Conventional Grinding Wheels Research Articles

Grinding of Austempered Ductile Iron Grade 3 as Function of the Microcrystalline Al<sub>2</sub>O<sub>3</sub> Grinding Wheels Composition

The conventional grinding wheels employment is an economically viable alternative on Austempered ductile iron (ADI) grinding. The machining of this iron is in most cases performed with superabrasive grinding wheels, requiring machine tools with higher costs. The ADI grinding with conventional grinding wheels can produce work results comparable to the superabrasive grinding wheels, followed by lower costs and flexibility in profile grinding, since these wheels can be easily re-profiled. The aim of this work is to verify the work results of grinding ADI Grade 3 employing conventional grinding wheels. The approach is based on the influence evaluation of different abrasive microcrystalline Al2O3 percentage in these tools on the force results and roughness values in the ADI grinding. The findings show a correlation between the grinding forces and the microcrystalline abrasive percentage of microcrystalline Al2O3, since lower forces were demanded for wheels with higher percentages. Regarding the surface parameters, there was a decrease in roughness values by employing less percentages. The originality of this research is reflected in the fact that it is the first time that the influence of the composition of conventional grinding wheels is investigated on ADI Grade 3 grinding. The results present in this research will contribute to the most appropriate conventional grinding wheel specification for the ADI Grade 3 grinding.

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.

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.

Cutting characteristics of electroplated diamond tools with laser-generated positive clearance

Conventional grinding wheels and dressing tools suffer from problematic chipping conditions at the abrasive grains, caused by near-zero or negative clearance angles at the micro-cutting edges. This paper introduces electroplated diamond dressing tools with positive clearance angles, generated by ultrashort pulsed laser ablation. A series of generic dressing experiments with varying parameters on vitrified bond corundum grinding wheels and long-term tests are presented for a comparative performance assessment of laser-conditioned and conventionally prepared tools. The results are applied to an analysis of the interdependency between the topography of the abrasive layer and the cutting characteristics of dressing tools.

Effect of Novel Grinding Wheels on Grinding Performance

Grinding, a technique for removing abrasive materials, is a chip-removal process that uses an individual abrasive grain as the cutting tool. Abrasive material removal processes can be very challenging owing to the high power requirements and the resulting high temperatures, especially at the workpiece-wheel interface. This paper presents a novel system that uses graphite particles impregnated in an aluminum oxide matrix to form a grinding wheel. This study specifically investigated grinding wheels with a graphite content of 0.5 wt%. The new grinding wheel was compared with conventional grinding wheels by comparing the factors of grinding performance, such as surface roughness, morphology, wheel wear ratio, grinding temperature, and grinding forces, when the wheels were used under two different coolant strategiesdry and with minimum quantity lubrication (MQL) using pure water. This study found that there is a considerable improvement in the grinding performance using graphite-impregnated grinding wheels over the performance obtained using conventional grinding wheels. The use of 0.5 wt% graphite provided better surface roughness and topography, lower grinding temperature, and decreased force; in addition, wheel consumption was lower, resulting in extended wheel life.

Experimental Investigation on Grinding Performance of Microcrystalline Alumina Abrasive Grinding Wheel for Superalloys

Superalloys are widely used in the aeronautic and astronautic industries owing to their excellent properties in aspects of high-temperature strength, heat stability and thermal fatigue resistance. However, the severe loading of grinding wheel and the poor integrity of grinding surface usually become the problem in grinding of superalloys with conventional grinding wheels. In this paper an experimental study was carried out to investigate the grinding characteristics of superalloys with microcrystalline alumina abrasive wheel. The roughness of grinding surface was tested, on which the effects of the grinding parameters were analyzed. Study results indicated that low loading of grinding wheel and high quality of grinding surface (Ra 0.2 μm) were obtained. The grinding parameters were optimized based on the experiment results.

A Study on Grinding Tungsten Carbide with Ultrasonic Assisted

In order to cope with high demanded industry requirements. The super-hard alloys such as Tungsten Carbide have been widely used in aerospace and defense industries. So far, the grinding operation is still the most popular machining process being used to cut these materials in shape. But, owing to the nature of these materials mechanical properties, always made it very difficult to grind as well as to cut. Nevertheless, the allowable grinding parameters are resisted to very limited range and always require use very expensive super abrasive grinding wheel. Recently, study by many researchers show that the ultrasonic assist grinding had the advantage of higher material removal rate, less cutting force and lower cutting temperature. In the mean time, the tool life had been improved greatly. In this study, the conventional GC grinding wheel was used in the experiments to study the material removal rate; grinding force; surface roughness as well as specific grinding energy with and without the ultrasonic assist. The results show that these difficult-to-cut materials can be ground easier with proper ultrasonic assist and low-priced grinding wheel.

