Laser cutting is to irradiate a laser beam on the material to be cut, so that the material is heated, melted, and vaporized, and the melt is blown away with high-pressure gas to form a hole, and then the beam moves on the material, and the hole continuously forms a slit.
In general thermal cutting technology, except for a few cases, which can be started from the edge of the plate, most of them need to punch a small hole in the plate, and then start cutting from the small hole.
The principle of laser perforation
The basic principle of laser perforation is: when a certain energy laser beam is irradiated on the surface of the metal sheet, in addition to a part of it being reflected, the energy absorbed by the metal melts the metal to form a molten metal pool. The absorption rate of the molten metal relative to the metal surface increases, that is, more energy can be absorbed to accelerate the melting of the metal. At this time, proper control of energy and air pressure can remove the molten metal in the molten pool, and continuously deepen the molten pool until the metal is penetrated.
And perforation is usually divided into two ways: pulse perforation and blast perforation.
Pulse perforation
The principle of pulse perforation is to use a pulsed laser with high peak power and low duty cycle to irradiate the plate to be cut, so that a small amount of material is melted or vaporized, and is discharged through the hole under the combined action of continuous beating and auxiliary gas, and continuously. Work gradually until the sheet is penetrated.
The time of laser irradiation is intermittent, and the average energy used is relatively low, so the heat absorbed by the entire material to be processed is relatively small. There is less residual heat around the perforation and less residue remains at the perforation site. The holes pierced in this way are also relatively regular and small in size, and basically have no effect on the initial cutting.
The process is shown in the figure below: after the laser beam is irradiated on the workpiece, the surface of the material will be heated first, as shown in (A); as the heating gradually deepens, it will play a role in perforation, that is, (B) ~ (C) ~(D) until the last penetration shown in (E). The entire perforation process is not completed at one time but is continued step by step and gradually deepens until it penetrates. Therefore, this method takes a relatively long time to perforate; however, the resulting holes are smaller and have less impact on the surrounding heat.
Blasting perforation
The principle of blasting perforation: irradiate the processed object with a continuous wave laser beam of a certain energy, so that it absorbs a large amount of energy and melts to form a pit, and then the molten material is removed by the auxiliary gas to form a hole to achieve rapid penetration purpose.
Due to the continuous irradiation of the laser, the hole diameter of the blasting perforation is large, and the splash is severe, which is not suitable for cutting with high precision requirements.
The whole process is shown in the picture below: set the focus above the surface of the material, and increase the aperture of the perforation to heat quickly. Although this piercing method produces a large amount of molten metal and sputters onto the surface of the processed material, it can greatly reduce the piercing time.
In most cases, the quality of pulse piercing is better than blast piercing.
