The types of gases used in general cutting are oxygen, nitrogen and air, and different cutting materials require different types of auxiliary gases. Oxygen is mainly used for high-speed cutting of carbon steel and stainless steel plates, and oxidative cutting of highly reflective materials. Oxygen as an auxiliary gas can also burn metals, and use the oxidation reaction heat for high-efficiency cutting, but at the same time on the cutting surface. Oxide film is produced on the surface; nitrogen is mainly used for non-oxidative cutting of stainless steel plates and non-slag cutting of galvanized sheets; air is mainly used for non-slag cutting and ordinary non-metal cutting of aluminum and galvanized steel sheets. The assist gas pressure varies depending on the type of gas used, the material of the cutting material, the thickness of the plate, and the laser output form (CW/pulse). The size of the auxiliary gas pressure affects the adhesion of the slag, the quality of the cut surface, and the size of the heat affected zone. The nozzle outlet air pressure conditions during processing are as follows:
Under the premise of determining the type of auxiliary gas, the gas pressure is an extremely important factor. If the auxiliary gas pressure is too high, eddy current will form on the surface of the workpiece, which will weaken the ability of the airflow to remove the molten material, resulting in rougher cutting surface and more slitting. Width; if the auxiliary gas pressure is too low, the molten material at the slit is not blown, and dross is generated on the back side of the material to be cut. Therefore, there is a good value for the assist gas pressure. When cutting thin materials at high speed, high gas pressure is required to prevent slag from forming on the back of the slit; when the thickness of the material is increased, or the cutting speed is slow, the gas pressure should be appropriately lowered. Taking the stainless steel plate laser cutting as an example, during the cutting process, the auxiliary gas can cool the adjacent area of the slit, reduce the heat affected zone, and prevent the burning object from damaging the lens. In addition, nitrogen is used as an auxiliary gas, which makes the molten metal have good fluidity.
In actual processing, processing defects are caused by improper process parameters, and the reasons are complicated. Based on decades of laser cutting process experience, it is meaningful to summarize the countermeasures for cutting defects to guide actual production.