Basic Grinding Theory 221

abrasive type

The specific material that makes up the abrasive grains in a grinding wheel. The workpiece material and grinding process determine the necessary abrasive type.

abrasives

A material made of hard, sharp particles used for cutting chips from a workpiece. Abrasives are bonded into wheels for use in grinding operations.

aluminum oxide

A very hard ceramic material composed of aluminum and oxygen. Aluminum oxide is often used as an abrasive grain because it is very hard.

American National Standards Institute

ANSI. A private, non-profit organization that coordinates voluntary standards and systems. The American National Standards Institute established the system for identifying grinding wheel specifications.

automatic

Functioning without the aid of an operator. Automatic grinders can perform multiple grinding operations through CNC programming.

balance stand

A device for testing the balance of a grinding wheel before installing it on a machine. A balance stand provides a level surface for determining where an out-of-balance wheel is heavy.

bond

The material that holds abrasive grains together in a grinding wheel. Bonds can be vitrified, metal, or organic.

bond type

The specific substance used to hold together abrasive grains in a grinding wheel. Bond type can vary from rigid vitrified or metal bonds to more flexible organic bonds such as rubber or shellac.

ceramics

A hard, brittle material made from metallic and nonmetallic substances that have been fused together. Ceramics are often used as abrasive grains in grinding.

chatter marks

Damage to a workpiece caused by the grinding wheel vibrating against the workpiece. Chatter marks can be caused by an out-of-balance or out-of-true grinding wheel.

coarse

An abrasive tool or set of abrasive grains that have large grains. Coarse grains produce the roughest surface finish.

concentricity

Sharing a common center between two or more circular or cylindrical features. Concentricity between the center hole on a grinding wheel and its outside edge is a characteristic of a trued grinding wheel.

cooling

The process of drawing heat away from the grinding area through the use of fluids. Cooling helps prevent heat damage to a workpiece.

cubic boron nitride

CBN. A material composed of boron and nitrogen. Cubic boron nitride is the second-hardest known substance, after diamond, and is used as an abrasive grain for grinding hard ferrous metals.

cutting

The grinding action during which sharp abrasive grains dig into a workpiece and remove well-formed chips. Cutting is the ideal grinding action.

dense

A wheel structure with little distance between its abrasive grains. Dense grinding wheels are best for grinding hard materials.

diamond

A mineral composed of carbon that is the hardest known substance. Diamond is used in manufacturing for cutting and grinding hard materials.

dressing

The process of sharpening a grinding wheel. Dressing uses a tool to remove a layer of dull grains from the wheel, revealing fresh, sharp grains.

face wheel

A grinding wheel on which the grinding action takes place on the wide face of the wheel. Face wheels, also called side wheels, are commonly used to remove large amounts of material from wide surface areas.

feldspar

A mineral commonly used in glassmaking and ceramics to improve a material's hardness and durability. Feldspar is a common bond material in grinding wheels.

ferrous metals

Metals that contain iron. The most common ferrous metal is steel.

fine

An abrasive tool or set of abrasive grains that have small grains. Fine grains produce tight tolerances and surface finishes.

fracture

The breaking of abrasive grains into smaller pieces. Fracturing creates a new cutting edge on dull grains.

friable

A grinding wheel's ability to wear and fracture. Friability allows grinding wheels to self-sharpen.

glazing

The gradual smoothing of a grinding wheel that occurs when abrasive grains on a grinding wheel become dull without breaking from the wheel. Glazing causes wheels to cut poorly and increases heat and friction, which can damage a workpiece.

grain size

The dimensions of the abrasive grains in a grinding wheel. Grain size affects a grinding wheel’s removal rate and surface finish.

grains

A tiny particle of a hard, abrasive substance. Grains are held in a bond to create a grinding wheel.

grinding

The use of abrasive grains to cut the surface of a workpiece and change its shape. Grinding operations commonly use abrasive grains bonded into the shape of a wheel.

grinding fluid

A liquid used to cool and lubricate the grinding wheel and workpiece during grinding. Grinding fluids can be composed of water, oil, and/or synthetic compounds, depending on the needs of the process.

grinding wheels

A wheel composed of abrasive grains held in a bond. Grinding wheels are used to remove small particles of material from a workpiece.

hardness

A material’s ability to resist penetration, indentation, or scratching. Hard materials tend to be brittle and resistant to wear.

horsepower

A unit of measurement used to describe the force exerted by a machine. One horsepower equals 33,000 ft.-lbs. of work per minute, or 746 watts.

loading

The accumulation of swarf trapped in a grinding wheel. Loading causes increased friction and chatter, which can damage a workpiece.

lubricating

The process of reducing friction between a workpiece and grinding wheel. Lubrication keeps abrasive grains sharp longer and prevents heat damage to a workpiece.

manual

To be controlled by hand. Operators using manual grinding machines control every part of a grinding operation.

material removal rate

MRR. The speed at which material is removed from a workpiece during grinding. Material removal rate should be high to remove material quickly.

