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GH4068 superalloy is a new type of nickel-based superalloy in the aerospace field. It is an important alloy material for the manufacture of aircraft tubular components and aero-engine hot-end components. These components need to be machined with good surface quality to meet their use requirements. New hybrid machining processes can improve the quality of surface finish compared to conventional machines. In this paper, ultrasonic assisted turning (UAT) technology was applied to the machining of GH4068 superalloy. The experimental system of UAT was established. Experiments of UAT and conventional turning (CT) of GH4068 superalloy were carried out to study the effects of cutting speed, feed speed, cutting depth and vibration amplitude on cutting force and surface roughness. The surface morphology of the workpiece and chip were observed. The experimental results show that Fx and Fy can be reduced by a maximum of 44% and 63%, respectively, and the surface roughness can be reduced by a maximum of 31% after adding ultrasonic vibration. Compared with CT, the UAT has a better machining quality, a more obvious chip-breaking effect, and a smaller chip bending radius, which guides the high-quality processing of the GH4068 superalloy.

High strength and large ductility of existing Mn-containing brass alloys need to be further improved when used as slippers of friction-pair materials, which could be achieved by tuning alloy composition and thermomechanical treatments appropriately. The present work optimized the amount of minor-alloying elements M (M = Mn, Fe, Si) in Cu-Zn alloy via a cluster formula approach and then investigated the microstructural evolution of the designed alloy with different thermomechanical treatments. As-cast alloy ingots were solid-solutioned at 1093 K (820 °C) for 3 h, hot-rolled at 923 ~ 1023 K (650 ~ 750 °C), and then aged at 673 ~ 723 K (400 ~ 450 °C) for 1 ~ 2 h, respectively. It is found that the alloy matrix consists of the main FCC-α phase plus a small amount of BCC-β and M5Si3 phases, among which the M5Si3 exhibits three types of primary, fine, and nano-scaled particles. The mechanical property varies with the thermomechanical treatments due to diverse microstructures (especially the morphology of M5Si3 particles), in which the high strength (σUTS > 580 MPa) and large ductility (δ = 16.3 ~ 29.4%) could be achieved simultaneously in 673 K (400 °C). The optimal matching of high strength and large ductility makes the current alloy more suitable as an alternative slipper material. The strengthening effect was further discussed in light of various strengthening mechanisms, and the calculated strength increment is well consistent with the experimentally measured yield strength.

Silicon carbide (SiC) is a promising semiconductor material for making high-performance power electronics with higher withstand voltage and lower loss. The development of cost-effective machining technology for fabricating SiC wafers requires a complete understanding of the deformation and removal mechanism. In this study, molecular dynamics (MD) simulations were carried out to investigate the origins of the differences in elastic–plastic deformation characteristics of the SiC polytypes, including 3C-SiC, 4H-SiC and 6H-SiC, during nanoindentation. The atomic structures, pair correlation function and dislocation distribution during nanoindentation were extracted and analyzed. The main factors that cause elastic–plastic deformation have been revealed. The simulation results show that the deformation mechanisms of SiC polytypes are all dominated by amorphous phase transformation and dislocation behaviors. Most of the amorphous atoms recovered after completed unload. Dislocation analysis shows that the dislocations of 3C-SiC are mainly perfect dislocations during loading, while the perfect dislocations in 4H-SiC and 6H-SiC are relatively few. In addition, 4H-SiC also formed two types of stacking faults.

Carbon fiber-reinforced plastic/titanium alloy (CFRP/Ti) stacks are widely used in the aerospace field based on their high strength to weight ratio and heat resistance. High-quality bolt hole assembly is critical for the safety of the aerospace industry. Reaming is a crucial process in precision machining and is extensively used to improve the quality of bolt holes. Due to the different properties of the material, machining with conventional reaming (CR) presents some challenges, such as tolerance variations across the hole group and difficulty in controlling thrust. In this paper, ultrasonic vibration is applied to the reaming process. A geometrical model of ultrasonic vibration reaming (UVR) was established to analyze its kinematic law. UVR experiments on CFRP/Ti stacks were carried out to study the influence of different ultrasonic amplitudes on reaming thrust and the influence of tool speed on thrust, dimensional accuracy, and surface roughness under optimal ultrasonic amplitude. The average thrust forces in UVR decreased by over 57% (Ti) and 40% (CFRP), respectively, compared to CR. The roughness of CFRP is reduced by 20% with UVR and 28% for titanium alloys. The surface topography of the holes is significantly improved by UVR. This work guides the manufacture of high-quality bolt holes for CFRP/Ti stacks.

