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**
**Deep melting cutting:** High power laser causes local vaporization of the material, forming elongated holes (Keyholes). The laser reflects multiple times inside the holes, and the energy is efficiently absorbed, achieving thick plate cutting.
**Dynamic balance:** The laser power, cutting speed, and gas pressure need to be matched to maintain continuous discharge of molten material and smooth cutting.
**5. Seam formation and quality control**
**Cut width:** determined by the diameter of the laser spot and gas pressure, usually ranging from 0.1 to 0.5 mm.
**Quality influencing factors:**
**Insufficient power:** resulting in incomplete cutting or slag hanging.
**Speed too fast:** discontinuous cutting seam; If it is too slow, the heat affected zone will increase.
**Focus position:** The best effect is achieved when the focus is located 1/3 thickness below the material surface (for thick plates).
**Differences in cutting mechanisms of different materials**
Main mechanism challenges of material types
Metal melting/vaporization+auxiliary gas blowing for high reflectivity (such as copper and aluminum requiring high power)
Plastic melting or chemical bond breaking (UV laser) can easily carbonize and produce toxic gases
Ceramic thermal stress cracking or vaporization brittleness is high, and microcracks are prone to occur
**summarize**
The essence of laser cutting is to rapidly heat up the material locally to the phase transition point through laser energy, combined with auxiliary gas to dynamically remove molten materials or reaction products. Its efficiency and quality depend on the material's absorption rate of laser, thermal conductivity characteristics, and precise control of process parameters (power, speed, gas). Understanding this interaction mechanism is crucial for optimizing cutting processes.