Laser Welding Technology

Laser welding is a process that uses the radiant energy of a laser to achieve effective welding. Its working principle is to excite a laser active medium (such as a mixed gas of CO2 and other gases, YAG yttrium aluminum garnet crystal, etc.) by a specific method. The reciprocating oscillation in the cavity forms a stimulated radiation beam. When the beam is in contact with the workpiece, its energy is absorbed by the workpiece, and welding can be performed when the temperature reaches the melting point of the material.

Laser welding can be divided into heat conduction welding and deep fusion welding. The former heat is diffused to the inside of the workpiece through heat transfer, and only the surface of the weld is melted. The inside of the workpiece is not completely penetrated, and basically no vaporization occurs, and it is mostly used for low-speed thin wall. The welding of the material; the latter not only completely penetrates the material, but also vaporizes the material to form a large amount of plasma. Due to the large heat, a keyhole phenomenon occurs at the front end of the molten pool. Deep-fusion welding can thoroughly penetrate the workpiece, and has high input energy and fast welding speed. It is the most widely used laser welding mode.

Laser welding can be divided into heat conduction welding and deep fusion welding. The former heat is diffused to the inside of the workpiece through heat transfer, and only the surface of the weld is melted. The inside of the workpiece is not completely penetrated, and basically no vaporization occurs, and it is mostly used for low-speed thin wall. The welding of the material; the latter not only completely penetrates the material, but also vaporizes the material to form a large amount of plasma. Due to the large heat, a keyhole phenomenon occurs at the front end of the molten pool. Deep-fusion welding can thoroughly penetrate the workpiece, and has high input energy and fast welding speed. It is the most widely used laser welding mode.

Because the laser produces a small spot size area, the heat affected zone around the weld is much smaller than the ordinary welding process, and the laser welding generally does not need to fill the metal, so the weld surface is continuous and uniform, and the appearance is beautiful. Surface defects such as pores and cracks are very suitable for applications where the weld profile is critical. Although the area of focus is relatively small, the energy density of the astronomy laser pointer beam is large (typically 103 to 108 W/cm2). During the welding process, the metal is heated and cooled very quickly. The temperature gradient around the molten pool is relatively large, so that the joint strength is often higher than that of the base metal, and the joint plasticity is relatively low. At present, joint quality can be improved by dual focus technology or composite welding technology.

Advantages of laser welding: Laser welding can achieve high quality joint strength and large aspect ratio, and the welding speed is faster. Since laser welding does not require a vacuum environment, remote control and automated production can be achieved through lenses and optical fibers. The laser has a large power density, has a good welding effect on difficult-to-weld materials such as titanium, quartz, etc., and can weld different performance materials. Micro soldering is possible. The laser beam is focused to obtain a small spot, and can be accurately positioned, and can be applied to the mass welding of micro- and small-sized workpieces produced by large quantities.

Disadvantages of laser welding: The price of laser and welding system parts is relatively expensive, so the initial investment and maintenance costs are higher than traditional welding processes, and the economic benefits are poor. Since the absorption rate of the laser by the solid material is low, especially after the plasma is present (the plasma has an absorption effect on the laser), the conversion efficiency of the laser welding is generally low (usually 5% to 30%). Due to the small spot size of the laser welding, the precision of the equipment for the workpiece joint is high, and a small equipment deviation will cause a large processing error.

The invisibility and energy of the laser emitted by the welding machine is too high, and non-professionals should not touch the laser source, otherwise it is dangerous. In addition, the laser is also an electromagnetic wave, but the laser used in the welding machine has a large wavelength, so there is no radiation hazard of short-wavelength light waves such as ultraviolet rays. Many gases are produced during the welding process, but most of them are inert gases. They are not toxic, but they should also be treated differently depending on the welding materials. It is best to take protective measures to reduce gas inhalation. The laser emitted by the welding machine has almost no radiation hazard, but there will be ionizing radiation and stimulated radiation during the welding process, preferably away from the welding site during the welding process. This kind of induced radiation is not short-lived, and it has a great influence on the eyes and the body. It is better to stay away from the solder joints. For close-up work, try to take protective measures such as wearing respiratory protective gear, wearing radiation protective clothing, and eye mask.

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