A laser cutting machine is a process in which a laser beam emitted from a laser is focused into a high power density laser beam by an optical circuit system. The laser beam is directed to the surface of the workpiece, causing the workpiece to reach its melting or boiling point, while a high-pressure gas coaxial with the beam blows away the molten or vaporized metal. As the beam moves relative to the position of the workpiece, it eventually creates a slit in the material, which results in cutting.
Laser cutting processing is to replace the traditional mechanical knife with an invisible beam, with high precision, fast cutting, not limited to the cutting pattern limitations, automatic layout to save materials, smooth kerf, low processing costs and other characteristics. Laser cutting machine mainly has the following processes :
1. vaporization cutting:
In the high power density laser beam heating, the material surface temperature rises to the boiling point temperature of the speed is fast enough to avoid heat conduction caused by melting, so part of the material vaporized into steam disappears, part of the material as the ejecta from the bottom of the slit is blown away by the auxiliary gas stream.
2. Melting cut:
When the incident laser beam power density exceeds a certain value, the beam irradiation point where the material begins to evaporate, the formation of holes. Once this small hole is formed, it acts as a blackbody absorbing all the energy of the incident beam. The hole is surrounded by a wall of molten metal, and then an auxiliary air stream coaxial to the beam carries away the molten material around the hole. As the workpiece moves, the small hole is synchronized to move across in the cutting direction to form a slit. The laser beam continues to shine along the front edge of this slit, and the molten material is continuously or pulsatingly blown away from the slit.
3. Oxidative melting cutting:
Melt cutting generally use inert gas, if replaced by oxygen or other active gases, the material in the laser beam irradiation is ignited, and oxygen and intense chemical reaction and produce another heat source, known as oxidation melt cutting. Specific description is as follows:
(1) The surface of the material is quickly heated to the ignition temperature under the irradiation of the laser beam, followed by an intense combustion reaction with oxygen, releasing a large amount of heat. Under the action of this heat, small holes filled with vapor are formed inside the material, and the holes are surrounded by the molten metal wall.
(2) The transfer of combustion material into slag controls the combustion rate of oxygen and metal, while the speed of oxygen diffusion through the slag to reach the ignition front also has a great influence on the combustion rate. The higher the oxygen flow rate, the faster the combustion chemical reaction and the removal of slag. Of course, the oxygen flow rate is not the higher the better, because the flow rate is too fast will lead to the rapid cooling of the reaction products, i.e., metal oxides, at the exit of the slit, which is also unfavorable to the cutting quality.
(3) Obviously, there are two sources of heat 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 given off by the oxidation reaction is going to account for about 60% of all the energy required for cutting. It is clear that a higher cutting speed can be obtained by using oxygen as an auxiliary gas compared to an inert gas.
(4) In an oxidation-melting cut with two heat sources, if the oxygen burns faster than the laser beam moves, the cut appears wide and rough. If the laser beam moves faster than the burning speed of oxygen, the resulting slit is narrow and smooth.
4. Controlled fracture cutting:
For brittle materials susceptible to thermal damage, through the laser beam heating for high-speed, controlled cut off, known as controlled fracture cutting. The main elements of this cutting process are: the laser beam heats a small area of 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 balanced heating gradient is maintained, the laser beam can be guided to produce cracks in any desired direction.
