Metal Bonded Diamond Wheel Research Articles

Metal-bonded diamond wheel dressing by using wire electrical discharge: principle and prototype machine design

Metal-bonded diamond wheel dressing by using wire electrical discharge: principle and prototype machine design

Microscale viscous sintering model application to the preparation of metal bonded diamond grinding wheels

During sintering, with the interfacial free energy decreasing, particles bond to each other and the dense density increases, which are familiar phenomena in the preparation of metal bond diamond wheels and affect the mechanical properties of the grinding wheel. Herein, a sintering model of metal bond diamond wheels at a microscopic scale was constructed based on the computational fluid dynamics (CFD) and discrete element method (DEM), which was carried out to reveal the flow field, pressure field, and kinetic properties of the metal material in the heating process. Meanwhile, the finite element method (FEM) was used to analyze the thermal stress of diamond particles. The results show that with the increase in temperature, the viscous flow of particles intensifies. In the middle and late stages of sintering, the porosity of the particles changes significantly, and the densification rate is accelerated. Under the same temperature conditions, compared with the dodecahedral diamond, the octahedron produces less thermal stress and has better mechanical properties.

Determining the conditions for decreasing cutting force and temperature during machining

The theoretical approach to calculating and controlling the force and temperature parameters of edge cutting and abrasive machining processes taking into account the provision of the minimum possible power consumption of the cutting process is given. The conditions for reducing cutting force and temperature and improving the quality and rate of grinding and edge cutting machining are theoretically determined. They consist mainly in reducing the relative shear angle of the machined material and, accordingly, power consumption by increasing the cutting capacity of the tool. It is analytically found that in grinding, cutting force and temperature are greater than in edge cutting machining due to the intense friction of the grinding wheel bond with the machined material and the presence of negative rake angles of cutting grains. It is shown that cutting temperature during grinding can be reduced using the multipass grinding pattern, as well as patterns of high-velocity creep-feed wheel-face and double-disc grinding. On this basis, the approach to creating technologies of effective high-velocity defect-free edge cutting and abrasive machining of machine parts and carbide cutting tools is developed. The developed technology of form grinding on the modern HOFLER RAPID 1250 gear grinding machine using a special highly porous form abrasive wheel tapered on both sides received practical application. This wheel has a high cutting capacity in conditions of high-velocity creep-feed grinding. Compared to the conventional method of gear grinding by the generating process, carried out under conditions of multipass grinding, this allowed increasing machining rate up to 5 times. The technology of high-velocity creep-feed external grinding of multipoint carbide cutting tools (milling cutters, reamers) with high-strength metal-bonded diamond wheels using the electrical discharge dressing method is developed. This made it possible to increase the rate by 2–3 times and provide high-quality defect-free machining of carbide tools

Development of a New Truing Device Based on Electro-Contact Discharge Machining for Metal Bond Grinding Wheels

Metal bond grinding wheels can retain their shape and size under extreme grinding conditions. On the other hand, it is difficult to true them accurately and efficiently due to the severe wear of truing tools. To solve the problem, this paper proposes a new truing device based on electro-contact discharge machining. The device is designed so that the position of the electrode working face remains unchanged even if the electrode is worn. Some truing experiments were carried out using a prototype truing device for a metal bond diamond wheel of grain size #1000 under dry conditions. As a result, relatively high truing accuracy has been achieved in combination with an additional truing by a GC stone.

Experimental study of surface performance of monocrystalline 6H-SiC substrates in plane grinding with a metal-bonded diamond wheel

Monocrystalline SiC has long been recognised as an ideal third-generation semiconductor material for application in situations where there is high frequency, high power and high voltage. Because of the hardness, stiffness and strength of monocrystalline SiC, these materials are extremely difficult to machine in order to produce the extremely flat, smooth and damage-free surfaces required in many industrial applications. This paper presents the results of plane grinding experiments which were carried out using a metal-bonded diamond wheel. The process parameters of these have demonstrated a significant influence on surface roughness. Surface quality improved and roughness decreased as the wheel feed rate decreased. On the substrate surfaces, the particle trajectory density increased closer to the centre, producing better surface quality. At large feed rates, the material removed is mainly brittle fracture, and the plough scratch widths and gully depths on the ground surface are greater. At small feed rates, plastic removal predominates, becoming more significant closer to the centre and giving a smoother surface. Median and transverse cracks occur in the subsurface damaged layer, and the crack depths are consistent with the surface roughness Rz and gully morphology. Then, the critical grit depth of cut and the maximum undeformed substrate thickness values under different grinding conditions were calculated in order to analyse the characteristics of the subsurface damage and the material removal mechanism. Finally, an optimised process was achieved using orthogonal experiments, with processing parameters for rough, half-fine and fine grinding. This process gives flat substrates with surface roughness Ra 0.012 μm, SSD < 4 μm and TTV < 3 μm, which achieves the same level of precision as lapping.

