Laser cutting of copper, aluminum and their alloys
During laser cutting, the laser with high energy density is focused by the focusing lens and irradiates on the workpiece. Part of the light energy is absorbed, and the other part of the light energy is reflected by the workpiece. The reflected laser returns to the inside of the laser along the optical path at the time of incidence, which will cause the power instability of the laser and even damage the laser. The laser cutting is interrupted and normal processing cannot be carried out.
Both copper and aluminum have the characteristics of high reflectivity, extremely low laser absorption, and good thermal conductivity. Therefore, when the laser irradiates this kind of material, only a small part of the energy is absorbed, and most of the energy will be reflected back. At the same time, it will quickly transfer the heat of the irradiated part to the surrounding. This makes laser cutting of copper, aluminum and their alloys extremely difficult, or even impossible.
Different wavelength laser absorption degree is different
Although the absorptivity of copper, aluminum and their alloys to laser is very low, the good thing is that with the change of laser wavelength, the absorptivity will also change. According to the research on the absorptivity of materials under the irradiation of lasers with different wavelengths, it can be found that copper aluminum materials have the lowest absorptivity of lasers near the wavelength of 10 microns, so the carbon dioxide laser with the wavelength of 10.6 microns is not suitable for cutting such materials, which will lead to low cutting quality and damage to the laser itself. In fact, most high-power carbon dioxide laser mirrors are made of copper based on this principle.
When the laser wavelength is around 355 nm and 532 nm, the absorptivity of copper and aluminum will be significantly higher. However, due to the low power of this kind of laser, the laser cutting speed is low and thick materials cannot be processed. Even for the processing of extremely thin copper foil and aluminum foil, the processing effect is good, but the cost is also high.
Only when the laser wavelength is around 1070 nm, not only the absorption rate of copper and aluminum is high, but also the output power of fiber laser is large. It is an ideal laser band for cutting copper and aluminum materials. Moreover, the fiber laser does not need maintenance, with high photoelectric conversion efficiency and relatively energy saving, so it has become the best choice for laser cutting of copper and aluminum alloys.
Advantages and precautions of fiber laser cutting copper and aluminum
When using fiber laser to cut copper, aluminum and their alloy materials, it has the advantages of fast processing speed, light load on the galvanometer, fast rotation, and high efficiency in processing complex graphics; It can realize roll to roll processing and online processing of materials; The edge of the processed workpiece is flat and the heat affected area is very small; Flexible machining can be realized, and the cutting style can be easily changed by changing the machining graphics; It consumes less electric energy and does not need other consumables.
As for the problem of laser damage caused by the reflected laser returning to the laser in the opposite direction of the incident optical path, the following methods can be used: first, select the laser with anti reflection function. When the laser is reflected back to the laser, the energy will be absorbed to prevent it from entering the laser resonator, so as to protect the normal operation of the laser. The second is to adopt special technology to prevent the laser from returning to the laser along the optical path. Finally, special processes can be used to increase the absorption rate of materials and accelerate the process of laser perforation and laser cutting.