Wheel Sharpness Research Articles

Performance evaluation of creep feed grinding of γ-TiAl intermetallics with electroplated diamond wheels

This paper evaluates the performance of creep feed grinding γ-TiAl intermetallic (Ti-45Al-2Mn-2Nb) using electroplated diamond wheels. Firstly, a comparative analysis with the grinding results by using electroplated CBN wheels was conducted, mainly involving abrasive wheel wear behavior and maximum material removal rate below surface burn limit. It was found that the diamond wheel would produce much better grinding results including lower wheel wear rate and higher maximum material removal rate. Then the surface integrity obtained at different level of material removal rate was characterized with the utilization of the diamond wheel. The poor ductility of this γ-TiAl intermetallic material was found to have a marginal effect on the surface integrity, as no severe surface defects such as material pullout were generated during the stable wheel wear stage. For the involved operating parameters, a deformation layer was produced with ∼10 μm or more in thickness depending on the material removal rate used. Meanwhile, a work-hardened layer extending to more than 100 μm was produced with a maximum microhardness of above 520 HV0.05 (bulk value 360 HV0.05). The residual stress remained compressive, with a value of above −100 MPa and even up to −500 MPa for an elevated material removal rate. Shearing chip was the main chip type, indicating good wheel sharpness in the grinding process.

Grinding performance and tribological behavior in solid lubricant assisted grinding of glass-ceramics

High dimensional stability of glass-ceramics is highly attractive to optical and precision engineering industries. This study aims to provide an efficient and stable grinding strategy for realizing high-quality surface and dimensional accuracy of glass-ceramics. The different solid additives (CeO2 and SiC) as lubricants and their performances were investigated regarding the grinding forces, friction coefficient, wheel wear and surface finish during grinding glass-ceramics. Friction and wear mechanism in solid lubricant assisted (SLA) grinding were analyzed. Three-body abrasive wear and chemical mechanical interaction were considered as the predominant lubrication mechanisms. The results showed that the low, stable grinding force and small friction coefficient can be obtained under SLA-SiC grinding. The study proved that the novel strategy can keep the wheel sharpness and improve the process performance.

Evaluation of grinding process using simultaneously MQL technique and cleaning jet on grinding wheel surface

In the last years, many researchers have proposed improvements to the minimum quantity lubrication (MQL) technique, in order to increase its efficiency and make it a viable alternative to the conventional application of cutting fluids for a cleaner machining. Besides the lubri-cooling effect inherent to the MQL technique, the cleaning of grinding wheel is pursued, since its surface undergoes the clogging phenomenon resulting in decreasing of the process performance. The main objective of this study is to assess the influence of the auxiliary wheel cleaning jet (WCJ) in an attempt to reduce the wheel clogging phenomenon and increase lubri-cooling and machining efficiencies in the cylindrical external grinding of AISI 4340 steel under the application of the MQL technique using aluminum oxide grinding wheel. The MQL combined with cleaning jet was compared to both flood application (conventional) and MQL without WCJ (traditional). MQL grinding employed oil flow rates of 30, 60 and 120 mL/h in order to evaluate the effects of amount of grinding fluid in the assessment. The conventional and MQL + WCJ methods produced lower surface roughness and roundness deviation compared to the other methods used due to the fact that they kept the wheel sharpness longer. Moreover, conventional and MQL + WCJ methods increased G ratio and reduced tangential grinding forces and specific energy in comparison to traditional MQL. The MQL + WCJ method enabled the removal of part of chips adhered on the grinding wheel active surface (GWAS) when compared to the traditional MQL, reducing the wheel clogging, which is one of the reasons for loss of wheel sharpness. Tubular chip form occurred not only in MQL + WCJ grinding but also in traditional MQL grinding, although it is not mentioned in literature.

Acoustic emission in dressing of grinding wheels: AE intensity, dressing energy, and quantification of dressing sharpness and increase in diamond wear-flat size

Abstract Although significant work has been done on the application of acoustic emission (AE) to grinding and to dressing of grinding wheels, several fundamental AE relationships between have not been established. These are: 1) the relationship between dressing energy and the measured AE signal; 2) how different diamond/grit contact modes (fracture, plastic deformation, rubbing, etc.) affect AE energy; and 3) how this can be used to quantify dressing efficiency, wheel sharpness and wear-induced changes in diamond shape. This paper describes an investigation into these fundamental concepts, with quantification of the relationship between AE intensity and dressing energy and the influence of different diamond/grit contact modes. A new parameter is introduced, the specific acoustic-emission dressing energy, which can be used to quantify dressing efficiency and wheel sharpness. Finally, the use of the AE intensity in evaluating diamond wear is explored, allowing the operator to know the size of the wear flat and when changes are necessary to avoid workpiece burn. Experimental work validates these concepts and practical recommendations are given on its application in industry.

