Laser cutting machines use different auxiliary gases to cut different materials. The required pressure and flow rate of the auxiliary gas vary due to the thickness of the material to be cut. The air pressure of the auxiliary gas has a direct influence on the laser cutting result.
The laser working gas is used to produce the laser; the protective gas is used to protect the optics and drive the light gate. The laser working gas consists of helium, nitrogen and carbon dioxide gas. The ratio of the mixed gases is predetermined at the factory to ensure the best performance. The auxiliary gas not only blows the slag away in time but also cools the workpiece and cleans the lens. The choice of different auxiliary gases can alter the cutting speed and the surface quality of the kerf, which is of great significance for the cutting of special metals.
The auxiliary gases include oxygen, air, nitrogen and argon. Air and nitrogen are used as protective gases when cutting to prevent the generation of the oxide film; Argon is used for cutting titanium.
Compressed air is suitable for cutting aluminum, non-metallic and galvanized steel plates, which, to a certain extent, can prevent the generation of the oxide film and save costs. Usually, compressed air is put into use when the cutting plate is not very thick and the requirements for the surface quality are not too stringent. Besides, compressed air is often used in the production of chassis, cabinets and kitchenware made from metal plates.
Nitrogen is an inert gas that prevents oxidation of the cutting surface of the product during cutting and prevents burning (which easily occurs when the sheet is relatively thick. Nitrogen can be adopted for products with high requirements on the exposed cutting surface such as some decorative products and special parts for aeronautic uses.
Oxygen mainly plays the role of combustion supporter, which accelerates the cutting speed and enables the cutting of thicker plates. Oxygen is suitable for thick plate cutting, high-speed cutting and very thin plate cutting like some relatively larger and thicker carbon steel plates.
Increasing the gas pressure can add to the cutting speed, but after reaching a maximum pressure, further increases in gas pressure can result in a decrease in cutting speed. The presence of inhomogeneous pressures and temperatures in the airflow causes changes in the density of the airflow field. Such a density gradient causes a change in the refractive index within the field, which interferes with the focusing of the beam energy and then causes beam refocusing or divergence. This interference affects melting efficiency and sometimes it may alter the mode structure, resulting in poor cutting quality. If the beam divergence is too great, the beam spot will become too large to effectively cut the plate.