Laser cutting can be done with or without assist gas to help remove molten or vaporized material. According to the different auxiliary gases used, laser cutting can be divided into four categories: vaporization cutting, melting cutting, oxidation flux cutting and controlled fracture cutting.

 

(1)Vaporization cutting

A high-energy-density laser beam is used to heat the workpiece, causing the surface temperature of the material to rise rapidly and reach the boiling point of the material in a very short time, which is enough to avoid melting caused by heat conduction. The material begins to vaporize, and part of the material vaporizes into steam and disappears. The ejection speed of these vapors is very fast. While the vapors are ejected, part of the material is blown away from the bottom of the slit by the auxiliary gas flow as ejections, forming a slit on the material. During the vaporization cutting process, the vapor takes away the melted particles and washed debris, forming holes. During the vaporization process, about 40% of the material disappears as vapor, while 60% of the material is removed by the airflow in the form of molten droplets. The vaporization heat of the material is generally very large, so laser vaporization cutting requires large power and power density. Some materials that cannot be melted, such as wood, carbon materials and certain plastics, are cut into shapes by this method.Laser vapor cutting is mostly used for cutting extremely thin metal materials and non-metal materials (such as paper, cloth, wood, plastic and rubber, etc.).

 

(2) Melting cutting

The metal material is melted by heating with a laser beam. When the power density of the incident laser beam exceeds a certain value, the interior of the material where the beam is irradiated begins to evaporate, forming holes. Once such a hole is formed, it acts as a black body and absorbs all incident beam energy. The small hole is surrounded by a wall of molten metal, and then non-oxidizing gas (Ar, He, N, etc.) is sprayed through a nozzle coaxial with the beam. The strong pressure of the gas causes the liquid metal around the hole to be discharged. As the workpiece moves, The small hole moves synchronously in the cutting direction to form a cut. The laser beam continues along the leading edge of the incision, and the molten material is blown away from the incision in a continuous or pulsating manner. Laser melting cutting does not require complete vaporization of the metal, and the energy required is only 1/10 of vaporization cutting. Laser melting cutting is mainly used for cutting some materials that are not easily oxidized or active metals, such as stainless steel, titanium, aluminum and their alloys.

 

(3) Oxidation flux cutting

The principle is similar to oxygen-acetylene cutting. It uses laser as preheating heat source and oxygen or other active gas as cutting gas. On the one hand, the blown gas undergoes an oxidation reaction with the cutting metal and releases a large amount of oxidation heat; on the other hand, the molten oxide and melt are blown out of the reaction zone to form a cut in the metal. Since the oxidation reaction during the cutting process generates a large amount of heat, the energy required for laser oxygen cutting is only 1/2 of that of melting cutting, and the cutting speed is much greater than laser vapor cutting and melting cutting.

 

(4) Controlled fracture cutting

For brittle materials that are easily damaged by heat, a high-energy-density laser beam is used to scan the surface of the brittle material to evaporate a small groove when the material is heated, and then a certain pressure is applied to perform high-speed, controllable cutting through laser beam heating. The material will split along the small grooves. The principle of this cutting process is that the laser beam heats a local area of ​​the brittle material, causing a large thermal gradient and severe mechanical deformation in the area, leading to the formation of cracks in the material. As long as a uniform heating gradient is maintained, the laser beam can guide crack creation and propagation in any desired direction.Controlled fracture utilizes the steep temperature distribution generated during laser notching to generate local thermal stress in the brittle material to cause the material to break along the small grooves. It should be noted that this controlled break cutting is not suitable for cutting sharp corners and corner seams. Cutting extra large closed shapes is also not easy to achieve successfully. The cutting speed of controlled fracture is fast and does not require too high power, otherwise it will cause the surface of the workpiece to melt and damage the edge of the cutting seam. The main control parameters are laser power and spot size.