What Is Grinding? 110 - Tooling U-SME

Transcription

What Is Grinding? 110
Welcome to the Tooling University. This course is designed to be used in conjunction with the online version of this class. The online version can be found at http://www.toolingu.com.
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Copyright © 2015 Tooling U, LLC. All Rights Reserved.
Class Outline
Class Outline
Objectives
What Is Grinding?
Chip Formation
Cutting Action
Grinding Wheels
Grain Fracture and Wheel Wear
Swarf
Negative Results of Grinding
Dressing
Truing
Grinding Fluids
Wheel Choice
Wheel Specifications
Wheel Maintenance and Safety
Summary
Lesson: 1/15
Objectives
l Describe the grinding process.
l Describe how grinding produces a chip.
l Describe the various actions that take place during grinding.
l Identify the chip-producing surfaces of grinding wheels.
l Explain the fracture process.
l Explain how swarf is produced.
l Describe variables that negatively affect grinding.
l Define dressing.
l Define truing.
l Explain how fluids improve grinding.
l Describe variables that impact grinding wheel selection.
l Identify common wheel specifications.
l Describe safety practices for grinding wheels.
Figure 1. Grinding wheels come in many
shapes and sizes.
Lesson: 2/15
What Is Grinding?
Lesson: 1/15
Objectives
l Describe the grinding process.
l Describe how grinding produces a chip.
l Describe the various actions that take place during grinding.
l Identify the chip-producing surfaces of grinding wheels.
l Explain the fracture process.
l Explain how swarf is produced.
l Describe variables that negatively affect grinding.
l Define dressing.
l Define truing.
l Explain how fluids improve grinding.
l Describe variables that impact grinding wheel selection.
l Identify common wheel specifications.
l Describe safety practices for grinding wheels.
Figure 1. Grinding wheels come in many
shapes and sizes.
Lesson: 2/15
What Is Grinding?
Grinding is a chip-producing, abrasive machining process used to improve the surface finish of
parts. Grinding uses abrasive grains bonded together into the shape of a wheel, as Figure 1
illustrates. The wheel, which is attached at its center to a grinding machine, rotates against the
workpiece and removes small amounts of material from the surface of a part. Figure 2 shows how
a typical grinding wheel is mounted to a machine. The goal is to make the parts fit better and
perform better.
This class will teach you the basics of grinding and how abrasive wheels work. You will learn about
what happens during grinding; the construction and shape of grinding wheels; and wheel
maintenance, safety, and storage.
Figure 1. Magnified view of grains in an
wheel.
abrasive
Lesson: 2/15
What Is Grinding?
Grinding is a chip-producing, abrasive machining process used to improve the surface finish of
parts. Grinding uses abrasive grains bonded together into the shape of a wheel, as Figure 1
illustrates. The wheel, which is attached at its center to a grinding machine, rotates against the
workpiece and removes small amounts of material from the surface of a part. Figure 2 shows how
a typical grinding wheel is mounted to a machine. The goal is to make the parts fit better and
perform better.
This class will teach you the basics of grinding and how abrasive wheels work. You will learn about
what happens during grinding; the construction and shape of grinding wheels; and wheel
maintenance, safety, and storage.
Figure 1. Magnified view of grains in an
wheel.
abrasive
Figure 2. Grinding wheels are mounted at the
center.
Lesson: 3/15
Chip Formation
To understand how grinding works, you must first understand how chips are made. Chips are the
small particles of metal removed from the part during machining. With any machining operation,
almost all chips are produced in the same manner: A sharp tool presses into the metal and begins
gouging it. Then, either the tool moves past the workpiece, or the workpiece moves past the tool.
Grinding wheels are composed of multiple, tiny grains that act as sharp tools. Each grain forms a
chip
as it ©
moves
past the
surface.
Figure 1 shows a single grain as it forms a chip. As the
Copyright
2015 Tooling
U,workpiece
LLC. All Rights
Reserved.
grain begins to gouge into the workpiece, a metal chip begins to form and curls in front of the tool. This action continues until the chip finally separates. The chip produced during grinding is very
Lesson: 3/15
Chip Formation
To understand how grinding works, you must first understand how chips are made. Chips are the
small particles of metal removed from the part during machining. With any machining operation,
almost all chips are produced in the same manner: A sharp tool presses into the metal and begins
gouging it. Then, either the tool moves past the workpiece, or the workpiece moves past the tool.
