Polishing Speed Research Articles

Chemical mechanical polishing of sapphire elucidated by densely discrete phase model and verified using atomic force microscopy

The chemical mechanical polishing (CMP) is extensively applied in sapphire substrate processing. However, the mechanism is unclear because of the challenging in the dynamic characterization. In this paper, effects of the polishing speeds, slurry concentrations, and abrasive sizes on the removal action of granular flow in sapphire CMP are investigated using the discrete particle model (DPM) and densely discrete phase model (DDPM). Contours of the residence time, concentration, and abrasive velocity present that rotation speeds of the wafer and pad (30 and 80 rpm respectively) are beneficial to improving sapphire CMP performance. When the SiO2 slurry concentration is higher than 1 wt%, DDPM is more suitable for the fluid-solid flow in sapphire CMP compared to DPM. As the slurry concentration increases, the growth trend of material removal rate (MRR) slows down because of the reduction of the integral particle erosion ratio (PER). The 100 nm SiO2 abrasive can obtain the maximum MRR (10.90×10−9 nm/s), although its PER is 2 × 10−5 of 5 µm particles’ PER. The in-situ atomic force microscopy experiments prove the MRR function of granular flow owing to the hydro-dynamic contact. In addition, the removal ability will be improved by enhancing the interactive force between the abrasive and sapphire. It provides a novel idea to boost the efficiency of sapphire CMP.

Effect of rotation frequency of polishing discs on the surface roughness of resin composite material.

The aim of this study was to evaluate the effect of rotation frequency (rpm) of different polishing discs on the surface roughness of a nanohybrid resin composite material. 126 specimens were prepared in metal molds of 10 mm diameter and 2 mm depth using a nanohybrid resin composite material. The prepared specimens were kept in distilled water for 24 hours. Polishing treatments at 5k, 10k, 15k, and 20k rpm were applied to the nanohybrid resin composite material by grouping different brand polishing discs: Sof-Lex Contouring and Polishing Discs (3M Espe, USA) (3M Group), Optidisc (Kerr Corporation, USA) (Kerr Group), Super-Snap Rainbow Technique Kit (Shofu Dental, Japan) (Shofu Group), Finishing Disc (Bisco Dental, USA) (Bisco Group). The surface roughness was evaluated at three different points by atomic force microscopy for all specimens and scanning electron microscopy was used for visual assessment. Data were evaluated by Two Way ANOVA and Tukey's HSD Test. The mean surface roughness (Ra, μm) of all prepared samples showed significant differences (α = 0.05). According to Two-Way ANOVA, there is a statistically significant relationship between the rpm values and the discs. The 3M group showed the highest roughness value at all rpm speeds. Shofu group at 15k, 20k rpm, Bisco group at 10k, 15k, 20k rpm, the Kerr group at 15k, 20k rpm showed the lowest roughness value and had roughness close to the surfaces finished with a mylar strip. The smoothest surfaces were obtained at 15k rpm, even though polishing discs from different brands were used. It was also observed that 5k and 20k rpm polishing speeds can increase the surface roughness of the nanohybrid resin composite material.

Effect of chemical action on shear thickening polishing of YAG

The shear-thickening polishing (STP) method, a flexible polishing technique developed in recent years, was utilized to obtain high surface quality of yttrium aluminum garnet (YAG) crystal effectively. The effect of polishing slurry pH value, which characterizes the chemical action between slurry and YAG crystal, on the material removal rate and surface roughness of YAG crystal was investigated, and the mechanism of the chemical action between YAG and slurry in STP process was revealed through X-ray photoelectron spectroscopy (XPS) analysis. The influence of polishing speed and abrasive concentration, which were relating with mechanical action, on the polishing effects was also studied. The experimental results show that when the pH value of the polishing slurry is lower than 11, the dissociation of chemical bonds and the formation of new bonds on the surface of the YAG crystal are predominantly found, resulting in a lower material removal rate. While the pH value of polishing slurry reaches 13, a reaction layer consisting of Al2SiO5 and Y2SiO5, which has lower hardness than abrasive, is formed on the surface, and this reaction layer can be removed by mechanical action efficiently. The surface roughness Sa decreases from 60 ± 10 nm to 0.38 ± 0.06 nm in 15 min with MRR reaches 117.30 nm/min, which is 4.3 times higher than that of chemical mechanical polishing. Based on the results of XPS analysis, the material removal mechanism of YAG polished by STP is proposed. As revealed by the results, STP with chemical action provide a high efficiency polishing method for the high surface quality YAG crystal.

