In laser cutting machine, for key parts with high cutting precision or thickness, several key technologies must be mastered and solved. Focus position control is one of them. One of the advantages of laser cutting is the high energy density of the beam, so the diameter of the focal spot is as small as possible in order to create a narrow slit. Because the smaller the focal depth of the focusing lens, the smaller the focal spot diameter. For high-quality cutting, the effective focal depth is also related to the lens diameter and the material being cut. It is therefore important to control the position of the focal point relative to the surface of the material being cut.
Since the laser power density has a great influence on the cutting speed, the choice of lens focal length is an important issue. After focusing, the spot size of the laser beam is proportional to the focal length of the lens. The spot size of the beam after focusing by the short focal length lens is small, and the power density at the focal point is very high, which is very beneficial for material cutting. However, it has the short focal depth and the adjustment margin. Small, generally suitable for high-speed cutting of thin materials. Because the telephoto lens has a wide focal depth, as long as it has sufficient power density, it is more suitable for cutting thick workpieces.
When the focus is in the proper position, the slit is small, the efficiency is high, and the cutting speed can obtain good cutting results. In most applications, the beam focus is adjusted just below the nozzle. The distance between the nozzle and the surface of the workpiece is generally about 1.5mm.During laser applications, problems such as focusing are often encountered. There are three common easy ways to determine the focus position:
(1) Printing method: The cutting head is moved from top to bottom, and laser beam printing is performed on a plastic plate. The smaller printing diameter is the focus.
(2) Inclined plate method: Use a plastic plate placed at an angle to the vertical axis to pull it horizontally, and look for the smaller part of the laser beam as the focus.
(3) Blue spark method: Remove the nozzle, blow air, hit the pulsed laser on the stainless steel plate, and move the cutting head from top to bottom until the blue spark is the focus.
