Single Abrasive Grain Research Articles

Mathematical modelling for prediction of surface roughness in Pneumatically Configurable Polishing process

Pneumatically configurable polishing is a superfinishing process which can generate nano-meter level surface finish on workpiece surfaces. It utilizes pneumatic pressure for controlled inflation of a cup shaped elastomeric membrane which has a stretchable polishing film fixed to its bottom surface. A slurry containing abrasive particles, thoroughly mixed in a carrier medium is applied on the workpiece surface. When the inflated membrane is brought in contact with a rigid surface, it adheres to the profile of the workpiece being polished, which ensures the entrapment of abrasive particles between the membrane and the surface to be polished. The abrasive slurry is replenished at a fixed interval during the process. This flexibility of the membranous tool enables it to finish complex 3D surface profiles. The final surface characteristics generated are a function of process parameters as well as material properties. This study proposes a mathematical model for the prediction of surface roughness as a function of workpiece properties such as hardness, tool characteristics, and significant process parameters such as working gap, applied pneumatic pressure, spindle speed, concentration of abrasive slurry, abrasive mesh size and dwell time. The model uses Hertz contact theory of elastic surfaces for modelling of contact pressure between the inflated membranous tool and the workpiece surface. A single abrasive particle is modelled for its influence on the workpiece surface as a function of its radial distance from the tool centre. This model is used to estimate the combined effect of all the active abrasive particles, participating in the finishing process. The final penetration depth obtained at different radial coordinates is used to estimate the theoretical surface roughness on the workpiece surface. The normal, shear and friction forces acting on a single abrasive grain have been modelled to determine the process capability during material removal. The model is finally validated by performing experiments under different conditions of process parameters. The experimental findings and theoretical results are found to be within an error range of −16.5%–11.8%.

Wear mechanisms of abrasive wheel for rail facing grinding

Facing grinding by abrasive wheel is the most widely used method to maintain the rails. The wear of abrasive wheel is inevitable and influences the grinding performance significantly. Therefore, a deep understanding on the wear mechanisms of abrasive wheel is beneficial for the development of grinding wheels and optimization of grinding processes. In the present study, rail grinding experiments were conducted using whole abrasive wheels and a single abrasive grain. The wear mechanisms of abrasive wheel were revealed, including the attrition wear, fracture and pulling-out of abrasive grains, material adhesion, clogging, and chemical wear. With the degradation of abrasive grain, the attrition wear, micro-fracture, macro-fracture and pulling-out of grain successively became the primary wear mode as the function of service time. With the primary wear state changing from attrition wear to grain fracture and grain pulling-out, the grinding efficiency was improved, but the grinding quality was decreased. The grinding wheel in the wear state of grain fracture had the optimum grinding performance.

Analysis of the high-efficiency and low-damage abrasive processing mechanism for SiC based on the SPH simulation of single-grain indentation and scratching

During the wafer fabrication procedure, abrasive machining occupies a large proportion in time and economic cost, mainly including grinding, lapping, and polishing. The third-generation semiconductor materials, represented by SiC, have the properties of high hardness, large brittleness, and strong chemical inertness, which make abrasive machining more challenging. To improve the machining efficiency and quality, this paper applied the smoothed particle hydrodynamics (SPH) method to simulate the machining behavior of single abrasive grain for SiC wafer. The micro-mechanical mechanisms of the main influencing parameters, such as velocity, depth, and angle, were studied in abrasive machining for SiC wafer. First, it is proved that using SPH coupled with a finite element to study the mechanical effects of abrasive machining for SiC wafer is a feasible and useful method. Then, the explanations for the beneficial effects of ultrasonic vibration-assisted machining, high-speed machining, and other abrasive machining are provided through the analysis of the simulated results. In addition, the optimization basis for parameters such as scratching velocity, scratching depth, and ultrasonic vibration frequency is obtained. This research provides a good insight into implying the micro-mechanical mechanisms of abrasive machining and achieving the optimization for the abrasive machining of hard-brittle wafer materials, which help avoid the shortcomings of experimental research and produce economic benefits.

