Principle of laser polishing

When the laser beam is focused on the material surface, there is a large amount of heat accumulation in the near surface area in a very short time, which will make the material surface temperature rise rapidly. When the temperature reaches the melting point of the material, the near surface layer begins to melt. When the temperature continues to rise to the boiling point of the material, the near surface layer begins to evaporate, and the temperature of the material matrix is basically maintained at room temperature. When the above physical change process is mainly melting, due to the different radius of curvature at the melting part of the material surface, the molten material flows to the place with low curvature (i.e. large radius of curvature), and the different radius of curvature makes the molten material flow to the place with low curvature (i.e. large radius of curvature), and the curvature tends to be the same everywhere. At the same time, the solid and liquid critical points solidify rapidly, and finally obtain an ideal smooth surface. In this process, if the material is in the molten state for a long time, the molten layer will expand to the depth, and the overall appearance and mechanical properties of the material will be reduced. Therefore, the interaction between laser beam and specific materials must produce a high temperature gradient to promote the rapid heating and cooling of materials. The melting limit, melting depth and the time of materials in melting state depend on different parameters in the interaction process between incident beam and materials. When the above physical change process is mainly evaporation, the essence of laser polishing is to remove a thin layer of material on the surface of the material.

Characteristics of laser polishing technology

Laser polishing is a kind of equipment that uses optical fiber laser beam to polish processing components. The equipment adopts an integrated overall structure, has no chemical pollution and working noise, has the characteristics of high efficiency, long service life and less maintenance, and greatly saves manpower and energy consumption. Laser polishing is a new material surface treatment technology with the development of laser technology. It mainly uses a certain energy density and wavelength of laser beam to radiate the workpiece, so that a thin material melting layer or evaporation appears on its surface, so as to obtain a smooth surface. Laser polishing machine fundamentally solves the workpiece surface with complex shape and appearance that is difficult or impossible to be solved by traditional polishing technology, thus providing the possibility of automatic processing. Therefore, laser polishing machine is a promising new material processing technology.

Laser has four characteristics: monochromaticity, coherence, directivity and high energy density. These properties make laser have unique advantages in processing. Laser can produce huge power density (or energy density) by focusing, which makes laser polishing possible. Table 1 shows the comparison between laser polishing and other polishing technologies. From the table, we can see that laser polishing has the following characteristics:

(1) it is a non-contact polishing. The contact polishing exerts an external force on the sample, and the sample is easy to crack under the external force; Non contact laser polishing will not exert any pressure on the sample;

(2) laser polishing has high flexibility. It can not only polish the plane, but also because laser polishing is a non-contact processing, it can polish all kinds of curved surfaces by using computer three-dimensional control. If it is a symmetrical curved surface, the effect is better. The surfaces that can be polished by laser include plane, spherical surface, ellipsoid, paraboloid, etc;

(3) when polishing the sample, other auxiliary agents are not required, so the pollution to the environment is very small;

(4) precision polishing can be realized; After laser polishing, the material surface can reach nano scale or even sub nano scale;

(5) it is especially suitable for fine polishing of superhard materials and brittle materials after rough polishing;

(6) it can realize micro polishing and locally polish the selected micro area;

(7) the working environment required for polishing is relatively simple, which is generally carried out at room temperature without special working environment.