Laser Polishing Process Research Articles

Research on laser polishing process of zirconia ceramic surface

Abstract In order to investigate the polishing results of carbon dioxide pulsed laser on the surface of zirconia ceramics, this paper analyzes the significance of the influence of each process parameter on the surface roughness in the laser polishing process based on the experimental design of the response surface method and taking the surface roughness as the optimization objective. And the best combination of process parameters for the laser polishing process is predicted by establishing a surface roughness prediction model. The results of the experiments show that among the laser polishing process parameters, the scanning speed and laser power have an extremely significant effect on surface roughness, while the pulse frequency has a more significant effect on surface roughness. The model predicts the optimum combination of working parameters as: laser power P = 75W, pulse frequency f = 4 kHz, scanning speed v = 380 mm/s. Under the optimum combination of process parameters, surface roughness Ra = 0.595μm of the material, which is 76% lower than that of the original surface roughness of 2.479μm after laser polishing.

Increasing productivity by combining laser processes

AbstractIncreasing the material ablation rate in micromachining of precise geometries by ultrashort‐pulsed laser treatment with high average power causes a decrease of achievable surface quality due to heat accumulation. To overcome this drawback, combined laser processes offer a significant increase of the overall productivity by the implementation of laser cleaning and polishing processes that require negligible additional processing time, but allow material removal to be performed with maximum process efficiency.

Multi-objective Optimization and Decision-Making Method for Laser Polishing Process Parameters of D2 Die Steel Based on NSGA-II and TOPSIS-EWM

Multi-objective Optimization and Decision-Making Method for Laser Polishing Process Parameters of D2 Die Steel Based on NSGA-II and TOPSIS-EWM

Role of fictive temperature distribution involved in CO2 laser polishing of fused silica and its optimization for achieving even heat-affected zones

CO2 laser polishing process is a highly effective way for enhancing the surface quality and laser-induced damage threshold of fused silica optics. Nevertheless, due to the thermal history and spatial gradient of the thermodynamic temperature, the heat-affected zones can be formed unevenly on the surface with an increased fictive temperature, which causes the material densification and residual stress. In this work, a 3D model of structural relaxation coupled with temperature and flow fields was innovatively established to explore the role of fictive temperature distribution involved in CO2 laser polishing of fused silica. The Raman spectrum was applied to verify this model. Subsequently, the impacts of laser beam power, scanning speed, track overlapping, substrate temperature on the fictive temperature were discussed. The results indicate that decreasing the scanning speed and increasing the substrate temperature can decrease the fictive temperature. Additionally, a higher track overlapping can reduce the height of the fictive temperature “tool mark”. Moreover, an optimization strategy based on laser beam scanning speed was proposed based on the uniform distribution of fictive temperature. The depth difference of the heat-affected zones was reduced from 164.26 μm to 31.74 μm. This work could be used to quantitatively predict the 3D fictive temperature distribution and proposed an optimization strategy based on scanning speed to suppress the non-uniformity of fictive temperature distribution, which can provide significant theoretical guidance for CO2 laser polishing technology of fused silica optics.

Numerical simulation of free-surface evolution in laser polishing of 100 Cr6 bearing steel

Abstract This research focuses on the laser surface polishing process of 100 Cr6, employing a moving Gaussian heat source. It establishes a two-dimensional transient model for laser polishing, taking into account the integrated effects of fluid flow and temperature fields, as well as the combined influence of capillary and thermocapillary forces. The model was used to perform numerical simulations to study the evolution of surface morphology during the laser polishing process. The investigation specifically examines how laser power and scanning speed influence the quality of the polishing outcome. The results demonstrate that an optimal surface roughness of approximately 0.571 μm is attained at a laser power setting of 200 W and a scanning speed of 300 mm/s.

A versatile setup for nanosecond laser polishing processes with in situ analysis capabilities.

Laser polishing of material surfaces is a complex process depending on many variable parameters, such as, e.g., the properties of the used laser and optics (wavelength, pulse duration, fluence, and profile), as well as the processing (spot size, feed rate, and line or point overlap), and the thermodynamical properties of the material to be polished (heat capacity, heat conduction, etc.). For the successful laser polishing of any material, a systematic variation of all the process parameters is required to obtain satisfactorily polished surfaces with an appropriate set of parameters for the material of interest. In order to allow systematic studies of laser polishing processes, a new setup employing a highly stable nanosecond laser with an adjustable wavelength has been realized. The sample is located in a small high-vacuum chamber with the capability of introducing additional gases in a controlled manner, and the entire chamber is scanned in the beam to allow laser polishing of selected spots, lines, or larger areas. The setup is fully remote-controlled and allows in situ inspection of the initiated processes by means of a long-range microscope, electrical measurements, reflected laser light from the sample surface, and an analysis of the vacuum within the process chamber. The main properties of the setup will be presented, and some exemplary results on niobium and molybdenum metal samples will be discussed.