Because of the high hardness, brittleness, and anisotropy of reaction-bonded silicon carbide composites (RB-SiC), it is challenging to process high-quality textures on their surfaces. With the advantages of high processing accuracy and low processing damage, femtosecond laser processing is the preferred technology for the precision processing of difficult-to-process materials. The present work used a femtosecond laser with a linear scanning path and a spot diameter of 18 µm to process microgrooves on RB-SiC. The influence of different processing parameters on the microgroove profile, dimensions, and ablation rate (AR) was investigated. The ablation width Wa and average ablation depth Da of microgrooves were evaluated, and the various patterns of varying processing parameters were obtained. A model for Wa prediction was developed based on the laser fluence within the finite length (FL). As a result, the experimental values were distributed near the prediction curve with a maximum error of 20.4%, showing an upward trend of gradually decreasing increments. For a single pass, the AR value was mainly determined by the laser energy, which could reach the scale of 106 μm3/s when the laser energy was greater than 50 μJ. For multiple passes, the AR value decreased as the number of passes increased and it finally stabilized. The above research will provide theoretical and experimental support for the high-quality and efficient processing of RB-SiC surface textures.

The vertical surface is a common and typical characteristic structure among Nomex honeycomb core components. However, the conventional high-speed milling and ultrasonic cutting struggle to meet the high-quality machining requirements of a vertical surface. In this study, an ultrasonic trepanning method is proposed and a special ultrasonic trepanning tool is developed, aiming to improve the machining quality of the vertical surface. The trepanning quality of the vertical surface is further studied from the aspects of dimensional error and trepanning incision quality. Based on the kinematic characteristics of ultrasonic trepanning, a theoretical model of dimensional error in trepanning is established. Meanwhile, the influence of ultrasonic vibration on the trepanning process is analyzed, and the result shows that ultrasonic vibration significantly improves the equivalent elastic constant of the honeycomb core material. The theoretical model is proposed to predict the trepanning dimensional error, which is verified by experiment. The effectiveness of the ultrasonic vibration on the incision quality is verified by several experiments, and the quantitative analysis results demonstrate that ultrasonic vibration significantly improves the trepanning quality of the vertical surface.

Additive forging is a newly developed method to manufacture heavy forgings by using multilayer hot-compression bonding. However, the relationship between surface cleaning and bonding performance of bonded samples in the additive forging process is unclear. This paper studies the effect of surface cleaning on interface bonding performance for the first time. A new characterization method of surface cleanliness consisting of water contact angles, relative fluorescence units, and optical observation was proposed to characterize the cleaning effect. The micromorphologies and tensile properties were used to evaluate interface bonding performance. Elemental analysis and morphological analysis were used to infer the hindrance mechanism of contaminants. The results show that the new characterization method can effectively characterize the surface cleanliness of substrates. Moreover, the interfacial bonding performance results indicate that surface cleaning had a great influence on the bonding performance for 316H stainless steel joints manufactured by additive forging. Finally, the hindrance mechanisms of particles, chips, and oil contaminants were attributed to the hindrance effect in a radial direction, along the interface direction, and perpendicular to the interface direction respectively. This research builds a relationship between surface cleaning and bonding performance, which helps achieve high-performance manufacturing of heavy forgings.

