Any thermal cutting technique, except in a few cases where it may start from the edge of the plate, generally requires a small hole in the plate. In the past, Precision Laser Cutting Equipment first punched a hole, and then the laser was used to cut from the small hole. There are two basic methods for piercing laser cutting machines without punching devices:
Blasting perforation – The material is irradiated with a continuous laser to form a pit in the center, and then the molten material is quickly removed by a stream of oxygen coaxial with the laser beam to form a hole. The size of the holes in small laser cutting equipment generally depends on the sheet thickness, and the average diameter of the beam perforation is half of the sheet thickness. Therefore, the opening of the beam perforation is larger and non-circular for thicker sheets, and should not be used for parts with high requirements for machining accuracy. It can be used only for waste materials. In addition, since perforating uses the same oxygen pressure as cutting, significant spattering occurs.
Pulse perforation – A small amount of material is melted or vaporized using a peak power pulse laser. Air or nitrogen is typically used as an assist gas to reduce hole expansion due to exothermic oxidation, and the gas pressure is lower than the oxygen pressure used in cutting. Each laser pulse produces only small particle beams that penetrate gradually, so the perforation time for thick sheets is only a few seconds. Once perforation is complete, the auxiliary gas for cutting is immediately replaced by oxygen. In this way, the perforation diameter is smaller and the perforation quality is better than beam perforation. The laser used for this purpose should not only have high output power; especially the temporal and spatial characteristics of the beam make it difficult for general CO2 cross- flow lasers to meet the requirements of laser cutting. In addition, pulse perforating also requires a reliable gas path control system to achieve the gas type, gas pressure switching and perforation timing.
In order to achieve high-quality cuts on small precision laser cutting machines with pulse grooving, the transition technology from pulse grooving with the workpiece stationary to continuous cutting of the workpiece at a constant speed should be taken seriously. 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 reality, it is unlikely to change these conditions due to the short time. In industrial production, it is more practical to mainly use the method of changing the average laser power. The specific method for small laser cutting machines is to change the pulse width, change the pulse frequency, and change the pulse width and frequency at the same time.