Poor Surface Quality Research Articles

Effect of Process Parameters on the Roughness and Wetting Characteristics of SS304 Surfaces Using Electrolytic and Plasma Electrolytic Polishing Techniques

Metallic parts manufactured by conventional machining and additive manufacturing techniques possess poor surface quality and require post-processing operations before their end-use. Many methods exist for the post-processing of parts with free-form surfaces. In this study, two of the most used polishing techniques, electrolytic polishing (EP) and plasma electrolytic polishing (PeP), were investigated to understand the morphology of the resultant surface after both techniques. Pilot experiments suggested that an aqueous solution of ammonium sulphate is the most effective electrolyte for both the polishing techniques in terms of the lowest achievable value of average surface roughness ( Ra ). A systematic investigation of the electrolyte concentration, applied voltage, and polishing time revealed an identical dependence on all these process parameters: First, a decrease and then an increase in Ra. A minimum Ra of 0.63 μm and 0.49 μm were achieved with EP and PeP, respectively. Samples polished by PeP possess high gloss with negligible changes to the shape and form of the samples. Furthermore, static contact angle measurements with water revealed that surfaces treated with PeP showed higher hydrophilicity compared to those polished with EP. This can be attributed to the lower Ra value achieved with PeP.

3D Printing of Optical Lenses Assisted by Precision Spin Coating

AbstractThough 3D printing shows potential in fabricating complex optical components rapidly, its poor surface quality and dimensional accuracy render it unqualified for industrial optics applications. The layer steps in the building direction and the pixelated steps on each layer's contour result in inevitable microscale defects on the 3D‐printed surface, far away from the nanoscale roughness required for optics. This paper reports a customized vat photopolymerization‐based lens printing process, integrating unfocused image projection and precision spin coating to solve lateral and vertical stair‐stepping defects. A precision aspherical lens with less than 1 nm surface roughness and 1 µm profile accuracy is demonstrated. The 3D‐printed convex lens achieves a maximum MTF resolution of 347.7 lp mm−1. A mathematical model is established to predict and control the spin coating process on 3D‐printed surfaces precisely. Leveraging this low‐cost yet highly robust and repeatable 3D printing process, the precision fabrication of multi‐scale spherical, aspherical, and axicon lenses are showcased with sizes ranging from 3 to 70 mm using high clear photocuring resins. Additionally, molds are also printed to form multi‐scale PDMS‐based lenses.

Effects of process parameters and geometry on dimensional accuracy and surface quality of thin strut heart valve frames manufactured by laser powder bed fusion

Laser powder bed fusion (LPBF) is one of the most popular metal additive manufacturing technologies, which has found its applications in high-value sectors such as aerospace and biomedical devices. Some recent studies on the LPBF of stents have demonstrated its feasibility in the fabrication in thin strut structures including heart valve frames, as used in transcatheter aortic valve implantation (TAVI) for the treatment of severe aortic stenosis. The state of the art method of laser cutting TAVI frame limits the scope for novel concepts which are made possible by additive manufacturing. However, the surface quality and dimensional accuracy of LPBF parts are lower than that produced by laser cutting. To start the development of new TAVI concepts, the feasibility of manufacturing thin frames by LPBF has been investigated based on the SAPIEN 3 frame by Edwards Lifesciences. In this study, simplified frames with strut size from 0.3 to 0.5 mm have been successfully manufactured. The effects of strut size, strut angle, laser power and scan speed on the dimensional accuracy and surface quality were systemically studied. In addition, a representative SAPIEN 3 frame was manufactured and assessed with high-resolution X-ray CT scans. Good overall dimensional accuracy and low porosity were obtained for the SAPIEN 3 frame. However, inclined struts were found to have relatively low dimensional accuracy and poor surface quality.

