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grinding wheel - an overview | sciencedirect topics

grinding wheel - an overview | sciencedirect topics

Grinding Wheel Manufacturers' LiteratureCincinnati MilacronDiamond and CBN grinding wheels (1990)Cincinnati MilacronGrinding wheel application guide (1983)DWHPrecision tools in diamond and CBN (n.d.)EHWAProduct catalog (n.d.)FAG (Efesis)SuperabrasivesCBN and diamond with vitrified bondrotating dressing tools, Publication # SK56 001 EA (n.d.)KinikGrinding wheels catalog #100E (n.d.)KrebsVitrified diamond and CBN grinding wheels (n.d.)Meister abrasivesMaster vitrified CBN (n.d.)NoritakeVit CBN wheel ultimate solution (1998)Vitrified bond CBN wheels (n.d.)NortonProject Optimosgrind in the fast lane (1999)Bonded abrasives specification manual (1999)Diamond vitrified VRF bond for roughing and finishing polycrystalline tools (2000)Norton CBN wheels precision production grinding (n.d.)Osaka diamondVitmate series vitrified bond CBN wheels (n.d.)Radiac abrasivesAn introduction to Radiac grinding wheels and their applications (1987)TeschDiamond and CBN grinding wheels for mechanical industries (1995)TVMKGeneral catalog (2001)TyrolitGrinding with Tyrolit (n.d.)Diamant-nitrure de bore cubique (CBN) (n.d.)UniversalPoros two (n.d.)Universal vitrified grinding wheels (1997)Universal stock catalogue & price list (1994)Universal super-abrasivesDiamond & CBN wheelsUnivel, vitrified, resin metal, plated (1998)Van-Moppes-IDPCrush-form diamond and CBN wheels (n.d.)Resimet (n.d.)WendtDiamond/CBN grinding and dressing toolsH/S/G-1 general Information (n.d.)Vit-CBN CBN grinding tools in vitrified bond (1991)WinterGrinding with diamond and CBN Book (1988) Winter HP High Precision Electroplated Wheels, Brochure B00A-38WinterthurPrecision grinding wheels (1998)

Types of grinding wheels are introduced and grinding wheel developments. Trends towards new abrasives are described including design of wheels for higher speeds and wheels for high accuracy. The latest developments in grinding wheels and dressing are essential for the development of ultraprecision grinding systems. It is shown how modern developments in abrasives and machines have enabled enormous increases in productivity and also, achievement of submicron tolerances. Chapter 4 introduces the technology of dressing for preparation and use of grinding wheels. Results are presented showing how different dressing conditions affect grinding performance. Techniques are described to cope with modern grinding wheels for both high production rates and for extremely high accuracies going into the nano range.

When the grinding wheel and dressing wheel have been specified for a particular grinding operation, adjustments can be made during the dressing operation that affect the surface roughness condition of the grinding wheel. The key factors that affect the grinding process during dressing are: dressing speed ratio, Vr/Vs, between dressing wheel and grinding wheel; dressing feed rate, ar, per grinding wheel revolution; and the number of run-out, or dwell, revolutions of the dressing wheel, na. By changing the dressing conditions, it is possible to rough and finish grind using the same diamond dressing wheel and the same grinding wheel. By controlling the speed of the dressing wheel, or by reversing its rotation, the effective roughness of the grinding wheel can be varied in the ratio of 1:2.

Grinding wheel and emery paper are the major outlets for phenolic resins in bonded and coated abrasives. Leo Baekeland introduced the first phenolic resin-bonded grinding wheel in 1909. Today, phenolic resin-bonded grinding wheels are the most popular type of grinding wheel. They have replaced ceramic wheels to a large extent, mainly due to the enhanced performance of phenolic resins. Phenolic resin bond is more thermal, water, and mechanical shock resistant than other bonding materials such as powdered clay and rubber. Also, these grinding wheels have higher tensile strength and can operate at higher speeds and remove metal more efficiently. Contrary to popular impression, grinding wheels are used more in industry than in home workshops. Steel manufacturing and fabricating plants are the biggest users of grinding wheels. A grinding wheel 18 inches in diameter and 0.1 inch thick can slice a 1-inch bar of steel in a few seconds leaving a mirrored finish. [3]