Grinding wheels are composed of multiple, tiny grains that act as sharp tools. Each grain forms a
chip as it moves past the workpiece surface. Figure 1 shows a single grain as it forms a chip. As the
grain begins to gouge into the workpiece, a metal chip begins to form and curls in front of the tool. This action continues until the chip finally separates. The chip produced during grinding is very
small, especially compared to other types of machining operations.
Figure 1. Closeup of an abrasive grain
producing a chip.
Lesson: 4/15
Cutting Action
During grinding, multiple grains contact the workpiece. The action of the abrasive grains against the
surface of the part being finished is actually a combination of cutting, plowing, and rubbing.
Cutting is the main grinding action because that is what removes the material. During cutting,
sharp, individual grains dig into the material and curl tiny chips away from the surface.
Although it is not desirable, plowing occurs when some of the individual grains are either not sharp
enough or are at too poor an angle to actually curl a chip. Instead, the grain digs a groove and
forces the material out in front of itself. Figures 1 and 2 compare cutting and plowing.
Rubbing, which is even less desirable than plowing, occurs when the remaining grains are not sharp
enough to cut or plow the material, and they slide over the surface instead. Every grinding process
involves a combination of these three actions.
Figure 1. Sharp grains cut and produce a chip.
Figure 2. Dull grains plow the surface rather
than cut it.
Lesson: 4/15
Cutting Action
During grinding, multiple grains contact the workpiece. The action of the abrasive grains against the
surface of the part being finished is actually a combination of cutting, plowing, and rubbing.
Cutting is the main grinding action because that is what removes the material. During cutting,
sharp, individual grains dig into the material and curl tiny chips away from the surface.
Although it is not desirable, plowing occurs when some of the individual grains are either not sharp
enough or are at too poor an angle to actually curl a chip. Instead, the grain digs a groove and
forces the material out in front of itself. Figures 1 and 2 compare cutting and plowing.
Rubbing, which is even less desirable than plowing, occurs when the remaining grains are not sharp
enough to cut or plow the material, and they slide over the surface instead. Every grinding process
involves a combination of these three actions.
Figure 1. Sharp grains cut and produce a chip.
Figure 2. Dull grains plow the surface rather
than cut it.
Lesson: 5/15
Grinding Wheels
In a grinding wheel, small abrasive grains are mixed with a bonding material and formed into
the shape of a wheel. This structure of grains, bond, and space acts like a set of tiny, randomly
placed chisels that work together to remove small amounts of material. Figure 1 illustrates this
arrangement. The chips they produce are equally small. Figure 2 represents a highly magnified look
at chips produced in grinding.
Like other cutting tools, grinding wheels come in different shapes and sizes, but most are one of
two types: peripheral wheels and side wheels. With peripheral wheels, the point of contact with
the workpiece is the outer rim of the wheel. With side wheels, also known as face wheels, the front
portion of the wheel is the point of contact. This is the part of the wheel that does the work. Figure
3 shows an example of a peripheral wheel and a side wheel.
No matter what type of wheel is involved, the interaction between the grinding wheel and the
workpiece is always the same. The grinding wheel rotates against the piece and the abrasive grains
in the wheel cut small chips from the part’s surface.
Figure 1. Grinding wheels consist of abrasive
grains, bonding material, and the space in
between them.
Lesson: 5/15
Grinding Wheels
In a grinding wheel, small abrasive grains are mixed with a bonding material and formed into
the shape of a wheel. This structure of grains, bond, and space acts like a set of tiny, randomly
placed chisels that work together to remove small amounts of material. Figure 1 illustrates this
arrangement. The chips they produce are equally small. Figure 2 represents a highly magnified look
at chips produced in grinding.
