Laser cutting is the use of a focused high-power-density laser beam to irradiate the workpiece, so that the irradiated material is rapidly melted, vaporized, ablated or reached the ignition point, and at the same time the molten material is blown away by the high-speed airflow coaxial with the beam, so as to realize the cutting of the workpiece. open. Laser cutting is one of the thermal cutting methods.
Laser cutting can be divided into four categories: laser vaporization cutting, #laser melting cutting, laser oxygen #cutting, and laser scribing and controlled fracture.
1. Laser vaporization cutting
The laser beam with high energy density is used to heat the workpiece, so that the temperature rises rapidly and reaches the boiling point of the material in a very short time, and the material begins to vaporize to form steam. These vapors are ejected at a high velocity, and at the same time as the vapors are ejected, incisions are formed in the material. The heat of vaporization of materials is generally very large, so laser vaporization cutting requires a lot of power and power density.
Laser vaporization cutting is mostly used for cutting extremely thin metal materials and non-metal materials (such as paper, cloth, wood, plastic and rubber, etc.).
2. Laser melting cutting
During laser melting and cutting, the metal material is melted by laser heating, and then a non-oxidizing gas (Ar, He, N, etc.) is sprayed through a nozzle coaxial with the beam, and the liquid metal is discharged by the strong pressure of the gas to form an incision. Laser fusion cutting does not need to completely vaporize the metal, and the energy required is only 1/10 of that of vaporization cutting.
Laser melting cutting is mainly used for cutting some materials that are not easily oxidized or active metals, such as stainless steel, titanium, aluminum and their alloys.
3. Laser oxygen cutting
The principle of laser oxygen cutting is similar to that of oxyacetylene cutting. It uses laser as a preheating heat source, and active gas such as oxygen as cutting gas. On the one hand, the blown gas interacts with the cutting metal to cause an oxidation reaction, releasing a large amount of oxidation heat; on the other hand, the molten oxide and melt are blown out from the reaction zone to form a cut in the metal. Because the oxidation reaction in the cutting process generates a lot of heat, the energy required for laser oxygen cutting is only 1/2 of that of fusion cutting, and the cutting speed is much higher than that of laser vaporization cutting and fusion cutting. Laser oxygen cutting is mainly used for easily oxidized metal materials such as carbon steel, titanium steel and heat-treated steel.
4. Laser scribing and controlled fracture
Laser scribing is to scan the surface of the brittle material with a high-energy-density laser, so that the material is heated and evaporated to form a small groove, and then a certain pressure is applied, and the brittle material will crack along the small groove. The lasers used for laser scribing are generally Q-switched lasers and CO2 lasers.
Controlled fracture is to use the steep temperature distribution generated during laser grooving to generate local thermal stress in the brittle material, so that the material is broken along the small groove.
features
Compared with other thermal cutting methods, laser cutting is generally characterized by fast cutting speed and high quality. Specifically summarized as the following aspects.
⑴ good cutting quality
Due to the small laser spot, high energy density and fast cutting speed, laser cutting can obtain better cutting quality.
① The laser cutting slit is thin and narrow, the two sides of the slit are parallel and perpendicular to the surface, and the dimensional accuracy of the cut parts can reach ±0.05mm.
② The cutting surface is smooth and beautiful, and the surface roughness is only tens of microns. Even laser cutting can be used as the last process without machining, and the parts can be used directly.
③ After the material is laser cut, the width of the heat-affected zone is very small, and the properties of the material near the kerf are hardly affected, and the deformation of the workpiece is small, the cutting precision is high, the geometry of the kerf is good, and the cross-sectional shape of the kerf is more regular rectangle. The comparison of laser cutting, oxyacetylene cutting and plasma cutting methods is shown in Table 1. The cutting material is 6.2mm thick low carbon steel plate.
⑵ High cutting efficiency Due to the transmission characteristics of the laser, the laser cutting machine is generally equipped with multiple numerical control workbenches, and the entire cutting process can be fully realized by numerical control. During operation, only need to change the CNC program, it can be applied to the cutting of parts of different shapes, both two-dimensional cutting and three-dimensional cutting can be realized.
⑶ Fast cutting speed
Using a laser with a power of 1200W to cut a 2mm thick low-carbon steel plate, the cutting speed can reach 600cm/min; when cutting a 5mm thick polypropylene resin plate, the cutting speed can reach 1200cm/min. The material does not need to be clamped and fixed during laser cutting, which not only saves tooling fixtures, but also saves auxiliary time for loading and unloading.
⑷ Non-contact cutting
There is no contact between the torch and the workpiece during laser cutting, and there is no tool wear. To process parts of different shapes, there is no need to change the “tool”, only the output parameters of the laser need to be changed. The laser cutting process has low noise, little vibration and no pollution.
⑸ Many types of cutting materials
Compared with oxyacetylene cutting and plasma cutting, there are many types of laser cutting materials, including metal, non-metal, metal-based and non-metal-based composite materials, leather, wood and fiber. However, for different materials, due to their own thermal physical properties and different absorption rates of laser light, they show different laser cutting adaptability. Using CO2 laser, the laser cutting performance of various materials is shown in Table 2.
⑹ Disadvantages Laser cutting Due to the limitation of laser power and equipment volume, laser cutting can only cut medium and small thickness plates and pipes, and as the thickness of the workpiece increases, the cutting speed decreases significantly.