IMP Chapter 26

The abrasive particles may be:

(1) free; (2) mounted in resin on a belt (3) close packed into wheels or stones, with abrasive grits held together by bonding material

Corundum

- (natural Al2O3) and diamonds are other naturally occurring abrasive materials.

Classification of Grinding Machines:

- Cylindrical external - Cylindrical internal - Surface conventional - Creep feed - Tool grinders - Other

Regulating wheel

- It is mounted at an angle to the plane of the grinding wheel

''pore-forming''

- Porosity is varied (to alter structure) by varying preform pressure or by using ______ additives to the bond material that are vaporized during the sintering cycle.

Carborundum and Crystolon

- Silicon carbide is sold under the trade names _____ and _____.

Emery

- a mixture of alumina (Al2O3) and magnetite (Fe3O4), is another natural abrasive still in use today and is used on coated paper and cloth (emery paper).

cutting, plowing, and rubbing

- abrasive machining is a mixture of _____, ______, and _____ with the percentage of each being highly dependent on the geometry of the grit.

Water-jet cutting (WJC)

- also known as water-jet machining or hydrodynamic machining, uses a high-velocity fluid jet impinging on the workpiece to perform a slitting operation.

Abrasive Machining

- applied to one particular form of the grinding process is unfortunate, because all these process are machining with abrasives.

Coated abrasives

- are available in sheets, rolls, endless belts, and disks of various sizes.

Coated abrasives

- are being used increasingly in finishing both metal and nonmetal products.

Vitrified bonds

- are composed of clays and other ceramic substances.

Production-type grinders

- are more fully automated and have higher metal removal rates and excellent dimensional accuracy

Chucking-type external grinders

- are production-type machines for use in rapid grinding of relatively short parts, such as ball-bearing races.

Abrasive grains

- are sorted into sizes by mechanical sieving machines.

Diamonds

- are the hardest of all materials.

Dependent variables

- are the resultant effects of those inputs.

Independent variables

- are those that are controllable (by the machine operator)

Dish-type wheels

- are used for grinding tools and saws.

Conventional grinding

- can be replaced by procedures that develop lower surface stresses when service failures due to fatigue or stress corrosion are possible.

Bonded product or a grinding wheel

- close packed into wheels or stones, with abrasive grits held together by bonding material

Honing stones

- differ from grinding wheels in that additional materials, such as sulfur, resin, or wax, are often added to the bonding agent to modify the cutting action.

Abrasive grinding

- done in an aggressive way can produce sufficient localized plastic deformation and heat in the surface so as to develop tensile residual stresses

Cutting off

- for slicing and slotting parts; use thin wheel, organic bond.

Internal cylindrical

- grinding bores and large holes

Cylindrical between centers

- grinding outside diameters of cylindrical workpieces.

Cylindrical, centerless

- grinding outside diameters with work rotated by regulating wheel.

Burn

- grinding wheels do become somewhat self-dressing, but the workpiece may become overheated and turn a bluish temper color.

Disk grinders

- have relatively large side-mounted abrasive disks. The work is held against one side of the disk for grinding

Abrasive

- is a hard material that can cut or abrade other substances.

Abrasive machining

- is a material removal process that involves the interaction of abrasive grits with the workpiece. - is the oldest of the basic machining processes.

Honing

- is a stock-removal process that uses fine abrasive stones to remove very small amounts of metal.

Snagging

- is a type of rough manual grinding that is done to remove fins, gates, risers, and rough spots from castings or flash from forgings, preparatory to further machining.

Superfinishing

- is a variation of honing that is typically used on flat surfaces.

Bonding material

- is a very important factor to be considered in selecting a grinding wheel.

Crush dressing

- is a very rapid method of dressing grinding wheels, and because it fractures abrasive grains, it results in free cutting and somewhat cooler grinding.

Lapping

- is an abrasive surface finishing process wherein fine abrasive particles are charged (caused to become embedded) into a soft material, called a lap.

Center-type cylindrical grinding

- is commonly used for producing external cylindrical surfaces

G ratio

- is defined as the cubic inches of stock removed divided by the cubic inches of wheel lost.

Silicon carbide

- is made by charging an electric furnace with silica sand, petroleum coke, salt, and sawdust.

