Carbon dioxide laser cutting technology has been widely used in China's industrial production, and still has great potential in the field of cutting technology of high speed cutting and thick steel plate. Laser cutting process mainly includes fusion cutting, vaporization cutting, oxidation melting, and control fracture. Let's discuss the principles and characteristics of each of the four processes.
Fusion cutting is used to heat the material with an incident laser beam. When the power density of the laser beam exceeds a certain value, the irradiated part of the material will start to evaporate internally, thus forming a very small hole. Such holes further absorb the laser's energy, melting the metal walls it guards. At the same time, auxiliary airflow in line with the beam carries away the molten material around the hole. As the workpiece moves, a slit can be cut in the metal surface.
Vaporization cutting requires a higher power of laser beam than fusion cutting. Under such a beam, the material being cut can reach the boiling point directly without melting. In this way, the material can be lost in a state of steam, which carries away melted particles and scour debris to form pores. During vaporization, about 40 percent of the material is lost as steam, while another 60 percent is removed by the airflow in the form of droplets, which are then blown off the bottom of the slit as ejecta. In the process of processing, may encounter a lot of non-melting materials, such as wood and carbon materials, can be processed through this cutting process.
The oxidation melting
Fusion cutting is done using reactive gases such as oxygen as an auxiliary flow. When cutting, the surface of the material is heated to the temperature of the ignition point under the irradiation of laser beam, and then the intense combustion reaction with oxygen occurs, and a large amount of heat is released. This heat heats the material to create small holes filled with steam inside and melts the metal walls that surround the holes.
The rate of combustion of the metal in oxygen is controlled by the transfer of the combustion material into slag, because the rate of combustion is directly determined by how fast the oxygen diffuses through the slag to the ignition front. The higher the oxygen flow rate, the more intense the combustion reaction, and the faster the slag removal, the higher the cutting speed can be achieved. Of course, the higher the oxygen flow rate, the better, because too fast flow rate may lead to rapid cooling of the reaction product at the slit outlet, that is, the metal oxide, which is very bad for the cutting quality.
In this cutting process, the metal is melted with two heat sources, one from the laser irradiation and the other from the chemical reaction of oxygen with the metal. It is estimated that about 60% of the total energy required for cutting steel is released by the oxidation reaction. Therefore, the combustion rate of oxygen and the moving speed of laser beam must be calculated precisely to achieve a perfect match. If the oxygen burns faster than the laser beam moves, the slit appears wide and rough. If the laser beam moves faster than the oxygen burns, the resulting slit is narrow and smooth.
Control of fracture
Controlled fracture is a high speed, controlled cut off of the material by laser beam heating. This process is very effective for brittle materials which are easily destroyed by heat. The specific process is: the laser beam is used to heat a small area of brittle material, causing a large thermal gradient and serious mechanical deformation in the area, resulting in the formation of cracks in the material. As long as the heating gradient is balanced, the laser beam can guide the cracks in any direction needed.
It is worth noting that this kind of controlled fracture cutting is not suitable for cutting acute Angle and corner edge cutting seam. It is not easy to succeed by cutting off the oversize closed shape. The control fracture cutting speed is fast, does not need too high power, otherwise will cause the workpiece surface to melt, destroy the seam edge. The main control parameters are laser power and spot size.