Laser cutting is to irradiate the laser beam on the material to be cut, heat up, melt and vaporize the material, blow away the melt with high-pressure gas to form a hole, and then the beam moves on the material, and the hole continuously forms a cutting seam.
In general thermal cutting technology, except for a few cases that can start from the edge of the plate, most of them need to penetrate a small hole on the plate, and then cut from the small hole.
Laser perforation principle
The basic principle of laser perforation is: when a certain energy laser beam irradiates on the surface of metal plate, except that part of it is reflected, the energy absorbed by the metal melts the metal to form a metal melting pool.
The absorption rate of molten metal relative to the metal surface increases, that is, it can absorb more energy and accelerate the melting of metal.
At this time, properly controlling the energy and air pressure can remove the molten metal in the molten pool and continuously deepen the molten pool until it penetrates the metal.
In practical application, perforation is usually divided into two ways: pulse perforation and blasting perforation.
01. Pulse perforation
The principle of pulse perforation is to irradiate the plate to be cut with pulse laser with high peak power and low duty cycle, so as to melt or vaporize a small amount of material, and be discharged from the hole through under the joint action of continuous beating and auxiliary gas, and continue to penetrate the plate step by step.
The time of laser irradiation is intermittent, and the average energy used is relatively low, so the heat absorbed by all the processed materials is relatively small.
There is less residual heat around the perforation and less residual residue at the perforation.
In this way, the through hole is also regular and small in size, which will basically have no impact on the initial cutting.
The process is shown in the following figure: after the laser beam irradiates the workpiece, the material surface will be heated first, as shown in (A);
With the gradual deepening of heating, it plays the role of perforation, that is (B) ~ (C) ~ (D), until the penetration shown in the last (E).
The whole perforation process is not completed at one time, but many times, step by step, gradually deepening until penetration.
Therefore, the perforation time of this method is relatively long; However, the obtained holes are smaller and have less thermal impact on the surrounding.
02. Blasting perforation
Principle of blasting perforation: irradiate the processed object with a certain energy continuous wave laser beam, make it absorb a large amount of energy and melt, form a pit, and then remove the molten material by auxiliary gas to form a hole, so as to achieve the purpose of rapid penetration.
Due to continuous laser irradiation, the hole diameter of blasting perforation is large and the splash is severe, so it is not suitable for cutting with high accuracy requirements.
The whole process is shown in the figure above: set the focus higher than the surface of the material and increase the aperture of the perforation to heat quickly.
Although this perforation method will produce a large amount of molten metal and sputter it onto the surface of the processed material, it can greatly reduce the perforation time.
The actual effects of the two perforation methods are shown in the figure below.
In most cases, the quality of pulse perforation is better than blasting perforation.