The distribution of undeformed chip thicknesses is the kinematic “copy” of grain space distribution on a workpiece and has an important influence on the grinding results. In this study, a wheel ...topography model is developed that can be integrated with a workpiece model, a kinematic model and a calculation model of undeformed chip thickness of a single grain to obtain the distribution of undeformed chip thicknesses. In order to verify the integrated model, a single-layer brazed diamond grinding wheel is fabricated, and the topography measurements of the grinding wheel are conducted. The measured data are used in the integrated model to perform a simulation; the simulation results are consistent with the test results. At the same time, the model is verified with grains that are uniformly distributed. Then, simulations utilizing the integrated model are used to thoroughly study the grinding process. The distribution of grain protrusion height can be controlled by radial numerical dressings on the grinding wheel. Thus, the role of the distribution of grain protrusion height on the undeformed chip thickness distribution can be quantified by using radial numerical dressings on the grinding wheel. Additionally, the relationship between the average value of the distribution of undeformed chip thicknesses, hmean, and the surface roughness can be determined by simulation. It is shown that the surface roughness can be controlled quantitatively by radial numerical dressings on the wheel.
•A universal model for the undeformed chip thickness distribution is established.•The model for maximum undeformed chip thickness is only a special case of the universal model.•The surface roughness can be quantitative controlled by adjusting the grain protrusion height distribution.
Serrated chips are produced at high frequency in the high-speed machining, which often induce a severe failure of the coated cutting tools. In such case, the high frequency fatigue properties of ...coatings are pivotal. A monolayer TiAlSiN coating and multilayer TiAlN/TiSiN nano-coating were deposited on the ISO P30 cemented carbide substrate. The cyclic impact tests with high frequency were performed with a developed impact tester, which could generate different oscillation amplitudes by using the ultrasonic actuator. The surface response and fatigue fracture of coatings were analyzed by the measurement of dynamic forces and investigation of SEM images. Besides, the sequential load-indentation tests were performed on these two coatings. These tests would be used as baseline reference for comparison purposes with the ones determined under cyclic loading conditions. The fatigue fracture processes of coatings in the high frequency cyclic impact tests were analyzed, and the crack propagation in the cross-sections of coatings were observed by using focused ion beam (FIB) machine to slot cut the impact imprints. It showed that the interfacial delamination of coating/substrate system was more susceptible to the high frequency cyclic impact tests. Furthermore, the multilayer TiAlN/TiSiN nano-coating exhibited higher cyclic impact resistance at low impact loading conditions, but worse cyclic impact resistance at large impact loading conditions compared to the monolayer TiAlSiN coating.
•High frequency cyclic impact tester based on ultrasonic actuator was developed.•High frequency cyclic impact tests were performed on TiAlSiN PVD coatings.•Fatigue fracture process of coating in the cyclic impact test was analyzed.•Crack initiation and propagation in cross-sections of coatings were investigated.
Wire sawing is widely used for wafer cutting in the photovoltaic and microelectronics industries. The quality of cutting wafers is affected by the wire bow deflection. In this study, wire bow ...deflections in a crystal sawing process were systematically measured with a high-speed camera. A simulation model of wire bow deflection was established using the Adams software on the basis of experimental conditions. It is shown that the curve of the wire bow deflection was a quadratic curve. Wire bow deflection was obviously affected by the wire tension force and the feeding speed. However, wire speed had little effect on the wire bow deflection. The experimental and the simulation results of wire bow deflection were similar for different process parameters. The force ratio played a key role in influencing the wire bow deflection.
Three-dimensional twice scratching and double scratching of monocrystalline silicon carbide with two cone-shaped grains were simulated by coupling the finite element (FEM) and smoothed particle ...hydrodynamics (SPH) to resolve the mesh distortion problem caused by using the FEM. Twice-scratching experiments were performed under three different conditions to validate the coupled finite element (FE) and SPH model in the scratching simulation with two diamond grits. The experimental results were compared to the simulation results. For twice scratching, the simulation results conform with the experimental results, indicating the validity of the coupled FE and SPH model. Thus, the coupled FE and SPH model was used to simulate the double-scratching process under different conditions. The results of the double-scratching simulation showed that the interference damages in the scratching process occurred under three circumstances: the interference of lateral cracks, the interference of lateral cracks and plastic damage, and the interference of plastic damage. The influence of distance on the interference damage of the two diamond grits in the Y-direction was analysed. The changes in the maximum depth and width in the interference region and the scratching force with the distance of the two grains in the Y-direction are illustrated.
•FE and SPH was utilized to simulate double-scratching of monocrystal SiC.•Three interference modes of SiC were illustrated in double-scratching.•Interference mechanisms in three interference modes were studied.•Interference in double-scratching is more significant than that in twice-scratching.•If interference occur between the same material damage, interference will intensify.
The semi-fixed and fixed polishing film with diamond and alumina abrasive are used for a contrastive experiment involving polishing SiC and sapphire substrates in this study. The material removal ...rate (MRR) and surface topography of substrate, the protrusion height of abrasive together with the wear debris, are investigated to reveal the processing characteristic of substrates. The removal mode of substrate is brittle removal when the material removal scale is tens of nanometers or more. It is plastic removal mode when the material removal scale is nanoscale. A smooth substrate surface with nanoscale roughness and a relatively high MRR can be achieved simultaneously only when the material removal scale is uniform with a size of tens of nanometers.