Studies on the Quality of Joints and Phenomena Therein for Welded Automotive Components Made of Aluminum Alloy—A Review

To fulfill the need to limit automotive emissions, reducing vehicle weight is widely recommended and achieved in many ways, both by the construction of individual elements of the vehicle and by the selection of light materials, including Al alloys. Connecting these elements with each other and with elements made of iron alloys can be realized, inter alia, by welding or stir welding. However, the quality of the welds obtained varies widely and depends on many design, operational, and environmental factors. The present study focused on a review of various welding techniques used to join both similar and dissimilar Al alloys utilized in the automotive industry, the effect of various process parameters on weld quality, and the phenomena observed in such welds. The research methodology was based on the analysis of the content of articles from main databases. Apart from capturing the current state of the art, this review evaluates reaching the possible highest joint quality and welding process disadvantages such as porosity, poor surface quality, a tendency toward hot cracking, and low ductility for the Al alloys applied in the automotive industry.

Numerical simulation of surface roughness effects on low-cycle fatigue properties of additively manufactured titanium alloys

Additive manufacturing (AM) is a complex process involving a multiscal physical phenomena (solid–liquid-gas), often resulting in poor surface quality. Although surface treatments such as polishing or chemical treatment can improve surface quality, localized sub-grain stress concentrations induced by surface roughness anomalies are still easily formed, which can lead to the reduction and dispersion of fatigue properties in AM alloys. In this study, a numerical simulation model is proposed to study the association between surface roughness and fatigue properties of AM alloys. Based on the continuum damage mechanics modeling framework, an idealised grain/grain boundary model is generated by employing the Voronoi tessellation meshing technology. The numerical simulations are performed for the model with different surface geometric states. The correlation between surface roughness geometric features and fatigue properties is analyzed and discussed. A parameter “G” which comprehensively considers the influence of the maximum surface height (Rz) and correlation length (Lcor) is proposed to quantify the influence of surface roughness geometric features on the fatigue properties of AM alloys. This finding can be of great significance in improving the surface integrity of components to increase service life.

Mapping of groundwater potential zones of Khordha District using GIS and AHP approaches

The most dependable source of fresh water is groundwater. Groundwater supplies are severely threatened by a number of factors, including urbanization, industrialization, and population growth. The amount, quality and variables affecting groundwater supplies are significantly impacted by climate variability. The fall in groundwater levels is often exacerbated by poor quality surface water resources and unreliable monsoons. Therefore, in order to supplement the groundwater supply, it is important to locate and define the groundwater potential zone (GPZ). The analysis is conducted for the Khordha district, where groundwater rather is a primary source for agricultural uses. In order to determine the possible groundwater zones, many factors, including geomorphology, geology, elevation, slope, precipitation, soil type, soil texture, drainage density (DD), lineament density (LD), Land use/Land cover (LULC), and lineament density (LD), are constructed as separate layers in the geographical information system (GIS) backdrop. The multi-criteria decision-making technique and the Analytic Hierarchy Process (AHP), which enable pairwise evaluation of criteria impacting the potential zone, were utilized to establish the weights for the different layers and after that, the weighted overlay analysis (WOA) tool in ArcGIS10.8 was used to produce the final groundwater potential map. The output map of specified region was delineated into five new classes-very good, good, moderate, poor, and very poor of which 12% (325.1745 km2) falls under ‘very low’, 22% (603.9765 km2) under ‘low’, 26% (700.7715 km2) under ‘moderate’, 26% (694.2591 km2) under ‘high’, 14% (376.7553 km2) under ‘very high’. Approximately 1395 km2 area concerning 52% of study region, falls under ‘high’ and ‘very high’ categories of GPZ. Validation of the generated GPWZ map was done with data acquired from Central groundwater board. The accuracy assessment was done by kappa coefficient error matrix, and based on overall accuracy, the obtained map was 81.538% accurate to field value. As dependable results were produced with the proposed methodology, future management plans incorporating natural and artificial recharge practices can be created in these locations with effectiveness.

