1. Cutting and piercing technology
Any kind of thermal cutting technology, except for a few cases that can start from the edge of the plate, must generally pierce a small hole in the plate. Before, a punch was used to punch a hole on the laser punching compound machine, and then the laser was used to cut from the small hole. There are two basic methods of piercing for laser cutting machines without punching devices:
Blasting perforation - the material is irradiated by a continuous laser to form a pit in the center, and then the molten material is quickly removed by the oxygen flow coaxial with the laser beam to form a hole. The size of general holes is related to the plate thickness, and the average diameter of blasting holes is half of the plate thickness. Therefore, for thicker plates, the blasting holes are larger and not round, so they should not be used on parts with higher processing accuracy requirements, but only on waste materials. In addition, because the oxygen pressure used for perforation is the same as that used for cutting, the spatter is large.
Pulse perforation - use the pulse laser with peak power to melt or vaporize a small amount of materials. Air or nitrogen is often used as the auxiliary gas to reduce the hole expansion due to exothermic oxidation. The gas pressure is lower than the oxygen pressure during cutting. Each pulsed laser only produces a small particle jet, which goes deeper and deeper, so it takes a few seconds for the thick plate to pierce. Once the perforation is completed, replace the auxiliary gas with oxygen for cutting. In this way, the perforation diameter is smaller, and the perforation quality is better than that of blasting perforation. The laser used for this purpose should not only have high output power; What is more important is the temporal and spatial characteristics of the beam, so the general cross flow CO2 laser cutter cannot meet the requirements of laser cutting. In addition, a reliable gas path control system is required for pulse perforation to realize the switching of gas type, gas pressure and control of perforation time.
In the case of pulse piercing, in order to obtain high-quality notch, attention should be paid to the transition technology from pulse piercing when the workpiece is stationary to constant speed continuous cutting of the workpiece. Theoretically, it is usually possible to change the cutting conditions in the acceleration section, such as focal length, nozzle position, gas pressure, etc., but in fact, it is unlikely to change the above conditions due to the short time. In industrial production, it is more realistic to change the average laser power by changing the pulse width; Change the pulse frequency; Change the pulse width and frequency at the same time. The actual results show that the third one is the best.
2. Analysis of deformation of cutting small holes (small diameter and plate thickness)
This is because the machine tool (only for high-power laser cutting machine) does not adopt the method of blasting perforation when processing small holes, but uses the method of pulse perforation (soft puncture), which makes the laser energy too concentrated in a small area, scorching the non processing area, causing hole deformation and affecting the processing quality. At this time, we should change the pulse perforation (soft puncture) mode to the blasting perforation (ordinary puncture) mode in the processing program to solve the problem. On the contrary, for the laser cutting machine with small power, pulse piercing should be adopted to obtain better surface finish.
3. Solution to burr of workpiece when laser cutting low carbon steel
According to the working and design principle of CO2 laser cutting, the following reasons are analyzed and concluded as the main reasons for burrs of workpieces: the upper and lower positions of laser focus are incorrect, so focus position test is required, and adjustment is made according to the offset of focus; The output power of the laser is not enough. Check whether the laser generator works normally. If it works normally, observe whether the output value of the laser control button is correct and adjust it; The linear speed of cutting is too slow, so it is necessary to increase the linear speed during operation control; The purity of cutting gas is not enough, and high-quality cutting working gas needs to be provided; For laser focus shift, focus position test shall be conducted, and adjustment shall be made according to focus shift; If the machine tool runs for too long and becomes unstable, it needs to be shut down and restarted.
Common Problems in Laser Cutting
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