How Does Laser Welding Work?

The working principle of laser welding is mainly to use a high-power laser beam generated by a laser to focus it using optical elements such as lenses or mirrors, so that the laser energy is concentrated on the solder joint. Then, when the laser beam strikes the surface of the workpiece, the laser energy is absorbed and converted into heat energy. This heat energy is gradually transferred along the metal conductive part of the welded joint through heat conduction, causing its temperature to rise.

When a metal surface is exposed to a high enough temperature, the metal begins to melt and a molten pool forms. Under the action of the laser beam, the molten pool rapidly diffuses and mixes to achieve the connection of metal joints. Finally, once the laser beam is stopped, the molten pool gradually cools and a welded joint is formed during the solidification process. During the solidification process, the metal molecules rearrange and crystallize, forming a strong welded connection.

In addition, laser welding can also be classified according to its two welding methods: heat conduction welding and laser deep penetration welding. Among them, the metallurgical physical process of laser deep penetration welding is very similar to that of electron beam welding, that is, the energy conversion mechanism is completed through the key-hole structure. At a high enough power density, the material evaporates and small holes are formed. This steam-filled hole is like a black body, absorbing almost all the incident beam energy. The equilibrium temperature in the hole reaches about 2500°C. Heat is transferred from the outer wall of the high-temperature hole to melt the metal around the hole. The hole is filled with high-temperature vapor generated by the continuous evaporation of the lower wall material irradiated by the beam. The hole is surrounded by molten metal, and the liquid metal is surrounded by solid material (in most traditional welding processes and laser conduction welding, energy is first deposited on the surface of the workpiece, and then passes through transmission to the interior). The liquid flow and wall surface tension outside the hole wall are consistent with the continuously generated steam pressure in the hole cavity, and maintain a dynamic balance. The beam continues to enter the small hole, and the material outside the small hole continues to flow. As the beam moves, the small hole is always in a stable flow state. That is to say, the small hole and the molten metal surrounding the hole wall move forward with the forward speed of the pilot beam. The molten metal fills the gap left after the small hole is removed, and then condenses to form a weld. All of these processes occur so quickly that welding speeds can easily reach several meters per minute.

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