The two most commonly used grits for these wheels are synthetic fused alumina made from hydrated aluminum oxide (bauxite, A12O3H2O) and silicon carbide (SiC) obtained from the high-temperature (2000C) reaction of silica (sand) and coke in an electric furnace. The grit has a grain size of 20m to 3mm. Alumina-based wheels, being tougher, are used for grinding high-strength products such as steel. Silicon carbide is harder and is used for grinding hard and brittle materials such as glass, ceramics, stone, and cast iron.

The bonding material is alkaline catalyst-cured liquid resole-based phenolic resin. Sometimes a combination of liquid resole-based and powder form novolac-based phenolic resins is used to enhance performance. Low-solids, low-viscosity phenolic is preferred for improved shelf life. Toughness and elasticity can be enhanced with modified phenolic resins. Phenolic resins can be modified for low flow by being co-curing with epoxy resin or polyvinyl butyral (interpenetrating network resins, IPNs).

Common fillers for grinding wheels are aluminum oxide, iron oxide, silicates, and chalk. (The use of asbestos as a filler has been discontinued.) Typical formulation for a grinding wheel is as follows: resole phenolic resin (1/m 100 parts per hundred resin, phr), novolac phenolic resin (1/m 250phr), grit (1/m 1500phr), filler (1/m 200phr), and curing agent/accelerator (calcium or magnesium oxides, 1/m 15phr).

Emery paper is a polishing material that has largely replaced animal hide glue-bonded sandpaper. Emery is an impure corundum (naturally occurring alumina, A12O3) mixed with iron oxide that serves as the grit or abrasive material in emery paper. The substrate or backing material is rubber or acrylic-modified paper, and the bonding material is phenolic resin (resole or novolac-based). Sometimes combinations of phenolic resins and animal glue are used. Emery paper is used primarily for wet-polishing automobile body coatings.

A grinding wheel removes material in a similar way to a micro-milling cutter. In micro-milling, the cutting tools are identical in shape. The situation is quite different in grinding. The cutting tools in a grinding wheel are the grains, and material removal depends on their shape and position. The shapes and positions are both random distributions that change with wear. Grinding forces, accuracy, and wheel wear all depend on the amount of material removed by individual grains. Blunt worn grains are much less efficient than sharp grains. Material removal by grains provides a basis for understanding forces, power, roughness, and temperature with different grinding geometries and abrasives.

The grinding wheel is still a surface of revolution whose axial profile curve coincides with (or, is very similar to) the cutting edge, whose geometry depends on the tool type (straight blade, curved blade, with Toprem, etc.). For a straight blade tool, the corresponding grinding wheel geometry is specified by the four parameters in Fig.4: re, edge radius; , blade angle; Rp, point radius; , flaring angle. The latter is used here to tilt the grinding wheel out of the workpiece (to avoid interference), but also to alter the local grinding wheel curvature relative to the gear tooth (see [11] for a similar idea applied to grinding of face-milled gears).

Parameter s is the arc length along the profile direction: s=0 at the beginning of the root fillet, and it increases going upwards. The grinding wheel surface is obtained by rotating the profile curve around the grinding wheel axis by an angle .

The presence of the subscript CNV next to the symbols Rp and (Fig.4) is due to the fact that, unlike in the Semi-Completing process, two different grinding wheels are used here for the concave (CNV) and the convex (CVX) sides. The reason is plain to see. With a large number of blade groups, the lengthwise tooth curvature at the toe is significantly larger than that at the heel (but its values on the concave side and those on the convex side are comparable). When the grinding wheel is finishing the concave side at the toe (maximum curvature), its lengthwise curvature must be larger than or comparable with that of the tooth, otherwise it would interfere with other tooth parts. Therefore, parameters RpCNV and CNV must be selected accordingly. On the other hand, when the grinding wheel is finishing the convex side at the heel (minimum curvature), its lengthwise curvature must be smaller than or comparable with that of the tooth. Now, suitable values of RpCVX and CVX should be determined, but they would be different from those selected for the concave side: in particular, we would end up with RpCVX>RpCNV. Under these circumstances, two different grinding wheels are required for the concave and convex sides (Fixed-Setting method).

