Abstract: Brittle solids with dominant covalent-ionic bonding, including single crystals, polycrystals, and optical glass, are core materials for modern microelectronic and optoelectronic devices that are widely used in energy, communication, transportation, and medicine sectors. In high performance device applications, those brittle materials must be machined into parts that often have an extremely smooth surface and a damage-free subsurface with sub-micron precision. Optimisation of an abrasive machining process for the brittle solids can significantly enhance production efficiency and reduce manufacturing cost, as well as prolong device life. The development of high efficiency and low damage ultraprecision shaping technologies for this class of solids requires an in-depth understanding of their deformation and removal mechanisms at nanoscale. In this work, the fundamental mechanisms of deformation and removal of brittle materials involved in individual or cumulative contacts with blunt and sharp grits are analysed, using the scratch-related micromechanics as the theoretical basis. Essentials of brittle-to-ductile transitions in abrasive machining are outlined. Influence of the diversity in material microstructures in determining local deformation and subsequent removal is highlighted. Practical requirements are suggested for further advancing ultraprecision abrasive machining of those brittle solids.
Abstract: Aimming at the problems such as low material removal rate and abrasive agglomeration when polishing single crystal silicon carbide wafers with traditional methods, this study proposed a ultrasonic vibration assisted lapping method. It studied the influence of different process parameters including speeds, abrasive concentrations, pressures and abrasive grain sizes on the lapping efficiency and lapping quality of single crystal silicon carbide wafers. The experimental results and theoretical analysis show that ultrasonic vibration effectively improves the material removal rate of single crystal silicon carbide wafer polishing. When the lapping disc speed is 50 r/min, the lapping fluid concentration is 2.5%, the pressure is 0.015 MPa and the abrasive grain size is 0.5 μm, the effect of improving the material removal rate is the most obvious, thus increased by 23.4%, 33.8%, 72.3% and 184.2% respectively. At the same time, by tracking and testing the surface roughness during the lapping process, the best time for ultrasonic vibration-assisted grinding of abrasives with different particle sizes was determined.
Abstract: To meet the increasing requirements on material removal efficiency, surface quality, and subsurface damage in the ultra-precision grinding process, a textured-fixed abrasive plate (T-FAP) with random grid structure based on the Voronoi Diagram is proposed. The abrasive tool is fabricated by using UV-curable resin and micro-level alumina abrasive grains. The influence of time-varying texture characteristics of surface wear on the machining performance is studied via MATLAB image analysis and numerical simulation of the grinding trajectory. The lap-grinding experiment of the aluminum workpieces is carried out to analyze the material removal efficiency and workpiece surface roughness obtained from the T-FAP grinding process. The results show that the surface roughness of the workpiece processed with the T-FAP grinding is 0.84 μm, and that the material removal rate is 3.21 μm/min. Compared with the traditional fixed abrasive grinding tool, the T-FAP grinding ensures the material removal efficiency and obtains high surface accuracy as well.
Abstract: Micro-diamond film, nano-diamond film and diamond-graphite composite film were deposited on silicon carbide substrate by hot filament chemical vapor deposition. The surface morphology and phase of the grown diamond films were analyzed using scanning electron microscope, atomic force microscope and Raman spectrometer. The friction coefficient and the wear rate of diamond films were measured by friction experiments. The friction and wear properties of diamond films were studied by comparing the experimental results. The results show that the diamond-graphite composite film has better friction and wear properties, the surface roughness of which is 53.8 nm. The friction coefficient (0.040) is similar to that of the nano-diamond film (0.037), while the wear rate is the lowest, 2.07×10−7 mm3·N−1·m−1. Compared with those of SiC substrate, the wear rate (9.89×10−5 mm3·N−1·m−1) and the friction coefficient (0.580) of the diamond films have been greatly improved, which indicates that depositing diamond on the surface of SiC substrate significantly improves the performance of the silicon carbide in the field of friction.
Abstract: The grinding performance of micro-textured grinding wheel with arrayed micro-hole and common grinding wheel are compared through experiments on alumina, aluminum nitride, zirconia and silicon nitride ceramic materials. The grinding force, the specific grinding energy, the surface roughness and the surface chipping are analyzed. In comparison with common grinding wheel, micro-textured grinding wheel improves the grinding force and the specific grinding energy in grinding of alumina, aluminum nitride and zirconia ceramics, reduces the surface roughness of these ceramics, but has a little effect on the grinding force and the surface roughness of silicon nitride ceramics. Silicon nitride has higher grinding force and specific grinding energy than other ceramic materials do. The surface characteristics of alumina and aluminum nitride mainly imply brittle removal mode, while a ductile removal mode is characterized on the surface of zirconia and silicon nitride has both plastic and brittle removal characteristics. The surface chipping thickness processed by the micro-textured grinding wheel is larger than that of the common grinding wheel, while the surface chipping thickness of both alumina and aluminum nitride ceramics is larger than those of zirconia and silicon nitride ceramics.
