How does laser welding work?

How does laser welding work?

Laser welding can be achieved using continuous or pulsed laser beam, the principle of laser welding can be divided into heat conduction welding and laser deep penetration welding. The power density is less than 104~105 W/cm2 for heat conduction welding, when the melt depth shallow, slow welding speed; power density is greater than 105~107 W/cm2, the metal surface is concave into a "hole" by heat, forming a deep penetration welding, with a fast welding speed, the characteristics of a large depth to width ratio.

The principle of heat conduction laser welding is that the laser radiation heats the surface to be processed, and the surface heat spreads to the inside through heat conduction.

Laser welding machines for gear welding and metallurgical sheet welding mainly involve laser deep penetration welding.

Laser deep penetration welding generally uses a continuous laser beam to join materials, and the metallurgical physical process is very similar to electron beam welding, i.e. the energy conversion mechanism is accomplished through a "Key-hole" structure. Under sufficiently high power density laser irradiation, the material evaporates and a small hole is formed. This small hole filled with vapor is like a black body that absorbs almost all of the incident beam energy, and the equilibrium temperature inside the hole cavity reaches about 2500 0C. Heat is transferred from the outer wall of this high-temperature hole, causing the metal surrounding the hole cavity to melt. The hole is filled with high-temperature steam generated by the continuous evaporation of the wall material under beam irradiation, and the four walls of the hole are surrounded by molten metal, and the liquid metal is surrounded by solid material (whereas 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 interior by transfer). The liquid flow and wall surface tension outside the hole walls are held and dynamically balanced with the continuously generated vapor pressure inside the hole cavity. The beam continuously enters the small hole, the material outside the hole is continuously flowing, and the hole is always in a stable state of flow as the beam moves. That is, the small hole and the molten metal surrounding the hole walls move forward with the forward speed of the leading beam, and the molten metal fills the void left after the hole moves away and condenses with it, and the weld is formed. All of this happens so quickly that the welding speed can easily reach several meters per minute.