Cutting force is one of the most important factors in the ultrasonically assisted grinding (UAG) of hard and brittle materials. Many theoretical and experimental studies show that UAG can effectively reduce cutting forces. The existing models for UAG mostly assume an ideal grinding wheel with abrasives in both the end and lateral faces to accomplish material removal, whereas the important role of the transition fillet surface is ignored. In this study, a theoretical cutting force model is presented to predict cutting forces with the consideration of the diamond abrasives in the end face, the lateral face, and the transition fillet surface of the grinding tool. This study analyzed and calculated the vibration amplitudes and the cutting forces in both the normal and tangential directions. It discusses the influences of the input parameters (rotation speed, feed rate, amplitude, depth and radius of transition fillet) on cutting forces. The study demonstrates that the fillet radius is an important factor affecting the grinding force. With an increase in fillet radius from 0.2 to 1.2 mm, the grinding force increases by 139.6% in the axial direction and decreases by 70% in the feed direction. The error of the proposed cutting force model is 10.3%, and the experimental results verify the correctness of the force model.

High chromium alloy is a kind of metal material with high corrosion resistance and high hardness. It is used in the thrust bearing bush of nuclear main pump in a severe environment. Based on the content of elements in high chromium alloy and the manufacturing preparation process of the alloy, a method for constructing the molecular dynamics (MD) model was proposed to study the machinability of the alloy. The MD simulation model of high chromium alloy was established based on alloy structure with the atomic random permutation and two bubble algorithms. Then, according to the actual manufacturing process of the high chromium alloy, a quenching process was introduced to simulate the actual manufacturing process of the high chromium alloy, so the property of the high chromium alloy model was improved and it was more suitable for precision machining. The accuracy of the model was verified by the internal structure and by calculating the nanohardness and density of the high chromium alloy model after adequate relaxation to studying the nanomachining performance. The coordination number of the high chromium alloy is about 4.3 calculated by integrating the radial distribution function. And there is not a perfect crystal structure in the alloy model. The density of the alloy model is about 7.549 g/cm₂, which agreed with the results of actual experimental measurement. A series of MD simulations were performed to investigate the nanomechanical property of the high chromium alloy by using the MD model. The maximum depth of 2 nm, 2.5 nm and 3 nm indentation simulations were carried out with 3 nm indenter. The results showed that the nanohardness is about 6.951 GPa-8.095 GPa, these properties are very close to the real measured results. The material and the deformation property of the high chromium alloy were stable during the indentation process.

Diamond CMP mechanisms have been widely investigated using the CMP experimental methods. However, the experiment could not observe the details of the removal process, it could not explain the mechanism of removal. The atom removal mechanism of chemical mechanical polishing (CMP) process on the diamond surface polished with a silica abrasive in aqueous H2O2/pure H2O was elucidated using ReaxFF molecular dynamics (MD) simulations. The research shows that the oxidation of diamond surface plays a dual role in the removal of C atoms. First, the diamond surface absorbs OH, O or H to form C O, C OH or C H bonds. Then, the C atoms on the oxidized diamond surface are removed under the mechanical action of abrasive in aqueous H2O2. Three types of C atom removal pathway are detected in the CMP process: it can be removed in the form of CO, CO2 or C chain and C atom removal occurs on the first layer. However, no C atoms are removed in pure H2O. The friction in pure H2O is less than that in aqueous H2O2 due to the lubrication of pure H2O. In addition, comparing the different pressures applied to the abrasive, it is found that the greater the pressure applied, the more OH adsorbed on the diamond surface so that the more C atoms are removed. This work shows that the removal of C atoms is the result of the combination of chemical and mechanical effects, which helps understand the removal process of C atoms at the atomic scale in the CMP process and provide an effective method to choose the CMP slurry.

Molecular dynamics simulations using ReaxFF reactive force field are employed to study the process of the silica abrasive particle sliding on the Cu(1 0 0) substrate in the aqueous H2O2 in order to clarify the atomistic mechanisms of the Cu chemical mechanical polishing process. Results reveal that there are mainly Cu H2O, OH Cu OH, Cu OH Cu, Cu OH H2O, O Cu OH etc on the substrate, among them, the number of Cu H2O is the most. And a part of H2O and OH in the above product come from H2O, some from H2O2, and the other are from the recombination of these two types molecule. Under the mechanical sliding effects, Cu atoms are mainly removed in the form of clusters by fracturing of Cu Cu bonds and Cu O bonds on the Cu substrate. When the polishing pressure is different, the more Cu atoms are removed, the greater the friction force between the abrasive particles and the substrate and the more H2O molecules are decomposed as the polishing pressure increases. Besides, H2O plays a dual effect by oxidizing the Cu substrate surface as well as by the effect of lubrication. Our results may shed light on the removal mechanism of Cu atoms in the CMP process at the atomic level and help to further understand the CMP of Cu.

