The integration of light, machine and electricity is the key technology of laser cutting machine. The laser beam parameters, the performance and accuracy of machine tools and CNC systems directly affect the efficiency and quality of laser cutting. Especially for parts with high cutting accuracy and large thickness, the following key technologies must be mastered and solved:
Laser cutting machine has two technologies: one is the pulse laser suitable for metal materials; The second is the applicability of continuous laser to non-metallic materials, and the second is the important application field of laser cutting technology.
One of the advantages of laser is high energy density, generally 10W/cm2. Because the energy density is inversely proportional to the area, the smaller the focal spot diameter, the narrower the incision; At the same time, the focal spot diameter is also proportional to the focal depth of the lens. The smaller the focal depth of the lens, the smaller the diameter of the focus spot. However, there will be splash in the cutting process, and the lens is too close to the lens, which is easy to damage the lens. Therefore, in the industrial application of general high-power CO2 laser cutting machine, the focal length of 5 ″~7.5 ″ (127~190mm) is widely used. The actual diameter of the focus is 0.1~0.4 mm. For high quality cutting, the effective focal depth is also related to the lens diameter and cutting materials. For example, when cutting carbon steel with a 5 ″ lens, the focal depth is within+2% of the focal length, that is, about 5mm. Therefore, relative to the surface of the material to be cut, the position of the control focus is very important. Considering the cutting quality, cutting speed and other factors, in principle, the metal material is 6mm, focusing on the surface; Carbon steel 6mm, focused on the surface; Stainless steel 6mm, focused below the surface. Determine the specific dimensions by test.
Focusing positioning control technology has three simple positioning methods in industrial production:
(1) Printing method: Move the cutting head up and down, print the laser beam on the plastic plate, and the focus print diameter is the smallest.
Inclination method: tilt the plastic sheet at an angle with the vertical axis, pull it out horizontally, and find the minimum point of the focused laser beam.
(3) Blue spark cutting method: remove the nozzle, blow out air, and hit the steel plate with laser pulse to move the cutting head from up to down until the blue spark reaches the maximum focus.
For the flying optical path cutter, the beam size before focusing is different due to the difference of beam divergence angle, near and far time length. The larger the diameter of the incident light, the smaller the diameter of the focal point. In order to reduce the change of the focus spot size caused by the change of the beam size before focusing, domestic and foreign laser cutting system manufacturers provide some special equipment for users to choose:
A. Directional light tube. A collimator is added to the CO2 laser output end for expansion processing. After expansion, the beam diameter increases, the divergence angle decreases, and the near end and far end beams are nearly identical within the cutting operation range.
(3) Water pressure control focusing mirror (usually metal reflection focusing system). If the beam size becomes smaller before focusing, resulting in an increase in the focus diameter, the focus diameter is reduced by automatically adjusting the curvature of the focus through water pressure.
An independent moving lens lower axis is added to the cutting head, and the distance between its Z axis and the distance from the control nozzle to the material surface (standoff) is two mutually independent parts. When the beam moves from the near end to the far end of the F axis, the machine tool table and the optical axis move at the same time. The diameter of the focused beam spot is consistent in the processing area. It can be seen from Figure 2.
(4) A compensation optical path system is added to the optical path cutting machine of the aircraft, with the direction of x, y. That is, when the optical path of the far end of the cutting increases, in order to maintain the consistency of the optical path length, the compensation optical path needs to be shortened; On the contrary, when the optical path of the far end of the cutting is reduced, the compensation optical path needs to be shortened.