Mar 02, 2019
Laser welding can be achieved by continuous or pulsed laser beam, the principle of laser welding can be divided into heat conduction type welding and laser deep melt welding. The power density is less than 104~105 W/cm2 is heat conduction welding, at this time the melting depth, the welding speed is slow, when the power density is greater than 105~107 W/cm2, the metal surface under the heating action concave into "holes", the formation of deep melt welding, with a fast welding speed, deep and wide ratio characteristics.
The principle of heat conduction laser welding is as: laser radiation heating to the surface to be processed, surface heat through heat conduction to the internal diffusion, by controlling the width of the laser pulse, energy, peak power and repetition frequency and other laser parameters, so that the workpiece melts, forming a specific melting pool. Laser welding machines for gear welding and metallurgical sheet welding mainly involve laser deep melt welding. Laser deep melt welding generally uses continuous laser beam to complete the connection of materials, its metallurgical physical process and electron beam welding is very similar, that is, the energy conversion mechanism is through the "small Hole" (Key-hole) structure to complete. At a high enough power density laser irradiation, the material evaporates and forms a small hole. This small, vapor-filled hole is like a black body that absorbs almost all of the incident beam energy, and the equilibrium temperature in the cavity is about 2500 0C, and the heat is transmitted from the outer wall of the high-temperature hole cavity, melting the metal surrounding the hole. The small hole is filled with high temperature steam produced by continuous evaporation of the wall material under the beam irradiation, the small hole four walls surrounds the molten metal, and the liquid metal surrounds the solid material (while in most conventional welding processes and laser conduction welding, the energy is first deposited on the surface of the workpiece and then transported to the interior by transmission). The liquid flow and wall surface tension outside the Combi and the continuous steam pressure in the orifice cavity are held and maintained with dynamic balance. The beam continues to enter the small hole, the material outside the small hole in the continuous flow, with the beam moving, the small hole is always in a stable state of flow. That is, the small hole and the molten metal around the wall of the hole move forward at the forward speed of the leading beam, and the molten metal is filled with the gap left by the small hole after it is removed and condensed, and the weld is formed. All of this process occurs so quickly that the welding speed is easily reached by a few meters per minute.