Polishing Experiments Research Articles

Diamond nanoscale surface processing and tribochemical wear mechanism

Diamond is widely used in many fields due to its numerous properties. Chemical mechanical polishing can achieve ultra-smooth and low-damage surface processing of diamond. We carried out the chemical mechanical polishing experiment of single crystal diamond using W0.5 diamond powder as abrasive in aqueous H2O2. The smooth surface with roughness (Ra) values of 0.917 nm was obtained and no obvious mechanical scratches. In addition, the atom removal mechanism of Chemical mechanical polishing process on the diamond surface polished with diamond powder in aqueous H2O2 was elucidated using Reactive Force Field molecular dynamics simulations. Hydroxylation on the diamond surface plays a dual role in the removal process. The diamond structure after being oxidized is damaged so the CC bonds become weak. The C atoms on the diamond surface form stronger CC bonds with the C atoms in abrasive, then the C atoms are carried away due to the mechanical action of abrasive. This work helps understand the removal process of C atoms at the atomic scale in the CMP process and provide an effective method to realize ultra-smooth and low-damage surface processing of diamond.

Preparation of flower-shaped silica abrasives by double system template method and its effect on polishing performance of sapphire wafers

As one of the most important factors of chemical mechanical polishing, abrasives have their unique mechanical grinding action and chemical action, providing the most critical support for the nanometer surface smoothness of workpieces. In this paper, the irregularly flower-shaped silica abrasives were prepared by a novel double-system microemulsion template method to replace conventional spherical silica abrasives. The synthesis principle was mainly based on heterogeneous polycondensation growth on irregular silica seeds. The morphology of the flower-shaped silica was verified by scanning electron microscopy. Due to the particularity of the synthesis method, a new environmentally friendly experimental device was designed. Chemical mechanical polishing experiments showed that the material removal rate of the flower-shaped silica with the solid content of only 6% is 217.4% of the spherical silica. The Ambios Xi-100 surface profiler showed that the surface roughness of flower-shaped silica was comparable to that of spherical silica. By establishing a contact wear model, it is analyzed that the actual contact area between the flower-shaped silica abrasives and the sapphire wafer is larger and the chemical solid phase reaction occurs more. This study provides a novel and feasible method for preparing irregularly shaped silica.

Thermal modelling for conformal polishing in inductively coupled atmospheric pressure plasma processing

Inductively coupled atmospheric pressure plasma processing (IC-APPP) is a novel polishing technique for silica-based optics to quickly mitigate the surface or subsurface damage due to its high efficiency and low cost. However, theoretically uniform removal of materials is difficult to achieve because of complex thermal effect. In this paper, numerical modelling and experimental study of global temperature field in IC-APPP is presented. First, a transient heat transfer model is established using finite element analysis to study the characteristics of temperature field distribution during the process. Then, the effects of substrate geometry and processing parameters are systematically analyzed. Finally, conformal polishing experiments are carried out to illustrate the correlation between the effectiveness of uniform removal and the temperature field. The surface shape can be maintained well with optimal processing parameters in IC-APPP.

A study on the control strategies of a series–parallel hybrid platform for blade polishing

Blades are key components of turbines, aircraft engines, and high-speed ship propulsion systems, such that their manufacturing quality has a considerable influence on a machine’s performance. This paper presented a series–parallel hybrid platform that employed abrasive belt as the tool and integrated the measuring equipment to achieve in-situ measurement for blade polishing. It studied the control strategies for solving the processing parameters aiming to the characteristics of the alternate measurement and processing in the process of polishing. According to singularity analysis of the parallel mechanism, the platform structure parameters were appropriately optimized to avoid the singular position. Then, based on the in-situ measuring data of the blade contour, a method was proposed for calculating the normal vector of machining points, while the platform kinematics were studied, and the total machining allowance was determined by comparing the actual and ideal contour profiles of the blade. Finally, a testing experiment was performed to validate the proposed method of the normal vector calculation, and blade polishing experiment was conducted on the developed platform, which proved the effectiveness and feasibility of the platform.

