Ultrasonic vibration-assisted grinding of silicon carbide ceramics based on actual amplitude measurement: Grinding force and surface quality

The actual vibration amplitude (AVA) during ultrasonic vibration-assisted face grinding (UVAFG) is an essential parameter that affects grinding force and surface quality. However, an effective method for the real-time measurement of AVA during grinding remains unavailable, hindering research on UVAFG. In this study, an experimental setup for measuring AVA is firstly established using an eddy current sensor. Ultrasonic amplitude curves under the condition of tool rotation without load are measured and analysed. Then, amplitude attenuation with different grinding forces is evaluated during the UVAFG of silicon carbide (SiC) ceramics. The influences of AVA on grinding force and surface quality are investigated through comparative experiments of the UVAFG and conventional grinding (CG) of SiC ceramics. Finally, experimental results indicate that AVA exhibits a negative correlation with grinding force. Compared with CG, UAVFG has lower grinding force when grinding SiC ceramics. AVA is the key factor that affects surface roughness during UVAFG, the AVA of UVAFG is less than 4.3 μm; thus, surface roughness during UAVFG will be less than that during CG. Moreover, vibration can reduce the scratches made by the tools on the grinding surface.     

Development of a probabilistic algorithm of surface residual materials on Si3N4 ceramics under longitudinal torsional ultrasonic grinding

Longitudinal torsional ultrasonic-assisted grinding (LTUG) is one of the main methods to achieve high-quality and high-efficiency machining of high-performance ceramic materials. However, it isn't easy to accurately characterize the three-dimensional (3-D) surface topography due to multiple random factors during LTUG. Aiming at the complex surface features caused by multiple random factors in the LTUG of Si3N4 ceramics, a probabilistic algorithm for the height of residual material on the surface (HRMS) in LTUG of Si3N4 ceramic was proposed, and the prediction model for the 3-D surface topography and 3-D surface roughness parameters of Si3N4 ceramics in LTUG was established by using this algorithm. Simulation and experimental results show that the prediction model of 3-D surface topography and 3-D surface roughness established by the HRMS algorithm can more realistically predict the general characteristics of 3-D surface topography in LTUG under different process parameters, and the error range of the 3-D surface roughness parameter is 0–14.07%, which realizes the high-precision and high-reliability prediction of the 3-D surface topography and 3-D surface roughness parameters of the Si3N4 ceramic under LTUG.     

Ultra-precision grinding of AlON ceramics: Surface finish and mechanisms

Aluminum oxynitride (AlON) can be effectively finished by ultra-precision grinding. In this work, the ultra-precision grinding experiment was conducted on AlON to investigate surface characteristics and material removal mechanism. The ground surface has an unusual non-uniform morphology resulted from the different material removal modes. Grazing incidence X-ray diffraction (GIXRD), nanoindentation and Electron Back-Scattered Diffraction (EBSD) were carried out to study the micro-properties of AlON. The results revealed that the micro mechanical properties vary with the grain orientation on the surface. The morphologies of ground surface are consistent in the twinned grains and change with the grain orientation. By comparing the relationship of machining size and grain size, the material removal modes of individual grains should be taken into consideration during ultra-precision grinding. Based on this, a simple theoretical model was proposed to explain the material removal mechanism of AlON under ultra-precision grinding.     

Ultra-precision finishing of low expansion ceramics by compliant abrasive technologies: A comparative study

Advanced ceramics have many attractive features such as high stability and wear resistance that find broad applications in various fields, e.g. optics, aerospace, etc. However, the accompanying difficult-to-machine property with complex geometry brings great challenges to the commonly used laser machining and rigid wheel based grinding in industry. To achieve optical surface quality with surface roughness below 10?nm Ra, three promising ultra-precision compliant machining technologies using adaptive elastic tools are presented in this paper, including bonnet polishing, compliant pitch polishing and shape adaptive grinding with fine grain size. A comparative study was conducted by machining three different low thermal expansion ceramics while continuously increasing attack angle, spindle speed and tool offset across rectangular regions. Material removal rate (MRR) and surface roughness (Ra) with respect to different process conditions are compared. With sufficient data, the processing ability using above three compliant machining technologies is summarized based on the MRR-Ra plots for different ceramics. In addition, microscopic observation and X-ray diffraction analysis are conducted to characterize differences in material behavior.     