Polishing-induced material attrition in surface-texturing AlN using a nanoscale polishing tool: An atomic-scale understanding

This study examines the alterations in the material properties and the effectiveness of the nano-polishing process applied to the surface of AlN substrate material through molecular dynamics simulations. Various controlled parameters at the outset of the polishing process, including polishing depth, polishing speed, and surface texture, exert both positive and negative influences on substrate characteristics, such as polishing force, friction coefficient, atomic phase transformation, subsurface damage layer (SDL), von Mises stress, temperature, dislocation characteristics, surface topography, atom removal, and root-mean-square (RMS). The results depicted that great polishing depth and slow polishing velocity have adverse effects on the internal structure of the material, leading to the creation of a substantial SDL and a dense network of dislocation formation. Conversely, increased material polishing velocity results in elevated von Mises stress and high generated temperatures. When combined with the initial surface structure conditions of the material, this mitigates detrimental effects on the internal structural characteristics while facilitating the phase transformation process and enhancing atom removal efficiency. The calculated RMS results of the substrate demonstrate that adjustments in polishing speed yield a higher improvement in surface roughness compared to alterations in polishing depth and surface texture. Therefore, a comprehensive understanding of the impact of initial conditions in the polishing process, as well as the atomic-level surface structure of the substrate, aids in selecting the most appropriate polishing conditions to produce the highest-quality products.

Electric discharge aided surface post-treatment of laser powder bed fused non-planar metallic components for enhanced form accuracy

Laser powder bed fusion (LPBF) of metals is an advanced technology gaining popularity in the manufacturing domain for producing near net shape products. The feasibility in batch production and design freedom highlights the promising scope of LPBF over conventional fabrication methods. However, loss of geometrical and dimensional accuracy is a critical challenge in LPBF due to solidification induced volumetric shrinkage and formation of surface irregularities. The aforementioned challenge gets aggravated whenever the fabricated components are non-planar. Studies on post-processing induced modification of dimensional and form accuracy of LPBF components is limited in literature. Moreover, the existing post-treatment operations using laser source, chemicals and mechanical forces exhibit limitations in ensuring desired geometrical accuracy in LPBF components. Therefore, the feasibility evaluation of integrating an alternate post-processing method with LPBF in improving geometrical accuracy become meaningful and worth exploring. Thus, the present study investigates the efficacy of a low energy thermo-electric post-processing method called wire electrical discharge polishing (WEDP) in ensuring geometrical form and dimensional accuracy of LPBF components. The study proposes a mathematical model which discloses the factors to be considered for dimension compensation in computer aided design (CAD) model. The results of the present study indicate that the proposed approach can impart notable reduction in form deviation leading to improved geometrical accuracy. The substantial error in terms of circularity over LPBF curved specimens were drastically reduced after WEDP process. Moreover, the cylindricity of curved specimens was improved by ~80 %. Despite the reduction in flatness error to ~7 μm, the irregularities pertaining to the edges were successfully removed from inclined LPBF surfaces resulting in sharp edged profile. The polishing speed was observed to be strongly dependent on the stair-stepping effect over vertically built LPBF surface. The discharge energy in WEDP played a vital role in influencing the circularity and surface integrity of the processed surface. Furthermore, the thermal impact of WEDP process leads to microstructural modification near the surface, whereas residual stress state after WEDP remains similar to LPBF condition. In a nutshell, the WEDP method looks promising in improving the geometrical and dimensional accuracy of LPBF components thereby enhancing the acceptability of parts in industrial applications.

Molecular Dynamics Study of Sapphire Polishing Considering Chemical Products

The sapphire chemical mechanical polishing (CMP) process is complicated. The silicate products such as Al2SiO5 are produced during the polishing process. This paper applies molecular dynamics (MD) to study sapphire CMP process considering chemical products. The effects of Al2SiO5 on sapphire polishing as well as the polishing depth, speed and abrasive particle’s radius on the polishing of sapphire covered with Al2SiO5 were investigated by comparing polishing force, coefficient of friction (COF), temperature, removed atoms and subsurface quality. The results show that the Al2SiO5 film is beneficial to improving the removal rate and the subsurface quality of sapphire. Increasing the polishing depth can raise the material removal rate, but will aggravate the subsurface damage. The balance of chemical products and polishing depth should be controlled to keep them equivalent during sapphire polishing to minimize subsurface damage. The temperature of the workpiece will rise and the polishing force will decline with the increasing polishing speed. The removed atoms become more but the subsurface damage fluctuates. As the radius of the particle increases, the COF decreases, and the subsurface quality first rises and then declines. The best polishing quality was obtained at 150 m s−1 and 40 Å.

