There are two types of laser cutting techniques: one is pulse laser suitable for metal materials. The second type is continuous laser suitable for non-metallic materials, which is an important application field of laser cutting technology.

Several key technologies of laser cutting machines are integrated technologies of light, machinery, and electricity. The parameters of the laser beam, the performance and accuracy of the machine and CNC system in the laser cutting machine directly affect the efficiency and quality of laser cutting. Especially for parts with high cutting accuracy or large thickness, it is necessary to master and solve the following key technologies.

Focus position control technology

One of the advantages of laser cutting is the high energy density of the beam, usually 10W/cm2. Due to the inverse ratio between energy density and area, the diameter of the focal spot should be kept as small as possible to produce a narrow slit; At the same time, the diameter of the focal spot is also proportional to the focal depth of the lens. The smaller the focal depth of the focusing lens, the smaller the diameter of the focal spot. However, there is splashing during cutting, and the lens can be easily damaged if it is too close to the workpiece. Therefore, high-power CO2 laser cutting machines are widely used in industrial applications with a focal length of 5 "~7.5" (127-190mm). The actual focal spot diameter is between 0.1 and 0.4mm. For high-quality cutting, the effective depth of focus is also related to the lens diameter and the material being cut. For example, using a 5 "lens to cut carbon steel, the focal depth is within the range of+2% of the focal length, which is about 5mm. Therefore, controlling the position of the focus relative to the surface of the material being cut is very important. Considering factors such as cutting quality and cutting speed, in principle, 6mm metal materials should focus on the surface; 6mm carbon steel with a focus on the surface; 6mm stainless steel with a focus below the surface. The specific size will be determined by experiments.

There are three simple methods for determining the focal point position in industrial production:

(1) Printing method: Move the cutting head from top to bottom and perform laser beam printing on a plastic plate, with the smallest printing diameter as the focus.

(2) Oblique plate method: Use a plastic plate placed at an angle to the vertical axis to pull it horizontally, searching for the minimum point of the laser beam as the focal point.

(3) Blue Spark Method: Remove the nozzle, blow air, and apply a pulse laser to the stainless steel plate, causing the cutting head to move from top to bottom until the maximum blue spark is the focus.

For cutting machines with flying optical paths, due to the divergence angle of the beam, the distance between the near and far ends of the cutting is different, and there is a certain difference in the beam size before focusing. The larger the diameter of the incident beam, the smaller the diameter of the focal spot. In order to reduce the changes in focal spot size caused by changes in beam size before focusing, domestic and foreign manufacturers of laser cutting systems have provided some specialized devices for users to choose from:

(1) Directional light tube. This is a commonly used method, which involves adding a collimator to the output end of a CO2 laser for beam expansion. The diameter of the expanded beam increases and the divergence angle decreases, making the beam size close to the same before focusing at the near and far ends within the cutting range.

(2) Add an independent lower axis of the moving lens on the cutting head, which is two independent parts from the Z-axis that controls the distance from the nozzle to the material surface (standoff). When the machine tool workbench moves or the optical axis moves, the beam also moves from the near end to the far end of the F-axis, so that the diameter of the spot remains consistent throughout the entire processing area after the beam is focused.

(3) Control the water pressure of the focusing mirror (usually a metal reflective focusing system). If the size of the beam before focusing decreases and the diameter of the focal spot increases, the automatic control of water pressure changes the focusing curvature to reduce the diameter of the focal spot.

(4) Add a compensation light path system in the x and y directions on the flying light path cutting machine. When the optical path at the far end of the cutting increases, the compensation optical path is shortened; On the contrary, when the cutting near end optical path decreases, the compensation optical path increases to maintain consistent optical path length.