How to cut high-quality products with a laser cutting machine?
In CO2 laser cutting machines, for parts with high cutting accuracy or large thickness, several key technologies must be mastered and solved. 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 focal spot diameter is as small as possible 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 being cut. Therefore, it is very important to control the position of the focus 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 the laser beam is focused, the spot size is proportional to the focal length of the lens. After the beam is focused by a short focal length lens, the spot size is very small, and the power density at the focus is very high, which is very beneficial for material cutting; but its disadvantage is that the focal depth is very short and the adjustment margin is small. It is generally more suitable for high-speed cutting of thin materials. Since the long focal length lens has a wider focal depth, as long as it has sufficient power density, it is more suitable for cutting thick workpieces.
After determining which focal length lens to use, the relative position of the focus and the workpiece surface is particularly important to ensure cutting quality. Since the power density is highest at the focal point, in most cases, the focal position is just on the workpiece surface or slightly below the surface during cutting. During the entire cutting process, ensuring that the relative position of the focus and the workpiece is constant is an important condition for obtaining stable cutting quality. Sometimes, due to poor cooling, the lens is heated during operation, causing the focal length to change, which requires timely adjustment of the focus position.
When the focus is at the optimal position, the cutting gap is the smallest, the efficiency is the highest, and the optimal cutting speed can obtain the best cutting result. In most applications, the beam focus is adjusted to just below 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. There are three common simple methods to determine the focus position:
(1) Printing method: Move the cutting head from top to bottom and print the laser beam on the plastic plate. The point with the smallest print 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 find the smallest point of the laser beam as the focus.
(3) Blue spark method: Remove the nozzle, blow air, and shine the pulse laser on the stainless steel plate. Move the cutting head from top to bottom until the blue spark is the largest point as the focus.