1. Vaporization cutting
In the process of laser vaporization cutting, the speed at which the surface temperature of the material rises to the boiling point temperature is so fast that melting caused by heat conduction can be avoided, 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. In this case, very high laser power is required. In order to prevent the material vapor from condensing on the slit wall, the thickness of the material must not be much greater than the diameter of the laser beam. This process is therefore only suitable for applications where the exclusion of molten material must be avoided. In fact, this processing is only used in very small application fields of iron-based alloys.
This process cannot be used for materials, such as wood and some ceramics, that are not in a molten state and are unlikely to allow the material vapor to condense again. In addition, these materials usually need to achieve thicker cuts. In laser vaporization cutting, Zui optimal beam focusing depends on material thickness and beam quality. Laser power and vaporization heat have only a certain influence on the position of Zui preferred focus. When the thickness of the plate is constant, the cutting speed of Zui is inversely proportional to the gasification temperature of the material. The required laser power density should be greater than 108w/cm2, and depends on the material, cutting depth and beam focus position. In the case of a certain thickness of the plate, assuming that there is sufficient laser power, the maximum cutting speed is limited by the gas jet speed.
2. Melt cutting
In laser melting cutting, after the workpiece is locally melted, the molten material is sprayed out with the help of air flow. Because the transfer of material only occurs in its liquid state, this process is called laser melting cutting.
The laser beam coupled with high-purity inert cutting gas makes the molten material leave the slit, and the gas itself does not participate in the cutting. Laser melting cutting can obtain higher cutting speed than gasification cutting. The energy required for gasification is usually higher than that required to melt the material. In laser melting cutting, the laser beam is only partially absorbed. Zui large cutting speed increases with the increase of laser power, and decreases almost inversely with the increase of plate thickness and material melting temperature. When the laser power is constant, the limiting factors are the air pressure at the slit and the thermal conductivity of the material. For iron and titanium materials, laser melting and cutting can obtain oxidation free cuts. The laser power density that produces melting but not gasification is between 104w/cm2 and 105 w/cm2 for steel materials.
3. Oxidation melting cutting (laser flame cutting)
Generally, inert gas is used for melting and cutting. If oxygen or other active gas is replaced, the material will be ignited under the irradiation of laser beam, and another heat source will be generated due to the intense chemical reaction with oxygen to further heat the material, which is called oxidation melting and cutting.
Because of this effect, for structural steel with the same thickness, the cutting rate obtained by this method is higher than that by melting cutting. On the other hand, compared with melting cutting, this method may have worse cutting quality. In fact, it will produce wider slits, obvious roughness, increased heat affected zone and worse edge quality. Laser flame cutting is not good for machining precision models and sharp corners (there is a risk of burning sharp corners). Pulse mode laser can be used to limit the thermal effect, and the power of the laser determines the cutting speed. When the laser power is constant, the limiting factors are the supply of oxygen and the thermal conductivity of materials.
4. Control fracture cutting
For brittle materials that are easy to be damaged by heat, high-speed and controllable cutting through 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 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 to produce in any desired direction.