Any kind of thermal cutting technique, except in a few cases, can start from the edge of the board, and generally, a small hole must be worn in the board. Previously, on a laser stamping compound machine, a punch was used to punch out a hole, and then a laser was used to cut from the small hole. There are two basic methods for perforating a laser cutter without a stamping device:
Blasting perforation - The material forms a pit at the centre after continuous laser irradiation, and then the molten material is quickly removed by the flow of oxygen 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 blasting hole of the thicker plate has a large hole diameter and is not round, and it is not suitable for use on parts with high processing precision. On the waste. In addition, since the oxygen pressure used for the perforation is the same as that at the time of cutting, the splash is large.
Pulse perforation - Pulsed laser with high peak power is used to melt or vaporize a small amount of material. Air or nitrogen is usually used as an auxiliary gas to reduce the expansion of pores due to exothermic oxidation. The gas pressure is lower than that when cutting. Each pulsed laser produces only a small particle jet that is progressively deeper, so the slab perforation time takes a few seconds. Once the perforation is completed, the auxiliary gas is immediately exchanged for oxygen for cutting. Thus, the perforation diameter is small, and the perforation quality is superior to the blasting perforation The laser used for this purpose should not only have 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. In addition, pulse perforation requires a more reliable pneumatic control system to achieve
gas type, gas pressure switching and perforation time control.
In the case of pulsed perforation, in order to obtain high-quality incisions, transition techniques from pulse perforation of the workpiece at rest to the constant-speed continuous cutting of the workpiece should be taken into account. In theory, 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 that the above conditions are changed due to too short a time. In industrial production, the method of changing the average laser power is mainly used. The specific method is to change the pulse width; change the pulse frequency; and change the pulse width and frequency at the same time. The actual results show that the third effect is the best.