Polishing trajectory planning of three-dimensional vibration assisted finishing the structured surface

There are extremely wide application fields for the structured surface because of excellent properties. Sometimes it must be polished finally in order to meet the practical requirements. It is very meaningful to explore a kind of vibration assisted polishing method suitable for the structured surface because vibration-assisted machining has been widely proved an effective finishing technology. A novel three-dimensional vibration assisted polishing technology is put forward in this work, and the polishing trajectory planning about finishing the structured surface is also further investigated. This polishing system consists of two parts: the machine tool and a three-dimensional vibration device. The machine tool provides the machining path, and the three-dimensional vibration device provides the vibration locus. The three-dimensional polishing trajectory is generated skillfully by combining machining path and vibration locus. When the parameters about workpiece surface and two-dimensional vibration are given, the projection method is proposed in this study to establish the models about the vibration locus and polishing trajectory in three-dimensional space. The effects of phase and frequency on the distribution features of the polishing trajectory are analyzed by using the simulation results in detail. It is concluded that the phase has effects on the local distribution density of the polishing trajectory, and the vibration frequency has effects on the shape of the polishing trajectory. The polishing trajectory suitable for the harmonic mesh surface is presented. Many polishing experiments were carried out, and the experimental results show that this three-dimensional vibration polishing technique is very suitable for polishing the structured surface.

Ultra-Rapid Determination of Material Removal Rates Based Solely on Tribological Data in Chemical Mechanical Planarization

Single-run Stribeck+ curves are constructed using real-time, high-frequency, shear force and normal force data from the wafer-slurry-pad interface during copper and cobalt (on ILD wafers) CMP in conjunction with multiple slurries, pads and conditioning discs at various pressures and relative velocities. To avoid having to perform actual polishing experiments to obtain blanket film removal rates, “big data” sets from the same Stribeck+ curves are used to construct new “Kinetic” curves to help infer relative blanket wafer removal rates. The “Kinetic” curves, which are based on the assumption that material removal is Prestonian, are eventually validated with actual removal rate studies involving different wafer types processed at various pressures-velocity combinations with the same pads, conditioning discs and slurries. A strong correlation is seen between the actual and “inferred” removal rates which renders credibility to our new ultra-rapid and ultra-low-budget approach for determining removal rates that does not require any wafer polishing nor any film thickness metrology.

A New Vibration Device Applied for Two-Dimensional Ultrasonic Polishing of Biomaterials

For the research of the performance of two-dimensional ultrasonic polishing (TDUP) on the biomaterials, a new vibration device was designed. Meanwhile, our aim is to study the mechanism of multiangle polishing to cope with the complex structure of biomaterials. The device is composed of piezoelectric rings, asymmetric transformer, ultrasonic generator, and so on. The structural dimension parameters were optimized by finite element analysis, and especially the groove size on the transformer was discussed in detail. Two kinds of experiments had been conducted to test the performance of the proposed device, including impedance analysis experiments and amplitudes measurement experiments. Furthermore, a mechanical model to explain the principle of the multiangle polishing was set up, which could assist to analyze the influence of different polishing angles in terms of machining. Finally, the machining experiments and multiangle polishing experiments were carried out to verify the effectiveness of the device. Compared with traditional mechanical polishing, the surface roughness is reduced from 235 nm to 140 nm. The results of multiangle polishing experiments indicate that the surface quality of biomaterials will be prominently affected by different polishing angles. In addition, the polishing mechanism will transform owing to the inversion of the normal velocity during the polishing process with the angle increasing. The surface morphology will also be affected. It has been proven that the experimental results agree with the model well.