Investigation on high-shear and low-pressure grinding characteristics for zirconia ceramics using newly developed flexible abrasive tool

Zirconia ceramics is widely employed in medical, chemical and aerospace domain due to its excellent combination of physical and chemical attributes. However, high hardness and brittleness property have limited its application in manufacturing industries. Therefore, the present work aimed at development of a flexible abrasive tool based on concept of liquid body armor with large ratio of tangential grinding force to normal grinding force in order to enhance the surface processing quality of zirconia ceramics. A flexible body-armor-like abrasive tool was developed. Fundamental dynamic simulation and micro material removal processing at high-shear and low-pressure grinding conditions was analyzed. A multi-group of grinding experiments were carried out on an industrial robot platform for zirconia ceramic workpieces to validate the grinding performance of flexible body-armor-like abrasive tool. The surface roughness, surface morphology, grinding force and grinding temperature were investigated. At the optimal grinding condition, the surface roughness (Ra) of the workpiece was reduced by 91.8% and decreased from 110 nm to 9 nm. The scratches from the surface of the workpiece vanished and uniform grinding textures were left. The experimental results revealed that the developed flexible body-armor-like abrasive tool could achieve ultra-precision grinding of zirconia ceramics.     

Material removal mechanism and grinding force modelling of ultrasonic vibration assisted grinding for SiC ceramics

In this paper, a varied-depth nano-scratch test of single grain is carried out on a nano indentation system. The critical depth of the elastic-plastic transition for SiC ceramics is 7.27 nm, as calculated by Hertz contact theory, and the critical depth of the brittle-to-ductile transition is 76.304 nm, as measured by AFM and SEM. Based on the varied-depth nano scratch test and the grain trajectory of ultrasonic vibration assisted grinding (UVAG), a theoretical model of the normal grinding force is acquired using the material removal in unit time as a bridge. The single factor experiment illustrates that the grinding force increases with the increase of the grinding depth, feed rate, and amplitude, while it decreases with the increase of the spindle speed. The contrast experiment results show that UVAG is beneficial for improving the surface quality and reducing the subsurface damage depth compared with common grinding (CG). A four-level and four-factor orthogonal experiment is designed, on the basis of which theoretical model of the normal grinding force for SiC ceramics is obtained using genetic algorithm. The tangential grinding force is obtained from the normal grinding force using the least square method. The experimental results show that the theoretical model is reliable.     

New observations of the fiber orientations effect on machinability in grinding of C/SiC ceramic matrix composite

In this paper, the effect of machining parameters on cutting force, force ratio, 3D surface roughness was studied, and the surface formation mechanism was deeply analyzed in view of the position relation between machining directions and fiber orientations. New observations of the fiber orientation effect on machinability are attempted to obtain in grinding of 2D C/SiC ceramic matrix composite with electroplated diamond grinding tool. Two machining directions (A and B) on one surface are taken into account to study the effect of fiber orientation on the grinding process. The results indicate that the cutting forces obtained in machining direction of A are greater than that in machining direction of B under all experimental conditions. However, the tangential force is greater than the normal force, which is different from grinding ordinary material. Whether in the machining direction of A or direction of B in grinding C/SiC composite, on the whole the surface roughness values (Sa and Sq) decrease as the feed rate increases. As depth of cut increasing, the surface roughness values in the machining direction of A and B come out inconsistency. At different feed rates, the surface roughness values in the machining direction of A and B also represent inconsistency with the change of cutting speed. The theoretical model of undeformed cutting thickness is unfit for evaluating its effect on the surface roughness. After analyzing of the surface formation, except for some fibers forming extruding fault and fracture, being pulled out, and fracture or broken, a new phenomenon that some fibers forming extruding fault and fracture is observed.     