Ultrasonic assisted grinding (UAG) has been demonstrated to be effective for processing hard and brittle materials. In some of the current UAG models, the high efficiency of UAG was attributed to the great maximum momentary force brought by ultrasonic vibration. However, the models were built based on multi-grains behavior which lacks of necessary support by single-grain models and experiments. In this paper, a model for ultrasonic assisted scratching (UAS) was proposed to investigate the cutting behavior of single-grains. The experiments with and without ultrasonic assistance were both conducted on a reaction-bonded silicon carbide specimen to verify the developed model. Results showed that even with the same maximum momentary force, the material removal rate increased greatly with ultrasonic assistance. The factor kL and kH did not remain constants as in the original indentation fracture mechanics models, and were highly related to the amplitude of the ultrasonic vibration.

The deformation of single-crystal beta-phase gallium oxide (or β-Ga2O3) micro-pillars under compression was investigated with the aid of transmission electron microscopy. High-density stacking faults were the dominant deformation defects in the plastically deformed micro-pillars. Micro-cracks were found along (200), (001) and (010) lattice planes and fracture occurred along (200) lattice plane when compressive strain was sufficiently great. Lattice bending was also observed in the fractured pillar. The average fracture stress and strain of β-Ga2O3 being measured are 7.25 ± 1.11 GPa and 3.80 ± 0.57%, respectively, which have never been reported previously.

Back Grinding of Wafer with Outer Rim (BGWOR) is a new method for carrier-less thinning of silicon wafers. There are few studies on the shape of wafer in BGWOR. In this paper, the mathematical models of three-dimensional grinding marks, surface shape and radial thickness of wafer in BGWOR were developed. With this model, the pattern of grinding marks and the radial thickness of the wafer under different inclination angles of grinding wheel were simulated by Matlab, then the relationship between the angle of grinding wheel shaft and the grinding marks, surface shape, radial thickness, total thickness variation (TTV) of wafer in BGWOR was also discussed. The inclination angles of grinding wheel have great influence on the surface shape and radial thickness distribution of wafer. Finally, the pilot experiments were conducted to verify the theoretical model of radial thickness of wafer in BGWOR. The study results will provide helpful instruction for improving the flatness of ground wafer.

In this study, the deformation mechanism of gallium-faces (Ga-faces) and nitrogen-faces (N-faces) gallium nitride (GaN) during nanogrinding were investigated by molecular dynamics (MD). The differences between the two were analyzed from force, temperature, potential energy, surface/subsurface damage, and material removal rate (MRR). The results show that N-faces GaN withstand lower grinding force, higher temperature, potential energy, and MRR. Meanwhile, the total length of dislocations and the number of zinc blende phase atoms are also greater than those in Ga-faces. Further research found that the difference in edge dislocation with b = 1/3 〈11–20〉 is the main reason that causes the dislocations in N-faces longer than that in Ga-faces, which can reach about 3 times. However, the Shockley incomplete dislocation with b = 1/3 〈1–100〉 and other dislocations are slightly smaller than those in Ga-faces. This study innovatively researched the difference in the processing properties of the two GaN at the nano-scale, which provide a theoretical basis for guiding GaN in the processing of ultra-precision.

Surface and deformation characteristics of single crystal β-Ga2O3 under nanogrinding were investigated using nanoindentation and transmission electron microscopy. Nanocrystals, stacking faults, twins and dislocations were the main deformation patterns found in the grinding of this semiconductor crystal. An amorphous phase was found when the specific grinding energy was significantly high, which was initiated behind the occurrence of other defects. The occurrence sequence of defects is somehow different from that of other semiconductors such as silicon, germanium and gallium arsenide. The hardness of grinding-induced deformed layer was higher than that of the perfect β-Ga2O3 crystal. The thickness and hardness of the defect layer were both reduced when a finer grit size was used. The mechanism responsible for deformation was found to be related to the intrinsic stacking fault energy of β-Ga2O3 and the specific grinding energy being used.

