The principle of laser cutting and the interaction mechanism between laser beam and material
**1. Energy absorption of laser beam**
When a laser beam is irradiated onto the surface of a material, photon energy is absorbed by the material, and the main mechanisms include:
**Electronic excitation:** Free electrons in metallic materials absorb photon energy, transition to high energy levels, and convert the energy into lattice vibrations (thermal energy) through electron phonon interactions.
**Multiphoton absorption:** The valence band electrons of non-metallic materials (such as plastics and ceramics) may transition to the conduction band through multiphoton absorption processes, leading to material ionization or chemical bond breakage.
**Reflection and transmission:** Metal surfaces have high reflectivity for lasers (especially infrared lasers), so it is necessary to increase absorption through high power density or special wavelengths (such as fiber lasers).
**2. Heating and melting of materials**
**Thermal conduction:** After absorbing laser energy, the local temperature of the material rapidly rises to the melting point (such as steel at about 1500 ° C), forming a molten pool.
**Energy concentration:** The high energy density of lasers (up to 10 ⁶~10 ⁸ W/cm ²) concentrates heat in small areas, reducing the heat affected zone (HAZ).
**3. Removal of molten material (critical cutting stage)**
**Auxiliary gas function:**
Oxidation reaction (oxygen assisted): When cutting carbon steel, oxygen undergoes an exothermic reaction with molten iron (Fe+O ₂ → FeO+heat), further increasing the temperature and accelerating the cutting process.
Inert gas blowing (nitrogen/argon): When cutting stainless steel or aluminum alloy, inert gas prevents oxidation and blows away molten metal purely by kinetic energy.
**Steam pressure:** Some materials vaporize to generate steam pressure, which assists in the discharge of slag.
**4. Stability of Cutting Frontiers and the "Keyhole" Effect**