Like other cutting tools, grinding wheels come in different shapes and sizes, but most are one of
two types: peripheral wheels and side wheels. With peripheral wheels, the point of contact with
the workpiece is the outer rim of the wheel. With side wheels, also known as face wheels, the front
portion of the wheel is the point of contact. This is the part of the wheel that does the work. Figure
3 shows an example of a peripheral wheel and a side wheel.
No matter what type of wheel is involved, the interaction between the grinding wheel and the
workpiece is always the same. The grinding wheel rotates against the piece and the abrasive grains
in the wheel cut small chips from the part’s surface.
between them.
Figure 2. Magnified view of chips produced by
grinding.
Figure 3. Most wheels grind with their
periphery or their sides. The arrows indicate
the points of contact these wheels would have
with a workpiece.
Lesson: 6/15
In
addition
theTooling
cutting
occurs
during grinding, there is also a certain amount of wear
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© to
2015
U,action
LLC. Allthat
Rights
Reserved.
that takes place on the wheel. While this would be a problem with other cutting tools, wear is an
expected and desirable part of grinding because it is actually what keeps the tool sharp.
Lesson: 6/15
In addition to the cutting action that occurs during grinding, there is also a certain amount of wear
that takes place on the wheel. While this would be a problem with other cutting tools, wear is an
expected and desirable part of grinding because it is actually what keeps the tool sharp.
In general, many grinding wheels are considered self-sharpening tools. As the wheel pushes against
the workpiece, the grains dig in and curl the chips away. At the same time, a number of grains are
failing under the pressure of grinding and breaking off. This action, called fracture or friability, is
how the tool sharpens itself. The grains break off and expose new, sharp cutting edges. Figure 1
illustrates grain fracture.
As the grains are fracturing, the bond between the grains also is wearing away. This releases worn
grains and allows new, sharp abrasives to surface. In this way, the combination of fracture, wear,
and grain release allows the wheel to sharpen itself. The images in Figure 2 show how this process
takes place.
Figure 1. Abrasive grains fracture to expose
new cutting edges.
Figure 2. As the wheel rotates, it releases
bonding material and dull, fractured grains to
expose a new, sharp surface.
Lesson: 7/15
Swarf
As the wheel both grinds the workpiece and self-sharpens, a large number of dust-like particles are
produced. Remember, the grains are like a set of randomly placed chisels. As they rotate, they dig
in and scoop chips of material from the part's surface. The chips are held in the spaces between the
grains, known as voids. Chips collect in the voids, along with fractured grain pieces and bits of
bonding material that are wearing off. Together, they are carried away from the workpiece surface
by the turning of the wheel.
This combination of chips, fractured pieces of grain, and broken bonding material is called swarf. If
no grinding fluid is being used, swarf is often visible in the form of sparks produced by the friction of grinding. The portion that does not burn off collects in the form of what looks like dust or
crumbs around the surfaces of the machine. If grinding fluid is used, the swarf is rinsed away
CopyrightSwarf
© 2015
Tooling
U, LLC. Allin
Rights
Reserved.
instead.
then
accumulates
a tray
on the machine, as Figure 1 demonstrates, while the fluid
is strained and recycled.
Lesson: 7/15
Swarf
As the wheel both grinds the workpiece and self-sharpens, a large number of dust-like particles are
produced. Remember, the grains are like a set of randomly placed chisels. As they rotate, they dig
in and scoop chips of material from the part's surface. The chips are held in the spaces between the
grains, known as voids. Chips collect in the voids, along with fractured grain pieces and bits of
bonding material that are wearing off. Together, they are carried away from the workpiece surface
by the turning of the wheel.
This combination of chips, fractured pieces of grain, and broken bonding material is called swarf. If
no grinding fluid is being used, swarf is often visible in the form of sparks produced by the friction of grinding. The portion that does not burn off collects in the form of what looks like dust or
crumbs around the surfaces of the machine. If grinding fluid is used, the swarf is rinsed away
instead. Swarf then accumulates in a tray on the machine, as Figure 1 demonstrates, while the fluid
is strained and recycled.
Figure 1. Swarf collects in a tray on the
grinding machine, while the fluid is recycled.
(Courtesy of United Grinding.)
