Wear Flat Area Research Articles

The effects of grit properties and dressing on grinding mechanics and wheel performance: Analytical assessment framework

This paper introduces an analytical assessment framework for evaluating grinding wheel performance derived from the model of cutting and sliding grinding force components. Four new parameters are proposed based on wheel topography. These parameters are normalized through the aggressiveness number, which circumvents the influences of grinding geometry and kinematics. The framework is validated through experiments with different wheel topographies obtained by changing dressing conditions and grit properties (toughness, thermal stability and shape). The framework and experiments quantify how wheel wear flat area influences the sliding component and how grit protrusion influences the intrinsic specific grinding energy. This framework provides a rational basis for evaluating grinding-wheel performance and abrasive-grit selection.

A force model for face grinding using digital graphic scanning (DGS) method

The prediction of grinding force has great significance in improving grinding quality and efficiency. This paper presents a predictive force model in plunge facing grinding considering both the cutting mechanism of single grain and the random nature of wheel topography. The model includes cutting deformation force and frictional force, which mainly depend on undeformed chip cross-section area and wear flat area of grains. In order to overcome the difficulties for calculating the cross-section area of irregular polyhedral grains, a digital graphic scanning (DGS) method is proposed in this research. Single grain scratch test and hardness test are carried out to obtain the model coefficients. The validation experiments performed on a face grinding machine show a good match of the predictive and measured forces for different grinding parameters.

Modeling of Cutting Rock: From PDC Cutter to PDC Bit—Modeling of PDC Cutter

Summary The main purpose of this paper is to present our polycrystalline diamond compact (PDC) cutter model and its verification. The PDC cutter model we developed is focused on a PDC cutter cutting a rock in 3D space. The model studies the forces between a cutter and a rock and applies the theory of poroelasticity to calculate the stress state of the rock during the cutting process. Once the stress state of the rock is obtained, the model can then predict rock failure by the modified Lade criterion (Ewy 1999). This work also developed a trial-and-error procedure to predict cutting forces, and the stress state of a rock before cutting process is also considered. A complete verification of the cutter model is conducted. The model results (i.e., predicted cutting forces) are compared with measured cutting forces from cutter tests in multiple published articles. The major influencing factors on cutting forces—backrake angle, side-rake angle, depths of cut, worn depth (or wear flat area), and hydrostatic pressure—are all studied and verified. A good agreement between the model results and cutter test data is found, and the overall mean relative error is approximately 15%. The influence of inhomogeneous precut stress state of a rock is also studied. Overall, the cutter model in this paper is complete and accurate. It is ready to be integrated into a PDC bit model.

Dynamic grinding force model for carbide insert peripheral grinding based on grain element method

Peripheral grinding force influences the accuracy of carbide inserts to a considerable extent, thereby making the study of grinding force crucial to improve the process of peripheral grinding. To predict the peripheral grinding force in the grinding process, a dynamic grinding force model based on the grain element method is proposed in this paper. The proposed model divides a grain into several grain elements and the cross-section of each element is assumed to be a rectangle. The actual cutting depth, including the influence of the other grain paths of each element, is calculated to simulate the actual cross-section cutting area and the wear flat area. Thus, the interference region between grain paths is included in this model. By combining the single grain grinding force model, the cross-section cutting area and the wear flat area, the peripheral grinding force can be simulated. Because the grinding force is simulated using the grinding wheel topography and the grinding kinematic directly, the influence of the workpiece residual is included. Therefore, the simulated grinding force is more accurate than the force predicted with the total material removal rate.

Grindability studies of thermomechanically processed advanced high strength steel using sol-gel and fused alumina grain-based grinding wheels