Nano-scale Al2O3-ZrO2 eutectic ceramic structures with shapes of thin-wall and cylinder were prepared by ultrasonic-assisted laser engineered net shaping. In the preparation process, the power of ultrasonic was adjusted in real-time on the molten pool. The generation of refining grain by ultrasonic were discussed based on the principle of crystallography. Two methods to improve the fracture toughness were analyzed. The average eutectic spacing was 60–70 nm, and the fracture toughness was 7.67 MPa·m1/2.

A fully fundamental understanding of the roles of the glassy phase (GP) in Glass-Ceramics (GCs) during the cascade collisions remains elusive. In this work, an efficient Molecular dynamics (MD) model with continuous controlled melting and quenching procedures is proposed to mimic the cascade collisions considering the electron stopping effect. Then, the details of both structure evolution and the primary knock-on atom (PKA) behavior induced by the cascade collisions as well as thermal peak effect are observed. The results show that the roles of the GP layer during the cascade collisions can be defined as role I and role II according to the behavior of the PKA. The kinetic energy of the PKA decreases sharply when the PKA passes through the role I. However, the energy exchange between the PKA and the atoms in the GP layer is relatively less and smoother under the role II. Combined with the electron stopping effect and the high energy distorted atoms, the cascade collisions induce a large amount of energy loss in the GP layer. Besides, the distribution of kinetic energy is in good agreement with that of the Frenkel pairs. The mechanism behind the roles of the GP layer is the interaction between the high/low energy distortion atom group and the PKA.

An effective molecular dynamics model to describe heterogeneous materials like glass-ceramics is proposed. Based on the model, we find that the velocity direction of the primary knock-on atom (PKA) is more prone to deflect sharply in glassy phases (GP) than that in crystalline phases (CP). And the high-stress region in CP is more concentrated, while the distribution of the high-stress region in GP is relatively discrete. Typical topologies of the Frenkel pairs (FPs) show that the direction of FPs propagation has an obviously turn at the boundary. In the hot peak period, the off-site atoms induced by the cascade collisions in CP could rearrange to avoid the number of defects coming to a high point. However, once the distorted clusters form in GP, the dislocated atoms of the distorted clusters are hard to move back to their site due to the high energy barriers. The annihilation of defects is also blocked in GP. The derived results could help to further understand the evolution mechanism of the heterostructure and defects at the nanoscale. And the method of model construction could contribute to more exciting simulations.

Mirror milling is a new efficient and green technology of aircraft skin processing. Currently, the support head of mirror milling system is mostly a metallic sphere and the support area is smaller ...

Molecular Dynamics simulations were carried out to study the formation mechanism of subsurface damage during the process of nano-grinding of gallium nitride (GaN). The effects of grinding depths and speeds on the temperature, the radial distribution function, phase transition, dislocation and the damage layer were systematically investigated. The results showed that quantities of interstitial atom, vacancy defects, atomic clusters, “U"-shaped half dislocation loops and Phase transition atoms exist in the subsurface layer. Additionally, the temperature, dislocation density and the number of phase transition atoms are positively related with the grinding depths, and then resulting in the quality of subsurface decreases with the increase of grinding depths. Although the damage layer is more sensitive to the grinding depth, when the speed increases from 25 m/s to 50 m/s, the above parameters also increase slightly, thus the subsurface quality decreases. As the speed continues to grow, these parameters gradually decrease due to the sharp decrease in processing time, and the quality of subsurface layer improves. This study provides an insight into the subsurface damage mechanism for the low-damage processing of GaN.

A new soft abrasive grinding wheel (SAGW) used in chemo-mechanical grinding (CMG) was developed for machining silicon wafers. The wheel consisted of magnesia (MgO) soft abrasives, calcium carbonate (CaCO 3 ) additives and magnesium oxychloride bond. Surface topography, roughness and subsurface damage of the silicon wafers ground using the new SAGW were comprehensively investigated. The results showed that the grinding with the new SAGW produced a surface roughness of about 0.5 nm in R a and a subsurface damage layer of about 10 nm in thickness, which is comparable to that produced by chemo-mechanical polishing. This study also revealed that the chemical reactions between MgO abrasive, CaCO 3 additives and silicon material did occur during grinding, thereby generating a soft reactant layer on the ground surface. The reactant layer was easily removed during the grinding process.