Lesson: 8/15
As the grinding wheel rotates, swarf is constantly being removed either by being thrown free,
burned off, or rinsed away. Sometimes, too much swarf sticks in the voids of the wheel, as Figure 1
shows. This clogging, known as loading, must be corrected or the wheel will no longer be able to
grind or self-sharpen. Instead, more plowing and rubbing takes place than cutting. Excess plowing
and rubbing generates heat.
If excess heat is produced, the wheel surface may actually become smooth and stop grinding
completely. This condition, illustrated in Figure 2, is called glazing. Sometimes, manufacturers will
increase the pressure during grinding to force the material out of the voids. However, this action
may cause the workpiece to overheat and burn, and the part will have to be scrapped. Figure 3
shows a part that has burn marks near its edge.
In addition to problems with loading, you will find that most wheels eventually lose their shape.
Either the wheel will no longer be round, or the profile it once had will be worn away. The wheel is
then said to be out of true. Out of true wheels do not grind properly and can produce chatter
marks, which are surface imperfections caused by the wheel vibrating against the workpiece. These
problems must be corrected before grinding can continue.
Figure 1. A grinding wheel showing a darker
area of loaded material.
Lesson: 8/15
As the grinding wheel rotates, swarf is constantly being removed either by being thrown free,
burned off, or rinsed away. Sometimes, too much swarf sticks in the voids of the wheel, as Figure 1
shows. This clogging, known as loading, must be corrected or the wheel will no longer be able to
grind or self-sharpen. Instead, more plowing and rubbing takes place than cutting. Excess plowing
and rubbing generates heat.
If excess heat is produced, the wheel surface may actually become smooth and stop grinding
completely. This condition, illustrated in Figure 2, is called glazing. Sometimes, manufacturers will
increase the pressure during grinding to force the material out of the voids. However, this action
may cause the workpiece to overheat and burn, and the part will have to be scrapped. Figure 3
shows a part that has burn marks near its edge.
In addition to problems with loading, you will find that most wheels eventually lose their shape.
Either the wheel will no longer be round, or the profile it once had will be worn away. The wheel is
then said to be out of true. Out of true wheels do not grind properly and can produce chatter
marks, which are surface imperfections caused by the wheel vibrating against the workpiece. These
problems must be corrected before grinding can continue.
Figure 1. A grinding wheel showing a darker
area of loaded material.
Figure 2. When a wheel is glazed, the surface
becomes smooth and will no longer grind.
Figure 3. A burned, darkened path on a
workpiece resulting from excessive feeds.
Lesson: 9/15
Dressing
To overcome loading, glazing, and deformation, wheels must be dressed and trued. Dressing and
truing can take place simultaneously or separately. Dressing is the use of a hard tool to expose a
sharpened surface of a grinding wheel. A dressing tool is forced against the surface of the wheel
to expose new, sharper grains. These dressing tools may be hand-held, or they may be mounted
on the machine and mechanically forced into the wheel. Figure 1 shows a grinding machine with a
hand-held dressing tool.
To dress the wheel, operators should carefully pass the dressing tool over the surface of the
spinning wheel. Because the dresser is harder than the abrasive and the bond in the wheel, it
breaks the bonds and fractures the grains to expose a fresh, sharp surface. Wheels may be
dressed with diamond tools, abrasive sticks, and metal cutters, among other devices.
Figure 1. Hand-held dressing tools are kept
nearby for application.
Lesson: 10/15
Truing
In addition to dressing, most grinding wheels require truing to extend the useful life of the
grinding wheel. Truing is the use of a hardened tool to return a grinding wheel to its original shape.
For the most part, truing and dressing are similar processes that use similar tools. In some cases,
as a wheel is trued and the grinding surface is evened out, it actually may become dull and require
dressing with an even sharper tool. This process may occur over and over again until the wheel is
completely trued.
Many modern machines are designed so that dressing and truing can take place continuously or
regularly without interrupting grinding. Figure 1 shows a surface grinder with an automated
dressing roll above the grinding wheel. One continuous method is crush dressing, in which a hard roll made with the proper contour is in constant contact with the wheel. The crushing action
fractures and dislodges some of the abrasive grains and bond. More importantly, on wheels with
special profiles, crush dressing maintains the wheel’s shape. This method is effective, but it leaves a
slightly rougher surface than dressing with a diamond tool.
