Laser cutting machines must master and solve several key technologies for cutting parts with high precision or large thickness. Focus position control technology 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 material being cut. Therefore, it is very important to control the position of the focus relative to the surface of the material being cut.

How to cut high-quality products with a sheet metal fiber laser cutting machine?

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; However, 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, 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 between the focus and the workpiece surface is particularly important to ensure the cutting quality. Because the power density at the focus is the highest, in most cases, the focus position is just on the workpiece surface or slightly below the surface when cutting. In the whole cutting process, ensuring that the relative position between the focus and the workpiece is constant is an important condition to obtain stable cutting quality. Sometimes, the lens is heated due to poor cooling during operation, resulting in changes in focal length, which requires timely adjustment of 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 result. In most applications, the beam focus is adjusted to just under the nozzle. The distance between the nozzle and workpiece surface is generally about 1.5mm.

In the process of laser application, we often encounter problems such as focusing. There are three simple methods to determine the focus position:

• Printing method: make the cutting head move from top to bottom, and carry out laser beam printing on the plastic plate, with the smallest printing diameter as the focus.

• Inclined plate method: use a plastic plate placed obliquely at an angle to the vertical axis to pull it horizontally to find the smallest part of the laser beam as the focus.

• Blue spark method: remove the nozzle, blow air, hit the pulse laser on the stainless steel plate, and make the cutting head move from top to bottom until the maximum blue spark is the focus.

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