In the CO2 laser cutting machine, several key technologies must be mastered and solved for parts with high precision or large thickness. Focus position control technology is one of them. One of the advantages of laser cutting is that the energy density of the beam is high, so the focus spot diameter is as small as possible in order to produce 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 to be cut. It is therefore important to control the focus relative to the position of 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 problem. The spot size of the laser beam after focusing is proportional to the focal length of the lens. The spot size of the laser beam after focusing by the short focal length lens is small, and the power density at the focal point is high, which is beneficial for material cutting. However, its disadvantage is that the focal depth is very short, the adjustment margin is small, and it is generally more suitable for high-speed cutting thin materials. Because the long lens has a wide focal depth, as long as it has sufficient power density, it is more suitable for cutting thick workpieces.

After determining what kind of focal length lens to use, the position of the focus relative to the workpiece surface is particularly important to ensure the quality of the cut. Due to the highest power density at the focus, in most cases, the focus position is just at the surface of the workpiece when cutting, or slightly below the surface. Throughout the cutting process, ensuring the constant position of the focus relative to the workpiece is an important condition for obtaining stable cutting quality. Sometimes, the lens is heated due to poor cooling during operation, which causes the focal length to change, which requires timely adjustment of the focus position.

When the focus is in the best position, the slit is the smallest, the efficiency is the highest, and the best cutting speed can obtain the best cutting results. In most applications, the beam focus is adjusted to just under the nozzle. The distance between the nozzle and the workpiece surface is generally about 1.5 mm.

In the process of laser application, problems such as focusing are often encountered, and there are three simple ways to determine the focus position:

(1) Printing method: make the cutting head move from top to bottom, print the laser beam on the plastic plate, and the smallest diameter of the print is the focus.

(2) Inclined plate method: The plastic plate placed at an Angle to the vertical axis is pulled horizontally, and the smallest point of the laser beam is found as the focus.

(3) Blue spark method: Remove the nozzle, blow air, pulse laser on the stainless steel plate, so that the cutting head moves from the top down until the blue spark is the largest focus.