Figure 1. Some grinding machines have
automatic dressing capabilities. (Courtesy of
Parker Majestic.)
Lesson: 10/15
Truing
In addition to dressing, most grinding wheels require truing to extend the useful life of the
grinding wheel. Truing is the use of a hardened tool to return a grinding wheel to its original shape.
For the most part, truing and dressing are similar processes that use similar tools. In some cases,
as a wheel is trued and the grinding surface is evened out, it actually may become dull and require
dressing with an even sharper tool. This process may occur over and over again until the wheel is
completely trued.
Many modern machines are designed so that dressing and truing can take place continuously or
regularly without interrupting grinding. Figure 1 shows a surface grinder with an automated
dressing roll above the grinding wheel. One continuous method is crush dressing, in which a hard roll made with the proper contour is in constant contact with the wheel. The crushing action
fractures and dislodges some of the abrasive grains and bond. More importantly, on wheels with
special profiles, crush dressing maintains the wheel’s shape. This method is effective, but it leaves a
slightly rougher surface than dressing with a diamond tool.
Figure 1. Some grinding machines have
automatic dressing capabilities. (Courtesy of
Parker Majestic.)
Lesson: 11/15
Grinding Fluids
Fluids are used primarily as coolants and secondly as lubricants. Fluids reduce friction. In the case
of grinding, they reduce rubbing. Reducing heat at the cutting site helps keep the workpiece from
overheating and extends tool life. Figure 1 shows barrels of grinding fluid typically found in a shop.
Water is effective as a coolant, but it is a poor lubricant, and it promotes rust. Oil is a less effective
coolant, but it is a good lubricant, and it does not cause rust. In fact, oil is sometimes used alone.
More often, however, cutting fluids are a mixture of oil and water or other liquid that has been
treated to prevent rust, aid lubrication, and promote mixing. Also, some cutting fluids contain
additives that enhance their performance with certain abrasives.
These fluids also wash away swarf and help keep grinding wheels from loading. They can be applied
as a fine mist or as a heavy flow. Fluids generally should be used in enough quantity to rinse the
swarf away and keep it from being trapped, as Figure 2 demonstrates. Removing swarf is especially
important in horizontal grinding operations. Cutting fluids are generally not used for offhand
grinding or for those grinding operations where using fluids would harm the surface finish.
Figure 1. Grinding fluid stored in barrels prior
to use.
Lesson: 11/15
Grinding Fluids
Fluids are used primarily as coolants and secondly as lubricants. Fluids reduce friction. In the case
of grinding, they reduce rubbing. Reducing heat at the cutting site helps keep the workpiece from
overheating and extends tool life. Figure 1 shows barrels of grinding fluid typically found in a shop.
Water is effective as a coolant, but it is a poor lubricant, and it promotes rust. Oil is a less effective
coolant, but it is a good lubricant, and it does not cause rust. In fact, oil is sometimes used alone.
More often, however, cutting fluids are a mixture of oil and water or other liquid that has been
treated to prevent rust, aid lubrication, and promote mixing. Also, some cutting fluids contain
additives that enhance their performance with certain abrasives.
These fluids also wash away swarf and help keep grinding wheels from loading. They can be applied
as a fine mist or as a heavy flow. Fluids generally should be used in enough quantity to rinse the
swarf away and keep it from being trapped, as Figure 2 demonstrates. Removing swarf is especially
important in horizontal grinding operations. Cutting fluids are generally not used for offhand
grinding or for those grinding operations where using fluids would harm the surface finish.
Figure 1. Grinding fluid stored in barrels prior
to use.
Figure 2. Grinding fluid should be used in large
enough quantities to rinse away swarf.
(Courtesy of Royal Master Grinders, Inc.)
Lesson: 12/15
Wheel Choice
There are several variables to consider when deciding what type of grinding wheel you should use
for a particular operation. In general, your choices are related to either the material you will be
grinding or the machine you will be using.
