The laser polishing process of metal materials has been extensively studied. This paper proposes a new type of beam-coupled laser polishing method to study the surface quality of polished stainless steel when the power and frequency change, and the changes of the surface roughness and topography with the laser power and frequency were analyzed. Under the condition of power 0.5W and frequency 10Khz, as the feed speed changes from 200mm/min to 1200mm/min, the surface roughness first decreases, then slightly increases. The single pulse energy decreases, and the surface roughness first increases and then decreases with increasing of the frequency from 10kHz to 20kHz. With low repetition frequency and single pulse energy, the surface roughness is significantly reduced to 0.19μm at the process parameters of 2.0W, 10Khz, and 600mm/min. Under the specific process parameters, the processed surface has a color change similar to that caused by surface quenching treatment. The surface material absorbs more laser light, and the processed surface microstructure changes. By adjusting the process parameters, the polishing quality can be improved. It is proved that the beam-coupled laser polishing of stainless steel is an effective polishing method.
The coupled nanosecond laser processing system was used for processing 6061 aluminum alloy in this paper. At first, we explored the relationship between laser processing parameters, such as laser power, laser repetition frequency, as well as scanning speed, and the processed surface quality for 6061 aluminum alloy plate sample. The optimal laser parameters were determined by the experiment of the flat plate sample processing, and then the paths of laser processing were designed and planned on the aluminum alloy with curved surface to explore the influence of curvature on the surface quality. The results show that the new processing technology of coupled nanosecond laser polishing could obtain good surface quality. The optimal laser processing parameters are average laser power of 5W, scanning speed of 500mm/min, and repetition frequency of 10kHz, which could reduce the surface roughness by 43%. In addition, the surface quality of the aluminum alloy is closer to the original surface as the curvature increased. And the convex surface has a lower surface roughness than the concave surface because the spot shape is different at different curvature positions. The coupled laser polishing process provides theoretical and technological support for the high-quality machining of 6061 aluminum alloy in this study.
Aluminum alloy has the advantages of high strength, corrosion resistance and good toughness, so it is widely used in aerospace, automotive manufacturing, and other fields. Laser processing has the advantages of controllable energy, high energy density, wide range of material adaptation, no contact, almost no cutting force, clean and environmentally friendly, etc. Moreover, the complex features and micro structure functionalization of components can be solved by laser processing. The oblique incidence of the laser will reduce the processing depth of beam waist from the geometric level. And the resulting space vector effect can introduce new processing mechanisms. The processing result could be improved by adjusting the vector effect with important value and novelty. In this paper, the mechanism and forming surface of 7075 be processed by nanosecond laser with different positive inclination angles under the same basic process parameters. It is shown that laser milling can effectively reduce the surface roughness of 7075. The result shows that the when the laser inclination angle (θ) is in the range of 0°~40°, the surface roughness of the machined surface decreases with the increase of θ, and the roughness can be as small as 0.15 μm. When 40° < θ ≤ 60°, the machined surface roughness increases with the increase of θ, but it is still significantly lower than the original surface roughness. The main reason for this phenomenon is that the projected area, shape, and energy distribution of the laser beam waist in the processing area are affected by the laser beam lead angle. The energy distribution affects the material removal mechanism: cladding, vaporization, or sublimation. And under the positive inclination angle, the processed surface is first irradiated and then processed for the second time by the laser beam. The relative posture of laser beam and workpiece is conducive to the discharge of slag, thus improving the processing quality. And pointed out that within the range of experimental conditions, θ = 40° is the optimal inclination angle, because the processed surface has the least undulation and the highest flatness. Moreover, this research has guiding significance for improving the surface quality of laser processing.
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