Probabilistic Approach for Modeling Electroerosion Removal of Grinding Wheel Bond

This study is focused on the development of mathematical models for the diamond-spark grinding process. The diamond-spark grinding is an efficient technique for the precision machining of hard and brittle materials. In comparison with conventional grinding, the diamond-spark grinding allows maintaining grinding wheel sharpness during machining cycle due to the directed destruction of its bond by electric discharges. The proposed model is based on probabilistic approach and it allows calculating the value of the bond layer removed with erosive discharges and predict the state of technological system at any moment. The example of the developed model practical use is also presented.

The measurement and analysis of micro bonding force for electroplated CBN grinding wheels based on response surface methodology

The superabrasive (e.g. CBN or diamond) grain dislodgement occurrence on the wheel surface due to insufficient bonding force is the major failure phenomena in the grinding process with electroplated grinding tools. This failure leads to the abrupt increase of load on the immediate grains, accelerating more grain dislodgement on wheel surface. Ultimately, the aggregated grain dislodgement causes the workpiece profile accuracy degradation and catastrophic wheel sharpness loss. Therefore, the provision of sufficient and uniform micro bonding force all through the wheel surface is the critical task in electroplated superabrasive grinding wheel design. Considering the complexity in the micro bonding force enabling factors, e.g. the grain shape, dimensional size, spatial orientation, and bond layer thickness, it is vital to establish the quantitative and comprehensive relationship between these factors with the micro bonding force for optimal electroplated grinding wheel design. In this paper, an inclined micro-thread turning test is developed to measure the single grain micro bonding force. In addition, the finite element model of single CBN grain bonding force is established and validated to simulate the grain dislodgement. Finally, the response surface methodology (RSM) is applied to build the comprehensive correlation of the bonding force with its dimensional size, spatial orientation, and bond layer thickness. Therefore, the optimal bonding condition through regressed prediction model is identified to provide the quantitative basis for the electroplated CBN grinding wheels design, which indicates that the bonding force can be predicted for specific wheel manufacturing parameters and improved by related variable adjustment.

Ultra-precision face grinding with constant pressure, lapping kinematics, and SiC grinding wheels dressed with overlap factor

Several machining processes have been created and improved in order to achieve the best results ever accomplished in hard and difficult to machine materials. Some of these abrasive manufacturing processes emerging on the science frontier can be defined as ultra-precision grinding. For finishing flat surfaces, researchers have been putting together the main advantages of traditional abrasive processes such as face grinding with constant pressure, fixed abrasives for two-body removal mechanism, total contact of the part with the tool, and lapping kinematics as well as some specific operations to keep grinding wheel sharpness and form. In the present work, both U d-lap grinding process and its machine tool were studied aiming nanometric finishing on flat metallic surfaces. Such hypothesis was investigated on AISI 420 stainless steel workpieces U d-lap ground with different values of overlap factor on dressing (U d = 1, 3, and 5) and grit sizes of conventional grinding wheels (silicon carbide (SiC) = #800, #600, and #300) applying a new machine tool especially designed and built for such finishing. The best results, obtained after 10 min of machining, were average surface roughness (Ra) of 1.92 nm, 1.19-μm flatness deviation of 25.4-mm-diameter workpieces, and mirrored surface finishing. Given the surface quality achieved, the U d-lap grinding process can be included among the ultra-precision abrasive processes and, depending on the application, the chaining steps of grinding, lapping, and polishing can be replaced by the proposed abrasive process.

Estudo comparativo entre a agressividade superficial obtida na retificação com rebolos de óxido de alumínio e CBN, fabricados com ligantes resinóide e vitrificado

Este artigo apresenta um estudo da agressividade do rebolo (habilidade de corte). A retificação é um processo de usinagem preciso, o qual é amplamente usado na manufatura de componentes que requerem tolerâncias estreitas e superfícies bem acabadas. Na retificação, a ferramenta abrasiva é o rebolo, que é basicamente composto por núcleo, ligante e grãos abrasivos. As ferramentas testadas nessa pesquisa foram rebolos convencional (Al2O3) e superabrasivo (CBN). Entre os superabrasivos, três tipos específicos de ligantes foram testados: resinóide, vitrificado e resinóide de alto desempenho. Conseqüentemente, foi possível avaliar a habilidade de corte entre os diferentes tipos de rebolos testados. Assim, o rebolo convencional de óxido de alumínio apresentou a maior agressividade.

