Formation mechanism of a smooth, defectfree surface of fused silica optics using rapid CO2 laser polishing

Surface defects introduced by conventional mechanical processing methods can induce irreversible damage and reduce the service life of optics applied in high-power lasers.Compared to mechanical processing,laser polishing with moving beam spot is a noncontact processing method,which is able to form a defect-free surface.This work aims to explore the mechanism of forming a smooth,defect-free fused silica surface by high-power density laser polishing with coupled multiple beams.The underlying mechanisms of laser polishing was revealed by numerical simulations and the theoretical results were verified by experiments.The simulated polishing depth and machined surface morphology were in close agreement with the experimental results.To obtain the optimized polishing quality,the effects of laser polishing parameters(e.g.overlap rate,pulse width and polishing times)on the polishing quality were experimentally investigated.It was found that the processing efficiency of fused silica materials by carbon dioxide(CO2)laser polishing could reach 8.68 mm2 s−1,and the surface roughness(Ra)was better than 25 nm.Besides,the cracks on pristine fused silica surfaces introduced by initial grinding process were completely removed by laser polishing to achieve a defect-free surface.The maximum laser polishing rate can reach 3.88μm s−1,much higher than that of the traditional mechanical polishing methods.The rapid CO2 laser polishing can effectively achieve smooth,defect-free surface,which is of great significance to improve the surface quality of fused silica optics applied in high-power laser facilities.

Laser Polishing of Laser Powder Bed Fusion AlSi10Mg Parts—Influence of Initial Surface Roughness on Achievable Surface Quality

Laser Powder Bed Fusion (LPBF) is an Additive Manufacturing technique, which allows production of highly complex solid metal parts with good mechanical properties, compared to conventionally manufactured parts. Nevertheless, the layer-by-layer fabrication process also offers several disadvantages, including a relatively high surface roughness depending on the shape of the component, its position and orientation during the fabrication process. This paper deals with investigations on the surface roughness reduction capability, and residual surface structures by laser polishing of LPBF AlSi10Mg parts under varying initial surface roughness in order to investigate the influence of the surface behavior and initial surface roughness to the achievable surface quality by laser polishing. Hereto test specimens with varying fabrication orientations regarding to the built platform are printed and further polished. Thereby the initial arithmetic roughness varies between 19.2 μm and 8.0 μm. It could be shown that the achievable surface roughness by laser polishing with continuous and pulsed laser radiation is increasing with rising initial roughness, but the relative roughness reduction is almost constant in the range of 95% - 97.5%. The analyzation of the residual roughness structures shows, that the main roughness differences is found in the middle and long structure wavelength regime, which are directly depending on the initial surface structures of 3D printing.

Laser polishing of a high-entropy alloy manufactured by selective laser melting

The selective laser melting(SLM)technique applied to high-entropy alloys(HEAs)has attracted considerable attention in recent years.However,its practical application has been restricted by poor surface quality.In this study,the capability of laser polishing on the rough surface of a Co-free HEA fabricated using SLM was examined.Results show that the initial SLM-manufactured(as-SLMed)surface of the Co-free HEA,with a roughness exceeding 3.0μm,could be refined to less than 0.5μm by laser polishing.Moreover,the microstructure,microhardness,and wear resistance of the laser-polished(LP-ed)zone were investigated.Results indicate that compared with the microhardness and wear resistance of the as-SLMed layer,those of the LP-ed layer decreased by 4%and 11%,respectively,because of the increase in grain size and reduction of the BCC phase.This study shows that laser polishing has an excellent application prospect in surface improvement of HEAs manufactured by SLM.

Implications of using two low-power continuous-wave lasers for polishing

Laser polishing is widely employed to reduce the surface roughness of products with complex geometries.Traditional laser polishing techniques use a single high-power Gaussian beam to melt and smooth a thin layer of surface material.However,the reliance on high power lasers can present practical challenges such as minimizing surface evaporation or reducing overall cost.In this work,we combined two identical low-power laser beams with a spatial offset in between them to construct an elliptical beam.By changing the spatial offset,combined beams with different lengths along the major axis can be created.We observe over 20%improvement in line roughness reduction using this approach compared to a single Gaussian laser beam with the same total power.Additionally,both experiment and simulation results suggest such improvement is because this dual-laser set-up can create a longer molten pool compared to a single laser.

A Laser Scanner-Stage Synchronized System Supporting the Large-Area Precision Polishing of Additive-Manufactured Metallic Surfaces

This paper proposes a scanner–stage synchronized approach emphasizing a novel control structure for the laser polishing of Inconel 718 components manufactured by selective laser melting in order to address increasing demands for high surface quality in metal additive manufacturing.The proposed synchronized control system is composed of a motion decomposition module and an error synthesis module.The experimental results show that stitching errors can be avoided thanks to continuous motion during laser processing.Moreover,in comparison with the existing step-scan method,the processing efficiency of the proposed method is improved by 38.22%and the surface quality of the laser-polished area is significantly enhanced due to a more homogeneous distribution of the laser energy during the material phase change.The proposed synchronized system paves the way for high-speed,high-precision,and large-area laser material processing without stitching errors.

A novel polishing technology for epoxy resin based on 355 nm UV laser

The electromagnetic shielding film has drawn much attention due to its wide applications in the integrated circuit package,which demands a high surface quality of epoxy resin.However,gaseous Cu will splash and adhere to epoxy resin surface when the Cu layer in PCB receives enough energy in the process of laser cutting,which has a negative effect on the quality of the shielding film.Laser polishing technology can solve this problem and it can effectively improve the quality of epoxy resin surface.The paper studies the mechanism of Cu powder spraying on the compound surface by 355 nm ultraviolet（UV） laser,including the parameters of laser polishing process and the remains of Cu content on compound surface.The results show that minimal Cu content can be realized with a scanning speed of 700 mm/s,a laser frequency of 50 kHz and the distance between laser focus and product top surface of-1.3 mm.This result is important to obtain an epoxy resin surface with high quality.

Laser material processing optimization using bayesian optimization: a generic tool

Optimizing laser processes is historically challenging,requiring extensive and costly experimentation.To solve this issue,we apply Bayesian optimization for process parameter optimization to laser cutting,welding,and polishing.We demonstrate how readily available Bayesian optimization frameworks enable efficient optimization of laser processes with only modest expert knowledge.Case studies on laser cutting,welding,and polishing highlight its adaptability to real-world manufacturing scenarios.Moreover,the examples emphasize that with suitable cost functions and boundaries an acceptable optimization result can be achieved after a reasonable number of experiments.