Experimental and numerical characterization of abrasive belt wear and debris formation during dry grinding of nickel-based superalloys with diamond abrasive belts

Nickel-based superalloys are the constituent materials of critical components of aero engines. Abrasive belt grinding is an effective method for the precision machining of such difficult-to-machine materials. However, the wear of the abrasive belt greatly affects the quality and integrity of the machined surface. In this study, a physical simulator of abrasive belt grinding was used to carry out diamond belt grinding experiments. The wear behavior of abrasive belts and the shape of debris at different temperatures were mainly investigated. In addition, a three-dimensional finite element model of single abrasive grain grinding was established to analyze the formation of debris. The variations of abrasive belt wear and debris morphology with temperature within the experimental temperature range were obtained. There are four types of wear behavior of diamond abrasive belts: grain flattening, grain shed, dependency blockage, and adhesion blockage. The self-sharpening of the abrasive belt plays an important role in improving the quality of the machined surface. The finite element model accurately simulates the shape of debris at different temperatures and the shape of debris changes apparently with temperature. The critical temperature for the formation of good surface quality is obtained. The research results provide guidance for the selection of abrasive belt grinding process parameters.

Study on the cutting mechanism of randomly deflected truncated cone shape single abrasive grain

Based on the random distribution characteristic of abrasive grains for the grinding wheel circumferential surface during the manufacturing process, considering the grinding parameters and deflection parameters comprehensively, a randomly deflected truncated cone shape single abrasive grain cutting simulation model was established. Then, studying its cutting mechanism, i.e., the trajectory length value by numerical method and formula method was compared, the consequence indicates that the error is extremely small; this demonstrates the accuracy of the numerical method. The calculation and analysis of the workpiece cutting surface topography and the undeformed chip shape were carried out; it shows that the cutting surface topography and the undeformed chip shape are coincident. And the calculation results of the model were compared to verify. The influence laws of each grinding process parameter on the material removal volume (MRV) and material removal rate (MRR) were investigated; the results display that the grinding method affects the changing pattern of MRV and MRR; when the grinding method was up-grinding, a high wheel speed or a small wheel diameter is able to enhance the MRR; the MRV and MRR are increments with the increasing workpiece feed speed or abrasive grain cutting depth; and the MRV and MRR decrease with the raising of the absolute value of single abrasive grain deflection angle. The situation is a similar or opposite trend in down grinding. This work can provide a theoretical reference for the selection and optimization of parameters and further lay a foundation for the research in the grinding mechanism of the grinding wheel.

Simulation of internal material loads caused by simultaneous contacts in grinding with predominantly mechanical impact

In grinding with predominantly mechanical impact, each abrasive grain contributes to the resulting surface integrity of the workpiece. The numerical modeling approach presented in this work is capable of calculating internal material loads, e.g. stresses and strains during the process for simultaneous abrasive grain engagements using the CEL-method. Different abrasive grain offsets and depths of cut were investigated. Incremental changes of the material modification resulting from the first abrasive grain engagement on the following ones were determined which lead to an overall modification. It can be seen that each single abrasive grain engagement contributes to the overall surface integrity of the workpiece.

Cortical bone grinding mechanism modeling and experimental studyfor damage minimization in craniotomy.

Craniotomy, as a part of neurosurgery, implies a safe opening of the skull with mechanical equipment. Grinding is a traditional machining method that can accurately and efficiently remove bone tissue. Aiming at low-damage and high-efficiency bone grinding, this study analyzed the kinematic law of a single abrasive grain during the grinding process. The theoretical model of grinding force was established based on the calculation of specific energy and friction force. The grinding test platform was set up, and the full factorial experimental design was performed to link the grinding force evolution with different processing parameters. The experimental results obtained on porcine femurs validated the model predictions where the grinding force grew with feed speed and grinding depth; it exhibited a decreasing trend with rotation speed, followed by increasing one.

Numerical and Experimental Research on the Brushing Aluminium Alloy Mechanism Using an Abrasive Filament Brush.

