Laser welding technology and application
focus close to the workpiece, workpiece will be melting and evaporation in milliseconds, this effect can be used for welding "ecomax"
power CO2 and the emergence of high power YAG laser, has opened up a new field of laser welding.Laser welding equipment is the key
to the high-power laser, there are mainly two categories, one is the solid laser, also known as Nd:YAG laser.Nd (neodymium) is a kind of
rare earth element. YAG stands for yttrium aluminum garnet. Its crystal structure is similar to ruby.Nd:YAG laser wavelength of 1.06 m, the
main advantage is that the generated beam can be transmitted through optical fiber, so it can save to the complex beam transmission
system, suitable for flexible manufacturing system or remote processing, usually used for welding accuracy requirements of higher
workpiece.The Nd:YAG laser with a power output of 3-4 kilowatts is commonly used in the automobile industry.The other is a gas laser,
also known as CO2 laser, molecular gas as the working medium, uniform 10.6 m infrared laser, can continue to work and output very high
power, standard laser power between 2-5 kilowatts.
The main advantages of laser welding are:
1. Fast speed, large depth and small deformation.
2, can be at room temperature or special conditions for welding, welding equipment is simple.For example, a laser beam passes through an electromagnetic field without being deflected;Lasers can be used to weld in vacuum, air, and certain gaseous environments, and to weld through glass or transparent materials of light beam.
3. Can weld refractory materials such as titanium and quartz, etc., and can weld opposite materials with good effect.
4. After laser focusing, the power density is high. In the welding of high-power devices, the depth-width ratio can reach 5:1 and the highest can reach 10:1.
5. Micro welding can be carried out.The laser beam can get very small spot after focusing, and can be precisely positioned, which can be used in the welding of micro and small workpieces produced automatically in large quantities.
6. Welding the parts that are difficult to access, non-contact remote interval welding is carried out, with great flexibility.Especially in recent years, fiber transmission technology has been adopted in YAG laser processing technology, which makes laser welding technology more widely popularized and applied.
7. Laser beam is easy to realize light beam splitting according to time and space, and can be processed simultaneously with multiple beams and multiple stations, providing conditions for more precise welding.
Laser welding process parameters
(1) Power density
Power density is one of the most important parameters in laser machining.With a high power density, the surface can be heated to the boiling point in the microsecond time range, producing a large amount of vaporization.Therefore, high power density is beneficial for material removal processing, such as drilling, cutting and engraving.For low power density, it takes several milliseconds for surface temperature to reach boiling point. Before surface vaporization, bottom layer reaches melting point, which is easy to form good melt welding.Therefore, the power density in conductive laser welding is in the range of 104~106W/cm2.
(2) Laser pulse waveform
Laser pulse waveform is an important problem in laser welding, especially for wafer welding.When the high-intensity laser beam is shot to the surface of the material, the metal surface will have 60-98% of the laser energy reflected and lost, and the reflectivity changes with the surface temperature.The reflectivity of the metal varies greatly during a laser pulse.
(3) Laser pulse width
Pulse width is one of the important parameters of pulse laser welding, which is not only different from material removal and material melting, but also the key parameter to determine the cost and volume of processing equipment.
(4) Influence of defocus amount on welding quality
Because the power density at the laser focus is too high, it is easy to evaporate into holes.The power density distribution is relatively uniform in each plane away from the laser focus.There are two ways of defocusing: positive defocusing and negative defocusing.If the focal plane is above the workpiece, it is positive defocusing, otherwise, it is negative defocusing.According to the theory of geometrical optics, when the distance between the positive and negative defocusing plane and the welding plane is equal, the power density on the corresponding plane is approximately the same, but the actual shape of the molten pool obtained is different.When negative defocusing, a larger depth of fusion can be obtained, which is related to the formation process of the pool.
The application field of laser welding
Laser welding is widely used in manufacturing industry, powder metallurgy field, automobile industry, electronics industry and other fields.
In particular, small series of the development of laser welding in the automobile manufacturing industry, the following reduction:
At present, Volkswagen USES laser welding on the roof of AudiA6, GolfA4, Passat and other brands, BMW and GENERAL Motors also use laser welding on the roof, and German Benz USES laser welding on transmission parts.
In addition to laser welding, other laser technologies have been widely used: Volkswagen, GM, Mercedes-benz, Nissan used laser to cut covering parts, Fiat and Toyota used laser to coat engine exhaust valves, and Volkswagen used laser surface hardening of engine camshafts.
Judging from the current domestic and international brand localization models: passat, polo, piece, audi, dongfeng Peugeot, fox and so on have been using laser welding technology, including faw-vw audi A6 tops and baolai back cover with laser welding and soar team and piece body laser weld length up to 30, 40 m, respectively.In addition, Brilliance, Chery and Geely auto of China have also applied laser welding technology to their new models.
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