Material considerations include the type of metal you will be grinding, how much material you want
to remove, and what kind of finish you expect to leave behind. Knowing these will help you choose
the right abrasive and best bonding material for the job. A good rule of thumb to remember is that
harder wheels are generally used to grind softer materials, and softer wheels are used to grind
harder materials. Figure 1 shows the variety of wheel types used for tool grinding by a typical
shop.
Machine-related considerations include the type of grinding that will take place, the wheel speed and
horsepower that will be used, and the severity of the grinding action. In this case, severity refers to
how much force is used to bring the grinding wheel and the workpiece together. For example,
Copyright © 2015
U, specially
LLC. All Rights
Reserved.
super-hard
steelsTooling
require
designed
abrasives that can withstand extreme pressures.
Figure 1. Shops require different wheels for
Lesson: 12/15
Wheel Choice
There are several variables to consider when deciding what type of grinding wheel you should use
for a particular operation. In general, your choices are related to either the material you will be
grinding or the machine you will be using.
Material considerations include the type of metal you will be grinding, how much material you want
to remove, and what kind of finish you expect to leave behind. Knowing these will help you choose
the right abrasive and best bonding material for the job. A good rule of thumb to remember is that
harder wheels are generally used to grind softer materials, and softer wheels are used to grind
harder materials. Figure 1 shows the variety of wheel types used for tool grinding by a typical
shop.
Machine-related considerations include the type of grinding that will take place, the wheel speed and
horsepower that will be used, and the severity of the grinding action. In this case, severity refers to
how much force is used to bring the grinding wheel and the workpiece together. For example,
super-hard steels require specially designed abrasives that can withstand extreme pressures.
Figure 1. Shops require different wheels for
the variety of workpiece shapes and material
types.
Lesson: 13/15
Once you generally know what type of wheel you need for your operation, you will have to make
your selection according to a set of specifications. Most manufacturers follow a standard system
established by the American National Standards Institute (ANSI) that indicates the abrasive
type, grain size, grade, structure, and bond. Most wheels have these markings printed right on
their sides, as Figure 1 shows.
For each specification, there is a corresponding letter or number, with an optional prefix or suffix
marking used by the manufacturer. Figure 2 illustrates the portion of the chart that covers abrasive
grain size. As the chart shows, the higher the number indicated, the finer the abrasive grain.
Figure 1. Most grinding wheels have
specification markings on their surface.
(Courtesy of Norton Abrasives.)
Lesson: 13/15
Once you generally know what type of wheel you need for your operation, you will have to make
your selection according to a set of specifications. Most manufacturers follow a standard system
established by the American National Standards Institute (ANSI) that indicates the abrasive
type, grain size, grade, structure, and bond. Most wheels have these markings printed right on
their sides, as Figure 1 shows.
For each specification, there is a corresponding letter or number, with an optional prefix or suffix
marking used by the manufacturer. Figure 2 illustrates the portion of the chart that covers abrasive
grain size. As the chart shows, the higher the number indicated, the finer the abrasive grain.
Figure 1. Most grinding wheels have
specification markings on their surface.
(Courtesy of Norton Abrasives.)
Figure 2. Abrasive grain sizes are classified by
number. Lower numbers indicate coarser
grains; higher numbers indicate finer grains.
Lesson: 14/15
Because of the extreme forces and pressures grinding wheels experience, they must be cared for
properly. Dropping or mishandling wheels can cause cracks or gouges that could cause serious
failure. Wheels have been known to break apart during grinding, with the flying pieces injuring the
operator and damaging the machine. Consequently, all grinding wheels should be inspected for
damage prior to each use.
The ring test is a common method for checking bonded wheels for damage. The simple way to
perform it is to suspend the wheel loosely and then lightly tap it with a hammer or other object.
Damaged wheels will sound dull, while undamaged wheels will give off a distinctive ringing sound.
Figure 1 shows the ring test being performed in a shop.
Grinding
also
be All
stored
Copyrightwheels
© 2015 should
Tooling U,
LLC.
Rightsaccording
Reserved.to the manufacturer’s recommendations and
protected from temperature and humidity changes, which weakens certain bonds. Wheels should
be transported carefully as well. For example, wheels should never be rolled from one location to
another.
