Diamond Cup Wheels Research Articles

Material removal characteristics of ultra-precision grinding silicon carbide ceramics

ABSTRACTSilicon carbide (SiC) ceramic has been widely applied to fabricate functional components relying on their excellent physical, chemical and mechanical properties. Meanwhile, it is always highly concerned to seek suitable manufacturing technology and processes for machining such difficult-to-cut material with high-precision, high-efficiency and low-cost. In the present paper, material removal characteristics of reaction-bonded silicon carbide (RB-SiC) and pressureless sintered silicon carbide (S-SiC) were investigated by ultra-precision grinding experiments. #120, #600, #2000 and #12000 diamond cup wheel were employed for coarse, semi-finished, fine and finish grinding, respectively. The surface topographies, surface morphologies and grinding grooves were measured. The results indicated that there are distinguishing material removal characteristics between RB-SiC and S-SiC, and #2000 diamond wheel can be chosen as the final grinding wheel for most high-performance SiC ceramic products. The present study provides a technological reference to ultra-precision grinding of hard materials.

Experimental study on ultra-precision grinding characteristics of WC-Ni hard metals

Tungsten carbide (WC) hard metals are universally used in industrial fields owing to their superior properties, and the machining accuracy of WC products is playing an important role in their service performance. However, how to achieve a balance between high accuracy and processing cost according to different applications is a key engineering issue. Thus, it is necessary to reveal the material removal characteristics of such difficult-to-cut hard metals. In this article, ultra-precision grinding characteristics of WC-Ni hard metals were investigated based on the wafer rotation grinding method using #120, #600, #2000, and #12000 diamond cup wheels as coarse, semi-finished, fine, and finish grinding wheels, respectively. A polished sample was taken for comparison. The optical surface profilers, scanning electron microscope, and atomic force microscope were employed for checking surface topographies, surface morphology, and cutting depth. An ultra-smooth and defect-free WC-Ni surface with less than 2 nm Ra and the average cutting depth of about 10 nm can be obtained using a #2000 diamond wheel, which can replace polishing and satisfy the requirements of most high-performance applications. This study provides useful observations for ultra-precision manufacturing of hard metal products.

Surface texture formation in precision machining of direct laser deposited tungsten carbide

This paper focuses on an analysis of the surface texture formed during precision machining of tungsten carbide. The work material was fabricated using direct laser deposition (DLD) technology. The experiment included precision milling of tungsten carbide samples with a monolithic torus cubic boron nitride tool and grinding with diamond and alumina cup wheels. An optical surface profiler was applied to the measurements of surface textures and roughness profiles. In addition, the micro-geometry of the milling cutter was measured with the application of an optical device. The surface roughness height was also estimated with the application of a model, which included kinematic-geometric parameters and minimum uncut chip thickness. The research revealed the occurrence of micro-grooves on the machined surface. The surface roughness height calculated on the basis of the traditional kinematic-geometric model was incompatible with the measurements. However, better agreement between the theoretical and experimental values was observed for the minimum uncut chip thickness model.

Experimental Evaluation of Respirable Dust and Crystalline Silica Controls During Simulated Performance of Stone Countertop Fabrication Tasks With Powered Hand Tools.

Workers who fabricate stone countertops using hand tools are at risk of silicosis from overexposure to respirable crystalline silica. This study explored the efficacy of simple engineering controls that can be used for dust suppression during use of hand tools by stone countertop fabricators. Controlled experiments were conducted to measure whether wet methods and on-tool local exhaust ventilation (LEV) reduced respirable dust (RD) exposures during use of various powered hand tools on quartz-rich engineered stone. RD samples collected during edge grinding with a diamond cup wheel and a silicon carbide abrasive wheel were analyzed gravimetrically as well as by X-ray diffraction to determine silica content. A personal optical aerosol monitor was used simultaneously with the RD samples and also for rapid assessment of controls for polishing, blade cutting, and core drilling. On-tool LEV and sheet-flow-wetting were effective in reducing exposures, especially when used in combination. Sheet-flow-wetting with LEV reduced geometric mean exposures by as much as 95%. However, typical water-spray-wetting on a grinding cup was less effective when combined with LEV than without LEV. Mean silica content of RD samples from grinding operations was 53%, and respirable mass and silica mass were very highly correlated (r = 0.980). Optical concentration measures were moderately well correlated with gravimetric measures (r = 0.817), but on average the optical measures during a single trial using the factory calibration were only one-fifth the simultaneous gravimetric measures. Sheet-flow-wetting combined with on-tool LEV is an effective engineering control for reducing RD exposures during engineered stone edge grinding and blade cutting. On the other hand, addition of LEV to some water-spray-wetted tools may reduce the effectiveness of the wet method.

