Auxiliary gas for laser cutting
The simple schematic diagram of laser cutting is shown in the figure below. During the process, auxiliary gas is needed to blow away the slag in the cut, cool the surface of the processed object to reduce the heated area, and cool and protect the lens of the laser head. Auxiliary gases generally include oxygen, nitrogen, compressed air, etc., which directly affect the cutting performance, cutting speed, cutting thickness, etc. Different auxiliary gases need to be used according to the difference in cutting materials.
Oxygen (O2) as auxiliary gas
Oxygen is often used to cut thicker carbon steel materials. Because the heat of its chemical reaction with iron elements will promote the endothermic melting of metals, it can greatly improve the cutting efficiency. However, oxygen will cause the cut material to produce a significant oxide film on the cut end face, and will have a quenching effect on the material around the cut surface, increase the hardness of this part of the material, and have a certain impact on subsequent processing. The cut end face of the material cut by oxygen is black or dark yellow. Generally, carbon steel plates are cut with oxygen, punched at low pressure, and cut at low pressure. Oxygen is generally vaporized from liquid oxygen provided by the air separation plant, so the gas source quality is clean and no special treatment is required.
Nitrogen (N2) as auxiliary gas
When nitrogen is used as an auxiliary gas for cutting, a protective atmosphere will be formed around the molten metal to prevent the material from being oxidized, avoid the formation of an oxide film, and achieve non-oxidation cutting of the material. However, the cutting ability is not as good as oxygen, and the nitrogen consumption of nitrogen cutting is large, and the cutting cost is high. The non-oxidation cutting surface has the characteristics of direct welding, coating, strong corrosion resistance, etc., and the cut end face is white. Generally, nitrogen is used to cut stainless steel, galvanized sheet, aluminum and aluminum alloy, brass and other materials, with low pressure perforation and high pressure cutting. When cutting with nitrogen, the change of gas flow has a great impact on cutting. Under the condition of ensuring the cutting gas pressure, it is necessary to ensure that the gas flow is sufficient. Nitrogen is generally vaporized from liquid nitrogen provided by the air separation plant, so the gas source quality is clean and no special treatment is required.
Compressed air as auxiliary gas
Compressed air is easier to obtain than oxygen and nitrogen, and the price is very cheap. The air contains about 20% oxygen and about 78% nitrogen. The cutting efficiency is far less than that of oxygen cutting, but the cutting capacity is close to that of nitrogen, and the air cutting efficiency is slightly higher than that of nitrogen cutting. Due to the presence of oxygen, the end face of the cut is yellow. When there is no strict requirement for the surface color of the material cut, using compressed air instead of nitrogen cutting is the most economical and practical choice. It is generally used to cut sheet metal, aluminum plates, non-metallic and galvanized sheet materials. To a certain extent, it can reduce the oxide film and save the cost of use. It is one of the cutting gas sources that is increasingly used.
Compressed air can be obtained directly from an air compressor, but the air itself is not clean. After compression, the air contains a large amount of pollutants such as water, oil, and particulate matter. If the compressed air is impure, it will cause high pressure to spray onto the protective mirror of the laser cutting head, which will contaminate the protective lens (as shown in the figure), seriously affect the transmission of the laser beam, disperse the focus, and cause the product to be cut through, easy to have burrs (as shown in the figure), and the cutting surface is rough (as shown in the figure), and even produce waste. If it is a high-power laser cutting machine, as long as the protective mirror or nozzle surface is attached with a little bit of extremely fine oil film or water mist, it may cause high-energy laser emission to burn the laser head.
Therefore, continuous and stable clean compressed air is required to ensure the cutting effect and protect the laser cutting machine from damage. At present, the gas application in this industry can meet the required indicators (according to ISO 8573-1-2010 classification) as follows: the pressure dew point is not less than level 5 (3~7℃) (generally, the working conditions when the temperature is the highest throughout the year should be considered. In addition, in areas in the north where the temperature is below zero, if the pipeline is outdoor or long, the impact of the temperature on the compressed air should be considered), the particulate matter content is not less than level 2, and the total oil content is not less than level 2 (<0.1mg/Nm3, including the oil vapor part).