Enhanced fabrication of conical array via two-stage through mask electrochemical machining process

In response to the issues of low processing precision, poor surface quality, and low array uniformity in the fabrication process of metal array conical structures, this paper proposes a two-stage enhanced process for fabricating metal array conical structures using through-mask electrochemical machining (TMECM). The micro-convex structure with high consistency can be quickly obtained through the first electrochemical machining (ECM), and then the mask is removed and the micro-convex structure is modified twice. The top diameter of the micro-structure is reduced by using the phenomenon of electric field concentration in the ECM process, and the top curvature radius of the micro-structure is further reduced, so as to increase the height diameter ratio of the micro-structure and improve the surface quality. The results show that during the initial ECM, when the machining time is 35 s, the voltage is 20 volts, the flow rate of the acid etching solution is 1 m /s, the duty cycle is 50 %, and the frequency is 200 Hz, the stable machining of the metal array conical structure can be achieved. In the secondary electrochemical surface modification, it was found that under the conditions of working solution containing 2 mol/L nickel-based etching agent, pulse voltage of 20 V and processing time of 35 s, the method effectively improved the surface quality of the workpiece and ensured the stable manufacturing of the micro-conical array structure. The prepared microstructure height was 198 μm and the top diameter was 28 μm.

Surface characteristics of additively manufactured γ-TiAl intermetallic alloys post-processed by electrochemical machining

Electron beam melting (EBM) process is the most preferable powder bed fusion process for high melting point alloys. γ-TiAl alloys are intermetallic chemical compounds, which are lightweight and resistant to oxidation and heat, and have low ductility as well. EBM is the best manufacturing process for such alloys to produce aerospace parts, but poor surface quality is the main drawback of this process. Thus, surface post-processing is needed after the EBM process. This study presents the surface characteristics of EBM γ-TiAl alloy surfaces post-processed by electrochemical machining (ECM). The surfaces were ECM and the surface roughness values (Sa, Sq and Sz) have been reduced significantly. The mean reduction values of the experiments are 98.6 %, 98.5 % and 95.3 % for Sa, Sq and Sz, respectively. Additionally, it is observed that the surface roughness is inversely proportional to the electrolyte conductivity up to a limit value (115 mS/cm), and after that the roughness increases via the stray current transition. Sq values decrease with the increased feed rate via the increased current density. However, an increase in feed rate negatively affects the Sku values, which statistically describe the sharpness or spread of surface roughness. Also, XRD results showed that Ti2AlN layer is formed on the surface via the HIP operation. This layer inhibits the electrochemical dissolution of γ-TiAl alloy and caused surface defects.

On machining-induced surface integrity of Inconel 718 fabricated by powder bed fusion

Additive manufacturing (AM) introduces unique grain feature and anisotropy in metals, as well as relatively poor surface quality, so the knowledge about the formation of post-machining-induced surface integrity needs to be extended. This study aims to understand the machining phenomena in orthogonal cutting of Inconel 718 produced via powder bed fusion of metals using a laser beam system (PBF-LB/M), paying particular attention to the cutting energy, chip formation, geometrical defects, and microstructural deformation. Experiments are conducted on both wrought (W 718) and PBF-LB/M (PBF 718) Inconel 718, whereby the cutting speed and the anisotropy of the workpiece in the raw state play an important role. The results indicate that less cutting energy is consumed when cutting PBF 718 in the direction perpendicular to its build direction (BD), followed by cutting in its BD. Denser shearing-induced slip lines and relatively continuous chip morphology are found when cutting PBF 718 in its BD, moreover, the effect of cutting speed on shearing deformation of columnar grains under this condition is analysed. More importantly, this study identifies a significant geometrical defect phenomenon which is unique to PBF 718 and highly depends on the cutting speed and anisotropy of grain feature. A detailed characterisation shows that this behaviour is caused by tearing within the grains in the matrix material and not by the presence of hard inclusions, which has rarely been reported in the literature. The microstructure in the subsurface area exhibits that the density of grain boundaries in the cutting direction plays the key role in plastic deformation, as the machining process mainly causes dragging behaviour in the area below the machined surface. Thus, cutting PBF 718 in the direction perpendicular to its BD shows similar deformation layer to W 718, while cutting PBF 718 in its BD displays much stronger subsurface deformation. The obtained results greatly help to understand the cutting phenomena in post-machining of additively manufactured Ni-based components, especially the integrity for a better functional surface.

