Laser cutting is a non-contact machining method that offers high energy and density control.
The laser beam is focused to form a high energy density light spot and has many advantages when used in the cutting process. Laser cutting mainly uses four different cutting methods to deal with various situations.
Fusion cutting
Laser fusion cutting partially melts the workpiece and ejects the molten material using airflow. Since the material transfer occurs only in the liquid state, the process is called laser fusion cutting. The laser beam is accompanied by a high-purity inert cutting gas that causes the molten material to exit the groove, and the gas itself does not participate in the cutting.
Laser fusion cutting achieves a higher cutting speed than gasification because the energy required for gasification is typically greater than the energy required to melt the material. In laser fusion cutting, the laser beam is only partially absorbed. The maximum cutting speed increases with laser power and decreases with increasing plate thickness and material melting temperature.
When the laser power is below a certain level, the limiting factor is the air pressure in the groove and the thermal conductivity of the material. Laser fusion cutting can create a non-oxidizing incision for iron, steel and titanium as there is melting, but it cannot achieve the laser power density required for gasification. For steel materials, this is in the range of 104W/cm 2 to 105 W/cm 2 .
Steam cutting
In the laser gasification process, the surface temperature of the material rises to the boiling point so quickly that it prevents melting caused by heat conduction. Some of the material vaporizes into vapor, while some of the material is expelled by the auxiliary gas flow from the bottom of the crack. This process requires very high laser power. To prevent material vapor from condensing on the slit wall, the thickness of the material should not exceed the diameter of the laser beam.
This process is only suitable for applications where there is a need to avoid removing molten material. It is only used in small areas for ferrous alloys and cannot be used for materials such as wood and certain ceramics that do not have a molten state and are therefore less likely to cause condensation in the material. Additionally, these materials generally require a thicker incision.
In laser gasification cutting, the ideal beam focus depends on the material thickness and beam quality. The laser power and gasification heat only have a certain effect on the ideal focus position. In the case of sheet thickness below a certain number, the maximum cutting speed is inversely proportional to the gasification temperature of the material. The required laser power density is greater than 108W/cm 2 and depends on the material, cutting depth and beam focus position.
Under certain sheet thicknesses, the maximum cutting speed is limited by the speed of the gas jet.
Fracture controlled cutting
Fracture-controlled cutting via laser beam heating is a controllable, high-speed cutting method for brittle materials prone to heat damage.
The main content of this cutting process involves heating the laser beam in a small area of the fragile material, causing a large thermal gradient and serious mechanical deformations in the region, which leads to the material cracking. As long as the balanced heating gradient is maintained, the laser beam can guide the cracks in any desired direction.
Oxidation Fusion Cutting （Laser Flame Cutting）
Fusion cutting generally uses an inert gas. If oxygen or another reactive gas is used, the material is illuminated under the irradiation of the laser beam and chemically reacts with the oxygen, producing another heat source that heats the material further. This process is called oxidation melt cutting.
Due to this effect, the cutting speed for the same thickness of structural steel is faster than that of fusion cutting, but the cutting incisions may be worse. It can produce wider cutting seams, obvious roughness, increased thermal impact zones and poorer edge quality.
Flame laser cutting is not suitable for machining precision models and sharp edges, as there is a risk of burning the sharp edges. Pulsed mode laser can be used to limit the effect of heat and the laser power determines the cutting speed.
In the case of a given laser power, the limiting factors are the oxygen supply and the thermal conductivity of the material.
Conclusion
These are the four most commonly used laser cutting methods, and users can determine the cutting plane based on the power of the cutting equipment, processing requirements and material characteristics.