New grinding wheels and grinding wheel designs have been introduced in recent decades, rapidly changing modern grinding practice. Removal rates and accuracies are achieved that previously could only have been dreamed about. New abrasives include seeded gel (SG) abrasives and superabrasives of resin, vitrified and metal-bonded forms. Porosity varies from extremely open to completely closed structures depending on process requirements. Users benefit from close liaison with abrasive manufacturers in either planning a new grinding system or in optimizing an existing grinding system.

Developments in abrasives and grinding wheels allow greatly increased removal rates particularly for high-precision grinding. Individual abrasives may be engineered to best suit a particular work material and grinding conditions. Simultaneous development has to take place to achieve the right bond, porosity and wheel design. Properties and application of abrasive materials are further described by Webster and Tricard (2004) and Marinescu et al. (2007).

A grinding wheel surface consists of abrasive grains that form the cutting edges, bond material to retain the grains in position and surface pores that allow space for material removal from the work surface. The wheel surface is usually prepared by a truing or dressing operation as described in Chapter 4. The nature of the wheel surface and contact effects are introduced in Chapter 5 after this basic introduction to abrasives, bond materials and wheel types.

In this chapter, basic characteristics of conventional and superabrasive grinding wheels are described and directions for grinding wheel developments including high-speed wheel design and application of novel abrasives are provided.

New grinding wheels and grinding wheel designs have been introduced in recent decades, rapidly changing modern grinding practice. Removal rates and accuracies are achieved that previously could only have been dreamed about. New abrasives include seeded gel abrasives and superabrasives of resin, vitrified, and metal-bonded forms. Porosity varies from extremely open to completely closed structures depending on process requirements. Users benefit from a close liaison with abrasive manufacturers in either planning a new grinding system or optimising an existing grinding system.

Developments in abrasives and grinding wheels have allowed increased removal rates particularly for high precision grinding. Individual abrasives are engineered to best suit a particular work material and grinding conditions. Simultaneous development has to take place to achieve the right bond, porosity, and wheel design. This chapter shows how these properties work together. Important features of abrasive materials are also described in depth by Marinescu et al. (2006).

A grinding wheel surface consists of abrasive grains that form the cutting edges, bond material to retain the grains in position, and surface pores that allow space for material removal from the work surface. The wheel surface is usually prepared by a truing or dressing operation as described in Chapter 4. The nature of the wheel surface and contact effects are introduced in Chapter 5, after this basic introduction to abrasives, bond materials, and wheel types.

In this chapter, the basic characteristics of conventional and superabrasive grinding wheels are described and directions for grinding wheel developments including high-speed wheel design and application of novel abrasives are provided.

Grinding wheels are made with single grain sizes bonded either with a resin bond or a glassy bond. The amount of bond varies with the structure desired. The ceramic bond is prepared with ingredients such as clay, feldspar, flint, and glass frits with the bond composition selected to approach the thermal expansion of SiC. The bond and SiC grains are mixed, pressed in steel molds, and fired to mature the glassy bond at maximum temperatures of 9001300 C. Because single grain sizes of SiC are used, there is little oxidation of the SiC during firing.

A grinding wheel removes material in a similar way to a micro-milling cutter. However, unlike the cutting tools in micro-milling, abrasive grains vary randomly in shape and in position. Grinding forces, accuracy and wheel wear all depend on the different amounts of material removed by individual grains. Grains that lie a little deeper below the wheel surface may only rub against the work surface while other grains may rub for part of their contact, plough for part of their contact and remove chips for part of their contact. Blunt worn grains are much less efficient than sharp grains and will spend a greater proportion of the time rubbing, as described in Chapter 2.

Analysis of material removal by the grains provides a basis for understanding variation of grain forces, grain wear, total grinding forces, power, wheel life, roughness, grinding efficiency and temperature when varying grinding conditions.

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