Analysis and optimization of process parameter intervals for surface quality in polishing Ti-6Al-4V blisk blade

Abstract As the predominant factor influencing the service performance and life cycle of finished parts, surface quality is always improved by polishing technology in the machining process of aero-engine blade. The reasonable selection of polishing process parameter intervals have significant impact on surface quality, which is critically bound up with the performances of finished blade. In this paper, two different characteristic values of surface quality, including morphology feature (surface roughness) and stress property (residual stress), were analyzed respectively. To obtain the global optimal parameter intervals for surface quality improvement in Ti-6Al-4V blade polishing process, the comprehensive analysis methods were presented in this paper. In order to develop the prediction models of surface roughness and residual stress, regression analysis was conducted based on the results of Central-Composite designed polishing experiments. The significance and adequacy of the developed model was verified by using the analysis of variance (ANOVA). The sensitivity analysis was carried out to evaluate the influence of polishing process parameters on surface quality. Subsequently, stability interval and instability interval were divided according to sensitivity curves. Finally, the optimization method of process parameter intervals was proposed and the comprehensive optimal intervals were obtained. The experiments were carried out to verify the developed prediction models and the obtained global optimal parameter intervals. The results of polishing confirmation experiments indicated that the surface-quality-oriented optimal intervals of polishing process parameters were dependable.

CFD simulation and experimental studies of suspension flow field in ultrasonic polishing

With the rapid development of science and technology, hard and brittle materials with high performance have been widely used. Meanwhile, it necessitates the development of compatible machining techniques. As the final processing step of precision component, polishing plays a decisive role. Ultrasonic polishing is a powerful method for improving polishing efficiency and surface quality, especially for hard and brittle materials. In this paper, effects of ultrasonic vibration on suspension flow field have been specifically studied in ultrasonic polishing. At micro level, a mathematical model for analyzing the effects of ultrasonic vibration on the velocity and stress of the inner microelement in polishing suspension flow filed was established. CFD simulation was adopted to study the behavior of polishing suspension flow filed under the action of ultrasonic vibration. It was proved that periodic dynamic changes occur and turbulence form in suspension flow field which are positive for polishing, suspension flow field velocity in x direction near workpiece surface could reach a maximum of about 2.3 m/s, while that in z direction is 0.13 m/s. Material removal thus mainly depends on generated transverse shear flow. And a surface rough change rule was summarized. At macro level, monocrystalline silicon polishing experiments have verified the positive role of ultrasonic vibration, within the same polishing time and polishing head rotation velocity, the surface roughness without ultrasonic vibration reduced from 102 nm to 15 nm, while that with ultrasonic vibration reduced from 109 nm to a minimum of 4 nm, only with ultrasonic amplitude of 15 μm, surface roughness reduced from 98 nm to 27 nm, with the rotation of polishing head and ultrasonic amplitude of 9 μm, 15 μm and 21 μm respectively, the surface roughness reduced to 6 μm, 4 μm and 4 μm respectively. The changes of surface roughness in all experiments were consistent with the summarized rule.

Soft abrasive flow polishing based on the cavitation effect

The fluid medium used for soft abrasive flow (SAF) is of low viscosity and high flow velocity. The conventional SAF processing method is widely used due its ability to avoid damage and its adaptability of the workpiece surface. However, the current SAF method also suffers from limitations such as long polishing times and low processing efficiency. To address these issues, this paper proposes a method based on the cavitation effect to assist the soft abrasive flow polishing, termed CSAF. First, the working mechanism of CSAF is introduced through a schematic diagram. In addition, a CSAF fluid mechanic model is configured on the basis of the mixture multiphase model and cavitation model. Then, the distribution of key flow parameters, such as the velocity, dynamic pressure, and turbulent kinetic energy, is obtained and compared through computational fluid dynamic software. Numerical analysis results show that the flow field assisted by the cavitation effects shows better processing performance than SAF. Finally, particle imaging velocity (PIV) observation and experimental processing platforms are established, and extensive experiments are conducted. The processing comparison experiments showed that the abrasive flow assisted by the cavitation effect can lower the workpiece surface roughness to 3.46 nm with a satisfactory surface quality over a shorter time than the SAF method. The numerical analysis results are aligned with the PIV observation and the polishing experiment results. The SAF polishing method based on the cavitation effect significantly increases the polishing efficiency.

