Continuous Laser Cutting Principle
When the laser power exceeds a certain threshold, before the material is penetrated by the laser, the melted material is propelled in the opposite direction by the airflow from the laser nozzle, while the ejected material continues to absorb laser energy, forming plasma.
This plasma has a high absorption rate for the laser, shielding some of the direct injection of the laser onto the material surface, reducing the material’s absorption of the laser, resulting in a longer heating and melting time and a larger heat-affected area, thus the initial laser piercing diameter is relatively large. The thicker the material, the larger the diameter of the laser penetration hole.
Once the material is penetrated by the laser, if the beam is moved at a certain speed, the material melted at the leading edge of the melt is propelled forward by the airflow from the laser nozzle, and the formed plasma will further absorb laser energy inside the hole (or cut), which will then be transferred to the material base through heat conduction.
This effectively increases the material’s absorption of the laser, reducing the heating and melting time and shrinking the heat-affected area, resulting in a narrower cut.
Classification of Continuous Laser Cutting
(1) Vaporization Cutting
When the laser power density focused on the material surface is extremely high, the temperature of the material surface rises very rapidly compared to heat conduction, reaching the vaporization temperature directly without melting.
Femtosecond laser cutting of any material falls under vaporization cutting, while nanosecond or continuous laser cutting is only considered vaporization cutting when cutting materials with low vaporization temperatures (such as wood, carbon materials, and certain plastics).
(2) Oxygen-assisted Melting Cutting
When laser cutting metal materials, if the assisted gas blown is oxygen or an oxygen-containing mixture, the heated metal material undergoes an exothermic reaction, creating another heat source outside of the laser energy – the heat generated by the metal chemical reaction. Both sources of heat work together to melt and cut the material, known as oxygen-assisted melting cutting.
(3) Oxygen-free Melting Cutting
When cutting materials with a laser, if the assisted gas blown is an inert gas, the melted material will not come into contact with the oxygen in the air, thus no chemical reaction occurs, hence it is referred to as oxygen-free melting cutting.