Cryogenic and ultrasonic-assisted micro-drilling of printed circuit boards using high-frequency-amplitude spindle

Printed circuit boards (PCBs) are key components in computers, 5G, 6G, and other wireless communication devices. On the other hand, the manufacture of micro-holes in PCBs faces severe challenges. Conventional micro-drilling methods often encounter challenges such as poor surface quality and limited tool life. To overcome these issues, a novel micro-drilling method called cryogenic and ultrasonic-assisted micro-drilling (CUAMD) has been developed. This study compared four drilling methods to investigate the benefits of cryogenic and ultrasonic-assisted drilling in hybrid machining processes: conventional micro-drilling (CMD), cryogenic-assisted micro-drilling (CAMD), ultrasonic-assisted micro-drilling (UAMD), and cryogenic and ultrasonic-assisted micro-drilling (CUAMD). The experimental results unequivocally indicate that the utilization of cryogenic-assisted drilling leads to a significant reduction in cutting heat during the machining process. This not only contributes to an improvement in machining accuracy but also exerts a positive influence on tool life and surface morphology. Ultrasonic-assisted drilling separates chips into smaller volumes through high-frequency-vibration, effectively reducing the cutting forces. The high frequency of 38.25 kHz and high amplitude vibration of 5.16 μm of the ultrasonic spindle induced vibrations on the drill bit. Liquid nitrogen with a pressure and temperature of 28 kPa and − 196 °C, respectively, was used in the cryogenic-assisted method. The superior machining performance of the CUAMD approach was evaluated by comparing it to various methods, including cutting forces, tool flank wear, entrance/exit hole morphology, and chip formation. The CUAMD method avoids chip entanglement, suppresses burrs, and reduces the maximum cutting force, maximum torque, and exit hole damage factor Fd by 47.7 %, 56.1 %, and 42.5 %, respectively, compared with CMD.

The influence mechanism of Halbach array magnetic field control on discharge channels in EDM

The use of magnetic field to actively control Electrical Discharge Machining(EDM) can effectively improve the problems of low material removal rate and poor surface quality, but due to the limitation of materials, the magnetic induction intensity of permanent magnets after magnetization is not high, and the magnetic induction lines of permanent magnets are too concentrated and difficult to control. In order to overcome the above shortcomings, this study applied the Halbach array magnetic field to the field of EDM for the first time, established a model of the trajectory of the charged particle beam in the discharge channel, analyzed the influence of the Halbach array magnetic field on the discharge channel, and clarified the improvement mechanism of the Halbacch array magnetic field in EDM. In addition, several sets of experiments were carried out by controlling the distance between the workpiece and the working surface of the Halbach array permanent magnets. The experimental results show that when the distance between the workpiece and the working surface of the Halbach array permanent magnet is less than 10mm, the material erosion rate of the workpiece increases significantly, and the electrode loss rate and surface roughness decrease significantly. When the workpiece is 0mm away from the working surface, the material removal rate is increased by 18.18%, from 0.4513mm3/min to 0.5333mm3/min, the tool wear ratio is reduced by 46.87%, from 0.2587 to 0.13745 mm3/min, and the surface roughness is reduced by 39.56%, from 4.186 μm to 2.53 μm.

