Single Diamond Grit Research Articles

Study on the material removal mechanism and the exit breakage of ultrasonic vibration-assisted grinding for microcrystalline glass

With the aim of solving problems such as exit breakage and surface microcracks during microcrystalline glass machining, an ellipsoidal erosion model is established by analyzing the motion trajectory and characteristics of single diamond grit in ultrasonic vibration-assisted grinding (UVAG), and the material removal volume of single diamond grit particles is obtained. A simulation model of UVAG of microcrystalline glass is established by the finite element method. The effect of process parameters such as rotational speed, grinding depth, feed rate on grinding force and workpiece edge stress has been investigated. The experiment of UVAG for microcrystalline glass is performed on a five-axis CNC machine with the same process parameters, and the surface morphology, surface roughness, and exit breakage sizes of microcrystalline glass are observed. The results show that with the increase in grinding depth, the average grinding force between the tool and the workpiece increases, and the proportion of material removal in a brittle fracture increases. As the rotational speed increases, the grinding force between the tool and the workpiece gradually decreases and results in an improvement in the surface quality of the workpiece. As the feed rate increases, the surface roughness increases by 16.76%, the width of the edge breakage increases by 109.19%, and the thickness of the edge breakage increases by 104.49%.

Single diamond grit scratching of unidirectional Cf/SiC composite: Mechanical responses and fracture mechanism

Cf/SiC composite is a typical heterogeneous brittle composite material, its precision machining has always been affected by the complicated removal mechanism. This paper conducted a single diamond grit scratching experiment on the unidirectional Cf/SiC composite to investigate the material’s mechanical response under different loads and scratching depths. The scratching force and acoustic emission signals were measured to reveal the removal characteristics. The scratching removal behavior of SiC matrix and carbon fibers in the two-phase component of unidirectional Cf/SiC composites was analyzed based on the fracture size and fiber fracture morphology. The results show that the parallel scratching process could produce a better strength resistance with mild rupture features of fiber extrusion fracture and shear removal. While the perpendicular scratching process is generally resulting in crack propagation along the fiber direction with interface failure and bending fracture failure along the moving direction.

Investigation of material removal mechanisms of laser-structured Si3N4 via single diamond grit scratching

Grinding hard-brittle materials like silicon nitride is faced with some challenges, including sub-surface damage, high tool wear, and low grinding efficiency. Ultrashort-pulse laser structuring of hard materials prior to the grinding process significantly reduces the cutting forces and temperature and increases the achievable material removal rate of the grinding process. These effects are partially due to controllable induced damages into the subsurface of the structured workpieces. However, the impacts of this surface structuring technique on the material removal mechanism of advanced ceramics, such as Si3N4, are not yet thoroughly investigated. The dominant material removal mechanism in grinding hard and brittle materials, such as silicon nitride (Si3N4), defines the surface integrity of the workpiece. For the first time, in-depth single diamond grit scratching experiments are carried out to investigate the changes in the dominant material removal mechanisms at various chip thicknesses by laser structuring of Si3N4. Two different structuring ratios (25% and 50%) were generated on sample surfaces by a femtosecond laser. The effects of laser structuring on material removal mechanism, pile-up area, area and width of the groove, grit path, normal and tangential forces, and specific cutting energy have been investigated. The results indicate that laser structuring considerably affects the reduction of depth ratio, normal (up to 89%) and tangential (up to 82%) forces, and specific cutting energy. The specific cutting energy of laser-structured Si3N4 workpieces converged to about 5 J/mm3, much lower than that of unstructured workpieces.

Experiment and Smooth Particle Hydrodynamics Simulation for the Wear Characteristics of Single Diamond Grit Scratching on Sapphire

Abrasive single crystal diamond (SCD) grit is widely used in the machining process of sapphire. The wear of SCD grit has a significant influence on the surface quality of sapphire. In this paper, smooth particle hydrodynamics (SPH) method is employed to reveal the wear mechanism of SCD grit with Steinberg constitutive equation and Grüneisen state equation. The wear morphology, wear volume and scratching forces are measured and analyzed by combination of SPH simulations and experiments. The results show that the scratching forces fluctuate in a certain range and decrease with the increasing of workpiece material removal volume. Different degrees of cleavage and fracture appear in the front and rear of SCD grit. The shear stress and extrusion stress are the main stresses of SCD grit during the scratching process. The wear progress and wear form are mainly determined by the stress state. Different stress state leads to different wear progress of the SCD grit. The SPH method is able to reflect and illustrate the wear characteristics of SCD grit scratching on sapphire.