MRR

Material removal rate. The speed at which material is removed from a workpiece during grinding. MRR should be high to remove material quickly.

non-ferrous metals

Metals that do not contain iron. Common non-ferrous metals are copper, nickel, and zinc.

open

A wheel structure with greater distance between its abrasive grains. Open grinding wheels are best for grinding soft materials.

organic

A bond type composed of materials derived from plant or animal byproducts. Common organic bonds are rubber and shellac.

out-of-balance

A state in which weight is not evenly distributed on a grinding wheel. Out-of-balance wheels create excessive vibrations when running on a machine and can damage the machine and workpiece, and also injure the operator.

out-of-true

The state in which a grinding wheel has lost its initial shape due to frequent use. An out-of-true wheel causes excessive vibrations and chatter marks on a workpiece.

peripheral wheels

A grinding wheel on which the grinding action takes place on the outer edge of the wheel. Peripheral wheels are commonly used for precise cutting on small surface areas.

plowing

The grinding action during which dull abrasive grains dig grooves into a workpiece without removing material. Plowing leads to increased heat, which can damage a workpiece.

pores

An empty space between the grains and bond in a grinding wheel. Pores, also called voids, carry chips and broken grains away from the grinding area.

revolutions per minute

rpm. The rotational frequency of a tool. In grinding, revolutions per minute refers to how many revolutions a wheel completes in one minute.

rigidity

The condition of a workpiece, machine, or machine setup characterized as stiff and immovable. Rigid components are fixed securely in place.

rubbing

The grinding action during which dull abrasive grains make contact with a workpiece without penetrating it. Rubbing leads to heat buildup, which can damage a workpiece.

semiautomatic

To be able to perform some parts of a work cycle independent of an operator. Semiautomatic grinding machines still require an operator to set up a workpiece and start each grinding cycle.

shellac

A resin secreted by the female lac bug of Southeast Asia. Shellac makes a good bond for wheels used in light-duty grinding and for smooth surfaces.

side wheels

A grinding wheel on which the grinding action takes place on the wide face of the wheel. Side wheels, also called face wheels, are commonly used to remove large amounts of material from wide surface areas.

silicon carbide

A hard ceramic material composed of silicon and carbon. Silicon carbide is used as an abrasive grain for grinding non-ferrous metals.

single-point diamond

A tool that uses a diamond bit to dress a grinding wheel. A single point diamond removes a layer of dull abrasive grains from the surface of a grinding wheel.

spindle

The part of a machine that rotates a cutting tool. In grinding the spindle rotates the grinding wheel.

swarf

A combination of finely ground chips of workpiece material and abrasive particles that are cast off during grinding. Swarf can often be seen as sparks in a grinding operation.

swarf

A combination of finely ground chips of workpiece material, bond material, and abrasive particles that are cast off during grinding. Swarf can often be seen as sparks in a grinding operation.

truing

The process of restoring an out-of-true grinding wheel to its original shape. Truing uses a tool to remove a layer of the wheel’s surface to restore concentricity.

vitrified

A bond type composed of fused materials such as clay or feldspar. Vitrified bonds are hard and rigid.

voids

An empty space between the grains and bond in a grinding wheel. Voids, also called pores, carry chips and broken grains away from the grinding area.

wear

The shedding of dull abrasive grains on a grinding wheel. Wear on a grinding wheel reveals fresh, sharp grains.

wheel flanges

The device that holds a grinding wheel on a machine's spindle. The wheel flanges contain weights that can be adjusted to balance a grinding wheel.

wheel grade

The strength of a grinding wheel. Wheel grade is determined by the wheel's bond type.

wheel structure

The spacing of abrasive grains on a grinding wheel. A wheel structure with grains that are far apart is described as open, and a wheel structure with grains close together is described as dense.