Electrolysis combined shear thickening polishing method

Electrolysis compounded shear thickening polishing (E-STP) was proposed to increase the polishing efficiency of the difficult-to-machine metal. A 316 L stainless steel workpiece was employed in the experiments. The effects of current density, duty ratio, supply frequency, polishing speed, and abrasive concentration on the polishing material removal rate (MRR) and surface roughness of workpiece were examined through single factor experiment. The surface roughness Ra drops from 315 nm to 5 nm with MRR 57 μm/h in 15 mins' processing under the conditions with current density of 0.3 A/cm2, the duty ratio of 0.625, power supply frequency of 100 kHz, the polishing speed of 2.09 m/s, and the abrasive concentration of 12 wt%. A mathematic model of MRR was established, and the difference of MRR between the theoretical and experimental results is <12 %. As revealed by the results, E-STP can serve as a high efficiency polishing method for the difficult-to-machine metal.

THE CHEMICAL ETCHING OF CdTe, ZnxCd1-xTe and CdxHg1-xTe SINGLE CRYSTALS WITH HNO3 – KI – DIMETHYLFORMAMIDE SOLUTIONS

The chemical dissolution of CdTe single crystals, ZnxCd1-xTe and CdxHg1-xTe solid solutions in HNO3 – KI – dimethylformamide solutions has been investigated under reproducible hydrodynamic conditions for the first time. It is shown that the etching compositions of this system are cheaper, create a less aggressive environment, are more stable over time and are more ecologically safe. The diagrams «solution composition versus dissolution rate» has been plotted and the concentration limits of polishing etchant have been determined. Chemical-dynamic polishing with the investigated solutions can be carried out with a volume content of HNO3 9-15 %, while the polishing speed the surface of CdTe single crystals, ZnxCd1-xTe and CdxHg1-xTe solid solutions is within 1.6-2.5 μm/min. The dependence of the ions concentration that passed into the solution after the interaction of solid solutions ZnxCd1-xTe with the investigated etchants, versus the content of the oxidant in the etchant has been determined, and it was shown that the content of ions in the solution corresponds to the molar ratio in the semiconductor and indicates uniform dissolution of the surface. Based on the results of kinetic study, the apparent activation energy of the polishing was calculated for a solution of the composition (in vol. %): 12 НNO3 + 88 KI (DMF), which does not exceed 15.1 kJ/mol for СdTe and 7.7 kJ/mol for solid solutions on its basis, which indicates the limitation of the process by diffusion stages. The effect of the lactic acid and the nature of the semiconductors on the kinetics of chemical-mechanical polishing of the studied single crystals were determined. When the polishing solution is diluted with organic acid to 40 vol. %, the speed of chemical and mechanical polishing decreases from 3.5 to 0.5 μm/min. The compositions of etching mixtures and modes of implementation of chemical-dynamic polishing, which is recommended to be carried out in a suitable installation at the temperature 293 K and the disk rotation speed 82 min‑1, and chemical-mechanical polishing of the mention above semiconductor single crystals with the addition of lactic acid and polishing rates of 3.5-0.5 μm/min.

Atomistic analysis of the phase transformation and wear regimes of textured Wurtzite-SiC hexagonality using molecular dynamics simulation

The surface nano-polishing features and wear regime of textured Silicon carbide (SiC) substrates are studied using molecular dynamics modelling. Surface groove-shaped textures improve nano-polishing performance. This method also reduces subsurface wear damage. Switching from cutting to adhering regime can enhance surface roughness, frictional coefficient, and wear regime by decreasing depth. Specifically, reducing polishing depths improved surface roughness from 1.77% to 9.33%. Increasing polishing speed or crystal direction indicates an adherent wear regime and improves surface roughness from 2.6% to 9.61%. Nano-polishing the (0001) plane produced more heat than other planes. Thus, the (0001) plane has more graphene-like structure atoms and is closer to completion than other planes. This discovery helps texture SiC-based materials increase their anti-friction and wear properties.

