Single Diamond Grain Research Articles

Study on the material removal mechanism of glass in single diamond grain grinding with ultrasonic vibration assisted

Study on the material removal mechanism of glass in single diamond grain grinding with ultrasonic vibration assisted

The effects of deposition parameters on the grain morphology and wear mechanism of monolayer diamond grinding tools fabricated by hot filament CVD method

The hot filament chemical vapor deposition technique (HFCVD) is used to fabricate monolayer grinding tools with high quality diamond abrasive grains. The high pressure and high temperature (HPHT) diamond seeds are distributed on SiC substrate randomly by a spin coater machine. Then epitaxial growth of CVD diamonds is conducted on both seeds and substrate simultaneously. The heteroepitaxial diamond film on substrate serves as a bonding layer to anchor the seeds, and the homoepitaxial growth of the seeds leads to changes in their morphology, purity, as well as mechanical properties. The grown seeds can be used as abrasive grains of the grinding tools. In this work, a systematic study is presented into the effects of deposition parameters (substrate temperature, carbon concentration, reactive pressure, bias current) on the growth behavior of diamond seeds. As a result, it is found that the well-faceted single crystal diamond (SCD) grains can be grown at 800 °C, 4.5 KPa, carbon concentration of 1.5% and bias current of 2 A. Besides, the increase of temperature and decrease of pressure allow the changes from SCD grains to microcrystalline diamond (MCD) clusters or further, to nanocrystalline diamond (NCD) clusters, while the high bias current and carbon concentration promote the growth of dislocated planes and secondary nucleation. Moreover, it is found that the protrusion of the diamond abrasives can be controlled by the difference in growth rates between seeds and diamond bonding films under various conditions. Finally, the wear resistance of diamond grains is tested. Results show that the wear of SCD grains is dominated by a high rate of wear flat and few fractures, and the wear of MCD grains exhibits less wear flat but more fractures, while the NCD grains exhibit the worst wear resistance in terms of both fracture and wear flat.

Single diamond grain cutting-edges morphology effect on grinding mechanism of Inconel 718

This study is focusing on exploring the effect of diamond grain cutting-edges morphology and grinding wheel speed on grinding performance of nickel-based superalloy Inconel 718. The grinding tests were carried out using a single diamond grain of different shapes. The variations of scratch mechanism, grinding force, pile-up ratio and specific grinding energy were investigated under different conditions. The results show that the chisel cutting-edge is beneficial to constrain the material pile-up. As a comparison, the inclined cutting-edge promotes the pile-up formation. More engaging cutting-edges result in larger grinding force. Additionally, with the increase of the wheel speed, the pile-up ratio increased but the single grinding force and specific grinding energy decreased. It is beneficial to have more grains with chisel cutting-edges and use high speed grinding (>80 m/s). These will help to reduce the grinding force and improve the grinding efficiency.

Numerical investigation on the influence of cutting-edge radius and grinding wheel speed on chip formation in SiC grinding

A finite element model (FEM) of single-grain surface grinding of SiC has been established to understand the effects of the cutting-edge radius and grinding wheel speed on SiC chip formation. Based on the mechanic deformation behavior of SiC, the critical chip formation thickness and critical ductile-brittle transition thickness were found. Results obtained show that critical ductile-brittle transition thickness has a peak value at Rc = 1.25 µm and vs = 80 m/s respectively. Normal grinding force increased firstly with the increasing cutting edge radius and then declined. The critical cutting edge radius Rc= 1.25 µm and grinding wheel speed vs = 80 m/s were determined depending on the variation of critical chip formation thickness, critical ductile-brittle transition thickness, grinding force, ground surface quality. Finally, the simulation results were verified experimentally by an indirect single diamond grain scratching SiC ceramics test.

Finite element implementation of the tension-shear coupled fracture criterion for numerical simulations of brittle-ductile transition in silicon carbide ceramic grinding

Despite great efforts have been made to understand the machining mechanism of brittle materials, few numerical models are available to describe the brittle-ductile transition (BDT) in engineering ceramic grinding due to the fracture mechanism difference in brittle and ductile removal modes. This paper introduces the tension-shear coupled (TSC) fracture criterion for the finite element method (FEM) analysis of the brittle material machining that is capable of describing BDT. With TSC fracture criterion, simulation results of single diamond grain grinding of silicon carbide (SiC) ceramic, including the ground surface/subsurface morphology, grinding forces, and equivalent plastic strain, were compared with those under effective plastic strain (EPS) fracture criterion, the one widely adopted by commercial finite element software. The results show that TSC fracture criterion can better characterize BDT in SiC grinding than EPS criterion, via ground surface/subsurface morphology and tangential grinding force. To experimentally validate the proposed TSC fracture criterion, single diamond grain grinding tests were conducted on SiC with various maximum undeformed chip thickness to demonstrate BDT and compare with the simulation results. The measured ground surface morphology evolution and BDT with the increased undeformed chip thickness matched the results of the FEM simulation with TSC fracture criterion.

