In the laser cutting machine, several key technologies must be mastered and solved for the parts with high cutting precision or large thickness. Focus position control is one of them. One of the advantages of laser cutting is the high energy density of the beam, so the focal spot diameter should be as small as possible to produce a narrow slit. Because the smaller the focal depth of the focus lens, the smaller the focal spot diameter. For high-quality cutting, the effective focal depth is also related to the lens diameter and the cut material. Therefore, it is very important to control the position of the focus relative to the surface of the material to be cut.
Because the laser power density has a great influence on the cutting speed, the choice of lens focal length is an important problem. After the laser beam is focused, the spot size is proportional to the focal length of the lens. After the beam is focused by the short focal length lens, the spot size is very small, and the power density at the focus is very high, which is very beneficial to material cutting; But its disadvantage is that the focal depth is very short and the adjustment allowance is small. It is generally suitable for high-speed cutting of thin materials. Because the long focal length lens has a wide focal depth, it is more suitable for cutting thick workpieces as long as it has sufficient power density.
After determining which focal length lens to use, the relative position between the focus and the workpiece surface is particularly important to ensure the cutting quality. Due to the high power density at the focus, in most cases, the focus position is just on the workpiece surface or slightly below the surface during cutting. In the whole cutting process, it is an important condition to ensure that the relative position between the focus and the workpiece is constant to obtain stable cutting quality. Sometimes, the lens is heated due to poor cooling during operation, resulting in focal length changes, which requires timely adjustment of the focus position.
Laser cutting machine
When the focus is in the appropriate position, the cutting seam is small, the efficiency is high, and the cutting speed can obtain good cutting results. In most applications, the beam focus is adjusted to just below the nozzle. The distance between nozzle and workpiece surface is generally about 1.5mm.
In the process of laser application, focusing and other problems are often encountered. There are three simple methods to determine the focus position:
(1) Printing method: make the cutting head move from top to bottom, and carry out laser beam printing on the plastic plate, with the smaller printing diameter as the focus.
(2) Inclined plate method: use a plastic plate placed at an angle to the vertical axis to pull it horizontally to find the smaller part of the laser beam as the focus.
(3) Blue spark method: remove the nozzle, blow air, strike the pulse laser on the stainless steel plate, and make the cutting head move from top to bottom until the larger blue spark is the focus.