Laser cutting process is divided into:
1. vaporization cutting:
When heated by a high power density laser beam, the surface temperature of the material rises to the boiling point temperature
The speed is fast enough to avoid melting caused by heat conduction, so some materials vaporize into steam and disappear, and some materials are blown away from the bottom of the slit as ejecta by the auxiliary gas flow.
2. melting cutting:
When the power density of the incident laser beam exceeds a certain value, the interior of the material at the beam irradiation point begins to evaporate and form holes. Once the hole is formed, it will act as a blackbody to absorb all the incident beam energy. The small hole is surrounded by the molten metal wall, and then the auxiliary air flow coaxial with the beam carries away the molten material around the hole. As the workpiece moves, the small hole moves horizontally and synchronously according to the cutting direction to form a cutting seam. The laser beam continues to irradiate along the front edge of the crack, and the molten material is blown away from the crack continuously or Pulsatively.
3. oxidation melting cutting:
Generally, inert gas is used for melting cutting. If oxygen or other active gas is used instead, the material will be ignited under the irradiation of laser beam, and another heat source will be generated due to intense chemical reaction with oxygen, which is called oxidation melting cutting. The specific description is as follows:
(1) Under the irradiation of laser beam, the surface of the material is quickly heated to the ignition point temperature, and then it has a fierce combustion reaction with oxygen, releasing a lot of heat. Under the action of this heat, a small hole filled with steam is formed inside the material, and the hole is surrounded by a molten metal wall.
(2) The combustion material is transferred into slag to control the combustion rate of oxygen and metal. At the same time, the speed of oxygen diffusion reaching the ignition front through slag also has a great impact on the combustion rate. The higher the oxygen flow rate, the faster the combustion chemical reaction and slag removal. Of course, the higher the oxygen flow rate, the better, because too fast the flow rate will lead to rapid cooling of the reaction product at the slit outlet, i.e. metal oxide, which is also detrimental to the cutting quality.
(3) Obviously, there are two heat sources in the oxidation melting cutting process, namely, the laser irradiation energy and the heat energy generated by the chemical reaction between oxygen and metal. It is estimated that when cutting steel, the heat released by oxidation reaction accounts for about 60% of the total energy required for cutting. It is obvious that higher cutting speed can be obtained by using oxygen as auxiliary gas compared with inert gas.
(4) In the oxidation melting cutting process with two heat sources, if the combustion speed of oxygen is higher than the moving speed of laser beam, the cutting gap appears wide and rough. If the laser beam moves faster than the combustion speed of oxygen, the resulting slit is narrow and smooth.
4. control fracture cutting:
For brittle materials that are easy to be damaged by heat, high-speed and controllable cutting by laser beam heating is called controlled fracture cutting. The main content of this cutting process is: the laser beam heats a small area of brittle material, causing large thermal gradient and serious mechanical deformation in the area, resulting in the formation of cracks in the material. As long as the uniform heating gradient is maintained, the laser beam can guide the crack in any desired direction.