Laser welding can be realized by continuous or pulse laserbeam. The principle of laser welding can be divided into heat conduction welding and laser deep fusion welding. When the power density is less than 104~105W/cm2, it is heat conduction welding, and the welding depth and welding speed are slow. When the power density is greater than 105~107W/cm2, the welding metal surface is concave into "holes" under the action of heat, forming deep fusion welding, which has the characteristics of fast welding speed and large depth-width ratio.
The principle of heat conduction laser welding is as follows.
Laser radiation heats the surface to be machined, and surface heat diffuses into the interior through heat conduction. By controlling laser parameters such as the width, energy, peak power and repetition frequency of laser pulse, the workpiece is melted, and a specific melting pool is formed.
Fiber laser welding machine used for gear welding and metallurgical sheet welding mainly involves laser deep fusion welding.The principle of laser deep fusion welding is mainly introduced below.
Laser deep fusion welding generally uses a continuous laser beam to complete the material connection, and its metallurgical physical process is very similar to electron beam welding, that is, the energy conversion mechanism is completed through the "key-hole" structure. At a high enough power density laser, the material evaporates and pores are formed. This vapor-filled hole is like a black hole, absorbing almost all the energy of the incident beam. The equilibrium temperature in the hole cavities reach at about 2500℃, and the heat is transferred from the outer wall to the high-temperature hole cavities, making the metal surrounding the hole cavities melt .The holes are filled with hot steam generated by the continuous evaporation of the wall material under the beam irradiation. The walls of the holes are surrounded by the molten metal and the liquid metal is surrounded by the solid material. (While in most traditional welding processes, the energy is first deposited on the surface of the workpiece and then transported to the interior). The fluid flow outside the pore wall and the surface tension of the wall layer are in constant equilibrium with the steam pressure in the pore cavities. The light beam keeps entering the small holes, and the material outside the small holes flows continuously. As the light beam moves, the small holes are always in a stable state of flow.That is, the holes and the molten metal surrounding the walls of the holes move forward with the speed of the leading beam. The molten metal fills the empty space left by the holes, and condenses accordingly, forming a weld seam. All of this happens so fast that welding speed can easily reach at meters per minute.