SiC陶瓷表面增韧用环氧树脂基增韧剂的制备与性能研究

碳化硅陶瓷在磨削加工中极易产生崩碎损伤,在碳化硅陶瓷磨削层实时涂覆增韧剂是降低崩碎损伤的新方法。以E51双酚A型环氧树脂、无水乙醇、651型低相对分子质量聚酰胺树脂和1,8-二氮杂二环十一碳-7-烯(DBU)为主要成分制备了一种增韧剂,通过测量增韧剂在碳化硅陶瓷表层的接触角、浸润深度与固化时间,探究了增韧剂各组分的添加量与碳化硅陶瓷表面粗糙度对增韧剂润湿性能与固化速率的影响规律,优化出一种润湿性能好、固化速率快的增韧剂。结果表明:增韧剂的最佳质量配比为m(E51双酚A型环氧树脂)∶m(无水乙醇)∶m(651型低相对分子质量聚酰胺树脂)∶m(DBU)=1∶0.9∶0.5∶0.02,该增韧剂在碳化硅陶瓷表层的浸润时间约为160 s,浸润深度约为40 μm,可使碳化硅陶瓷的表层硬度降低约25%;增韧剂的润湿性能随着溶剂的增加或碳化硅表面粗糙度的增大而提高,促进剂添加量的改变对增韧剂的润湿性能几乎无影响;增韧剂的固化速率随溶剂的增加而降低,随促进剂的增加而提高,但当促进剂达到饱和时,固化速率不再提高。     

Grinding performance improvement of laser micro-structured silicon nitride ceramics by laser macro-structured diamond wheels

Silicon nitride ceramics are widely used in various industrial fields because of their excellent characteristics: high hardness, high elastic modulus, abrasion resistance, and high heat resistance. Diamond wheel grinding is the predominant and most productive method to machine silicon nitride ceramics. However, a lot of heat is generated due to high friction between a diamond grinding wheel and extremely rigid silicon nitride during grinding. This causes surface/subsurface damage, wheel wear, etc., which impairs the surface quality of silicon nitride. This impairment can restrict the use of silicon nitride ceramic components. To improve the surface quality and service life of grinding wheels, a laser macro-micro combination structured grinding (LMMCSG) method was presented. The results indicated that the grinding force ratio and surface roughness when using LMMCSG were respectively 31% and 40% lower than the grinding force ratio and surface roughness when using conventional grinding. Moreover, the LMMCSG method effectively reduced the wheel wear and workpiece subsurface damage.     

Grinding characteristics and removal mechanisms of unidirectional carbon fibre reinforced silicon carbide ceramic matrix composites

The grinding performance of unidirectional carbon fibre reinforced silicon carbide ceramic matrix composites (C_f/SiC) was investigated in this paper. The effects of the fibre orientation and grinding depth on the surface integrity and grinding forces and an understanding of the grinding mechanisms are the primary concerns of this article. This problem is relatively unexplored; therefore, the main value of this research is to improve the processing quality and reduce the production cost. In the C_f/SiC grinding procedure, cracks, fibre wear, interfacial debonding, fibre pull-out and outcrop can be detected on the ground surface. The grinding depth and deflection angle have been shown to have a notable influence on the surface quality in different datum planes. A suitable grinding depth and deflection angle should be carefully chosen to achieve good surface quality in different machined surfaces. Specifically, the surface quality decreases and the grinding forces increase with increasing grinding depth. In addition, greater grinding surface quality is observed at β?=?90°, i.e., γ?=?0°, but poorer machined surfaces are obtained at α?=?0°, i.e., γ?=?90°. The surface topography, roughness and grinding forces of unidirectional C_f/SiC could be forecasted according to the analysis conclusions. This research is expected to offer guidelines for increasing the machining quality of C_f/SiC.     

Smoothed particle hydrodynamics simulation and experimental analysis of SiC ceramic grinding mechanism

Crack induced surface/subsurface damage in SiC ceramic grinding limits the industrial application. A single-grain scratching simulation based on the smoothed particle hydrodynamics (SPH) has been used to analyze the SiC grinding mechanism, including the material removal process, scratching speed effect on crack propagation, ground surface roughness, and scratching force. The simulation results showed that the material removal process went through the pure ductile mode, brittle assisted ductile mode, and brittle mode with the increase of the depth of cut. The critical depth of cut for ductile-brittle transition was about 0.35?µm based on the change of ground surface crack condition, surface roughness, and maximum scratching force. Increasing the scratching speed promoted the transformation of deep and narrow longitudinal crack in the subsurface into the shallow and wide transverse crack on the surface, which improved the surface quality. The SPH simulation results were indirectly validated by the cylindrical grinding experiments in terms of the critical single grain depth of cut for ductile-brittle transition, and the trend of ground surface roughness and grinding forces.     