Abrasive filament brushes have been widely used in surface processes for a wide range of applications, including blending, edge-radiusing, and polishing. However, the associated brush mechanics of material removal is still not clear. In order to analyze the brush grinding of aluminium alloy, this paper constructed a kinematic model of a single filament, simulated the scratch process of a single abrasive grain, and investigated the brush force and material removal based on the finite element approach. The simulated result shows that the brush grinding can be changed from elastic–plastic deformation to chip formation when increasing the brush speed to 1000 r/min. The normal and tangential forces increase linearly and quadratically with the increase in the rotation speed (500–5000 r/min), respectively, and increase linearly with the increase in the penetration depth (0.1–1 mm), which is consistent with the experiment results. In addition, the amount of material removal initially increases with the increase in penetration depth, and then decreases. This paper provides a new approach to understanding the process of material removal and is helpful for the selection of reasonable brush parameters in the intelligent grinding control application.

Modelling and analysis of the effect of nonlinear time-varying contact deformation on flexible precision grinding process

Belt grinding is gradually considered to be an effective method for precision machining those aeronautical parts with weak rigidity and complex surface. However, the characteristic of flexible grinding makes it difficult to precisely control the machining process and hinders its further development. In this paper, a series of detailed numerical studies are conducted to study the effect of complex contact deformation on the flexible precision grinding operation of titanium alloy. The flexible process of belt grinding was simulated numerically, and the spatial trajectory equation of abrasive grains in nonlinear time-varying contact state was obtained. Subsequently, the finite element simulation modelling and analysis of a single abrasive grain cutting titanium alloy workpiece under three different boundary conditions (no contact deformation, sinusoidal transformation contact deformation, nonlinear time-varying contact deformation) were performed. The characteristics of grinding morphology and the variation trends of grinding force obtained by simulation were almost consistent with the results of scratch experiments. On this basis, a series of orthogonal simulation studies were conducted to obtain the optimal processing parameters of belt grinding, in consideration of the changes in the spatial positions of abrasive grains caused by the time-varying contact deformation. The above research provides a theoretical framework for investigating the effect of nonlinear time-varying contact deformation, which is of great significance to reveal the mechanism of belt flexible grinding and expand its application in precision machining of aviation parts.

Повышение режущей способности шлифовального круга при обработке заготовок из пластичных сталей наложением ультразвуковых колебаний на заготовку

The study aimed to identify the relations between the sticking intensity and ultrasonic vibrations (UV) used for processing and evaluate the wheels’ performance when grinding ductile materials blank parts. The authors carried out the numerical simulation of local temperatures and the 3H3M3F steel workpiece temperature when grinding by ultrasonic activation. The study determined that the application of ultrasonic vibrations with the amplitude of 3 µm causes the decrease in local temperatures by 13…40 %, and in blank part temperature – up to 20 %. The calculation identified that the activation of ultrasonic vibrations with the amplitude of 3 µm causes the decrease in the glazing coefficient by 33 % for cutting grain and by 7 % for deforming grain. When increasing the longitudinal feed rate or the grinding depth, the glazing coefficient increases to a lesser degree when using the ultrasonic vibration than in the case without ultrasonic activation. The authors carried out the numerical simulation of local temperatures when scratching the 3H3M3F steel specimens by single abrasive grains with ultrasonic activation. The sticking deformation and the stresses resulted from this deformation and affecting the junction points of sticking with grains with and without ultrasonic vibrations application are calculated. The experimental research included the micro-cutting of specimens with single abrasive grains. The experiments identified that the abrasive grains wear out and glaze to a lesser degree when micro-cutting a workpiece with ultrasonic vibrations activation. The lowering of the intensity of sticking of the workpiece material particles to the abrasive grains due to the adhesion causes the decrease in the glazing coefficient when using ultrasonic activation. The study considered the possibility to enhance the efficiency of flat grinding through the use of the energy of ultrasonic vibrations applied to a blank part in the direction with the grinding wheel axis. A workpiece fixed in the device between the vibration transducer and the support is one of the components of a vibration system. The authors performed the experiment when grinding 3H3M3F and 12H18N10T steel workpieces with the wheel face. When grinding with ultrasonic vibrations, the grinding coefficient increases up to 70 %, and the redress life increases twice or thrice.