Atomistic insights on the nanoscale single grain scratching mechanism of silicon carbide ceramic based on molecular dynamics simulation

The precision and crack-free surface of brittle silicon carbide (SiC) ceramic was achieved in the nanoscale ductile grinding. However, the nanoscale scratching mechanism and the root causes of SiC ductile response, especially in the atomistic aspects, have not been fully understood yet. In this study, the SiC atomistic scale scratching mechanism was investigated by single diamond grain scratching simulation based on molecular dynamics. The results indicated that the ductile scratching process of SiC could be achieved in the nanoscale depth of cut through the phase transition to an amorphous structure with few hexagonal diamond structure. Furthermore, the silicon atoms in SiC could penetrate into diamond grain which may cause wear of diamond grain. It was further found out that the chip material in the front of grain flowed along the grain side surface to form the groove protrusion as the scratching speed increases. The higher scratching speed promoted more atoms to transfer into the amorphous structure and reduced the hexagonal diamond and dislocation atoms number, which resulted in higher temperature, smaller scratching force, smaller normal stress, and thinner subsurface damage thickness, due to larger speed impaction causing more bonds broken which makes the SiC more ductile.

Experimental investigation on materials removal mechanism during grinding silicon carbide ceramics with single diamond grain

A single grain grinding experiment with fixed speed ratio vs/vw was designed to decouple the effect of grinding speed and undeformed chip thickness (UCT) on the SiC material removal mechanism during elevating the grinding wheel speed. Ground surface and subsurface topography, grinding forces, and specific energy were measured with grinding speed ranging from 20 to 160m/s and maximum UCT agmax from 0.02 to 3μm. The results demonstrated the grinding force and specific grinding energy show an evident decreased tendency with the increasing of grinding speed, despite the agmax value was kept at 0.03, 1μm. However, at agmax=0.3μm, the grinding force has a peak value with the increment of grinding wheel speed. The subsurface has the same trend. Based on the subsurface morphologies, grinding forces, grinding energy, the critical grinding wheel speeds vs=100, 80, 80m/s were determined at the agmax=0.03, 0.3, 1μm, respectively. Besides, grinding forces show different growth rates with the gradually increasing agmax at three stages under typical grinding speeds due to the transition of material removal mechanism. The critical agmax values for ductile-brittle transition and beginning of brittle regime grinding are determined as 0.3 and 1μm by surface and subsurface morphologies, grinding forces, grinding energy, respectively.

The influence of grain geometry and wear conditions on the material removal mechanism in silicon carbide grinding with single grain

Abstract High efficiency and precision grinding of brittle materials is challenging due to material physical and chemical properties. To understand the effect of grain geometry and wear conditions on the material removal mechanism in brittle material precision grinding, a single diamond grain grinding experiment was conducted on Silicon Carbide (SiC). The cutting edge radius and deflection angle were measured by confocal scanning. Under six different cutting edge radius and three maximum undeformed chip thickness, grinding force and ground surface were measured. Diamond grain wear was investigated by observing the grain morphology, wear rate, grinding force, and ground surface change over accumulative material removal volume. The result showed the existence of a critical cutting edge radius for improving SiC ground surface quality.. Normal grinding force increased with the cutting edge radius increase. Tangential grinding force increased with the cutting edge radius increase and reached the peak value at the critical cutting edge radius. Flank wear was the major wear mode in precision SiC grinding. The grain wear was associated with the grinding force and ground surface.

Theoretical model of brittle material removal fraction related to surface roughness and subsurface damage depth of optical glass during precision grinding

Brittle material removal fraction (BRF) is defined as the area fraction of brittle material removed on machined surface. In the present study, a novel theoretical model of BRF was proposed based on indentation profile caused by intersecting of lateral cracks. The proposed model is related to surface roughness and the subsurface damage (SSD) depth of optical glass during precision grinding. To investigate the indentation profile, indentation tests of K9 optical glass were conducted using single random-shape diamond grains. The experimental results indicate that the indentation profile is an exponent function. To verify the proposed BRF model, BRF, surface roughness and SSD depth of K9 optical glasses were investigated by a series of grinding experiments with different cutting depths. The experimental results show that BRF is dependent on surface roughness and SSD depth. The relationship between BRF, surface roughness and SSD depth is in good accordance with the proposed theoretical model. The proposed BRF model is a reasonable approach for estimating surface roughness and SSD depth during precision grinding of optical glass.