残余碳对碳化硅陶瓷光学表面加工性能的影响

为深入了解碳化硅陶瓷的光学表面加工性能,采用常压固相烧结法制备了碳化硅陶瓷,在保证致密度的前提下,通过改变碳的含量,研究了残余碳对SiC陶瓷抛光面的表面质量和光学性能的影响。研究发现,C的质量含量为3%～7%时,SiC陶瓷抛光表面的RMS(root mean square)粗糙度均约为2nm。当C含量为3%～6%时,SiC陶瓷抛光表面在400～750nm波段的全反射率、漫反射率和镜面反射率无明显变化;当C含量升至7%时,全反射率稍有降低,漫反射率稍有上升,镜面反射率稍有降低。其原因可能是过多的残余碳引起SiC陶瓷的折射率下降和产生光学散射,最终造成镜面反射率降低。     

Mechanistic difference between Si-face and C-face polishing of 4H–SiC substrates in aqueous and non-aqueous slurries

The traditional aqueous-based polishing slurries have been extensively used in the ultra-precision machining process of SiC substrates, but their processing efficiency remains a major challenge in making SiC wafers with high surface quality. SiC polishing slurries based on non-aqueous solvents have been explored and reported, however, the mechanism for the accelerated SiC material removal rate (MRR) remains unknown. In this work, the Si-face and C-face of the SiC wafer were polished with water and methanol as polishing liquid carriers, respectively. The MRR of Si-face using the methanol-based slurry, can reach 260.9 nm/h, and the polished Si-face surface roughness Ra reduces to 0.150 nm. In contrast, the MRR of Si-face by using the aqueous-based slurry, is 66.8 nm/h, the polished Si-face surface roughness Ra is 0.691 nm. However, the results of MRR and Ra for C-face are opposite. The reaction between the polishing liquid carriers and the atomic structures of Si-face and C-face lead to differences of the MRRs by analyzing contact angle, XPS, and molecular dynamics (MD) simulation results. The newly revealed polishing mechanisms shined light for speeding up the development of SiC polishing slurries based on the specific aspects of the polishing surface of SiC.     

Enhancing ductile removal of Cf/SiC composites during abrasive belt grinding using low-hardness rubber contact wheels

C_f/SiC composites are used as advanced thermal protection and friction materials. However, machining these materials is difficult because of their hard, brittle, anisotropic, and heterogeneous characteristics. This study investigated the removal behavior and surface integrity of C_f/SiC composites during abrasive belt grinding using rubber contact wheels of various hardness. Additionally, detailed analysis was performed on their thermal-mechanical coupling characteristics, surface integrity (that is, surface roughness, surface micro morphology, and subsurface damages), and the grinding chips produced. Results revealed that with decreasing hardness of the contact wheel, the surface roughness in all directions, grinding force, and temperature decreased significantly. Moreover, the surface removal morphology of the C_f/SiC composites changed from macro-fracture to micro-fracture, and the subsurface morphology changed from SiC matrix cracking and carbon fibers pull-out to matrix plastic flow and fiber micro-fracture, respectively. Furthermore, strip chips with plastically squeezed and cut surfaces were visible in the grinding chips obtained under the 40-HA contact wheel. Therefore, the ductile removal behavior of the C_f/SiC composites was enhanced, and the surface quality in abrasive belt grinding with low-hardness contact wheels was markedly improved.     

Experimental investigations on grinding characteristics and removal mechanisms of 2D–Cf/C-SiC composites based on reinforced fiber orientations

The effects of fiber orientations on the grinding force and ground surface roughness in grinding 2D–C_f/C–SiC composites were investigated in this work. The characteristics of surface microstructure and the mechanism of the grinding phenomena are also discussed. The results show that the prominent removal mechanism for grinding the 2D-C_f/C-SiC composites is the brittle fracture, and the destruction of the composites is mainly via breaking of interfacial bonds, fiber fracture, and matrix cracking. The grinding force of different grinding surfaces follows the order: Surface B > Surface A > Surface C, and the surface roughness follows: Surface C > Surface A > Surface B. Grinding parameters, such as feeding speed, depth of cut, and wheel speed, have a great influence on the grinding force and surface roughness. This result suggests that this body of work offers a useful guideline for improving the design and processing of 2D–C_f/C–SiC composites.     

