One of the advantages of fiber laser cutting is that the specific energy of light is high, generally ＞ 10W / cm2. Because the specific energy is proportional to 4 / ND2, the focus spot diameter should be as small as possible to create a narrow slit; in addition, the focusing spot diameter is also proportional to the relative aperture of the lens. The smaller the relative aperture of focusing lens is, the smaller the diameter of focusing spot is. However, there is splash in laser cutting, the lens is too close to the workpiece, which is very easy to damage the lens. Therefore, 5 ~ 7.5 /?? is generally used in the industrial production application of CO2 fiber laser cutting with high power??

(127 ~ 190mm). The specific focus point diameter is between 0.1 mm 0.4 mm. For high quality laser cutting, reasonable relative aperture is also related to lens diameter cutting off raw materials. For example, when cutting carbon steel with a 5 / 5 lens, the relative aperture is within + 2% of the focal length of the lens, that is, 5mm up down. Therefore, it is very important to manipulate the relativity of focus on the part the surface of raw material is cut off. Considering the laser cutting quality, laser cutting rate other factors under normal conditions

For metal composite materials < 6 mm, focus surface layer; for carbon steel > 6 mm, focus is above surface layer; for stainless steel plate > 6 mm, focus is under surface. The actual specification is determined by test.

In industrial production, there are three simple ways to clearly focus on the focus

(1) Copy method: make the laser cutting head keep fit top to bottom, carry out particle beam copying on the plastic plate in the pipe cutting mode, focus on the point with the least copy diameter.

(2) Inclined column method: the plastic plate placed on the side of the vertical axis is used to make it move horizontally to find the focus at the least point of the particle beam.

(3) Dark blue flame method: remove the nozzle, blow gas, pulse light on the stainless steel plate, so that the laser cutting head top to bottom fitness movement, until the dark blue flame big point focus. For the automatic cutting machine of navigation laser light path, because of the light emission angle, the laser cutting far far side of the optical path length is the same, the light specifications before the focus are different. The larger the diameter of the incident angle beam, the smaller the diameter of the focusing point.