Laser Surface Polishing Research Articles

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.

Effect of Laser Surface Polishing on the Surface Characteristics, Tribological, and Mechanical Behavior of 3D-Printed Acrylonitrile Styrene Acrylate Parts

Effect of Laser Surface Polishing on the Surface Characteristics, Tribological, and Mechanical Behavior of 3D-Printed Acrylonitrile Styrene Acrylate Parts

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.

High-speed X-ray study of process dynamics caused by surface features during continuous-wave laser polishing

During high-speed X-ray imaging of laser surface polishing experiments of specimens of 316L stainless steel at Argonne National Lab's Advanced Photon Source, it was discovered that the induced keyhole changes shape and dimensions while crossing an engineered surface feature without altering process parameters. It was observed that the post-surface feature keyhole was deeper than that of the pre surface feature keyhole. This work reports on the first in-situ observation of the effect of localized surface geometry on underlying melt pool behavior. This has implications for defect formation mechanisms during laser melting processes that rely on melt pool geometry.

Reducing Surface Roughness of 3D Printed Short-Carbon Fiber Reinforced Composites.

A 100 W fibre laser source was used to minimize the surface roughness of 3D-printed Onyx parts. Furthermore, this study aimed to determine the mechanism of surface finishing, the influence of the laser process parameters (laser power, pulse frequency, and laser scanning path) on the surface morphology, and the influence of the scanning path on the dimensional accuracy of the investigated Onyx 3D-printed specimens. A significant reduction in surface roughness of 91.15% was achieved on the S3 Onyx 3D-printed specimen following laser surface polishing treatment using a 50 W laser power and a frequency of 50 kHz. The laser scanning path had little influence on the surface roughness, but had a major impact on the geometrical deviation of the treated sample.

Laser surface polishing of Ti-6Al-4V parts manufactured by laser powder bed fusion

Poor surface quality of Additively Manufactured (AM) components, can greatly increase the overall cost and lead time of high-performance components. Examples are medical devices where surfaces may contact the patient's skin and hence need to be smooth and aerospace components with high fatigue strength requirements where surface roughness could reduce fatigue life. The average surface roughness (Ra) of AM parts can reach high levels greater than 50 μm and maximum distance between the high peaks and the low valleys of more than 300 μm. As such, there is a need for fast, cost effective and selective finishing methods of AM produced components targeted at high-performance industries. In this paper Ti-6Al-4V Grade 23 ELI, popular for medical devices and aerospace parts production, was L-PBF processed to manufacture parts which were subsequently treated via laser polishing. Here in this work, CO2 laser polishing was used for the surface modification of the Ti-6Al-4V produced samples. The most significant processing parameters were optimised to achieve approximately an 80% reduction in the average surface roughness and a 90% reduction in the peak-to-valley distance with a processing time of 0.1 s/mm2 and cost of 0.2 €/cm2.

Research Progress in Laser Surface Polishing of Hard and Brittle Materials

Research Progress in Laser Surface Polishing of Hard and Brittle Materials

Laser Surface Polishing of Ti6Al4V Titanium Alloy in Air, Nitrogen and Argon Environments

This paper presents the laser surface polishing of titanium alloy (Ti6Al4V) by using a nanosecond pulse laser. Air, nitrogen and argon were employed as a shielding gas in this study, where the areal roughness (Sa) of laser-polished surface was measured and compared. The results showed that argon was the suitable assist gas for improving the metal surface without causing the oxidation. The effect of laser pulse repetition rate and scan speed on the surface roughness was also investigated in this study. The use of high repetition rate together with slow scan speed was able to reduce the surface roughness of titanium alloy. The roughness was found to be reduced by 47% when the pulse repetition rate of 500 kHz and scan speed of 50 mm/s were applied.

Measurement Assurance of Additive Manufacturing on the Example of Laser Surface Polishing Products by Remelting

The article presents the results of studies of the surfaces of parts processed by the contactless method of laser polishing. The results of technological surface treatment using a laser technological complex based on an ytterbium fibre laser with a power of 5 kW are presented. The results of studies of the surface roughness of the samples after laser treatment, including the non-uniform character due to the redistribution of the liquid metal melt over the surface, are shown. Requirements for metrological support of additive technology have been developed using the example of the process of laser remelting in order to improve quality and further automation.

