Laser cutting operates in continuous or repetitive pulse mode. In the cutting process, the laser beam is focused into a very small spot (the minimum diameter can be less than 0.1mm), which makes the focusing reach a very high power density (can exceed 106W/cm2). At this time, the heat input by the beam (converted from light energy) far exceeds the part reflected, conducted or diffused by the material, and the material is rapidly heated to the melting and vaporization temperature. At the same time, a high-speed airflow blows the melted or gasified materials from the lower part of the materials from the coaxial or non coaxial direction. With the relative movement of the beam and the material, the hole forms a narrow (0.1~0.3mm) slit to divide the material. In addition to the lens, it also has a coaxial nozzle, which can eject auxiliary air flow.
The characteristics of laser cutting can be summarized as follows:
1. The cutting quality is good, the geometric shape of the kerf is good, and the two sides of the kerf are nearly parallel and perpendicular to the bottom;
2. No slag sticking, narrow slit, small heat affected zone, basically no deformation of workpiece;
3.There are many kinds of materials that can be cut. Gas cutting can only cut low carbon steel, medium carbon steel and alloy steel with small Cr content, while laser cutting can cut metal, non-metal, metal matrix and non-metal matrix composites, leather and wood;
4. High cutting efficiency;
5. Non contact processing;
6. Low noise;
7. Low pollution.
Classification and mechanism of laser cutting
According to its mechanism, laser cutting can be divided into vaporization cutting, melting cutting, laser oxygen melting cutting and controllable fracture cutting.
(1) Vaporization cutting
The workpiece is rapidly heated to the boiling point under the action of laser, some materials escape in the form of steam, and some materials are blown away from the bottom of the cutting seam in the form of jet. The laser power density required by this cutting mechanism is generally about 10W/cm2, which is a cutting method for non melting materials (wood, graphite plastic, etc.).
(2) Fusing
The laser heats the workpiece to the molten state, and uses argon, helium, auxiliary gas flow, such as nitrogen, to blow the molten material away from the notch. The laser power density required for welding is generally about 107w/cm2.
(3) Oxygen assisted melt cutting
This method is mainly used for cutting metal materials. The metal is rapidly heated to above the ignition point by the laser, and has a violent oxidation reaction (combustion) with oxygen, releasing a lot of heat; Continue to heat the next layer of metal, the metal will continue to be oxidized, and the oxide will blow away from the gap with the help of air pressure. The cutting process can be summarized as preheating → combustion → slag removal. To realize laser oxygen melting cutting, the following processing conditions must be met.
The ignition point of the metal to be cut shall be lower than its melting point. For example, the ignition point of iron is 1350 ° C, 1500 ° C lower than its melting point. The melting point of the slag obtained shall be lower than that of the metal. For example, the melting point of iron slag is 1300~1500 ℃.
Burning can give off a lot of heat. For example, the heat energy released by iron burning in oxygen accounts for 60% of the total energy when iron is resistant to oxygen melting when cutting steel. The energy required for oxygen assisted melting cutting is 5% of that for vaporization cutting. It can be seen that the laser oxygen melting cutting mainly uses the heat released by the oxidation of steel and other metals in the cutting process to cut.
Source: Shanghai Panyun Technology
