The laser beam provides a high concentration of energy (up to 10 ^ 8 W/cm2), with the ability to focus at a point with a diameter of several micrometers. This concentration is much higher than, for example, in the arc. Has a comparable energy density electron beam (up to 10 ^ b W/cm2). However, electron-beam welding is carried out only in the vacuum chambers - it is necessary for carrying out sustainable process, laser welding does not require the same vacuum that simplifies and accelerates those. process. The process of laser welding is carried out either in air or in shielding gases: Ar, He, CO2 laser beam, etc., as well as e-mail is easily rejected, is transported by an optical system.
For the welding of metals used solid-state and gas lasers as a periodic, and continuous operation.
Due to the high concentration of laser energy during the welding process is provided by a small amount of molten metal, small spot size of heating, high velocity heating and cooling of the weld metal and heat affected zone. These characteristics determine the thermal effects of the minimum deformation of welded structures, the specific physical, chemical and metallurgical processes in the weld metal, high technological and structural strength of welded joints. Laser welding is carried out in a wide range of modes, providing high-performance process of connecting a variety of materials with a thickness of several micrometers to tens of millimeters. A variety of methods and techniques of laser welding difficult to develop a specific process.
Laser welding process is very complex and there is currently no theoretical calculation model, which describes it in its entirety. Typically, the calculations relate to any one of the physical characteristics of the process of laser radiation on the material being processed.
Spot welding has spread from the early days of pulsed solid-state lasers for permanent joints in electronics and instrumentation. Spot welding of sheet material connected (with a thickness of 0,5 ... 2,0 mm), wire diameter from 10 to 500 microns, the wire to the substrate, thin sheets of massive elements (Figure 2.12).
weld pool dimensions that determine the strength of the weld compounds depend primarily on the laser pulse duration and energy. In addition, the size of the weld pool depends on the thermal conductivity of the material (for more heat conductive copper weld pool size is smaller than that of steel)
When spot welding of pulsed radiation, depending on the type of materials to be welded using a range of power density q = 1O5 1O6 ... W / cm2 and a range of pulse durations taui = 2 ... 10 ms. The diameter of the weld points of D = 0,1 .. 1,2 mm and the depth of penetration h = 0,0 Z. .. 1.3 mm. Performance is determined by the spot welding speed pulse generating f, the speed of moving parts (beam), the well-established process reached speeds of up to 200 spot welds per second.
Seam welding provides a secure mechanical connection, a high sealing seam. Seam welding performed by using a pulsed radiation with a high frequency pulse generation, and with the help of continuous radiation. The latter allows welding thick-walled parts. Some types of compounds, performed by laser welding seam are shown in Fig. 2.14.
Main parameters of the process of pulsed and continuous seam weld that determine the quality of welded joints, are: pulse energy E, the duration of action of laser radiation on the processed material taui, the diameter of the focused radiation d, the pulse repetition frequency (for ASI) f and the position of the focal plane of the laser beam with respect to the surface of the workpiece F. All parameters are usually determined experimentally, depending on the requirements engineering process. Approximately, tp = 10-4 ... 10-2 d = 0.05 ... 1 mm, the average travel speed - up to 5 mm / s, f - 20 Hz The quality of the metal of welded joints made by a continuous laser beam, as compared with traditional types of welding is very high. Typically, in this case, the mechanical properties of weld metal properties superior to the base metal in the initial state. Improved mechanical properties associated with obtaining a fine-grained structure of the fused metal and metal cleaning and degassing of the molten weld pool during laser exposure.Laser welding with deep penetration. Fundamentally different from the shallow-penetration welding, the fact that the formation of a welded joint is formed a gas channel through which rises the evaporated metal. Zone penetration has an elongated shape, the seam is not a wide and deep.
Protection during laser welding.
used to protect the seam gases argon and helium, in addition to the protection they provide a more effective penetration by changing the parameters of the resulting plasma, accelerate the output of gases, vaporized metal. You can achieve a significant increase in the depth of penetration, but the quality of the weld at high gas flow rate, worse, there are pores.
Increasing the efficiency of welding can be achieved using an additional source of heating. As such a source can be used, for example, electric arc, summing up on either side of the seam. Increased depth of penetration, the cutting speed. In summing up the arc, comparable in power to the laser penetration rate increases by four times.
Pros:
1) In contrast to the electron beam welding, does not require a vacuum chamber, there is no X-rays, the beam is not affected by magnetic fields, magnetic materials can be welded, as well , laser welding is cheaper than the electron beam welding.
2) Spot heating is very small, with great depth of penetration, as a consequence of small deformations of welded parts, high precision, high quality weld.
3) The contactless - is possible welding in confined spaces, carrying out welding through the transparent material in liquid transparent media.
4) Flexible, wide tuning process, without having to change tooling, slight displacement of the beam on the surface of the part of any path links:
- The laser crystals of aluminum-yttrium garnet (YAG) from Mitsibishi.
- Chinese industry lasers, including welding.
- German lasers.
Laser Welding Technology
Laser Welding
Classification of welded joints and seams
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