Laser surface polishing of NiCrSiBC – 60WC ceramic-metal matrix composite deposited by laser directed energy deposition process

Deposition of ceramic-metal matrix composite using laser directed energy deposition process presents multi-fold challenges. High melting point ceramic particles often remain partially melted and increase the roughness of the deposit, which essentially requires secondary finishing operation. Besides high surface roughness, the high gradient of thermal and physical properties between ceramic reinforcement and metal matrix introduces cracks in the composite. Therefore, in the present work, the effect of laser surface polishing and substrate heating on improving the surface quality of NiCrSiBC – 60WC ceramic-metal composite deposited by laser directed energy deposition process was investigated. The molten pool thermal history was monitored using an IR pyrometer during laser surface polishing. The effect of rate of heat input on heating rate, cooling rate, molten pool lifetime and peak temperature was investigated and correlated with the surface quality parameters viz. arithmetic surface roughness (Ra) and ten-point height (Rz). A combination of intermediate laser power and scanning speed (600 W and 2000 mm/min) resulted in proper spread of molten pool and rendered better surface finish. The surface roughness (Ra) was found to improve from 19.2 μm ± 1.36 to 1.75 μm ± 0.20. Further, different orientations of laser polishing (0°, 45°and 90°) with respect to the material deposition direction were examined, and 45° was found to yield better surface finish. Surface cracks were observed for all the cases irrespective of process parameters and cooling rates, which were mitigated by substrate pre-heating.

Improving the Surface Finish and other Properties of Engineering Metal Parts

The manufacture of metal parts requires post processing in most cases. These processes include heat treatment for releasing of the residual stresses resulting on the metal surface due to the excessive mechanical forces applies to cut the metal during machining, i.e. milling, turning and drilling. Another example would be the polishing of parts using different techniques. In predominant, polishing is used enhance the part’s roughness to improve the friction coefficient, to give the parts a better view and most important is to adjust the final dimensional accuracy in the microns and sub-microns scale. Traditional polishing methods include the mechanical polishing by using abrasive media or grinding machines, chemical polishing which has the benefit of reaching the inaccessible features although this method requires longer processing time in addition to the impact on environment. Sometimes the thermal deburring method is also applied for the chamfer of sharp edges and corners. In the recent years, the laser polishing technique exhibits interesting efforts and results regarding reproducibility, high control over the processing parameters which allow for the processing of different metals and non-metals materials in addition to the ultrashort processing time. This study is focusing on the laser surface polishing of metal parts, its potentials and limitations. In this study, laser surface polishing using CO2 laser beam irradiation was implemented on stainless steel Additive Manufactured produced surfaces. Two design of experiment models were implemented for the optimization of the main laser input processing parameters. The processing parameters examined were the laser beam power, the scanning speed, the number of laser scan passes, the percentage overlap of the laser tracks between the consecutive passes and the laser beam focal position. The characterization of the measured surface roughness and the modified layer microstructure were carried out using scanning electron microscopy (SEM) and 3D optical.

Laser Polishing of Additive Manufactured 316L Stainless Steel Synthesized by Selective Laser Melting.

One of the established limitations of metal additive manufacturing (AM) methods, such as selective laser melting (SLM), is the resulting rough surface finish. Laser polishing is one method that can be used to achieve an improved surface finish on AM printed parts. This study is focused on the laser surface polishing of AM parts using CO2 laser beam irradiation. Despite the fact that several researchers have investigated the traditional abrasive polishing method, there is still a lack of information reporting on the laser surface polishing of metal parts. In this study, AM 316L stainless steel cylindrical samples were polished using CO2 laser beam irradiation in continuous wave (CW) working mode. Two design of experiment models were developed for the optimization of the input processing parameters by statistical analysis of their effect on the resulting roughness. The processing parameters investigated were the laser beam power, the rotational speed of the sample, the number of laser scan passes, the laser beam focal position, and the percentage overlap of the laser tracks between consecutive passes. The characterization of the measured roughness and the modified layer microstructure was carried out using 3D optical and scanning electron microscopy (SEM). A maximum reduction of the roughness from 10.4 to 2.7 µm was achieved and no significant change in the microstructure phase type and micro-hardness was observed.