Lesson: 14/15
Because of the extreme forces and pressures grinding wheels experience, they must be cared for
properly. Dropping or mishandling wheels can cause cracks or gouges that could cause serious
failure. Wheels have been known to break apart during grinding, with the flying pieces injuring the
operator and damaging the machine. Consequently, all grinding wheels should be inspected for
damage prior to each use.
The ring test is a common method for checking bonded wheels for damage. The simple way to
perform it is to suspend the wheel loosely and then lightly tap it with a hammer or other object.
Damaged wheels will sound dull, while undamaged wheels will give off a distinctive ringing sound.
Figure 1 shows the ring test being performed in a shop.
Grinding wheels should also be stored according to the manufacturer’s recommendations and
protected from temperature and humidity changes, which weakens certain bonds. Wheels should
be transported carefully as well. For example, wheels should never be rolled from one location to
another.
In general, always obey the wheel and machine manufacturers’ recommendations for all aspects of
grinding wheel storage, use, and safety. This includes directions for wheel mounting, grinding
speed, and use of wheel guards.
Figure 1. The ring test helps determine
whether or not a wheel has been damaged.
Lesson: 15/15
Summary
Grinding is the most common abrasive process used to shape and finish parts. A grinding wheel
rotates against the surface of a part to remove material in the form of chips. Wheels consist of
grains, bond, and space. Each grain produces a tiny chip as it gouges the workpiece. Collectively,
chips appear as swarf.
During grinding, abrasive grains gradually wear away and fracture. This fracturing is actually
desirable because it exposes new, sharper grains. However, grinding wheels may also experience
loading or glazing. Loading is the clogging of swarf within the spaces of the wheel, and glazing is
the formation of a dull, smooth wheel surface that is incapable of grinding. Wheels may also lose
their shape, or become out of true, as they grind parts.
To keep wheels working properly, operators dress and true the wheel. Dressing exposes new,
sharpened grains, and truing returns the wheel to its original shape. Dressing and truing may be
done simultaneously.
The most effective grinding wheel for a particular operation depends on workpiece material, surface finish requirements, amount of material removal, and other factors. Keep in mind that grinding
wheels are easily damaged, and they must be used and stored properly at all times.
between them.
Figure 2. The abrasive grains remove material
by cutting into the work surface and producing
chips.
Lesson: 15/15
Summary
Grinding is the most common abrasive process used to shape and finish parts. A grinding wheel
rotates against the surface of a part to remove material in the form of chips. Wheels consist of
grains, bond, and space. Each grain produces a tiny chip as it gouges the workpiece. Collectively,
chips appear as swarf.
During grinding, abrasive grains gradually wear away and fracture. This fracturing is actually
desirable because it exposes new, sharper grains. However, grinding wheels may also experience
loading or glazing. Loading is the clogging of swarf within the spaces of the wheel, and glazing is
the formation of a dull, smooth wheel surface that is incapable of grinding. Wheels may also lose
their shape, or become out of true, as they grind parts.
To keep wheels working properly, operators dress and true the wheel. Dressing exposes new,
sharpened grains, and truing returns the wheel to its original shape. Dressing and truing may be
done simultaneously.
The most effective grinding wheel for a particular operation depends on workpiece material, surface finish requirements, amount of material removal, and other factors. Keep in mind that grinding
wheels are easily damaged, and they must be used and stored properly at all times.
between them.
Figure 2. The abrasive grains remove material
by cutting into the work surface and producing
chips.
Class Vocabulary
Term
Definition
Additive
American National Standards Institute
Bonding Material
Chatter Mark
Chip
Coolant
A substance added in small amounts to another substance or material to change or improve its
performance.
A private, non-profit organization that administers and coordinates voluntary standards and
systems.
The material that holds abrasive grains together in a grinding tool. Bonding materials may
consist of rubber, metal, or other material.
An irregular mark left on a workpiece that has been ground with a wheel that is out of true.
An unwanted piece of metal that is removed from a workpiece. Chips are formed when a tool
cuts or grinds metal.
A substance, usually liquid, used to reduce or maintain the temperature of a part being ground.
Crush Dressing The use of rolls or special forms to dress the face of a grinding wheel to a specific shape or
contour.
