Aug 03, 2020
Laser welding can be realized by 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 105 W/cm2 for heat conduction welding. At this time, the penetration depth is shallow and the welding speed is slow; when the power density is greater than 105 W/cm2, the metal surface is recessed into "holes" by heating, forming deep penetration welding, which has fast welding speed, The feature of large aspect ratio.
The principle of thermal conduction laser welding is: laser radiation heats the surface to be processed, and the surface heat diffuses into the interior through thermal 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 sheet welding mainly involves laser deep penetration welding. The following focuses on the principle of laser deep penetration welding.
Laser deep penetration welding generally uses continuous laser beams to complete the connection of materials. The metallurgical physical process is very similar to electron beam welding, that is, the energy conversion mechanism is completed through a "key-hole" structure. Under sufficiently high power density laser irradiation, the material evaporates and forms small holes. This steam-filled small hole is like a black body, absorbing almost all of the incident beam energy. The equilibrium temperature in the cavity reaches about 2500°C. Heat is transferred from the outer wall of the high-temperature cavity to melt the metal surrounding the 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 are surrounded by molten metal, and the liquid metal is surrounded by solid materials (and in most conventional welding processes and laser conduction welding, the energy first Deposited on the surface of the workpiece, and then transported to the inside by transfer). The liquid flow outside the pore wall and the surface tension of the wall layer are maintained in a dynamic balance with the continuously generated steam pressure in the cavity. The light 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 to say, the small hole and the molten metal surrounding the hole wall move forward after the leading beam, fill the gap left after the small hole is removed and condense, thus forming a weld. The above process happens quickly, making the welding speed easily reach several meters per minute.