펄스레이저에 의한 NAK80 금형강 표면연마의 해석적 연구

Laser surface polishing is a polishing method for improving surface roughness using an integrated laser beam. Using a laser for surface polishing can improve the surface condition without physical contact or chemical action. Laser polishing has mainly been used to polish the surface of diamond or optical articles, such as lenses and glasses. Recently, diverse studies on laser polishing for metals have been conducted. The analytic study of laser surface polishing has been conducted with experimental trials for comparison, so that the proper conditions for laser polishing can be recommended. In this study, laser surface polishing was simulated in order to predict the heat-affected zone on the die steel depending on the power of the pulsed laser. The simulated results were verified by comparing them to those of the experimental trials. Through this study, therefore, the application of FEM to the selection of appropriate laser conditions could be possible.

Control of fluid dynamics by nanoparticles in laser melting

Effective control of fluid dynamics is of remarkable scientific and practical significance. It is hypothesized that nanoparticles could offer a novel means to control fluid dynamics. In this study, laser melting was used to investigate the feasibility of tuning fluid dynamics by nanoparticles and possibly breaking existing limits of conventional laser processing techniques. Alumina nanoparticles reinforced nickel samples, fabricated through electrocodeposition, were used for laser melting experiments. Since the melt pool surface is controlled by the fluid dynamics, surface topographies were carefully studied to reveal the nanoparticle effect on the fluid dynamics. Characterizations of surface topographies and microstructures of pure Ni and Ni/Al2O3 nanocomposite were carried out before and after laser melting. The surface roughness of the Ni/Al2O3 nanocomposite sample was reduced significantly by laser melting, which broke the existing limit of laser surface polishing of pure Ni. It is believed that the nanoparticles increased the viscosity of the molten metal, thereby enhancing the viscous damping of the capillary oscillations in the melt pool, to produce a much smoother surface. Moreover, the experimental study also revealed that the viscosity enhancement by the nanoparticles effectively suppressed the thermocapillary flows which would introduce artificial asperities on a surface. The experimental results suggest that nanoparticles are effective in controlling melt pool dynamics and overcoming the existing limits of laser processing. The new methodology, fluid dynamics control by nanoparticles, opens a new pathway to enrich liquid based processes for broad applications.

An approach to modelling of laser polishing of metals

Based on heat transfer analysis and the consideration of the evaporation of surface asperities, a simplified model for laser surface polishing was established. As the dimension of asperities is usually in the scale of sub-micron, the model thus assumed uniform temperature over and in an asperity entity and the heat transfer could thus be treated as a point unit problem. The model aimed at preliminary prediction of the adequate setting of the processing parameters (typically the laser irradiation time) for laser polishing of a metal with known geometric surface consisting of micro-asperities and material properties. Prediction for polishing metallic materials of Fe, Al, Ti, and the 304 stainless steel showed the temperature rise in asperity varying significantly with the original surface topography of the substrates. Results indicate that, for the polishing of most metals with pulsed laser, laser with short pulse duration normally in the range of nano-second or less is required. Laser polishing of steel using a KF excimer laser with the pulse duration of 30 ns was subsequently performed. Characterizing the irradiated surface morphology by scanning electron microscope (SEM) and atomic force microscope (AFM) showed evident improvement in surface finish of the tested specimens.

Surface Over-Melt During Laser Polishing of Indirect-SLS Metal Parts

ABSTRACTLaser polishing of indirect-SLS parts made from 420 stainless powder infiltrated with bronze has been achieved using CO2 and Nd:YAG lasers. Two mechanisms have been previously proposed for the reduction in surface roughness, namely: shallow surface melting (SMM) and surface over-melt (SOM). In SMM reflow of the molten surface minimizes the peak-valley height driven by capillary pressure and liquid curvature. On the other hand, during SOM the melting depth is such that the entire surface becomes liquid and formation of surface periodical structures dominates driven by a surface tension gradient. This surface morphology was identified by means of optical and scanning electron microscopy (SEM). The onset of this regime is dictated by the energy density (i.e., ratio of laser power to scan speed and beam diameter) as well as the initial roughness Ra value prior to laser surface polishing. In contrast with SMM, onset of the latter mechanism increases the roughness Ra with speed reduction. A thermo-physical model is presented, signaling good agreement with roughness Ra and characteristic surface wavelength results obtained for varying laser beam scan speeds. Understanding the surface over-melt mechanism is critical for determining the optimum polishing conditions that minimize roughness.