Welding robot laser welding is a welding method that uses energy (visible light or ultraviolet) as a heat source to melt and connect workpieces. Laser energy can be achieved not only because the laser itself has high energy, but more importantly, because the laser energy is highly focused to a point, which increases its energy density.
During laser welding, the laser irradiates the surface of the material to be welded and acts on it. Part of it is reflected and part is absorbed 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 converted into heat energy, which causes the temperature of the metal surface to rise, and then transmits to the inside of the metal.
The photon bombards the metal surface to form vapor, and the evaporated metal prevents the remaining energy from being reflected by the metal. If the welded metal has good thermal conductivity, a greater penetration depth will be obtained. The reflection, transmission and absorption of laser light on the surface of the material are essentially the result of the interaction between the electromagnetic field of light waves and the material. When the laser light wave enters the material, the charged particles in the material vibrate in accordance with the pace of the light wave electric vector, so that the radiation energy of the photon becomes the kinetic energy of the electron. After a substance absorbs laser light, it first produces excess energy of certain particles, such as the kinetic energy of free electrons, the excitation energy of bound electrons, or excess phonons. These original excitation energy are converted into heat energy through a certain process.
In addition to being electromagnetic waves like other light sources, lasers also have characteristics that other light sources do not possess, such as high directivity, high brightness (photon intensity), high monochromaticity and high coherence. During laser welding, the conversion of light energy absorbed by the material to heat energy is completed in a short time (about 10s). During this time, the heat energy is only limited to the laser radiation area of the material, and then through heat conduction, the heat is transferred from the high temperature area to the low temperature area.
The absorption of laser light by metal is mainly related to factors such as laser wavelength, material properties, temperature, surface condition and laser power density. Generally speaking, the absorption rate of the metal to the laser increases with the increase of temperature, and increases with the increase of the resistivity.