The nozzle plays an important role in the laser cutting process, so we will not repeat it here. However, we must know the role of auxiliary gas. In addition to slag removal, auxiliary gas also has the following three important roles in the cutting process:
1. It can accelerate the cooling speed of the side of the slit, reduce the heat affected zone of laser cutting, and facilitate the formation of a smooth cutting surface.
2. When oxygen is used as auxiliary gas, oxidation reaction can provide heat source to achieve thick plate cutting. However, due to the high viscosity of metal oxide, oxygen assisted cutting is mainly used for carbon steel.
3. When the inert gas is used as the auxiliary gas, it can protect the cutting surface from oxidation reaction, and at the same time protect the material properties in the cutting seam from changing, so as to form a uniform and clean cutting surface.
Tips: Generally, laser cutting nozzles are divided into single and double layers. Single layer nozzles are cut by dry melting, that is, air and nitrogen are used as auxiliary gases, which are usually used to cut stainless steel, aluminum alloy, brass, etc; The double-layer nozzle is generally used for oxidation cutting, that is, oxygen is used as auxiliary gas, which is usually used for cutting carbon steel.
What is a subsonic nozzle?
In terms of the brand, shape and model of the jettison nozzle, there are two main nozzle designs prevailing in the market at present: "low-speed nozzle" (the gas velocity is less than the sound velocity) and "high-speed nozzle" (the gas velocity is close to the sound velocity). The above two nozzles are "subsonic nozzles", because the gas velocity passing through the nozzle is less than the sound speed.
What is a supersonic nozzle?
By analogy, we can know that a supersonic nozzle is a nozzle whose gas velocity through the nozzle is greater than the sound speed. Its structure can be simply expressed as follows:
Why use supersonic nozzles?
【1】 Effect of oxide viscosity
In all the process parameters of laser cutting, the auxiliary gas pressure and gas flow characteristics are important factors affecting the cutting quality. When cutting thick steel plates, such as carbon steel, oxygen is used as an auxiliary gas, because the oxide viscosity of iron is low, it is easier to remove it from the notch.
Normally, although there is a thin layer of iron oxide on the side of the carbon steel laser cut, the quality of the carbon steel laser cut surface is acceptable in most cases. However, because stainless steel contains chromium, and molten chromium oxide has a high viscosity and is easy to adhere to the side wall of the incision, oxygen is also used as an auxiliary gas, and the processing quality of stainless steel is worse than that of carbon steel. If the gas pressure is not high at this time, it is difficult to remove these oxides.
The same problem occurs when cutting aluminum and titanium alloys, because molten aluminum and titanium oxides also have high viscosity. In order to obtain good cutting quality, the auxiliary gas must have higher pressure. In fact, Cr, Al and Ti alloys are difficult to cut.
【2】 Effect of slag viscosity in molten state
Laser cutting with inert gas as auxiliary gas can reduce the impact of the above problems to some extent. However, the inert gas usually needs to work in a very high pressure range of 8~25Bar, and the molten metal in the notch can only be taken away under the effect of airflow shear force. Because there is no oxygen in the air flow, metal oxides will not be formed in the incision. Generally, pure metal in the molten state has a much smaller viscosity than its oxides, which can be easily blown away, so it is easy to form a smaller heat affected zone and a more smooth and oxide free cutting surface.
Therefore, the special structure of the supersonic nozzle can convert almost all the pressure of the auxiliary gas into dynamic energy, blow off the slag, and achieve a more perfect laser cutting surface.
To sum up, users can choose whether to use supersonic nozzle according to the suggestions of after-sales engineers and the model of the purchased Ourui laser cutting machine. After all, the cutting effect of supersonic nozzle is very good.