Advanced high strength steels have excellent strength-to-weight ratio and are widely used for automotive and structural applications. Grinding is commonly used as a final machining process for these materials to achieve the required dimensional tolerance and surface quality. In this work, the grindability of as-received microstructure of ferrite-pearlite and in-house developed ferrite-bainite-martensite steels using polycrystalline white fused alumina and microcrystalline sol-gel alumina grinding wheels under flood and minimum quantity lubrication conditions is studied. Grindability of these steels was evaluated based on the wheel wear, grinding forces, force ratio, specific cutting energy, surface roughness (Ra), and surface morphology. The sol-gel alumina wheel was observed with higher wear flat area and forces under all the grinding conditions as compared with white fused alumina wheel. The white fused alumina wheel exhibited higher force ratio values for all the grinding conditions than the sol-gel alumina wheel. The energy required per unit volume of material removal is lower for the white fused alumina wheel in both the steels under flood and minimum quantity lubrication conditions. This is due to the retention of sharpness of abrasive grains by self-sharpening for white fused alumina wheel than the sol-gel alumina. The presence of fractured, melted, and hollow chips on the ferrite-pearlite and ferrite-bainite-martensite steels under both the grinding condition confirms the change in material removal mechanism with the presence of higher wear flat area of the sol-gel alumina wheel. Based on the obtained results, the white fused alumina wheel was found to be a suitable grinding wheel for grinding of both the steels under all grinding conditions compared to the sol-gel alumina wheel.

Thermal damage control for dry grinding of MgO/CeO2 glass ceramic

MgO/CeO2 glass ceramic is a key solid catalyst and accelerant produced by raw mixing, prilling and pressure sintering. Grinding, as a high-efficiency machining method was used to obtain MgO/CeO2 glass ceramic components with accurate size to meet the size requirements of design. However, thermal damage occurring on the ground surface may change the properties of the components and affect their performance in subsequent applications. In this work, a grinding thermal model was established and validated by experiments. On the basis of this thermal model, the grinding temperature can be controlled to < 100 °C by selecting optimal grinding parameters and thus prevent grinding burn. The mechanism of potential chemical reactions on the grinding surface was further studied by analysing the transient temperature jump at a grain wear flat area and comparing the change in element mass fraction before and after grinding. The performance of a normal resin bond diamond wheel and a resin bond wheel with Ni–P alloy coating on the diamond grains was compared. Results showed that the latter intensified the redox reaction because of the catalytic actions of Ni and P, and the mass fraction of each elements on the workpiece surface shows obvious uneven distribution due to the surface spalling of Ni–P alloy. All these results indicated that key issues are the optimal setup of process parameters to control the grinding zone temperature and the selection of a proper grinding wheel to avoid catalytic elements such as Ni and P.

Theoretical and experimental investigation of material removal mechanism in compliant shape adaptive grinding process

Modeling of grinding process, especially the grinding forces, has been studied extensively. Most previous work concerns the conventional grinding process using a rigid wheel, where the forces are generally based on the preset depth of grinding. However, for compliant grinding such as Shape Adaptive Grinding (SAG) that adopts an elastic tool covered with abrasive pellets, the penetration depth of individual abrasive grains is not simply equal to the preset value. As elastic contact occurs between the tool and workpiece, previous models are not able to estimate the material removal mechanism. Besides, the progressive transitions in grain-workpiece interaction for compliant cutting tools have not been reported yet. To fill these gaps and to offer a fundamental understanding of the compliant grinding process, we propose in this study a new multi-scale model spanning from macroscopic tool-workpiece contact to microscopic grain-workpiece interaction in the unique conditions of using a compliant grinding tool, i.e. SAG tool. Based on the spring-grain model and considering the stochastic nature of grain size and wear flat area, the static penetration and dynamic removal of individual grain can be predicted. Particularly, the removal mechanism is clarified with a new consideration of the transition between rubbing, plowing and cutting stages for each individual grain of the compliant tool. Experiments including scratch tests and removal footprints were carried out, and the high consistency with theoretical predictions validates the proposed model. Finally, considering the progressive abrasive wear in grinding, in-process wear compensation was conducted to enable consistent material removal on aspheric steel molds. The proposed method is not only meaningful to reveal the mechanism of SAG process, but also offers a new foundation for studying other compliant grinding processes in future.

On the development and evolution of wear flats in microcrystalline sintered alumina grinding wheels

Wheel wear is a critical issue for grinding process optimization. This is why it receives so much attention both from Academia and industry. The development of new generations of abrasive wheels requires improving the understanding of the mechanisms involved in the loss of abrasive capacity of the wheels. In the case of alumina wheels, which are largely used in many grinding operations, the development of microcrystalline sintered alumina grains is one of the most important innovations to emerge since the early 1980’s. In comparison with white fused alumina this grains are characterized by higher ductility and have approximately 5% more hardness. However, the mechanisms of occurrence of wear flats in these new abrasives are still to be fully understood. In this work, a novel approach to the study of the underlying phenomena that occur during the development of wear flats in microcrystalline sintered alumina grains is presented. Experimental results in terms of grinding forces, friction coefficient and surface analysis are presented and compared to those obtained with conventional white fused alumina. The value of wear flat area is as much as 25% higher in the case of microcrystalline sintered alumina grains. Results will be useful to prevent the development of grinding burns resulting from wear flat development in these new alumina wheels.