Cutting Force Prediction Models by FEA and RSM When Machining X56 Steel with Single Diamond Grit.

In the field of underwater emergency maintenance, submarine pipeline cutting is generally performed by a diamond wire saw. The process, in essence, involves diamond grits distributed on the surface of the beads cutting X56 pipeline steel bit by bit at high speed. To find the effect of the different parameters (cutting speed, coefficient of friction and depth of cut) on cutting force, the finite element (FEA) method and response surface method (RSM) were adopted to obtain cutting force prediction models. The former was based on 64 simulations; the latter was designed according to DoE (Design of Experiments). Confirmation experiments were executed to validate the regression models. The results indicate that most of the prediction errors were within 10%, which were acceptable in engineering. Based on variance analyses of the RSM models, it could be concluded that the depth of the cut played the most important role in determining the cutting force and coefficient the of friction was less influential. Despite making little direct contribution to the cutting force, the cutting speed is not supposed to be high for reducing the coefficient of friction. The cutting force models are instructive in manufacturing the diamond beads by determining the protrusion height of the diamond grits and the future planning of the cutting parameters.

Wear characteristics of single diamond grit scratching on sapphire with different contact forms

Abrasive single crystal diamond (SCD) is widely used in the machining process of sapphire. The wear characteristics of SCD grit have a significant influence on the tool wear and machining precision of sapphire. However, the influence of grit-workpiece contact form on the wear characteristics of SCD grit scratching on sapphire is not clear. In this paper, the wear characteristics of single SCD grit scratching on sapphire with three different grit-workpiece contact forms (point/line/face) are systematically investigated. Wear volume, wear morphology and scratching force are measured and tracked. Stress models of different contact forms are further established and analyzed. The results show that the SCD grit with face contact form can remove the most sapphire volume and it is the most wear-resistant. The SCD grit with point contact form can remove the fewest sapphire volume and it is the most prone to cleavage and fracture. Smaller stress results in more wear-resistant of the SCD grit during scratching on sapphire. Contact form is closely related to the stress state and has an important influence on the wear characteristics of SCD grit. The investigation results could provide a theoretical basis for the fabrication of abrasive tools.

Influence of contact form on mechanical wear characteristics of single diamond scratching on Ta12W

Purpose Mechanical wear is the main wear form of abrasive single crystal diamond (SCD) grit. The mechanical wear of SCD grit has a significant influence on the tool life and machining quality. This paper aims to investigate the influence of grit–workpiece contact form on the mechanical wear characteristics of SCD grit. Design/methodology/approach Three different grit–workpiece contact forms, which involved point/line/face contact forms, are investigated to reveal the wear mechanism of SCD grit scratching on Ta12W. The wear morphology, wear volume and scratching forces are measured, and the stress models of different contact forms are analyzed. Findings The results show that mechanical wear mainly occurs in the grit–workpiece contact area and increases gradually from contact area to entire SCD grit. The scratching forces vary with the mechanical wear progress of SCD grits. The SCD grit with point contact form is the most prone to produce wear. The SCD grit with face contact form can remove more material volume than the other two SCD grits, and it is the most wear resistant. The stress state is closely related with the mechanical wear of SCD grit. The contact form has a significant influence on the mechanical wear of SCD grit. Originality/value The results of this study can provide a theoretical basis for the fabrication of abrasive tools.

Vibration Characteristics of Force Signal for Single Diamond Grit Scratching Process

Scratching force is a significant factor to evaluate the characteristics of single diamond grit scratching process. In this paper, experimental study was carried out to investigate the vibration characteristics of force signals during the scratching process. A precise multicomponent dynamometer is employed in the force measurement during a single diamond grit scratching on pure copper. The frequencies of the vibration section of force signals with different scratching parameters are calculated and analyzed. The influence of force signal vibration on the measuring accuracy of dynamometer is systematically analyzed further. The results show that higher scratching speed and larger scratching depth lead to larger vibration amplitudes of the force signals. Strong impact on the quartz piezoelectric crystal of dynamometer, which is produced indirectly by single diamond grit scratching process, leads to the vibration of scratching force signal. The first semi-sinusoidal force signal is the actual scratching force. The vibration of the scratching force signal has little effect on the measuring accuracy of the dynamometer.

