Specific Grinding Energy Research Articles

Comparative grindability study of composite ceramic and conventional ceramic

Grinding is a widely used machining and finishing operation for the ceramic materials. Nowadays, a new variant of composite ceramics has also been developed. In many applications, these composite ceramics too need to be ground. The present study aims to experimentally investigate the grindability aspects of such a composite ceramic (AlSiTi) and also compare those grindability aspects of the composite ceramic with a conventional ceramic (SiC). Grinding forces, specific grinding energy and the surface integrity including the subsurface damage and surface roughness are the responses measured during the detailed experiments performed where grinding parameters like wheel speed, table speed and depth of cut are varied over a domain. Optical microscope and scanning electron microscope (SEM) have been used to analyse the ground surface, subsurface damage and the grinding swarfs. The results provide valuable insight into the grindability aspects of the composite ceramic (AlSiTi). Cracks and voids produced on the surface and subsurface of the composite ceramic are found to be significantly different from those observed while grinding the conventional ceramic under the same process parametric conditions.

Study to analyze the influence of sprouting of the wheat grain on the grinding process

Several studies have been carried out on the grinding characteristic of three species of common wheat ( Triticum aestivum, ssp. vulgare). The three-day germinated kernels were pulverized in a micro hammer mill equipped with a changeable screen. The moisture of samples was 12% (w.b.). The results showed that the sprouting of wheat had a significant influence on the grinding process. The average particle size of the pulverized material obtained from the sprouted kernels was almost always significantly lower than those from the sound kernels. The highest changes were observed in the increase of the fraction of particles below a size of 200 μm, caused by sprouting. The sprouting caused a decrease in the value of specific grinding energy in all cultivars. Based on the parameters of screen openings and cultivar, the values of specific grinding energy ranged from 35.5 to 141.6 kJ kg −1 and from 41.4 to 164.3 kJ kg −1 for the sprouted and sound kernels, respectively. In addition, the other values of grinding energy indices confirmed that sprouting significantly reduced the grinding energy requirements. The average value of the grinding ability index was 3.9 and 4.8 kJ m −2 for the sprouted and sound wheat, respectively. Whereas, sprouting caused a decrease in the average value of the grinding index from 71.2 to 58.0 kJ kg −1 mm 0.5.

Grinding Forces and Grinding Energy in High Speed Grinding for Quenched Steel

Grinding experiments for quenched high-speed tool steel by resin bonded CBN (cubic boron nitride) wheel were conducted with a surface grinder. The grinding forces were measured under different grinding parameters. The effects of grinding parameters on grinding forces and grinding force ratio are discussed. Specific grinding energy and heat flux over the grinding zone are computed according to grinding parameters and grinding forces. The effects of grinding parameters on specific grinding energy and heat flux are investigated.

Experimental Research on Deep Hole Honing of Difficult-to-Cut Materials Based on Mixture-Abrasive Honing Stones

The deep hole honing is an effective and precise method in deep hole processing. It can remove the machining allowance to ensure the hole size and the shape accuracy, and have better surface quality of a hole. The difficult-to-cut materials such as precipitation-hardening stainless steel, stainless steel (1Cr18Ni9Ti) and titanium alloy have the properties of high hardness, wear resistance, heat resistance, and corrosion resistance. The conventional single-abrasive honing stones can not handle the difficult-to-cut materials effectively because of their single-abrasive property. For higher efficiency, more than ten of mixture-abrasive honing stones with different proportion of different abrasives have been designed and the contrast experiments have been done for different mixture-abrasive honing stones to grind precipitation-hardening stainless steel, stainless steel (1Cr18Ni9Ti) and titanium alloy. According to several comprehensive evaluation factors of the grinding ratio, the specific grinding energy and the area that the honed chips stick the oilstones surface, the optimum proportion of different abrasives have been found for honing difficult-to-cut materials. It can be observed that the mixture-abrasive honing stones have better performance than that of single-abrasive stones when honing certain kind of difficult-to-cut materials.