Grinding wheel motion, force, temperature, and material removal in rotational atherectomy of calcified plaque

Abstract This study investigates the grinding wheel motion, force, material removal, and temperature in rotational atherectomy (RA). RA utilizes a metal-bond diamond wheel to remove plaque from arteries to treat cardiovascular diseases. As a plaque surrogate, a bone workpiece was placed in a vessel simulator and subjected to RA with a wheel rotational speed of 160,000 rpm. This grinding process was monitored by a high-speed camera, a dynamometer, and embedded thermocouples. The results show this process has a 108 Hz wheel orbital frequency, an oscillating grinding force of 0.23 N, 90% debris smaller than 31 μm, and a 4.1 °C temperature rise.

Polishing mechanism and surface damage analysis of type IIa single crystal diamond processed by mechanical and chemical polishing methods

The polishing mechanisms and surface damages of mechanically and chemically polished diamond crystals were investigated. A metal bonded diamond wheel was used for mechanical polishing, while an SiO2 wheel was used for chemical polishing. After polishing, samples underwent surface treatment with hydrogen plasma to exhibit negative electron affinity. SEM observation revealed that the scratches consisted of dark cracks with cleavage facets. Dark contrast was observed around the cracks on the hydrogen terminated diamond surface, indicating that carriers excited by primary electrons were eliminated by crystal defects around the cracks. The polishing rate increased nonlinearly with the rotating speed of the SiO2 wheel. The difference of polishing rate of the (100) surface between the <110> direction and the <100> direction became smaller when using the SiO2 wheel than when using the metal bonded diamond grinding wheel. The polishing rates became more isotropic, suggesting that the wear reactions of the diamond and the SiO2 wheel were mainly chemical. Although abrasion traces were also observed by optical microscopy on the sample polished by an SiO2 wheel, dark contrast due to lattice distortion or crystal defects was not observed by SEM. This result shows that the sample surface and subsurface chemically polished by the SiO2 wheel had very little damages.

Effect of hot pressing temperature on microstructure, mechanical properties and grinding performance of vitrified-metal bond diamond wheels

The self-sharpening vitrified-metal bond diamond wheels added with a 3wt.% brittle Na2O-B2O3-SiO2-Al2O3-Li2O vitrified bond were fabricated by hot pressed sintering technique. Using the methods of scan-electroscope, energy spectrum analysis, X-diffraction analysis, XPS analysis, Rockwell hardness test and three-point bending test, the effects of hot pressing temperature on the microstructure, hardness and the transverse rupture strength (TRS) of vitrified-metal bond were investigated. Then the grinding performance of cylinder of the diamond wheels was also studied. The results showed that, when the hot pressing temperature was 850°C, a thin FeAl2O4 transition layer formed, which enhanced the interfacial bending strength between metal and glass phase, and the TRS of vitrified-metal bond reached the maximum value 826.54MPa. Comparing with metal bond diamond wheel's, the average value of the roundness and straightness of the 50 cylinders ground by the vitrified-metal diamond wheel reduced from 3.1μm and 2.5μm to 2.7μm and 2.1μm.

On-machine precision form truing of arc-shaped diamond wheels

In order to realize the efficient and precision truing of arc-shaped diamond wheel for precision grinding of spherical, aspherical and free-form surfaces, a novel on-machine precision form truing of resin and metal bonded arc-shaped diamond wheels is proposed utilizing rotary green silicon carbon (GC) rod. Through this on-machine rotary GC rod (ORGCR) mutual-wear truing, any required radius of wheel arc profile could be formed by programmed truing paths, meanwhile, the vertical direction position error of the wheel center could be corrected after truing. Firstly, the principle of ORGCR mutual-wear truing for arc-shaped diamond wheel was introduced, and new evaluation methods of truing performance and truing ratio were provided. Then the truing performance and truing ratio were observed for different grains and bond of arc-shaped diamond wheels, the effects of ORGCR mutual-wear truing parameters on profile radius and form accuracy of wheels were investigated. Finally, the convex aspherical surface of single crystal silicon was ground by trued arc-shaped diamond wheel. The experimental results showed that the resin and metal bonded diamond wheels could be efficiently and precisely trued with high truing ratio. The form error of wheel arc profile reached 2.5–6μm/3mm which decreased about 90% compared to pre-truing wheel. Besides, the diamond grains were well distributed on the wheel surface, and protruded out of the wheel bond after truing. The precision aspherical surface of single crystal silicon with the form accuracy PV of 507nm and the average roughness Ra of 57.1nm was achieved by parallel grinding with the trued D7 resin bonded wheel.