A precision polishing method for Wolter-I type optical mandrel

In the application of the 13.5-nm extreme ultraviolet (EUV) collector optics of the discharge produced plasma (DPP) source, the Wolter-I structure based on the X-ray grazing incidence optical design is usually adopted. The requirement of the surface roughness of this collector optics is demanding, which should reach to several nanometers. Currently, the mandrel replication is the main fabrication technology of this collector optics. Obviously, the requirement of the surface roughness of the mandrel used for the replication process should reach to the same level of the collector optics. However, the fabrication of the Wolter-I mandrel with high surface quality requirement still faces great challenge. In this paper, we propose a method that applies an elastic spherical tool to polish the surface of the Wolter-I mandrel, in which the shape of the elastic sphere can be changed relatively easily to accommodate the aspherical surface of the Wolter-I mandrel. A mathematical model regarding the movement trace of the polishing tool was established. Based on this model, the contact force between the polishing sphere and the aspherical surface can be controlled to point from the center of the polishing sphere in the normal direction to the polishing point. The influence of the polishing parameters on the material removal thicknesses is simulated and analyzed. The polishing experiments of ellipsoid and hyperboloid are carried out considering the difference of the diameter of each radial section on the Wolter-I mandrel surface. The proposed method is proved to reduce the surface roughness of the mandrel coated with chemically deposited nickel-phosphorous (NiP) alloy after diamond turning effectively. The root mean square (RMS) roughness of the mandrel surface after polishing can be reduced to 1.56 nm. It indicates that this method is suitable for further polishing of nickel-plated Wolter-I mandrel after ultra-precision turning. As a result, the manufacturing precision and efficiency of the Wolter-I mandrels can be improved by using the proposed polishing approach in this study, and the manufacturing cost can be reduced accordingly.

The integral sliding mode control of a pneumatic force servo for the polishing process

The automation of the polishing process is essential to improve the production efficiency and the quality of the part surfaces. The control strategy, which involves the position/force control, is a big bottleneck for the automated polishing process. This paper focuses on the precise control of the pneumatic force in polishing. Firstly, a position/force decoupled polishing system is described, which consists of a tool-path control subsystem and a polishing force control subsystem based on a pneumatic force servo. Then, the dynamic model of the pneumatic force servo is identified by evaluating the system output while the input is provided by the Pseudo Random Binary Sequence (PRBS) signals. Based on this dynamic input-output model, a new integral sliding mode controller (ISMC), which is composed by equivalent control and switching control, is especially designed for the non-minimum phase system identified. The force control experiments show that the proposed controller is effective in suppressing the external disturbance of spindle rotation and model uncertainties due to the nonlinear characteristics of the pneumatic system; and the control accuracy of the polishing force is improved compared to the traditional PID controller and RST controller. Finally, the polishing experiment of a spherical surface with uniform material removal has been conducted and the polishing results show that the surface roughness greatly improved from 135.8 nm to 14.7 nm. This new integral sliding model control method is effective and has great potential application in the further industrial polishing force control.

Approaches enhancing the process accuracy of fluid jet polishing for making ultra-precision optical components

Recent research has shown that the computer-controlled fluid jet polishing (FJP) process can generate nanometer-level form accuracy on free surface optical components. The key issues affecting the machining accuracy of the FJP process, including the deviation of the removal function, dynamic response of the moving tables and the change of material removal rates at a small-scale dwell time, have been investigated. Approaches using signal filtering and alignment methods to reduce the measurement errors of the removal functions in FJP are presented. An enhancing algorithm is proposed to improve the rotational symmetry of the removal function, with correction factors being included in the quality assessment to adjust the change in the quality of the removal function with different dwell times. The dynamic responses and moving accuracy of the worktable were measured, and their effects on the FJP polishing process were analyzed. Fluid jet polishing experiments using small-scale dwell time (less than 5 s) under intermittent motion and continuous motion modes were also performed. The experimental results show that the fluctuation of enhanced removal functions is less than that of the original functions. The residual information on the surface, related to the path distance, is barely noticeable when the distance is less than 0.4 mm, when a nozzle with a diameter of 1 mm diameter is used. The material removal experiments with small-scale dwell times indicate that the removal rate is stable when the worktable is in continuous motion.