Cubic boron nitride (CBN)

- is not found in nature. It is produced by a combination of intensive heat and pressure in the presence of a catalyst.

Infeed

- is provided by movement of the wheelhead at right angles to the longitudinal axis of the table.

Aluminum oxide

- is the most widely used artificial abrasive.

Quartz

- is used primarily in coated abrasives and in air blasting, but artificial abrasives are also making inroads in these applications.

Rubber bonding

- is used to produce wheels that can operate at high speeds but must have a considerable degree of flexibility so as to resist side thrust.

Centerless grinding

- makes it possible to grind both external and internal cylindrical surfaces without requiring the workpiece to be mounted between centers or in a chuck.

Crush dressing

- modern grinding machines are equipped so that the wheel can be dressed and/or trued continuously or intermittently while grinding continues.

Universal tool and cutter grinders

- more complex tools, such as milling cutters, reamers, hobs, and single-point tools for production-type operations require more sophisticated grinding machines

Coated product

- mounted in resin on a belt

Abrasive jet machining (AJM)

- one of the least expensive of the nontraditional processes. - removes material by a focused jet of abrasives and is similar in many respects to AWC.

Resinoid bonds

- or phenolic resins, can be used. Because plastics can be compounded to have a wide range of properties, such wheels can be obtained to cover a variety of work conditions.

Attrition

- refers to the abrasive wear action of the grits resulting in dulled edges, grit flattening, and wheel glazing.

Friability

- refers to the fracture of the grits and is the opposite of toughness.

Snagging

- removing large amounts of metal without regard to surface finish or tolerances.

Truing

- restores the original shape.

Grinding wheel

- shapes have been standardized, and eight of the most commonly used types.

Garnets

- that are not suitable for gems, or small, synthetic stones that are produced specifically for abrasive purposes.

Hardness

- the ability to resist penetration, is the key property for an abrasive.

Plunge-cut grinding

- the basic movement is of the wheel being fed radially into the work while the latter revolves on centers.

Chucking-type internal grinding machines

- the chuck-held workpiece revolves, and a relatively small, high-speed grinding wheel is rotated on a spindle arranged so that it can be reciprocated in and out of the workpiece.

Grade

- the fracturing of the grits is controlled by the bond strength.

Abrasive water-jet cutting (AWC)

- the majority of the metalworking applications for water-jet cutting require the addition of abrasives.

Structure

- the spacing of the abrasive particles with respect to each other.

Creep feed grinding (CFG)

- the work is fed very slowly past the wheel and the total downfeed or depth (d) is accomplished in a single pass.

Swing grinders

- this is a form of abrasive machining except that pedestal-type or ______ ordinarily are used.

Wheel profiling

- this procedure is usually employed to produce and maintain a special contour to the abrasive wheel.

Design for Manufacturing (DFM)

- two important design recommendations are to reduce the area to be ground and to keep all surfaces that are to be ground in the same or parallel planes

Superabrasive bond

- wheels are either electroplated (single layer of super abrasive plated to outside diameter of a steel blank) or a thin-segmented drum of vitrified CBN surrounds a steel core.

Shellac-bonded

- wheels are made by mixing the abrasive grains with shellac in a heated mixture, pressing or rolling into the desired shapes, and baking for several hours at about 300F.

Silicate bond

- wheels use silicate of soda (waterglass) as the bond material.

Grinding

- wherein the abrasives are bonded together into a wheel, is the most common abrasive machining process.

Grinding operations major use categories are the following:

1. Cutting off 2. Cylindrical between centers 3. Cylindrical, centerless 4. Internal cylindrical 5. Snagging 6. Surface grinding 7. Tool grinding 8. Offhand grinding

Bonding materials in common use are the following:

1. Vitrified bonds 2. Resinoid bonds 3. Silicate bond 4. Shellac-bonded 5. Rubber bonding 6. Superabrasive bond

off-hand grinding

Simple, single-point tools are often sharpened by hand on bench or pedestal grinders (_____).

Ultrasonic machining (USM)

sometimes called ultrasonic impact grinding, employs an ultrasonically vibrating tool to impel the abrasives in a slurry at high velocity against the workpiece.