1. Power density
Power density is one of the most critical parameters in laser processing. With a higher power density, the surface layer can be heated to the boiling point within microseconds, resulting in a large amount of vaporization. Therefore, high power density is beneficial for material removal processes such as drilling, cutting, and engraving. For a lower power density, 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 a good fusion weld. Therefore, in conductive laser welding, the power density is in the range of 104~106W/cm2.
2. Pulse waveform
Pulse waveform is an important issue in welding, especially for sheet welding. When the high-intensity beam hits the surface of the material, some energy on the metal surface will be reflected and lost, and the reflectivity will vary with the surface temperature. During a pulse, the metal reflectivity changes greatly.
3. Pulse width
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 to determine the cost and volume of processing equipment.
4. Influence of defocus amount
Because the power density in the center of the spot at the laser focus is too high, it is easy to evaporate into holes. On each plane away from the laser focus, the power density distribution is relatively uniform. There are two types of defocus: positive defocus and negative defocus. If the focal plane is above the workpiece, it is positive defocus, otherwise it is negative defocus. According to the theory of geometric optics, when the distance between the positive and negative defocus planes is equal to the welding plane, the power density on the corresponding planes is approximately the same, but in fact the obtained molten pool shapes are different. When the defocus is negative, a greater penetration depth can be obtained, which is related to the formation process of the molten pool.