An investigation on the dressing contact behavior between vitrified bonded CBN abrasive wheel and diamond grit dresser

Abstract In order to better understand the dressing behavior, an investigation was carried out to detect the contact zone between vitrified bonded cubic boron nitride (V-CBN) abrasive wheel and diamond grit dresser. The grinding experiment of single diamond grit dresser on V-CBN abrasive segment was designed and conducted to approach the actual dressing process. The moving trajectory during dressing was calculated and discussed. Acoustic emission (AE) signals were applied to evaluate the wear progression of V-CBN abrasive wheel. Results obtained discovered that the different trajectory length would result in different wear patterns of diamond grit dresser and vitrified bond of V-CBN abrasive wheel. With the increase of wear ratio, the AE root-mean-square (RMS) voltages also had an increasing trend during dressing V-CBN wheel. Furthermore, a shorter dressing trajectory length produced a lower and more stable surface roughness, a lower tool radial wear and a higher grinding ratio in the grinding experiment of Inconel 718 nickel-based superalloy.

Mechanism of the scratching of monocrystalline silicon carbide with a diamond grit at different wear stages

An investigation was conducted to explore the mechanisms of the scratching of monocrystalline silicon carbide with a single diamond grit. The scratching was repeated on a silicon carbide workpiece to generate different wear shapes of the diamond grit. The forces were recorded during each scratching and the wear of the diamond grit together with the silicon carbide morphologies was monitored at a fixed interval. Based on the different diamond wear shapes determined through scratching experiments, a smoothed particle hydrodynamics method was used to simulate the scratching process. In addition to the items monitored in the experiments, the simulation was also used to analyze the change of subsurface damages on silicon carbide and to predict the mechanisms of diamond damage. It is shown that double-edged abrasive grits might lead to a better silicon carbide surface quality in scratching. The simulation results indicate that the maximum equivalent stress distribution might be used to predict the damage of the diamond grits during scratching. The findings of this article will be of benefit to the optimal selection of machining parameters and the optimal design of diamond tools for abrasive machining of monocrystalline silicon carbide.

Evolution of chemo-mechanical effects during single grit diamond scratching of monocrystalline silicon in the presence of potassium hydroxide

Efficiency and workability of silicon wafers for various applications depend on theirs surface integrity and damage free structures. Productivity of mechanical processing on silicon wafers is always limited by occurrence of cracks and brittle mode material removal at high depth of cut. This study presents a method of using controlled concentration of KOH solution during diamond micro-scratching of silicon and investigates the chemo-mechanical effects of KOH solution with respect to cutting speed. To establish the chemo-mechanical theory of cutting, responses of physical and material properties of silicon in presence of KOH solution are captured and correlated with mechanical responses during micro-scratching. Zeta potential and nanohardness are greatly reduced in KOH environment. Ductile mode is found to be extended by using 10 wt% KOH. Crack/chipping length is observed to be first increasing with increase in cutting speed at low range (0.6–20 mm/min) and then decreasing on further increase in the cutting speed (20–200 mm/min). Stability in cutting force signature and behavior of material flow along the scratch length is also found to be improved by using KOH. Adhesive wear and abrasive wear are found to be the main forms of single grit wear, which is significantly reduced in the presence of KOH. The experimental results on different mechanical and physical phenomena in this study are of great importance for establishing the theoretical insight into material removal behavior and selection of machining parameters during micro-machining of silicon wafer.

Particle Removal Mechanism of High Volume Fraction SiCp/Al Composites by Single Diamond Grit Tool

Particle removal mechanism was presented during machining particle SiC/Al composites with diamond grinding tool. The relevant removal modes and their mechanisms were discussed considering the impact and squeezing effect of diamond grit on the SiC particle. The experimental results show that the aluminum matrix has larger plastic deformation, so the aluminum mixed with the surplus SiC particles is cut from the surface. The SiC particles can be removed in multiple ways, such as broken/fractured, micro cracks, shearing and pulled out, etc. More particles removed by shearing, and less particles removed by fractured during material removal progress can produce a better machined surface.

