Laser cutting equipment (4)

(1) Focusing lens

A focusing lens is used to focus the parallel laser beam that is incident on the torch to obtain a smaller spot and a higher power density. Lenses are often made of materials that transmit laser wavelengths. Solid-state lasers are commonly used for optical glass, while CO2 gas lasers are made of materials such as ZnSe, GaAs, and Ge because they are not transparent to ordinary glass. The most common one is ZnSe.

The shape of the lens has three types of a convex shape, a flat convex shape, and a concave-convex shape. The focal length of the lens has a large effect on the spot diameter and depth of focus after focusing. The relationship between the focused spot diameter do and the lens focal length f and the incident laser beam diameter D is shown in Fig. 5. As can be seen from the figure, when the incident laser beam diameter D is constant, there is an optimum lens focal length f value which minimizes the focused spot diameter do.

The relationship between the focal depth fd and the focal length f of the lens is shown in Fig. 6. As the focal length of the lens decreases, the depth of focus also becomes smaller.

For laser cutting, it is desirable to focus the spot diameter as much as possible. In this way, the power density can be increased, which is advantageous for high-speed cutting. However, when the focal length of the lens is reduced, the depth of focus is also small, and it is difficult to obtain a cutting surface with a good verticality when cutting a plate having a large thickness. In addition, when the focal length of the lens is small, the distance between the lens and the workpiece is also reduced, and the lens is easily stained by slag substances such as splashing during the cutting process, which affects the normal cutting. Therefore, it is required to comprehensively consider factors such as cutting thickness and cutting quality requirements to determine an appropriate focal length.

(2) Mirror

The function of the mirror is to change the direction of the beam from the laser. The beam from the solid-state laser can use a mirror made of optical glass, while the mirror in the CO ₂ gas laser cutting device is usually made of copper or a metal with high reflectivity. During the use of the mirror, in order to avoid damage to the mirror due to overheating of the light, it is usually required to cool with water.

(3) Nozzle

The nozzle is used to spray the auxiliary gas to the cutting zone, and its structural shape has an influence on the cutting efficiency and quality. Figure 7 shows the nozzle shape commonly used for laser cutting, and the shape of the orifice is cylindrical, tapered and scaled. The selection of the nozzle is generally determined according to the material, thickness, and auxiliary gas pressure of the workpiece to be cut.

Laser cutting generally uses coaxial (airflow and optical axis concentric) nozzles. If the airflow is different from the beam, it will cause a lot of splashing during cutting. The hole wall of the nozzle hole should be smooth to ensure the smooth flow and avoid the influence of turbulence on the quality of the cut. In order to ensure the stability of the cutting process, the distance from the nozzle end surface to the workpiece surface should generally be minimized, usually taking 0.5 to 2.0 mm.

When cutting certain metals with inert gas, it is advisable to use a nozzle with a protective cover to protect the metal in the cut-out area from air intrusion (usually when the nozzle is suddenly entangled in the cutting area when the cutting direction changes abruptly). . The nozzle structure of the glass wool protective cover is shown in Figure 8.

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Transparent Roller Shutter Door

Material: polycarbonate (PC bulletproof plastic)