Abstract: In order to explore the influence of the grinding process parameters on the surface roughness and surface layer residual stress of 18CrNiMo7–6 steel, the cylindrical longitudinal grinding experiment was carried out by using an end cylindrical grinder. With using the workpiece speed nw, grinding depth ap and longitudinal feed speed vf, the single-factor experimental research is carried out. The research results show that with the increase of nw, the surface roughness Ra of the workpiece decreases first and then increases. When nw is 120 r/min, the surface roughness Ra reaches the minimum value, and the surface residual compressive stress value is the largest at this condition, and when nw is greater than 120 r/min, the surface residual stress exists fluctuation. With the increase of ap, the surface roughness Ra of the workpiece decreases first and then increases, and the tensile stress influence on the surface layer of the workpiece increases with the increase of the grinding depth. The surface roughness Ra first decreases and then increases with the increase of vf. When vf is 210 mm/min, the surface roughness value Ra is the smallest. With the increase of vf, the residual compressive stress of the surface layer gradually decreases and gradually changes to increasing residual tensile stress.
Abstract: Diamond abrasive tools play an important role in high-efficient and precision machining of hard and brittle materials such as engineering ceramics, glass and semiconductors. Due to the great challenge presented by the increase of part manufacturing quality, forming requirements and processing efficiency, the improvement of tool’s structure has become the key way for abrasive tools to overcome this challenge, but it has brought difficulties to tool manufacturing. In recent years, additive manufacturing technology has attracted much attention because of its excellent ability to form complex structures. The use of additive manufacturing technology for fabricating diamond abrasive tools has been considered as a potential means to solve the problem, therefore, it has become a research hotspot. Based on the existing relevant research reports, the work of this paper mainly focuses on stereo lithography apparatus technology (SLA), selective laser sintering technology (SLS) and laser selective melting technology (SLM), summarizes the research progress of existing additive manufacturing technology in the fabrication of diamond abrasive tools, analyzes the different characteristics of each method in its manufacturing process, and puts forward prospects and suggestions for making diamond abrasive tools by using this type of technology.
Abstract: Nano-NbC and nano-WC were added to the WC-bronze based matrix to improve the performance of the matrix of the impregnated diamond bit. The uniform design method, regression analysis and solver were used to obtain the optimal addition. Laboratory drilling experiments of the strengthened bits were carried out. The results show that after adding nanoparticles, the hardness and the bending strength of the matrix are improved by up to 25.23% and 5.73%. The wear resistance of the diamond composites is significantly increased, with wear ratio increased by up to 57.4%, indicating that the diamond and the matrix are more closely bonded. In conclusion, adding nanoparticles has positive significance on the performance of diamond composites. The mechanical drilling speed of the strengthened bits is 19.63% higher than that of the blank diamond bit, and that the matrix wear is reduced by 32.84%, indicating that the addition of nanoparticles to the matrix can strengthen the drill bit and improve drilling efficiency.
Abstract: In order to solve the problems of low grinding efficiency, easy to burn rail and large dust pollution, when grinding rail with traditional resin wheel, the feasibility of taking advantage of brazed diamond technique for preparing a new rail grinding wheel was studied. The brazed diamond grinding wheel with slotted structure was prepared by using of the diamond orderly arrangement process. The comparative grinding tests were carried out on U71Mn rail steel. The results show that compares with resin corundum grinding wheel, the new brazed diamond grinding wheel can improve the grinding efficiency by about 50%, effectively reduce the grinding temperature and avoid rail burn. The new grinding wheel has remarkable chip removal effect in the process of rail grinding, and there is almost no chip adhesion. However, the slots on the grinding wheel increases the grinding vibration, aggravates the breakage of diamond abrasive particles and increases the surface roughness of rail. The grinding debris of the new grinding wheel is mostly band-shape with large size but no molten balls.
Abstract: To optimize the parameters of slicing ferrite with high precision diamond ring saw, an orthogonal test is designed with the fabricating surface accuracy and the surface roughness as evaluation indicators and the spindle speed, the feed speed and the tension force as factors. Based on the grey theory, the data analysis and the comprehensive evaluation of the multiple process targets are carried out to obtain an optimized process parameter combination, namely the spindle speed 1 000 r/min, the feed speed 1.0 mm/min and the tension force 90 N. The slicing test results show that the optimized parameter combination can obtain a surface accuracy of PV 7.37 μm and a surface roughness Ra of 0.882 μm, and the slicing surface quality is improved, which verifies the effectiveness and practicability of this method in the optimization of ferrite slicing process parameters.
Abstract: Side milling experiments with small diameter grinding rods were carried out on TiC particle-reinforced steel-matrix composite to investigate the reasonable machining parameters and the cooling and lubrication conditions for this material, and to understand the influence of machining parameters on cutting forces, surface quality and tool wear. The results show that dry cutting and water-based synthetic grinding fluids lubrication are not as effective as extreme pressure grinding oil lubrication, especially that dry cutting causes tool burn. With extreme pressure grinding oil lubrication, the tool wear is stable after 12 minutes of continuous grinding, the main wear forms of which are fracture of abrasive grain wear, abrasive grain breakage and abrasive grain shedding. It is also found that the influence of spindle speed on cutting force is greater than that of feed speed, namely higher spindle speed leading to smaller cutting force, and that the machined surface roughness is mainly related to the level of tool abrasive grain but less affected by spindle speed and feed speed. In conclusion, when grinding TiC particle-reinforced steel-matrix composites, the conditions of extreme pressure grinding oil lubrication, high spindle speed and medium feed rate are recommended to obtain good tool life, surface quality and appropriate processing efficiency.