A System Development Approach for Electrolytic In-Process Dressing (ELID) Grinding

This study aims to present the development and performance evaluation of an ultra-precision ELID grinding machine. The machine is a 3-axis machine, including three conventional linear axes (X,Y, andZ). On top, another rotational axis has been included to assist aspheric/spherical lens grinding. In order to introduce intelligence to the machine, several on-machine measuring systems have been developed and incorporated. In ELID grinding, pulsed DC voltage is applied to the metal-bonded diamond wheels to ensure the constant protrusion of sharp cutting grit throughout the grinding cycle. The peak dressing voltage is kept constant irrespective of the wheel sharpness in conventional ELID grinding, which may lead to over dressing of the grinding wheel. The grinding force ratio, also known asKvalue, is an indicator of grit sharpness. In this study, a new approach to wheel dressing is proposed: the peak dressing voltage is varied according to the change in theKvalue during grinding. In conventional ELID grinding, the duty ratio of the dressing power supply is kept constant throughout the grinding cycle. However, this method does not achieve grinding wheel truing, which is very important to maintaining the stability of the grinding. This research work proposes a novel approach to wheel truing by controlling the dressing voltage duty ratio for ELID grinding.

A study of grinding wheel sharpness using neural network and fuzzy logic approaches

In this study, two different models were developed to estimate the skewness factor of an alumina grinding wheel which is a criterion for wheel sharpness. Development of the models is based on the back propagation neural network (BPNN) and the fuzzy logic approaches. Some experiments have been performed to train the BPNN to get it to estimate the wheel sharpness. Also, all membership functions and rule-bases have been presented in details for a fuzzy model. In experiments procedure, the grits of an alumina grinding wheel is dressed using a rotary diamond disc dresser. The predicted values of the skewness factor by using the neural network represented that this model has an acceptable precision in estimation of wheel sharpness. Also well acceptable performance of the fuzzy model was achieved. Comparison of two models shows that they were successful in estimation of the wheel sharpness.

Efficient dressing of the wheel in ELID grinding by controllable voltage with force feed back

Electrolytic in-process dressing (ELID) grinding is a new method for achieving ultraprecision surface on hard and brittle materials. In ELID grinding, pulsed direct current voltage is applied on the metal-bonded diamond wheels to ensure constant protrusion of sharp cutting grits throughout the grinding cycle. The peak dressing voltage is kept constant irrespective of the wheel sharpness in conventional ELID grinding, which may lead to overdressing of the grinding wheel. Grinding force ratio (which is also known as K value) is an indicator for the grit sharpness. In this paper, a new approach of wheel dressing has been proposed where the peak dressing voltage is varied according to the change in the K value during grinding. A Kistler three-component dynamometer has been used to monitor the grinding force ratio in real time for this purpose. The methodology to implement the new “dressing-on-demand” concept has been discussed thoroughly in this paper. The experimental comparison with the conventional ELID grinding has also been carried out to prove the advantages of the proposed system.

Analytical and Experimental Investigation of the Nickel Based Superalloy Using Cryogenic Cooling Grinding

Grinding processes are mainly technique employed widely as a finishing and difficult-to machine such as hardness and brittleness materials machining. However in grinding process, high grinding zone temperature may lead to thermal damage to the work surface, induces micro-cracks and tensile residual stresses at the ground surfaces, which deteriorate surface quality and integrality of the ground surface. The work presented in this paper aims at evaluating the grindability and surface integrity of the nickel base superalloy resulting from the application of cryogenic cooling. Grinding experiments were conducted under three different environments: dry, mineral oil and cryogenic cooling jet. The grindability results have shown that while the cryogenic cooling generates the lowest grinding temperature, no significant differences over the specific grinding force components were observed. As for the ground surface integrity, however, substantial improvements were realized. The novel process not only obviously enhances surface quality and integrality of grinding surface, but also enables retention of the wheel sharpness for a longer period and reduces pollution of grinding fluid to nature.

State classification of CBN grinding with support vector machine

When grinding high-strength ferrous alloy with CBN wheel, attention is often paid to the variation of wheel surface condition to ensure work surface quality, since wheel sharpness is directly related to the ground surface. The on-line wheel condition can be obtained via process monitoring, which integrates the operations of process sensing, featured data extraction, and state assessment. When grinding with wheel state under control, work quality is ensured. On-line process state recognition usually relies on a pre-built classification model. This paper is to classify the intercepted grinding acoustic emission data using support vector machine (SVM) based on ground roughness variation during grindable period. An SVM model was constructed from the result of a grinding experiment and confirmed to find an 85% of prediction accuracy.