Predicting subsurface damage in silicon nitride ceramics subjected to rotary ultrasonic assisted face grinding

Silicon nitride is an advanced ceramic used in high performance applications. One of the main problems in machining of brittle materials such as silicon nitride is subsurface damage (SSD). On the other hand, rotary ultrasonic assisted face grinding (RUAFG) is considered as state of the art machining process for brittle and hard to machining materials such as ceramics and optical glasses. In this research, a new study on SSD generation in RUAFG by establishing both ductile deformation and brittle fracture conducted. To achieve this goal, initially single diamond grit cutting force based on Vickers hardness correlation and indentation fracture mechanics established and placed in crack propagation formulas to anticipate SSD. Verification tests performed and average 8% error detected. Moreover, RUAFG depicted up to 30% SSD reduction in comparing to conventional face grinding (CFG). Besides, scanning electron microscope utilized to investigate cracks morphology.

The influence of crystallographic orientation on wear characteristics during single abrasive diamond grit scratching on sapphire

PurposeThe wear of an abrasive single-crystal diamond (SCD) grit affects the machining quality of the sapphire wafer. This paper aims to investigate the influence of crystallographic orientation on the wear characteristics of SCD grit scratching on sapphire.Design/methodology/approachThe wear characteristics of two SCD grits (SCD100 and SCD111) with different crystallographic orientations were systematically investigated. The wear mechanism involved in the scratching process was explored. The wear morphology, scratching forces and friction coefficient during the scratching process were measured and analyzed.FindingsThe experiment results show that the wear progress of the two SCD grits is obviously different. The wear resistance of SCD111 grit is greater than that of SCD100 grit in normal wear stage. However, the SCD100 grit could remove more sapphire material than SCD111 grit. The SCD grits mainly sustain extrusion stress and shear stress during scratching on sapphire. The crystallographic orientation of SCD grits plays a significant role in the wear progress during scratching on sapphire.Originality/valueThe results of the experimental studies could provide a theoretical foundation for improving the fabrication of abrasive diamond tools.

Simulation and Experimental Study on Surface Formation Mechanism in Machining of SiCp/Al Composites

To intuitively reveal the surface formation mechanism in machining of SiCp/Al composites, in this paper the removal mode of reinforced particle and aluminum matrix, and their influence on surface formation mechanism were analyzed by single diamond grit cutting simulation and single diamond grit scratch experiment. Simulation and experiment results show that when the depth of cut is small, the scratched surface of the workpiece is relatively smooth; however, there are also irregular pits on the machined surface. When increasing the depth of cut, there are many obvious laminar structures on the scratched surface, and the surface appearance becomes coarser. When the cutting speed is small, the squeezing action of abrasive grit on SiC particles plays a dominant role in the extrusion of SiC particles. When increasing the cutting speed, SiC particles also occur broken or fractured; but the machined surface becomes smooth. When machining SiCp/Al composites, the SiC may happen in such removal ways, such as fracture, debonding, broken, sheared, pulled into and pulled out, etc. By means of reasonably developing micro cutting finite element simulation model of SiCp/Al composites could be used to analyze the surface formation process and particle removal way in different machining conditions.

Feature learning method of acoustic emission signal during single-grit scratching on BK7 in brittle regime

Acoustic emission (AE) signal is released from a material as it undergoes deformation and fracture processes. AE signal provides enough information for monitoring of the interaction between tool and material. AE RMS, AE count rates, and frequency characteristics are always employed in AE-based monitoring techniques. Monitoring sensitivity is not satisfied because information implies in AE signal is lost or weaken to some extent for the present monitoring parameters. When a hard-brittle material is removed in brittle regime, burst-type AE (b-AE) associated with crack and chip is predominant compared with low-amplitude continuous-type AE. It will be more objective and physically meaningful if b-AE event is taken as a unit to be monitored. This paper is dedicated to the method of monitoring b-AE event in AE signal. Ignoring background noise, an AE signal can be looked as a convolution of b-AE events and corresponding coefficients. b-AE events correspond to brittle transient behaviors and include information of fracture mechanism. Coefficients represent intensity and location of crack and chip during removal processes. The two elements of the convolution contain different aspects of signal feature. Considering randomness of AE signals, the convolution form will be realized by self-learning from training data set of AE signals. Dictionary-learning algorithm for decaying oscillation modes of b-AE and sparse representation procedure of an AE signal are detailed in this paper based on the convex optimization theory. AE signals in brittle regime are acquired from tests of single diamond grit scratching on BK7. Simulation and experimental results verify the correctness of the feature learning method. According to the method proposed in this paper, b-AE can be objectively monitored without the interference of varying machining parameters.

