Laser welding, as an efficient and high-precision modern welding technology, has been widely used in fields such as aerospace, automotive manufacturing, and electronic components. In the process of laser welding, the setting of defocusing amount is one of the important parameters that affect welding quality. Reasonable setting of defocusing amount can not only improve the forming quality of the weld but also effectively control the welding depth and width, thus meeting the process requirements under different working conditions.



What is defocusing amount?



In laser welding, after the laser beam passes through the focusing lens, it will form the smallest spot at a certain point, which is called the focal point. The defocusing amount refers to the distance between the workpiece surface and the laser focal point, usually expressed in positive and negative values. When the focal point is above the workpiece surface, it is called positive defocusing (defocusing amount is positive), and when the focal point is below the workpiece surface, it is called negative defocusing (defocusing amount is negative).

　　Influence of defocusing amount on welding effect



1. Influence of positive defocusing

　　When positive defocusing is used, the energy density is relatively low, and the heating area is wider, suitable for thin plate welding or materials sensitive to heat input. At this time, the weld is wide and shallow, which is conducive to reducing weld cracks and pores and other defects.



2. Influence of negative defocusing



When negative defocusing is used, the focal point is located inside the material, which can achieve higher energy density and stronger penetration ability, suitable for thick plate welding or situations requiring deep penetration. At this time, the weld is deep and narrow, with high welding efficiency, but it is easy to produce spatter and pores.



3. Zero focal point (focal point located on the surface)

　　If the focal point is exactly on the surface of the material during the welding process, it is commonly used for welding medium-thickness materials, balancing the depth and width of welding, suitable for most conventional welding tasks.



How to set a reasonable defocusing amount?



1. Selecting according to material thickness



For thin plate materials (such as less than 1mm), it is recommended to use positive defocusing to prevent burn-through; for thick plate materials (such as greater than 3mm), negative defocusing should be used to increase the penetration depth.



2. Selecting according to welding requirements



If a wider weld width and a shallow penetration depth are required, such as lap welding or corner welding, positive defocusing can be chosen; if deep penetration is desired, such as butt welding or through-welding, negative defocusing is recommended.

　　3. Adjusting laser power and welding speed together



When high-power welding is performed, appropriately increasing the negative defocusing amount can enhance the penetration depth; for low-power welding, it is appropriate to reduce the defocusing amount even adopt positive defocusing to avoid insufficient penetration depth.



4. Conducting process test verification



The setting of the defocusing amount should be adjusted through experiments in combination with specific welding equipment, material types, and welding structures. The optimal defocusing amount is ultimately determined by observing the weld shape and detecting the internal quality of the weld (such as X-ray inspection, metallographic analysis).



Four, Conclusion



In summary, the correct setting of the defocusing amount is one of the key factors for achieving high-quality laser welding. In actual operation, it is necessary to comprehensively consider factors such as material properties, welding structure, laser power, and welding speed, and continuously optimize parameters through experiments in order to obtain ideal welding results. With the continuous development and improvement of laser welding technology, the precise control of defocusing amount will also become one of the important means to improve product quality and production efficiency.