Characterization and Analysis of Inconel 718 Alloy Ground at Different Speeds

Inconel 718 (IN718) alloy is widely applied to fabricate high temperature resistant or corrosion resistant parts due to its excellent mechanical performance. However, the machining of IN718 alloy is difficult as it may cause serious tool wear and poor surface quality (SQ) of the workpiece. In this work, grinding experiments on IN718 alloy at different speeds were conducted by using a CBN grinding wheel. The relationship between grinding speed, SQ and subsurface damage (SSD) was well studied. With increasing grinding speed, surface roughness decreased, and SQ was greatly improved. Meanwhile, the microhardness of the grinding surface declined as the grinding speed increased. The SSD depth was almost unchanged when the grinding speed was lower than 15 m/s, then it decreased with higher grinding speeds. It was attributed to the mechanical-thermal synergistic effect in the grinding process. The results indicated that increasing grinding speed can effectively improve the SQ and reduce the SSD of IN718 alloy. The conclusion in the work may also provide insight into processing other hard-to-machining materials.

Investigation of processing characteristics of PCD in ultrasonic-assisted graphene powder mixed EDM

Polycrystalline diamond is widely used in many fields including ultra-precise machining, optical material and semiconductor electronic devices due to its excellent physical properties. However, traditional mechanical processing methods of polycrystalline diamond leads to severe tool wear, low efficiency and high costs. Although electrical discharge machining can overcome some limitations, it usually exhibits a low material removal rate and poor surface quality. This study aims to explore the effect of graphene powder and ultrasonic vibration on polycrystalline diamond by electrical discharge machining. It was found that the synergistic effect of graphene powder and ultrasonic vibration can achieve a good surface quality. The results show that ultrasonic-assisted powder mixed electrical discharge machining can obtain the smallest surface roughness (1.98 μm) at low parameter and the biggest material removal rate (0.773 mg/min) at high parameter compared with ultrasonic assisted electrical discharge machining and powder mixed electrical discharge machining. In addition, after ultrasonic-assisted powder mixed electrical discharge machining, the minimum value (0.807) of ID/IG is obtained. For polycrystalline diamond, this study also proposes a removal mechanism that diamond converts into graphite and is peeled under tensile stress.

Incorporating surface roughness into numerical modeling for predicting fatigue properties of L-PBF AlSi10Mg specimens

Laser-powder bed fusion (L-PBF) is a popular additive manufacturing method for fabricating metal parts with complex geometries. However, one of the primary setbacks lies in the surface quality of the as-built components. Poor surface quality influences the dynamic fatigue properties of L-PBF parts. Experimental investigation of fatigue properties is time-intensive and expensive. Hence, computational modeling can be implemented to critically evaluate the impact of surface roughness on fatigue. In this work, a numerical modeling framework is developed that considers the influence of part-scale surface roughness on fatigue properties. To calibrate and validate the numerical modeling framework, mechanical investigations of miniature AlSi10Mg specimens are conducted in a custom-built tensile-fatigue testing apparatus. First, the tensile properties are evaluated to find out the reliability of the apparatus. Thereafter, the fatigue investigations of two sets of specimens are conducted: five specimens (FS1-FS5) for calibrating the numerical model and three specimens (VFS1-VFS3) for model validation. The numerical modeling framework involves the 3D reconstructed specimen geometries from computed tomography (CT) imaging of the VFS1-VFS3 specimens. The resultant 3D geometries are discretized using Ansys finite element software and analyzed to simulate the fatigue behavior. The numerical results of fatigue life and failure locations of the VFS1-VFS3 specimens are compared with the experimental observations. The comparison shows that the numerical results are within 5 % of the experimental observations. Additionally, the location of maximum strain localization in numerical modeling matches the crack initiation location. In conclusion, the numerical modeling can predict low cycle fatigue life and failure location of L-PBF AM specimens.

