Power Density
Power density is one of the most critical parameters in laser processing. With higher power densities, the surface layer can be heated to its boiling point within microseconds, generating significant vaporization. Therefore, high power density is advantageous for material removal processes such as drilling, cutting, and engraving. With lower power densities, the surface temperature takes several milliseconds to reach its boiling point; before the surface vaporizes, the underlying layer reaches its melting point, facilitating good fusion welding. Therefore, in conduction laser welding, the power density ranges from 10⁴ to 10⁶ W/cm².
Pulse Waveform
Pulse waveform is an important issue in welding, especially for thin-film welding. When a high-intensity beam strikes the material surface, energy is reflected and lost, and reflectivity varies with surface temperature. The reflectivity of the metal changes significantly within a single pulse.
Pulse Width
Pulse width is one of the important parameters in pulse welding. It is not only a key parameter distinguishing it from material removal and melting, but also a crucial parameter determining the cost and size of the processing equipment.
The Influence of Defocus Amount
Because the power density at the center of the laser spot is too high, it easily evaporates and forms holes. On planes away from the laser focus, the power density distribution is relatively uniform. There are two defocusing methods: positive defocusing and negative defocusing. Positive defocusing occurs when the focal plane is above the workpiece, and negative defocusing occurs when it is away. According to geometric optics theory, when the positive and negative defocusing planes are equidistant from the welding plane, the power density on the corresponding planes is approximately the same, but the resulting molten pool shapes are different. Negative defocusing can achieve a greater weld depth, which is related to the molten pool formation process.