencies in the front and back of the cutting.

Air typePurity(%)Water vaporHydrocarbon
O299.95<5 ppm<1 ppm 
N299.995<5 ppm<1 ppm 

Auxiliary gas pressure standard

During the cutting process, the auxiliary gas can prevent slag return and protect the lens inside the laser head.

In other words, under the same conditions of processing power, material and sheet thickness, the greater the air pressure, the more smoke and dust can be blown off per unit speed.

Therefore, the higher the pressure value used, the faster the laser cutting speed can be. This is why we usually use nitrogen when cutting thin plates on the fly cutting.

Air typeO2AIRN2
Maximum air pressure<1 Mpa1.8 Mpa2.0 Mpa

The general law of the cutting speed of thin plates can be obtained:

Oxygen < Air < Nitrogen

In the above content, many gases can be used universally, and the important thing is to consider the cutting cost and the requirements for the product.

For example, when cutting stainless steel materials, when the quality or surface quality of the product is not very demanding, such as painting and other processing procedures in the later stage of cutting the product, air can be used as the cutting gas, which can reduce a lot of costs. When the cut product is the final product, and there is no follow-up process, it is necessary to use a protective gas, such as a craft product. Therefore, in the process of cutting materials, the auxiliary gas must be selected according to the characteristics of the product.

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