Wheel setting is difficult in a grinding process and may directly apply a negative impact on grinding accuracy and efficiency. This study presents a novel method for grinding wheel setting based on acoustic emissions. The method experimentally detects the acoustic emission (AE) signals that come from the touch-down of the grinding wheel with the workpiece. The experimental results show that the measured AE signals monotonically increase with grinding depth and can be used for detection of wheel setting in a grinding process with a detection accuracy better than 0.5μm.

Dressing parameters, which directly affect the flatness of the plate, are very important in planetary double-sided grinding dressing process. In this paper, trajectory and velocity equations of grit are studied. By comparing to the trajectory density of different annular regions, this paper puts forward an evaluation method of the shape of the plate and explores the impact of rotation speed on the shape of the plate. Finally, the experiments are performed by adjusting the rotation speed of the sun wheel and the plate. The results show that the flatness of the plate can be dressed below 0.01 mm, which validates the correctness of the theory.

A new support method used in aircraft skin mirror milling, liquid lubricating support, is proposed in order to solve the problems of scratching aircraft skin surface caused by rolling support or sliding support. The thickness and stiffness of liquid film between skin and support head are obtained with different feed pressure. The effects of thickness and stiffness of liquid film on surface quality and dimensional uniformity of workpiece are analyzed. The surface roughness is better under the condition of liquid film. With better film stiffness, dimensional uniformity is better, and actual axial cutting depth is closer to nominal axial cutting depth.

The effects of pressure and sliding velocity on the interface friction behavior during the chemical mechanical polishing process of diamond were investigated utilizing ReaxFF molecular dynamics, with a focus on the subsurface damage, friction force, and atom removal. Simulation results indicate that in the initial stage, the friction force depends on the number of interfacial C-C bonds and C-O-C bonds and shows a positive correlation with the pressure and sliding velocity. Later on, the friction force relies on the number of amorphous carbon atoms, and exhibits a negative correlation with the pressure and sliding velocity. Under low pressure, the carbon atoms are mainly removed along with the formation of C-C single bonds. In contrast, with increasing pressure, the carbon atoms are removed together with the formation of more C-C single and multiple bonds. This accounts for more extensive atom removal, followed by the more severe wear, as well as deeper subsurface damage. This study systematically evaluates the underlying influence mechanism of pressure and sliding velocity on the interface friction behavior from atomistic scale, thus elucidating technological parameters for ultra-precision and low-damage machining of diamond.

The molecular dynamic (MD) simulation of monocrystalline silicon under multiple grinding is carried out to study the effect of multiple grinding on the thickness of damage layer. Four grinding processes are conducted on (0 0 1) along 〈−1 0 0〉 direction. The depth of grinding of the first grinding is 20 A. The subsequent grinding is machining on the machined surface with a damage layer left by the first grinding. The second grinding is a spark-out process and the depth of grinding of the third and fourth grinding increases by 5 A compared with the previous grinding. The changes of structures and mechanical properties of the damage layer in the machined surface after the first grinding are investigated by coordination number (CN), the radial distribution functions (RDF) and nanoindentation. The thickness of the damage layer left by the first grinding can be reduced stably in the second and third grinding, but it will increase in the fourth grinding. Therefore, two more grinding steps between the third and fourth grinding are carried out. One is the spark-out process and the depth of grinding of the other increases by 2 A compared with the third grinding. The results show the spark-out process can remove the springback left by the previous grinding and promote the residual compressive stress in the machined surface, which can improve the accuracy and quality of grinding. The thickness of damage layer induced by the first grinding can be reduced without new damage structures generating. However, it cannot be reduced unlimited. When the thickness of damage layer reaches half of the original thickness, a re-grinding will cause new damage structures, and the thickness of damage layer will increase. The depth of grinding is suggested to be less than half of the original damage thickness to reduce the damage layer. The research results can be applied in the ultra-precision grinding of monocrystalline silicon to control the thickness of damage layer and improve the quality of machining.

