Search Results (34)

To address the issue of surface glazing that occurs during prolonged polishing with gel tools, this study employs a triethanolamine (TEA)-based polishing fluid system to enhance the self-sharpening capability of the gel polishing disc. The inhibitory mechanism of TEA concentration on disc glazing is systematically analyzed, along with its impact on the gel disc’s frictional wear behaviour. Furthermore, the synergistic effects of process parameters on both surface quality and material removal rate (MRR) of SiC are examined. The results demonstrate that TEA concentration is a critical factor in regulating polishing performance. At an optimal concentration of 4 wt%, an ideal balance between chemical chelation and mechanical wear is achieved, effectively preventing glazing while avoiding excessive tool wear, thereby ensuring sustained self-sharpening capability and process stability. Through orthogonal experiment optimization, the best parameter combination for SiC polishing is determined: 4 wt% TEA concentration, 98 N polishing pressure, and 90 rpm rotational speed. This configuration delivers both superior surface quality and desirable MRR. Experimental data confirm that TEA significantly enhances the self-sharpening performance of gel discs through its unique complex reaction. During the rough polishing stage, the MRR increases by 34.9% to 0.85 μm/h, while the surface roughness S_a is reduced by 51.3% to 6.29 nm. After subsequent CMP fine polishing, an ultra-smooth surface with a final roughness of 2.33 nm is achieved. Full article

To improve the surface morphology quality of ultra-precision optical components, particularly in the suppression of mid-spatial frequency (MSF) errors, this paper proposes a morphology gradient-aware spatiotemporal coupled smoothing model based on convolutional material removal. By introducing the Laplacian curvature into the surface evolution framework, a curvature-sensitive “peak-priority” mechanism is established to dynamically guide the local dwell time. A nonlinear spatiotemporal coupling equation is constructed, in which the dwell time is adaptively modulated by surface gradient magnitude, local curvature, and periodic fluctuation terms. The material removal process is modeled as the convolution of a spatially invariant removal function with a locally varying dwell time distribution. Moreover, analytical evolution expressions of PV, RMS, and PSD metrics are derived, enabling a quantitative assessment of smoothing performance. Simulation results and experimental validations demonstrate that the proposed model can significantly improve smoothing performance and enhance MSF error suppression. Full article

Purpose Maintaining the surface quality of ceramic restorations after clinical adjustments is critical for both aesthetic outcomes and long-term oral health, yet the optimal approach to restoring gloss and smoothness remains unclear. The purpose of this study is to investigate the effect of different surface finishing and grinding procedures on the surface gloss and roughness of three different monolithic lithium disilicate ceramics and one monolithic ultra-translucent zirconia ceramic. Materials and Methods A total of 104 specimens (1.5 × 12 × 14 mm) were prepared from four ceramic materials: LiSi CEREC Tessera (CT), GC Initial LiSi (LS), IPS e.max CAD (EC), and zirconia disc (KATANA UTML (KAT)). Each was divided into two subgroups based on surface finishing (mechanical polishing or glazing; n = 10). Gloss and surface roughness were measured using a glossmeter and a profilometer, respectively. One specimen per subgroup was analyzed under SEM at ×1000 magnification. Results Gloss and roughness values were analyzed with the two-way robust ANOVA test and multiple comparisons were made with Bonferroni correction. The significance level was set at p < 0.05. Mechanical polishing, glazing, and repolishing increased the gloss values of the materials, with the KAT group achieving the highest gloss in the repolishing groups. The lowest gloss values were observed in the grinding groups. Additionally, these surface treatments reduced the roughness of the surface of all the materials. Conclusions Surface finishing procedures significantly influenced the gloss and roughness of monolithic lithium disilicate and zirconia ceramics. Mechanical polishing systems performed similarly or better than glazing. However, selecting an appropriate polishing system for each material is essential. Full article