An experimental study on preparation of vitrified bond diamond grinding wheel with hollow spherical corundum granules as pore former

Hollow spherical corundum granules were introduced into a vitrified bond diamond grinding wheel as pore former. The influences of content and particle size of the hollow spherical corundum granules on porosity, flexural strength, and hardness of the vitrified bond diamond wheel samples were systematically investigated. The grinding performance of the designed vitrified bond diamond cup wheel on sapphire and 6H-silicon carbide (SiC) substrates was examined, and morphological properties of the ground surface were evaluated. Results showed that higher content and smaller size of hollow spherical corundum granules could lead to the increase of the porosity and the decrease of flexural strength and hardness. Sapphire and 6H-SiC substrates could be effectively ground by the vitrified bond diamond cup wheel containing 8% hollow spherical corundum granules. During the grinding, although a brittle mode dominated the material removal of two substrates, more ductile removals and lower surface roughness could be identified from 6H-SiC substrate than from sapphire.

Precision Surface Grinding of Silicon Carbide

Silicon carbide (SiC) is well known for its excellent material properties, high durability, high wear resistance, light weight and extreme hardness. Among the engineering applications of this material, it is an excellent candidate for optic mirrors used in an Airbone Laser (ABL) device. However, the low fracture toughness and extreme brittleness characteristics of SiC are predominant factors for its poor machinability. This paper presents surface grinding of SiC using diamond cup wheels to assess the performance of diamond grits with respect to the roughness produced on the machined surfaces and also the morphology of the ground work-piece. Resin bonded diamond cup wheels of grit sizes 46 µm, 76 µm and 107 µm; depth of cut of 10 µm, 20 µm and 30 µm; and feed rate of 2 mm/min, 12 mm/min and 22 mm/min were used during this machining investigation. It has been observed that the 76 grit performs better in terms of low surface roughness value and morphology.

Diamond-ECM Grinding of Sintered Hard Alloys of WC-Ni

Continuing the theme raised by the authors on the ISEM-2013 and related to the diamond - ECM grinding of ceramic-metal tungsten (DECMG) they discuss the results of the study of this method of machining of sintered alloys WC-Ni, as construction material. Difficulties arising during their DECMG machining and associated features of the structure and chemical links formed in the tungsten carbides are noted. The conditions to overcome these difficulties through the optimal combination of anodic dissolution and micro-cutting, manifestations of different effects, including the effect of the adsorption strength reduction, electro-capillary, ultrasonic and sound capillary effects and their synergy are shown. The main reactions of anodic dissolution of alloys in the electrolyte - an aqueous solution of Na2HPO4 and Na2CO3 with additives and regularities governing the functioning of the electrolyte in the gap are defined. The grinding using diamond cup wheels 12A2-45° bonded by the Cu-Al-Zn according the scheme of elastic frontal grinding DECMG with rotation of the work-piece is recommended to achieve the roughness Ra ≤ 0.63-0.32 mμ at the surface planes such as planes of disk supports for tests according to GOST 27034-86 (ISO 4506-79), or planes of washers for power thyristors and rectifiers having the area up to 2000 mm2. Limit conditions of zero-defect DECMG (no burn marks, no micro-cracks in the surface layers and in the grains of the alloy) are determined as following: grinding speed of 12-18 m/s; operating voltage of 3-4V; the normal component of the grinding force 0.25-0.27kN/cm2. Information about the regularities of anodic dissolution of alloys, the functioning of the electrolyte, modes and characteristics of DECMG with the end face of a cup grinding wheel can be useful for researchers and developers of physical, chemical and combined methods of machining.

