Welding robot laser is a kind of monochromatic and directionally focused energy beam produced by using the principle of light amplification realized by stimulated radiation. It can obtain energy beam with diameter less than 0.01mm and power density as high as 10W/m2.
Laser welding of welding robot is a welding method which uses visible light or ultraviolet light as heat source to melt and connect workpieces.
The realization of laser energy is not only because the laser itself has a very high energy, but also because the laser energy is highly focused to a point, which makes its energy density increase.
In laser welding, the laser irradiates the surface of the material to be welded and acts with it. Part of it is reflected, part of it is absorbed and enters into the material.
For opaque materials, the transmitted light is absorbed, and the linear absorption coefficient of metal is 107 ~ 108 /m.
For metals, the laser is absorbed in the thickness of 0.01 ~ 0.1m on the metal surface and transformed into heat energy, which causes the temperature of the metal surface to rise and then transmit to the metal interior.
The vaporized metal can prevent the residual energy from being reflected by the metal.
If the metal to be welded has good thermal conductivity, it will get greater penetration.
The reflection, transmission and absorption of laser on the material surface are essentially the result of the interaction between the electromagnetic field of light wave and the material.
When the laser light wave is incident on the material, the charged particles in the material vibrate according to the pace of the light wave electric vector, so that the radiation energy of the photon becomes the kinetic energy of the electron.
After matter absorbs laser, it first produces excess energy of some particles, such as kinetic energy of free electron, excitation energy of bound electron, and excess phonon.
The original excitation energy is transformed into heat energy through a certain process.
Besides being electromagnetic wave like other light sources, laser also has some characteristics that other light sources don’t have, such as high directivity, high brightness (photon intensity), high monochromaticity and high coherence.
In laser welding, the conversion of light energy absorbed by materials to heat energy is completed in a very short time (about 10s).
In this time, the heat energy is only limited to the laser radiation region of the material, and then through heat conduction, the heat is transferred from the high temperature region to the low temperature region.
The absorption of laser by metal is mainly related to laser wavelength, material properties, temperature, surface condition and laser power density.
Generally speaking, the absorptivity of metal increases with the increase of temperature and resistivity.
At present, two kinds of lasers are mainly used in welding field: YAG solid state laser (Yttri-um-Aluminium-Garnet, abbr. YAG) and CO2 gas laser.
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