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Laser cutting plays a dominant role in metal processing today. High power beam sources, fiber delivery and highly automated peripheral material handling systems are the reasons for high cutting speeds, extreme accuracy and high productivity in both 2D and 3D applications.
Laser cutting is divided into three processes: Oxygen Cutting, Nitrogen Cutting (also called Clean Cutting) and Sublimation Cutting.
When cutting with oxygen, the material is burned and vaporized after being heated up to ignition temperature by the laser beam. The reaction between the oxygen and the metal actually creates additional energy in form of heat, which supports the cutting process. These exothermic reactions are the reasons why oxygen enables penetration of thick and reflective material when it is used as a cutting gas. In order to control the cutting process, it is essential to control the amount of exothermic reactions. Especially, when cutting thicker plate material, it is important to reduce the oxygen flow since otherwise, violent reactions will occur and reduces the cut quality. So in general, whenever oxygen is used as cutting gas for mild steel, the rule of thumb is: the thicker the material the lower the gas flow. Cutting with oxygen leaves a layer of oxides on the cut edge and can cause a reduction of alloying elements. It is predominantly used for cutting of carbon steels.
When cutting with nitrogen (or any other inert gas) the material is melted solely by the laser power and blown out of the cut kerf by the kinetic energy of the gas jet. Since these gases do not react with the molten metal and no additional heat is generated, the laser power required is usually much higher than cutting the same thickness in oxygen. Also the material is not overheated by exothermic reactions. This means higher pressure is needed to expel the molten metal out of the cut kerf. In nitrogen cutting, it is therefore required to use higher pressures as the material thickness increases. Cutting with nitrogen is used often for aluminum and stainless steel to achieve good edge quality and maintain corrosion resistance. However, it is also applied to carbon steels whenever subsequent painting or powder coating is required.
In Sublimation Cutting, the solid material is converted into vapor without passing through liquid phase, i.e. when cutting paper, wood or certain fabrics. |