Investigation of Cooling Environments in Grinding EN 31 Steel

Liquid nitrogen finds increased application as a coolant in various machining processes, due to its effectiveness in controlling the machining temperature and also in being a clean technology. EN31 is a difficult-to-cut material, and Sol-Gel (SG) alumina is a modern grinding wheel with self-sharpening characteristics. In this research, the influence of liquid nitrogen (LN2) as a cryogenic coolant, and its delivery pressure in terms of grinding forces and surface roughness, were analyzed. The experiment was conducted with conventional Al2O3 (aluminium oxide) and SG grinding wheels. The liquid nitrogen coolant was supplied at 3, 4, and 5 bar pressure. The liquid nitrogen produces a reduction of 24% and 16% grinding forces over dry and wet grinding. The surface roughness reduced by a maximum of 43% and 26% over dry and wet grinding. The SG wheel delivers the maximum reduction in the grinding forces and surface roughness, compared to the Al2O3 wheel. The experimental results show that the increased delivery pressure of the liquid nitrogen produced a reduction of 4–8% in the grinding forces, and 3–8% in the surface roughness.

Abrasion Monitoring and Automatic Chatter Detection in Cylindrical Plunge Grinding

Using conventional grinding wheels, wheel-sided chatter vibration is one of the limiting factors in terms of productivity and surface fin-ish. Initial vibration related to the dynamic behavior of the machine tool copy on the grinding wheel and its amplitude amplifies by abra-sion. To ensure high workpiece quality many expensive truing cycles are needed. In this context, we suggest a new set-up for the auto-matic chatter detection and elimination for external cylindrical grinding machines, reducing not only the high amount of true running cycles, but also improving the efficiency. In order to suppress the generation of the waviness on the grinding wheel the effect has to be identified during an early stage of its development. Therefore, a grinding machine is equipped with different types of sensors, i.e., eddy current, force, acoustic emission, acceleration sensors, and a tactile probe. Experimental results show, that exclusively measuring the displacement at the workpiece is sufficient for online computing wheel's waviness. Based on a model of the grinding process the other redundant sensors are used for validation. In addition, a robust online chatter detector based on the wavelet transformation is developed recognizing an instable grinding process. This model-based detection and estimation of waviness delivers solid results, it should be used for suppression of chatter in further work.

Development of a micro-graphite impregnated grinding wheel

This paper introduces a newly designed grinding wheel where micro-graphite particles are impregnated in an aluminum oxide matrix to form a grinding wheel to lubricate the grinding site; these are known as graphite-impregnated grinding wheels. The graphite particles were heat-treated under a layer of hydrogen ions at a temperature of about 500°C for 30min to disperse them uniformly in the aluminum oxide matrix. In this study, grinding wheels with five different graphite contents (0.1, 0.5, 1, 3, and 5wt%) were investigated. Different aspects of the grinding performance (e.g., surface roughness, morphology, wheel wear ratio, grinding temperature, and grinding forces) using these grinding wheels under two different coolant strategies (dry and minimum quantity lubrication with pure water) were compared with the corresponding values for a conventional grinding wheel. The experimental results indicate that using graphite-impregnated grinding wheels considerably improves the grinding process performance compared to using a conventional grinding wheel. A graphite content of below 0.5wt% is recommended because this provides not only better surface roughness and topography, and lower grinding temperature and force but also less grinding wheel consumption; hence, the wheel life was extended. In summary, combining graphite-impregnated grinding wheels with minimum-quantity lubrication technology has the potential to effectively eliminate the use of any oils or toxic organic lubricants in the grinding process.

Ordered diamond micro-arrays for ultra-precision grinding—An evaluation in Ti–6Al–4V

The surface topography of a conventional diamond grinding wheel can be characterised as having a perplexity of abrasive particles with random crystallographic orientations resulting in different heights of protrusion from the bond and inherent varying inter-particle spacing. The number and effectiveness of the abrasive particles during grinding depends on factors such as the abrasive concentration, the crystallographic shape and the extent of particle protrusion from the wheel’s surface. The consequence of this random layout inhibits the optimal performance of individual abrasives in the process of material removal, and where particles are clustered, chip flow is negatively affected. This paper reports on the evaluation of purpose designed precision diamond micro-arrays for the grinding a case-study material, Ti–6Al–4V and compares their performance against conventional diamond electroplated micro-cutting elements of D91 and D46 abrasive size in an imitated grinding setup. The precision diamond micro-arrays, produced from thick film CVD diamond utilising energy beam ablation offer an optimised layout of abrasive elements, each having a cutting width of 100 μm of identical crystallographic orientation, protrusion height and regular spacing to provide chip flow paths. In addition, the primary/secondary rake angles γ=−32°/+1° and clearance angle α=4.5° of each abrasive cutting element have been controlled in order to provide an enhanced cutting action. The precise layout of the abrasive cutting elements of the micro-arrays produced superior chip flow compared with the diamond electroplated grinding elements; this has been proven by in-depth scanning electron microscopy of the clogged workpiece material on the studied abrasive elements. The results show a 3.5 times improvement to surface finish and a 21.5 times improvement to flatness of the Ti–6Al–4V workpieces when ground with the proposed innovative diamond micro-arrays.

