As a way to achieve permanent connection of materials, welding is widely used in mechanical manufacturing, petrochemical industry, bridges, ships, buildings, power engineering, transportation vehicles, aerospace and other sectors. It has become an indispensable processing technology in the machinery manufacturing industry. Moreover, with the development of the national economy, its application field will continue to be widened.
Since the laser as a twentieth Century, the atomic energy, computer, semiconductor, another great invention of human beings, with the characteristics of high energy density, high precision, strong adaptability, as cutting and welding methods used in industrial production, has great potential for development. Laser welding has made full use of its advanced, fast and flexible processing characteristics in industrial production. It is not only a technical guarantee for the development of new industrial products, but also an indispensable technical means for high quality and low cost production.
The development background of laser welding
1) the development of laser
The first Chinese laser is called "laser", "Les", it is the name of English LASER transliteration, is an abbreviation for Light Amplification by Stimulated Emission from English of the word Radiation first letter. It means "light amplified by stimulated emission". In 1964, the "light stimulated emission" was renamed "laser" according to Tsien Hsueshen, a famous scientist in China. The principle of laser was discovered by the famous American physicist Einstein in 1916, but the laser was first made for the first time in 1960. The laser is emerged in theory and practice in the context of the urgent need, it came out, quickly get an unusual development, not only make the development of laser optical science and optical technology old gained a new life, but also lead to the emergence of a new industry. Laser can enable people to effectively use the unprecedented advanced methods and means to achieve unprecedented benefits and results, thus promoting the development of productivity.
2) development of laser for welding
Due to the excellent advantages of laser, the laser technology has been applied in the field of welding in 70s. Currently, the proportion of laser welding is about 20%, which is inferior to gas shielded arc welding. The welding laser requires high power density (104 - 105W/cm2), the power density distribution is based on the base mode and the beam quality is good. The commonly used welding lasers mainly include the following:
(1) CO2 gas laser;
A gas laser with CO2 gas as a working substance. The structure is simple, the cost is low, the operation is convenient, the working medium is uniform, the beam quality is good, and the advantage of continuous work for a long time is more stable. This is the most commonly used type of laser helium neon laser, which is the most widely used type of laser.
(2) Nd:YAG laser and disc YAG laser;
It is a solid state laser with yttrium aluminum garnet crystals as the matrix. The chemical formula of yttrium aluminum garnet is Y3Al5O15, called YAG.
(3) fiber laser;
(4) semiconductor lasers;
3) development of welding robot
The application of laser to welding robot is an important form of laser welding. Welding robot has the characteristics of multi degree of freedom, flexible programming, high degree of automation and high degree of flexibility. It is an important part of welding line. The laser welding installation in welding robot, welding robot can greatly improve the welding quality and scope in the ship, automobile production line of laser welding robot has become more and more important. Figure 4 Diagram for welding of CO2 laser welding robot
Principle and process of 3 laser welding
Laser welding of metal materials is essentially a process of interaction between laser and non transparent material. The process is extremely complex, on the microcosmic level is a quantum process, and on the macroscopic view, it is reflected, absorbed, melted, vaporized and so on. Laser welding can be realized by continuous or pulsed laser beams. The principle of laser welding can be divided into heat conduction type and laser deep penetration welding. The power density is less than 104 - 105 W/cm2 for heat conduction welding, the welding depth and welding speed; power density greater than 105 - 107 W/cm2, heating the metal surface is recessed into a "hole" under the action of the formation of deep penetration welding, with high welding speed, high aspect ratio features.
In the process of laser and workpiece, there will be self oscillation, and the flow phenomena of small holes and metal in molten pool and molten pool have periodic changes. The frequency of this oscillation is related to the parameters of the laser beam, the thermal physical properties of the metal and the kinetic characteristics of the metal vapor. The periodic change of the molten pool will be generated in the weld of two special phenomena: one is full of holes of metal vapor, due to cyclical changes, while the metal molten pool and around it backwards along the flow, combined with metal evaporation caused by disturbance, there may be holes cut in half, so that steam stay in the weld after solidification porosity formation, the other is a periodic change of the penetration depth of the weld root, which is related to the periodic change of the hole.
Contact: Yousheng Fang
Add: Floor 5, Building B, Dingfeng Science and Technology Park, Songgang Tantou 5th Industrial Zone, Baoan District, Shenzhen, China.