Behavior and quantitative characterization of CBN wheel wear in high-speed grinding of nickel-based superalloy

This work aims to clarify the wear behavior and quantitatively characterize the wear in cubic boron nitride (CBN) wheels during the high-speed grinding of the nickel alloy, Inconel 718. Grinding experiments were performed first to qualitatively investigate the wear behavior of CBN wheels. To simplify the grinding process, single-grit grinding experiments were carried out to quantitatively characterize the degree of wear on the CBN grain afterwards. The influence of maximum chip thickness on the wear and grinding ratio of CBN grains was studied. Finally, the wear of the CBN wheel was quantitatively characterized by using the wear flat area percentage. It was found that the wear of a single CBN grain increases dramatically at first and then varies little with the increase in the accumulated material removal. The wear flat area percentage of the CBN grinding wheel is able to remain at a low level, and a high and stable grinding ratio can be achieved for CBN wheels. This demonstrates the feasibility of CBN wheels in the high-speed grinding of nickel alloys.

A Comparison of Techniques to Measure the Wear Flat Area of Conventional and Superabrasive Grinding Wheels

Wear of abrasive grains is one of the key issues influencing the grinding process and the resulting workpiece quality. Being able to quantify wheel wear in-process allows parameterization of grinding models that can help assuring part surface integrity. However, one of the main problems in measuring wear of abrasive grains is their small size, which makes this task to be not trivial. In this paper, several measuring techniques are compared in order to determine which one offers the best potential to quantify the wear of conventional and superabrasive grinding wheels. The selected techniques include optical macroscopy, optical microscopy, profilometry, and scanning electron microscopy (SEM). Among other results, direct comparisons of the same exact wear flat area measured with different techniques are shown.

EFFECT OF WHEEL WEAR ON CONTACT LENGTH, UNCUT CHIP THICKNESS AND FORCES FOR A DEFORMABLE GRINDING WHEEL AND WORKPIECE

In this paper, contact length, uncut chip thickness, and contact forces were studied as the wheel wore during dry surface grinding of 4130 normalized steel for three different depths of cut (0.0025, 0.005, 0.0075 mm). An aluminum oxide grinding wheel (Norton 38A46HVBE) was used for all the experiments and the work and wheel speeds were 0.22 and 32.3 mis, respectively. In each experiment, the wear flat area, the cutting edge density, the cutting edge width and length were determined using an automated optical measurement system. The grinding forces were measured using a force dynamometer. The contact length was determined using rigid-body, smooth­ body and rough-body contact assumptions. The uncut chip thickness was determined using a continnity analysis. In this approach, the average volume of material is lJrSt determined by dividing the total material removal rate by the number of cutting edges. Then an assumption of the shape of the chip is made. In this work, the uncut chip was assumed to have a triangular profile and a rectangular cross-section. The uncut chip thickness can then be determined by dividing the average chip volume by the average contact length and chip width. In the experiments, grinding forces, wear flat area, cutting edge density increased and uncut chip thickness decreased as a result of wheel wear. In addition, the wheel wear increased the contact length significantly in the rough-body assumption, marginally in the smooth-body. assumption but not in the rigid-body assumption. The normal contact pressure was determined by dividing the normal force by the product of the percent wear flat area and contact area. This result suggested that the rough body assumption represented the data most accurately.

Heat transfer model for creep-feed grinding

A heat diffusion-free model based on the assumption of high Peclet number is used to describe the problem of heat transfer in a creep-feed grinding process. The model uses the basic analysis of a moving heat source. Calculation of temperature in the very near region surrounding the grinding wheel grits is shown. A calculation of the background temperature of the workpiece in terms of the percentage of wear flat area on the wheel and with the inclusion of the coolant effects is also presented. Consideration for film and nucleate boiling of the liquid coolant is taken into account. Effects of heat transfer coefficient and thermal conductivity on temperature are shown. Effect of partitioning of energy is also shown.

