Laser Welding Technology Principle

Laser welding can be achieved by continuous or pulsed laser beams. The principle of laser welding can be divided into heat conduction welding and laser deep penetration welding. When the power density is less than 104~105 W/cm2, it is heat conduction welding, in which the melting depth is shallow and the welding speed is slow; when the power density is greater than 105~107 W/cm2, the metal surface is heated and concave into a "hole", forming a deep penetration welding, which has the characteristics of fast welding speed and large depth-to-width ratio.
Among them, the principle of heat conduction laser welding is: the laser radiation heats the surface to be processed, and the surface heat diffuses to the inside through heat conduction. By controlling the laser parameters such as the width, energy, peak power and repetition frequency of the laser pulse, the workpiece is melted to form a specific molten pool.
The laser welding machine used for gear welding and metallurgical thin plate welding mainly involves laser deep penetration welding.
Laser deep penetration welding generally uses a continuous laser beam to complete the connection of materials. Its metallurgical physical process is very similar to electron beam welding, that is, the energy conversion mechanism is completed through the "key-hole" structure. Under sufficiently high power density laser irradiation, the material evaporates and forms a keyhole. This small hole filled with steam acts like a black body, absorbing almost all the energy of the incident beam. The equilibrium temperature in the hole cavity reaches about 2500℃ [1]. Heat is transferred from the outer wall of this high-temperature hole cavity, melting the metal surrounding the hole cavity. The small hole is filled with high-temperature steam generated by the continuous evaporation of the wall material under the irradiation of the beam. The four walls of the small hole surround the molten metal, and the liquid metal is surrounded by solid materials (in most conventional welding processes and laser conduction welding, the energy is first deposited on the surface of the workpiece and then transferred to the inside). The liquid flow outside the hole wall and the surface tension of the wall layer maintain a dynamic balance with the steam pressure continuously generated in the hole cavity. The beam continuously enters the small hole, and the material outside the small hole is continuously flowing. As the beam moves, the small hole is always in a stable state of flow. That is, the small hole and the molten metal surrounding the hole wall move forward with the forward speed of the leading beam. The molten metal fills the gap left after the small hole is removed and condenses, and the weld is formed. All of the above processes happen so quickly that the welding speed can easily reach several meters per minute.