工业陶瓷超声辅助加工技术研究

陶瓷材料具有耐高温、硬度高、绝缘性好的优良性能,在航空航天、军事医疗、电子信息等领域具有广泛的应用。旋转超声辅助加工的刀具磨损小、材料去除率高、加工精度高,在工业陶瓷精密加工领域取得了较好的运用。本文以常用的石英陶瓷和氮化硅陶瓷为加工对象,进行了表面磨削及钻孔试验研究,通过宏观形貌观察、测量表面粗糙度值、工件及刀具微观形貌分析,确定了PCD砂轮结合超声辅助磨削加工,可以得到较好的表面加工质量。开展了石英陶瓷凹槽面、平面及过渡面的磨削加工试验,取得了较好的表面形貌;利用不同类型的砂轮加工氮化硅陶瓷孔,从而确定高强度的金刚石磨头是加工硬性材料的最优砂轮。     

Si/SiC coated Cf/SiC composites via tape casting and reaction bonding: The effect of carbon content

In this paper, a novel surface modification method for C_f/SiC composites is proposed. Si/SiC coating on C_f/SiC composites is prepared by tape casting and reaction bonding method. The effects of carbon content on the rheological property of the slurries along with the microstructure of the sintered coatings are investigated. The best result has been obtained by infiltrating liquid silicon into a porous green tape with a carbon density of 0.84 g/cm³. In addition, the effect of sintering parameters on the phase composition of the coatings is studied. Dense Si/SiC coating with high density as well as strong bonding onto the substrate is obtained. This Si/SiC coating exhibits an excellent mechanical property with HV hardness of 16.29±0.53 GPa and fracture toughness of 3.01±0.32 MPa m^1/2. Fine surface with roughness (RMS) as low as 2.164 nm is achieved after precision grinding and polishing. This study inspires a novel and effective surface modification method for C_f/SiC composites.     

Investigation of the material removal process in in-situ laser-assisted diamond cutting of reaction-bonded silicon carbide

Reaction-bonded silicon carbide (RB-SiC) is an important optical material used widely in the aerospace industry. The machining accuracy of RB-SiC optical elements must satisfy the requirements of high-performance system development. However, RB-SiC is typically hard and brittle, making precise machining difficult. Thus, the material removal and synergistic deformation mechanisms of SiC and silicon (Si) must be investigated for ultraprecision machining. In-situ laser-assisted diamond cutting is an effective method for the ultraprecision cutting of hard and brittle materials. In this research, we investigated the influence of temperature on the material deformation process in detail. Firstly, the physical properties of RB-SiC, including its hardness and depth of plastic deformation, were investigated through high-temperature nano-indentation experiments. Furthermore, grooving experiments were carried out to investigate the brittle-to-ductile transition under ordinary and in-situ laser-assisted diamond cutting, respectively. Finally, the deformation of the machined surface/subsurface was revealed via scanning electron microscopy and transmission electron microscopy observations.     

Preparation of a polyimide composite filled with corundum as a kind of precision grinding slice

By using a two‐step synthetic method, a novel grinding material, SiC and polyimide grinding slice, is prepared. This grinding slice can be used for mechanical planarization of hard and brittle materials, such as silicon, optical glass, advanced ceramics, specials metal, jewelry, disks etc. For observing the physical and chemical properties of the slice, scanning electron microscopy, FTIR spectroscopy, thermal gravimetric analysis, tensile strength, and elongation at break are used. All the experimental data indicate that the SiC/PI slice will be a very useful grinding material for obtaining a precision surface. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Theoretical model of warping deformation during self-rotating grinding of YAG wafers

YAG wafers are the most host laser crystals used for high-power lasers, which are usually machined by grinding to meet the required accuracy for laser components. Warping deformation induced by the residual stress is one of the main damages for YAG wafers after the grinding process, which will seriously decrease the service accuracy and life of the lasers. Developing theoretical model of warping deformation is of great significance to achieving the ultra-precision machining of YAG wafers. The cutting depth of single abrasive and grinding force in self-rotating grinding were investigated by considering the kinematic trajectory of abrasives, brittle-to-ductile transition, elastic mechanics, elastic deformation of the grinding wheel and strain rate effect. A theoretical model of warping deformation in self-rotating grinding of YAG wafers was developed based on the cutting depth and grinding force. The influence of subsurface damage and residual stress on warping deformation was analyzed based on the theoretical model and finite element simulation. Self-rotating grinding tests of YAG wafers were performed, and the results showed that the warping deformation decreased as the wheel rotational speed increased, and increased as the abrasive size, workpiece rotational speed and feed speed increased. The experimental results agreed well with the simulated results of the theoretical model, indicating that the theoretical model can accurately predict the warping deformation induced by self-rotating grinding process. This work will not only enhance the understanding of the essence of the wafer warping induced by ultra-precision machining, but also provide a guide for optimizing the processing parameters in self-rotating grinding of YAG wafers.