High-efficiency rotary dressing method for cubic boron nitride wheels

The paper addresses kinematics of the rotary method whereby a grinding wheel is dressed by a rotating diamond cup wheel. Through the example of grinding high-temperature nickel and titanium alloys and high-alloy steels using highly porous vitrified cubic boron nitride wheels, the authors have demonstrated the advantages of the proposed dressing method over that with a single-point diamond dresser.

Surface roughness analysis after machining of direct laser deposited tungsten carbide

In this paper, an experimental surface roughness analysis in machining of tungsten carbide is presented. The tungsten carbide was received using direct laser deposition technology (DLD). Experiments carried out included milling of tungsten carbide samples using monolithic torus cubic boron nitride (CBN) tool and grinding with the diamond cup wheel. The effect of machining method on the generated surface topography was analysed. The 3D surface topographies were measured using optical surface profiler. The research revealed, that surface roughness generated after the machining of tungsten carbide is affected by feed per tooth (fz) value related to kinematic-geometric projection only in a minor extent. The main factor affecting machined surface roughness is the occurrence of micro grooves and protuberances on the machined surface, as well as other phenomena connected, inter alia, with the mechanism for material removal.

Performance of Diamond Cup Wheels with Nano-Scale Rare-Earth Oxide and Carbide

Diamond cup wheel is one of important tools for machining of ceramic tile. In this paper, ceramic tiles were ground by diamond cup wheels which segments adding nano-scale rare-earth oxide and nano-scale carbide on a special designed test machine. The wear resistance of diamond cup wheels and materials’ removal process of ceramic tiles had been tested, and grinding ratio were calculated and compared. Different grinding ratios can be obtained according to different technological parameters. The segments of adding nano-scale rare-earth oxide and nano-scale carbide were observed from microgram and metallography structural pattern. The results showed that nano-scale rare-earth oxide and nano-scale carbide can fine structure, make grain boundary clear and increase grasping of diamond grits.

Study of Surface of Edge Grinding of Ceramic Tile by Diamond Cup Wheels

As one of the excellent decorative materials, ceramic tiles must be ground and polished to present the glossy surface. Diamond cup wheel is one of important tools. Ceramic tiles were ground by diamond cup wheel with a special designed test machine. The materials’ removal process of ceramic tiles had been tested, and surface roughness was measured. The surface micromorphology of the polished ceramic tiles under different depth of grinding and feed speed was examined by Scanning Electron Microscopy (SEM). The results showed that a lot of materials’ removal can be obtained by increasing the depth of grinding and feed speed in rough process of ceramic tile. On the contrary, good surface can be obtained by reducing depth of grinding and feed speed in fine process of ceramic tile.

Edge Grinding of Ceramic Tile by Diamond Cup Wheels

As one of the excellent decorative materials ceramic tiles must be ground and polished to present the glossy surface. In this paper the ceramic tiles were edge ground by diamond cup wheels in the special designed test machine. The surface morphology of the polished ceramic tiles and the wear of diamond cup wheel were examined by Scanning electron microscopy (SEM). The wear resistance of diamond cup wheel and the materials’ removal process of ceramic tiles had been tested. The results showed that the wear of diamond cup wheel was stable when grinding with high grinding ratio. The ground surface showed that only the fracture of ceramic tiles was acted by diamond grits during grinding with water by means of good quality diamond cup wheel.