Grinding of Nanostructured WC Coatings with Single Fibrous-Abrasive Wheel

The random nature of the abrasive geometries and their distribution in a grinding wheel results in high specific grinding energy and temperature rise, large grinding forces and large deflection in the grinding system. To overcome the shortcomings encountered in grinding, it is necessary to design a new grinding wheel that is structured in controlled abrasive geometries with preferred spatial positioning and orientation. This paper deals with an experimental research of single fibrous-abrasive grinding of a nanostructured WC/12Co Coating. Prepared by the laser cutting of polycrystalline diamond compact (PDC), the single fibrous-abrasive has the dimensions of 0.3×0.6×10mm. The paper reports the research findings on normal and tangential grinding forces in terms of depth of cut and feed rate and discusses the material removal mechanism of nanostructured WC/12Co Coating ground by fibrous abrasive.

Study on the rotary cup dressing of CBN grinding wheel and the grinding performance

A systematic research is conducted to investigate the effect of rotary cup dressing on vitrified cubic boron nitride grinding performance in grinding of nickel-based superalloys. Grinding performance is evaluated mainly in terms of specific grinding energy and radial wheel wear. The number of active grits per unit area and their slope is considered as the two grinding wheel topographical key parameters for studying grinding performance. Cup dressing conditions with various speed ratios and overlap factors were investigated. In each case, the specific grinding energy and the radial wheel wear were experimentally measured, and then the effect of changing dressing parameters on the grinding performance is analyzed. To provide a view on how various parameters influence specific energy and the importance of wheel topography and grit workpiece interaction, a new specific grinding energy model is developed. Inputs to this model are workpiece parameters, grinding process parameters, and, in particular, the grinding wheel topographical parameters. This model is validated by experimental results. The theoretical values considering the complexity of the grinding process reasonably compare with the experimental results. The effect of number of active grits per unit area and their slope on specific grinding energy and then metal removal mechanism is investigated. The results revealed that the number of active grits per unit area has less effect on specific grinding energy than grits slope.

Experimental Research of Grinding Force and Specific Grinding Energy of TC4 Titanium Alloy in High Speed Deep Grinding

Focusing on the characteristic of hard-to-grind for titanium alloy, experiments were conducted about grinding TC4 titanium alloy under high speed deep grinding (HSDG) condition. The changing of grinding force per unit area with maximum undeformed chip thickness hmax and equivalent cutting thickness aeq are analyzed in this paper. The effect of maximum undeformed chip thickness hmax and specific material removal rate Zw' on specific grinding energy es, material removal mechanism and consumption of grinding power in HSDG process are also discussed. The experiment results reveal that application of HSDG can improve machining efficiency of grinding TC4.

Specific energy in grinding of tungsten carbides of various grain sizes

The objective of this study is to investigate specific energy in grinding of tungsten carbides of various grain sizes. Through the construction of a mathematical model, the study demonstrates the correlation of specific energy with the grinding process parameters and the material property parameters for the tungsten carbides. The study also examines material-removal mechanisms and surface finish in grinding of such materials using scanning electron microscopy, X-ray diffractometry and energy dispersive spectrometry techniques, etc. The study concludes that specific energy is related not only to grinding process parameters, but also to the physical–mechanical properties of the workpiece material.

Recent advances and future perspectives in grinding wheel structures

The random nature of the abrasive geometries and their distribution in a grinding wheel results in high specific grinding energy and temperature rise, large grinding forces and large deflection in the grinding system. It can also cause the abrasives to fall off the grinding wheel prematurely, leading to an inefficient use of the abrasives. Moreover, grinding wheel wear and loading problems become more severe when grinding hard and/or 'sticky' materials, which requires more frequent wheel truing and dressing, and thus reduces grinding efficiency. To overcome the problems encountered in grinding, it is necessary to design a new grinding wheel that is structured in predefined abrasive geometries with preferred spatial positioning and orientation. The new grinding wheel should be dressing-free due to its self-sharpening capability. The specific grinding energy in using the new wheel should be comparable to that of machining with predefined tools. This paper discusses the current state-of-the-art and future challenges in the grinding wheel structures, as well as the recent advances and future perspectives in grinding wheels through analysing and comparing grinding against machining processes with predefined tools.