This study investigates the impact of polycarbonate diol (PCDL)-modified toluene diisocyanate (TDI)-based polyester polyurethane polishing pads on the chemical mechanical polishing of 4H silicon carbide (4H-SiC) substrates. Employing a unique metho, PCDL alters the ratio of polyurethane soft and hard segments, facilitating the one-step synthesis of a polishing pad via chemical foaming. The extent of the reaction of isocyanate groups was characterized by Fourier transform infrared spectroscopy, while the changes in the glass transition temperature of the material before and after modification were evaluated using differential scanning calorimetry. The mechanical properties and surface morphology of the modified pad have been systematically characterized. The results showed that compared with the polyurethane polishing pad without PCDL, tensile strength was augmented by a factor of 2.1, the elastic modulus surged by a factor of 4.2, the elongation at break improved by a factor 1.6, and the wear index decreased by a factor of 0.5 by 40 wt.% PCDL loading. Furthermore, the modified pad demonstrated a 14.5% increase in material removal rate and a reduction in surface roughness of 4H-SiC from 0.124 nm to 0.067 nm. Additionally, the compact surface pore structure and enhanced chemical stability in the strong oxidizing slurry of the modified pad enabled superior polishing performance, achieving an ultrasmooth 4H-SiC surface. The study highlights the potential of tailored polyurethane formulations in enhancing polishing efficiency and surface finish in semiconductor manufacturing processes. Full article

Zinc sulfide (ZnS) is extensively utilized in various applications due to its exceptional optical transmittance across numerous spectral bands. To achieve ultra-high surface quality ZnS optical components, shear thickening polishing (STP) is employed to reduce roughness. A comparison between traditional fixed abrasive polishing (FAP) and STP for ZnS glass showed that FAP results in poor surface quality due to its low removal efficiency and uneven abrasive exposure, while STP provides better surface quality due to its flexible removal process, proving its feasibility and advancement. The Taguchi method was used to study the impact of three key polishing parameters on surface roughness (Ra) and the material removal rate (MRR), finding that polishing angle most influenced roughness and speed most influenced MRR. With optimal parameters, ZnS glass surface roughness was reduced from 110 ± 15 nm to 8.85 ± 0.5 nm, with an MRR of 32.5 nm/min. Scanning electron microscope (SEM) images further confirmed STP’s effectiveness in removing microdefects and smoothing the ZnS glass surface, offering a new method for the efficient, high-quality polishing of chalcogenide glasses without surface damage. Full article

In silicon carbide processing, the surface and subsurface damage caused by fixed abrasive grinding significantly affects the allowance of the next polishing process. A novel grinding wheel with a soft and hard composite structure was fabricated for the ultra-precision processing of SiC substrates, and the grinding performance of the grinding wheel was assessed in this study. Different types of gels, heating temperatures, and composition ratios were used to fabricate the grinding wheel. The grinding performance of the grinding wheel was investigated based on the surface integrity and subsurface damage of SiC substrates. The results showed that the grinding wheel with a soft and hard composite structure was successfully fabricated using freeze-dried gel with a heating temperature of 110 °C, and the component ratio of resin to gel was 4:6. A smooth SiC substrate surface with almost no cracks was obtained after processing with the grinding wheel. The abrasive exposure height was controlled by manipulating the type and ratio of the gel. Furthermore, the cutting depth in nanoscale could be achieved by controlling the abrasive exposure height. Therefore, the fabrication and application of the grinding wheels with soft and hard composite structures is important for the ultra-precision processing of large-size SiC substrates. Full article

Advancements in astronomical telescopes and cutting-edge technologies, including deep ultraviolet (DUV) and extreme ultraviolet (EUV) lithography, have escalated demands and imposed stringent surface quality requirements on optical system components. Achieving near-ideal optical components requires ultra-smooth surfaces with sub-nanometer roughness, no sub-surface damage, minimal surface defects, low residual stresses, and intact lattice integrity. This necessity has driven the rapid development and diversification of ultra-smooth surface fabrication technologies. This paper summarizes recent advances in ultra-smooth surface processing technologies, categorized by their material removal mechanisms. A subsequent comparative analysis evaluates the roughness and polishing characteristics of ultra-smooth surfaces processed on various materials, including fused silica, monocrystalline silicon, silicon carbide, and sapphire. To maximize each process’s advantages and achieve higher-quality surfaces, the paper discusses tailored processing methods and iterations for different materials. Finally, the paper anticipates future development trends in response to current challenges in ultra-smooth surface processing technology, providing a systematic reference for the study of the production of large-sized freeform surfaces. Full article

