Cutting perforation technology
Any kind of thermal cutting technology, except for a few cases, which can start from the edge of the board, generally a small hole must be drilled in the board. Earlier on the laser punching compound machine, a punch was used to punch out a hole, and then a laser was used to start cutting from the small hole. For the laser cutting machine without punching device, there are two basic methods of perforation:
⑴Blast drilling: (Blast drilling), the material is irradiated by the continuous laser to form a pit in the center, and then the molten material is quickly removed by the oxygen stream coaxial with the laser beam to form a hole. Generally, the size of the hole is related to the plate thickness. The average diameter of the blasting perforation is half of the plate thickness. Therefore, for thicker plates, the blasting perforation has a larger aperture and is not round. It is not suitable for use on parts with higher requirements (such as oil screen pipes). ), can only be used on scrap. In addition, since the oxygen pressure used for perforation is the same as that used for cutting, the splash is larger.
⑵Pulse drilling: (Pulse drilling) uses high peak power pulse laser to melt or vaporize a small amount of material. Air or nitrogen is often used as auxiliary gas to reduce the expansion of holes due to exothermic oxidation. The gas pressure is lower than the oxygen pressure during cutting. Each pulse laser only produces small particle jets, which gradually penetrate deeper, so it takes a few seconds for the thick plate to perforate. Once the perforation is completed, immediately change the auxiliary gas to oxygen for cutting. In this way, the diameter of the perforation is smaller, and the perforation quality is better than that of blasting perforation. For this reason, the laser used should not only have a higher 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.
Key technology two
Nozzle design and control technology
When laser cutting steel, oxygen and a focused laser beam are shot through the nozzle to the material to be cut, thereby forming an air stream. The basic requirement for air flow is that the air flow into the incision should be large and the speed should be high, so that enough oxidation can make the incision material fully carry out the exothermic reaction; at the same time, there is enough momentum to spray the molten material out. 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 airflow (such as the nozzle pressure, the position of the work piece in the airflow, etc.) are also very important factors. Nowadays, the nozzle used for laser cutting adopts a simple structure, that is, a tapered hole with a small round hole at the end. Usually design with experiment and error method. Since the nozzle is generally made of red copper, the volume is small, and it is a vulnerable part that needs to be replaced frequently, so fluid mechanics calculation and analysis are not performed. When in use, a certain pressure Pn (gauge pressure is Pg) gas is introduced from the side of the nozzle, which is called the nozzle pressure, which is sprayed from the nozzle outlet and reaches the surface of the work piece after a certain distance. The pressure is called the cutting pressure Pc, and finally the gas expands to atmospheric pressure. Pa. Research work has shown that with the increase of Pn, the air flow rate increases, and Pc also increases.
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