On-machine dry electric discharge truing of diamond wheels for micro-structured surfaces grinding

Precision grinding with diamond wheels gives a promising alternative to achieve high quality micro-structured surfaces on optical molds. However, it is difficult to true these diamond wheels efficiently, because of the remarkable resistance property and the geometrical limitation of small wheel profile. In this paper, an on-machine dry-EDT method to precision shape and prepare diamond wheels with various profiles was proposed for micro-structured surface grinding. Firstly, the fundamental truing errors were analyzed based on the dry-EDT kinematics. And then the capabilities of dry-EDT truing for high abrasive concentration metal bonded diamond wheels were presented. Next, the effects of kinematic parameters variables on trued wheel profile accuracy were investigated. Finally, the micro-structured surfaces on SiC ceramic and tungsten carbide WC were ground by these trued diamond wheels. The experiments results showed that the arc-shaped diamond wheel (diameter of 200mm) with 4μm profile error (PV) and 1.0023mm profile radius, and the V-shaped diamond wheel with 22.5μm V-tip radius and 120.03° profile angle could be obtained by on-machine dry EDT. The kinematic parameters of dry-EDT have an important influence on truing profile accuracy of diamond wheels, especially for the tip of V-shaped wheel. The subsequent grinding show that the edge radius of V groove array on SiC is less than 2μm, while the radius of included corner is around 55μm. The PV error of ground arc groove array on WC is less than 5μm. The surface roughness of ground micro-structured surface Ra is 142nm and 97nm for SiC and WC, respectively.

Effect of Pulsed Laser Dressing of Metal-Bonded Diamond Wheels on Cutting Performance

An investigation of laser dressing of metal-bonded diamond blades is reported. The influence of laser irradiation on the diamond particles and bond material was reported, and the bonding material was removed without deterioration of the diamond particles. The average protrusion height of diamond particles in laser-dressed condition was found to be 80–90 µm compared to 50–60 µm in case of mechanically dressed wheel. The results indicate a significant increase in cutting performance and decrease of burr height for laser-dressed diamond blades as compared to conventional dressing methods.

Mirror surface grinding of sapphire by coarse grain size diamond wheels

This paper discusses the grinding of sapphire for mirror surfaces by coarse grain size diamond wheels. Sapphire is a hard-to-machine material because it has excellent mechanical properties and indentation hardness. Since it is effective for hard materials to use metal-bonded diamond wheels, the authors had two experiments to investigate mirror surface grinding by coarse grain size diamond wheels. The 1st experiment was investigating appropriate grinding conditions, and the 2nd experiment was investigating protrusion height of abrasive grains. Although the conventional methods could not acquire mirror surface, the results of the experiments show that mirror surface (Ra: 5 nm <) were obtained by the #270 and #325 mesh size wheels. These results indicate the possibility of decreasing grinding processes by coarse grain size diamond wheels.

Modelling and simulation of spark assisted diamond face grinding of tungsten carbide-cobalt composite using ANN

The aim of this study is to develop an artificial neural network (ANN) model for spark assisted diamond face grinding (SADFG) of cobalt bonded tungsten carbide (WC-Co) composite to predict the material removal rate (MRR) and average surface roughness (Ra). The experiments were conducted on a self-developed face grinding setup, which is attached with EDM machine. A bronze metal bonded diamond wheel is used for experimentations. All the experiments were performed according to the central rotatable design. The current, pulse on-time, duty factor and wheel speed were taken as input process parameters and responses are measured in terms of MRR and Ra. Central rotatable design is used for experimentation. The obtained experimental data set was used to train the ANN model. The ANN architecture with back propagation algorithm has been used for modelling of process parameters of SADFG process. It has been found that the developed ANN model is capable to predict the MRR and Ra with absolute average percentage error of 10.40% and 6.81%, respectively. It has been also found that wheel speed at 1,300 RPM is suitable for achieving of the better surface finish while duty factor at 0.70 has been found more appropriate for higher MRR.

On-machine precision preparation and dressing of ball-headed diamond wheel for the grinding of fused silica

In the grinding of high quality fused silica parts with complex surface or structure using ball-headed metal bonded diamond wheel with small diameter, the existing dressing methods are not suitable to dress the ball-headed diamond wheel precisely due to that they are either on-line in process dressing which may causes collision problem or without consideration for the effects of the tool setting error and electrode wear. An on-machine precision preparation and dressing method is proposed for ball-headed diamond wheel based on electrical discharge machining. By using this method the cylindrical diamond wheel with small diameter is manufactured to hemispherical-headed form. The obtained ball-headed diamond wheel is dressed after several grinding passes to recover geometrical accuracy and sharpness which is lost due to the wheel wear. A tool setting method based on high precision optical system is presented to reduce the wheel center setting error and dimension error. The effect of electrode tool wear is investigated by electrical dressing experiments, and the electrode tool wear compensation model is established based on the experimental results which show that the value of wear ratio coefficient K′ tends to be constant with the increasing of the feed length of electrode and the mean value of K′ is 0.156. Grinding experiments of fused silica are carried out on a test bench to evaluate the performance of the preparation and dressing method. The experimental results show that the surface roughness of the finished workpiece is 0.03 μm. The effect of the grinding parameter and dressing frequency on the surface roughness is investigated based on the measurement results of the surface roughness. This research provides an on-machine preparation and dressing method for ball-headed metal bonded diamond wheel used in the grinding of fused silica, which provides a solution to the tool setting method and the effect of electrode tool wear.