Influence of partial charge on the material removal rate during chemical polishing

AbstractA partial charge‐based chemical polishing model has been developed, which can serve as metric for describing the relative polishing material removal rate for different combinations of slurries and workpieces. A series of controlled polishing experiments utilizing a variety of colloidal polishing slurries (SiO2, CeO2, ZrO2, MgO, Sb2O5) and optical materials [single crystals of Al2O3 (sapphire), SiC, Y3Al5O12 (YAG), CaF2, and LiB3O5 (LBO); a SiO2‐Al2O3‐P2O5‐Li2O glass ceramic (Zerodur); and glasses of SiO2:TiO2 (ULE), SiO2 (fused silica), and P2O5‐Al2O3‐K2O‐BaO (Phosphate)] was performed and its material removal rate was measured. As previously proposed by Cook (J Non‐Cryst Solids. 1990;120:152), for many polishing systems, the removal rate is governed by a series of chemical reactions which include the formation of a surface hydroxide, followed by condensation of that hydroxyl moiety with the polishing particle, and a subsequent hydrolysis reaction. The rate of condensation can often be the rate limiting step, thus it can determine the polishing material removal rate. By largely keeping the numerous other factors that influence material removal rate fixed (such as due to particle size distributions, interface interactions, pad topography, kinematics, and applied pressure), the material removal rate is shown to scale exponentially with the partial charge difference (δwp‐s) between the workpiece and polishing slurry particle for many of the slurry‐workpiece combinations indicating that condensation rate is the rate limiting step. The partial charge (δ) describes the equilibrium distribution of electron density between chemically bonded atoms and is related to the electronegativity of the atoms chemically bonded to one another. This partial charge model also explains the age‐old experimental finding of why cerium oxide is the most effective polishing slurry for chemical removal of many workpieces. Some of the slurry‐workpiece combinations that did not follow the partial charge dependence offer insight to other removal mechanisms or rate limiting reaction pathways.

Improvement in polishing effect of silicon wafer due to low-amplitude megasonic vibration assisting chemical-mechanical polishing

A low-amplitude megasonic vibrator with a frequency of 1.7 MHz has been designed in order to improve the polishing effect of silicon wafers in the process of megasonic-assisted chemical-mechanical polishing. This vibrator can generate the vibrations with the amplitude of several nanometers on the surface of silicon wafers. The polishing experiments with this vibrator assisting provide us with a direct evidence that such megasonic vibrations are helpful in improving the polishing effect. However, the experiments of megasonic vibration polishing indicate that these vibrations cannot drive abrasive particles to grind the corrosion layer or utilize cavitation to remove it. The theoretical analyses demonstrate that, in the process of megasonic-assisted chemical-mechanical polishing, the vibrations enable a part of idle particles, stored in the cells of the polishing pad, to squeeze into the contact areas. These additional active particles can increase the number of the effective particles that can be driven by the pad to grind the corrosion layer. The calculated results indicate that the number of megasonic-induced effective particles increases with frequency. Therefore, the megasonic vibration is a better choice to assist chemical-mechanical polishing, compared with the low-frequency ultrasonic vibration. The calculated results also reveal a notable fact that the megasonic-induced effective particles will be concentrated more and more in the centre area of silicon wafers with frequency increasing.

Synergistic integrated design of an electrochemical mechanical polishing end-effector for robotic polishing applications

Abstract In this paper, we present a novel design of a robotic electrochemical mechanical polishing (ECMP) process. Firstly, the process is presented to replace the conventional ECMP process by a robotic-based one. The advantage of using industrial robots lies in their flexibility, reconfigurability, large workspace and low prices compared to the conventional systems. Secondly, a novel design of a force-controlled end-effector for this purpose is presented. The end-effector is integrated into a macro-mini robot polishing cell. The macro robot (an industrial robotic manipulator) is used to position the mini robot (the proposed end-effector) according to the workpiece profile while the mini robot controls the polishing force. The effectiveness of the proposed device to polish un-milled and milled surfaces has been examined through polishing experiments. The results demonstrate the effectiveness of the presented device to reduce the surface roughness and improve the reflectability and appearance.