The Material Removal Mechanism of Monocrystal SiC Scratching by Single Diamond Grit with Different Tip Radius

The Material Removal Mechanism of Monocrystal SiC Scratching by Single Diamond Grit with Different Tip Radius

Experimental study on the single grit interaction behaviour and brittle–ductile transition of grinding with a diamond micro-grinding tool

This study presents new information on single grit interaction behaviour and its brittle–ductile transition in micro-grinding single crystal silicon using a single grit diamond tool. A model to describe the energy interaction between the cutting behaviour of a single grit and the workpiece in micro-grinding is established based on the single grit geometry model, which was indicated in Fig. 1a, the critical condition of the volume of material removed and the conservation of energy. The tip angle of the single-point diamond tool has been considered. To reveal the material removal mechanism of micro-grinding, a series of scratching experiments, which conducted with a low cutting speed (0.036 to 0.6 m/s), have been performed in this study. The fractures of the micro-grooves machined using single-point diamond tools have been examined by a microscope and a surface profilometer, thus revealing different processing modes (brittle and ductile). The variation curves of the fracture length c have been presented on the condition of different tool tip angles θ (60° and 120°). It is found that the fracture size of grooves machined by a grit with a blunt angle is comparatively larger than that of a grit with a sharp angle for the same scratching parameters. The scratching speed v and penetration depth p0 have a direct effect on the fracture length c, which increases obviously with the rising of v and p0. The critical condition has been investigated based on the experimental results; the blunt grit (with a larger tip angle: θ = 120°) and the sharp grit (with a smaller tip angle: θ = 60°) have different brittle–ductile transitions and different critical cutting depths, which are 334 nm (θ = 60°) and 607 nm (θ = 120°), respectively. The effects of the scratching speed v are investigated. The brittle–ductile transitions of the different scratching speeds have been compared. The relationship between the fracture length c and the volume of material removed in unit time V has been discussed; V is an important measuring constant for the fracture formation and critical ductile cutting condition. This study reveals the mechanism of the single grit interaction in micro-grinding with an ultra-small grinding tool and provides theoretical and experimental validation for ductile micro-grinding of single crystal silicon.

SPH and FE coupled 3D simulation of monocrystal SiC scratching by single diamond grit

An investigation was carried out to study the material removal modes in single diamond grinding of monocrystal SiC. In order to reveal the influences of diamond shapes on the removal regions of SiC, six diamonds of different shapes were used for scratching. Three shapes - cube, rectangular pyramid, and cubic octahedral were chosen to simulate ideal diamond shapes, whereas cone, ball, and triangular pyramid were used to express wear diamond shapes. Through combining two different simulation methods - FEM and SPH, the material removal process was simulated respectively for the grinding of SiC with single diamond grit of different shapes. A grinding test was also carried out for the diamond of cone shape in order to check the validity of simulation. It was shown that the simulation results agree basically well with the corresponding experimental results. Therefore, the influences of the different diamond shapes on the removal modes of SiC were analyzed and discussed mainly based on the simulation. The scratching length and the ratio of width to depth of the groove generated in scratching were used as the parameters to discuss the influence of diamond shapes. The forces in grinding with different diamond grits were also analyzed.

Precision grinding of BK7 glasses using conditioned coarse-grained diamond wheel

For precision machining of large-sized optical elements, more attention is being paid to the ground surface quality, the processing costs and the machining efficiency. Besides the commonly used fine-grained diamond wheels, the coarse-grained diamond wheel is now also expected to be a promising tool with lower wheel wear rate and higher efficiency. However, conditioning of this kind of wheel is always a difficult issue to deal with. In this article, the efficient conditioning of the electroplated diamond wheel and precision grinding of BK7 glasses were investigated. Through the single diamond grit wear simulation, D3 steel was chosen as the conditioning tool. The worn diamond abrasive morphology and Raman spectroscopy analysis revealed the conditioning mechanism. Under different conditioning stages, the BK7 glasses were correspondingly ground exhibiting different surface integrity and grinding forces. The experimental results indicated that the wheel’s run-out error could be rapidly reduced to 5.8 µm because of the blend graphitization, passivation, diffusion and microcrushing of the diamond abrasives. The precision ground BK7 glasses could achieve a surface roughness of Ra < 20 nm and a subsurface crack depth around 2 µm, illustrating that the electroplated coarse-grained diamond wheel could be an alternative for precision grinding large-sized optical elements in terms of high accuracy, cost-effectiveness and high efficiency.