The impact of different polishing systems on yttria-stabilized tetragonal zirconia polycrystalline crowns in relation to heat generation.

To investigate the heat generation on yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) crowns during polishing with coarse and fine polishing systems at various speeds. Two polishers (coarse and fine) at three polishing speeds were investigated. Two simulation models of the first mandibular molars were prepared for full coverage Y-TZP restorations with different reduction dimensions. Preheated water was pumped into the abutment chamber, to simulate the intrapulpal temperature and blood flow. Twelve Y-TZP crowns (3M™ Lava™ Esthetic) were milled for each prepared tooth abutment and each cusp (n = 10) was individually ground for 30 s and polished for 2 min. Thermocouple wire was secured to the intaglio surface of the crown and linked to a data logger for recording temperature changes. Selected scanning electron microscopy (SEM) images of the treated surfaces and polishers were analyzed. The data was statistically analyzed using Prism 9. The highest temperature rise was observed in the 20,000 RPM polishing speed groups for both coarse and fine polishing, and higher than the threshold value of 5.5°C for pulp damage. The Kruskal-Wallis test, revealed statistically significant differences (p < .0001) in heat generation between low (10,000 RPM) and high (20,000 RPM) polishing speeds. High-speed polishing at 20,000 RPM generated the most heat over the threshold of 5.5°C, which would threaten the dental pulp. The results suggest that a cautionary approach should be taken to high-speed intraoral polishing. Dental clinicians should be aware of the choice of polishing systems and speeds to avoid pulp damage from intraoral polishing of Y-TZP restorations.

Simulation and experimental study of ultrasonic-assisted shear thickening polishing of cemented carbide

In order to obtain a good surface quality of carbide inserts, an ultrasonic-assisted shear thickening polishing (UASTP) method is proposed in this paper. Using the shear thickening property of non-Newtonian fluids and combining with the principle of ultrasonic vibration, the abrasive grains wrapped by the polishing slurry carry out both flexible micro-cutting and high-frequency micro-collision on the material surface. This enables more efficient polishing of the microscopic surface of the material. In this paper, the polishing principle of this method is analyzed. The rheological characteristics of shear thickening polishing slurry are studied, and a continuity model that can adapt to nonlinear rheological behavior is proposed based on the Gross constitutive equation. The effects of fluid velocity, ultrasonic amplitude and ultrasonic frequency on polishing speed and polishing pressure in the Preston equation are studied by COMSOL Multiphysics simulation software. This method's material removal rate model is established based on the high-frequency periodic characteristics of ultrasonic action, combining the simulation results with polishing experiments, which accurately describe the variation law of material removal rate with polishing time. After polishing the carbide insert for 60 min with this method, a smooth surface is obtained with continuous surface ripple measurements and small floating values; the surface roughness is reduced from 195 nm to 16.1 nm with an improvement rate of 91.7 %, and the material removal rate reached 0.71 μm/h, which improved the surface roughness improvement rate and material removal rate by 27.6 % and 44.9 %, respectively, compared with the STP method. The experimental results show that the UASTP method is an efficient composite polishing technology to enhance the cemented carbide's surface quality further.

Improving the Polishing Speed and Surface Quality of 4H-SiC Wafers with an MnO&lt;sub&gt;2&lt;/sub&gt;- Based Slurry

We carried out chemical mechanical polishing (CMP) on commercially available 6 inch SiC wafers (epi-ready products) with slurries containing different abrasive types and evaluated the latent scratch density from the mapping measurement of the wafers using mirror projection electron microscope (MPJ). Comparing to the wafer before polishing, the latent scratch density decreased on the wafer polished with MnO2+KMnO4, while that increased by polishing with Al2O3+KMnO4. The two-step polishing using first Al2O3+KMnO4 and then SiO2+H2O2 can reduce the latent scratch density to the same level as that with MnO2+KMnO4, but long polishing time is required because of the low polishing rate in the process with SiO2+H2O2. We investigated the reason why MnO2 slurry can suppress the occurrence of latent scratches by a polishing test on a wafer with an SiO2 film on its (0001)Si surface. The results suggest the oxidation of the SiC surface is rate-determining step for polishing with MnO2+KMnO4. It was also found that wafers without an SiO2 film could not be polished with only MnO2 abrasives. Thus the mechanical contribution to polishing by MnO2 abrasives in KMnO4-based slurry is smaller than the chemical contribution, which can suppress the occurrence of latent scratches. KMnO4-based slurry containing MnO2 abrasives performs the CMP process with low latent scratch density in a time shorter than that containing Al2O3 or SiO2 abrasives.

