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Handheld, why should automatic laser welding machine be protected by gas? What kind of gas is better?

In the laser welding process, inert gas is often used to protect the molten pool. When some materials are welded without regard to surface oxidation, protection is not considered. However, for most applications, gases such as helium, argon and nitrogen are often used to protect the workpiece. Protected from oxidation during welding.
Handheld continuous fiber laser welding machine
手持连续光纤激光焊接机
Protective gas has three functions:

First, prevent oxidation of the metal surface;
Second: suppress the metal vapor pollution generated during the welding process and the spatter after the metal is melted;
Third: Dispel the plasma shielding produced by high-power laser welding because this plasma shielding affects the transmission of the laser and reduces the laser power reaching the surface of the solder.
激光焊接保护氩气
Laser welding protects argon
The advantages and disadvantages of the three inert gases are as follows:

    Helium: It is not easy to ionize (high ionization energy), allowing the laser to pass smoothly, and the beam energy is unimpeded to the surface of the workpiece. This is the most effective protective gas used in laser welding, but it is more expensive.


    Argon: It is cheaper and has a higher density, so the protection effect is better. However, it is susceptible to high-temperature metal plasma ionization, and as a result, part of the beam is shielded from the workpiece, which reduces the effective laser power of the soldering and also impairs the welding speed and penetration. The surface of the weldment protected with argon is smoother than when it is protected with helium.



     Nitrogen: It is the cheapest as a protective gas, but it is not suitable for welding certain types of stainless steel, mainly due to metallurgical problems such as absorption, which sometimes creates pores in the overlap zone.



     The first function of the shielding gas is to isolate the oxygen and the air during the welding, so as to reduce the oxidation reaction when the metal is welded, so that the blackening can be effectively reduced when welding.



    The second effect of using a shielding gas is to protect the focusing lens from metal vapor contamination and sputtering of liquid droplets. Especially in high-power laser welding, since the ejection material becomes very powerful, it is more necessary to protect the lens at this time.


     The third role of the shielding gas is to effectively dissipate the plasma shielding produced by high power laser welding. The metal vapor absorbing laser beam ionizes into a plasma cloud, and the shielding gas around the metal vapor is also ionized by heat. If the plasma is excessive, the laser beam is consumed to some extent by the plasma. The plasma exists as a second energy on the working surface, so that the penetration becomes shallow and the surface of the weld pool becomes wider. Increasing the recombination rate of electrons by increasing the collision of electrons with ions and neutral atoms to reduce the electron density in the plasma. The lighter the neutral atom, the higher the collision frequency and the higher the recombination rate. On the other hand, only the shielding gas with high ionization energy will not increase the electron density due to the ionization of the gas itself.



   The design problem of the nozzle hole: the shielding gas is emitted to the surface of the workpiece through a nozzle port with a certain pressure, and the hydrodynamic shape of the nozzle and the diameter of the outlet are very important. It must be large enough to drive the sprayed protective gas over the soldering surface, but to effectively protect the lens from metal vapor contamination or metal splash damage to the lens, the nozzle size is also limited. The flow rate should also be controlled, otherwise the laminar flow of the shielding gas becomes turbulent, and the atmosphere is drawn into the molten pool, eventually forming pores.


    In order to improve the protective effect, an additional lateral blowing can also be used, that is, the shielding gas is directly injected into the deep-welded small holes at a certain angle by a small-diameter nozzle. The shielding gas not only suppresses the plasma cloud on the surface of the workpiece, but also affects the formation of plasma and small pores in the pores, and the penetration depth is further increased to obtain a weld seam having an ideal depth and width. However, this method requires precise control of the size and direction of the gas flow, otherwise turbulence is easily generated to destroy the molten pool, which makes the welding process difficult to stabilize.

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