Abrasive Grain Efficiency and Surface Roughness in Machining Magnesium Alloys by Newly Developed Cup-Type Diamond-Grinding-Wheels

New cup-type diamond-grinding-wheels with hexagonal pattern have been developed. Grinding stone ratio, R is defined as the ratio between the hexagonal edge area containing abrasive grains and the total area of the wheel surface. In the present work, four kinds of hexagonal grinding wheels with different R (13 %, 19 %, 25 % and 36 %) and a conventional wheel (R: 100 %) were used to grind a light metals, which was represented by magnesium alloy AZ31B. Efficiency of abrasive grains and ground surface for machining a light metals were evaluated by calculating the number of abrasive grains which pass through a unit length of a sample surface for each grinding pass, Ng. The results show that surface roughness becomes smaller, i. e., smoother surfaces as Ng increases. Surfaces ground by the conventional wheel are rougher than those by using newly developed hexagonal grinding-wheels in spite of the larger Ng for the conventional wheel. Surface roughness data forms one curve in roughness vs. Ng graph for all hexagonal wheels, and forms another curve for the conventional grinding-wheel. The difference of two curves indicates that the number of effective working abrasive grains in hexagonal wheels is about 5 times higher than that of the conventional wheel. The similar results were obtained for machining sapphire according to our previous work. Hexagonal wheels show higher abrasive grain efficiency for machining not only hard-to-machine ceramics but also light metals such as magnesium alloys than conventional wheels.

Grinding of Carbon/Epoxy Composites Using Electroplated CBN Wheel with Controlled Abrasive Clusters

Aiming at solving the problems of wheel loading in dry grinding of Carbon/Epoxy composite materials, a novel electroplated grinding wheel with controlled abrasive cluster was developed, in which the diameter of clusters is in Φ0.2 mm to Φ1.0 mm and the interspace between them is about 0.5 mm to 1.0 mm. A conventional electroplated grinding wheel with abrasive grains distributed randomly was fabricated in the same way. The comparison experiments involving C/E composite were conducted on a vertical spindle grinder with the novel and conventional grinding wheels. The results show that the grinding forces of novel wheel developed is more lower though little larger surface roughness, and the wheel loading phenomenon is markedly decreased compared with conventional electroplated wheel.

Processes and trends for the dressing of superabrasive and conventional grinding wheels

The demands on surface quality are increasing continuously. This causes high demands on the machining processes. Especially for grinding, conditioning is of great importance for the surface roughnesses that are to be generated. The conditioning process consists of trueing and sharpening and depends on workpiece material, abrasive grain, bond type and grinding wheel profile. The basic types of dressing tools and their corresponding parameters will be presented in this paper. The aim of this paper is to give an overview on existing and new conditioning processes.

Research on Grind-Hardening Temperature and Cooling Rate of 48MnV Microalloyed Steel

The temperature, time and cooling rate are key factors in the hardening process using the grinding heat instead of the high frequency induction heat source. Thus, this paper established the mathematical model estimating the grind-hardening temperature, experimentally determined the grinding temperature and the cooling rate of different grinding parameters for 48MnV microalloyed steel using the conventional aluminum grinding wheel on a surface grinder, and investigated the grind-hardening effects and the forming mechanism of grind-hardening layer. The results show that the estimating temperatures are comparatively close to the measuring ones and hence the model could be utilized to optimize the processing parameters, and the satisfactory grind-hardening temperature and cooling rate could be achieved under the optimized processing parameters. The microstructure of the grind-hardening layer, the fine needlelike martensite in the entirely hardened zone, the martensite and ferrite in the transitional region is similar to that acquired through the high frequency induction technique. Especially, the average hardness of the entirely hardened zone is 740HV and the depth of the hardened layer is adjacent to 1.5mm, which indicate that the grind-hardening effects are very excellent. Different from the forming mechanism of the high frequency induction hardened layer, higher grind-hardening temperature is needed to compensate shorter time austenitization, and because of thermo-mechanical loading induced during grinding, from surface to inside, the morphology of martensite changes from fine to thicker, then to finer, other than from thick to finer.