In‐depth investigation and industry plan for enhancing surface finishing of 3D printed polymer composite components: A critical review

AbstractAdditive manufacturing (AM) is pivotal in modern manufacturing, allowing diverse materials to create functional parts. Polymer composites, with superior properties like enhanced mechanics and conductivity, are highly regarded. Fused deposition modeling (FDM) is a favored, cost‐effective AM technique. Despite popularity, FDM struggles with poor surface quality, impacting final part properties. This challenge affects composite part performance, prompting a need for surface quality enhancements in AM processes, like FDM. The review explores essential post‐treatments required to optimize composite parts for various applications. It examines surface finishing techniques for FDM 3D printed polymeric composites, categorizing them into chemical, thermal, and physical methods. Recent research is extensively analyzed, offering a comprehensive guide for academia and industry. The review covers diverse aspects, including properties, surface morphology, electrical conductivity, and mechanical properties pre‐ and post‐finishing methods. Additionally, it summarizes leading companies worldwide providing surface finishing services for 3D printed polymer parts. Discussions on future trends, challenges, and research gaps in this field are included, emphasizing its significance in refining surface finishing methods for FDM 3D‐printed polymeric composites and encouraging broader industrial adoption of AM. This overview serves as a crucial roadmap for engineers, scientists, customers, and companies interested in surface finishing services.

Electrochemical polishing with glycol-based electrolyte of the curved internal channels fabricated via laser powder bed fusion

Electrochemical polishing (ECP) is used to process metal additive manufacturing parts with poor surface qualities arising from powder adhesion, spheroidal effect, and step effect during forming. Conventional ECP uses stationary acid-based solutions and very low current densities, which makes it challenging to efficiently polish complex-shaped internal channels. Typically, an oxide layer forms in the conventional aqueous-based electrolyte, which prevents uniform dissolution and consequently deteriorates surface quality. In this study, we proposed a modified ECP method for polishing curved internal channels in laser powder bed fusion (LPBF) 316 L stainless steel (SS) specimens using a high-speed flow of a NaCl–ethylene glycol (EG) solution at low current densities. During electrochemical tests, LPBF 316LSS specimens did not exhibit passivation in the NaCl–EG solution, and the current efficiency was high at low current densities (i < 4 A·cm−2). The reaction mechanism of ECP LPBF 316LSS in the NaCl–EG solution was clarified by observing the experimental phenomena and testing the composition of the reaction products. The ECP experiments showed that the decrease of roughness value is directly related to the charge. A small roughness value can also be obtained at low current densities (i < 2 A·cm−2). Finally, S-shaped curved holes with a diameter of Φ3 mm were efficiently polished using a flexible cathode in the NaCl–EG solution. In the case of an aperture increase rate of only about 7 %, it would only take 400 s to drastically reduce the surface roughness value Sa from 12.73 to 12.94 μm to 2.16– 2.43 μm.

Chatter Identification of Vibration Signals and Surface Roughness using Wavelet Transform and I-kazTM Methods

The paper describes the method to identify chatter in low-cutting-speed operations. It is based on vibration and surface roughness measurements. Tool chatter is the self-excited relative motion between the cutting tool and work piece. Tool chatter leads to poor surface quality and tool wear. The LMS Scadas testing system and accelerometer were used to measure the vibration signals during the turning operation, and Marsuft Psi was used to measure the surface roughness. When various cutting parameter combinations, such as cutting speed, feed rate, and depth of cut, were employed throughout the machining process, chatter and vibrating phenomena occurred. After the recorded signals were analyzed using the wavelet transform (WT), a chatter index (CI) was produced to determine how severe the chatter was. According to the results analysis, the experimental study demonstrated the close relationship between the surface roughness values and the chatter index when evaluating chatter identification.

