According to its mechanism, laser cutting can be divided into vaporization cutting, melting cutting, laser oxygen-assisted melting cutting, and controlled fracture cutting.
(1) Vaporized cutting
The parts are rapidly heated to the boiling point under the action of the laser, part of the material turns into steam and escapes, and part of the material is blown away from the cutting part as a jet. The laser power density required for this cutting mechanism is generally about 1W/cm2, which is a cutting method without melting materials (wood, graphite, plastic, etc.).
(2) Melt cutting
The laser heats the workpiece to a molten state, and the auxiliary gas flow of argon, helium, nitrogen, etc. coaxial with the beam blows the molten material away from the slit. The laser power density required for melting and cutting is generally about 10W/cm2.
(3) Oxygen-assisted melting and cutting
This method is mainly used for cutting metal materials. The metal is quickly heated by the laser to above the ignition point, and it undergoes a violent oxidation reaction (ie 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 be blown from the slit with the help of gas pressure Drop. The cutting process can be attributed to repeated preheating→combustion→slag removal. To realize laser oxygen-assisted melting and cutting, the following processing conditions must be met.
① The ignition point of the cut metal is lower than its melting point.
For example, the ignition point of iron is 1350°C, which is 1500°C lower than its melting point.
②The melting point of the generated slag should be lower than the melting point of the metal.
For example, the melting point of iron slag is 1300~1500°C.
③The combustion can release a lot of heat.
For example, the reaction formula of iron when cutting is
Fe+0.50,–Fe0+64. 3 cal/mol
2Fe+l 502 -+Fe, 0, +198.5 cal/mol
3Fe+20, -Fe, 0,+266.9 cal/mol
When oxygen helps to melt and cut steel, the heat energy released by combustion in oxygen accounts for 60% of the total energy. The energy required for oxygen-assisted melting and cutting is 5% of that of vaporized cutting. It can be seen that the laser oxygen-assisted melting and cutting is mainly carried out by using the heat released by the oxidation of steel and other metals in the cutting process.