Grinding force is an important indicator related to processing efficiency and residual strength in the progress of grinding SiC. With the method of ultrasonic assisted grinding (UAG), this paper studied the influence of four parameters on grinding force based on orthogonal experiment, namely vibration amplitude, depth of grinding, feed rate and spindle speed. A series of results with high efficiency and low grinding force were obtained. A regression empirical model under the condition of UAG was established and verified. It was also proved that ultrasonic vibration was conducive to improve the ground surface quality of workpiece.

The origin of drilling force in drilling with twist drill is quite complicated owning to the complex shape of the drill bit cutting edges. In this paper, the drilling experiments both with and without the ultrasonic were designed and conducted on aluminum alloy with pre-drilled hole. The drilling force was tested and the different effects between the cutting edges of the twist drill on the drilling force were analyzed under various drilling parameters including the spindle speed, feed rate and vibration amplitude. The drilling force of conventional drilling (CD) and ultrasonic assisted drilling (UAD) was characterized and the roles of the ultrasonic vibration in drilling were discussed.

In order to improve machining efficiency of sapphire wafer machining using the conventional loose abrasive process, fixed-abrasive diamond plates are investigated in this study for sapphire wafer grinding. Four vitrified bond diamond plates of different grain sizes (40 µm, 20 µm, 7 µm, and 2.5 µm) are developed and evaluated for grinding performance including surface roughness, surface topography, surface and subsurface damage, and material removal rate (MRR) of sapphire wafers. The material removal mechanisms, wafer surface finish, and quality of the diamond plates are also compared and discussed. The experiment results demonstrate that the surface material is removed in brittle mode when sapphire wafers are ground by the diamond plates with a grain size of 40 µm and 20 µm, and in ductile mode when that are ground by the diamond plates of grain sizes of 7 µm and 2.5 µm. The highest MRR value of 145.7 µm/min is acquired with the diamond plate with an abrasive size of 40 µm and the lowest surface roughness...

To study the regular pattern of vapor-to-melt ratio in laser cutting sheet metal, a physical model of vapor-to-melt ratio is developed to demonstrate the material remove forms of vaporization-melt in cutting area and the state of energy and mass flow in the molten layer. Variation of vapor-to-melt ratio with laser power and cutting velocity is obtained by laser cutting of 6063 aluminum alloy sheet. The 0.5-mm sheet thickness is carried out on a JK701H Nd:YAG pulse laser cutting system by simulating under the regression correction of cut radius. Observation on the cut samples with different parameters (65 W, 85 W, 105 W varied with laser power increasing, and 2.2 mm/s, 2.0 mm/s, 1.8 mm/s with decreasing of beam cutting speed) and the calculations show that vapor-to-melt ratio increases (0.595–1.995, 0.672–2.631, 0.787–4.171) with laser power (65 W–110 W) and decreases with cutting velocity (1.8 mm/s–2.4 mm/s). At the same time, the laser cutting quality increases with vapor-to-melt ratio and the de...

Mechanical drilling can change the microstructure of the regions near the hole wall, remarkably affecting the working performance of precision parts. The present work investigated the microstructural evolution in the regions from the drilled hole wall to the inner matrix of the soft magnetic 49Fe-49Co-2V alloy after the common drilling experiments were carried out. The microstructures and microhardness in different regions near the hole wall along the radial direction were characterized with OM, SEM, TEM, EBSD and Vickers Microhardness tester. The experimental results show that the nearest region to the hole wall is constituted of nano-sized refined grains. It exhibits a disordered BCC phase due to the rapid cooling from the high temperature during the drilling, different from the dual-phase of BCC and B2 of the matrix. The second-nearest region to the hole wall is distributed by a huge number of dislocations, leading to a maximum in microhardness. The microstructural evolution contributes to the variation of the microhardness, which increases firstly, reaches a maximum, and then decreases to the level of the matrix with the distance increasing from the hole wall. This variation tendency is discussed in light of both refined grain-boundary strengthening and dislocation strengthening mechanisms. Keywords: 49Fe-49Co-2V alloy, Drilling, Microstructural evolution, Microhardness, Strengthening mechanisms