Effects of ELID on High Speed Grinding of Partially Stabilized Zirconia

Electrolytic In-process Dressing (ELID) has been applied in high speed grinding of partially stabilized zirconia. Using a developed electrode system, the ELID effect on a bronze bond diamond wheel was significant. This resulted in a decrease in grinding force, and thus improved the ground surface quality. The improvement of grinding performance was attributed to the good maintenance of wheel sharpness by ELID dressing.

The sharpness of grinding wheels: An important measure of grinding behaviour

This paper aims to make a clearer picture of the sharpness of grinding wheels in terms of the wheel performance in grinding. It was found that the system time constant is the most sensitive to any change in wheel dressing operation, which has strong effects on the wheel topography. The effects of dressing conditions were investigated together with the grinding conditions. Some control strategies for improvement of the grinding operation by considering wheel sharpness are presented in the paper.

Modelling surface roughness improvement in grinding

Grinding is a precision machining process used to improve workpiece surface roughness. This paper demonstrates that spark-out is the most important stage of a plunge grinding cycle for achievement of a low value of roughness. The nature of the spark-out process is investigated including the effects of machine stiffness, system deflection, wheel sharpness and plastic deformation on improvement of surface roughness. Experiments and a comparison with predictions from a computer simulation programme demonstrate the effects of the fundamental factors. It is demonstrated that the time constant for roughness is more than twice the time constant for system deflections.

In-process Identification of System Time Constant for the Adaptive Control of Grinding

The forces generated during the grinding process cause deflections of the machine-grinding wheel-workpiece system which are large compared to the accuracies required. The deflections cannot be precisely predicted and the optimum grinding conditions vary because the grinding wheel sharpness changes with grinding wheel wear and dressing. In practice conservative machining conditions and feed cycles are used in order to maintain the quality of the finished workpieces. This paper presents a new method of characterizing the time constant of the system from the grinding power consumption during the infeed section of a grinding cycle. Adaptive grinding cycles have been implemented which use the measured value of system time constant to control the target axis position and the dwell time. In this way the control system adapts the machining cycle for the wheel condition at the time of grinding, and can cope with the large variations in deflection that occur when using high feedrates.

Wheel sharpness measurement for force prediction in grinding

The application of a new method of measuring the sharpness of a grinding wheel by profilometry is described. Used on wheels which have ground cylindrical steel workpieces of varying hardness, it allows theoretical charts of force against equivalent chip thickness to be predicted which agree well with the forces measured in the grinding tests. It merits further investigation as a means of controlling the grinding process.

Effects of cryo-cooling in grinding steels

The grinding process is inherently characterised by high specific energy and high temperature, which are responsible for high wheel loading, increased grinding forces, reduced metal-removal rate, rapid wheel wear and deterioration in the quality of the ground surface through oxidation, the induction of tensile residual stress and micro-cracks. These problems become more acute when the product is of HSHR material and subjected to dynamic loading while functioning. Therefore, in industry the user should pay special attention to control and optimise all the significant parameters for minimising the afore-said problems, aiming at higher grindability, productivity and overall economy in grinding. The basic principles of controlling such high temperature are: (i) proper selection and optimisation of wheel and process parameters; (ii) the removal of heat from the grinding zone by the application of proper grinding fluid. Profuse cooling with conventional grinding fluids, even in the form of mist or jet, is virtually unable to solve the problem. However, cryogenic cooling by agents such as liquid nitrogen is expected to meet this challenge. In the present work, specimens of different steels, namely MS, HCS, cold- and hot-die steel and HSS, have been surface ground at different infeeds under dry conditions and with soluble oil and liquid nitrogen. The effects of such cryo-cooling relative to soluble oil and dry grinding have been investigated in respect of chip formation, grinding forces, specific energy, burning and surface characterisation. The experimental results indicate that the grinding temperature and burning decreased remarkably under cryo-cooling. Thermal damage of the ground surface has been reduced substantially by cryo-cooling, but to different degree in different steels. Cryo-cooling also enables retention of the wheel sharpness for a longer period and results in less force and specific energy being required.

The statistics of the extrema of surfaces as a means of assessing their mechanical performance

The application of a new spectral technique to the analysis of some surface profiles is described. Where a physical model of the effect of surface features on performance is available, it is possible to define the parameters to be measured and the bandwidth of measurement in such a way that performance can be quantitatively predicted. For the three examples given — friction and wear coefficients, grinding wheel sharpness, and peening damage — it was found necessary to confine the measurements to surface extrema to obtain good predictions. It is suggested that this method could profitably be used in many other cases.