•Analyzing the effect of material removal scale on processing quality of substrate.•The protrusion height of abrasives directly affects integrity of substrate surface.•The removal mode of substrate is revealed through material removal scale.•Removal scale with tens of nanometers can obtain a better pre-machined surface.
Single crystal silicon carbide (SiC) is widely used for optoelectronics applications. Due to the anisotropic characteristics of single crystal materials, the C face and Si face of single crystal SiC ...have different physical properties, which may fit for particular application purposes. This paper presents an investigation of the material removal and associated subsurface defects in a set of scratching tests on the C face and Si face of 4H-SiC and 6H-SiC materials using molecular dynamics simulations. The investigation reveals that the sample material deformation consists of plastic, amorphous transformations and dislocation slips that may be prone to brittle split. The results showed that the material removal at the C face is more effective with less amorphous deformation than that at the Si face. Such a phenomenon in scratching relates to the dislocations on the basal plane (0001) of the SiC crystal. Subsurface defects were reduced by applying scratching cut depths equal to integer multiples of a half molecular lattice thickness, which formed a foundation for selecting machining control parameters for the best surface quality.
The mechanical planarization machining of sapphire substrates including the C- (0001), A- (112¯0), and M- (101¯0) orientations with the sol-gel (SG) polishing pad has been performed in this paper. ...The polishing results show that the C-orientation with a surface roughness about 2nm is smoother than the A- and M-orientations, and the material removal rate (MRR) of C-orientation is higher than that of them. The removal mechanism of sapphire substrate was investigated by the wear debris and subsurface structure through transmission electron microscopy (TEM). And the instrumented nanomechanical tests were applied to further reveal the removal mechanism by nanoindentation. The analysis results indicate that the variation tendency of MRRs depends on the crystalline structure and nanomechanical properties of sapphire substrates. In addition, the processing of sapphire substrates is mainly dominated by the mechanical removal sapphire material during mechanical planarization machining.
•Analyzed the material removal mode of sapphire in mechanical planarization machining.•Different crystal structures affect the material removal rate of sapphire substrate.•Nanomechanical property of sapphire substrates further reveals its removal mechanism.•A better pre-machined surface can shorten the total processing time and cut the cost.
In this paper, the effect of additive particles on the mechanical properties of ultraviolet (UV)-cured resin was evaluated based on tensile strength and shear strength. The experimental results ...showed that the tensile strength was improved with proper particle addition, but the shear strength was always decreased. Moreover, the effects of additive particles on the holding force of diamond abrasive, critical exposure energy, and penetration depth of UV-cured resin were elucidated. The holding force of resin with 15 wt.% Al
2
O
3
addition was found to be higher than that of pure UV resin. Based on the experimentally determined critical UV exposure energy and penetration depth, UV-cured resins with and without additive particles were used to fabricate grinding wheels using additive manufacturing technology. Grinding experiment demonstrated the performance of UV resinoid grinding wheels was significantly improved with the addition of 15 wt.% Al
2
O
3
particles
.
•NiMo-Mo2C/C hybrid non-noble electrocatalyst is synthesized by a two-step method.•The NiMo-Mo2C/C exhibits a high electrocatalytic activity and stability for HER.•The high catalytic activity is due ...to electrochemical performance of NiMo and Mo2C.•The high stability of NiMo-Mo2C/C can be ascribed to the appearance of Mo2C.
Highly active and stable of carbon supported nickel molybdenum alloy and molybdenum carbide hybrid electrocatalyst (NiMo-Mo2C/C) has been developed for hydrogen evolution reaction (HER) in an acidic solution. The NiMo-Mo2C/C electrocatalyst was synthesized by a two-step microwave-assisted deposition/carbonthermal reduction method. Compared with commercial Mo2C, it is found that NiMo-Mo2C/C showed much better electrocatalytic activity for HER with a small onset overpotential of 90mV (j=1mAcm−2) and Tafel slope of 73mVdec−1 as well as good stability in acidic solution. Such enhanced catalytic activities may originate from its anchored structure and electrochemical performance of NiMo and Mo2C.
In grinding, regenerative vibration and forced vibration due to grinding wheel eccentric rotation are main excited-vibration sources that interact with grinding material removal mechanism. In the ...paper, instantaneous undeformed chip thickness in down-grinding cutting phase may consist of two components, i.e. linear kinetic thickness and nonlinear dynamic thickness. Considering abrasive grit-workpiece interaction in the grinding contact zone, the grinding vibration system is presented by a new set of differential equations of two degrees of freedom (DOF) with a close-loop feedback control system models. Conventional grinding control parameters, including wheel spindle speed, work-speed in feed direction and radial cutting depth, are often regarded as linear constants in many existing simplified models. When considering time delay, they can be transferred to nonlinear variables, so the capability of prediction and the accuracy of solution of the grit-workpiece dynamic performance are improved. Based on quantitative comparison of force and vibration magnitudes, the influence of the eccentric rotation of abrasive wheel and the negative rake angle of working grit cutting edges on grinding performance are demonstrated in the paper.
PDF