Simulation of internal material loads caused by multiple contacts in grinding with predominantly mechanical impact

Grinding processes and their mechanical impact on the workpiece material are mainly characterized by multiple contacts between the workpiece surface and the single abrasive grains of the grinding wheel. The numerical modeling approach presented in this work is capable of calculating internal material loads, e.g., stresses and strains during machining, for multiple contacts of abrasive grains utilizing the CEL-method. Different numbers of repeated consecutive contacts as well as varying machining parameters such as depth of cut ae and cutting speed vc are applied. The effect of different grain shapes is investigated by utilizing spherical, flat and pyramidal grains with comparable sizes. Thereby, the surface contact area is varied. The results reveal an effect of grain shape and depth of cut as well as a saturation effect of the corresponding material modifications, e.g., shown in the source stress and plastic strain depth curves, which is reached after a certain number of contacts with specific impact intensities on the workpiece surface including the particular material removal. The approach can be applied to show principle correlations between internal material loads and material modifications in grinding processes focusing on the mechanical impact on the surface integrity.

Analysis and Modeling of the Micro-Cutting Process of Ti-6Al-4V Titanium Alloy with Single Abrasive Grain

Modeling of material displacements in the microcutting zone is complex due to the number and interdependence of factors affecting the results of the process. An important problem in the modeling process is the selection of the constitutive model and its parameters, which will correctly describe the properties of the material under the conditions of triaxial compression, which is characteristic for the areas of the contact zone of the blade and the processed material in abrasive machining processes. The aim of the work was to develop computer models (with the use of the finite element method) of the microcutting process with a single abrasive grain, which were verified with the results of experimental tests. The paper presents the methodology of modeling the processes of microcutting with abrasive grains, whose geometrical models were created based on optical scanning methods. Observations of the microcutting process were carried out with the use of a high-speed camera and an optical profilometer. This enabled a detailed observation of the chip formation process, as well as the analysis of the surface topography of microcutting traces. The results presented in the paper indicate the convergence of the results of the numerical and experimental simulations with regard to the geometric parameters describing the scratches formed in the microcutting process and the compliance of the chip-forming process. Thus, the correctness of the selection of the constitutive model (Johnson Cook equation) and its parameters was demonstrated, as well as the correctness of the applied methodology for creating a geometric model that allowed for a reflection of the geometrical parameters of the abrasive grains that coincided with the real objects, thanks to which it was possible to reflect in detail the phenomena occurring in the vicinity of the abrasive grain tip.

Grinding mechanism of high-temperature nickel-based alloy using FEM-FBM technique

The models, simulation, and validation were presented during the last decade over various moving particle investigations with thermal convection and disclosed the challenges as well. The present work provides the simulation and validation of the grinding mechanism of high-temperature nickel-based alloy with single abrasive grain. Several nickel-based alloys provide better performances for temperatures above 1000 °C and those suited for extremely difficult conditions as well. In this study, we simulate and analyze the grinding mechanism of high-temperature nickel-based alloy using single abrasive grain cutting. Using a grinding, it introduces variation in friction coefficient as per the variations of the grinding parameters. The grinding force system of single abrasive grain is designed and simulated to investigate high-temperature nickel-based alloy using various grinding conditions like particle settling modes such as rolling, horizontal, and vertical with thermal convection. The multi-grid finite element fictitious boundary method (FEM-FBM) is used to simulate and study the grinding mechanism of high-temperature nickel-based alloy in terms of fluid-particle sedimentations. The material used for this simulation study is Inconel 718 alloy. The simulation results investigate the various grinding force conditions of high-temperature nickel-based 718 alloys using the dimensional physical parameters and numbers such as Prandtl number and Grashof number. Finally, the simulation results were validated with a conventional FEM model.