Characteristics of four commonly used self-expanding biliary stents: an in vitro study

BackgroundKnowledge of the characteristics of self-expanding metal stents (SEMSs) is essential during selection process to ensure the best therapeutic outcomes for patients with malignant biliary obstruction. The aim of this study was to evaluate the characteristics of four commonly used SEMSs.MethodsThis in vitro study analyzed the radial force (RF), crush resistance (CR), axial force (AF), conformability, surface quality, foreshortening, and radiopacity of the following SEMSs: uncovered Wallflex™, EGIS single bare, Zilver 635®, and E-Luminexx™. Two samples of each SEMS type were included in this study, all having identical specifications with a diameter of 10 mm and a length of 6 cm. One sample from each type was analyzed for surface quality, followed by CR, conformability, and foreshortening. The other sample was analyzed for radiopacity, followed by RF and AF.ResultsThe uncovered Wallflex™ exhibited low RF, high CR, high AF, good conformability, poor surface quality, high foreshortening, and good radiopacity. The EGIS single bare demonstrated high RF, high CR, low AF, moderate conformability, good surface quality, high foreshortening, and poor radiopacity. The Zilver 635® displayed moderate RF, low CR, low AF, moderate conformability, moderate surface quality, no foreshortening, and good radiopacity. The E-Luminexx™ showed high RF, moderate CR, high AF, poor conformability, poor surface quality, no foreshortening, and good radiopacity.ConclusionsThere was considerable variation in the characteristics among the four evaluated SEMSs. These characteristics should be carefully considered during selection to ensure optimal therapeutic outcomes for patients.Relevance statementThe selection of self-expanding metal stents for treating malignant biliary obstruction requires careful consideration of various characteristics, including their radial force, crush resistance, axial force, conformability, surface quality, foreshortening, and radiopacity.Key points• The characteristics of self-expanding metal stents (SEMSs) can vary considerably.• Specific situations may warrant the use of SEMSs with particular characteristics over others.• Characteristics of SEMSs must be considered during selection for optimal outcomes.Graphical

Comparison of turning process performance using modified cutting inserts under minimum quantity lubrication

ABSTRACT While machining of high-strength alloy steel materials, poor surface quality and decreased tool life are result by an increase in the cutting zone temperature close to the machining region. To overcome this, surface texture with green manufacturing environment is an alternate path to enhancing machining performance. In the present work, novel Parallel Grooved Textured Tools (PGT) was developed and studied the performance of so developed tools. Further, the Untextured Tool (UT) and PGT performance was compared while machining EN24 alloy steel under Minimum Quantity Lubrication (MQL) condition. It was perceived from result that textured tools reduced the cutting temperature (CT), rake wear (RW), flank wear (FW), surface roughness (Ra) and cutting force (CF) up to 18.96%, 18.79%, 24.31%, 12.69%, and18.96% respectively compared to UT.

Atomic-level insight into process and mechanism of ion beam machining on aluminum optical surface

Polycrystalline Al workpieces go through a complex surface atom sputtering and surface/subsurface atom diffusion throughout the ion beam machining process that plays a critical role in determining machining quality of optical mirror surfaces. Here, we leverage molecular dynamics method for the first time to reveal the machining mechanism and the polycrystalline effect of aluminum during ion beam sputtering, in term of cascade collision, atom trajectory, sputtering yield, and surface characteristic. Polycrystalline Al presents a significant low potential energy state, leading to milder cascade collision and weaker sputtering effects than monocrystalline Al during ion beam machining. The atom trajectory demonstrates irregular variation as the atom diffusion is blocked by grain boundary (GB) in polycrystalline Al, leading to the relief microstructure and poor surface quality. With incident ions increasing, the GBs are broken and atom diffusion enhancing, as well as lower subsurface defects and better finishing surface quality. The microscopic morphology evolves into gravel microstructure. Simulation results also reveal that atom diffusion will benefit from high ion concentration and low ion energy. Sputtering yield variation is more sensitive to ion energy. To acquiring better finishing surface quality of Al without influencing machining efficiency, ion concentration must be increased while the ion energy needs to be decreased appropriately but a large number of cascading collisions need to be ensured.