Studies on the cooling minimum quantity and conventional cooling at hardened steels in grinding process

The purpose of this work is to explain the concept of cutting fluids reasonable usage through the fluid minimum quantity in grinding processes. On that purpose, the development of a new nozzle and an own and adequate methodology should be required in order to obtain good results and compare them to the conventional methods. The analysis of the grinding wheel/cutting fluid performance was accomplished from the following input parameters: flow rate variation by nozzle diameter changes (three diameters values: 3mm, 4mm and 5mm), besides the conventional round nozzle already within the machine. Integral oil and a synthetic emulsion were used as cutting fluids and a conventional grinding wheel was employed. The workpieces were made of steel VC 131, tempered and quenched with 60HRc. Thus, as the flow rate and the nozzle diameter changes, keeping steady fluid jet velocity (equal to cutting velocity), attempted to find the best machining conditions, with the purpose to obtain a decrease on the cutting fluid volume, taking into consideration the analysis of the process output variables such as cutting strength, cutting specific energy, grinding wheel wear and surface roughness. It was verified that the 3mm diameter optimized nozzle and the integral oil, in general, was the best combination among all proposed.

An experimental investigation of temperatures during conventional and CBN grinding

In many grinding applications, the material removal rate is constrained by the undesired thermal effects such as surface burn, tensile residual stresses, and micro-cracks on the ground parts. Thermal damage is a common productivity limitation factor for conventional grinding wheels largely employed in industry due to their convenient cost and known behavior. The development of superabrasive materials having high heat conduction coefficients allowed for higher material removal rates, pushing up the limits of productivity previously achieved with conventional wheels. This paper presents the results of a comparative investigation of maximum surface temperatures generated during the plunge grinding of 52100 steel using Al2O3 and CBN wheels. The experiments were conducted under wet as well as dry grinding conditions. The temperatures measured experimentally were compared to those determined analytically. A discussion relative to heat partition coefficients concludes this paper.

Experimental Investigation of Burr Formation in the Surface Grinding of Tool Steel

Increasing industrial requirements concerning the precision of edge geometry lead to the investigation of burr formation, particularly in finishing operations such as grinding. In the present paper, a fundamental investigation of burr formation in the flat surface grinding of tempered tool steel (90MnCrV8) is presented. Conventional and superabrasive grinding wheels with different grain sizes and materials are used under varying cutting conditions. In addition, a ‘hybrid grinding wheel’, which essentially is the wheel hub of a superabrasive wheel with an aluminium oxide abrasive layer, is used in order to isolate the influence of the abrasive material. The geometry of the generated exit burrs at the workpiece edge is investigated. The geometrical burr parameters are measured using optical microscopy. Furthermore, measured grinding forces and temperatures are correlated with the burr parameters. In addition, the microstructure of the burr material is analysed by metallographic sections. As a result of the experimental investigations, an approach to describing burr formation mechanisms in grinding as well as the influences of grinding wheel and cutting parameters on burr shape and size is obtained.

Study on Forming Mechanism of Surface Hardening in Two-Pass Grinding 40Cr Steel

We had done the two-pass grind-hardening experiment on 40Cr steel using the conventional aluminum grinding wheel on a surface grinder, compared the structure and performance of the hardened layer of one-pass grinding with those of two-pass grinding and analyzed the forming mechanism of two-pass grinding hardened layers. The results show that there are a similar martensite structure and change rules of hardened layer of one-pass grinding and two-pass grinding in spite of the different of initial structures, for martensite has tempered by the action of the creep feed grinding temperature field. The depths of hardened layer, microhardness and wear resistance have further improved, but the maximal compressive residual stress and its influencing depth of hardened layer have decreased. The forming mechanism of the two-pass grinding hardened layer is the same as that of the grinding hardened layer of quenched steel.

Tribological design of grinding wheels using X-ray diffraction techniques

Grinding wheel wear is a significant problem when the wheel has to be continuously dressed in order to maintain high productivity and high-quality ground surfaces, especially during the manufacture of camshafts and crankshafts for certain automotive applications. This paper describes the use of X-rays to specifically engineer bonding systems for conventional abrasive grinding wheels so that the wheel wears considerably less during cylindrical grinding operations including the peculiarities associated with camshaft and crankshaft grinding. A significant factor associated with the wear of grinding wheels is the amount of free quartz that remains in heat-treated vitrified bonding systems. A number of quartz dissolution models have been developed that show how grinding wheel manufacturers can reduce the occurrence of bond fracture during grinding, and these models are compared with each other in this paper using X-ray diffraction techniques. This paper also explains how the use of X-rays can be used to develop the next generation of vitrified bonding systems that will allow grinding wheels to be cleaned and dressed with a laser without damaging the structure of the grinding wheel. A new method of dressing is reported that promotes preferred orientation of aluminium oxide abrasive grains that allows grinding wheels to operate in the roughing, finishing, and superfinishing grinding regimes.