There are two main types of lasers used for welding, namely CO2 lasers and Nd:YAG lasers.
Both the CO2 laser and the Nd:YAG laser are invisible to the naked eye.
The light beam generated by the Nd: YAG laser is mainly near-infrared light, and has a wavelength of 1. 06 Lm.
The heat conductor has a high light absorption rate for this wavelength.
For most metals, its reflectivity is 20% to 30%.
The light beam in the near-infrared band is focused to a diameter of 0.25 mm using a standard light microscope.
The light beam of the CO2 laser is far infrared, and the wavelength is 10. 6Lm.
Most metals have a reflectivity of 80% to 90% for this light.
The special light microscope should used to focus the beam to a diameter of 0. 75 – 0. 1mm.
Nd: YAG laser power can generally reach about 4 000 ~ 6 000W.
The maximum power has now reached 10,000W.
The CO2 laser power can easily reach 20,000W or even larger.
High-power CO2 laser solves the problem of high reflectivity through the small hole effect.
When the surface of the material irradiated by the spot melts, a small hole is formed. This vapor-filled hole is like a black body, and almost completely absorbs the energy of the incident light.
The equilibrium temperature in the cavity is about 25,000 e.
In a few microseconds, the reflectivity drops rapidly.
Although the focus of CO2 laser development is still focused on the development of equipment, it is not about improving the maximum output power, but how to improve the beam quality and its focusing performance.
In addition, when a CO2 laser is used for high-power welding of 10 kW or more, if an argon gas is used, a strong plasma is often induced to make the penetration shallow.
Therefore, in the high-power welding of CO2 lasers, helium gas that does not generate plasma is often used as a shielding gas.
The application of diode laser combination for exciting high-power Nd: YAG crystals is an important development issue, which will greatly improve the quality of the laser beam and form more efficient laser processing.
A direct diode array is used to excite lasers with an output wavelength in the near-infrared region. The average power has reached 1 kW and the photoelectric conversion efficiency is close to 50%.
The diode also has a longer lifetime (10,000 h), which helps to reduce the maintenance costs of the laser equipment.