The key technology of metal laser cutting machine

One of the advantages of laser cutting is the high energy density of the beam. Since the energy density is proportional to 4/Ï€d2, the focal spot diameter is as small as possible to produce a narrow slit; the focal spot diameter is also directly proportional to the focal depth of the lens. The smaller the focal depth of the focusing lens, the smaller the focal spot diameter. However, there is splashing and the lens is damaged when the lens is too close to the workpiece. Therefore, the focal length of 5 to 7.5 inches (127 to 190 mm) is widely used in high-power CO2 laser cutting industrial applications. The actual spot diameter is between 0.1 and 0.4mm. For high quality cuts, the effective depth of focus is also related to the lens diameter and the material being cut. For example, the carbon steel is cut with a 5 inch lens, and the depth of focus is within 2% of the focal length, that is, about 5 mm. Therefore, it is important to control the position of the focal point relative to the surface of the material being cut. Concerned with the cutting quality, cutting speed and other factors, in principle <6mm metal material, the focus on the surface;> 6mm carbon steel, the focus on the surface;> 6mm stainless steel, the focus is below the surface. The specific size is determined by experiment.

There are three printing methods to determine the focus position in industrial production: the cutting head is moved from the top down, the laser beam printing is performed on the plastic plate, and the spot where the diameter is the smallest is printed.

Inclined plate method: Use a plastic plate tilted at an angle to the vertical axis to pull it horizontally, looking for the focal point of the laser beam at its minimum.

The blue spark method: Remove the nozzle, blow the air, and place the pulsed laser on the stainless steel plate, moving the cutting head from top to bottom, until the blue spark is in focus.

For the cutting machine of the flying light path, due to the divergence angle of the light beam, the length of the light path is different when cutting the near end and the far end, and the beam size before the focusing has a certain difference. The larger the diameter of the incident beam, the smaller the diameter of the focal spot. In order to reduce the change of focal spot size brought about by the change of the beam size before focusing, manufacturers of laser cutting systems at home and abroad provide some special devices for users to choose:

The collimator, which is a common method, adds a collimator at the output of the CO2 laser to expand the beam. After the beam expands, the diameter of the beam becomes larger and the divergence angle becomes smaller. The end-to-end focus beam size is nearly uniform.

A separate lower axis of the moving lens is added to the cutting head. The Z axis which controls the standoff of the nozzle to the material surface is two independent parts. When the machine table moves or the optical axis moves, the beam also moves from the near end to the far end F axis, so that the spot diameter remains the same throughout the entire processing area after the beam is focused.