Any thermal cutting technique, except in a few cases where it can start from the edge of the board, generally has to make a small hole in the board. Earlier, on the laser stamping compound machine, a punch was used to punch a hole, and then a laser was used to start cutting from the small hole. There are two basic methods of perforation for laser cutting machines without punching devices:
(1) Blast drilling: (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 of the thickness of the plate. Therefore, the diameter of the blasting perforation for thicker plates is larger and not round, so it should not be used on parts with higher requirements (such as oil screen slit pipes). ), can only be used on scrap. In addition, since the oxygen pressure used for perforation is the same as that for cutting, the splash is larger.
(2) Pulse drilling: (Pulse drilling) uses a pulsed laser with high peak power to melt or vaporize a small amount of material. Air or nitrogen is often used as an auxiliary gas to reduce the expansion of the hole due to exothermic oxidation. The gas pressure is lower than the oxygen pressure during cutting. Each pulsed laser produces only a small jet of particles, progressively deeper, so the perforation time for thick plates takes a few seconds. Once the piercing is complete, immediately change the assist 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. The laser used for this purpose should not only have high output power; more importantly, the time and space characteristics of the beam, so the general cross-flow CO2 laser can not meet the requirements of laser cutting. In addition, pulse perforation also needs a more reliable gas circuit control system 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 cuts, the transition technology from pulse piercing when the workpiece is stationary to constant-speed continuous cutting of the workpiece should be paid attention to. Theoretically speaking, it is usually possible to change the cutting conditions of the acceleration section: such as focal length, nozzle position, gas pressure, etc., but in practice, it is unlikely to change the above conditions because the time is too short. In industrial production, it is more realistic to mainly use the method of changing the average laser power. There are three specific methods:
(1) Change the pulse width;
⑵ change the pulse frequency;
(3) Simultaneously change the pulse width and frequency. The actual results show that the third kind has the best effect.