A017 Thermal Dressing of Metal Bonded Diamond Wheel by Nd:YAG Laser : Optimization of air-jet irradiation angle

In this study, a pulsed Nd:YAG laser beam is used as a non-contact thermal dressing tool for a metal bonded diamond wheel. In order to efficiently remove the bond material, it is necessary to direct air on the spot irradiated by the laser so as to blow away the molten binder. The new integrated laser-air head makes it possible to make an appropriate chip pocket depth with less residual re-solidification layer of bond material. The grinding experiments of the hot-pressed SiC reveals that the laser-dressed wheel has somewhat better grinding performance than the conventional rotary dressed wheel.

Grinding characteristics of mould steel with micro 3D structure in ultrasonically assisted precision grinding

This study aims to develop a high precision machining method for difficult-to-machine materials with micro 3D structure. For this purpose, ultrasonically assisted on-surface grinding technique has been proposed and experimental investigations involving difficult-to-machine material workpiece with micro strait ribs of several hundreds μm in width have been carried out using metal bonded diamond wheels. As a result, manufacturing of mirror surface on micro 3D structure can be achieved easily and the grinding forces are decreased by ultrasonically assisted grinding. Additionally, the correlation of the grinding characteristics and with the wheel surface topography during grinding process has also been demonstrated. The obtained results indicate the ultrasonically assisted grinding is extremely effective for high precision machining of difficult-to-machine materials with micro 3D structure.

In-process wire electrical discharge dressing (IWEDD) of metal bonded diamond wheels

Electrical discharge dressing has been established as alternative for conditioning metal bonded diamond wheels, which will be exploited to develop in-process wire electrical discharge dressing (IWEDD). The main requirements for its successful implementation are first presented in this work. Small depth of dressing cuts was found to be feasible and high material removal rates were achieved without damaging diamonds. Dulled grains are finally removed by mechanical contact with the work piece. It was found that grinding forces can be kept constant over time while non-productive time is reduced, showing that IWEDD is a suitable conditioning method with great potential for future industrial applications.

Development of a Vitrified Bonded Superabrasive Wheel with Electrical Conductivity and its Application

A vitrified bonded diamond wheel having electrical conductivity was manufactured on a trial basis. The electrically conductive (EC) vitrified bonded diamond wheel has enabled an electrodischarge truing and an electrical contact sensing. In this study, the EC vitrified bonded diamond wheel is applied to the EDM (Electro Discharge Machining) assisted grinding of PCD materials. The result shows that a lower and more stable grinding force can be realized and a better surface finish is attained compared with those achievable with a metal bonded diamond wheel.

Fundamental Study on Setting of Diamond Abrasive Grains Using Electrostatic Force for Single-Layered Metal Bond Wheel

Single-layered metal bond diamond wheels are useful to high efficient grinding of difficult-to-grind materials because of the high gripping force of abrasive grains and the controllable grain density. In this paper, fundamental information are obtained for an application of electrostatic force to setting of diamond grains into pasted metal bond slurry layer on wheel surface, investigating experimentally jumping phenomenon of diamond grains in an electrostatic field between a electrode plate and metal bond slurry layer. The SD grains and the SDC grains coated with Ti are selected. SDC grains jump into a metal bond layer as quick as making an electrostatic field, however SD grains jump with short time lags. The setting rate of SDC grains is larger than that of SD grains, and setting position accuracy of SDC grain array is better than SD grain array. The possibility of setting abrasive grains into single-layered metal bond diamond wheel surface using electrostatic force is obtained and SDC grains are suitable to the proposed abrasive setting method.

Electrical discharge dressing and its influence on metal bonded diamond wheels

Although EDM is a thermal removal process, when it is applied for dressing diamond grinding wheels, usually little or no thermal damage is caused to the diamonds. In this work, a better explanation for this fact is provided. A thermo-electrical model is used to calculate the temperature distribution inside diamonds showing that even for high discharge energies small amount of graphitization occur. Here, the exceptional properties of diamond contribute to minimize thermal damages. Still, a concentration of discharges can occur around the diamonds and thus lead to thermal damages. However, this phenomenon is more evident for large diamonds.