Surface roughness and microhardness improvement of laser cladding stainless-steel 316 by laser polishing based on multiple remelting

Laser polishing (LP) has emerged as a promising alternative to traditional post-treatment technologies. Nonetheless, the LP process encounters challenges when dealing with surfaces of high roughness, since the excessive thermal input could induce undesirable effects, including the formation of mid-frequency waviness, expansion of heat-affected zone (HAZ), etc. In this study, we investigated the surface roughness and the characters of the remelted layer and HAZ of polishing the laser-cladding 316 stainless steel layer deposited on the surface of a 45# steel cylinder by a 1064 nm hundred-watt pulsed laser and a 1080 nm thousand-watt CW laser respectively. It is observed that the combination of low power density and extended interaction time failed to produce minimum roughness by the pulse laser, contradicting existing LP theories. To address this, we developed a multi-physics model to elucidate the underlying mechanisms and propose an LP scheme based on multiple remelting cycles with the pulsed laser. The Sa roughness is reduced from 20.958 μm to 0.242 μm, decreasing 98.8 %. The processing quality is equivalent to the surface of the high-power CW laser (Sa of 0.283 μm), while the remelted layer and HAZ are significantly smaller. The pulse laser polishing based on multiple remelting increased the surface microhardness by 22 % to 560 HV, while the CW laser remelting reduced it by 33 % to 309 HV. And the HAZ microhardness all decreased in all cases. This study can provide a theoretical basis and solution for the surface finishing of additive manufacturing parts.

Twyman effect in laser polishing of fused silica wafers

This paper investigates the challenges of minimizing wafer deformation during laser polishing of fused silica. The focus is on the Twyman effect, which causes unwanted curvature in thin plates. Strategies to reduce stress-induced deformation are proposed to enhance the reproducibility of the laser polishing process.

LASER POLISHING OF ADDITIVELY MANUFACTURED TITANIUM ALLOY IN OPEN AIR ATMOSPHERE

Additive manufacturing has witnessed remarkable growth, transforming the production of intricate geometries. However, post-processing is often required to enhance surface quality and alleviate residual stresses in additively manufactured components. Laser polishing, an advanced technique, efficiently reduces surface roughness in metals. This study stands out by conducting laser polishing without protective gas in an open atmosphere. Results demonstrate that surface roughness can be improved by up to 50% under these conditions. Nevertheless, the process introduces a recast layer with significant oxidation due to atmospheric oxygen, leading to the formation of a Titanium Oxide layer and the development of surface microcracks. As oxidation increases, surface hardness also rises. Achieving high-quality surfaces for additively manufactured Ti alloys in an open atmosphere is attainable, provided vigilant monitoring of oxidation-related challenges. This study reveals the intricate relationship between laser polishing, surface characteristics, and the effects of open-air conditions on Ti-6Al-4V components.

Surface morphological evolution and microhardness change of Cr12MoV steel by pulsed laser polishing

Laser polishing is gaining more and more attention because of its environmental friendliness and ability to process complex surfaces. It is considered as one of the technologies to replace traditional methods in the mold industry. In this work, the variation pattern of surface roughness with single pulse energy density and light-out overlap rate during nanosecond pulsed laser polishing of Cr12MoV steel was investigated. The surface roughness increased and then decreased with increasing single-pulse energy density and beam overlap rate, respectively. The lowest surface roughness was found to be 0.50 μm, which is a decrease of 79.34 % compared to the untreated sample. The effect of each parameter on the surface morphology during the laser polishing process is explained. There is minimal austenitization on the surface of the sample after laser polishing. The second phase of the remelting layer disappeared. The microhardness of the remelting layer increased by 36.17 % because the grain size was reduced by 30.65 %. This work further explains the mechanism transformation threshold for pulsed laser polishing of steel. With 95 % beam overlap, the melting and gasification energy density thresholds for Cr12MoV steel are respectively 1.269 J/cm2 and 2.937 J/cm2. The beam overlap rate of 95.5 % is the critical condition for continuous melt movement. It provides a new idea for the mechanism judgment of pulsed laser polishing.