Application of region growing method to evaluate the surface condition of grinding wheels

Grinding is a time-varying process affected by factors such as wheel construction, dressing parameters, operating parameters, workpiece material and cooling. The influence of these factors on wheel wear can be evaluated by monitoring the wheel condition. Measurement of wear flat area provides information on the condition of the wheel, but unfortunately it can be a tedious, time consuming, and expensive process. In this paper, a new system to measure wear flat area is presented. This system is mounted on the grinding machine and automates the measurement process by using computer control to automatically position the wheel and capture digital images of the wheel between grinding cycles. Image processing software is then used to analyze the digital images and measure the wear flat area. The proposed measurement system was validated using a scanning electron microscope. Experiments were performed on a Brown & Sharpe Micromaster 824 surface grinder to examine the relationship between wear flat area, normal force and depth of cut. The results agree with the literature.

Development of an automated system for measuring grinding wheel wear flats

Grinding is a time-varying process affected by factors such as wheel construction, dressing parameters, operating parameters, workpiece material, and cooling. As the grinding wheel wears, flat areas form on the wheel surface. Wear flat measurement provides information on the condition of the wheel and is, therefore, an essential tool to study the grinding process. Measuring wear flat area can be a tedious, time-consuming, or expensive process. In this paper, a new system has been developed to measure wear flat area. This system is mounted on the grinding machine and automates wear flat measurement by using computer control to automatically position the wheel and capture digital images of the wheel between grinding cycles. Image processing software is used to automatically analyze the digital images and measure wear flat area in the images. The proposed measurement system was validated using a scanning electron microscope. Experiments were performed on a Brown & Sharpe Micromaster 824 surface grinder to examine the relationship between wear flat area and normal force. The results agree with the literature.

Effect of grinding forces on the vibration of grinding machine spindle system

In this paper the effects of dynamic changes in the grinding force components due to changes in the grinding wheel wear flat area and the workpiece material on the vibration behavior of the grinding spindle are studied. The steady-state dynamics and vibration behavior of the grinding machine spindle is simulated by a five degree of freedom model. The results indicate that when grinding different materials using a grinding wheel with fixed wear flat area, different vibration behavior is noticed. As the grinding wheel flat area increases, the level of vibration increases for all the degrees of freedom, which indicates that there is an upper limit for the level of wear on the grinding wheel that can be tolerated, and after that level dressing operation must be conducted on the grinding wheel.

Wear mechanisms of diamond abrasives during transition and steady stages in creep-feed grinding of structural ceramics

A study was performed to quantify the wear mechanisms of diamond abrasives of a resin bonded diamond wheel (320 US mesh and 100 concentration) in creep-feed grinding of a silicon nitride material. This was achieved with a combined use of a lead-tape imprint technique and SEM. The wear mechanisms observed include attritious wear, fracture (or chipping), mixed mode of wear and fracture, and dislodgment (or pullout). The percentage of each wear mechanism was quantified for different points of the grinding process: five during the transition stage and six during the steady stage. The results indicate that: (1) the percentage of grits not involved in removing the first 10 cm 3/cm volume of material per unit width was high (∼70%) and decreased as more material was removed (from −50% to 20% during the steady stage). (2) Attritious wear dominated the wear mechanism and the percentage increased as more material was removed (from ∼15% to 30% during the transition stage and from ∼50% to 75% during the steady stage). Correspondingly, the percentage of wear-flat area also increased. (3) The percentages of grit dislodgment and grit fracture were relatively higher during the transition stage than during the steady stage. (4) The number of active grits per unit area increased with cumulative volume of material removed. (5) Specific forces increase nonlinearly with wear-flat percentage and the percentage of worn grits.