The lapping and grinding induced wafers surface damage layers with the same roughness Ra were compared in terms of surface morphology, surface roughness PV, subsurface damage, material removal mechanism, and material removal rate of later chemical mechanical polishing. The results indicated that surface material on silicon wafer lapped using loose abrasive was removed in brittle mode, and that ground using diamond wheel was removed in both brittle mode and ductile mode. The silicon wafer produced by lapping and grinding had almost the same surface roughness Ra, however, the corresponding surface roughness PV induced by lapping was less than that induced by grinding. When using the chemical mechanical polishing to remove damage layer generated by lapping and grinding, the surface roughness Ra of lapped wafer decreased faster than that of ground wafer, but the material removal rate of lapped wafer was higher than that of ground wafer. Discussion was provided to explore the influence of surface morphology on material removal rate during polishing.

The lightweight design of the sandwich mirror, as a commonly used space primary mirror structure, is one of the key topics for the design of space-based optomechanical systems. Owing to the...

Large size mechanical seals are one of the most important components used in reactor coolant pumps. However, the hydrodynamic seal rings with wavy face are difficult to machine due to their high hardness and high form accuracy demand. In order to solve this difficult problem, a novel four-axis linkage grinding method using a cup wheel to process the hydrodynamic seal rings by line contact was proposed. A preliminary study indicates that the form error of the ground seal ring surface is extremely sensitive to different linkage relations of the four axes. By taking the center height of the cup wheel and the laws of motion along the X-axis, Z-axis, B-axis and C-axis as control variables, their effects on the principle form error of the ground surface are evaluated. Six implementation strategies are proposed to reach lower principle form errors. It is found that the minimal principle form error is only 9.64 nm and hence its influence on the ground seal ring shape can be neglected in designing an ultra-precision grinding machine. In addition, the results indicate that the position accuracy of the X-axis at the microscale is acceptable no matter which implementation strategy is selected. This study is expected to serve as a theoretical basis for design and development of the four-axis ultra-precision grinding machine.

Unidirectionally coherent and boundary-free nanotwinned (nt) mercury cadmium telluride (HgCdTe or MCT) was achieved under plastic deformation of nanoindentation. The hardness of nt-MCT is up to 47.2 GPa, which is two orders magnitude higher than that of monocrystalline MCT. This increased hardness originates from the unique composite nt structure, which exhibits a repeated pattern comprising a lamellar twin >11.5 nm thick, followed by one or several lamellar twins with thicknesses

Nanotwinned (nt) mercury cadmium telluride (HgCdTe or MCT) was prepared using nanoindentations. The hardness of nt-MCT is 100 times higher than that of monocrystalline counterparts. Transmission electron microscopy shows that the twin lamellae of nt-MCT prior to cyclic nanoindentations are distributed along two directions, intersecting at an angle of 76°. The nanotwinned microstructure of nt-MCT is stable after 100 cyclic nanoindentations. The loading–unloading curves of nt-MCT are basically invariable after 50 cycles, and have elastic characteristics.

HgCdTe crystals have been accepted as a very important material of infrared detectors, and due to their soft-brittle nature, machining HgCdTe wafers is a challenge in the field of ultraprecision ma...

High cleaning quality for silicon wafers without damage is a challenge in laser cleaning technologies. Laser cleaning of Al2O3 micro-particles, which are the main contaminants of silicon wafer lapping and polishing solutions used in industry, from silicon wafers was studied for determining laser energy for high efficient particle removal while not causing damage to the wafers. As the cleaning force is generated from laser-energy absorption and conduction of the wafer, heat-conduction model on silicon wafer was developed during laser irradiation using a finer finite element method, from which cleaning force exerting on the particles greater than the adhesion force between the particle and the substrate, but less than the wafer damage energy of laser input was determined. Calculations of the laser energy threshold values for both particle cleaning and wafer damage were conducted for silicon wafers of 200 mm in diameter and 0.2 mm in thickness, and they were found to be about 60 mJ/cm2 and 320 mJ/cm2, respec...