Laser polishing of PBF-LB manufactured stainless steel surfaces

Laser powder bed fusion (PBF-LB) is additive manufacturing where material is added layer by layer. This technology has revolutionized the manufacturing during last few recent years by enabling more efficient material usage and more functions to each component. However, for many industrial cases, the PBF-LB surfaces need an additional finishing operation like the machining or polishing operation. Laser polishing process was studied to solve the problems of traditional technologies to improve the surface quality and to enable automation of it. In this study parts were manufactured by PBF-LB of austenitic stainless steel (AISI 316L) into shapes of mechanical property testing samples in different orientations and locations in building platform. The surface roughness was measured prior and after polishing. The experiments showed that considerable surface smoothening even up to 85% (Sa from 48 μm to 11 μm) was reached in two treatments.

Numerical and Experimental Analysis of Dual-Beam Laser Polishing Additive Manufacturing Ti6Al4V.

Laser polishing is an emerging efficient technique to remove surface asperity without polluting the environment. However, the insufficient understanding of the mechanism of laser polishing has limited its practical application in industry. In this study, a dual-beam laser polishing experiment was carried out to reduce the roughness of a primary Ti6Al4V sample, and the polishing mechanism was well studied using simulation analysis. The results showed that the surface roughness of the sample was efficiently reduced from an initial 10.96 μm to 1.421 μm using dual-beam laser processing. The simulation analysis regarding the evolution of material surface morphology and the flow behavior of the molten pool during laser the polishing process revealed that the capillary force attributed to surface tension was the main driving force for flattening the large curvature surface of the molten pool at the initial stage, whereas the thermocapillary force influenced from temperature gradient played the key role of eliminating the secondary roughness at the edge of the molten pool during the continuous wave laser polishing process. However, the effect of thermocapillary force can be ignored during the second processing stage in dual-beam laser polishing. The simulation result is well in agreement with the experimental result, indicating the accuracy of the mechanism for the dual-beam laser polishing process. In summary, this work reveals the effect of capillary force and thermocapillary force on molten pool flows during the dual-beam laser polishing processes. Moreover, it is also proved that the dual-beam laser polishing process can further reduce the surface roughness of a sample and obtain a smoother surface.

Correction to: Influence of laser polishing process parameters on surface integrity and morphology of Ti‑6Al‑4V parts produced via electron beam melting

Correction to: Influence of laser polishing process parameters on surface integrity and morphology of Ti‑6Al‑4V parts produced via electron beam melting

Laser Polishing of Polymer Parts Produced with Material Jetting Technology: Effect of Laser Scan Speed, Overlapping and Loop Cycles

In the last year, the industrial production is characterized by the request of high level of product variety that generates a decrease of production volume changing manufacturing from mass production to mass customization. This trend let the conventional production processes, as forming, casting or moulding, expensive because of initial tools production cost that is not more amortized by the high-volume production. A solution to this scenario is to integrate Additive Manufacturing in tools production; this solution guarantees tools cost reduction also if post processes operations are needful to reduce the surface roughness produced by additive processes. Among additive processes, Material Jetting is able produce parts with guaranteed high accuracy and low average surface roughness (0.5 µm). However, these standards mainly refer to upfacing surfaces parallel to the print plate, and the roughness obtained on the other surfaces could increase up to 15 µm because of production mechanism. To improve parts roughness in this study, the laser polishing process was tested; different experimental tests were executed to investigate the effects of scan speed, overlapping and loop cycles. The results demonstrated that it is possible to improve the surface finish and reduce the roughness by 70% at the expense of dimensional accuracy.

Influence of laser polishing process parameters on surface integrity and morphology of Ti-6Al-4V parts produced via electron beam melting

Influence of laser polishing process parameters on surface integrity and morphology of Ti-6Al-4V parts produced via electron beam melting

Recent Advancements in Post Processing of Additively Manufactured Metals Using Laser Polishing

The poor surface roughness associated with additively manufactured parts can influence the surface integrity and geometric tolerances of produced components. In response to this issue, laser polishing (LP) has emerged as a potential technique for improving the surface finish and producing parts with enhanced properties. Many studies have been conducted to investigate the effect of LP on parts produced using additive manufacturing. The results showed that applying such a unique treatment can significantly enhance the overall performance of the part. In LP processes, the surface of the part is re-melted by the laser, resulting in smaller peaks and shallower valleys, which enable the development of smoother surfaces with the help of gravity and surface tension. Precise selection of laser parameters is essential to achieve optimal enhancement in the surface finish, microstructure, and mechanical properties of the treated parts. This paper aims to compile state-of-the-art knowledge in LP of additively manufactured metals and presents the optimal process parameters experimentally and modeling using artificial machine learning. The effects of laser power, the number of laser re-melting passes, and scanning speed on the final surface roughness and mechanical properties are comprehensively discussed in this work.

