Excite electrons or molecules to produce a concentrated and phase-identical beam of light in the process of converting them into energy. Laser comes from Light Amplification by Stimulated the first letter of the Emission Radiation.
It consists of an optical oscillator and a medium placed between the mirrors at both ends of the oscillator cavity. When the medium is excited to a high-energy state, it begins to generate the same phase light wave and reflects back and forth between the mirrors at both ends, forming a photoelectric series junction effect, amplifying the light wave, and obtaining enough energy to start emitting laser. A laser can also be interpreted as a 1 device that converts raw energy such as electrical, chemical, thermal, optical or nuclear energy into a beam of electromagnetic radiation of some specific optical frequency (ultraviolet, visible or infrared light. The conversion form is easily carried out in some solid, liquid or gaseous media. When these media are excited in the form of atoms or molecules, they produce almost the same phase and almost a single wavelength of the beam-the laser. Due to the same phase and single wavelength, the difference angle is very small, and the distance that can be transmitted is quite long before being highly concentrated to provide functions such as welding, cutting and heat treatment.
The world's first laser beam was produced in 1960 by using flash bulbs to excite ruby grains. Due to the limited heat capacity of the crystal, it can only produce a very short pulse beam and the frequency is very low. Although the peak energy of the instantaneous pulse can be as high as 10 ^ 6 watts, it is still a low energy output. Yttrium aluminum garnet crystal rods (Nd:YAG) using neodymium (ND) as the excitation element can produce a continuous single wavelength beam of 1 --- 8KW. YAG laser, with a wavelength of 1.06uM, can be connected to the laser processing head through a flexible optical fiber, the equipment layout is flexible, and the welding thickness is 0.5-6mm. Using CO2 laser (wavelength 10.6uM) as the exciter, the output energy can reach 25KW, and the single-pass full penetration welding with a thickness of 2mm can be made. The industry has been widely used in metal processing.
Most of the early laser welding research experiments are using ruby pulsed lasers, when high pulse energy can be obtained, but the average output power of these lasers is quite low, which is mainly determined by the very low working efficiency of the laser and the excitation of the luminescent material. Laser welding mainly uses CO2 laser and YAG laser, YAG laser because of its high average power, after it appears to become the preferred equipment for laser spot welding and laser seam welding. Laser welding differs significantly from electron beam welding in that laser radiation does not produce a through-hole weld pattern. In fact, when the laser pulse energy density reaches 10 to the sixth power W/CM2, a welding hole is formed on the welding interface of the metal material to be welded, and the formation condition of the small hole is satisfied, so that the laser beam can be used for deep penetration welding.
Before the 1970 s, because high-power continuous waveform lasers had not yet been developed, research focused on pulsed laser welding. Most of the early laser welding research experiments are using ruby pulse laser. The welding process of YAG laser is carried out by welding joints, and the real laser seam welding can only be realized after the birth of continuous power waveform laser with more than 1KW.
With the success of the kilowatt-level continuous CO2 laser welding test, laser welding technology made a breakthrough in the early 1970 s. CO2 laser welding was performed on a large thickness stainless steel specimen to form a penetration weld, thus clearly indicating the formation of small holes, and the deep penetration weld produced by laser welding is similar to that of electron beam welding. These early work in metal welding with CO2 lasers demonstrated the great potential of high power continuous laser welding. In the aviation industry and many other applications, laser welding can realize the connection of many types of materials, and laser welding usually has many advantages that other fusion welding processes can not match, especially laser welding can connect the more difficult to weld sheet alloy materials in the aviation and automobile industries, such as aluminum alloy, and the deformation of the components is small, the joint quality is high. Another attractive application aspect of laser processing is the use of the laser to achieve local small-scale heating characteristics, the laser has this hot spot makes it very suitable for printed circuit board and other electronic devices, laser can produce a very high average temperature in a very small area on the electronic device, and the area outside the joint is basically not affected.
It belongs to melting welding, which uses laser beam as energy source and impacts on weldment joint. The laser beam can be guided by a planar optical element, such as a mirror, and then the beam is projected onto the weld with a reflective focusing element or lens. Laser welding is a non-contact welding, the operation process does not need to be pressurized, but the use of inert gas to prevent oxidation of the molten pool, filler metal is occasionally used. Laser welding can be combined with MIG welding to achieve large penetration welding, while the heat input is greatly reduced compared to MIG welding.
