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 a microsecond time range, resulting in a large amount of vaporization. Therefore, high power density is beneficial for material removal processing, such as punching, 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 makes it easy to form a good fusion weld. Therefore, in conductive laser welding, the power density is in the range of 104~106W/cm2.
Pulse shape
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 changes with the surface temperature. During a pulse action period, the reflectivity of the metal changes greatly.
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 that determines the cost and volume of processing equipment.
The effect of defocus
Because the power density in the center of the spot at the laser focal point is too high, it is easy to evaporate into a hole. On each plane away from the laser focus, the power density distribution is relatively uniform. There are two defocusing methods: positive defocus and negative defocus. If the focal plane is above the workpiece, it is a positive defocus, otherwise it is a negative defocus. According to geometric optics theory, when the distance between the positive and negative defocus plane and the welding plane is equal, the power density on the corresponding plane is approximately the same, but in fact the shape of the molten pool obtained is different. When the defocus is negative, a greater penetration depth can be obtained, which is related to the formation process of the molten pool.
