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As a green hand in laser cutting field, do you often feel a headache in the laser cutting process?

It seems that you have tried various plates, with various gases, various air pressures, different powers, etc… and then it seems that you’re still very confuse about it.

Then…, how to choose an auxiliary gas? ! ! !

  • What aspects of cutting quality will be affected by different gases? ! ! !
  • Which auxiliary gas should be selected for different plates?
  • How is the pressure of the auxiliary gas controlled?
  • Also, the purity requirement is…?

First of all, are you aware of the role of the auxiliary gas, what is it?

  1. Use the auxiliary gas to blow away the slag in the coaxial kerf
  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 cause the protective lens to overheat
  4. Some cutting gases can also protect the base metal.

 

Auxiliary gas types and characteristics

The auxiliary gases commonly used in laser cutting are nitrogen, oxygen and air.

Laser cutting auxiliary gas types

Suitable material for cutting for auxiliary gas

Since the auxiliary gases have corresponding characteristics for each of them, the materials suitable for cutting are also different.

Auxiliary gas purity standard

The laser processing of different materials requires the use of matching auxiliary gases.

Impurities in the auxiliary gas can damage the lens, causing fluctuations in the cutting power and also causing inconsistencies in the front and back cutting surface.

Oxygen purity standard Nitrogen purity standard

Auxiliary gas pressure standard

The amount of air pressure that can be used for various types of auxiliary gases is different.

Based on the characteristics of the gas, such as flammability and combustion, and various attempts, the following experience is obtained.

The auxiliary gas can prevent slag returning during the cutting process, thereby protecting the internal lens of the laser head.

That is to say, in the case where the processing power, the material, and the thickness of the sheet are the same, the larger the gas pressure, the more smoke dust that can be blown off at the unit speed.

Therefore, the higher the air pressure value used, the faster the laser cutting speed can be. This is why we use nitrogen when cutting thin sheets.

According to the above inference, the general rule of the cutting speed of the thin plate can be obtained:

Oxygen < Air < Nitrogen

The freshman can also use this rule as the basis for selecting auxiliary gases.

Note: Laser cutting of thick plates does not apply to the above general rules. The type of cutting gas to be targeted needs to be selected according to the characteristics of the individual sheets.

I believe that you have a preliminary understanding of some of the characteristics of the three auxiliary gases when you read here. Let’s take a closer look.

 

Oxygen

Mainly used for cutting carbon steel.

While the oxygen reaction heat is used to increase the cutting efficiency, the resulting oxide film increases the beam spectral absorption factor of the reflective material.

The end of the slit is black or dark yellow.

Mainly used for rolling steel, rolled steel for welding structure, carbon steel for mechanical construction, high tension plate, tool plate, stainless steel, electroplated steel sheet, copper, copper alloy, etc.

Its purity requirement is generally 99.95% or higher.

The main function is to help burn and blow off the cut melt.

The pressure and flow rate are different, which is inseparable from the size of the nozzle model and the thickness of the cutting material.

Generally, the required pressure is 0.3-1Mpa, and the flow rate varies according to the thickness of the cutting material. For example, cutting 22mm carbon steel, the flow rate should reach 10m3/h (including the protection oxygen of the double-nozzle).

Oxygen cutting surface

Nitrogen

Some metals use oxygen to form an oxide film on the cutting surface during cutting, and nitrogen can be used to prevent oxidation-free cutting of the oxide film.

Therefore, there is a feature that it can be directly welded, smeared, and has high corrosion resistance.

The end face of the slit is whitish.

The main applicable plates are stainless steel, plated steel, brass, aluminum, aluminum alloy, etc. The role is to prevent oxidation and blow off the melt.

There is a high requirement for the purity of nitrogen (especially stainless steel of 8mm or more, which generally requires 99.999% purity), and the pressure requirement is relatively large, generally about 1.5Mpa.

If you want to cut stainless steel of 12mm, or thicker to 25mm, the pressure is required to be 2Mpa or higher.

The flow rate varies depending on the type of nozzle, but generally it is large. For example, cutting 12mm stainless steel requires 150m3/h, while cutting 3mm requires only 50m3/h.

 

Air

Air can be supplied directly from the air compressor, so it is very cheap compared to 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 trace oxide film appears on the cut surface, but it can be used as a measure to prevent the coating layer from falling off.

The end of the incision is yellow.

The main applicable materials are aluminum, stainless copper, brass, electroplated steel sheet, non-metal and so on.

However, when the quality requirements of the cut product are high, aluminum, aluminum alloy, stainless steel, etc. are not suitable for air because the air will oxidize the base material.

In general, many gases are versatile. The key considerations are the cost of cutting and the requirements for the product.

For example, when cutting stainless steel materials, when the requirement for the quality or surface quality of the products is not high (for example, after the cutting the products need to be painted and through other processing process), air can be used as the cutting gas, which can reduce the cost.

When the cut product is the final product, there is no subsequent process, and it is necessary to use a protective gas, such as a craft product.

Therefore, in the process of cutting materials, it is necessary to select the auxiliary gas according to the characteristics of the product.