Class Vocabulary
Term
Definition
Additive
American National Standards Institute
Bonding Material
Chatter Mark
Chip
Coolant
Crush Dressing
Cutting
Cutting Fluid
Dressing
A substance added in small amounts to another substance or material to change or improve its
performance.
A private, non-profit organization that administers and coordinates voluntary standards and
systems.
The material that holds abrasive grains together in a grinding tool. Bonding materials may
consist of rubber, metal, or other material.
An irregular mark left on a workpiece that has been ground with a wheel that is out of true.
An unwanted piece of metal that is removed from a workpiece. Chips are formed when a tool
cuts or grinds metal.
A substance, usually liquid, used to reduce or maintain the temperature of a part being ground.
The use of rolls or special forms to dress the face of a grinding wheel to a specific shape or
contour.
In grinding, the main action that occurs when sharp grains dig into the workpiece and remove
chips.
A liquid used during grinding to clean, cool, and lubricate the grinding site.
The removal of swarf, dull grains, and bonding material from a grinding wheel. Essentially,
dressing sharpens the wheel.
Dressing Tool
A device used to remove loading and sharpen a grinding wheel. It might consist of an abrasive
stick, a single-point diamond, or other tool.
Fracture
The breaking apart of grains in an abrasive wheel during grinding. It is part of the wheel's selfsharpening process.
Friability
The ability of abrasive grains to fracture and self-sharpen under stress.
Glazing
Grain
Grinding
Grinding Wheel
Horizontal Grinding
Loading
Lubricant
Machining
Offhand Grinding
Out Of True
The unwanted formation of a smooth surface on a grinding wheel. Glazing occurs when the heat
from grinding reacts with a loaded wheel.
A small, hard particle or crystal of abrasive material.
The use of an abrasive to wear away at the surface of a workpiece and change its shape.
A wheel made of a bonded abrasive used to grind the surfaces of parts.
A grinding machine with a spindle that is parallel to the work surface.
A build up of swarf in a grinding wheel that clogs the spaces between grains.
A substance, often a liquid, used to reduce or prevent friction, resistance, heat, and wear during
grinding.
The process of removing metal to form or finish a part, either with traditional methods like
turning, drilling, cutting, and grinding, or with less traditional methods that use electricity or
ultrasound.
Generally, grinding in which the workpiece is held in the operator's hand and placed against the
grinding wheel. It is used for material removal without regard to surface finish.
The loss of a grinding wheel's original shape resulting in a wheel that is no longer symmetrical.
Copyright © 2015 Tooling U,
LLC. All Rights
Reserved.
Peripheral
Wheel
A grinding wheel in which the outer rim is in contact with the workpiece.
Plowing
An action that occurs during grinding when dull grains push into the workpiece without cutting
Out Of True
Peripheral Wheel
Plowing
Ring Test
Roll
Rubbing
Side Wheel
The loss of a grinding wheel's original shape resulting in a wheel that is no longer symmetrical.
A grinding wheel in which the outer rim is in contact with the workpiece.
An action that occurs during grinding when dull grains push into the workpiece without cutting
it. Plowing leaves grooves in the work surface.
A manual test used to determine the presence of damage in bonded grinding wheels. Operators
suspend a wheel loosely and tap it with a tool. Wheels that emit a ringing sound are likely
undamaged.
A hard wheel used in crush dressing to improve or shape the surface of a grinding wheel.
A sliding action that occurs during grinding when dull grains glide over the surface of a workpiece
without cutting it.
A grinding wheel in which the front portion, or face, is in contact with the workpiece.
Swarf
The gritty combination of chips, abrasive grains, and worn bonding material that is produced
during grinding.
Tool Grinding
A specialized type of grinding performed to sharpen cutting tools. Tool grinding is often very
precise.
Truing
Void
Workpiece
The dressing of a wheel in order to return the wheel to its original shape.
An empty space between abrasive grains on a grinding wheel where chips collect.
A part that is being worked on. It may be subject to grinding, cutting, welding, forming, or other
operations.

What Is Grinding? 110 - Tooling U-SME

Transcription

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