Single-crystal silicon carbide has excellent electrical, mechanical, and chemical properties. However, due to its high hardness material properties, achieving high-precision manufacturing of single-crystal silicon carbide with an ultra-smooth surface is difficult. In this work, quantum dots were introduced as a sacrificial layer in polishing for pulsed-ion-beam sputtering of single-crystal SiC. The surface of single-crystal silicon carbide with a quantum-dot sacrificial layer was sputtered using a pulsed-ion beam and compared with the surface of single-crystal silicon carbide sputtered directly. The surface roughness evolution of single-crystal silicon carbide etched using a pulsed ion beam was studied, and the mechanism of sacrificial layer sputtering was analyzed theoretically. The results show that direct sputtering of single-crystal silicon carbide will deteriorate the surface quality. On the contrary, the surface roughness of single-crystal silicon carbide with a quantum-dot sacrificial layer added using pulsed-ion-beam sputtering was effectively suppressed, the surface shape accuracy of the Ø120 mm sample was converged to 7.63 nm RMS, and the roughness was reduced to 0.21 nm RMS. Therefore, the single-crystal silicon carbide with the quantum-dot sacrificial layer added via pulsed-ion-beam sputtering can effectively reduce the micro-morphology roughness phenomenon caused by ion-beam sputtering, and it is expected to realize the manufacture of a high-precision ultra-smooth surface of single-crystal silicon carbide. Full article

Single-crystal sapphire (α-Al₂O₃) has been widely used in semiconductor, optics, communication, national defense, and other fields. Before application, an ultra-smooth surface which is scratch free and subsurface damage free is essential. Furthermore, the sapphire has unique qualities such as significant rigidity and chemical stability, which make it extremely arduous to process. Chemical mechanical polishing (CMP) is recognized as the final process to reduce the roughness and eliminate surface defects of a sapphire surface. In this review, the materials and equipment used for the chemical polishing of a sapphire wafer are summarized, and the surface nanoscale changes of sapphire wafer are reviewed from the angles of regulating polishing-process parameters, composition of polishing slurry including that which is nano-abrasive, a pH regulator, a complexing agent, and other additives, as well as hybrid CMP technologies. The outlook and future applications are also summarized. Full article

Diamond needs to have a perfectly smooth surface due to the growing requirements in the fields of electronic semiconductors, optical windows and high-fidelity loudspeakers. However, the polishing of diamonds is highly challenging due to their exceptional hardness and chemical stability. In this study, a new polishing slurry is prepared for the proposed photocatalysis-assisted chemical mechanical polishing (PCMP) approach to obtain an ultra-smooth surface for large-area diamond. The analyses and experimental findings revealed the significance of the photocatalyst, abrasive, electron capture agent and pH regulator as essential components of the PCMP slurry. TiO₂ with a 5 nm pore size and P25 TiO₂ possess improved photocatalysis efficiency. Moreover, diamond removal is smooth under the acidic environment of H₃PO₄ due to the high oxidation–reduction potential (ORP) of the slurry, and, during the methyl orange test, P25 TiO₂ exhibits reasonable photocatalytic effects. Moreover, in 8 h, a smooth surface free of mechanical scratches can be obtained by reducing the surface roughness from Ra 33.6 nm to Ra 2.6 nm. Full article

In this study, shear rheological polishing was used to polish the Si surface of six-inch 4H-SiC wafers to improve polishing efficiency. The surface roughness of the Si surface was the main evaluation index, and the material removal rate was the secondary evaluation index. An experiment was designed using the Taguchi method to analyze the effects of four critical parameters (abrasive particle size, abrasive particle concentration, polishing speed, and polishing pressure) on the Si surface polishing of SiC wafers. By evaluating the experimental results for the signal-to-noise ratio, the weight of each factor was calculated using the analysis of variance method. The optimal combination of the process parameters was obtained. Below are the weightings for the influence of each process on the polishing result. A higher value for the percentage means that the process has a greater influence on the polishing result. The wear particle size (85.98%) had the most significant influence on the surface roughness, followed by the polishing pressure (9.45%) and abrasive concentration (3.25%). The polishing speed had the least significant effect on the surface roughness (1.32%). Polishing was conducted under optimized process conditions of a 1.5 μm abrasive particle size, 3% abrasive particle concentration, 80 r/min polishing speed, and 20 kg polishing pressure. After polishing for 60 min, the surface roughness, R_a, decreased from 114.8 to 0.9 nm, with a change rate of 99.2%. After further polishing for 60 min, an ultrasmooth surface with an R_a of 0.5 nm and MRR of 20.83 nm/min was obtained. Machining the Si surface of 4H-SiC wafers under optimal polishing conditions can effectively remove scratches on the Si surface of 4H-SiC wafers and improve the surface quality. Full article

