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How to choose laser nozzles?

In the process of laser cutting, the laser nozzle is the most common wear and tear on the laser head, and it is also one of the most important parts in laser cutting. It is located at the bottom of the laser head and is closest to the workpiece. The focused laser and high-pressure air flow are emitted through the nozzle, so it plays a key role in the cutting process.

What is the function of laser nozzles?

  • Through the internal shape of the nozzle of the laser head, the airflow direction and air pressure of the high pressure air flow are adjusted to maintain the pressure between the workpiece and the nozzle. 
  • Prevent the melting material of the workpiece from splashing into the inside of the laser head, thereby protecting the internal lens of the laser head. 
  • The capacitance signal is provided to the height adjustment system, so as to ensure the stable operation of the height adjustment system.

Models and Characteristics of laser nozzles

ModelFeaturesApplication
Single layer1. Generally used for melting and cutting, using nitrogen or compressed air as auxiliary gas. 2. It is used for fine cutting with high precision and high surface requirements.Used for cutting stainless steel and aluminum alloy with nitrogen or compressed air
Double layer1. Generally used for oxidizing and cutting, using oxygen as auxiliary gas. 2. The effect of cutting carbon steel is remarkable by secondary convergence and compression of air flow.Used for oxygen cutting carbon steel and stainless steel, etc.

After passing through the inner core, the double-layer nozzle gas will go through the secondary expansion to increase the gas speed, and then reach the working face through the end hole. 

The advantage of this is that it can reduce the generation of shock waves and increase the speed of gas, thus improving the efficiency of gas participation in cutting, taking away slag and heat.

Matching of nozzle caliber and sheet thickness

PowerThickness(Carton steel)Auxiliary gasCaliber
<1500w1-3mmO2Double layer 1.2-2.5mm
<3000w1-3mmNitrogen or compressed airSingle layer 1.5-3.0mm
<6000w3-10mmO2Double layer 0.8-1.2mm
<12000w10-30mmO2Double layer 1.2-2.0mm

The larger the caliber of the nozzle is, the less the protective effect on the focusing mirror is. 

Therefore, the reasonable selection of the aperture size of the nozzle of the laser cutting machine can carry out the production more effectively.

Cautions

  • The caliber of the nozzle has a certain influence on the cutting speed, and the size of the nozzle also affects the pressure distribution at the exit. 

With the increase of the nozzle caliber, the HAZ becomes narrower due to the strong cooling effect of the jet flow on the base metal in the cutting area, but it will also lead to the slit being too wide, and the caliber of the nozzle will cause the difficulty of collimation, and the nozzle mouth is in danger of being cut off by the light beam, and the slit is too narrow, it will hinder the smooth discharge of molten slag at high cutting speed.

  • The distance between the nozzle and the workpiece directly affects the coupling between the airflow of the nozzle and the slit of the workpiece. 

If the nozzle is too close to the surface of the workpiece, it will produce a strong return pressure on the lens, which weakens the ability to disperse the material points produced by splash cutting, which has a negative impact on the cutting quality, but too far away will cause unnecessary kinetic energy loss. it’s also bad for effective cutting. 

Generally, the distance between the nozzle and the workpiece should be controlled at 1~2mm, and the cutting torches of modern laser cutting systems are equipped with inductive or capacitive sensor feedback devices to automatically adjust the distance between them within a predetermined height range.

What is a good laser nozzle?

  1. Make sure the material is good. 

Good nozzles must use TU2 copper, because of its high electrical conductivity, good thermal conductivity, so as to ensure a good capacitance signal. 

  1. It is necessary to have high machining precision. 

A good laser head nozzle, its concentric degree should reach 0.03mm, and the size of the sprinkler below 1.0mm, the concentric degree should reach 0.02mm. 

The nozzle with high precision and concentricity can not only reduce the early debugging in the machining process, but also effectively prevent the high-energy laser from hitting the inner wall of the laser head, thus avoiding damage to the laser head. 

  1. It is necessary to have a highly smooth surface of the laser head. 

The laser head nozzle has a roughness requirement of up to 0.8 on both the inner and outer surfaces. 

The outer surface of the highlight can effectively reduce the adhesion of the melt in the cutting process, thus prolonging the life of the nozzle, while the inner surface of the highlight can effectively avoid eddy current when the high-pressure gas flows out. 

Improve cutting quality and efficiency. 

  1. It is necessary to have strict anti-oxidation treatment. 

After processing, copper parts are easily oxidized and discolored when exposed in the air. 

After high-gloss processing, the inner and outer surfaces of the laser head nozzles are more likely to be oxidized, blackened and yellowed.

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