AN INNOVATIVE CONCEPT AND ITS EFFECTS ON WHEEL SURFACE TOPOGRAPHY IN DRY GRINDING BY RESIN AND VITRIFIED BOND CBN WHEEL

In the dry grinding process, as there is no coolant lubricant to transfer the heat from the contact zone, minimizing the grinding specific energy and grinding forces is a matter of importance. Some of the results of the systematic research works, based on a novel concept to make a step forward for pure dry grinding, are presented. The new concept is based on the fact that the optimisation of the chip formation reduces the friction and rubbing in the process. Such optimisation was achieved by a special conditioning process. The result showed a drastic reduction in grinding forces and no burning or damages on the surface of workpiece using the novel method comparing to conventional wheel with the same material removal rate. A theoretical discussion is also presented to support the experimental results.

Performance of a new segmented grinding wheel system

This paper investigates the mechanical and thermal effectiveness of a new segmented grinding wheel system with controlled radial coolant supply. The applicability of the system was examined in terms of grinding forces, specific energy and ground surface integrity in plunge grinding of AISI 4140 steel. It was found that compared with a standard grinding wheel, the new system enhanced the grindability with a lower specific energy and less application of coolant. It was also found that the new grinding system could effectively maintain the sharpness of active cutting edges, evidenced by the minimisation of ploughing and rubbing deformation in ground workpieces. The cleaning capacity of the wheel was improved and chip loading on wheel surfaces was avoided. Meanwhile, the new wheel system generated better surface integrity without tensile residual stresses.

Effects of abrasive type cooling mode and peripheral grinding wheel speed on the AISI D2 steel ground surface integrity

In this work the AISI D2 steel ground surface integrity was evaluated at different grinding conditions. Two sets of experiments were conducted. The first and the second sets are referred to as conventional grinding tests (CGTs) and high-speed grinding tests (HSGTs), respectively. For the CGTs two different types of abrasives (aluminium oxide and sol–gel alumina) and two cooling modes (oil-based grinding fluid and cryogenic cooling) were tested at a peripheral wheel speed v s =22 m/s. For the HSGTs, an electroplated cBN grinding wheel was used at a peripheral wheel speed ranging from 60 to 260 m/s. Experimental results show that the grindability and the surface integrity of the AISI D2 steel could be substantially improved by using the sol–gel grinding wheel and cooling by liquid nitrogen comparatively with conditions using aluminium oxide and cooling with oil-based grinding fluid. These conditions reduce the grinding force components, lower the level of tensile residual stresses and expand the range of stock removals rate for which compressive residual stresses can be obtained. In this case the stock removal rate could be increased 7 times and still having compressive residual stresses. These experimental results were further explored and it was possible to establish linear relationships between the specific energy and the amplitudes of the surface residual stresses when grinding under the CGTs conditions. This relationship is very useful for process control and optimization. Results of the HSGTs show that the highest levels of the compressive surface residual stresses were obtained at a peripheral wheel speed v s =120 m/s ( σ ∥=−520 MPa, σ ⊥=−770 MPa). These values are much higher than those measured at the ground surface generated using the sol–gel grinding wheel and cooling by liquid nitrogen ( σ ∥=−295 MPa, σ ⊥=−250 MPa). Further, the CGTs and HSGTs results were used to establish the burn-free and burn conditions in relation with the specific grinding energy. It was shown that condition using the sol–gel grinding wheel and cooling with liquid nitrogen and condition using cBN grinding wheel at peripheral wheel speed up to 180 m/s generate specific grinding energy that are significantly lower than the burning threshold energy.

Ultrasonic assisted dry grinding of 42CrMo4

In recent years, many cooling lubricants are classified as health hazards, while their end-of-life treatment poses numerous ecological threats. Dry machining is a solution for greener production and also is a favorable process from an economical point of view. However, compared to other machining processes, conventional grinding has a low material removal rate and involves high specific energy. A major part of the specific energy in grinding is changed to heat that makes harmful effect on surface quality. Therefore, in conventional dry grinding, as there are no cutting fluids to transfer the heat from the contact zone, the temperature of workpiece surface and grinding wheel surface will be increased resulted to thermal damage and poor surface integrity, increasing of wheel wear and inefficient grinding compared to conventional grinding. To make a step forward to pure dry grinding and to eliminate the negative environmental impact of the cutting fluids, a new technique called ultrasonic assisted dry grinding has been used. The advantages of ultrasonic assisted grinding were proved mostly for the brittle material. Our investigations show the improvement on the surface roughness, considerable reduction of the normal grinding force, and thermal damage in case of using ultrasonic assisted dry grinding compared to conventional dry grinding for a soft material, 42CrMo4. A decrease of up to 60% of normal grinding forces has been achieved.