High Speed Grinding of Silicon Nitride With Electroplated Diamond Wheels, Part 2: Wheel Topography and Grinding Mechanisms

This is the second in a series of two papers concerned with high speed grinding of silicon nitride with electroplated diamond wheels. In the first article (ASME J. Manuf. Sci. Eng., 122, pp. 32–41), it was shown that grinding of silicon nitride is accompanied by dulling of the abrasive grains and a significant increase in the grinding forces and power. High wheel speed caused more wheel wear, which was attributed to a longer accumulated sliding length between the abrasive grains and the workpiece. This second paper is concerned with the progressive change in wheel topography during grinding and how it affects the grinding process. A statistical model is developed to characterize the wheel topography during grinding in terms of active cutting grains and wear flat area. According to this model, continued grinding is accompanied by an increase in both the number of active grains and the wear flat area on the wheel surface as the wheel wears down. The measured increase in grinding forces and power was found to be proportional to the wear flat area, which implies a constant average contact pressure and friction coefficient between the wear flats and the workpiece. Increasing the wheel speed from 85 to 149 m/s significantly reduced the contact pressure, which may be attributed to a reduction of the interference angle, but had almost no effect on the attritious wear rate of the diamond abrasive. Therefore, more rapid wear of the diamond wheel at higher wheel speeds due to a longer sliding length may be offset by reduced contact pressures and lower grinding forces. [S1087-1357(00)00401-9]

画像解析による砥石作業面の評価 (第1報)

The working surface of a grinding wheel is characterized by means of an image processing, in which a picture of a wheel surface is taken by the CCD camera through the optical microscope on the grinding machine and analyzed with the personal computer. In this study, surface distributions of abrasive grains and wear-flat area of cutting edges on the wheel surface -the static number of abrasive grains G and cutting edges C per unit area, the successive cutting-edge spacing λ and the cutting-edge ratio η -are measured as a first step. Abrasive grains and wear-flat areas can be extracted mainly by the hue and the brilliance informations of the picture, respectively for resin bond diamond wheel (SDC 140 N 75 B) with relatively high accuracy. Overall processing time required for measuring these parameters is about 150 seconds per picture. The value of G is distributed in the range of 20 to 25 mm-2 in the circumferential wheel direction. The mean value of η is about 3.1% even in the initial stage after the truing and dressing. Those values do not change very much with grinding of normally sintered Si3N4 at an certain grinding condition because that few grains are fractured or fallen off.

A Variable Heat Flux Model of Heat Transfer in Grinding: Model Development

In any grinding process, thermal damage is one of the main limitations to accelerating the completion of the product while maintaining high quality. Therefore, the objective of the present study is to understand the thermal behavior in the grinding process and possibly achieve the ultimate goal of avoiding thermal damage in the grinding process. A model previously developed is improved to analyze the heat transfer mechanisms in the grinding process. Heat generated at the interface between the abrasive grains and workpiece (i.e., the wear flat area) is considered. A conjugate heat transfer problem is then solved to predict the temperature in the grinding zone. In the previous model, all the heat fluxes were assumed to be uniformly distributed along the grinding zone. This led to a contradiction in the temperature matching condition. This reveals that the heat fluxes into each of the various materials are not uniform along the grinding zone. An improved model, accounting for the variation of the heat fluxes along the grinding zone, is presented. The temperature and heat flux distributions along the grinding zone are presented, along with comparisons to previous theoretical results.

Thermal analysis of creep-feed grinding

One of the major problems encountered in industrial experience of creep-feed grinding is thermal damage to the workpiece and grinding wheel. Thus, the application of cutting fluids is especially crucial. In this paper an analytical model of the heat transfer between the wheel, the workpiece surface and the grinding fluids is derived and verified. The model enables the prediction of the maximum surface temperature when grinding fluids are applied, demonstrates the thermal energy partitions between the abrasive wheel, the cutting fluids and the workpiece, and also determines the threshold of the occurrence of film-boiling. Despite its simplicity, the model provides remarkable agreement with published data from experimental investigations and from finite-element analysis, for various creep-feed grinding conditions. The cooling effect of water-based grinding fluids is better than that of oil-based cutting fluids, but the resistance to workpiece burning using water-based cutting fluids is worse than that using oil-based cutting fluids. When cutting fluids are applied in the grinding process, the strong cooling effect of the cutting fluids is apparent. In addition, a CBN grinding wheel shows a better performance than an Al 2O 3 grinding wheel in the avoidance of workpiece burning. The cooling effect of grinding fluid, R c, can be improved by decreasing the effective contact ratio. In general, this effective contact ratio can be achieved by selecting a grinding wheel with a higher porosity of structure number. Further, a shorter dressing time-interval is a better choice for decreasing the wear flat area and thus for improving the cooling effect of the coolant on the workpiece.