In the application of laser marking technology, the effect of CO2 laser marking machine on non-metallic materials is good, but the performance on metal materials is unsatisfactory, which involves many principles and factors.
The wavelength of CO2 laser is 10.6μm, which is in the far-infrared band. The atomic structure and electronic energy level distribution of metal materials determine that their absorption rate of lasers of this wavelength is low. In terms of physical principles, free electrons in metals can effectively reflect most of the incident light when facing far-infrared lasers. Common metals such as stainless steel and aluminum alloy have a reflectivity of 70% - 90% or more at a wavelength of 10.6μm. As a result, when marking metals, only a small amount of laser energy can act on the material, and the marking effect is naturally not ideal.
CO2 laser marking relies on thermal action, which melts, vaporizes or carbonizes the surface of the material by heating it up to form a mark. However, the good thermal conductivity of metals has become a disadvantage here. When the laser irradiates the metal surface, the heat is quickly conducted and diffused inside, making it difficult for the temperature of the action area to rise and unable to effectively form a mark. When marking metal parts, the heat is dispersed instantly and it is difficult to accumulate to the extent of forming a clear mark. For non-metallic materials with poor thermal conductivity such as wood, carbon dioxide laser can make the heat accumulate quickly locally, so that marking can be easily achieved.
The reflection and heat conduction characteristics of metals to carbon dioxide lasers make it difficult to control the depth and width of the mark. When marking, it is difficult to concentrate the heat on the surface, and it is even more difficult to accurately control the laser energy to achieve the required depth change, and uneven depth often occurs. The dispersion of laser energy and heat conduction make the mark edge blurred and easy to diffuse. Taking the marking of metal medical devices as an example, it is difficult for carbon dioxide Laser marking machines to achieve the high precision required for tiny marks such as product models and batch numbers, while UV laser marking can form clear and smooth marks inside the metal, which meets the strict requirements of medical and pharmaceutical fields for metal marking.
In theory, increasing the power of carbon dioxide Laser marking machines can enhance the marking effect, but there are many problems when used for metal processing. Too high power will increase the heat conduction and thermal impact of metals, excessive heat diffusion, increase the heat-affected zone, increase the risk of metal deformation and oxidation, and affect performance. For example, marking precision metal parts may damage dimensional accuracy. For fine metal products, it may also cause excessive ablation, destroying surface integrity and structural stability.
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