Experimental investigation of the magnetorheological polishing process with roller

PurposeThis paper aims to develop a new magnetorheological polishing (MRP) device with roller and investigate the polishing mechanism of MRP fluids using this new device.Design/methodology/approachThe principle of MRP process with roller is discussed, and then the structure of the polishing device is designed in detail. The polishing experiments of K9 glass are carried out using MRP device with roller.FindingsA series of tests are performed to evaluate the effect of the excitation gaps, working gap and polishing time on the polishing characteristics, and the optimized polishing parameters can be obtained. The surface roughness Ra of the sample is reduced from 359 to 38 nm under optimized polishing parameters.Originality/valueMRP method with roller is proposed in this paper, and the MRP device with roller can reduce the surface roughness Ra significantly. After being polished, the circular ring-shaped polishing belt disappears on the workpiece surface, which means it has great potential for polishing.

A novel magnetically driven polishing technique for internal surface finishing

This paper presents a novel magnetically driven polishing tool for internal surface finishing. Differing from the existing magnetic abrasive finishing or magnetic field assisted finishing (MAF) methods; this new technique performs material removal inside a tube using a spherical magnet with abrasives driven by external bar magnets. This configuration of magnets not only simplifies the design but also allows more flexibility in the potential application to internal finishing of manifolds. The physical principle was introduced and polishing experiments were conducted to investigate the effect of magnetic abrasive particles and abrasive size based on the two major criteria of surface roughness and material removal. The results unequivocally substantiated the capability of the developed method with a more than 98% improvement in surface roughness for ring polishing and an 86% improvement for section polishing. An analytical model was devised to illustrate the material removal mechanism of the proposed internal polishing technique based on the experimental results. The technique developed in the paper shows signs of future success in finishing internal surface of complex components in a wide range of industrial applications.

Flexible CNC polishing process and surface integrity of blades

The surface integrity of aero-engine blades directly affects its mechanical behavior. To improve the surface integrity and address the problem, that is, the blade is mainly polished manually, a flexible polishing process was proposed and surface integrity was investigated. First, flexible polishing technology and the machine tool that the authors researched and developed were introduced. Second, a polishing experiment was conducted on a TC4 titanium alloy blade. Finally, the surface integrity before and after polishing was measured and the results were compared and analyzed. Results showed that the knife marks, pits, unevenness, and other defects of the blade surface were effectively removed through flexible polishing; the surface residual compressive stress was reduced from 483 MPa to 397 MPa; the surface roughness was reduced to Ra 0.4 μm; the surface micro-hardness increased by 18 HV; and the surface metamorphic layer caused by milling was removed. Flexible polishing effectively improved the surface quality without affecting the depth layer quality of the workpiece.

Analysis of material removal rate and stability in lap-magnetorheological finishing

A magnetorheological finishing (MRF) method, which is named lap-MRF, is proposed in this paper. A lap, instead of a large polishing wheel, is used to expand the polishing area, which significantly improves the material removal rate. Lap-MRF uses the flexible magnetorheological fluid (MR fluid) as a polishing pad to match the surface well. Moreover, the MR fluid in the polishing zone can be renewed continuously to ensure the stability of the material removal rate. The principle of Lap-MRF and the theoretical model of the material removal rate are presented. The effects of the spindle speed and the working gap distance on the polishing normal pressure and the material removal rate are analyzed. Finally, a series of polishing experiments and simulations are carried out. The volume removal rate for K9 is up to 0.76 mm3 / min and the comprehensive material removal stability is 6.7%. Using MATLAB simulation process method, the convergence efficiency for a ϕ1000 mm mirror is 98.5%. The results verify the validity of the proposed method.