Equilibrium and compatibility simulation of plunge centreless grinding

A computer simulation of plunge centreless grinding is presented. The key assumption is that the forces on the workpiece equilibrate fast enough to treat the process as a sequence of equilibrium states. Equilibrium forces are calculated at each time step, allowing machine and contact deflections to be accounted for when imposing compatibility upon the workpiece. Machine deflections of the grinding wheel, workblade, and regulating wheel are assumed proportional to the applied forces, with constants obtainable from independent experiments. Contact deflections are calculated with a Hertzian analysis and known material properties. Empirical data relating grinding force to actual depth of cut iteratively ‘close the loop’ between equilibrium and compatibility. Results of the simulation technique include histories of the workpiece shape, apparent and actual depths of cut, all forces on the workpiece, and all contact and machine deflections. It is shown that regenerative lobing is influenced by the specific grinding energy, and that actual depth of cut might be much lower, and specific grinding energy significantly higher, than in comparable surface grinding processes. It is pointed out that the application of additional, known forces to the top of the workpiece could allow equilibrium and compatibility in centreless grinding to be controlled.

An experimental study on the grinding of alumina with a monolayer brazed diamond wheel

A monolayer diamond grinding wheel was fabricated by brazing in vacuum. The wheel was then used to grind alumina at three different grinding speeds. The horizontal and vertical grinding forces, and the grinding temperatures were measured during grinding. SEM observations were made for the ground workpiece surfaces. The influences of the peripheral wheel speed on the grinding forces, specific grinding energy and grinding temperatures were analyzed under different combinations of depth of cut and workpiece velocity. The dependence of the average grinding force per grain and specific grinding energy on the maximum undeformed chip thickness was discussed respectively. It was found that an increase in the peripheral wheel speed reduced grinding force, but increased force ratio, specific grinding energy, and grinding temperature.

Improving surface integrity and economics of grinding by optimum coolant application, with consideration of abrasive tool and process regime

As compared to machining, the chip thickness in grinding is small and the specific grinding energy is generally much higher than the specific cutting energy in machining. With such small chip thickness values, a lot of heat is created by non-chip removal interactions, such as ploughing and rubbing. These interactions occur between the chip and grain, chip and bond, and the chip and the work. Identification and manipulation of these interactions can allow the engineer to minimize the thermal limitation, improve surface finish, increase wheel life, etc. This paper discusses the thermal energy partitioning that occurs with different modes of grinding, and guides the reader towards processes with a lower specific energy and more desirable energy partitioning with respect to the energy that enters the final workpiece surface. The high efficiency deep grinding regime, is compared to creep-feed and shallow-cut grinding. The paper also looks at the cooling effect of grinding fluids and how they can be applied more effectively to cool and lubricate the workpiece surface. Best practices will be presented, based on analytical models and field experience. Flowrate and pressure models are used to optimize the main fluid jet that is applied to the grinding process. The heat transfer characteristics of superabrasive wheels, as compared to conventional abrasives, will also be presented and discussed. Finally, a case study is presented, that clearly shows the economic and technological advantages of coherent-jet nozzles over a more conventional approach.

A Study on Grinding Performance of Porous NiTi Shape Memory Alloy

The machining performance of porous NiTi shape memory alloys prepared using powder metallurgical production technique has been investigated experimentally in the grinding operation. Grinding force ratio, specific grinding energy, surface characteristics were detected. The result reveals that, much difference of grinding characteristics exists among three kinds of NiTi alloy because of the pore rate and the mechanical performance induced by TiH2. Under the experimental conditions, the integrated effects of predominant plastic flow and slight brittle fracture were taken for porous NiTi alloy during grinding. Additionally, the grinding parameters should be chosen carefully, otherwise the surface quality deteriorates and even the microcrack perhaps appears.