Laser surface polishing of 3D printed polylactic acid (PLA) with different levels of absorption

Fused deposition modeling (FDM) based 3D printed polymer parts have received extensive attention in the industries. However, their high surface roughness due to the intrinsic layer deposition method limits the applicability, necessitating the printed parts' post-processing. Herein, we used colored (white, blue, and gray) 3D-printed polylactic acid (PLA) parts and investigated the color influence on the laser polishing process in detail. Interestingly, the level of laser absorption at an irradiated wavelength of 1060 nm differed in the order of PLA-gray > PLA-blue > PLA-white. Laser-polished PLA-white samples showed a negligible difference in the arithmetic average surface roughness (Ra) compared to the printed sample, corresponding to the low absorption level and melting behavior. On the other hand, the laser-polished PLA-blue sample exhibited a 96.4 % reduction in Ra value at a laser power of 15 W. The PLA-gray sample showed a 98.6 % reduction at 3 W. The Ra variation of the laser-polished samples confirmed a dramatic surface roughness improvement that could be made by controlling laser processing parameters and varying light absorption levels of the colored PLA substrates. Besides, PLA-blue and PLA-gray samples had different polishing conditions; Scanning electron microscope (SEM) images, thermal studies, and finite element model simulation results confirmed the polishing and melting behavior of the PLA samples. The comparative experimental results followed by statistical analysis also showed the significant effect of PLA color and laser parameters such as the power and scan speed. Through the advantages of the highly improved laser finishing results with optimal process parameters considering the different light absorption, this approach will broaden the application of efficient laser polishing of 3D printed materials.

Surface quality improvement of a laser-polished Co-free high entropy alloy prepared by selective laser melting

In order to improve the quality of the Co-free high entropy alloy surface, a Co-free high entropy alloy specimen prepared by selective laser melting was polished by laser in this work. Optimal laser polishing process parameters were explored, and the best surface roughness Sa value reached 0.4626µm, which is much lower than the original surface roughness. Through microscope, SEM, EDS and other tests, the surface quality after polishing is obviously improved The big improvement in high entropy alloy specimen’ surface quality has potential significance in promoting the application of this material in high precision situations.

Flame-Assisted Laser Polishing of Alumina Ceramic Surface Properties

Laser polishing was used to reduce the surface roughness and improve the surface properties of alumina ceramics. In this paper, a response surface experimental design scheme is used to establish a mathematical model based on the Box-Behnken central combination principle, with the surface roughness as the optimization target to optimize the optimal process parameters for the laser polishing of alumina ceramics, to suppress the polished surface cracks by preheating the material, and to study the changes of surface properties of laser-polished alumina ceramics under different preheating temperatures. The optimal laser polishing process parameters were optimized by response surface experiments with a scanning speed of 323.5 mm/s, a laser power of 73.63 W, a pulse frequency of 2.3 kHz, and a scanning spacing of 0.09 mm; compared with the initial surface roughness of 4.67 μm, the polished surface roughness was 0.96 μm under the experimentally optimized polishing parameters, and the surface cracks were suppressed after the preheating treatment. The surface roughness was further reduced to 0.74 μm, and the surface wear coefficient was reduced from 0.5939 to 0.5725, while the surface hardness was increased from 1810 to 2063 HV. Optimization of the laser polishing process parameters through the response surface can significantly reduce the surface roughness of the material, while the flame preheating, assisted by the laser-polished surface wear resistance and hardness, is improved.

Surface characteristics enhancement and morphology evolution of selective-laser-melting (SLM) fabricated stainless steel 316L by laser polishing

Additive manufacturing (AM) metal parts often have internal defects and rough surfaces. Particularly for materials with corrosion resistance requirements, such as stainless steel 316L, the AM parts require post-treatment processes. Laser polishing is an efficient and environmentally friendly polishing technique to enhance their serviceability. Nevertheless, investigations into the evolution of surface morphology, defect formation, and surface characteristics of laser-polished AM parts are still lacking nowadays. To investigate the evolution of surface morphology and defect formation, orthogonal experiments on the laser polishing process were conducted on SS316L fabricated by selective laser melting (SLM). The influences of laser power, scanning rate, and spacing distance on surface roughness and integrity were investigated. The surface roughness Sa was reduced from 7.02 µm to 0.28 µm. The conditions for the development of porosity defects on the polished surface were analyzed. Multi-physics models were established to simulate the molten metal flow and surface morphology evolution, as well as defect formation in the cooling stage. The convergence and overflow of sub-surface defects were likely to form pores with excessive laser power. To compare the surface characteristics with the common polishing method, the potentiodynamic polarization curve, energy dispersive X-ray spectroscopy, and X-ray diffraction analysis were conducted. The corrosion resistance and surface microstructure after laser polishing and abrasive blasting were compared. The effectiveness of the optimized laser polishing process was verified, which is essential for broadening the application of AM parts.