One of the advantages of laser cutting is that the energy density of the beam is high, so the diameter of the focus spot will be as small as possible, so as to produce extremely small slits. Because the smaller the focal depth of the focusing lens, the smaller the diameter of the focal spot. For high-quality and high-precision cutting, the effective focal depth is also related to the lens diameter and the material to be cut, so it is very important to control the position of the focus and the surface of the material to be cut.
So, what is focus control? Users familiar with high-speed laser cutting machine tools know that when high-speed laser cutting is used to cut plates with different material thicknesses, in order to present a perfect cutting effect, the focus of the laser beam will be set in different places, which is called focusing.
In the early days of laser cutting application, focusing depended on manual. Now, with the development of laser technology, manual focusing will eventually be eliminated, and automatic focusing function will be explored instead. For example, high-performance high-speed laser cutting machine tools all have high-efficiency automatic focusing function. Then, some people will say that the light path is integrated in the cutting head, so it is not OK to simply change the laser height? When the cutting head is raised, the focus position is high, and when the cutting head is lowered, the focus position is low.
However, the facts proved that it was not as simple as everyone imagined. The bottom of the cutting head is the nozzle. During the cutting process, the distance between the nozzle and the workpiece (nozzle height) is about 0.5~1.5mm, which can be regarded as a fixed value, that is, the nozzle height remains unchanged, so it is not possible to focus by lifting the laser head.
One way of focusing is that the focus of the focusing mirror cannot be changed, so it is unrealistic to focus by changing the focus. If the position of the focusing mirror is changed, the focus position is correspondingly changed: if the focusing mirror drops, the focus drops, and if the focusing mirror rises, the focus rises– This is really a way of focusing. Auto focusing can be realized by using a motor to drive the focusing mirror to move up and down.
Another automatic focusing method is to set a variable curvature mirror (or adjustable mirror) before the beam enters the focusing mirror, and change the divergence angle of the reflected beam and the focus position by changing the curvature of the mirror. With the auto focusing function, when processing workpieces of different materials and thicknesses, the machine can automatically and quickly adjust the focus to the appropriate position by relying on NC. This can significantly improve the processing efficiency of high-speed laser cutting machine tools, and the thick plate piercing time will be greatly reduced.
Therefore, for high-speed laser cutting machine, auto focusing function is an important and indispensable function.