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Auxiliary Gas in Metal Cutting with Fiber Laser

Laser cutting is a thermal process. Laser power and auxiliary gas will significantly impact the overall quality and processing time. The most common gases are oxygen, nitrogen and compressed air. They are selected based on the type of material being cut, its thickness and the edge quality required.

Oxygen is often used as auxiliary gas to cut carbon steels. Oxygen can blow away the molten metal liquid (slag), and also react with carbon to release heat that can promote the melting of metal. Thus, oxygen significantly improves the processing power of laser. The cutting speed for a 1500 W laser using oxygen as an auxiliary gas in carbon steel could be the same for a 6000 watt laser without oxygen. The cutting surface of carbon steel will be significantly oxidized in the presence of oxygen. Besides, oxygen quenches the material around the cutting surface, which improves the hardness of the material.  

Nitrogen is generally used when cutting stainless or aluminum. Nitrogen can form a protective atmosphere around the liquid metal formed by laser heating, thus prevent the material from being oxidized to ensure the quality of the cut surface. This means that power determines cutting speed: more power enables higher speed. The large volume of nitrogen causes higher cutting costs than other gases. Liquid nitrogen can be used at relatively lower cost if the production yield is high. 

When cutting with air, the cutting section has an oxidation reaction due to oxygen. But, due to a large amount of nitrogen, oxidation reaction is not enough to enhance heat transfer, and the cutting ability will not be improved. Thus, air cutting effect can be understood as between nitrogen cutting and oxygen cutting. The advantage is that the cost of air cutting is low. All costs are the power consumption caused by air compressor to provide air, and the consumption of filter element in the air pipeline.

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