MODELING OF THE GRINDING PROCESS BY MICRO-CUTTING SINGLE ABRASIVE GRAINS. PART 1. DETERMINATION OF THE STRENGTH OF ABRASIVE GRAINS

Main performance indicators of grinding wheels are the strength and wear resistance of abrasive grains. The description of the installation for studying the process of micro-cutting of various materials with single abrasive grains, which allows you to approximate the working conditions of a single abrasive grain to the conditions of real grinding in a wide range of cutting speeds. The effect of the cutting speed on the maximum cut thickness maintained by the grain vertexes without their destruction is shown. The influence of physical and mechanical properties of the workpiece material and the abrasive tool material, together with technological factors, on the micro-cutting process is considered.

Cutting ability of abrasive grains in the processing of billets of plastic materials with the applying of ultrasonic vibrations

The research was carried out in order to identify the relationship between the intensity of sticking of the workpiece material particles on the abrasive grains (AZ) of the grinding wheel with the physical and mechanical properties of the grains and ultrasonic vibrations (UZK) used in the processing process. Numerical simulation of local temperatures during micro-cutting (scratching) of samples made of 3X3M3F steel with abrasive grains made of various materials, including with the imposition of a narrow band. The deformation of the bulk and the stresses resulting from this deformation acting on the connection of the bulk with grains from materials with different coefficients of linear expansion are calculated. It was found that with increasing difference in the coefficients of linear expansion of the materials of the billet and AZ, the stresses that contribute to the separation of the adhesive from the surface of the AZ increase. In the course of experimental studies, samples were micro-cut with single abrasive grains. We controlled the salting coefficient equal to the ratio of the area of nalip to the area of the blunting site at the gas station and the wear of grain. It was found that AZ from Elbor wear out and become salted to a lesser extent when grinding with the imposition of a narrow-gauge blank.

Dependence of abrasive tool wear-resistance on abrasive grain microstrength

Microstrength determined applying the microindentation method is an essential indicator of micromechanical properties of abrasive tools’ grains. Assessment is carried out according to the damage area dimensions and the imprint depth. The test results of various materials, including abrasive materials, in a friction machine revealed that relative wear-resistance of those materials depends on microstrength. The higher microstrength is, the lower wear-resistance of materials is. Such dependence was revealed in the course of studying the process of microcutting by single abrasive grains, as well as evaluating specific capacity of abrasive tools in operation. Thus, the microstrength parameter can be used to forecast operational efficiency of materials and tools.

Model for Predicting the Micro-Grinding Force of K9 Glass Based on Material Removal Mechanisms.

K9 optical glass has superb material properties used for various industrial applications. However, the high hardness and low fracture toughness greatly fluctuate the cutting force generated during the grinding process, which are the main factors affecting machining accuracy and surface integrity. With a view to further understand the grinding mechanism of K9 glass and improve the machining quality, a new arithmetical force model and parameter optimization for grinding the K9 glass are introduced in this study. Originally, the grinding force components and the grinding path were analyzed according to the critical depth of plowing, rubbing, and brittle tear. Thereafter, the arithmetical model of grinding force was established based on the geometrical model of a single abrasive grain, taking into account the random distribution of grinding grains, and this fact was considered when establishing the number of active grains participating in cutting Nd-Tot. It should be noted that the tool diameter changed with machining, therefore this change was taking into account when building the arithmetical force model during processing as well as the variable value of the maximum chip thickness amax accordingly. Besides, the force analysis recommends how to control the processing parameters to achieve high surface and subsurface quality. Finally, the force model was evaluated by comparing theoretical results with experimental ones. The experimental values of surface grinding forces are in good conformity with the predicted results with changes in the grinding parameters, which proves that the mathematical model is reliable.

