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Laser cutting machine technology

07.01.2020 22:59

 
Several key technologies of laser cutting machine are integrated technology of light, machine and electricity integration. In the laser cutting machine, the parameters of the laser beam, the performance and accuracy of the machine and the CNC system directly affect the efficiency and quality of the laser cutting. Especially for parts with high cutting accuracy or thickness, the following key technologies must be mastered and solved: 1. Focus position control technology: One of the advantages of laser cutting is the high energy density of the beam, generally 10W / cm2. Since the energy density is 4 /
Several key technologies of laser cutting machine are integrated technology of light, machine and electricity integration.
 
In the laser cutting machine, the parameters of the laser beam, the performance and accuracy of the machine and the CNC system directly affect the efficiency and quality of the laser cutting. Especially for parts with high cutting accuracy or thickness, the following key technologies must be mastered and solved: 1. Focus position control technology: One of the advantages of laser cutting is the high energy density of the beam, generally 10W / cm2. Because the energy density is proportional to 4 / πd2, the focal spot diameter is as small as possible to produce a narrow slit; 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 focusing lens, the smaller the focal spot diameter. However, the cutting has splashes, and the lens is too close to the workpiece, which easily damages the lens. Therefore, in general industrial applications of high-power CO2 laser cutting machines, a focal length of 5〃 ~ 7.5〃 (127 ~ 190mm) is widely used. The actual focal spot diameter is 0.1 ~ 0.4 mm. For high-quality cutting, the effective focal depth is also related to the lens diameter and the material being cut. For example, if you cut carbon steel with a 5mm lens, the focal depth is within + 2% of the focal length, which is about 5mm. The position of the focal point relative to the surface of the material being cut is very important. In consideration of cutting quality, cutting speed and other factors, in principle 6mm metal materials, the focus is on the surface; 6mm carbon steel, the focus is on the surface; 6mm stainless steel, the focus Below the surface. Specific dimensions are determined experimentally.
 
There are three easy ways to determine the focus position in industrial production:
 
 (1) Printing method: The cutting head is moved from top to bottom, and laser beam printing is performed on a plastic plate, and the smallest printing diameter is the focus.
 (2) Inclined plate method: Use a plastic plate inclined at an angle to the vertical axis to pull it horizontally, and look for the smallest part of the laser beam as the focus.
 (3) 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 blue spark is the focus.
 
 For the cutting machine of the flying optical path, due to the divergence angle of the beam, the length of the optical path is different when cutting the near end and the far end, and the beam size before focusing is different. The larger the diameter of the incident beam, the smaller the diameter of the focal spot. In order to reduce the change in the size of the focal spot caused by the change in the beam size before focusing, manufacturers of laser cutting systems at home and abroad have provided some special devices for users to choose from:
 
 (1) Parallel light tube. This is a commonly used method, that is, adding a parallel light tube to the output end of the CO2 laser to expand the beam. The diameter of the expanded beam becomes larger and the divergence angle becomes smaller, so that the near and far ends are within the cutting working range. The beam size is nearly uniform before focusing.
 (2) An independent moving lens lower axis is added to the cutting head, and it is two independent parts with the Z axis which controls the distance from the nozzle to the surface of the material (stand off). When the machine tool table is moved or the optical axis is moved, the beam is also moved from the near end to the far F axis at the same time, so that the spot diameter after the beam is focused remains the same throughout the processing area.
 (3) Control the water pressure of the focusing mirror (usually a metal reflection focusing system). If the beam size before focusing becomes smaller and the focal spot diameter becomes larger, the water pressure is automatically controlled to change the focusing curvature to make the focal spot diameter smaller.
 (4) The compensation optical path system for the x and y directions is added to the flying optical path cutter. That is, the compensation optical path is shortened when the cutting end optical path is increased; otherwise, when the cutting near end optical path is decreased, the compensation optical path is increased to keep the optical path length consistent.
 
2. Cutting and perforating technology: Any kind of thermal cutting technology, except for a few cases, can start from the edge of the board. Generally, a small hole must be punched in the board. Earlier on the laser punching compound machine, a hole was first punched out with a punch, and then the laser was used to cut from the small hole. There are two basic methods of perforating a laser cutting machine without a stamping device:
 
 (1) Blast drilling: After the material is irradiated by continuous laser, a pit is formed in the center, and then the molten material is quickly removed by the oxygen flow coaxial with the laser beam to form a hole. Generally, the size of the hole is related to the thickness of the plate. The average diameter of the blasting perforation is half the thickness of the plate. Therefore, the blasting perforation of the thicker plate is larger and not round, so it should not be used on more demanding parts (such as petroleum sieve slit pipe). ), Can only be used on waste. In addition, because the oxygen pressure used for perforation is the same as that for cutting, the splash is large.
 (2) Pulse drilling: (Pulse drilling) uses a high peak power pulse laser to melt or vaporize a small amount of material, usually using air or nitrogen as an auxiliary gas to reduce the hole expansion due to exothermic oxidation, and the gas pressure is higher than the oxygen pressure during cutting small. Each pulsed laser produces only a small particle jet, which is gradually deepened, so the perforation time of the thick plate takes a few seconds. Once the perforation is completed, the auxiliary gas is immediately replaced with oxygen for cutting. In this way, the diameter of the perforation is small, and the quality of the perforation is better than that of blasting. The laser used for this purpose should not only have a high output power; more importantly, the time and space characteristics of the beam, so the general cross-flow CO2 laser cannot meet the requirements of laser cutting. In addition, pulse perforation also requires a more reliable gas path control system to achieve the switching of gas type, gas pressure, and perforation time. In the case of pulse perforation, in order to obtain high-quality incisions, the transition technology from pulse perforation when the workpiece is stationary to continuous constant-speed cutting of the workpiece should be taken seriously. In theory, the cutting conditions of the acceleration section can usually be changed: focal length, nozzle position, gas pressure, etc., but it is unlikely that the above conditions will be changed because the time is too short.
 
 In industrial production, it is more realistic to mainly adopt the method of changing the average laser power. The specific methods are as follows:
 
 (1) Change the pulse width;
 (2) Change the pulse frequency;
 (3) Change the pulse width and frequency at the same time. The actual results show that (3) is the best.
 
3. Nozzle design and airflow control technology: When laser cutting steel, oxygen and focused laser beam are shot through the nozzle to the material to be cut, thereby forming an airflow beam. The basic requirements for the air flow are that the air flow into the incision should be large and the speed should be high, so that sufficient oxidation can make the incision material fully exothermic; at the same time, there is sufficient momentum to eject the molten material. Therefore, in addition to the quality of the beam and its control directly affecting the cutting quality, the design of the nozzle and the control of the air flow (such as the nozzle pressure and the position of the workpiece in the air flow) are also very important factors. At present, the nozzle for laser cutting adopts a simple structure, that is, a tapered hole with a small round hole at the end. Design is usually done experimentally and error-wise. Because the nozzle is generally made of copper, its volume is small, it is a fragile part, and it needs to be replaced frequently. Therefore, fluid mechanics calculation and analysis are not performed. When in use, a gas with a certain pressure Pn (gauge pressure is Pg) is introduced from the side of the nozzle, which is called the nozzle pressure, which is ejected from the nozzle outlet and reaches the workpiece surface after a certain distance. The pressure is called the cutting pressure Pc, and the gas expands to atmospheric pressure. Pa. Research work shows that with the increase of Pn, the air flow velocity increases and Pc also increases.
 
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Source: jichuang.net