Comparative Analysis of Finite Element Simulation and Experiment on the Polished Surface Quality of Hard Anodized Film of Aluminum Alloy

According to the abrasive morphology and distribution of sandpaper surface, the finite element model of hard anodic oxide film polishing was established by using ABAQUS finite element software, and the hard anodic oxide film and aluminum alloy matrix were defined respectively. The effects of hard anodic oxide film polishing process, polishing surface quality and polishing parameters on the polishing force were simulated. The polishing surface quality and polishing force simulated by finite element model were verified by experiments. The results show that in the polishing process, the residual stress of polishing surface is mainly distributed in the range of 0.0034mm, and the chips produced by polishing are mainly broken and long strips with microscopic morphology, and polishing mainly depends on the front part of abrasive particles in the feeding direction of sandpaper. Under the action of abrasive particles of sandpaper, the results of finite element simulation and test show that there are certain grooves on the surface of oxide film. The finite element simulation of the normal polishing force of hard anodic oxide film is consistent with the polishing test results. During the process of polishing hard anodic oxide film, the normal polishing force increases as the polishing speed increases; the normal polishing force increases as the polishing removal amount increases; the polishing removal amount parameter has a greater degree of influence on the polishing force.

Experimental Study on Shear Rheological Polishing of Si Surface of 4H-SiC Wafer

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, Ra, 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 Ra 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.

Research on Spherical Self-rotating Polishing Technology

Polishing technology is widely used in the polishing process of aspheric optical elements, complex curved surface molds, and so on because of its high machining accuracy, good flexibility, and other advantages. Based on the Preston equation, this paper deduces the material removal function of spherical self-rotating polishing by applying the kinematics principle, obtains the removal function with approximate Gaussian distribution by using computer simulation method, conducts processing technology experiments through the spherical self-rotating polishing device, analyzes the influence of polishing pressure and polishing speed on the polishing removal characteristics of ceramic materials by simulation, and verifies the stability of the removal function through experiments. The results show that the removal function graph is Gaussian distribution, which is conducive to the surface shape convergence of airbag machining. The influence of process parameters on material removal rate is in good agreement with the theory and practice and has a good linear relationship. It is a controllable and deterministic processing mode.

Experimental research on the polished surface quality of hard anodized film of aluminum alloy

An experimental study was conducted for the surface polishing of the oxide film after hard anodizing of 2D70 aluminum alloy. The surface roughness and surface morphology of aluminum alloy before, after anodizing and after polishing were analyzed, and the effects of polishing force, polishing speed, feeding amount and sandpaper grit on the polished surface roughness were investigated experimentally. The results showed that the surface roughness of 2D70 aluminum alloy decreased by 1 grade on average after hard anodizing. The hard anodized film surface has more linear protrusions, large pits and a large number of small pores. After polishing, the linear protrusions and small pores disappear, and a small number of new linear grooves appear, while the condition of large pits does not change much. The depth of small pores on the oxide film surface is within 11μm in most cases. As the polishing force, feeding amount and sandpaper grit increase, the decreasing trend of roughness value also gradually increases, and the decreasing trend of the thickness of hard anodic oxide film gradually increases. As the polishing speed increases, there is no clear trend in the decreasing trend of rough

Experimental Study on Flexible Fiber Assisted Shear Thickening Polishing for Cutting Edge Preparation of Core Drill

