1) Laser power density
Power density is one of the most important parameters in laser processing. With higher power density, it can heat the surface layer to the boiling point in microseconds, thus generating a large amount of vaporization. Therefore, high power density is conducive to material removal processing, such as stamping, cutting and engraving. For lower power densities, it takes several milliseconds for the surface temperature to reach the boiling point. Before the surface layer vaporizes, the bottom layer reaches the melting point, which is easy to form good fusion welding. Therefore, in conductive laser welding, the power density is in the range of 104~106W/cm2. Beam spot size is one of the most important variables in laser welding, because it determines the power density.
2) Material absorption value
The absorption of laser by materials depends on some important properties of materials, such as absorptivity, reflectivity, thermal conductivity, melting temperature, evaporation temperature, etc., of which the most important is absorptivity.
The factors that affect the absorption of materials to laser beams include two aspects: one is the resistivity of materials. After measuring the absorptivity of the polished surface of the material, it is found that the absorptivity of the material is proportional to the square root of the resistivity, and the resistivity changes with temperature. And change; Secondly, the surface state (or finish) of the material has a more important influence on the light beam absorptivity, and has a significant impact on the welding effect. Non metals such as ceramics, glass, rubber and plastics have high absorption at room temperature, while metal materials have poor absorption at room temperature until the materials melt or even deflate. Its absorption will only increase dramatically. The method of using surface coating or forming oxide film on the surface is very effective for improving the absorption of light beam by materials.
3) Pulse shape and width
Pulse waveform is an important problem in welding, especially for thin plate welding. When the high intensity beam hits the material surface, part of the energy on the metal surface will be lost by reflection, and the reflectivity will change with the surface temperature. During the pulse action, the reflectivity of the metal varies greatly.
Pulse width is one of the important parameters of pulse welding. It is not only an important parameter different from material removal and material melting, but also a key parameter determining the cost and volume of processing equipment.
4) Effect of defocus
Due to the high power density of the spot center at the laser focus, it is easy to evaporate into holes. In each plane far from the laser focus, the power density distribution is relatively uniform. There are two defocusing methods: positive defocusing and negative defocusing. If the focal plane is above the workpiece, it is positive defocusing, otherwise it is negative defocusing. According to the geometrical optics theory, when the distance between the positive and negative defocusing planes and the welding plane is equal, the power density on the corresponding plane is approximately the same, but the actual shape of the weld pool obtained is different. When the defocusing is negative, greater penetration depth can be obtained, which is related to the formation process of the molten pool.
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Understand the parameter settings of the laser welding machine
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