The crushing of wheat kernels and its consequence on the grinding process

This article presents the results of investigations on the grinding energy requirements for crushed and whole wheat kernels regarding different moisture levels. Two common wheat cultivars Turnia and Slade were used for tests. According to the Single Kernel Characterization System (SKCS) hardness index (HI), Turnia was classified as hard and Slade as a soft wheat (HI = 71 and 32, respectively). The results showed that the crushing of wheat kernels prior to hammer mill grinding had a significant influence on the grinding process. The average particle size of the ground material obtained from the crushed kernels of Slade was always significantly lower than from the whole kernels. A similar situation was observed for Turnia samples, when the moisture of kernels was 12, 14, and 16%. For soft wheat in particular, the highest changes were observed in the fraction of particles below 200 μm, where the crushing caused an increase in this fraction. However, this tendency was not observed for hard wheat. The specific grinding energy of uncrushed kernels ranged from 72.3 to 146.7 kJ·kg − 1 and from 67.0 to 114.4 kJ·kg − 1 for Turnia and Slade, respectively. The crushing caused a decrease of specific grinding energy in both cultivars. The total specific grinding energy of crushed kernels (the sum of crushing energy and grinding energy) ranged from 47.6 to 100.5 kJ·kg − 1 and from 44.6 to 85.3 kJ·kg − 1 for hard and soft wheat, respectively. In addition, the other grinding energy indices confirmed that crushing of kernels prior to hammer mill grinding considerably reduced the grinding energy requirements.

The characterization of structural changes in hematite ground in a confined particle bed using Rietveld analysis

The interparticle breakage of fine feed fraction of hematite concentrate was investigated by stressing two particle beds with a pressure between 255 and 1000 MPa. The experiments were conducted in such a way that the wall friction effects during compression were eliminated. The effects of interparticle breakage in a confined bed on the structural changes of hematite concentrate were studied using a combination analysis of XRD line broadening, BET and particle size measurements. The specific energy comminution was estimated using loading and de-loading hysteresis curves. It was found that energy absorption by the particle bed varies between 6 and 31 J/g depending on the applied pressures and bed heights. The experiments indicated that energy absorption was a major factor for the interparticle breakage of hematite. In addition, it was revealed that an increasing bed height brought about a higher stiffness and hence reduced energy absorption and subsequently declined the surface area, solid content as well as structural changes. The linear energy–force relationship stands well even if the particle-bed heights are changed. The maximum BET surface area was measured about 1.4 m 2/g after energy absorption of 31 J/g by the particle bed. Structural changes were followed by XRD line broadening analysis using Rietveld refinement and Warren–Averbach approach. It was found that the intensity and the broadening of XRD diffraction patterns decreased and increased, respectively, by increasing energy absorption with a first approximation. With increasing absorbed energy by the bed up to 15 J/g the degree of amorphization increased sharply and afterwards continued to change slightly. The maximum X-ray amorphization was calculated at maximum energy absorption, accounting for 31%. The volume and surface weighted crystallite sizes reduced to about 108 and 53 nm, respectively, after releasing 31 J/g specific grinding energy. For the same energy, the root mean square strain (RMSS), < ε L 2 = 10 nm > 1/2, and maximum lattice strain, e, increased to 9.4 × 10 − 4 and 4.1 × 10 − 3 respectively. The comparison of bed grinding with tumbling milling revealed that the grinding in tumbling mill needs much more energy to induce the same structural changes as in bed grinding. The results obtained from the two methods are discussed and compared in details.

In vitro study on high rotation deep removal of ceramic prostheses in dental surgery

In vitro study on high rotation (up to over 300,000 rpm) deep removal (up to 150 microm) of ceramic prostheses, made of a machinable ceramic, Vita Mark II, was performed in dental surgery using a high-speed dental handpiece. Dental clinical removal relevance, including tangential and normal grinding forces, specific grinding energy, and surface roughness, was investigated to establish the relationships among the surgery parameters, chip geometry, and fracture mechanism. The results show that both the tangential and normal grinding forces increased with increases in both depth of cut and maximum undeformed chip thickness, but decreased with an increase in grinding speed. Specific grinding energy decreased with increase in the depth of cut and the maximum undeformed chip thickness, but increased with an increase in grinding speed. Surface roughness and morphology appeared to be independent of the increases in depth of cut, grinding speed, and maximum chip thickness. The limitation for deep removal using the dental handpiece was found that the operation at the depth of cut of 150 microm or beyond resulted in a huge normal force exertion of 3 N with a great variation. The microfracture, the lateral fracture, and the ductile microcutting were found to occur simultaneously in dental surgery to remove the ceramic prostheses.