Molecular Dynamics Model of Nano-metric Peripheral Grinding

Ultra high precision grinding can render sub-micrometric surface finish of workpieces in an effective way. Accordingly, grinding in the nano-level can be used to produce surface finish of nanometric level or removal of several atomic layers of the substrate. As direct measurements in this scale are either expensive or impossible to be conducted, appropriate simulation models need to be created in order to study the underlying mechanisms of nanometric machining processes. Molecular Dynamics (MD) method is a widely accepted simulation method for this purpose, as it enables direct observation of the process at atomistic level. In this study, an MD simulation of nanometric peripheral grinding with two single crystal diamond grains is conducted with a view to determine cutting forces and temperatures as well as surface integrity and subsurface damage in the workpiece. Using this model, favourable cutting conditions for this process will be able to be determined.

Influence of grain wear on material removal behavior during grinding nickel-based superalloy with a single diamond grain

In order to explore the effect of grain wear on material removal behavior during grinding nickel-based superalloy Inconel 718, the grinding experiment with a single diamond grain was carried out. The variations of grain wear, grinding force and force ratio, and pile-up ratio were investigated under the conditions of undeformed chip thickness (UCT) ranging from 0.2 to 1µm. The results show that a critical UCT value, such as 0.3µm, could be determined according to the pile-up ratio and could also be used to quantify the material removal process. The wear behavior of a diamond grain shows four types, such as crescent depression on the rake face, abrasion on the flank face, grain micro-fracture, and grain macro-fracture. Furthermore, these classifications are determined by the dwell time of rubbing, ploughing and cutting at different UCT values applied. The grinding force ratio increases with increasing of the negative rake angle of a diamond grain. In the rubbing and ploughing stages, the material removal efficiency is proportional to the wear width on the rake face. However, in the cutting stage, the material removal efficiency is diminished in the absence process of crescent depression.

A new value for Johnson Cook damage limit criterion in machining with large negative rake angle as basis for understanding of grinding

Grinding is one of the most complex manufacturing processes in industry and understanding its physics is still fairly limited due to the stochastic nature of the process. The physics behind the grinding process can be better understood through thermomechanical analysis of grain-material interactions, enabling the optimization of the process and grinding tool. When simulating the chip formation in machining processes, difficulties arise when the negative rake angle is large, when thermal effects on the tool and workpiece become prominent and when there is the necessity to consider damage within the constitutive equations of the workpiece material. These difficulties become further intensified given small depths of cut as in the case of grinding and the need for three-dimensional models.A coupled thermomechanical dynamic analysis is performed to simulate linear machining experiments effectuated by single diamond grains. Damage is described within a Johnson-Cook model. The damage parameters when machining Ti-6Al-4V are optimized in a three dimensional model and a new concept of applying a damage limit when machining with negative rake angle is suggested. Here, a Fortran subroutine is written to calculate the damage field variable. The simulated cutting forces and temperature in the tool as well as the workpiece are validated. Validation experiments are carried out by single grain machining experiments at a depth of cut of 30 μm and at a linear cutting velocity of 0.8m/s. Numerical challenges, such as chip separation criterion and settings of adaptive remeshing are addressed. Finally, it is shown that with an increase in the cutting edge radius, cutting forces and especially passive forces increase.

Simulation and Experiment Study for Silicon Nitride Cutting with Single Diamond Grain

Simulation and Experiment Study for Silicon Nitride Cutting with Single Diamond Grain

Simulation of Chip Formation Behavior during Single Diamond Grains Grinding by CEL Method

The grain orientation plays a great important role during single grain grinding. Single grain grinding simulation could offer an insight into the material removal behavior. However, grinding simulation with FE methods has problems arising from large deformations at the chip root and negative rake angles of the grain. In this work, a coupled Eulerian-Lagrangian method (CEL) is used to model the grinding behavior of single diamond grain in different orientations. The influence of the grain orientations on the grinding forces, grinding process (sliding, ploughing and cutting) and critical undeformed chip thickness are analyzed. The force ratio shows great accordance with the analytical calculation data. The simulation results show that the chip generates quickly and the special grinding force is relatively small when the diamond particle is in octahedral orientation (111)-(100). The workpiece material flows to the side and front owing to the pressing of cutting crystal face. The swelling of the material is generated beside the abrasive grain. The range and height of swelling are increased gradually and kept invariant after chip formation. The deformation of workpiece material contacting with grain edge is very severe. Therefore the biggest residual stress appears at the grain edge of the groove.