Loose abrasive truing and dressing of resin bond diamond cup wheels for grinding fibre optic connectors

A loose abrasive lapping technology was developed for truing and dressing ultrafine diamond cup wheels for grinding spherical end faces of fibre optic connectors. The relative densities of exposed grits and grit pull-outs measured from wheel surfaces prepared using the loose abrasive lapping and the bonded abrasive dressing were compared. It was found that the lapping method with loose abrasives produced wheel surfaces with more exposed grits and less grit pull-outs, especially for finer grit size wheels. For dressing ultrafine grit size wheels, the particle size of the lapping paste should be smaller than the wheel grit size to achieve a better result. It is also found that the wheels dressed using the lapping method demonstrate an excellent grinding performance.

Micro/meso ultra precision grinding of fibre optic connectors

The present paper reports on the development of a micro/meso grinding technology using inclined resin bond diamond cup wheels for machining spherical end faces of fibre optic connectors. The ground spherical end faces obtained using the wheel of grit size of 4 μm have an average roughness ( R a) value of ∼7 nm in the fibre area and a profile error of below 0.4 μm. The corresponding average return and insertion losses are ∼55 and 0.1 dB, respectively. The results are competitive to those obtained from the polishing process that is currently used in industries. Furthermore, this study has revealed the relationships between the ground surface quality characterized by roughness and profile accuracy and the optic performance evaluated by insertion and return losses.

High-Precision Surface Grinding of Ceramics with Superfine Grain Diamond Cup Wheels

High-precision surface grinding has been performed on the Si 3N 4 and AI 2O 3-TiC ceramics and Mn-Zn Ferrite using an ultra-precision surface grinder and very fine grain diamond cup wheels, where the maximum depth of cut was 2 μm and the maximum through feed rate being 100 mm/min. The surface roughness and percent brittle mode area were measured using an atomic force microscopy (AFM). These characteristics were discussed by a parameter “ S max” defined as S max = μa v f/ v s (μ: successive cutting edge spacing, a: depth of cut, v f: through feed rate, v s: wheel speed). With decreasing grain size from #1200 to #16000, the surface roughness Rmax decreases to 20 to 30 nm. Similarly, a remarkable reduction in percent brittle mode area is seen by changing grain size. The effect of dressing stone on the ground surface was also investigated using 3D wheel surface topography.

Generation of Parabolic and Toroidal Surfaces on Silicon and Silicon-Based Compounds Using Diamond Cup Grinding Wheels

This paper presents the methods and experimental results using diamond cup wheels and CNC machining centers for grinding parabolic and toroidal surfaces made of Si and SiC, the former for use as a thermal imaging lens and the latter for synchrotron radiation facilities. Generation of aspheric surfaces, by zonal material removal, on Si using cup grinding wheels and a 5-axis machining center was investigated. Theoretical and experimental investigation of the grinding and material parameters that influence ductile grinding are discussed. Ductile grinding is possible with wheels having small grit size and with proper combination of feed and unit normal load; a resinoid bonded wheel promotes this more easily than a metal bonded wheel, though at the expense of profile accuracy. Profile analysis, surface integrity, and examination of grinding swarf using digital imaging are discussed. Also, generation of toroidal surfaces on SiC using metal-bonded cup wheels, a 3-axis machining center and a micro-displacement table with piezoelectric actuators was studied. Toroidal SiC mirrors were ground with good shape accuracy, mirror finish, and low surface roughness. The time consumed in the process is very short. The machines used are inexpensive and not specially designed for ultra-precision grinding.

研削砥石のドレッシングに関する研究 (第2報)

A dressing technique with a diamond cup wheel as a dresser is introduced for higher performance of grinding wheel. In the technique, the rotating diamond cup wheel is fed parallel to the wheel axis. Grinding performance is experimentally investigated under various setting conditions of the dresser, dressing conditions and grinding coditions, analyzing size generation process, grinding force, surface finish, wheel wear and so on. Sharper cutting edges are generated on the acting wheel face in the technique, while the number of cutting edges is slightly fewer than that in conventional method with a single point diamond dresser. Grinding force is therefore smaller while surface finish is rougher and wheel wear is larger as compared with coventional one. Furthermore, the grinding results are hardly affected by dresser wear in the technique, while those are significantly affected in conventional one.