Melt cutting
Melting cutting is 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 begin to evaporate internally, thus forming small holes. Such holes will further absorb the energy of the laser beam and melt the metal wall that protects them. At the same time, the auxiliary air flow coaxial with the beam takes away the molten material around the hole. With the movement of the workpiece, a slit can be cut on the metal surface.
Vaporization cutting
Vaporization cutting requires higher laser beam power than melting cutting. Under the irradiation of such a beam, the cut material can directly reach the boiling point without melting. In this way, the material can disappear in the state of steam, and the steam carries away the molten particles and scouring debris, thus forming holes. In the process of vaporization, about 40% of the materials disappear as steam, while another 60% of the materials are driven away by the air flow in the form of droplets, which will be blown away from the bottom of the slit as ejecta. In the process of processing, you may encounter many materials that cannot be melted, such as wood and carbon materials, which can be processed by this cutting process.
Oxidative melting
Melting cutting uses active gases such as oxygen as auxiliary gas flow. During cutting, the surface of the material is heated to the ignition temperature under the irradiation of the laser beam, and then a fierce combustion reaction occurs with oxygen, and a large amount of heat is released. This heat will heat the material to form a small hole filled with steam inside, and melt the metal wall surrounding the small hole.
The combustion rate of metal in oxygen is controlled by the transfer of combustion substances into slag, because the speed of oxygen diffusion through slag to the front of ignition will directly determine the combustion rate. The higher the oxygen flow rate is, the more intense the combustion reaction is. At the same time, the faster the slag is removed, and a higher cutting speed can be achieved. Of course, the higher the oxygen flow rate, the better, because too fast the flow rate may lead to rapid cooling of the reaction product at the slit outlet, that is, metal oxide, which is very detrimental to the cutting quality.
In this cutting process, there are two heat sources for the melting of metal, one is the heat generated by laser irradiation, and the other is the heat generated by the chemical reaction between oxygen and metal. It is estimated that when cutting steel materials, the heat released by oxidation reaction accounts for about 60% of the total energy required for cutting. Therefore, the combustion speed of oxygen and the moving speed of laser beam should be accurately calculated to achieve a perfect match. If the combustion speed of oxygen is higher than the moving speed of laser beam, the slit appears wide and rough. If the laser beam moves faster than the combustion speed of oxygen, the resulting slit is narrow and smooth.
Control fracture
Fracture control is to cut the material at a high speed and controllable by heating with a laser beam. This process is very effective for brittle materials that are easy to be damaged by heat. The specific process is: heating a small area of brittle material with a laser beam, 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 uniform heating gradient is maintained, the laser beam can guide the crack in any desired direction.
It is worth noting that this controlled fracture cutting is not suitable for cutting acute angles and corner edges. It is not easy to succeed in cutting super large closed shapes. Control the fracture cutting speed, and do not need too high power, otherwise it will cause the workpiece surface to melt and damage the cutting edge. The main control parameters are laser power and spot size.