Structure, properties, and applications of ceramic composite produced of nanostructured powders of composition ZrO2 + 3% Y2O3

The results of the investigations of a ceramic composite sintered from ZrO2-based powders produced by ultrasonic spray pyrolysis have been considered. The scratch tests and microcutting with a single diamond grain have been used to evaluate the strength and deformation properties of surface layers of the resultant composite. The possibility to apply these composites in finishing products of non-ferrous metals has been discussed.

Forces and Chip Morphology of Nickel-Based Superalloy Inconel 718 during High Speed Grinding with Single Grain

Single-grain grinding test plays an important part in studying the high speed grinding mechanism of materials. In this paper, a new experimental system for high speed grinding test with single diamond grain is presented. The differences of surface topography and chip morphology of Inconel 718 machined by single diamond grain and single CBN grain were evaluated. The grinding forces and corresponding maximum undeformed chip thickness were measured under different grinding speeds. The chips, characterized by crack and segment band feature like the cutting segmented chips, were collected to study the high speed grinding mechanism of nickel-based superalloy. The results show that the grinding speed has an important effect on the forces and chip formation, partly due to the temperature variation. As the speed increases, the groove surface becomes smoother.

Discrete Element Numerical Analysis and Experimental Study of Forces in Grinding of Granite

Grinding test was carried out to study the grinding of granite with single diamond grain. Forces were measured to investigate the mean normal and tangential forces acted on the diamond grain. The relationship between the forces and either spindle speed or the maximum thickness of the undeformed chip produced by a diamond grain was discussed. The digital models of granite were constructed by discrete element method. Based on the model, two-dimensional and 3-D analysis was carried out to simulate the grinding process with the single diamond grain. The simulation results were compared with experimental data, and some useful conclusions were obtained: the 3-D results agree well with the experiment data at the sameand largeas well as the sameand large; the 3-D and 2-D results are comparable to the experiment data at other machining parameters..

Local bond length variations in boron-doped nanocrystalline diamond measured by spatially resolved electron energy-loss spectroscopy

Variations in local bond length and coordination in boron-doped nanocrystalline diamond (NCD) films have been studied through changes in the fine structure of boron and carbon K-edges in electron energy-loss spectra, acquired in a scanning transmission electron microscope. The presence of high concentrations of B in pristine diamond regions and enrichment of B at defects in single NCD grains is demonstrated. Local bond length variations are evidenced through an energy shift of the carbon 1s → σ* edge at B-rich defective regions within single diamond grains, indicating an expansion of the diamond bond length at sites with local high B content.

Discrete Element Method Simulation of Residual Stresses in Grinding of Granite with Single Diamond Grain

The discrete element model and the model of single diamond grain grinding process of granite were constructed through numerical simulation and calibration of mechanical properties. Based on the models, the grinding processes of granite was dynamically simulated, and the effects of different rank angles, grinding speeds and cutting depths on the distribution of residual stresses as the depth of workpiece were also analyzed. The results show that the residual stress in the workpiece is relatively small after grinding when the tool rank angle lays in a small negative (-200 to 00). Otherwise, when the tool rank angle is too large or too small, there is a significant residual stress. The residual stresses in the workpiece increase with the increase of grinding speed and cutting depth. The residual stress nephogram was accomplished and the generated mechanism of residual stress was also analyzed. The results proved that the discrete element method (DEM) is an effective way to analyze the residual stress

Failure mechanisms and cutting characteristics of brazed single diamond grains

The knowledge about the cutting characteristics and the critical loading of brazed diamonds is essential for a safe and economic application of engineered grinding tools. Scratch tests were performed with single grains. The experiments were conducted with standard polyhedral diamond grains of different sizes, ranging from 300 to 850 μm, brazed with an Ag-Cu-based and a Cu-Sn-based active filler alloy onto a steel pin. Two failure mechanisms were revealed, namely “grain pullout” and “grain fracture”. Large grits mainly fail by grain fracture, whereas the smaller ones were mostly pulled out. This trend is supported by a simple mechanical model. The critical values, i.e. cutting force/scratch area, for grain fracture and grain pullout show a decrease with bigger grit size. Scratches are also analysed in terms of cutting characteristics. The dependency of the cutting and the normal force on the scratch area can be described by a power law with powers ranging between about 0.2 and 0.7, respectively. The measured cutting forces strongly depend on the rake angle, which was tested for −19.5° and −35.3°.