To improve the cutting performance of the core drill, the flexible fiber assisted shear-thickening polishing (FF-STP) for cutting edge preparation was proposed to eliminate the microscopic defect and obtain proper radius of the cutting edge of the core drill. The flexible fiber was introduced into the shear-thickening polishing process to break the thickened agglomerates and improve the efficiency of cutting edge preparation. The influence of the polishing speed, abrasive concentration and the flexible fiber contact length with the core drill on the cutting edge radius r and surface morphology of the core drill edge was analyzed, and the drilling experiments were carried out after preparation, the cutting heat and drilled holes’ roughness were employed as evaluation indexes to evaluate the performance of the core drill. The results show that the cutting edge radius increases with the increase of polishing speed, abrasive concentration and contact length. However, too high a polishing speed and contact length reduce the abrasive particles involved in the polishing process, and then lead to a decline in preparation efficiency. Under the selected processing conditions, the cutting edge radius increases from the initial 5 μm to 14 μm and 27 μm with 4 min of treatment and 6 min of treatment preparation, respectively. The sharp cutting edge becomes rounded, the burrs and chipping on the cutting edge are eliminated, and the average roughness (Ra) of the flank face decreases from 110.4 ± 10 nm to 8.0 ± 3 nm. Nine holes were drilled consecutively by core drills after cutting edge preparation, and the cutting temperature and drilled holes’ roughness were recorded. The maximum cutting temperature (122.4 °C) in the process with the prepared core drill (radius r = 14 μm) is about 20 °C lower than that with untreated one, and the roughness of the drilled hole (Ra 510.5 nm) about 189.9 nm lower. The results indicates that FF-STP is a promising method for high consistency preparation of the core drill cutting edge.

Effect of a water film on the material removal behavior of Invar during chemical mechanical polishing

Understanding polishing mechanisms in water-lubricated environments has an important guiding value for surface engineering of precision devices. This work reveals the chemical mechanical polishing (CMP) mechanism of the Invar alloy under water lubrication by use of molecular dynamics simulation. The results show that the appropriate thickness of the water film and polishing speed can significantly reduce the surface roughness of the work piece and eliminate subsurface defects. With the increasing rolling speed, the variation of the surface roughness and subsurface damage thickness exhibits a trend of slowly decreasing and then reaching stability. In addition, with an increase in water film thickness, more defects were formed in the subsurface region due to greater surface stresses, although the roughness could be reduced due to an increase of passivated atoms on the work piece surface. These results would be helpful for understanding the CMP mechanism under water-lubricated conditions and for promoting the development of surface engineering for micro/nano components.

Material removal mechanism in magnetorheological foam plane finishing

The material removal process of magnetorheological foam plane finishing (MRFPF) method which considers various processing conditions was studied in this paper. A material removal rate (MRR) model based on the updating type of workpiece moving trajectory, magnetic field distribution, and polishing speed in the polishing area was established for MRFPF. In this model, MRR is generated by integrating the polishing pressure and speed over the time that polishing pressure on workpiece updating for 1 cycle with the relative error between theoretical and experimental results less than 11.63 %. Moreover, MRFPF can achieve much higher MRR and surface flatness improvement rate than that of magnetorheological finishing (MRF) under different processing conditions, which further indicates the effectiveness of MRFPF in planar finishing.

Effect of different polishing systems and speeds on the surface roughness of resin composites.

The objective of this study was to compare surface roughness of a nano-spherical resin composite using four different multi-step polishing disc systems at five different speeds. In total, 154 discs samples were prepared using a supra-nano spherical resin composite. The samples were divided into negative and positive control groups and the following four finishing and polishing disc systems: Sof-Lex, Bisco Finishing Discs, OptiDisc, and Super-Snap. Each polishing disc system was applied at five different speeds (2000, 5000, 10,000, 15,000, and 20,000 revolutions per minute [RPM]) (n = 7). The surface roughness of samples was measured using a profilometer. One sample from each group was evaluated by scanning electron microscopy and atomic force microscopy. Two-way analysis of variance was used to evaluate the average roughness (Ra) data from the profilometric experiments using statistical software (GraphPad Prism4-GraphPad Software; La Jolla, CA, USA). The mean values were compared using the Bonferroni test (P = 0.05). The mean roughness ranged from 0.07 μm to 0.41 μm. The smoothest surfaces were obtained with OptiDisc at 20,000 RPM and Super-Snap at 20,000 RPM. The Bisco Finishing Discs group at 2,000 RPM showed the highest surface roughness values. For all polishing systems, the roughness at 20,000 RPM was lower than that at other speeds. Within the limitations of the present in vitro study, it can be concluded that the polishing performance was in the following order: Super-Snap > OptiDisc > Sof-Lex > Bisco Finishing Discs. In addition, the surface roughness decreased as the polishing speed increased.