Grain wear evolution of cubic boron nitride abrasives during single grain grinding of powder metallurgy superalloy FGH96

The grain wear evolution during grinding powder metallurgy superalloy FGH96 using a single abrasive grain of cubic boron nitride (CBN) under different undeformed chip thickness and abrasive wheel speed was investigated. The wear behavior of single abrasive grain (SAG) was extracted based on the variation feature of grinding force, radial wear, grain topography and material remove characteristics. Meanwhile, acoustic emission (AE) testing is used to analyze the grain wear evolution. The results show that micro fracture firstly occurs at the original defects of SAG at the initial wear stage. Attrition wear and micro fracture are responsible for the steady wear stage, while micro and macro fracture are dominant at severe wear stage. Besides, the manner of the plastic adiabatic shear remove occurs in the process of grinding FGH96. Furthermore, sudden increase of root mean square (RMS) of AE signal can be applied to reflect the fracture of SAG, whereas the continuously gradual decrease can be considered the attrition wear or material adhesion, which can provide a technical support for monitoring the grain wear during grinding.

Experimental study on the working performance of different milling tools for multistage fracturing ball seats

To achieve the secondary production in multistage fracturing wells of tight oil, milling tools are usually used to remove the multistage fracturing ball seats to achieve production with a large diameter in later. In this paper, first of all, the working mechanism of milling tools for multistage fracturing ball seats was studied and a mechanical analysis model of single abrasive grain was established. Then, an experimental system for milling tools was developed, and the experimental tests of the flat, the blade, and the slope milling tool were conducted in order. Besides, the morphology of chips and the surface morphology of the workpiece after the experiment were analyzed. Also, the working performance of milling tools was evaluated from the perspectives of working safety, working efficiency, and wear resistance of the milling tool. The results show that the torque of the milling tool increases nonlinearly with the increase in the cutting depth of the abrasive grain and increases linearly with the increase in the cutting width. Also, the chips are irregular particles and the size is mainly from 10 to 50 μm. So, the chips should be pumped up with a small pump pressure and a large displacement. Besides this, the cutting depths of the abrasive grains are from 216.20 to 635.47 μm and the bottom surface of the milling tool should be eccentric to avoid the zero point of cutting speed. Furthermore, the torque of the slope milling tool is 23.8% larger than that of the flat milling tool, which is also 30.4% smaller than that of the blade milling tool. Compared with the flat milling tool, the working efficiency of the blade milling tool improves by 79.9% and the slope milling tool improves by 111.1%. Also, the wear resistance of the blade milling tool decreases by 102.7%, while the slope milling tool declines by 32.6% when compared with the flat milling tool. Therefore, the slope milling tool has the characteristics of moderate torque, stable working conditions, the highest working efficiency, and fine wear resistance, which is preferably used to mill multistage fracturing ball seats. This study provides a theoretical basis and guidance for milling multistage fracturing ball seats on-site and realizing production with a large diameter in later stages of multistage fracturing wells.

An investigation on material removal mechanism in ultra-high-speed grinding of nickel-based superalloy: three-dimensional simulation and experimental verification

Ultra-high-speed grinding is a significant method for the advanced manufacturing of the difficult-to-machine material components, e.g., nickel-based superalloy. However, unclear mechanism of material removal behavior is still the main problem. The present work intends to establish the three-dimensional (3D) finite element simulation model of ultra-high-speed grinding with single abrasive grain. The effects of undeformed chip thickness and grinding speed on the morphology of grinding traces and chips are investigated. The parameters, such as pile-up ratio and shear slip frequency, are characterized experimentally, and the mechanism of material removal behavior in the process of ultra-high-speed grinding has been accordingly researched deeply. The results indicate that the pile-up ratio decreases firstly and then increases with an increase of undeformed chip thickness; the lowest pile-up ratio would be obtained when the undeformed chip thickness is 0.8~1 μm. When the grinding speed is below 240 m/s, with the increase of grinding speed, the distance between the sawtooth of the grinding chips is reduced, while the sawtooth degree is increased. When the grinding speed exceeds 400 m/s, the chip shape changes from serrated fracture to banded continuity, and the frequency of adiabatic shear slip goes up with the increase of grinding speed, which helps to reduce the grinding force, making the grinding process more stable and decreasing the difficult machinability of Inconel 718 nickel-based superalloy.