Abstract: Brazed diamond abrasive drill was suitable for drilling holes in carbon fiber reinforced silicon carbide ceramic matrix composites, but a large amount of chips could adversely affect the drilling process of the holes. Therefore, according to the chip discharge process, the chip morphology was analyzed, and the effects of chips on the axial drilling force, the hole processing quality and the drill wear during drilling were studied. The results show that the chips have an effects on the axial drilling forces, especially when drilling deep holes. The chips have little effects on the machining quality of the hole inlet, only a slight edge collapses at the hole inlet. The chips have a significant impacts on the processing quality of the hole outlet, which can cause serious fiber breakage, tear defects, and large areas of the matrix shedding. At the same time, the chip intensifies the drill wear, which not only causes slight wear such as edge collapse and micro crack, but also produces serious wear behaviors such as matrix peeling and diamond peeling.
Abstract: The grinding power monitoring experimental platform was built with PPC−3 power sensor and NI 9203 acquisition card. An intelligent grinding process decision-making system driven by monitored power data was developed based on LabVIEW software to promote green, efficient and intelligent grinding. In order to overcome the problems of huge amount of bottom process monitoring data (i.e. grinding dynamic power signals collected online) of the decision-making system, mixture with noise and unclear typical characteristics, a method of feature extraction of grinding power signals and establishment of relational database is proposed. The type Ⅱ Chebyshev low-pass filter was used to filter and improve the signal-to-noise ratio of grinding power signals. The peak and the valley characteristic points of power signals were extracted and marked in time domain based on the peak and the valley searching method, and the head and the tail correction and interpolation correction were carried out to ensure the integrity and accuracy of grinding power data. At the same time, the working state of grinding process was marked based on binarization, and the dynamic flow data was converted into string and stored in the cells of relational database. The grinding test results of bearing steel show that the database establishment method can accurately extract the grinding power characteristics and transform 2090000 dynamic data points into 2×52998 cell data, the data volume is reduced to 5.07% of the source data, which significantly reduces the storage scale of data and speeds up the access speed of grinding database.
Abstract: In order to solve the difficult problem of dressing micro-grooves on the surface of metal-bonded diamond wheel, an infrared nanosecond laser was used to carry out the dressing test. The influences of laser average power, pulse repetition frequency, laser ablation time and other factors on the material removal of metal-bonded diamond grinding wheel was investigated. A gradient step laser dressing process was proposed for U-shaped and V-shaped grinding wheel micro-grooves. The results show that the actual contour of the grinding wheel micro-groove after dressing is compared with the designed contour, the maximum absolute value of the relative error of the actual width at the top and bottom is 4.4%, and the maximum absolute value of the relative error of the actual depth is 9.6%. The edge of the sapphire wafer with a diameter of 4 inches (10.16 cm) is chamfered with the V-shaped micro-groove of the trimmed grinding wheel. The sharp edge of the wafer is trimmed into a regular shape, and the symmetry of the edge contour is good, which is consistent with the micro-groove contour of the surface of the laser trimmed grinding wheel. The feasibility of laser shaping and dressing of the micro-groove on the surface of metal-bonded diamond grinding wheel is verified.
Abstract: The oxidation reaction mechanism of diamond grits in diamond/borosilicate glass composites was studied. The composites were sintered at different conditions and the samples were analyzed through TG–DSC, XRD and Raman. The results showed no chemical reaction occurred when borosilicate glass was sintered below 1000 ℃. But when sintering diamond/borosilicate glass composites at temperatures above 814 ℃, there appeared volume expansion and bending strength decreasing. The volume expansion is 10% and the bending strength is 39.0 MPa when the composites are sintered at 780 ℃. Through thermodynamic analysis, XDR analysis and Raman analysis, it is found that when the sintering temperature is lower than 908.4 ℃, the diamond is oxidized by the free oxygen other than the oxides in the glass.
Abstract: The application of the cast WC, the Co powder coated cast WC and the Ni powder coated cast WC particles in diamond saw blades were studied, and their effects on the mechanical properties, the micro morphologies and the cutting properties of the diamond saw blade matrix were explored. The results show that when the mass ratio of the three kinds of WC material to the metal powder is 3∶1, the hardness of the three kinds of matrix is equivalent. The bending strength of the matrix containing Co powder coated cast WC is the highest, the interface between the WC particles and the matrix is the closest, and the microstructure of the matrix is the densest. The bending strength of the matrix containing Ni powder coated cast WC is the second. The matrix with only cast WC has the worst bending strength. Compared with the saw blade with only cast WC added, the cutting life of the saw blade with Co powder coated cast WC is the longest and increases by 40%.
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