A large-aperture silicon carbide (SiC) aspheric mirror has the advantages of being light weight and having a high specific stiffness, which is the key component of a space optical system. However, SiC has the characteristics of high hardness and multi-component, which makes it difficult to realize efficient, high-precision, and low-defect processing. To solve this problem, a novel process chain combining ultra-precision shaping based on parallel grinding, rapid polishing with central fluid supply, and magnetorheological finishing (MRF) is proposed in this paper. The key technologies include the passivation and life prediction of the wheel in SiC ultra-precision grinding (UPG), the generation and suppression mechanism of pit defects on the SiC surface, deterministic and ultra-smooth polishing by MRF, and compensation interference detection of the high-order aspheric surface by a computer-generated hologram (CGH). The verification experiment was conducted on a Ø460 mm SiC aspheric mirror, whose initial surface shape error was 4.15 μm in peak-to-valley (PV) and a root-mean-square roughness (Rq) of 44.56 nm. After conducting the proposed process chain, a surface error of RMS 7.42 nm and a Rq of 0.33 nm were successfully obtained. Moreover, the whole processing cycle is only about 216 h, which sheds light on the mass production of large-aperture silicon carbide aspheric mirrors. Full article

This paper proposes a gel-formed abrasive tool to address the problem of abrasive agglomeration in a traditional hot-pressing abrasive tool. The effect of Polyimide resin content on the mechanical properties of the gel abrasive tools were tested, and a comparison of the mechanical properties of the gel abrasive tool and the hot-pressing tool was conducted. An orthogonal experiment was conducted to explore the best combination of machining parameters. A polishing experiment of sapphire was conducted to compare the processing effect of the gel abrasive tool and hot-pressing tool. The results from testing the mechanical properties showed that the tensile, flexural, and impact strength of the gel abrasive tool was better than that of the hot-pressing abrasive tool. The results of the orthogonal experiment showed that the best process parameters of the gel abrasive tool were a spindle speed of 900 rpm, a feed rate of 8 μm/min, and a grinding depth of 16 μm. The polishing experiment showed that the gel abrasive tool had a better processing effect on sapphire. The sapphire surface processed by the gel abrasive tool had no deep scratches, and an ultrasmooth surface could be obtained after chemical mechanical polishing (CMP). Full article

Corrosive and toxic solutions are normally employed to polish sapphire wafers, which easily cause environmental pollution. Applying green polishing techniques to obtain an ultrasmooth sapphire surface that is scratch-free and has low damage at high polishing efficiency is a great challenge. In this paper, novel diamond/SiO₂ composite abrasives were successfully synthesized by a simplified sol-gel strategy. The prepared composite abrasives were used in the semi-fixed polishing technology of sapphire wafers, where the polishing slurry contains only deionized water and no other chemicals during the whole polishing process, effectively avoiding environmental pollution. The experimental results showed that diamond/SiO₂ composite abrasives exhibited excellent polishing performance, along with a 27.2% decrease in surface roughness, and the material removal rate was increased by more than 8.8% compared with pure diamond. Furthermore, through characterizations of polished sapphire surfaces and wear debris, the chemical action mechanism of composite abrasives was investigated, which confirmed the solid-state reaction between the SiO₂ shell and the sapphire surface. Finally, applying the elastic-plastic contact model revealed that the reduction of indentation depth and the synergistic effect of chemical corrosion and mechanical removal are the keys to improving polishing performance. Full article

Tungsten carbide (WC) has the characteristics of high hardness, high strength, corrosion resistance, wear resistance and excellent fracture toughness. Accordingly, it has been commonly used as the material for cutting tools and molds in glass-forming techniques. To obtain ultra-smooth surfaces, fine polishing of WC is indispensable. However, the efficiency of WC polishing is low using the existing polishing methods, and the mechanism behind the polishing process requires further investigation. Specifically, the effect of the binder in WC polishing is not clear since there are different kinds of WC with various weight percentages of the binder. In this paper, we present the findings of a study on the polishing performance of two kinds of WC material, with and without the binder, using a semi-rigid (SR) bonnet polishing tool. A series of experiments were performed on a 6-DOF robotic polishing instrument to investigate the material-removal characteristics, surface integrity and sub-surface damage after polishing. The results demonstrate that the SR bonnet polishing tool successfully reduced the surface roughness of WC with and without the binder to the nanometric level, though the lowest surface roughness was obtained on binder-less WC. No obvious sub-surface damage was observed under SEM inspection, while the processing efficiency was greatly improved owing to the high material removal rate of the tool. Based on our analysis of key polishing parameters and corresponding surface integrities, the effect of the binder on the polishing performance is explained, which offers excellent guidance for WC polishing. Full article