Laser Welding Machine Welded Stainless Steel and Aluminum

   
    Laser welding is an efficient and precise welding method that uses a high-energy-density laser beam as a heat source. Laser welding is one of the important aspects of the application of laser material processing technology. In the 1970s, it was mainly used for welding thin-walled materials and low-speed welding. The welding process is of thermal conduction type, that is, the surface of the workpiece is heated by laser radiation, and the surface heat diffuses to the interior through thermal conduction. By controlling the width, energy, peak power and repetition frequency of the laser pulse and other parameters to melt the workpiece and form a specific molten pool. Due to its unique advantages, it has been successfully used in the precision welding of micro and small parts.
       


   Process parameters
(1) 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 the boiling point in the microsecond time range, resulting in a large amount of vaporization. Therefore, high power density is beneficial for material removal processes such as punching, cutting, and engraving. For lower power density, it takes several milliseconds for the surface temperature to reach the boiling point. Before the surface vaporizes, the bottom layer reaches the melting point, which is easy to form a good fusion weld. Therefore, in conduction laser welding, the power density is in the range of 10^4~10^6W/CM^2.

(2) Laser pulse waveform. Laser pulse shape is an important issue in laser welding, especially for thin sheet welding. When the high-intensity laser beam hits the surface of the material, 60~98% of the laser energy will be reflected and lost on the metal surface, and the reflectivity varies with the surface temperature. During the action of a laser pulse, the reflectivity of metals varies greatly.

(3) Laser pulse width. Pulse width is one of the important parameters of pulse laser welding. It is not only an important parameter that is different from material removal and material melting, but also a key parameter that determines the cost and volume of processing equipment.

(4) The influence of defocus amount on welding quality. Laser welding usually requires a certain amount of defocus, because the power density in the center of the spot at the laser focus is too high, and it is easy to evaporate into a hole. The power density distribution is relatively uniform across the planes away from the laser focus. There are two ways of defocusing: positive defocusing and negative defocusing. The focal plane above the workpiece 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 and the welding plane is equal, the power density on the corresponding plane is approximately the same, but the shape of the molten pool obtained is actually different. When the defocus is negative, a larger penetration depth can be obtained, which is related to the formation process of the molten pool. Experiments show that when the laser is heated for 50~200us, the material begins to melt, forming a liquid phase metal and partially vaporizing, forming a high-pressure steam, and ejecting it at a very high speed, emitting a dazzling white light. At the same time, the high concentration of vapor moves the liquid metal to the edge of the molten pool, forming a depression in the center of the molten pool. When the defocus is negative, the internal power density of the material is higher than that of the surface, and it is easy to form stronger melting and vaporization, so that the light energy can be transmitted deeper into the material. Therefore, in practical applications, when the penetration depth is required to be large, negative defocusing is used; when welding thin materials, positive defocusing should be used.

(5) Welding speed. The speed of the welding speed will affect the heat input per unit time. If the welding speed is too slow, the heat input will be too large, causing the workpiece to burn through. If the welding speed is too fast, the heat input will be too small, causing the workpiece to be welded.