Basic Grinding Theory 221

"Basic Grinding Theory" provides an overview of the general process of grinding . Grinding occurs at the point of contact between an abrasive wheel and a workpiece. Like any other cutting process, grinding removes material in the form of chips. In order for a wheel to grind properly, its abrasive grains must wear and self-sharpen at a consistent rate. Otherwise, wheel problems such as loading and glazing may occur. Truing and dressing wheels and applying grinding fluids can fix or prevent these issues.

An understanding of grinding wheels and processes allows operators to perform grinding operations effectively and recognize and address any grinding wheel problems that may occur. This understanding and recognition will improve the accuracy, precision, and overall success of grinding operations, reducing scrap parts and increasing productivity.

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Class Details

Class Name:: Basic Grinding Theory 221
Version:: 2.0
Difficulty:: Intermediate
Number of Lessons:: 15
Related 1.0 Class:: What Is Grinding? 110

Class Outline

The Grinding Process
Grinding Wheels
Grinding Wheel Selection
Grinding Wheel Specifications
Grinding Wheel Specification Example
Grinding Wheel Review
Chip Formation
Grinding Action
Wheel Wear and Grain Fracture
Swarf
Grinding Process Review
Common Grinding Problems
Truing and Dressing
Grinding Fluids
Final Review

Objectives

Describe grinding.
Describe grinding wheels.
Identify variables that impact grinding wheel selection.
Identify common wheel specifications.
Describe chip formation.
Describe the different grinding actions.
Describe wheel wear and grain fracture.
Describe swarf.
Identify common grinding problems.
Define truing and dressing.
Describe how fluids improve grinding.

Job Roles

Certifications

NIMS

Grinding I

Glossary

Vocabulary Term	Definition
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.